EXAM 1 NOTES:
CHAPTER 56: A&P AND ASSESSMENT OF THE NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM (CNS): consists of the brain, spinal cord, and cranial nerves I and II
PERIPHERAL NERVOUS SYSTEM (PNS): consists of cranial nerves III to XII, spinal nerves, and the
peripheral components of the autonomic nervous system (ANS)
NEURONS: primary functional unit of the nervous system
Consists of a cell body
Multiple dendrites (receivers)
An axon (transmitter)
3 characteristics of neurons:
EXCITABILITY: The ability to generate a nerve impulse
CONDUCTIVITY: the ability to transmit an impulse
INFLUENCE: the ability to influence other neurons, muscle cells, or glandular cells by transmitting
nerve impulses to them
GLIAL CELLS (glia or neuroglia): provide support, nourishment and protection to the neurons
Constitute almost half of the brain and spinal cord mass
5 to 10 times more numerous than neurons
Most primary CNS tumors involve glial cells – primary malignancies involving neurons are rare
Are mitotic and can replicate
Divided into MICROGLIA and MACROGLIA
o MICROGLIA: specialized macrophages capable of phagocytosis
Protect the neurons
Mobile within the brain
Multiply when the brain is damaged
o MACROGLIA:
Include ASTROCYTES (most abundant)
Found primarily in gray matter
Provide structural support to neurons
Their processes form the blood-brain barrier
Play a major role in synaptic transmission
When brain is injured, they act as phagocytes for neuronal debris
Proliferation of astrocytes contributes to the formation of scar tissues
(GLIOSIS) in the CNS
OLIGODENDROCYTES
o Specialized cell that produce the myelin sheath of nerve fibers in the CNS
o Primarily found in white matter of the CNS
, o SCHWANN CELLS myelinate the nerve fibers in the periphery
EPENDYMAL CELLS
o line the brain ventricles
o aid in the secretion of cerebrospinal fluid
NERVE REGENERATION
If the axon is damaged, the cell attempts to repair itself
Try to grow back to their original destinations by sprouting many branches from the damaged
ends of the axons
Generally less successful in the CNS than in the PNS
NERVE IMPULSE
Initiation of a nerve impulse involves the generation of an action potential
o Once an action potential is initiated, a series of action potentials travels along the axon
o When the impulse reaches the end of the nerve fiber, it is transmitted across the
synapse (junction) by a chemical interaction involving neurotransmitters
o This chemical interaction generates another set of action potentials in the next neurons
o Process repeats until the impulse reaches its destination
Many peripheral nerve axons have NODES OF RANVIER( gaps in the myelin sheath)
o Allow an action potential to travel much faster by jumping from node to node without
traversing the insulated membrane segment
This process is called SATLATORY (hopping) CONDUCTION
o In an unmyelinated fiber, the wave of depolarization travels the entire length of the
axon, with each portion of the membrane becoming depolarized in turn
SYNAPSE: the structural and functional junction between two neurons
NEUROTRANSMITTERS: chemicals that affect the transmission of impulses across the synaptic
clef
o Excitatory neurotransmitters activate postsynaptic receptors that increase the likelihood
that an action potential will be generated
o Inhibitory neurotransmitters activate postsynaptic receptors that inhibit the likelihood
that an action potential will be generated
o ACETYLCHOLINE
A decrease in acetylcholine-secreting neurons is seen in Alzheimer’s disease
Myasthenia gravis results from a reduction in acetylcholine receptors
A weakness and rapid fatigue of muscles under voluntary control
Symptoms: droopy eyelid and mouth, difficulty swallowing, double
vision, unsteady walk
o AMINES
EPINEPHRINE (ADRENALIN)
Both a hormone and neurotransmitter
Produced in neurons of CNS and neurosecretory cells of adrenal medulla
, Critical component of the fight-or-flight response of the SNS
(sympathetic nervous system)
NOREPINEPHRINE
Both a hormone and neurotransmitter
