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The Nervous System
Overview of the
Nervous System
Nervous System Overview
 organization of the nervous system
 two major divisions
 central nervous system (CNS)
 peripheral nervous system (PNS)
 sensory receptors
 afferent (sensory) nerves
 efferent (motor) nerves
The Efferent Nerves
 somatic nervous system
 voluntary
 autonomic nervous system
 involuntary
 sympathetic
 parasympathetic
Nervous Tissues
 neuroglia
 also known as glial cells
 support the neurons
 protect the neurons
 neurons
 transmit nerve impulses
Two Major Divisions
Funtions of the Nervous System
1. Sensory Functions derive from sensory
receptors at the end of peripheral neurons.
Receptors gather information by detecting
changes inside and outside the body and
then convert the info into nerve impulses,
which are transmitted over peripheral
nerves to the CNS.
Funtions of the Nervous System
2. Integrative functions are receiving signals
and bringing them together, creating
sensations, adding to memory, or helping
to produce thoughts that translate
sensations into perceptions.
Funtions of the Nervous System
3. Motor functions employ peripheral
neurons, which carry impulses from the
CNS to responsive structures called
effectors (muscles and glands that secrete
when stimulated).
Neurons: Basic Unit of the
Nervous System
Neuron Structure
Cell Body (Soma)–
consists of granular
cytoplasm, cell
membrane,
organelles, and a
network of fine
threads called
neurofibrils, which
extend into nerve
fibers
Neuron Structure
Nerve Fibers – extend
from the cell body
Neuron Structure
Dendrites – one neuron
may have many
dendrites; short and
highly branched;
together with the
membrane, dendrites
are the neuron’s main
receptive surfaces with
which fibers from other
neurons communicate
Neuron Structure
Axons – one neuron has
only one axon; arises
from slight elevations of
the cell body; begins as
a single fiber but may
give off side branches;
near its end it may
have fine extensions
that contact the
receptive surfaces of
other cells
Neuron Structure
Schwann cells – neuroglial
cells that enclose large
axons forming myelin
sheaths that wind tightly
around the axon; portions
of the Schwann cells that
contain most of the
cytoplasm and the nuclei
remain outside the myelin
sheath and make up the
nuerilemma (neurilemmal
sheath); narrow gaps in the
myelin sheath between
Schwann cells are called
nodes of Ranvier
Neuron Structure
CNS – myelinated nerve fibers are also
found in the central nervous system;
myelinated fibers appear white, and
masses of such fibers form white
matter in the CNS; unmyelinted nerve
fibers and neuron cell bodies form gray
matter within the CNS
Types of Neuron and
Neuroglial Cells
Neuron Structures
 bipolar
 one axon
and one
dendrite
• unipolar
– one axon
• multipolar
– one axon
and many
dendrites
Classification of Neurons:
Structural Differences
Bipolar Neurons – cell
body has two nerve fibers
one arising from each
end; one is an axon and
the other is a dendrite;
located within specialized
parts of the eye, nose and
ears
Classification of Neurons:
Structural Differences
Unipolar Neurons – single nerve
fiber that extends from the cell
body then divides into two
branches; one connecting to a
peripheral body part and
functioning as a dendrite, and the
other entering the brain or spinal
cord and functioning as an axon;
some cell bodies gather in
specialized masses of nervous
tissue called ganglia(located
outside the brain or spinal cord)
Classification of Neurons:
Structural Differences
 Multipolar Neurons –
have many nerve fibers
arising from their cell
bodies; only one fiber is an
axon and the rest are
dendrites; neurons which
lie within the brain or spinal
cord
Classification of Neurons:
Functional Differences
Sensory Neurons (afferent neurons) –
carry impulses from peripheral body parts
into the brain or spinal cord; most are
unipolar, but some are bipolar
Classification of Neurons:
Functional Differences
Interneurons (internuncial or
association neurons) – lie within the
brain and spinal cord; multipolar and link
other neurons; transmit impulses from
one part of the brain or spinal cord to
another; direct incoming sensory
impulses to appropriate parts for
processing and interpreting
Classification of Neurons:
Functional Differences
Motor Neurons (efferent neurons) –
multipolar and carry impulses out of the
brain or spinal cord to effectors; stimulate
muscles to contract or glands to secrete
Classification of
Neuroglial Cells:
Neuroglial cells fill spaces, provide structural
frameworks, produce myelin, and carry on
phagocytosis.
