Summary All of portage modules BIOD 152 Intro to the Nervous System

All of portage modules BIOD 152 Intro to the Nervous System All of portage modules BIOD 152 Intro to the Nervous System Notice: To optimize your learning in this course, we advise that you complete the labs and modules as indicated in the BIOD 152 Lab Schedule. The nervous system receives and processes information and sends out signals to the muscles and glands to elicit an appropriate response. In this way, the nervous system integrates and controls the other systems of the body. In the human nervous system, the central nervous system (Figure below) includes the brain and the spinal cord (dorsal nerve cord), which lie in the midline of the body. The skull protects the brain and the vertebrae protect the spinal cord. The central nervous system can send signals or impulses to and receive impulses from the peripheral nervous system. The peripheral nervous system includes all nerves not in the brain or spinal cord which are the cranial nerves that connect directly to the brain and the spinal nerves which project from either side of the spinal cord. The peripheral nervous system connects all parts of the body to the central nervous system and can be divided into a sensory or afferent division and a motor or efferent division. The peripheral nervous system receives impulses from the sensory organs via the afferent division and then relays signals or impulses from the central nervous system to muscles and glands via the motor or efferent division. The efferent division can be further divided into the somatic system and the autonomic system. The somatic system nerves control skeletal muscles, skin, and joints. The autonomic system nerves control the glands and smooth muscles of the internal organs and are not generally under conscious control and can be divided into two systems: the sympathetic system which activates and prepares the body for vigorous muscular activity, stress, and emergencies and the parasympathetic system which lowers activity, operates during normal situations, permits digestion, and conserves energy. Problem Set 1: 1. The function of the nervous system is to integrate and control the other body systems. Explain how the nervous system does this. 2. List the 2 parts of the central nervous system. 3. How are the parts of the central nervous system protected? 4. How do the central nervous system and the peripheral nervous system interact? 5. What is included in the peripheral nervous system? 6. What are the 2 divisions of the peripheral nervous system? 7. Describe the movement of nerve impulses in the peripheral nervous system. 8. What are the 2 divisions of the efferent division of the peripheral nervous system? 9. What is controlled by the somatic and autonomic nervous systems? 10. What are the 2 divisions of the autonomic nervous system? 11. What is the function of the sympathetic nervous system? 12. What is the function of the parasympathetic nervous system? Neurons Neurons (Figure below) are nerve cells that vary in size and shape. They do not undergo mitosis (cell division), require enormous amounts of fuel, are able to survive just minutes without oxygen, and can last an entire human lifetime. Neurons all have three parts: the dendrites, the cell body, and the axon. The neuron cell body, which synthesizes all nerve cell products, consists of a large nucleus with surrounding cytoplasm containing the normal organelles. The dendrites are numerous short extensions that emanate from the cell body which receive information from other neurons conducting those nerve impulses toward the cell body. The single axon, on the other hand, conducts nerve impulses away from the cell body to its axon terminals where it is emitted across a synapse to the dendrite of another neuron. Axons can vary in length being very short or as long as three feet, the length of the axon which extends from the bottom of the spine to the big toe. Axons are composed of cells like the cell body but lack rough endoplasmic reticulum, depending on the cell body for necessary proteins. The peripheral nerve axon is coated in short sections called Schwann cells which are mainly composed of a white fatty layer called the myelin sheath rolled around the axon which insulates the nerve fiber from others and increases the speed of nerve impulses. There are also unmyelinated fibers, which are common in the gray matter of the brain and spinal cord, in which the Schwann cells do not wrap around the axon but are just loosely associated with the axon. The Schwann cell insulating sections are not continuous, having gaps between them called Nodes of Ranvier. At these exposed nodes, the nerve impulse is forced to jump to the next node in a manner called salutatory conduction, greatly increasing the nerve impulse transmission along the axon. The cell body contains the nucleus and other organelles typically found in cells with the exception of centrioles (since it is not capable of mitosis). One of the main functions of the cell body is to manufacture neurotransmitters, which are chemicals stored in secretory vesicles at the end of axon terminals. When neurotransmitters are released by the axon terminal vesicles, they participate in the transmission of the nerve impulse from one neuron to another. Problem Set 2: 13. Identify the parts of the neuron shown in the diagram below. 14. List 3 unusual characteristics of neurons. 15. List the 3 parts of a neuron. 16. Describe the structure and function of the neuron cell body. 17. Describe the structure and function of the dendrite. 18. Describe the axon, including the number in each neuron, function, structure and organelles. 19. Describe the composition and function of Schwann cells. 20. Describe the location and function of the Nodes of Ranvier. 21. What important organelle is absent from the neuron cell body and what does the absence of this organelle indicate about activity of the cell body? 22. Describe the function and site of synthesis and storage of neurotransmitters. Neuroglial Cells A nerve consists of hundreds of thousands of axons (#3) wrapped together in a connective tissue. In the peripheral nervous system the cell bodies of neurons (#2) are grouped together in masses called ganglia which are part of a single nerve. The neurons are also accompanied by non-nerve "supporting" cells known collectively as neuroglial cells which include (as shown in the diagram below) ependymal cells (#1), oligodendrocytes (#4), astrocytes (#5) and microglial cells (#7). The functions of these supporting cells are as follows: ependymal cells (circulate cerebrospinal fluid and allow fluid exchange between brain, spinal cord and CSF), oligodendrocytes (insulation of central nervous system axons), astrocytes (control chemical environment of neurons) and microglial cells (protect CNS by scavenging dead cells and infectious microoganisms). Neurons can be classified as to their structure and function. Structurally, neurons are classified according to the number of extension from their cell body, as multipolar, bipolar and unipolar neurons. Multipolar neurons, the most common type in humans found as motor neurons or interneurons within the CNS, have three or more extensions, one axon and many dendrites. Bipolar neurons, found as receptors cells in the visual and olfactory systems, have two extensions, one axon and one dendrite. Unipolar neurons, found as sensory neurons in the peripheral nervous system, have one extension which branches into two, one central process running to the CNS and another peripheral process running to the sensory receptor. Functionally, neurons are classified as sensory or afferent neurons, motor or efferent neurons and association or interneurons. Most sensory neurons are unipolar and carry impulses from receptors in the skin or internal organs toward the CNS. Most motor neurons are multipolar and carry impulses from the central nervous system to muscle fibers or