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AP BIOLOGY:
THE NERVOUS SYSTEM
DIVISIONS OF THE NERVOUS
SYSTEM:
1.
Central nervous
system (CNS) — brain
and spinal cord
2.
Peripheral nervous
system (PNS) — all
nerves

A. Autonomic nervous
system (ANS)


BP, digestion, heart rate
B. Somatic nervous
system (SNS)

Voluntary muscle
movements
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A. AUTONOMIC NERVOUS SYSTEM

regulates the body’s automatic or involuntary
functions

motor neurons that conduct impulses from:
central nervous system to cardiac muscle
 smooth muscle
 glandular epithelial tissue

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AUTONOMIC NERVOUS SYSTEM

1.
Composed of two divisions:
Sympathetic Nervous System = flight or fight




2.
Anger
fear
Hate
anxiety
Parasympathetic Nervous System = rest and digest






sexual arousal
Salivation
lacrimation (tears)
Urination
digestion
defecation
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PARASYMPATHETIC AND SYMPATHETIC GROUPS
Normally work antagonistically
 Regulates the body’s automatic functions in
ways that maintain or quickly restore
homeostasis
 Many visceral effectors are doubly innervated
 receive fibers from parasympathetic and
sympathetic divisions


are influenced in opposite ways by the two divisions
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B. SOMATIC NERVOUS SYSTEM

the voluntary control of body movements via
skeletal muscles

consists of efferent nerves responsible for
stimulating muscle contraction

including all the non sensory neurons connected with
skeletal muscles and skin
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GENERAL INFORMATION ABOUT
THE NERVOUS SYSTEM
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NEURONS
Classification according to function:

Sensory (afferent) neurons: conduct impulses
to the spinal cord and brain

Motor (efferent) neurons: conduct impulses
away from brain and spinal cord to muscles and
glands

Interneurons: conduct impulses from sensory
neurons to motor neurons
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1. NEURONS – REVIEW!

Consist of three main
parts:
dendrites
2. cell body of neuron
3. Axon
1.
Dendrites conduct
impulses to cell body of
neuron
 Axons conduct impulses
away from cell body of
neuron

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AXON DIFFERENCES
1.
Myelinated axons:

Myelin = white, fatty substance created by Schwann
cells

2.
Neurilemma = outer membrane of schwann cells
responsible for regeneration of cut or injured axons

Only in the PNS

Nodes of Ranvier
Unmyelinated axons:
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2. GLIA (NEUROGLIA)

Support cells, bringing the cells of nervous tissue together
structurally and functionally

Three main types of glial cells of the CNS:
1. Astrocytes — star-shaped cells that anchor small blood
vessels to neurons

Forms blood-brain-barrier
2.
3.
Microglia — small cells that move in inflamed brain
tissue carrying on phagocytosis (scavengers)
Oligodendrocytes — form myelin sheaths on axons in
the CNS

Holds tissue together
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GLIA
Glioma – common brain tumor
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NERVES

Nerve = bundle of axons

Tract — bundle of CNS axons
 White matter — tissue composed primarily of
myelinated axons (nerves or tracts)
 Gray matter — tissue composed primarily of
cell bodies and unmyelinated fibers
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REFLEX ARCS

Nerve impulses are conducted from receptors to
effectors over neuron pathways
One way conduction only
 results in a reflex (contraction by a muscle or secretion
by a gland)


Two-neuron arcs — consisting of sensory
neurons synapsing in the spinal cord with motor
neurons

Three-neuron arcs consist of sensory neurons
synapsing in the spinal cord with interneurons that
synapse with motor neurons
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Know these terms:
• receptor
• sensory neuron
• synapse
• motor neuron
• effector
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ANATOMY OF REFLEX ARC

Receptor –
Located in tendons, skin, mucous membranes
 Beginning of dendrites of sensory neuron


Sensory Neuron –


Synapse –


Microscope space between two neurons
Motor Neuron –


Sends generated impulse to spinal cord
Carries impulse away from spinal cord to the effector
Effector –

Tissue that puts the impulse into effect
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NERVE IMPULSES

Self-propagating wave of electrical disturbance that
travels along the surface of a neuron

AKA – action potential
Mechanism:
 A stimulus triggers the opening of Na+ channels in
the plasma membrane of the neuron

Inward movement of positive sodium ions leaves a
slight excess of negative ions outside at a stimulated
point; marks the beginning of a nerve impulse
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ACTION POTENTIALS ARE ALL-ORNOTHING

Only occurs if the stimulus causes enough sodium
ions to enter the cell to change the membrane
potential (depolarization) to a certain threshold
level.