Within the PNS neuroglial cells include
Schwann cells and satellite cells
In the CNS they greatly outnumber neurons
and are of the following types:
Neuroglia
 peripheral nervous system
 Schwann cells
 satellite cells
Neuroglia
 central nervous system




astrocytes
microglia
ependymal
oligodendrocytes
Classification of Neuroglial
Cells:
Microglial Cells –
scattered throughout;
support neurons and
phagocytize bacterial
cells and cellular debris
Classification of Neuroglial
Cells:
Astrocytes – found between neurons and blood
vessels; provide structural support, join parts
by numerous cellular processes, help regulate
the concentrations of nutrients within tissue;
form scar tissue that fills spaces following injury
to the CNS
Classification of Neuroglial
Cells:
Ependymal Cells – form an epithelial like membrane
that covers specialized brain parts and forms the
linings that enclose spaces within the brain and
spinal cord
Classification of Neuroglial
Cells:
Oligodendrocytes: provide
support and insulation to
axons in the CNS;
equivalent to the function
performed by Schwann
cells in the PNS
Review and Assessment
Match these words with 1–4 below:
sympathetic nervous system, myelin,
synapse, axon.
1. high alert
2. transmits impulses away from cell body
3. fatty insulating material
4. gap between neurons
Transmission of
Nerve Impulses
Cell Membrane Potential
A cell membrane is usually polarized as a
result of unequal ion distribution.
Cell Membrane Potential
Distribution of Ions
a. Ion distribution is due to pores and
channels in the membranes that allow
passages of some ions but not others
b. Potassium ions (K+) pass more easily
through cell membranes than do Sodium
ions (Na+)
Cell Membrane Potential
Resting Potential
a. a high concentration of sodium ions is on
the outside of a membrane, and a high
concentration of potassium ions is on the
inside of the cell.
b. Many negatively charged ions are inside a
cell.
c. In a resting cell, more positive ions leave
than enter, so the outside of the cell
membrane develops a positive charge, while
the inside develops a negative charge.
Cell Membrane Potential
Potential Changes
a. Stimulation of a membrane affects the
membrane’s resting potential.
b. When its resting potential becomes more
positive, a membrane becomes depolarized.
c. Potential changes are subject to
summation.
d. Achieving threshold potential triggers an
action potential.
Cell Membrane Potential
Action Potential
a. At threshold, sodium channels open, and sodium
ions diffuse inward, depolarizing the membrane.
b. About the same time, potassium channels open,
and potassium ions diffuse outward, repolarizing the
membrane
c. This rapid change in potential is an action
potential.
d. Many action potentials can occur before active
transport re-establishes the resting potential.
Nerve Impulses:
A wave of
action potentials is a nerve impulse.
Impulse Conduction
1. Unmyelinated fibers conduct impulses over
the entire surface of the nerve.
2. Myelinated fibers conduct impulses more
rapidly because the impulse jumps between
the nodes of Ranvier.
3. Nerves with large diameters conduct impulses
faster than those with small diameters.
Nerve Impulses
All-or-None Response
1. A nerve impulse is conducted in an all-ornone manner when a stimulus of threshold
intensity is applied to a fiber.
2. All the impulses conducted on a fiber are of
the same strength.
The Synapse –
A synapse is the
junction between two neurons.
Synaptic Transmission
1. Impulses usually travel from a dendrite to a
cell body, then along the axon to a synapse.
2. Axons have synaptic knobs at their ends,
which secrete neurotransmitters.
3. A neurotransmitter is released when a nerve
impulse reaches the end of an axon.
4. A neurotransmitter reaching the nerve fiber on
the distal side of the synaptic cleft triggers a
nerve impulse.
The Synapse
The Synapse
Excitatory and Inhibitory Actions
1. Neurotransmitters that trigger nerve
impulses are excitatory. Those that
inhibit impulses are inhibitory.