glands. Interneurons are usually multipolar and found within the central nervous system only. They transmit impulses between sensory and motors neurons conveying messages between various parts of the central nervous system, such as from one side of the brain or spinal cord to the other, or from the brain to the spinal cord, and vice versa. Problem Set 3: 23. List the four types of support neuroglial cells and a function of each. 24. List the 3 structural classes of neurons, and describe the structure and an example of each. 25. List the 3 functional classes of neurons, and describe the structure and an example of each. Action Potentials Neurons are specialized to conduct electric impulses called action potentials. The nerve impulse is an electrochemical charge moving along an axon created by the movement of unequally distributed ions on either side of an axon’s plasma membrane. At rest the plasma membrane is said to be polarized, meaning that one side has a different charge than the other side. When the axon is not conducting an impulse, this difference in electrical charge is called resting potential and is equal to about -70mV (millivolts). This means that the charge on the inside of the axon's cell membrane is 70 millivolts less than the outside of the membrane. This is maintained by a sodium-potassium pump which uses active transport to carry ions across the plasma membrane. The pump works by using an integral carrier protein that, for every three Na+ ions that are pumped out, two K+ ions are pumped in. The pump must keep in constant operation, because the Na+ and K+ ions will naturally diffuse back to where they originated. Because the plasma membrane is more permeable to K+ diffusing outward and because more Na+ ions are being pumped outward than K+ pumped inward, a relative positive charge develops and is maintained on the outside of the membrane. If the axon is stimulated to conduct a nerve impulse, there is a rapid change in the polarity. This change in polarity is called the action potential. First, the membrane potential becomes more positive (called depolarization), indicating that the inside of the membrane is now more positive than the outside. Then the potential returns to normal (called re-polarization), indicating that the inside of the axon is negative again. The action potential is due to special protein-lined channels in the membrane, which can open to allow either sodium or potassium ions to pass through. These channels have gates, called sodium gates and potassium gates. During the resting phase both sodium and potassium gates are closed. The sodium gates open and sodium rushes into the axon during the depolarization phase of the action potential. Voltage travels to zero and then on up to +40mV. Once this phase is complete, re-polarization occurs. The sodium gates close and potassium gates open allowing potassium to rush out of the axon. This returns a negative voltage to the inside of the axon but these gates are slow to close and there is generally an afterpolarization undershoot of the potential. These channels and their gates are voltage activated, as proteins respond to changes in voltage with changes in shape. The action potential travels along the length of an axon like a wave. It is self-propagating because the ion channels are prompted to open whenever the membrane potential decreases (depolarizes) in an adjacent area. An action potential is an all-or-nothing response either occurring or not. Since no variation exists in the strength of a single impulse, we distinguish the difference in intensity of a sensation (minor pain/major pain) by the number of neurons stimulated and the frequency with which they are activated. An impulse passing from one vertebrate nerve cell to another always moves in only one direction and there is a very short delay in transmission of the nerve impulse from one neuron to another. Neurons do not touch. There is a minute fluid-filled space, called a synapse, between the axon terminal of the sending (presynaptic) neuron and the dendrite of the receiving (postsynaptic) neuron. The transmission of nerve impulses is electrochemical in nature as chemicals called neurotransmitters allow the signal to jump the synaptic gap. When a nerve impulse reaches the end of an axon, voltage-gated calcium channels open. As Ca+2 rushes in, it causes vesicles containing the neurotransmitter to fuse with the plasma membrane and release the neurotransmitter into the synapse. When the neurotransmitter released binds with a receptor on the next neuron, Na+ channels in the receiving dendrites open. Depolarization occurs and the impulse is carried. Acetylcholine and norepinephrine are well-known neurotransmitters, active in both the peripheral nervous system and the central nervous system. Once a neurotransmitter has been released into a synapse, it has only a short time to act. Some synapses contain enzymes that rapidly inactivate the neurotransmitter. For example, the enzyme acetylcholinesterase, or simply cholinesterase, breaks down acetylcholine. In other synapses, the synaptic ending rapidly absorbs the neurotransmitter, possibly for repacking in synaptic vesicles or for chemical breakdown. The short existence of neurotransmitters in the synapse prevents continuous stimulation (or inhibition) of postsynaptic membranes. Problem Set 4: 26. What is the technical term used to describe a nerve impulse and what causes the impulse? 27. An axon's membrane is polarized with a resting potential of -70 mV. Explain what this means and what maintains this resting potential. 28. Label each numbered section (1-4) of the diagram below which describes an action potential. 29. Describe what happens to the charges on the axon cell membrane during depolarization and what causes this to happen. Describe what happens to the charges on the axon cell membrane during repolarization and what causes this to happen. 30. Describe what happens during afterpolarization. 31. What causes the difference in intensity of a sensation? 32. How is an impulse passed from one nerve cell to another? 33. What prevents continuous stimulation of a nerve synapse and how is this accomplished? Peripheral Nervous System The peripheral nervous system lies outside the central nervous system. The peripheral nervous system is made up of nerves, which are part of either the somatic system or the autonomic system. The somatic system contains nerves that control skeletal muscles, skin, and joints. The autonomic system contains nerves that control the smooth muscles of the internal organs and the glands. Humans have twelve pairs of cranial nerves attached to the brain. Cranial nerves are either sensory nerves (having long dendrites of sensory neurons only), motor nerves (having long axons of motor neurons only), or mixed nerves (having both long dendrites and long axons). With the exception of the vagus nerve, all cranial nerves control the head, neck, and face. The vagus nerve controls the internal organs. The first cranial nerve is the olfactory. It is a sensory nerve responsible for the sense of smell. The second cranial nerve is the optic. It is a sensory nerve responsible for the sense of sight. The third cranial nerve is the oculomotor. It is a motor nerve responsible for eye movement. The fourth cranial nerve is the trochlear. It is a motor nerve also responsible for eye movement. The fifth cranial nerve is the trigeminal. It is a motor and sensory nerve. It is responsible for chewing or mastication and sensation of the face, nose, and mouth. The sixth cranial nerve is the abducens. It is a motor nerve responsible for eye movement. The seventh nerve is the facial. It is a motor and sensory nerve. It is responsible for facial expressions and sensation of the tongue. The eighth cranial nerve is the vestibulocochlear. It is a sensory nerve responsible for hearing and balance. The ninth cranial nerve is the glossopharyngeal. It is a motor and sensory nerve. It is responsible