Download 1 NOTES – CHAPTER 9 (Brief) The Nervous System – LECTURE

NOTES – CHAPTER 9 (Brief)
The Nervous System – LECTURE NOTES
I. Divisions of the Nervous System – two major divisions
A. Central Nervous System (CNS)
1. brain
2. spinal cord
B. Peripheral Nervous System (PNS)
1. Nervous structures that lie outside of the CNS
2. Two subdivisions
a. Afferent division
1) transmits impulses from sensory organs to the CNS
2) Afferent fibers/neurons – nerve fibers that transmit action
potentials from the periphery to the CNS
b. Efferent (motor) division
1) transmits impulses from the CNS to effectors
a) effectors include muscles or glands
2) Efferent fibers/neurons – nerve fibers that transmit action
potentials from the CNS toward the periphery
3) Two subdivisions of Efferent division:
a) Somatic Motor Nervous System – transmits
impulses from CNS to skeletal muscles
b) Autonomic Nervous System (ANS) – transmits
from the CNS to smooth muscle, cardiac muscle,
and glands; Can be divided into two subdivisions:
i.) Sympathetic Nervous System – prepares the
person for physical activity
ii.) Parasympathetic Nervous System – activates
function for daily maintenance of body
(Example: digestion)
II. Cells of the Nervous System
A. Neurons – receive and transmit stimuli (action potentials) to effectors or other
neurons; these are nonreproductive cells; have three (3) major parts:
1. Cell Body – contains the nucleus
a. site of protein synthesis; if axon is separated from cell body, it
will die because no new proteins are being made for it
b. Nissl bodies – areas of rough ER concentration
2. Dendrites – short, often highly branched cytoplasmic extensions coming
off the cell body;
a. usually several
b. carry action potentials (impulse) to the cell body
3. Axons – long cell process extending from the cell body
a. only one per neuron
b. carries action potential away from the cell body
c. collateral axons – branches off axon
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d. myelin sheath – highly specialized insulating layer of cells
around some axons
1) Specialized wrappings around axon; made of fat; is white
in color
2) Excellent insulator and conductor; prevents almost all ion
flow through the cell membrane
3) Nodes of Ranvier – gaps or indentations between
neurolemmocytes; allow for the nerve impulses to travel
faster; allows ions to flow easily & help action potentials
develop and travel
4) Mylenated axons conduct action potentials faster
a) Salutatory conduction – impulse jumps from node of
Ranvier to node of Ranvier
5) Uses less energy because less ions travel across membrane
B. Neuroglia or glial cells – non-conducting cells within the nervous system
1. more numerous than neurons
2. retain ability to divide
3. Four types:
a. Astrocytes – star-shaped cells
1) major supporting cell in the CNS
2) attached neurons to blood vessels
3) blood-brain barrier – permeability barrier between blood
& nerve cells
b. Ependymal cells – line fluid-filled cavities in CNS
1) produce cerebrospinal fluid or help move this fluid through
the CNS
c. Microglia – help remove bacteria & cell debris from CNS
d. Neurolemmocytes - cells that produce myelin sheaths
1) Oligodendrocytes– cells with many dendries; surround
axons in CNS
2) Schwann cells - Oligodendrocytes in PNS
C. Organization of Nervous Tissue
1. Gray Matter – groups of neuron cells bodies & their dendrites
a. Cortex- gray matter on the surface of the brain
b. Nuclei- clusters of gray matter deeper within the brain
c. Ganglion – in PNS, cluster of neuron cell bodies
2. White Matter – bundles of parallel axons with their myelin sheaths
a. Nerve tracts – conduction pathways formed by white matter of
the CNS; propagate action potentials from one area of CNS to
another
b. Nerves – bundles of axons and their connective tissue sheaths in
PNS
III. Transmission of action potentials in nervous system
A. Synapse – the junction at which the axon of one neuron interacts with the
dendrites of another neuron or an effector organ (muscle or gland)
1. Presynaptic terminal – end of the axon
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2. Synaptic cleft – space separating the presynaptic & postsynaptic terminals
3. Neurotransmitters – chemical substances released by presynaptic terminal
in response to an action potential
a. Either allow or inhibit the impulse to cross the synaptic cleft to
the postsynaptic membrane
4. Postsynaptic membrane – membrane of the dendrite or effector
B. Reflexes – involuntary reaction in response to a stimulus applied to the periphery
& transmitted to the CNS
1. allows a quicker response than would be possible if conscious thought was
involved
2. Reflex arc – neuronal pathway by which a reflex occurs
a. basic functional unit of the nervous system
b. smallest, simplest pathway capable of receiving a stimulus and
yielding a response
c. Five basic components
1) sensory receptor
2) afferent or sensory neuron
3) association neurons
4) efferent or motor neuron
5) effector organ
d. most involve the spinal cord or brainstem & not higher brain
centers
e. Examples:
1) Withdrawal
2) knee jerk
IV. Central Nervous System (CNS) – consists of brain and spinal cord
A. Include the four (4) major parts of the brain
1. brainstem
2. diencephalons
3. cerebrum
4. cerebellum
B. Brainstem
1. Connects brain to spinal cord
2. Has many nuclei involved in vital body functions
a. damage to small areas of the brainstem can cause death
