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Chapter 10
Central Nervous
System, Spinal
Nerves, and Cranial
Nerves
https://www.youtube.com/user/BrainInjuryInfo?v=TZRq_26aAEM
Copyright 2010, John Wiley & Sons, Inc.
Objectives:


Describe how the spinal cord is protected
Describe the structure of the spinal cord
Spinal Cord Structure: Protection and Coverings


Inside Vertebrae
Spinal meninges

Three layers of connective tissue
1.
2.
3.


Dura mater
Arachnoid mater
Pia mater
Continuous with cranial meninges
Cerebrospinal fluid (CSF)
Copyright 2010, John Wiley & Sons, Inc.
Spinal Meninges and Spaces (Outside to Inside)


Epidural space: between vertebrae and dura
mater
Dura mater- tough, dense connective tissue


Arachnoid mater: resembles spider’s web


Extends into subarachnoid space
Subarachnoid space


Extends to vertebra S2 (well beyond spinal cord)
CSF circulates in this space
Pia mater: thin, delicate layer


Adheres to surface spinal cord (and brain)
Contains blood vessels
Copyright 2010, John Wiley & Sons, Inc.
Spinal Meninges
and Spaces
Copyright 2010, John Wiley & Sons, Inc.
Gross Anatomy of Spinal Cord


Extends from medulla of brain to L2 vertebra
Cauda equina (horse’s tail)



Left and right halves partially separated by



Extends inferior to end of spinal cord
Consists of roots of lumbar, sacral and coccygeal
spinal nerves
Anterior median fissure and posterior median
sulcus
Small central canal (filled with CSF) in middle
Enlargements: Cervical and Lumbar regions

Points of origins of nerves to upper and lower limbs
Copyright 2010, John Wiley & Sons, Inc.
Copyright 2010, John Wiley & Sons, Inc.
Internal Structure of Spinal Cord

Gray matter forms “H” (“butterfly”)

Three horns on each side; sites of cell bodies
Posterior gray horns: contain sensory neurons
 Anterior gray horns: contain somatic motor neurons
 Lateral gray horn: contain autonomic motor neurons


White matter (surrounds gray “H”)

Consists of white columns
Posterior, Anterior, and Lateral columns
 Contain tracts (bundles of axons)
 Sensory tracts: ascending to brain
 Motor tracts: descending from brain

Copyright 2010, John Wiley & Sons, Inc.
Internal Structure of Spinal Cord
Copyright 2010, John Wiley & Sons, Inc.
Spinal Nerves

31 pairs




Named according to level of vertebra
C1-C8, T1-T12, L1-L5, S1-S5, 1 coccygeal
Emerge from spinal cord through intervertebral
foramina
Nerves attached to spinal cord by 2 roots
1.
Dorsal root: made of axons of sensory neurons

2.
Dorsal root ganglion: swelling containing cell bodies of
sensory neurons
Ventral root: composed of axons of motor neurons

Both somatic motor and autonomic motor
Copyright 2010, John Wiley & Sons, Inc.
Objectives:

Describe the composition, coverings, and
distribution of spinal nerves.
Spinal Nerve Composition

Are Mixed:


Formed from dorsal root (sensory) and ventral root
(motor) root
Connective tissue coverings



Individual axons wrapped in endoneurium
Axons grouped in fascicles wrapped in perineurium
Outer covering = epineurium
Copyright 2010, John Wiley & Sons, Inc.
Spinal Nerve Composition
Copyright 2010, John Wiley & Sons, Inc.
Distribution of Spinal Nerves




Spinal nerves branch after pass through
intervertebral foramina
Some join with branches from neighboring nerves
to form Plexuses
Nerve names relate to region innervated
Spinal nerves T2-T12 do not form plexuses

Called Intercostal nerves

Supply abdominal muscles, skin of chest and back, and
muscles between ribs.
Copyright 2010, John Wiley & Sons, Inc.
Plexuses

Cervical plexus



Supplies posterior head, neck, shoulders, and
diaphragm
Important nerves: phrenic - diaphragm
Brachial plexus


Supplies upper limbs + some neck and shoulder
muscles
Important nerves: radial, ulnar, axial - median to arm,
forearm, hand
Copyright 2010, John Wiley & Sons, Inc.
Brachial Plexus
11-58
Copyright 2010, John Wiley & Sons, Inc.
Plexuses

Lumbar plexus



Supplies abdominal wall, external genitalia, and part of
lower limbs
Important nerves: femoral (to anterior thigh: quads)
Sacral plexus