for swallowing and taste. The tenth cranial nerve is the vagus. It is a motor and sensory nerve. It is responsible for digestion, regulation of heart rate, and sensation of the digestive tract. The eleventh nerve is the accessory. It is a motor nerve and is responsible for the rotation of the head and shrugging of the shoulders. The twelfth cranial nerve is the hypoglossal. It is a motor nerve that is responsible for tongue movements. Humans have thirty-one pairs of spinal nerves. There are eight pairs of cervical (cranial) nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. Each spinal nerve emerges from the spinal cord by two short branches, or roots, which lie within the vertebral column. The dorsal root contains the axons of afferent sensory neurons, which conduct impulses to the cord. The ventral root contains the axons of efferent motor neurons, which conduct impulses away from the cord. These two roots join just before a spinal nerve leaves the vertebral column. Therefore, all spinal nerves are mixed nerves that take impulses to and from the spinal cord. Spinal nerves project from the spinal cord, which is a part of the central nervous system. The spinal cord is a thick, whitish nerve cord that extends longitudinally down the back, where it is protected by the vertebrae. The cord contains a tiny central canal filled with cerebrospinal fluid, gray matter consisting of cell bodies and short fibers, and white matter consisting of myelinated fibers. Almost immediately after immerging from the vertebral column, a spinal nerve divides into branches called the dorsal ramus and ventral ramus. The smaller dorsal ramus contains nerves that serve the dorsal portions of the trunk carrying visceral motor, somatic motor, and sensory information to and from the skin and muscles of the back. The larger ventral ramus contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the body surface, structures in the body wall, and the limbs. Some ventral rami merge with adjacent ventral rami to form a nerve plexus, a network of interconnecting nerves. Nerves emerging from a plexus contain fibers from various spinal nerves, which are now carried together to some target location. Major plexuses include the cervical, brachial, lumbar, and sacral plexuses. The phrenic nerve is the most important nerve of the cervical plexus and supplies both motor and sensory fibers to the diaphragm. Irritation of this nerve causes hiccups and severing this nerve would cause paralysis of the diaphragm and require use of a ventilator (mechanical respiratory). The saying “three, four, five keeps the diaphragm alive” is an easy way to remember that the phrenic nerve arrives from the ventral rami of C3-C5. Five nerves that originate from the ventral rami of C5-T1 issue from the Brachial plexus. The axillary nerve supplies three muscles: the deltoid (a muscle of the shoulder), the teres minor (one of the rotator cuff muscles) and the long head of the triceps brachii (an elbow extensor). The axillary nerve also carries sensory information from the shoulder joint. The radial nerve supplies the triceps brachii muscle of the arm, as well as 12 muscles in the forearm and the associated joints and overlying skin. The median nerve supplies flexor muscles of the forearm and the skin of the first three and a half fingers. Compression of the median nerve in the carpal tunnel causes carpal tunnel syndrome or decreased sensation in the first three and a half fingers. The musculocutaneous nerve supplies the flexor muscles of the arm. The ulnar nerve supplies part of the flexor muscles of the forearm, wrist, and hand as well as the skin of half the ring finger and pinky finger. If the ulnar nerve is damaged it results in a condition known as claw hand, the inability to open the fourth and fifth fingers. The Lumbar plexus nerves arise from the ventral rami of L1-L4 and the femoral nerve is the major nerve that comes from this plexus. The femoral nerve supplies the hip flexors and knee extensors as well as sensation to the skin of the anterior thigh. Finally, the sacral plexus nerves arise from the ventral rami of L4-S4 and the sciatic nerve is the major nerve that comes from this plexus. The sciatic nerve is the largest nerve in the human body. It supplies the inferior trunk and posterior surface of the thigh. Increased pressure on this nerve can result in the condition known as sciatica. The somatic nervous system includes all nerves that serve the musculoskeletal system and the exterior sense organs, including the skin. Exterior sense organs (and skin) are receptors, which receive environmental stimuli and then initiate nerve impulses. Muscle fibers are effectors, which bring about a reaction to the stimulus. Problem Set 5 34. How many pairs of cranial nerves do humans have and what do most of them (except for one) control? 35. For each of the following cranial nerves, list its name, type and what it controls. Name Type Controls What? 5th 36. Describe the detail the structure of spinal nerves within the vertebral column. 37. Describe the detail the structure of spinal nerves after leaving the vertebral column. 38. Describe a nerve plexus and list the four major body nerve plexuses. 39. What is the most important nerve of the cervical plexus and what structure does it supply?. 40. List the five nerves that form the Brachial plexus. . 41. What 3 muscles are served by the axillary nerve? 42. What muscles are served by the radial nerve? 43. What muscle is served by the median nerve? 44. What condition is caused by compression of the median nerve?. 45. What muscles are served by the musculocutaneous nerve? 46. What muscles are served by the ulnar nerve? 47. What is the major nerve of the Lumbar plexus? 48. What is the major nerve of the sacral plexus and what is unusual about this nerve? 49. What muscles are served by the femoral nerve? 50. What areas are served by the sciatic nerve? 51. What structures are served by the somatic nervous system 52. What is a receptor and what structures serve as receptors within the somatic nervous system? 53. What is an effector and what structures serve as effectors within the somatic nervous system?. Reflexes Reflexes are nearly instantaneous, automatic, involuntary motor responses to stimuli occurring inside or outside of the body. Reflexes may be subconscious as the regulation of blood sugar by the hormones, may be noticeable as shivering in response to a drop in body temperature; or may be obvious as touching a very hot object and immediately withdrawing your hand. Some reflexes, such as blinking the eye, involve the brainstem, but others, such as the flexor reflex involved when withdrawing your hand from the hot object involve only the nerves and the spinal cord in an action known as the reflex arc. To help an organism avoid injury, a reflex arc provides an immediate withdrawal from dangerous stimuli. While all sensory information does reach the brain for processing, the advantage of the reflex arc is production of a response by way of the spinal cord without the need to wait for processing by the brain. In this way a response occurs even before is consciously perceived. If you touch a very hot object, a receptor in the skin generates nerve impulses, which move along the dendrite of a sensory neuron toward the cell body and the central nervous system. The cell body of a sensory neuron is located in the dorsal-root ganglion just outside the spinal cord. From the cell body, the impulses travel along the axon of the sensory nerve. The impulses then pass to many interneurons, one of which connects with a motor neuron. The short dendrites and the cell body of the motor neuron lead to the axon, which leaves the cord by way of the ventral root of the spinal nerve. The nerve impulses travel along the axon to muscle fibers, which then contract so that you withdraw your hand from the hot object. This whole series of responses occurs because the sensory neuron stimulates