2. The net effect of synaptic knobs
communicating with a neuron depends
on which knobs are activated from
moment to moment.
The Synapse
Neurotransmitters
1. The nervous system produces many different
neurotransmitters, such as acetylcholine,
monoamines, amino acids, and peptides.
2. A synaptic knob releases neurotransmitters when an
action potential increases membrane permeability to
calcium ions.
3. After being released, neurotransmitters are
decomposed or removed from synaptic clefts.
Neurotransmitters
Review and Assessment
Fill in the blanks with: reflexes, saltatory
conduction, neurotransmitter, or action potential.
1. A(n) _______________ is an all or none
response.
2. _______________ occurs only in myelinated
axons.
3. _______________ are rapid, involuntary
responses.
4. The axon terminal has tiny vesicles filled with
_______________.
Types of Nerves
Nerves are cordlike bundles of nerve fibers
held together by layers of connective
tissue.
Types of Nerves
1. Sensory Nerves – conduct impulses
into the brain or spinal cord
2. Motor Nerves – carry impulses to
muscles or glands
3. Mixed nerves – include both sensory
and motor fibers
Nerve Pathways
A nerve pathway is a route an
impulse follows through the
nervous sytem.
Nerve Pathways
Reflex arc – usually includes a sensory
neuron, a reflex center composed of an
interneuron, and a motor neuron
Reflex Behavior
1. Reflexes are autonomic, subconscious
responses to changes (stimuli) within or
outside the body.
2. Reflexes help maintain homeostasis by
controlling may involuntary processes.
3. Reflexes carry out autonomic actions of
swallowing, sneezing, coughing, and
vomiting.
4. The knee-jerk reflex (patellar tendon
reflex) employs two neurons (sensory
and motor).
5. Withdrawal reflexes are protective.
Employs all three types of nerves.
Functional Anatomy of the
Central Nervous System
The Brain: An Overview
Weight – between 2.25 and 3.25 pounds
100 billion neurons (approximately); even more
neuroglial cells
About 6.7% of individual variation in intelligence is
attributed to brain size.
4 major anatomic regions:
cerebrum
diencephalon
brain stem
cerebellum
Meninges
Meninges are membranes that lie between
the bones and soft tissues of the cranial
cavity and vertebral canal. They protect
the brain and spinal cord
Meninges
They consists of three layers:
1. Dura Mater – outermost layer
2. Arachnoid Mater – located between the dura and pia
mater
a. Subarachnoid space – lies between the arachnoid and pia
mater and contains the clear watery cerebrospinal fluid
(CFS)
3. Pia Mater – very thin and contains nerves and blood
vessels that nourish underlying cells of the brain and
spinal cord; hugs the surface of these organs
following their irregular contours, passing over high
areas and dipping into depressions
The Brain
Structures of the
Cerebrum
Cerebral Hemisphere – 2 large masses
which are essentially mirror images of
each other connected by a deep bridge
of nerve fibers called the corpus
callosum; the surface has many
convolutions (ridges) separated by
grooves (shallow groove is called a
sulcus and a deep groove is called a
fissure)
Cerebrum
The lobes of the cerebral
hemisphere are named after
the skull bones they underlie:
 Frontal Lobe
 Parietal Lobe
 Temporal Lobe
 Occipital Lobe
Structures of the
Cerebrum
Cerebral Cortex
thin layer of gray matter
that forms the
outermost portion of
the cerebrum;
contains nearly 75%
of all the neuron cell
bodies in the
nervous system
Mass of White Matter
lies just beneath the
cerebral cortex and
makes up the bulk
of the cerebrum;
bundles of
myelinated fibers
Functions of the Cerebrum
Functional Regions of the
Cerebral Cortex
Primary Motor Areas – lie in the frontal
lobes; fibers cross over in the brain stem
from one side of the brain to the other
(right CH motor area generally controls
skeletal muscles on the left side of the
body and vise versa)
motor speech area
frontal eye field
Primary Motor Areas
Functional Regions of the
Cerebral Cortex
Sensory Areas – located
in several lobes
a. cutaneous senses –
sensations of the skin
b. visual area
c. auditory area
d. taste area
e. smell area
Functional Regions of the
Cerebral Cortex
Association Area –
neither primarily
sensory or motor;
analyzes and
interprets sensory
experiences and
oversees memory,
reasoning, verbalizing,
judgment, and
emotion
Functional Regions of the
Cerebral Cortex
General Interpretive
Area – complex
thought processing
Hemisphere Dominance
Although both cerebral hemispheres
participate in basic functions, in most
people, one side of the cerebrum is the
dominant hemisphere, controlling other
functions.
