CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM AND NERVOUS TISSUE
OVERVIEW OF NERVOUS SYSTEM
Nervous system: Although the nervous system is the smallest organ system based on surface area, it is the most
complex based on its variety of structures and functions. The nervous system is a highly organized network of billons of
neurons and neuroglia and includes the brain, spinal cord, cranial and spinal nerves, sensory receptors, ganglia, and
enteric plexuses.
Brain: The brain is an organ composed primarily of nervous tissue and consists of about 100 billion neurons. It is
enclosed and protected by the cranial bones and cranial meninges.
Cranial nerves: Cranial nerves emerge from the base of the brain, and there are a total of 12 pairs. Depending
on the location they are innervating, they can have sensory and/or motor functions.
Spinal cord: The spinal cord is an organ composed primarily of nervous tissue and consists of about 100 million
neurons. It is enclosed and protected by the vertebrae and spinal meninges.
Spinal nerves: Spinal nerves emerge at regular intervals from the spinal cord, and there are a total of 31 pairs.
They function to innervate specific regions on the right and left sides of the body.
Ganglia: Ganglia are small masses of nervous tissue that consist primarily of neuronal cell bodies and are part of
the peripheral nervous system.
Enteric plexuses: Enteric plexuses are extensive networks of neurons that innervate the walls of organs in the
gastrointestinal (GI) tract and are part of the peripheral nervous system, specifically autonomic nervous system.
Sensory receptors: Sensory receptors are dendrites of sensory neurons or specialized cells that function to
monitor and detect changes in the internal and external environments of the body.
FUNCTIONS OF NERVOUS SYSTEM
Sensory function: The sensory function of the nervous system involves sensory receptors detecting internal and external
stimuli and relaying this information to the brain and spinal cord via sensory neurons. The sensory function allows
detection of internal and external stimuli.
Integrative function: The integrative function of the nervous system involves interneurons receiving sensory information
and integrating and storing it, which allows appropriate responses to be initiated.
Motor function: The motor function of the nervous system involves motor neurons receiving information from interneurons
and eliciting an output response based on this information. Motor neurons relay motor information away from the brain
and spinal cord to effectors (i.e. muscles, skin, glands).
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, CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM AND NERVOUS TISSUE
DIVISIONS OF NERVOUS SYSTEM
Central nervous system (CNS): The CNS is the brain and spinal cord.
Peripheral nervous system (PNS): The PNS includes all cranial and spinal nerves, sensory receptors, ganglia, and
enteric plexuses.
Sensory (afferent) division: The sensory division of the PNS involves sensory neurons conveying nerve impulses
about sensory information from the periphery to the CNS. Two types of sensory neurons exist: somatic afferent
neurons and visceral afferent neurons. Somatic afferent neurons convey sensory information from skin, skeletal
muscle tissue, and joints to the CNS. Visceral afferent neurons convey sensory information from visceral organs
to the CNS.
Motor (efferent) division: The motor division of the PNS involves motor neurons eliciting output responses to
convey motor information from the CNS to the periphery. These nerve impulses regulate skeletal, smooth, and
cardiac muscle contractions and glandular secretions.
Somatic nervous system (SNS): The SNS involves motor neurons innervating skeletal muscle tissue.
Many of the motor responses elicited by the SNS are consciously controlled, which is why it’s considered
the “voluntary” nervous system.
Autonomic nervous system (ANS): The ANS involves motor neurons innervating smooth and cardiac
muscle tissues and glands. The motor responses elicited by the ANS are subconscious controlled, which
is why it’s considered the “involuntary” nervous system. Two motor divisions of the ANS are evident:
sympathetic division and parasympathetic division.
Sympathetic division: The sympathetic division of the ANS involves motor neurons that elicit the
“fight-or-flight” responses of the body, which include:
Dilation of the pupils
Increase in heart rate, blood pressure, and forcefulness of heart contractions
Dilation of bronchioles (airway passages in the lungs)
Constriction of abdominal blood vessels
Dilation of blood vessels in cardiac and skeletal muscles
Catabolism of triglycerides (fat) in adipose tissue to synthesize ATP
Anabolism (synthesis) of glucose from glycogen via the liver to synthesize ATP
These responses are elicited during periods of physical and/or emotional stress.
Parasympathetic division: The parasympathetic division of the ANS involves motor neurons that
elicit the “rest-and-digest” responses of the body, which include:
Salivation
Lacrimation (crying)
Urination
Digestion
Defecation (releasing feces)
Constriction of the pupils
Decrease in heart rate
Constriction of bronchioles (airway passages in the lungs)
These responses are elicited during periods of relaxation and digestion.
Enteric nervous system (ENS): The ENS is a division of the PNS, which is known as the “brain of the
gut”. It is an involuntary system that involves the enteric plexuses. Sensory neurons in the ENS function
to detect chemical changes and stretching of the gastrointestinal (GI) tract, and motor neurons function to
innervate and control contractions of the smooth muscle tissue of the GI organs (i.e. esophagus,
stomach, small intestine, and large intestine) to move food through the tract.