several interneurons. They take impulses to all parts of the central nervous system, including the cerebrum, which in turn makes the person conscious of the stimulus and the reaction to it. A reflex arc refers to the neural pathway that a nerve impulse follows. The reflex arc typically consists of five components: The receptor at the end of a sensory neuron reacts to a stimulus. The sensory (afferent) neuron conducts nerve impulses along an afferent pathway towards the central nervous system (CNS). The integration center consists of one or more synapses in the CNS. A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector. An effector responds to the efferent impulses by contracting (a muscle) or secreting a product (a gland). Spinal reflexes occur much faster, not only because they involve fewer neurons, but also because the electrical signal does not have to travel to the brain and back. Spinal reflexes only travel to the spinal cord and back which is a much shorter distance. On average, humans have a reaction time of 0.25 seconds to a visual stimulus, 0.17 for an audio stimulus, and 0.15 seconds for a touch stimulus. Several examples of spinal reflexes are the flexor reflex (withdrawal of your hand from a very hot object) and the stretch reflex on an opposing muscle to prevent over- stretching of its antagonist. Stretch reflexes are a special type of muscle reflex which protect the muscle against increases in length which may tear or damage muscle fibers. Stretch reflexes are very important in maintaining upright posture in humans. Consider the patellar reflex, the knee-jerk flex used in physicians' offices to test the function of the muscles and nervous system. The primary purpose of the patellar reflex, which is the stretch reflex of the quadriceps femoris muscle in your thigh, is to prevent the over-stretching of the quadriceps. The patellar tendon attaches the quadriceps muscle to the tibia bone of the lower leg. The quadriceps is an extensor muscle raising the lower leg as it contracts thereby extending the angle of the knee joint. Tapping the patellar tendon stretches the quadriceps muscle and causes the sensory nerve receptor of the muscle to send a signal along the afferent neuron to the spinal cord. This causes the efferent neuron to return a signal to the quadriceps muscle to contract and lift the lower leg. Problem Set 6: 54. Define the term reflex and give a subconscious example and an obvious example. 55. Explain why a reflex arc occurs so quickly and why this speed is necessary. 56. List the 5 components of a reflex arc. 59. Why do spinal reflexes occur much faster than ones involving the brain? 60. Give 2 examples of spinal reflexes. Autonomic Nervous System The autonomic nervous system, a part of the peripheral nervous system, is made up of motor neurons that control the internal organs automatically and usually without need for conscious intervention. The sensory neurons that come from the internal organs allow us to feel internal pain. The cell bodies for these sensory neurons are in dorsal-root ganglia, along with the cell bodies of somatic sensory neurons. There are two divisions of the autonomic system: the sympathetic and parasympathetic systems. Both of these function automatically and usually subconsciously in an involuntary manner. These two divisions cause essentially opposite effects on the same visceral organ; if one stimulates, the other inhibits. The sympathetic system is especially important during emergency situations and is associated with "fight or flight". If you try to fend off a foe or flee from danger, active muscles require a ready supply of glucose and oxygen. The sympathetic system accelerates the heartbeat, dilates the bronchi, and increases the breathing rate, the combination of which supplies the needed oxygen. At the same time, the sympathetic system causes the liver to deliver more glucose and inhibits the digestive tract since digestion is not an immediate necessity if you are under attack. The primary neurotransmitter utilized by the sympathetic system is norepinepherine. The parasympathetic system, sometimes called the housekeeper system, promotes all the internal responses we associate with a relaxed state. For example, it causes the pupil of the eye to constrict, promotes digestion of food, and retards the heartbeat. The neurotransmitter utilized by the parasympathetic system is acetylcholine. The effect of these two divisions on some organs is listed below: Parasympathetic effect Sympathetic effect eye constricts pupils dilates pupils glands (salivary, pancreas) stimulates secretion inhibits secretion sweat glands no effect stimulates sweating heart (muscle) slows heartbeat increases heartbeat heart blood vessels no effect dilates vessels lungs constricts bronchioles dilates bronchioles digestive tract increases peristalis relaxes sphincters decreases activity constricts sphincters liver no effect epinephrine stimulates release of glucose kidney no effect decreases urine output vagina/clitoris excites clitoris contracts vagina penis causes erection causes ejaculation blood vessels no effect constricts blood vessels cell metabolism no effect increases metabolic rate Problem Set 7: 61. What are the two division of the autonomic nervous system and how do they function relative to each other? 62. Explain in detail how the sympathetic nervous system functions during an emergency situation. 63. What type of internal responses are promoted by the parasympathetic nervous system? 64. Describe the effects caused by the parasympathetic and sympathetic nervous systems on heart blood vessels, the lungs and the digestive tract. The Brain The human brain can be considered to be made up of the following parts: cerebral hemispheres, diencephalon (thalamus, hypothalamus, and epithalamus), brain stem (mid-brain, pons, and medulla oblongata), and cerebellum. In addition, there are four ventricles in the interior of the brain, chambers filled with cerebrospinal fluid which is produced there. The medulla oblongata, the pons, and the midbrain lie in a portion of the brain known as the brain stem. The medulla oblongata lies between the spinal cord and the pons and is anterior to the cerebellum. It contains a number of vital centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccupping, and swallowing. The medulla contains tracts that ascend or descend between the spinal cord and the brain's higher centers. The pons contains bundles of axons traveling between the cerebellum and the rest of the central nervous system. In addition, the pons functions with the medulla to regulate the breathing rate and has reflex centers concerned with head movements in response to visual and auditory stimuli. Aside from acting as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum, the midbrain has reflex centers for visual, auditory, and tactile responses. The hypothalamus, thalamus and epithalamus are in a portion of the brain known as the diencephalon. The hypothalamus, forming the floor of the third ventricle, maintains homeostasis, or the constancy of the internal environment, and contains centers for regulating hunger, sleep, thirst, body temperature, water balance, and blood pressure. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus, in the roof of the third ventricle, is the last portion of the brain for sensory input before the cerebrum. It serves as a central relay station for sensory impulses traveling upward from other parts of the body and the brain to the cerebrum. It receives all sensory impulses (except those associated with the sense of smell) and channels them to appropriate regions of the cerebrum for interpretation. The epithalamus forms the roof of the third ventricle and is composed of the pineal body which secretes melatonin to control the wake-sleep cycle and the choroid plexus which produces cerebrospinal fluid. The cerebellum, below and at the back of the brain, is convoluted and divided into two hemispheres with deep fissures subdividing it into three lobes. It is composed of a thin outer cortex of gray matter and internal white matter. The anterior and posterior lobes of the cerebellum act to coordinate body movements by receiving information from the body trunk and influence the motor activities of the trunk and shoulder and pectoral girdle muscles by relaying information to the cerebral motor cortex. The intermediate lobe coordinates limb movements. The cerebellum is also involved with planning movements, maintaining balance, controlling certain eye movements, maintaining normal muscle tone and maintaining posture. The cerebrum, the foremost part of the brain, is the largest part of the brain in humans comprising about 83% of total brain mass. It consists of two large masses called cerebral hemispheres, which are connected by a bridge of nerve fibers called the corpus callosum. The outer portion of the cerebral hemispheres, the cerebral cortex, is highly convoluted and gray in color marked by raised ridges of tissue called gyri, separated by shallow grooves called sulci. The deeper grooves, called fissures, separate large regions of the brain. The median longitudinal fissure separates the cerebral hemispheres from one another and the transverse fissure separates the cerebral hemispheres from the cerebellum. Some of the deeper sulci divide each hemisphere into four surface lobes: frontal, parietal, temporal and occipital. The cerebral cortex contains three kinds of functional areas: motor areas that control voluntary motor functions; sensory areas that provide for conscious awareness of sensation; and association areas that act mainly to integrate information for purposeful action. Different functions are associated with each lobe. Only the cerebrum is responsible for consciousness, and it is the portion of the brain that governs intelligence and reason qualities which are particularly well developed in humans. The frontal lobe controls motor functions and permits us to control our muscles consciously. The parietal lobe receives information from receptors located in the skin, such as those for touch, pressure, and pain. The occipital lobe interprets visual input. The temporal lobe has sensory areas for hearing and smelling. The cerebrum controls the activities of lower parts of the brain. The cerebrum can override the functioning of the brain stem and diencephalon, as when meditation or biofeedback helps control the heart rate. Acting on sensory input from the thalamus, the cerebrum initiates voluntary motor activities and controls the actions of the cerebellum. Certain areas of the cerebral cortex have been mapped in great detail. We know which portions of the frontal lobe control various parts of the body and which portions of the parietal lobe receive sensory information from these same parts. Each of the four lobes of the cerebral cortex contains an association area, which receives information from the other lobes and integrates it into higher, more complex levels of consciousness. These are concerned with intellect, artistic and creative ability, learning, and memory. The limbic system involves portions of both the unconscious and conscious brain. It lies just beneath the cerebral cortex and contains neural pathways that connect portions of the frontal lobes, the temporal lobes, the thalamus, and the hypothalamus. The basal nuclei, masses of gray matter that lie deep within each hemisphere of the cerebrum, are also part of the limbic system. The limbic system is our feeling brain since stimulation of different areas of the limbic system causes rage, pain, pleasure, or sorrow. The limbic system affects the emotional aspects of behavior, evaluates rewards and is important in motivation. Extensive connections between the limbic system and lower and higher brain regions cause acute emotional stress to produce visceral illnesses, such as stomach ulcers, high blood pressure, and irritable bowel syndrome. The limbic system is also involved in the processes of learning and memory. Learning requires memory, but just what permits memory development is not definitely known. Investigators have been working with invertebrates such as slugs and snails because their nervous system is very simple and yet they can be conditioned to perform a particular behavior. To study this simple type of learning, it has been possible to insert electrodes into individual cells and to later record the electrochemical responses of these cells. This type of research has shown that learning is accompanied by an increase in the number of synapses, while forgetting involves a decrease in the number of synapses. In other words, the nerve-circuit patterns are constantly changing as learning, remembering, and forgetting occur. Within the individual neuron, learning involves a change in gene regulation and nerve protein synthesis and an increased ability to secrete transmitter substances. Research indicates that the limbic system is absolutely essential to both short-term and long-term memory. An example of short-term memory in humans is the ability to recall a telephone number long enough to dial the number; an example of long-term memory is the ability to recall the events of the day. After nerve impulses circulate within the limbic system, the basal nuclei stimulate the sensory areas where memories are stored. The involvement of the limbic system certainly explains why emotionally charged events result in our most vivid memories. The fact that the limbic system communicates with the sensory areas for touch, smell, vision, and so forth accounts for the ability of a particular sensory stimulus to awaken a complex memory. Neurons are not replaceable and are damaged by even the slightest pressure but the brain is protected by the skull of the skeletal system, membranes, a cushion of cerebrospinal fluid and the “blood-brain barrier”. The meninges are three connective tissue membranes that cover and protect central nervous system organs and enclose cerebrospinal fluid. The leathery dura mater is the double-layered outer meninx. The middle arachnoid meninx is a loose layer separated from the dura mater by the subdural space. Beneath the arachnoid meninx is the subarachnoid space which contains blood vessels and is filled with cerebrospinal fluid. The inner pia mater meninx is composed of connective tissue and is tightly attached to the brain. Cerebrospinal fluid (CSF), similar to and formed in the ventricles from blood plasma, cushions the brain and spinal cord by providing buoyancy. CSF is similar in composition to blood plasma, from which it arises by permeating through the choroid plexus capillaries. Once formed the CSF circulates through the ventricles and into the subarachnoid space bathing and floating the brain. The blood-brain barrier is due to the relatively impermeable brain capillaries which provide a stable chemical environment for the brain protecting it from variations which would cause uncontrollable firing of neurons. Problem Set 8: 65. List the four parts of the human brain. 1) Cerebral hemispheres 2) Diencephalon (Thalamus, Hypothalamus, Epithalamus) 3) Brain stem ( mid-brain, pons, medulla oblongata) 4) Cerebellum 66. List the three parts of the diencephalon. Diencephalon (Thalamus, Hypothalamus, Epithalamus) 67. List the three major parts of the brain stem. Brain stem ( mid-brain, pons, medulla oblongata) 68. Describe the number, location and function of the brain ventricles. There are four ventricles in the inferior brain where cerebrospinal fluid is produced. 69. How is the medulla oblongata involved with the heart and lungs? Regulates the heartbeat and breathing. 70. How is the pons involved with the eyes and ears? The pons have reflex centers that contribute to head movements in response to visual and auditory stimuli. 71. The pons functions to relay impulses between what centers? The pons containn bundles of axons that travel between the cerebellum, cerebrum and spinal cord. They are known as the "bridge". 