Hemisphere Dominance
In over 90% of the population, the
left hemisphere is dominant for
language-related activities of
speech, writing, reading, and for
complex intellectual functions
requiring verbal, analytical, and
computational skills.
Hemisphere Dominance
In addition to carrying on basic
functions, the non-dominant
hemisphere specializes in nonverbal
functions, such as motor tasks that
require orientation of body in space,
understanding, and interpreting
musical patterns, and nonverbal visual
experiences, as well as emotional and
intuitive thinking.
Cerebrospinal Fluid
Cerebrospinal Fluid is secreted by
capillaries from the pia mater.
It completely surrounds the brain and
spinal cord.
These organs float in the fluid, which
supports and protects them.
It also provides a pathway to the blood for
waste
Diencephalon
The diencephalon is located between the
cerebral hemispheres and above the
midbrain.
It is largely composed of gray matter
Parts of the Diencephalon
Thalamus – relay
station for sensory
impulses (except
smell); produces a
general awareness
of certain
sensations, such as
pain, touch, and
temperature
Parts of the Diencephalon
Hypothalamus – below thalamus; maintains homeostasis
by regulating a variety of visceral activities and by
linking the nervous and endocrine systems; regulates:
 heart rate and arterial blood pressure
 body temperature
 water and electrolyte balance
 control of hunger and body weight
 control of movements and glandular secretions of
stomach and intestines
 production of neurosecretory substances that
stimulate the pituitary gland to secrete hormones
 sleep and wakefulness
Hypothalamus
Diencephalon
 Epithalamus: act as a connection
between the limbic system to other parts
of the brain.
 Some functions of its components
include the secretion of melatonin by the
pineal gland (involved in circadian
rhythms) and regulation of motor
pathways and emotions.
Diencephalon
Limbic System – controls emotional
experiences and expression
- can modify the way a person acts by
producing such feelings as fear, anger,
pleasure, and sorrow
- recognizes upsets in a person’s physical
and psychological condition that might
threaten life
- guides a person into behavior that is
likely to increase the chance of survival
Limbic System
Other Structures of the
Diencephalon
1. Optic Tract Optic Chiasma - vision
2. infundibulum – structures in which the
pituitary gland is attached
3. pituitary gland – master gland
4. olfactory bulbs - smell
5. pineal gland – structure that secretes
melatonin, which affects the sleep cycle; the
darker it is the more melatonin is released, the
lighter it is the less melatonin is released
optic tracts and optic
chiasma
optic tracts and optic
chiasma
infundibulum – structures in which
the pituitary gland is attached
pituitary gland
olfactory bulbs
pineal gland
structure that secretes
melatonin, which
affects the sleep
cycle; the darker it is
the more melatonin
is released, the
lighter it is the less
melatonin is released
Brain Stem
a bundle of nerve tissue
that connects the
cerebrum to the
spinal cord
Midbrain
joins lower parts of the
brain stem and
spinal cord with
higher parts of the
brain
contains centers for
certain visual and
auditory reflexes
Reticular Formation (reticular
activating system) – in the midbrain
The reticular formation extends from the upper
portion of the spinal cord into the
diencephalon and is connected to all
ascending and descending fiber tracts.
When sensory impulses are received it activates
the cerebral cortex into wakefulness.
Without this arousal, the cortex remains unaware
of stimulation and cannot interpret
information or carry out thought processes.
Decreased activity results in sleep.
Injury to it causes a person to be unconscious
and cannot be aroused, even with strong
stimulation (comatose state).
