Nervous System
Review
Functions of the Nervous
System
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Receive sensory input (gather info)
Integration (interpret input)
Maintain homeostasis (monitor change)
Mental activity (consciousness, memory
& thinking)
• Control of skeletal muscles (movement).
Divisions of the Nervous System
• CNS
– Develops from embryonic neural tube
– Consists of brain & spinal cord
– Integrating & command center (interprets sensory
input)
• PNS
– Nerves outside brain & spinal cord
– Refer to question # 22 for cranial & spinal nerves
Divisions of the Nervous System
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PNS
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Afferent division – towards CNS (sensory) –
somatic & visceral sensory fibers (sense organs)
Efferent division – away from CNS (motor); 2
subdivisions:
a. somatic motor nervous system – voluntary – control of
skeletal muscles
b. autonomic nervous system – involuntary – controls
cardiac & smooth muscle & glands; 2 subdivisions:
1. sympathetic division – prepares one for physical
activity – “fight or flight”
2. parasympathetic division – activates functions that
are associated with the body
Divisions of the Nervous System
Cells of the Nervous System
• Nerve
– a bundle of axons in the PNS that functions to conduct
action potentials to & from the CNS (called tracts in
CNS).
– There are no cell bodies in nerves.
• Neuron
– A nerve cell with cell body, axon & dendrites.
– Axons carry impulse away from the cell body
– Dendrites carry impulse towards cell body.
Cells of the Nervous System
• Sensory (afferent) nerve
– Carry impulses to CNS from sense organs
– Cell bodies are outside the CNS.
• Motor (efferent) nerve
– Carry impulses from CNS to muscles and glands
– Cell bodies are always in CNS
• Mixed nerves
– Contain both sensory and motor nerves.
• Interneurons or association neurons
– Neurons that provide connections between sensory
and motor neurons, as well as between themselves.
Examples
• Sensory (afferent) nerve
– Olfactory sensory neurons
– Mechanoreceptors
– Chemoreceptors
• Motor (efferent) nerve
– Somatic motor neurons (innervate skeletal
muscles)
– Visceral motor neurons (innervate cardiac &
smooth muscle)
• Mixed nerves
– Median nerve at the wrist
– Spinal nerves
3 Neuron Types & Functions
• Multipolar
– A type of neuron that possesses a single (usually long) axon
and many dendrites, allowing for the integration of a great deal
of information from other neurons
– Most efferent neurons and most CNS neurons.
• Bipolar
– A single axon and dendrite arise at opposite poles of the cell
body
– Found only in sensory neurons, such as in the retina, olfactory
and auditory systems.
• Unipolar
– Presence of only a single axon, branching at the terminal end;
most afferent neurons.
5 Different Neuroglia & Their
Functions
• Astrocytes
– Star-shaped
– Anchor neurons to capillaries
– Form barrier between capillaries and neurons (blood brain
barrier)
– Control chemical environment of brain.
• Microglia
– Spider-like phagocytes
– Dispose of debris
– Protect CNS from infection.
• Ependymal cells
– Line cavities of the brain and spinal cord
– Beating cilia circulate cerebrospinal fluid
5 Different Neuroglia & Their
Functions
• Oligodendrocytes
– Produce myelin sheath around nerve fibers
in the central nervous system
– Unable to transmit nerve impulses
– Never lose their ability to divide
– Most brain tumors are gliomas - tumors
formed by neuroglia
• Schwann cells
• Form myelin sheaths around axons, or enclose
unmyelinated axons, in PNS
Ganglia
• Groups of neuron cell bodies in the PNS
• Preganglionic neurons are autonomic neurons
whose cell bodies are located in the CNS & that
synapse with postganglionic neurons.
• Postganglionic neurons are autonomic neurons
whose cell bodies are located outside the CNS
and that receive synaptic stimulation from
preganglionic autonomic neurons.
Gray Matter vs. White Matter
• Gray matter
– Groups of neuron cell bodies and their dendrites
– Composed of unmyelinated neurons
– Distributed at the surface of the cerebrum &
cerebellum, as well as in the depth of the cerebral,
cerebellar, and spinal white matter
– Function of gray matter is to route sensory or motor
stimulus to interneurons of the CNS for creation of
response to stimulus through chemical synapse
activity.
Gray Matter vs. White Matter
• White matter
– Composed of myelinated nerve cell processes, or
axons, which connect various gray matter areas (the
locations of nerve cell bodies) of the brain to each
other and carry nerve impulses between neurons
– Forms the bulk of the deep parts of the brain and the
superficial parts of the spinal cord
• Generally, white matter can be understood as the parts of
the brain and spinal cord responsible for information
transmission (axons)
• Whereas, gray matter is mainly responsible for
information processing (neuron bodies)
Propagation of Action
Potentials
• Resting membrane potential
– Charge difference across the membrane of a resting
cell (slightly (+) on the outside and (–) on the inside)
– Higher concentration of Na+ on the outside & higher
concentration of K+ on the inside
• Action potential
– Charge reversal (resulting from Na+ moving into the
cell) & return to its resting level (result of Na channels
closing & K channels opening - K+ moving out of the
cell)
Propagation of Action
Potentials
• Depolarization
– Occurs when Na+ enter the cell & cause the
inside of the cell to become more positive and
the outside more negative.
• Repolarization
– A change in charge back to the resting
membrane potential
– Occurs when Na channels close & K channels
open & K+ move out of the cell
Propagation of Action
Potentials
• Mitochondria
– Produce the large amount of energy (ATP)
required by the neuron
Proprioceptors
• Nerves that innervate the joints & tendons &
provide information about the position of the
body & its various parts.