72. How is the hypothalamus involved with the entire internal environment of the body and the endocrine system in particular? The hypothalamus contributes to the nervous and endocrine systems by controlling the pituitary gland. Also helps maintain homeostasis, the constancy of the internal environment. 73. All except what sensory impulses are channeled through the thalamus? The thalamus receives all sensory impulses except for sense of smell. 74. What is the function of the pineal body? The epithalamus hosts the pineal body which controls the wake-sleep cycle by secreting melatonin. 75. What is the function of the choroid plexus? Within the epithalamus, cerebrospinal fluid is produced by choroid plexus. 76. Describe the location and structure of the cerebellum? The cerebellum is made up of a thin outer cortex of gray matter and internal white mattter. It is located in the back and below the brain. Looks like a mini brain. It is broken up into two hemispheres with deep fissures that subdivide into three lobes. 77. The major function of the cerebellum is to control what type of body function? The cerebellum help coordinate body movements. 78. Describe the cerebrum noting its size and appearance. The cerebrum is the largest part of the brain weighing at 83% of the total brain mass. It consists of two hemispheres which are connected by corpus collosum. 79. Describe, in detail, surface appearance of the cerebral cortex. The cerebral cortex is the layer of the brain. It is complex with raised ridges of tissue called gyri, separated by shallow grooves called sulci. The deeper grooves called fissures, separate large regions of the brain. The median longitudinal fissures separate the cerebral hemispheres from one another and the transverse fissure separates the cerebral hemispheres from the cerebellum. 80. List the four lobes of the cerebrum. 1) Frontal lobe 2) Parietal lobe 3) Temporal lobe 4) Occipital lobe 81. List and describe the 3 functional areas of the cerebrum. 1) Motor areas, that control voluntary motor functions 2) Sensory areas, conscious awareness of sensation 3) Associated areas, that act mainly to combined information for purposeful actions 82. What does the frontal lobe control? The frontal lobe, voluntary, motor controls muscles consciously. 83. What is the function of the parietal lobe? Receives information from receptors in the skin, by touch, sensation or pain. 84. What is the function of the occipital lobe? Interprets visual output 85. What is the function of the temporal lobe? Has sensory areas for hearing and smelling 86. What areas of the brain does the limbic system connect? The limbic system connects the frontal lobes, the thalamus and the hypothalamus. 87. Why is the limbic system called our "feeling brain"? The limbic system stimulates all types of feels by stimulating of different areas of the limbic system results in rage, pain, pleasure, or sorrow. 88. List three illnesses caused by the limbic system's involvement in stress production. Extensive connections between the limbic system and lower and higher brain regions cause acute emotional stress to produce visceral illnesses, such as stomach ulcers, high blood pressure, and irritable bowel syndrome. 89. What determines learning and forgetting? Learning is a result of an increased number of synapse. Forgetting is a result of a decreased number of synapse. 90. List the 4 protections for the brain. 1) The skull 2) Membranes 3) A cushion cerebrospinal fluid and the blood-brain barrier 91. Describe the 3 brain meninges. 1) Dura mater, is leathery and has a double-layered outer meninix. 2) The middle archnoid meninix, is a loose layer separated from the dura mater by the subdural space. 3) The inner pia mater meninix,is made up of connective tissue and is tightly attached to the brain. 92. Describe cerebrospinal fluid including its composition, formation and function. Is similar to blood plasma, from which it arises by permeating through the choroid plexus capillaries. Once formed the CSF circulates through the ventricles and into the subarachoid space bathing and floating the brain. 93. What causes the blood-brain barrier and what is its function? The blood-brain barrier is a result of relatively impermeable brain capillaries, these provide a stable chemical environment for the brain protecting it from vibrations which would cause uncontrollable firing of neurons. The Spinal Cord The spinal cord is about 17 inches in length, is protected by the surrounding vertebral column and extends from the brain stem to the first lumbar vertebra where it officially terminates as the conus medullaris. The extension of the cord beyond L1 is a collection of nerve roots called the cauda equina which runs to its end at the coccyx. The spinal cord and its extension is the means by which all impulses travel between the brain and the rest of the body by way of the set of 31 pair of spinal nerves. Like the brain, the spinal cord is protected by the bony vertebral column, meninges and cerebrospinal fluid. The outer meninx, a single layer called the spinal dural (mater) sheath is separated from the vertebral column by a cushioning fat-filled epidural space. The space between the middle arachnoid and inner pia mater meninges is filled with cerebrospinal fluid. An extension of pia mater runs from the conus medullaris to the coccyx where it provides the inferior anchor for the spinal cord. Because the cord ends at L1, the cerebrospinal filled subarachnoid space inferior to this point is the location chosen to perform a spinal tap removal of fluid for diagnostic testing. The surface of the spinal cord has two grooves: the anterior median fissure and the shallower posterior median sulcus. The interior gray matter of the cord is composed of a mixture of multipolar neurons and supporting cells. The outer white matter is composed of myelinated and un-myelinated nerve fibers. The gray matter of the cord consists of two posterior (dorsal) horns, two anterior (ventral) horns and much smaller anterior horns connected by a cross-bar called the gray commissure. The anterior (ventral) horns contain somatic motor neurons whose axons serve as efferent pathways to skeletal muscles by way of the ventral roots of the spinal cord. The lateral horn neurons contain autonomic sympathetic motor neurons whose axons serve as efferent pathways to visceral organs by way of the ventral roots of the spinal cord along with those of the somatic motor neurons. The posterior (dorsal) horns serve as one of the afferent pathways from receptors by way of the dorsal roots of the spinal cord. The white matter fibers of the spinal cord are mostly composed of ascending tracts that proceed up to the brain carrying sensory inputs and descending tracts that proceed down to (or within) the cord carrying motor outputs with a few commissural tracts across the cord. Problem Set 9 94. Describe the spinal cord and its extension. The spinal cord is protected by vertebra column, meninges and cerebrospinal fluid. It extends from the brain stem to the first lumbar vertebra where it officially terminates as the conus medullaris. The cauda equina is the extension of the cord beyond L1is a collection of nerve roots. It runs to the coccyx. 95. What is the function of the spinal cord and how does it accomplish this? The spinal cord's extensions is the means by which all impulses travel between the brain and the rest of the body by the way of the 31 spinal nerves. 96. List the 3 protections for the spinal cord. The spinal cord is protected by vertebra column, meninges and cerebrospinal fluid 97. Describe the 3 spinal cord meninges and their associated tissues and fluids. 1) Spinal dural (mater)sheath, the outer meninx, a single layer. It is separated from the vertebral column by a cushioning fat-filled epidural space. 2) The space between the middle arachnoid and 3) inner pia mater meninges is filled with cerebrospinal fluid. 