Pons
rounded bulges on the
underside of the brain
stem
transmits impulses to and
from the cerebrum and
medulla oblongata and
the cerebrum and
cerebellum
relays messages from the
PNS to high brain centers
functions with the medulla
oblongata in regulating
the rate and depth of
breathing
Medulla Oblongata
All descending and ascending nerve fibers pass
through the medulla oblongata.
It is composed of gray matter surrounded by white
matter and contains centers for controlling visceral
activities:
a. cardiac center – alters heart rate
b. vasomotor center
- certain cells initiate impulses which stimulate blood
vessels to contract (vasoconstriction) elevating blood
pressure
- other cells have the opposite affect – dilating blood
vessels (vasodilation) dropping blood pressure
c. respiratory center – acts with centers in the pons to
regulate the rate, rhythm, and depth of breathing
Medulla Oblongata
Cerebellum
large mass located
below the occipital
lobes and posterior
to the pons and
medulla oblongata;
two hemispheres
composed largely of
white matter
surrounded by a thin
layer of gray matter;
Cerebellum
communicates with other parts of the CNS by means of
three pairs of nerve tracts called cerebellar peduncles:
inferior peduncle – brings sensory information concerning
the position of the limbs, joints, and other body parts to the
cerebellum
middle peduncle – transmits signals from the cerebral
cortex to the cerebellum concerning the desired positions
of the above mentioned parts
after integrating and analyzing this information the
cerebellum sends correcting information via the superior
peduncle
Cerebellum
Cerebellum
The cerebellum is a reflex center for
integrating sensory information
concerning position of the body parts
and for coordinating complex skeletal
muscle movements.
Damage is likely to result in tremors,
inaccurate movements of voluntary
muscles, loss of muscle tone, a reeling
walk, and loss of equilibrium.
Spinal Cord
The spinal cord is a
nerve column that
extends from the
brain into the
vertebral canal.
Functions of the Spinal
Cord
Conduction of Nerve Impulses –
provides a two-way communication
system between the brain and body
parts. Ascending tracts carry sensory
information to the brain and
descending tracts conduct motor
impulses from the brain to muscles and
glands.
Center for Spinal Reflexes
Structure of the Spinal
Cord
The spinal cord is composed of thirty-one
segments, each of which gives rise to a
pair of spinal nerves.
The spinal cord has a cervical
enlargement, which gives off nerves to
the upper limbs, and a lumbar
enlargement, which gives off nerves to
the lower limbs.
Spinal Nerves
Spinal Cord
Structure of the Spinal
Cord
Two grooves, a deep anterior
fissure and a shallow
posterior median sulcus,
extend the length of the
spinal cord, dividing it into
right and left halves.
It has a central core of gray
matter within white matter.
The white matter is composed
of bundles of myelinated
nerve fibers that comprise
major nerve pathways
called nerve tracts.
Peripheral Nervous
System
Somatic Nervous System
The somatic nervous system consists of
the cranial and spinal nerve fibers that
connect the CNS to the skin and
skeletal muscles.
It oversees conscious activities (voluntary).
Autonomic Nervous
System
The autonomic nervous system consists of sensory
neurons and motor neurons that run between the
central nervous system (especially the
hypothalamus and medulla oblongata) and
various internal organs such as the:




heart
lungs
viscera
glands (both exocrine and endocrine)
Autonomic Nervous System
The autonomic nervous system is the portion of the PNS
that functions independently
(autonomously/involuntary) and continuously without
conscious effort.
1. It controls visceral functions by regulating the actions
of smooth muscles, cardiac muscles, and glands.
2. It regulates heart rate, blood pressure, breathing rate,
body temperature, and other visceral activities that
maintain homeostasis.