Has important role as neurotransmitter released from SNS affecting the
heart
Along with epinephrine, has important role in fight-or-flight response,
increasing heart rate, triggering the release of glucose from energy
stores, and increasing blood flow to skeletal muscle
SEROTONIN
Primarily found in GI tract, platelets and CNS
Involved in moods, emotions, and sleep
DOPAMINE
Produced in several areas of the brain
Involved in emotions and moods and regulating motor control
Parkinson’s disease results from destruction of dopamine-secreting
neurons
o AMINO ACIDS
GABA (GAMMA-AMINOBUTYRIC ACID)
Chief inhibitory neurotransmitter in CNS
Regulated neuronal excitability throughout the nervous system
Drugs that increase GABA function have been used to treat seizure
disorders
GLUTMATE and ASPARTATE
Play key role in learning and memory
Sustained release of glutamate and prolonged excitation is toxic to nerve
cells
Glutamate is a destruction factor in amyotrophic lateral sclerosis
o NEUROPEPTIDES
ENDORPHINS and ENKEPHALINS
Endogenous opioids that function as neurotransmitters
Produced in pituitary gland and hypothalamus
Produce analgesia and a feeling of well being
The opioids morphine and heroin bind to endorphin and enkephaline
receptors and produce same effect as the endogenous opioids
SUBSTANCE P
Neurotransmitter in pain transmission pathways
Morphine blocks its release
Neurotransmitters continue to combine with the receptor sites at the postsynaptic membrane
until they are inactivated by enzymes, are taken up by the presynaptic endings, or diffuse away
from the synaptic regions
CENTRAL NERVOUS SYSTEM
SPINAL CORD
, o Continuous with the brainstem
o Exits from the cranial cavity through the foramen magnum
o Cross section reveals gray matter centrally located in an H shape and is surrounded by
white matter
o Gray matter contains:
the cell bodies of voluntary motor neurons
preganglionic autonomic motor neurons
association neurons (interneurons)
o white matter contains the axons of the ascending sensory and the descending
(suprasegmental) motor fibers)
the myelin surrounding these fibers gives them their white appearance
o ASCENDING TRACTS
In general, carry specific sensory information to higher levels of the CNS
Info comes from special sensory receptors in the skin, muscles and joints,
viscera, and blood vessels
Enters the spinal cord by way of the dorsal roots of the spinal nerves
The FASCICULUS GRACILIS and the FASCICULUS CUNEATUS (commonly called the
dorsal or posterior columns) carry information and transmit impulses concerned
with touch, deep pressure, vibrations, position sense, and kinesthesia
(appreciation of movement, weight and body parts)
SPINOCEREBELLAR TRACTS: carry information about muscle tension and body
position to the cerebellum for coordination of movement
SPINOTHALAMIC TRACTS carry pain and temperature sensations
o DESCENDING TRACTS
Carry impulses that are responsible for muscle movement
Among the most important are the CORTICOBULBAR and CORTICOSPINAL
TRACTS collectively termed the PYRAMIDAL TRACT
These tracts carry volitional (voluntary) impulses from the cerebral cortex to the
cranial and peripheral nerves
Another group of descending motor tracts carries impulses from the
extrapyramidal system (all motor systems except the pyramidal) concerned with
voluntary movement
o LOWER AND UPPER MOTOR NEURONS
Lower motor neurons are the final common pathway through which descending
motor tracts influence skeletal muscle
The cell bodies of the LMNs (lower motor neurons), which send axons to
innervate the skeletal muscles of the arms, trunk, and legs, are located
in the anterior horn of the corresponding segments of the spinal cord
(e.g., cervical segments contain LMNs for the arms)
LMN lesions generally cause weakness or paralysis, denervation atrophy,
hyporeflexia or areflexia and decreased muscle tone
Upper motor neurons originate in the cerebral cortex and project downward
The corticobulbar tract ends in the brainstem
The corticospinal tract descends into the spinal cord