98. Why is a spinal tap performed in the subarachnoid space inferior to L1. Due to the cord ending at L1, the cerebrospinal fluid subarachnoid space inferior to this is the location for spinal taps or diagnostic testing. 99. Identify the parts of the spinal cord shown in the diagram below. 1) Anterior horn 2) Posterior horn 3) Gray commissure 8 = Anterior median fissure 9 = Posterior median sulcus 10 = Central canal 11 = Anterior root 12 = Posterior root 100. Describe the composition of the gray matter of the spinal cord. The gray matter of the cord is composed of multipolar neurons and supporting cells. 101. Describe the composition of the white matter of the spinal cord. Composed of myelinated and un-myelinated nerve fibers. 102. Describe the function of the white matter of the spinal cord. The white matter fibers of the spinal cord are composed of ascending tracts that proceed up to the brain carrying sensory inputs and descending tracts that proceed down to (or within) the cord carrying motor outputs. Brain and Spinal Injuries and Diseases If your head is moving and then is suddenly stopped as it hits an object, brain damage can occur at the site of the impact and also as the brain hits the opposite side of the skull. A slight injury of this type is called a concussion since the symptoms are mild and transient including dizziness or brief loss of consciousness, but no permanent neurological damage is sustained. A more serious impact injury, a brain contusion, results in significant tissue damage which usually causes unconsciousness (coma), ranging in duration from hours to a lifetime. Following head blows, hemorrhage can cause blood to accumulate increasing intracranial pressure and compressing brain tissue. If this pressure forces the brain stem into the foramen magnum, control of blood pressure, heart rate, and respiration is lost with possible fatal consequences. Traumatic head injuries can also result in swelling of the brain due to water uptake by brain tissue. Degenerative diseases of the brain include stroke and Alzheimer’s disease with stroke being the most common nervous system disorder and the third leading cause of death in the US. Strokes occur when blood circulation to a brain area is blocked resulting in tissue death due to lack of oxygen and nutrients being supplied to brain cells. This is most often caused by a clot or fat deposit blocking a cerebral artery but can also be due to compression of brain tissue by hemorrhage or edema. Stroke victims often die but those who survive usually suffer paralysis, cognitive deficits, speech problems, emotional difficulties and pain. Some patients recover at least a portion of their lost faculties, because undamaged neurons sprout new branches that spread into the area of injury and take over some lost functions. Alzheimer’s Disease is a progressive degenerative disease of the brain, usually seen in elderly people, that ultimately results in mental decline. Its victims exhibit early difficulty remembering newly learned information and then increasingly severe symptoms, including disorientation, mood and behavior changes; deepening confusion about events, time and place; unfounded suspicions about family, friends and caregivers; more serious memory loss and behavior changes; and difficulty speaking, swallowing and walking. Alzheimer’s disease is associated with structural changes in the brain, particularly in the cerebral cortex. Spinal Cord Injuries and Diseases Amyotrophic lateral sclerosis (ALS), Lou Gehrig’s disease, is a neuromuscular condition that involves progressive destruction of anterior horn motor neurons and brain pyramidal tract fibers. As the disease progresses, the sufferer loses the ability to speak, swallow, and breathe; death typically occurs within 5 years. Paralysis (loss of motor function) or sensory losses is caused by any localized damage to the spinal cord or spinal nerve roots. Damage to the ventral root or anterior horn cells results in paralysis of the associated skeletal muscles since nerve impulses cannot reach these muscles which after time begin to atrophy. If the spinal cord is severed at any level, total motor and sensory loss is experienced in body regions below the site of the damage. Paraplegia, lower limb paralysis, occurs if the spinal cord is severed between T1 and L1. Quadriplegia, paralysis of all four limbs, occurs if the spinal cord is severed in the cervical region. Problem Set 10: 103. List and describe 4 types of brain damage. Brain damage can occur at the site of an impact. A slight injury of this type is called a concussion since the symptoms are mild and transient including dizziness or brief loss of consciousness. A more serious impact injury, a brain contusion, results in significant tissue damage which usually causes unconsciousness (coma), ranging in duration from hours to a lifetime. Hemorrhage can cause blood to accumulate increasing intracranial pressure and compressing brain tissue. Traumatic head injuries can also result in swelling of the brain due to water uptake by brain tissue. 104. Describe stroke. Is a result of blocked blood circulation to to the brain causing tissue death due to the loss of oxygen and nutrient supply by brain cells. The most often caused by a clot or fat deposit blocking a cerebral artery but can also be due to compression of brain tissue by hemorrhage or edema. Stroke victims often die, but those who survive usually suffer paralysis, cognitive disorders. speech problems, emotional difficulties ad pain. Some patients recover at least a portion of their lost faculties, because undamaged neurons sprout new branches that spread into the area of injury and take over lost function. 105. Describe Alzheimer's disease Alzheimer's Disease is a progressive degenerative disease of the brain, usually seen in elderly people, that ultimately results in mental decline. Its victims exhibit early difficulty remembering newly learned information and then increasingly severe symptoms, including disorientation, mood and behavior changes; deepening confusion about events, time and place; unfounded suspicions about family, friends and caregivers; more serious memory loss and behavior changes; and difficulty speaking, swallowing and walking. Alzheimer's disease is associated with structural changes in the brain, particularly in the cerebral cortex. The Special Senses The five special senses vision, smell, taste, hearing and equilibrium (balance) are the senses that have specialized organs containing specialized receptor cells which carry their impulses by way of specialized somatic and visceral afferents. The other sense, touch, is a somatic sense which does not have a specialized organ and uses general receptors composed of modified dendrites of sensory neurons. Touch includes pressure, vibration, pain and heat and such information is carried in general somatic afferents and general visceral afferents. Vision and the Eye The organ responsible for sight is the eye and it consists of three layers. The outer fibrous layer includes the posterior portion known as the sclera and the anterior portion known as the cornea. The sclera is the “white of the eye”, the cornea is the transparent part of the eye where light enters. The middle vascular layer of the eye includes the darkly-colored posterior choroid which prevents light from dispersing throughout the eye and supplies blood to the other layers of the eye. The anterior ciliary body changes the shape of the lens allowing it to focus. The iris is anterior to the ciliary body and contains the pupil which controls the amount of light entering the eye by using its muscle fibers to contract or dilate based on the amount of light in the environment. The interior sensory layer includes the retina which contains two types of cells. The more numerous rods, our dim light and peripheral vision receptors which are more sensitive to light but do not generate sharp or color images. The