The Nervous System
Dr. Smith
Chapter 7
Pgs. 136-171
Systems for Communication and
Control – Nervous System
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Homeostasis the the balanced and controlled
internal environment of the body that is basic to
life itself – only possible if our physiological
control and integration systems function
properly.
Transmits info very rapidly by nerve impulses
conducted from one body area to another.
Provide control that is rapid ands brief.
Systems for Communication and
Control – Endocrine System
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Transmits info more slowly by chemical secreted
by ductless glands to other parts of the body.
Also provides longer lasting control through
hormones.
Organs and Divisions of the
Nervous System
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Nervous System:
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Brain
Spinal Cord
Specialized Sense Organs
• Ex. Eyes,Ears, Microscopic sense organs found in skin
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Three Divisions of the Nervous System:
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Central Nervous System (CNS)
Peripheral Nervous System (PNS)
Autonomic Nervous System (ANS)
Cells of the Nervous System Neurons
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3 Parts:
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Cell body (main part)
Dendrites – one or more branching projections
Axon – one elongated projection
Axon – processes that transmit impulses away
from the neuron cell bodies or dendrites.
Dendrites – processes or projections that
transmit impulses to the neuron cell bodies or
axons.
Cell Body – function is to receive and send
messages
Neuron Classification
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Sensory Neurons/Afferent – transmits impulses
to the spinal cord and brain from all parts of the
body.
Motor Neurons/Efferent – Transmits impulses in
the opposite direction – away from the brain and
spinal cord. Do not conduct impulses to all parts
of the body, but only to two kind of tissue –
muscle and glandular epithelial
Interneurons/Central or Connecting Neurons –
Conduct impulses from sensory neurons to
motor neurons
Neuroglia
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Neuroglia (glia) are special types of tissue cells.
Name is derived from Greek word glia meaning
“glue”
Function – Holds functioning neurons together
and protects them.
One of the most common types of brain tumor –
called glioma – develops from glia.
Glia vary in shape and size – some are relatively
large – thread like extension make them look
like stars.
Astrocytes
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Means “star cells”
Attached to neurons and small blood vessels
holding them close together.
Form a 2 layer structure called a blood-brain
barrier (BBB).
Separates blood tissue from harmful chemicals
in blood.
Microglias
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Smaller than astrocytes.
Usually stationary, but in inflamed or
degenerating brain tissues, they enlarge, move
about, act as microbe-eaters.
Phagocytosis – surround microbes, drown into
cytoplasm, and digests them.
Oligodendrocytes
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Help to hold nerve fibers together and produce
fatty myelin sheath that envelops nerve fibers
located in the brain and spinal cord.
Nerves
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A nerve is a group of peripheral nerve fibers
bundled together like a cable.
Nerve fibers have myelin sheath, myelin is white
Nerves are called white matter of PNS
Cross –section of myelin sheath
Reflex Arc
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Nerve impulses or action potential travel routes
made up of neurons because they are the cells
that conduct impulses.
Paths are called neuron pathways.
Reflex arc is specialized type of neuron pathway
– important to function of the nervous system.
Receptors (impulse conduction starts)
beginnings of dendrites of sensory neurons.
Causes muscle contraction of gland secretion
Two Neuron Type
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Synapse – a microscopic space separates the
axon ending of 1 neuron from dendrites of
another neuron.
Has a sensory neuron and motor neuron with
one synapse between them.
Most common two neuron effect is the “knee
jerk”.
Nerve impulse is generated by stimulation of
stretch receptors travels along length of sensory
neuron’s dendrite to its cell body.
Three neuron reflex arc
Sensory ,interneuron motor
 example: withdrawal reflex
 in contact with CNS, feel pain sometimes after
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Nerve Impulses
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Self-propagating wave of electrical disturbance that travels
along the surface of a neuron’s plasma membrane.
Initiated by a stimulus – a change in the neuron’s
environment, pressure, temp. and chemical changes are
common stimuli.
Saltatory conduction – traveling impulse encounters a
section of membrane covered with insulating myelin, this
type of impulse is much faster in nonmyelinated sections
Synapse – place where impulses are transmitted from one
neuron called presynaptic neuron to another neuron called
the postsynaptic neuron.
Connects neurons and passes stimuli.
Neurotransmitters
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Chemicals by which neurons communicate.
Presynaptic neurons release neurotransmitters
that assist, stimulate or inhibit postsynaptic
neurons.
Specific neurotransmitters are localized in
discrete groups of neurons and released in
specific pathways.
Acetylocholine, Serotonin,
Dopamine
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Acetylcholine – released at some synapses in
spinal cord and neuromuscular junctions.
Serotonin and Dopamine belong to group of
compounds called catecholamines – play a role
in sleep, motor function, mood and pleasure
recognition.
Morphine-Like Neurotransmitters
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Endorphine and Enkephalins are released at
various spinal cord and brain synapses in the
pain conduction pathway.
Neurotranmitters inhibit conduction of pain
impulses.
They are not pain killers.