If the depolarization is not great enough to reach
the threshold, then an action potential (and hence
an impulse) WILL NOT be produced.
Resting state has slight + charge
on outside and slight - on the inside
Due to excess Na+ on
outside of membrane
When stimulated Na+
channels open - the
opening and closing is a
domino effect down the
nerve cell
THE ACTION POTENTIAL SPIKES WHEN
THRESHOLD IS REACHED
TYPES OF CONDUCTION

Salutatory Conduction:
If impulse encounters myelin it jumps around myelin
 faster


Continuous Conduction:
NO myelin
 slower

ANATOMY OF A SYNAPSE
Presynaptic neuron
 Postsynaptic neuron
 Synaptic knob
 Neurotransmitter
 Synaptic cleft
 Receptors

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THE SYNAPSE

Chemical compounds released
from axon terminals (of a
presynaptic neuron) into a
synaptic cleft

Compounds then bind to
specific receptor molecules in
the membrane of a
postsynaptic neuron,
opening ion channels and
thereby stimulating impulse
conduction by the membrane
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NEUROTRANSMITTERS
Acetylcholine – stimulates skeletal muscle
contractions
 Norepinephrine – stress hormone involved in
fight or flight response
 Serotonin
 Dopamine

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THE CENTRAL NERVOUS SYSTEM
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1. THE BRAIN
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DIVISIONS OF THE BRAIN
Brainstem
 Consists of three parts of brain:





Structure — white matter with bits of gray matter scattered
through it
Function — gray matter in the brainstem functions as reflex
centers



medulla oblongata
pons
midbrain
heartbeat, respirations, and blood vessel diameter
Sensory tracts conduct impulses to the higher parts of the brain
Motor tracts conduct from the higher parts of the brain to the
spinal cord
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DIVISIONS OF THE BRAIN

Diencephalon = hypothalamus & thalamus
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DIVISIONS OF THE BRAIN
Hypothalamus
 Consists mainly of the:
 posterior pituitary gland
 pituitary stalk
 gray matter

1.
2.
3.
Functions:
Helps control the functioning of most internal organs
 Acts as the major center for controlling the ANS
Controls hormone secretion by anterior and posterior
pituitary glands
 indirectly helps control hormone secretion by most other
endocrine glands
Contains centers for controlling body temperature, appetite,
wakefulness, and pleasure
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DIVISIONS OF THE BRAIN
Thalamus
 Dumbbell-shaped mass of gray matter in each
cerebral hemisphere

1.
2.
Functions:
Relays sensory impulses to cerebral cortex sensory
areas
Produces the emotions of pleasantness or
unpleasantness associated with sensations
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DIVISIONS OF THE BRAIN
Cerebellum
 Second largest part of the human brain
 Helps control muscle contractions to produce
coordinated movements to maintain balance, move
smoothly, and sustain normal postures
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DIVISIONS OF THE BRAIN
Cerebrum
 Largest part of the human brain
 Outer layer of gray matter = cerebral cortex



Interior of the cerebrum composed mainly of white
matter


made up of lobes
composed mainly of dendrites and cell bodies of
neurons
nerve fibers arranged in bundles called tracts
Functions: mental processes of all types, including
sensations, consciousness, memory, and voluntary
control of movements
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2. SPINAL
CORD
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SPINAL CORD
Outer part - white matter made up of many bundles
of axons = tracts
 Interior - gray matter made up mainly of neuron
dendrites and cell bodies


Functions:
 center for all spinal cord reflexes
 sensory tracts conduct impulses to the brain
 motor tracts conduct impulses from the brain
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Touch & pressure
Muscle length
Voluntary movements
Muscle length
Crude touch, pain & temp
COVERINGS AND FLUID SPACES OF THE
BRAIN AND SPINAL CORD
1.
Cranial bones and vertebrae
2.
Cerebral and spinal meninges::



3.
dura mater
pia mater
arachnoid mater
Fluid spaces:



subarachnoid spaces of
meninges
central canal inside cord
ventricles in brain
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PERIPHERAL NERVOUS SYSTEM
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NERVE TYPES

Cranial nerves:



Twelve pairs — attached to undersurface of the brain
Connect brain with the neck and structures in the
thorax and abdomen
Spinal nerves:
Structure — contain dendrites of sensory neurons and
axons of motor neurons
 Functions — conduct impulses necessary for sensations
and voluntary movements

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KNOW THESE CRANIAL NERVES!
I – olfactory
II – optic
III – oculomotor
IV – trochlear
V – trigeminal
VI – abducens
VII – facial
VIII – vestibulocochlear
IX – glossopharyngeal
X – vagus
XI – accessory
XII - hypoglossal
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INTERESTING REVIEW:
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