5 Components of a Reflex Arc
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Sensory receptor (ex: skin)
Sensory or afferent neuron
Integration center (association neuron in CNS)
Motor or efferent neuron
Effector organ (ex: muscle or gland)
Central Nervous System (CNS)
• Brain
• Spinal cord
4 Major Regions of Brain
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Cerebrum
Diencephalon
Brain stem
Cerebellum
Brain Stem
• Midbrain
– Cerebral peduncles (2 bulging fiber tracts) convey ascending &
descending impulses
– Corpora quadrigemina (4 rounded protrusions) – reflex centers
for vision and hearing
• Pons (Bridge)
– Involved in control of breathing
• Medulla oblongata
– Important control center for
• Heart rate control
• Blood pressure regulation
• Breathing
• Swallowing
• Vomiting
Diencephalon
• Thalamus
– Relay station for sensory impulses & sensory cortex
• Hypothalamus
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Helps regulate body temperature
Controls H2O balance
Regulates metabolism
Part of limbic system – emotions
Pituitary gland hangs from anterior floor by slender stalk
Regulates pituitary gland
Produces 2 of its own hormones
Diencephalon
• Epithalamus
– Forms roof of 3rd ventricle
– Houses the pineal body which
• May influence onset of puberty
• Appears to play a major role in sexual development,
hibernation & migration in animals, metabolism, and
seasonal breeding.
• Produces melatonin, which is stimulated by darkness and
inhibited by light
– Includes the choroids plexus that forms
cerebrospinal fluid (CSF)
– Involved in the emotional & visceral response to
odors
Cerebrum
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Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
Cerebrum
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Frontal lobe
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Primary motor area
Motivation, aggression, mood & olfactory
(smell) reception
Language comprehension (word
meanings)
Broca’s area – located in only one
hemisphere usually the left
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Language processing
Speech production
Comprehension
Cerebrum
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Parietal lobe
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Somatic sensory area for touch, pain, &
temperature
– Gustatory area – taste
– Wernicke’s area (usually in left
hemisphere) – sensory speech area
• Involved in understanding &
comprehension of spoken language
Cerebrum
• Occipital lobe
– Visual area
• Temporal lobe
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Auditory area – hearing
Olfactory area – smell
Plays an important role in memory
Abstract thought & judgment
Main Fissures of Cerebrum
• Longitudinal fissure
– Separates the left & right cerebrum.
• Parieto-occipital sulcus
– Separates the parietal lobes and the
occipital lobes in both hemispheres.
Gyri vs. Sulci
• Gyri
– Rounded elevations or folds on the
surface of the brain.
– Increase the surface area for neurons.
• Sulci
– Grooves on the surface of the brain
between the gyri.
Functional Areas of Cerebral
Cortex
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Olfactory area
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Language comprehension area
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Word meanings
Motor speech area (Broca’s Area)
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Smell
Ability to speak or say words properly
Frontal association area
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Carrying out “higher” functions such as
perception, decision-making as well as
controlling thoughts
Functional Areas of Cerebral
Cortex
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Premotor area
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Primary motor area
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Sends impulses to skeletal muscles
Somatic sensory area
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Muscle action is learned through practice
Receives impulses from the body’s sensory
receptors & interprets them
Gustatory area
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Taste
Functional Areas of Cerebral
Cortex
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Speech/Language area (Wernicke’s
area)
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General interpretation area
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Interpretation of input
Visual area
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Allows one to sound out words
Sight
Auditory area
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Hearing
Corpus Callosum
• A large, thick nerve fiber tract
connecting the 2 cerebral
hemispheres for communication.
• White matter
• Connects the 2 cerebral
hemispheres for communication
Right vs. Left Hemispheres
• Important b/c some functional
areas are only in one hemisphere.
• The right side of the brain controls
the left side of the body and vice
versa.
Meninges vs. Ventricles
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Meninges
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A series of 3 connective tissue membranes
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Dura mater
Arachnoid mater
Pia mater
Surround & protect the brain & spinal cord
Ventricles
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One of 4 cavities in the brain filled w/
cerebrospinal fluid.
Cerebellum Functions
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Provides involuntary coordination of
body movements (balance &
equilibrium)
Monitors body position & corrects
(“autopilot”)
Connects to inner ear & eye
Involved in learning a motor skill such
as riding a bicycle or playing a piano
3 Membranes of CNS
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Dura mater
– Consisting of the periosteal (attached to
surface of the skull) and meningeal (outer
covering of the brain) layers
• Arachnoid mater
– Middle covering, attached to the inside of the
dura, surrounds the brain and spinal cord
but does not line the brain down into its
sulci.
• Pia mater
– Internal layer, clings to the surface of the
brain.
Cerebrospinal Fluid
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Fills the brain ventricles, the central
canal of the spinal cord, and the
subarachnoid space.
Bathes the brain & spinal cord, providing
a protective cushion around the CNS.
Peripheral Nervous System
(PNS)
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Cranial nerves
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Peripheral nerve originating in the brain
Part of the PNS
Consists of 12 pairs
Some are only sensory, & some are only somatic
motor, whereas others have more than one function
Cranial nerves with both afferent & efferent
functions are called mixed nerves.
Spinal nerves
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Arise along the spinal cord from the union of the
dorsal roots and ventral roots
All are mixed nerves.