3. Portions respond to emotional stress and prepare the
body to meet demands of strenuous physical activity
Autonomic Nervous
System
General Characteristics:
1. regulated by reflexes
2. typically, peripheral nerve fibers lead to
ganglia outside the CNS where they are
integrated and relayed back to viscera
(muscles and glands) that respond by
contracting, releasing secretions, or being
inhibited
3. provides the autonomic system with a
degree of independence from the brain and
spinal cord includes two divisions:
Autonomic Nervous
System
The autonomic nervous system includes two
divisions:
Sympathetic division – prepares the body for
energy-expending, stressful, or emergency
situations (fight-or-flight)
Parasympathetic division – most active during
ordinary, restful conditions; counterbalances
the effects of the sympathetic division and
restores the body to a resting state following
a stressful experience
Sympathetic division
The preganglionic motor
neurons of the
sympathetic system
(shown in black) arise in
the spinal cord. They pass
into sympathetic ganglia
which are organized into
two chains that run parallel
to and on either side of the
spinal cord.
Sympathetic division
The preganglionic neuron may do one of three
things in the sympathetic ganglion:
1. synapse with postganglionic neurons (shown in
white) which then reenter the spinal nerve and
ultimately pass out to the sweat glands and the
walls of blood vessels near the surface of the
body.
2. pass up or down the sympathetic chain and finally
synapse with postganglionic neurons in a higher
or lower ganglion
Sympathetic division
3. leave the ganglion by way of a cord leading to
special ganglia (e.g. the solar plexus) in the viscera.
Here it may synapse with postganglionic sympathetic
neurons running to the smooth muscular walls of the
viscera. However, some of these preganglionic
neurons pass right on through this second ganglion
and into the adrenal medulla (endocrine gland on
top of the kidney). Here they synapse with the
highly-modified postganglionic cells that make up the
secretory portion of the adrenal medulla.
Sympathetic division
 The neurotransmitter of the preganglionic
sympathetic neurons is acetylcholine (ACh). It
stimulates action potentials in the postganglionic
neurons.
 The neurotransmitter released by the
postganglionic neurons is noradrenaline (also
called norepinephrine).
 The action of noradrenaline on a particular gland or
muscle is excitatory in some cases, inhibitory in
others. (At excitatory terminals, ATP may be
released along with noradrenaline.)
Sympathetic division
The release of noradrenaline





stimulates heartbeat
raises blood pressure
dilates the pupils
dilates the trachea and bronchi
stimulates glycogenolysis — the conversion of
liver glycogen into glucose
 shunts blood away from the skin and viscera to the
skeletal muscles, brain, and heart
 inhibits peristalsis in the gastrointestinal (GI) tract
 inhibits contraction of the bladder and rectum
Sympathetic division
 Stimulation of the sympathetic branch of the
autonomic nervous system prepares the body for
emergencies: for "fight or flight" (and, perhaps,
enhances the memory of the event that triggered
the response).
 Activation of the sympathetic system is quite
general because a single preganglionic neuron
usually synapses with many postganglionic
neurons; the release of adrenaline from the
adrenal medulla into the blood ensures that all the
cells of the body will be exposed to sympathetic
stimulation even if no postganglionic neurons
reach them directly.
Parasympathetic Nervous
System
The main nerves of the parasympathetic
system are the tenth cranial nerves, the
vagus nerves. They originate in the
medulla oblongata. Other preganglionic
parasympathetic neurons also extend
from the brain as well as from the lower
tip of the spinal cord.
Parasympathetic Nervous
System
Each preganglionic parasympathetic neuron
synapses with just a few postganglionic
neurons, which are located near — or in — the
effector organ, a muscle or gland.
Acetylcholine (ACh) is the neurotransmitter at
all the pre- and many of the postganglionic
neurons of the parasympathetic system.
However, some of the postganglionic neurons
release nitric oxide (NO) as their
neurotransmitter.
Parasympathetic Nervous
System
Parasympathetic stimulation causes:
 slowing down of the heartbeat lowering of
blood pressure
 constriction of the pupils
 increased blood flow to the skin and
viscera
 peristalsis of the GI tract
Parasympathetic Nervous
System
The parasympathetic system returns the
body functions to normal after they have
been altered by sympathetic stimulation.
In times of danger, the sympathetic system
prepares the body for violent activity. The
parasympathetic system reverses these
changes when the danger is over.