CHAPTER 56: A&P AND ASSESSMENT OF THE NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM (CNS): consists of the brain, spinal cord, and cranial nerves I and II
PERIPHERAL NERVOUS SYSTEM (PNS): consists of cranial nerves III to XII, spinal nerves, and the
peripheral components of the autonomic nervous system (ANS)
NEURONS: primary functional unit of the nervous system
Consists of a cell body
Multiple dendrites (receivers)
An axon (transmitter)
3 characteristics of neurons:
EXCITABILITY: The ability to generate a nerve impulse
CONDUCTIVITY: the ability to transmit an impulse
INFLUENCE: the ability to influence other neurons, muscle cells, or glandular cells by transmitting
nerve impulses to them
GLIAL CELLS (glia or neuroglia): provide support, nourishment and protection to the neurons
Constitute almost half of the brain and spinal cord mass
5 to 10 times more numerous than neurons
Most primary CNS tumors involve glial cells – primary malignancies involving neurons are rare
Are mitotic and can replicate
Divided into MICROGLIA and MACROGLIA
o MICROGLIA: specialized macrophages capable of phagocytosis
Protect the neurons
Mobile within the brain
Multiply when the brain is damaged
o MACROGLIA:
Include ASTROCYTES (most abundant)
Found primarily in gray matter
Provide structural support to neurons
Their processes form the blood-brain barrier
Play a major role in synaptic transmission
When brain is injured, they act as phagocytes for neuronal debris
Proliferation of astrocytes contributes to the formation of scar tissues
(GLIOSIS) in the CNS
OLIGODENDROCYTES
o Specialized cell that produce the myelin sheath of nerve fibers in the CNS
o Primarily found in white matter of the CNS
, o SCHWANN CELLS myelinate the nerve fibers in the periphery
EPENDYMAL CELLS
o line the brain ventricles
o aid in the secretion of cerebrospinal fluid
NERVE REGENERATION
If the axon is damaged, the cell attempts to repair itself
Try to grow back to their original destinations by sprouting many branches from the damaged
ends of the axons
Generally less successful in the CNS than in the PNS
NERVE IMPULSE
Initiation of a nerve impulse involves the generation of an action potential
o Once an action potential is initiated, a series of action potentials travels along the axon
o When the impulse reaches the end of the nerve fiber, it is transmitted across the
synapse (junction) by a chemical interaction involving neurotransmitters
o This chemical interaction generates another set of action potentials in the next neurons
o Process repeats until the impulse reaches its destination
Many peripheral nerve axons have NODES OF RANVIER( gaps in the myelin sheath)
o Allow an action potential to travel much faster by jumping from node to node without
traversing the insulated membrane segment
This process is called SATLATORY (hopping) CONDUCTION
o In an unmyelinated fiber, the wave of depolarization travels the entire length of the
axon, with each portion of the membrane becoming depolarized in turn
SYNAPSE: the structural and functional junction between two neurons
NEUROTRANSMITTERS: chemicals that affect the transmission of impulses across the synaptic
clef
o Excitatory neurotransmitters activate postsynaptic receptors that increase the likelihood
that an action potential will be generated
o Inhibitory neurotransmitters activate postsynaptic receptors that inhibit the likelihood
that an action potential will be generated
o ACETYLCHOLINE
A decrease in acetylcholine-secreting neurons is seen in Alzheimer’s disease
Myasthenia gravis results from a reduction in acetylcholine receptors
A weakness and rapid fatigue of muscles under voluntary control
Symptoms: droopy eyelid and mouth, difficulty swallowing, double
vision, unsteady walk
o AMINES
EPINEPHRINE (ADRENALIN)
Both a hormone and neurotransmitter
Produced in neurons of CNS and neurosecretory cells of adrenal medulla
, Critical component of the fight-or-flight response of the SNS
(sympathetic nervous system)
NOREPINEPHRINE
Both a hormone and neurotransmitter