cones operate in bright light generating sharp color images. Eye movements are controlled by six muscles. The medial rectus, inferior rectus, superior rectus, and inferior oblique are all innervated by the third cranial nerve, the oculomotor. The medial rectus turns the eye medially. The inferior rectus moves the eye medially and depresses it. The superior rectus moves the eye medially and elevates it. The inferior oblique moves the eye laterally and elevates it. The fifth muscle is the superior oblique, which is controlled by the fourth cranial nerve, the trochlear nerve, and moves the eye laterally and depresses it. Finally, the sixth muscle, the lateral rectus, is controlled by the sixth cranial nerve, the abducens, and turns the eye laterally. Light passes into eye moving progressively through the cornea, aqueous humor, lens and vitreous humor to the surface of the retina which sends a signal through the optic nerve on to the optic chiasm at the base of the hypothalamus. The medial fibers of the optic nerve cross to the other side when they reach the optic chiasm where the optic tracts are formed. As a result of this crossover of fibers, the right side of the brain receives signs from the lateral side of the right eye and the medial side of the left eye, and the situation is reversed for the left side of the brain. If the right optic nerve is damaged, the right eye will be unable to see. However, if the right optic tract is damaged this causes blindness in the left half of the field of vision in both eyes. Problem Set 11: 106. List the five special senses. 1) vision 2) smell 3) taste 4) hearing 5) equilibrium 107. Why is touch not listed as a special sense? Touch is not a special sense because it is a somatic sense and does not have a specialized organ. It uses general receptors composed of modified dendrites of sensory neurons. 108. Describe the sclera and the cornea of the eye. The sclera and cornea are located in the outermost fibrous layer of the eye. The sclera is in the posterior portion and demonstrates the white portion of the eye. The cornea is in the anterior portion and is seen as the transparent part where light enters. 109. Describe the choroid, and the pupil of the eye. The choroid and the pupil are located in the middle vascular layer of the eye. The choroid is posterior. It is darkly colored which prevents light from dispersing throughout the eye and supplies blood to the other layers or the eye. The anterior ciliary body changes the shape of the lens allowing to focus. Within the iris which is anterior to the ciliary body contains the pupil which controls the amount of light entering the eye by using its muscle fibers to contract or dilate based on the amount of light in the environment. 110. Describe the functioning of the rod and cone cells of the eye. In the interior sensory layer of the eye hosts the retina which has two types of cells, the rods and cones. The more numerous rods are our dim light and peripheral receptors that a more sensitive to light but do not generate sharp color images. The cones operate in bright light, generating sharp color images. 111. Trace the pass of light through the eye. Light passes into eye moving progressively through the cornea, aqueous humor, lens and vitreous humor to the surface of the retina which sends a signal through the optic nerve on to the optic chiasm at the base of the hypothalamus. Hearing and the Ear The ear is the sensory organ for hearing and it can be divided into three areas: the external, middle, and inner ears. The external ear consists of the auricle and the external acoustic canal (meatus). The auricle directs sound waves into the external acoustic canal so that they can be detected. It is the part of the ear that can be seen from the outside and is composed of elastic cartilage covered with thin skin making up the rim (helix) and the lobule that lacks cartilage. The external acoustic canal is the tunnel between the auricle and the eardrum and is composed of elastic cartilage near the auricle and a cylinder through the temporal bone. The canal is lined with skin containing hairs and glands that secrete earwax which traps foreign materials. The inner end of the acoustic canal terminates at the tympanic membrane (eardrum), a thin membrane of connective tissue whose vibration transmits sound energy to the middle ear. The middle ear or tympanic cavity is an air-filled chamber containing the three smallest bones in the body which are known as the ossicles: the malleus (hammer), the incus (anvil), and the stapes (stirrup). The malleus receives the vibrations from the eardrum and transfers them along progressively through the incus to the stapes which conveys them to the inner ear. The inner ear is composed of the bony labyrinth a system of perilymph fluid-filled channels which contain the membranous labyrinth a group of endolymph fluid-filled membranous sacs and ducts all of which is divided into three sections the vestibule, the semicircular canals and the cochlea. The vestibule houses receptors which provide the body's balance system. The semicircular canals are the anterior vertical, posterior vertical and horizontal lateral canals which each contain at their junction an equilibrium receptor which respond to head movements, thereby contributing to the body's balance and orientation. The cochlea is a spiral, bony chamber containing the membranous endolymph-filled cochlear duct which houses the organ of Corti and terminates at the cochlear nerve. The organ of Corti contains tiny hairs which initiate an action potential that is transmitted through the cochlear nerve to the brain for processing. So hearing is caused by (1) sound waves passing into the external auditory canal and (2) causing the ear drum to vibrate which (3) transmits the vibrations to the ossicles which (4) push against fluid in the cochlear duct which (5) causes the hairs in the organ of Corti to move which (6) stimulates nearby neurons to (7) send impulses through the cochlear nerve to the brain. Problem Set 12: 112. List the parts and functions of the external ear. The external ear consists of the 1) auricle, which directs sound waves into the external acoustic canal so that they can be detected. 2) The external acoustic canal (meatus), is between the auricle and the eardrum which is lined with skin containing hair and glads that secrete earwax which traps foreign materials. 3) The inner ear of the acoustic canal terminates at the tympanic membrane (eardrum), a thin membrane of connective tissue whose vibrations transmit energy to the middle ear. 113. List the bones of the middle ear. The malleus (hammer), the incus (anvil) and the stapes (stirrup). 114. List the parts and functions of the membranous labyrinth of the inner ear. Vestibule-houses receptors which provide the body's balance system. Semicircular canals - are the anterior vertical, posterior vertical and horizontal lateral canals which each contain at their junction an equilibrium receptor which respond to head movements, thereby contributing to the body's balance and orientation. Cochlea- spiral, bony chamber containing the membranous endolymph-filled cochlear duct which houses the organ of Corti and terminates at the cochlear nerve. The organ of Corti contains tiny hairs which initiate an action potential that is transmitted through the cochlear nerve to the brain for processing. 115. Explain the steps in the hearing process. So hearing is caused by sound waves passing into the external auditory canal which causes the ear drum to vibrate which transmits the vibrations to the ossicles which push against fluid in the cochlear duct which (5) causes the hairs in the organ of Corti to move which stimulates nearby neurons to send impulses through the cochlear nerve to the brain. 116. Identify the parts of the ear shown in the diagram below. Part ID 3 Auricle 4 eardrum 6 malleus 7 incus 8 stapes 9 semicircular canals 10 cochlea 11 cochlear nerve Smell