Parasympathetic Nervous
System
The vagus nerves also help keep inflammation under
control. Inflammation stimulates nearby sensory
neurons of the vagus. When these nerve impulses
reach the medulla oblongata, they are relayed back
along motor fibers to the inflamed area. The
acetylcholine from the motor neurons suppresses
the release of inflammatory cytokines, e.g., tumor
necrosis factor (TNF), from macrophages in the
inflamed tissue.
Parasympathetic Nervous
System
Although the autonomic nervous system is
considered to be involuntary, this is not entirely
true.
A certain amount of conscious control can be exerted
over it as has long been demonstrated by
practitioners of Yoga and Zen Buddhism. During
their periods of meditation, these people are clearly
able to alter a number of autonomic functions
including heart rate and the rate of oxygen
consumption. These changes are not simply a
reflection of decreased physical activity because
they exceed the amount of change occurring
during sleep or hypnosis.
Autonomic Nervous
System
Functional Anatomy
of the Peripheral
Nervous System
Nerve Structure
 endoneurium
 covers axons
 perineurium
 bundles fascicles
 epineurium
 wraps nerves
Cranial Nerves
1. 12 pairs
2. arise from the underside of the brain; except
for the first pair, which begins within the
cerebrum
3. lead to parts of the head, neck, and trunk
4. most are mixed nerves, but some associated
with smell and vision contain only sensory
fibers
5. some that control muscles and glands in this
area are primarily motor fibers
Cranial Nerves
Cranial Nerves
Spinal Nerves
1. 31 pairs
2. originate from the spinal cord
3. All of the spinal nerves are "mixed"; that
is, they contain both sensory and motor
neurons. They provide two way
communication between the spinal cord
and parts of the upper and lower limbs,
neck, and trunk.
Spinal Nerves
Spinal nerves are grouped according to the
level in which they arise:
 cervical nerves (C1-C8) – 8 pairs
 thoracic nerves (T1-T12) – 12 pairs
 lumbar nerves (L1-L5) – 5 pairs
 sacral nerves (S1-S5) – 5 pairs
 coccygeal nerve (C0) – one pair
Spinal Nerves
The adult spinal cord ends at the level
between the first and second lumbar
vertebrae, so the lumbar, sacral, and
coccygeal nerves descend beyond the
end of the cord, forming a structure
called the cauda equina (horse’s tail).
Spinal Nerves
Injuries and Disorders of
the Nervous System
Injuries to the Brain and
Spinal Cord
 traumatic brain injury
 cerebral palsy
 spinal cord injury
Traumatic Brain Injury
 violent impact to head
 mild
 moderate
 severe
Traumatic Brain Injury
Cerebral Palsy
 damage to brain
 before birth
 during birth
 during infancy
 motor function impairment
Spinal Cord Injuries




C1–C3: usually fatal
C1–C4: quadriplegia
C5–C7: paralysis of lower extremities
T1–L5: paraplegia
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Common Diseases and
Disorders of the CNS
 Meningitis: infection that affects the delicate membranes -called meninges (men-in'-jeez) -- that cover the brain and spinal cord.
Bacterial meningitis can be deadly and contagious among people in
close contact.
 Viral meningitis tends to be less severe and most people recover
completely without specific therapy.
 Fungal meningitis is a rare form of meningitis and generally occurs only
in people with weakened immune systems.
 Multiple sclerosis: unpredictable, often disabling disease of
the central nervous system that disrupts the flow of information within
the brain, and between the brain and body.
Common Diseases and
Disorders of the CNS
 Epilepsy: CNS disorder (neurological disorder) in which nerve
cell activity in the brain becomes disrupted, causing seizures or periods
of unusual behavior, sensations and sometimes loss of consciousness.
 Parkinson’s disease: progressive disorder of the nervous
system that affects movement.
 Dementia and Alzheimer’s disease: Alzheimer's
is the most common form of dementia, a general term for memory
loss and other intellectual abilities serious enough to interfere with daily
life.
Review and Assessment
Match these words with 1–4 below:
quadriplegia, multiple sclerosis, dementia,
cerebral palsy.
1. inflammation destroys myelin sheath
2. loss of memory and thinking
3. loss of function below the neck
4. may begin before birth