Has important role as neurotransmitter released from SNS affecting the
heart
Along with epinephrine, has important role in fight-or-flight response,
increasing heart rate, triggering the release of glucose from energy
stores, and increasing blood flow to skeletal muscle
SEROTONIN
Primarily found in GI tract, platelets and CNS
Involved in moods, emotions, and sleep
DOPAMINE
Produced in several areas of the brain
Involved in emotions and moods and regulating motor control
Parkinson’s disease results from destruction of dopamine-secreting
neurons
o AMINO ACIDS
GABA (GAMMA-AMINOBUTYRIC ACID)
Chief inhibitory neurotransmitter in CNS
Regulated neuronal excitability throughout the nervous system
Drugs that increase GABA function have been used to treat seizure
disorders
GLUTMATE and ASPARTATE
Play key role in learning and memory
Sustained release of glutamate and prolonged excitation is toxic to nerve
cells
Glutamate is a destruction factor in amyotrophic lateral sclerosis
o NEUROPEPTIDES
ENDORPHINS and ENKEPHALINS
Endogenous opioids that function as neurotransmitters
Produced in pituitary gland and hypothalamus
Produce analgesia and a feeling of well being
The opioids morphine and heroin bind to endorphin and enkephaline
receptors and produce same effect as the endogenous opioids
SUBSTANCE P
Neurotransmitter in pain transmission pathways
Morphine blocks its release
Neurotransmitters continue to combine with the receptor sites at the postsynaptic membrane
until they are inactivated by enzymes, are taken up by the presynaptic endings, or diffuse away
from the synaptic regions
CENTRAL NERVOUS SYSTEM
SPINAL CORD
, o Continuous with the brainstem
o Exits from the cranial cavity through the foramen magnum
o Cross section reveals gray matter centrally located in an H shape and is surrounded by
white matter
o Gray matter contains:
the cell bodies of voluntary motor neurons
preganglionic autonomic motor neurons
association neurons (interneurons)
o white matter contains the axons of the ascending sensory and the descending
(suprasegmental) motor fibers)
the myelin surrounding these fibers gives them their white appearance
o ASCENDING TRACTS
In general, carry specific sensory information to higher levels of the CNS
Info comes from special sensory receptors in the skin, muscles and joints,
viscera, and blood vessels
Enters the spinal cord by way of the dorsal roots of the spinal nerves
The FASCICULUS GRACILIS and the FASCICULUS CUNEATUS (commonly called the
dorsal or posterior columns) carry information and transmit impulses concerned
with touch, deep pressure, vibrations, position sense, and kinesthesia
(appreciation of movement, weight and body parts)
SPINOCEREBELLAR TRACTS: carry information about muscle tension and body
position to the cerebellum for coordination of movement
SPINOTHALAMIC TRACTS carry pain and temperature sensations
o DESCENDING TRACTS
Carry impulses that are responsible for muscle movement
Among the most important are the CORTICOBULBAR and CORTICOSPINAL
TRACTS collectively termed the PYRAMIDAL TRACT
These tracts carry volitional (voluntary) impulses from the cerebral cortex to the
cranial and peripheral nerves
Another group of descending motor tracts carries impulses from the
extrapyramidal system (all motor systems except the pyramidal) concerned with
voluntary movement
o LOWER AND UPPER MOTOR NEURONS
Lower motor neurons are the final common pathway through which descending
motor tracts influence skeletal muscle
The cell bodies of the LMNs (lower motor neurons), which send axons to
innervate the skeletal muscles of the arms, trunk, and legs, are located
in the anterior horn of the corresponding segments of the spinal cord
(e.g., cervical segments contain LMNs for the arms)
LMN lesions generally cause weakness or paralysis, denervation atrophy,
hyporeflexia or areflexia and decreased muscle tone
Upper motor neurons originate in the cerebral cortex and project downward
The corticobulbar tract ends in the brainstem
The corticospinal tract descends into the spinal cord