3. Has three major areas including medulla oblongata, pons, and midbrain:
a. Medulla oblongata
1) most inferior part of brainstem & continues inferiorly with
spinal cord
2) Contain nuclei with specific functions:
a) regulation of heart rate & blood vessel diameter
b) breathing
b. Pons - name means “bridge”
1) superior to medulla oblongata
2) relays information between cerebrum and cerebellum
c. Midbrain
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1)
2)
3)
4)
superior to pons
smallest region in the brainstem
contains centers for auditory & visual pathways
substantia nigra – black mass that regulates general body
movements
4. Reticular Formation
a. group of nuclei scattered throughout the brainstem
b. plays a major role in arousing & maintaining consciousness and
in regulating the sleep/wake cycle
c. damage to may cause a coma
C. Diencephalon
1. part of the brain between the brainstem and the cerebrum
2. made up of thalamus, epithalamus, & hypothalamus
a. thalamus
1) largest part of diencephalons
2) Functions:
a) passes sensory input from body to cerebral cortex
b. epithalamus
1) small area superior and posterior to the thalamus
2) Functions:
a) controls emotional & visceral response to odors
b) contains pineal body – an endocrine gland
i.) influences the onset of puberty
c. hypothalamus
1) most inferior part of diencephalons
2) Functions:
a) plays a major role in maintaining homeostasis
b) controls body temperature, hunger, & thirst
3) infundibulum – funnel-shaped stalk of the hypothalamus
that extends to the pituitary gland
a) controls secretions of hormones from pituitary
gland
D. Cerebrum
1. largest part of the brain
a. centers for thought process, memory, and voluntary muscle
action
2. divided into left & right hemispheres by a longitudinal fissure
a. Right hemisphere
1) Receives information fromand controls left side of the body
2) more creative abilities like music, art, drama, literature, etc
b. Left hemisphere
1) controls right side of the body
2) involves analytical, logical skills like math and science and
speech
c. Commissures – connections between hemispheres where sensory
information is shared made of broad bands of nerve tracts
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1) corpus callosum – largest commissure
a) a broad band of nerve tracts at the base of the
longitudinal fissure
3. Gyri – numerous folds on the surface of each hemisphere; increase the
surface area of the cortex
4. Sulci – shallow grooves between gyri
5. Fissure – deep grooves between areas of brain
6. Divided into four (4) lobes (sections) named for the skull bones overlying
them
a. Frontal lobe – functions voluntary motor functions, motivation,
aggression, mood, and olfactory reception
b. Parietal lobe – principal center for reception and evaluation of
most sensory information such as taste, pain, touch, temperature,
and balance
1) Central sulcus – prominent sulcus separating the frontal
and parietal lobes
c. Occipital lobe
1) function in reception & integration of visual input
2) not distinctly separated from other lobes
d. Temporal lobe
1) evaluates olfactory and auditory input
2) plays a role in memory
E. Cerebellum – “little brain”
1. Cortex is made of gray matter; gyri are smaller than cerebrum
2. Internally consists of nuclei and nerve tracts
3. Functions:
a. comparator – compares the intended movement with the actual
movement and adjusts for any discrepancies
1) alcohol inhibits function of cerebellum
b. balance, maintenance of muscle tone, & coordination of fine
motor movement
c. Accomplishes “learned” movements automatically after they
have been initiated by cerebrum
1) Ex. learning to ride a bicycle
F. Spinal cord
1. extends from foramen magnum to second lumbar vertebra
2. made up of central gray area in the shape of an “H” surrounded by white
matter
3. axons make up the white matter and are grouped by function in tracts or
pathways
G. Meninges- connective tissue layers surrounding and protecting the brain and
spinal cord
1. Layers:
a. Dura mater – means “tough mother”
1) outermost & thickest layer
2) attached to the periosteum of skull (in the cranium)
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3) surrounded by epidural space (in spinal cord)
4) extends into longitudinal fissure between cerebral
hemispheres & between cerebrum & cerebellum.
b. Arachnoid layer – “spiderlike or cobwebs”
1) thin, whispy later that looks like spider web
c. Pia mater – “affectionate mother”
1) tightly bound to surface of the brain and spinal cord
2) thin & transparent
H. Ventricles - fluid- filled cavities
1. Lateral ventricles - (2) located in each cerebral hemisphere; relatively
large cavities
I. Cerebrospinal fluid (CSF)
1. bathes the brain and spinal cord
2. provides a protective cushion around the CNS
3. Choroid Plexus – a specialized structure of ependymal cells located in the
lateral and fourth ventricles; produces cerebrospinal fluid
4. fills brain ventricles, the central canal of the spinal cord, and the
subarachnoid space
V. Peripheral Nervous System (PNS)
A. consists of all the neurons located outside the brain and spinal cord
B. Two structural parts of PNS:
1. Cranial nerves – 12 pairs; two major types are sensory (afferent) and
motor (efferent) nerves
2. Spinal nerves – 31 pairs; categorized by the region of the vertebral
column from which they emerge
a. Example: C = cervical and number = C-1
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