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OVERVIEW OF NERVOUS SYSTEM
Nervous system: Although the nervous system is the smallest organ system based on surface area, it is the most
complex based on its variety of structures and functions. The nervous system is a highly organized network of billons of
neurons and neuroglia and includes the brain, spinal cord, cranial and spinal nerves, sensory receptors, ganglia, and
enteric plexuses.
Brain: The brain is an organ composed primarily of nervous tissue and consists of about 100 billion neurons. It is
enclosed and protected by the cranial bones and cranial meninges.
Cranial nerves: Cranial nerves emerge from the base of the brain, and there are a total of 12 pairs. Depending
on the location they are innervating, they can have sensory and/or motor functions.
Spinal cord: The spinal cord is an organ composed primarily of nervous tissue and consists of about 100 million
neurons. It is enclosed and protected by the vertebrae and spinal meninges.
Spinal nerves: Spinal nerves emerge at regular intervals from the spinal cord, and there are a total of 31 pairs.
They function to innervate specific regions on the right and left sides of the body.
Ganglia: Ganglia are small masses of nervous tissue that consist primarily of neuronal cell bodies and are part of
the peripheral nervous system.
Enteric plexuses: Enteric plexuses are extensive networks of neurons that innervate the walls of organs in the
gastrointestinal (GI) tract and are part of the peripheral nervous system, specifically autonomic nervous system.
Sensory receptors: Sensory receptors are dendrites of sensory neurons or specialized cells that function to
monitor and detect changes in the internal and external environments of the body.
FUNCTIONS OF NERVOUS SYSTEM
Sensory function: The sensory function of the nervous system involves sensory receptors detecting internal and external
stimuli and relaying this information to the brain and spinal cord via sensory neurons. The sensory function allows
detection of internal and external stimuli.
Integrative function: The integrative function of the nervous system involves interneurons receiving sensory information
and integrating and storing it, which allows appropriate responses to be initiated.
Motor function: The motor function of the nervous system involves motor neurons receiving information from interneurons
and eliciting an output response based on this information. Motor neurons relay motor information away from the brain
and spinal cord to effectors (i.e. muscles, skin, glands).
Page 1
, CHAPTER 11: FUNDAMENTALS OF THE NERVOUS SYSTEM AND NERVOUS TISSUE
DIVISIONS OF NERVOUS SYSTEM
Central nervous system (CNS): The CNS is the brain and spinal cord.
Peripheral nervous system (PNS): The PNS includes all cranial and spinal nerves, sensory receptors, ganglia, and
enteric plexuses.
Sensory (afferent) division: The sensory division of the PNS involves sensory neurons conveying nerve impulses
about sensory information from the periphery to the CNS. Two types of sensory neurons exist: somatic afferent
neurons and visceral afferent neurons. Somatic afferent neurons convey sensory information from skin, skeletal
muscle tissue, and joints to the CNS. Visceral afferent neurons convey sensory information from visceral organs
to the CNS.
Motor (efferent) division: The motor division of the PNS involves motor neurons eliciting output responses to
convey motor information from the CNS to the periphery. These nerve impulses regulate skeletal, smooth, and
cardiac muscle contractions and glandular secretions.
Somatic nervous system (SNS): The SNS involves motor neurons innervating skeletal muscle tissue.
Many of the motor responses elicited by the SNS are consciously controlled, which is why it’s considered
the “voluntary” nervous system.
Autonomic nervous system (ANS): The ANS involves motor neurons innervating smooth and cardiac
muscle tissues and glands. The motor responses elicited by the ANS are subconscious controlled, which
is why it’s considered the “involuntary” nervous system. Two motor divisions of the ANS are evident:
sympathetic division and parasympathetic division.
Sympathetic division: The sympathetic division of the ANS involves motor neurons that elicit the
“fight-or-flight” responses of the body, which include:
Dilation of the pupils
Increase in heart rate, blood pressure, and forcefulness of heart contractions
Dilation of bronchioles (airway passages in the lungs)
Constriction of abdominal blood vessels
Dilation of blood vessels in cardiac and skeletal muscles
Catabolism of triglycerides (fat) in adipose tissue to synthesize ATP
Anabolism (synthesis) of glucose from glycogen via the liver to synthesize ATP
These responses are elicited during periods of physical and/or emotional stress.
Parasympathetic division: The parasympathetic division of the ANS involves motor neurons that
elicit the “rest-and-digest” responses of the body, which include:
Salivation
Lacrimation (crying)
Urination
Digestion
Defecation (releasing feces)
Constriction of the pupils
Decrease in heart rate
Constriction of bronchioles (airway passages in the lungs)
These responses are elicited during periods of relaxation and digestion.
Enteric nervous system (ENS): The ENS is a division of the PNS, which is known as the “brain of the
gut”. It is an involuntary system that involves the enteric plexuses. Sensory neurons in the ENS function
to detect chemical changes and stretching of the gastrointestinal (GI) tract, and motor neurons function to
innervate and control contractions of the smooth muscle tissue of the GI organs (i.e. esophagus,
stomach, small intestine, and large intestine) to move food through the tract.
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