Central Nervous System (CNS)
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Consists of the brain
and spinal cord which
occupy a midline or
central location in the
body.
Brain - Stem
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Stem – lowest part:medulla oblongata – immed.
above pons above that midbrain origin of cranial
nerves.
3 parts function as two way conduction paths:
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Sensory fibers conduct impulses up from the cord to
other parts of the brain.
Motor fibers conduct impulses down from brain to cord.
Cardiac, respiratory, and vasometer collectively called
the vital centers are located in the medulla. Impulses
from these centers control heartbeat, respiration, and
blood vessel diameter which is important in controlling
blood pressure.
BRAIN STEM
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Medulla - - lowest part, enlarged
continuation of spinal cord, one inch in
length, mylinated tracts, connects cranial
nerve origin of craial nerves IX X XI XII
Pons connected to cerebellum, medulla
and midbrain, nuclei of cranial nerves V
VI VII VIII
Midbrain - Above pons - cranial nerves III
IV originate
Diencephalon – between midbrain
and cerebrum
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HYPOTHALAMUS
Located below thalamus –
controls all internal organs
Heartbeat, constrictions of
blood vessels, contractions of
blood vessels, contractions of
stomach and intestines.
Maintains body temp.
Involved in functions such as
regulation of H2O balance,
sleep cycles, and many
emotions involved in pleasure,
fear, anger, sexual arousal
and pain.
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THALAMUS
Composed of dendrites
and cell bodies of neurons
that have axons extending
up toward the sensory
areas of the cerebrum.
Functions:
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Helps produce sensations
Emotions associated with
sensations
Arousal or alerting
mechanism
Cerebrum
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Cerebral cortex and thin layer of gray matter
made up of neuron dendrites and cell bodies
composes surface of the cerebrum.
Largest and uppermost part of brain – many
ridges (gyris) and groves (sulci).
Two hemispheres (longitudinal fissure) seperates
the two
4 major regions, temporal, parietal, frontal,
occipital
Functions:
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Consciousness, thinking, memory, sensations,
emotions, willed movements, smell (olfactory bulb.
Cerebellum
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2nd largest brain part lies under occipital lobe of
cerebrum.
Controls balance,movement, posture, and
coordination.
Spinal Cord
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Approx. 17-18 inches long at average ends at
2nd lumbar.
Lies inside spinal column in spinal cavity and
extends from occipital bone down to the bottom
of the 1st lumbar vertebra.
Core consists of gray matter and is composed of
mainly dendrites and cell bodies of neurons.
White matter from outer portion of spinal cord
descending tracts, which transmit impulses
controlling many voluntary movements.
More Spinal Cord
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Meninges - tough fluid containing membrane
that protects nerve tissue, brain, and spinal
cord.
Dura Mater – tough outer layer that lines the
vertebral canal.
Pia Mater – innermost membrane covering the
spinal cord itself.
Arachnoid – membrane between dura and pia
mater. Resembles a cobweb with fluid in its
spaces. Arachnoid – “cobweb like” Arachne –
Greek for “spider”.
Cerebral Spinal Fluid (CSF) – fluid in the
subarachnoid spaces between pia mater and
arachnoid in brain and spinal cord.
Cross section - H -shaped or butterfly shaped
Gray Matter – cell bodies and dendrites
White Matter – axon bundles spinal tracts
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Dura mater - adhere to
cranial bones
arachnoid - w CSF
pia mater - adhere to
brain
Brain cavities - filled with
CSF
 lateral ventricles (I and
II) located in each half
of cerebrum
 third ventricle in center
of deincephalon
 fourth ventricle in fron
of cerebellum
Peripheral Nervous System
Cranial and Spinal nerves - connect
brain and spinal cord to skin and
structures
 Autonomic Nervous System - part of
PNS that controls instinctive
behavior
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Spinal Nerves
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31 pairs of Spinal Nerves attached to the spinal
cord
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8 pairs attached to cervical segment
12 pairs to the thoracic segment
5 pairs to the sacrospinal segment
1 pair to coccygeal segment
Spinal Nerves have no special name –identified
by a letter and number
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C1 – indicated spinal nerves attached to 1st segment of
cervical part of cord
T8 – attached to 8th segment of thoracic part of cord
Spinal Nerves
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31 Pairs Total
8 pairs – Cervical segment
12 pairs – Thoracic segment
5 parts – Lumbar segment
5 Parts – Sacrospinal segment
1 Part – Coccygeal segment
Dermatome - surface area
maps of nerves
Autonomic
Nervous System
(ANS)
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A subdivision of the
peripheral nervous
system which controls
the body’s involuntary
actions such as the
heart rate and stomach
contractions.
Consists of two
divisions called the
sympathetic nervous
system and
parasympathetic
nervous system.
Sympathetic vs
Parasympathetic
Sympathetic - fight or flight
 Parasympathetic - rest and digest
 Sympathetic - thoraculmbar
 Parasympathetic - craniosacral
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Pre, Post ganglion
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In the ANS, there are two neurons one that comes from the CNS preganglionic, (ganglion), and a post
ganglion to a visceral effector