Supplies buttocks, perineum, and most of lower limbs
Important nerves: gluteal, sciatic (to posterior thigh and
all of leg and foot)
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Lumbosacral Plexus
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11-59
Dermatome
• An area of skin that the sensory nerve fibers of a particular spinal
nerve innervate
11-56
Copyright 2010, John Wiley & Sons, Inc.
Objectives:


Describe the functions of the spinal cord
Describe the components of a reflex arc
Spinal Cord Functions

Pathways for nerve impulses within tracts



Ascending (sensory)
Descending (motor)
Reflexes: fast, involuntary sequences of
actions in response to stimuli


Can be simple (withdrawal) or complex (learned
sequence such as driving car)
Levels
Spinal (reflex arc): simple
 Cranial: more complex

Copyright 2010, John Wiley & Sons, Inc.
Reflex Arc
1. Sensory receptor: responds to stimulus
2. Sensory neuron: through dorsal root
ganglion and root  posterior horn
3. Integrating center: single synapse
between sensory and motor neurons
4. Motor neuron: from anterior horn 
ventral root  spinal nerve 
5. Effector: muscle responds
Copyright 2010, John Wiley & Sons, Inc.
Example of Reflex Arc: Patellar Reflex
1. Sensory receptor is stimulated by tap on
patellar tendon
2. Sensory neuron: through dorsal root 
spinal cord
3. Integrating center: single synapse in
spinal cord
4. Motor neuron: through ventral root 
spinal nerve  femoral nerve 
5. Effector: quads contract, extend leg
Copyright 2010, John Wiley & Sons, Inc.
Example of Reflex Arc: Patellar Reflex
helps maintain posture
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Withdrawal Reflex
• Protective
11-11
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Crossed-Extensor Reflex
• Flexor muscles contract
• Flexor muscles on opposite side inhibited
• Extensor muscles on opposite side contract for balance
11-12
Copyright 2010, John Wiley & Sons, Inc.
Objectives:



Discuss how the brain is protected and supplied
with blood
Name the 4 major parts of the brain and explain
the function of each part
Describe three somatic sensory and somatic
motor pathways
Brain Development
Three Major Vesicles
1. Forebrain
2. Midbrain
3. Hindbrain
Forebrain (prosencephalon)
• Anterior portion (telencephalon)
• Cerebrum
• Basal ganglia
• Posterior portion (diencephalon)
• Thalamus
• Hypothalamus
• Posterior pituitary
• Pineal gland
11-17
Copyright 2010, John Wiley & Sons, Inc.
Brain Development
Midbrain (Mesencephalon)
• Midbrain
Hindbrain (Rhombencephalon)
• Anterior portion
(Metencephalon)
• Cerebellum
• Pons
• Posterior portion
(Myelencephalon)
• Medulla oblongata
11-18
Copyright 2010, John Wiley & Sons, Inc.
Brain: 4 Major Parts
Brain stem: continuous with spinal cord
1.

(A) Medulla oblongata, (B) pons, (C) midbrain
Diencephalon: superior to brain stem
2.

Thalamus, hypothalamus, and pineal gland
Cerebrum: largest part and most superior
3.


Surface covered with gray matter: cortex
Deep to cortex is cerebral white matter
Cerebellum: posterior and inferior
4.

Means “little brain”
Brain is protected by: Cranial meninges: dura mater, arachnoid
mater, and pia mater
Copyright 2010, John Wiley & Sons, Inc.
Brain: Major Parts
Copyright 2010, John Wiley & Sons, Inc.
Brain: Major Parts
Copyright 2010, John Wiley & Sons, Inc.
(1) Brain Stem: (A) Medulla Oblongata

Most inferior part of brainstem


White matter connects spinal cord and other parts
of brain
Contains vital nuclei

Cardiovascular center


Medullary rhythmicity area



Regulates heart rate, blood pressure
Adjusts respiratory rhythm
Other sensory and reflex motor areas
Cranial nerves VIII-XII attached here
Copyright 2010, John Wiley & Sons, Inc.
(1) Brain Stem: (B) Pons

Serves as a “bridge”




Connects medulla to midbrain and above
Contains ascending and descending tracts
Connects left and right sides of cerebellum
Contains nuclei



Motor relays from cerebrum to cerebellum
Helps control breathing
Cranial nerves V-VIII attached here
Copyright 2010, John Wiley & Sons, Inc.
(1) Brain Stem
Copyright 2010, John Wiley & Sons, Inc.
(1) Brain Stem: (C) Midbrain

Connects pons to diencephalon


Large tracts: Cerebral peduncles
Nuclei:




Substantia nigra: related to Parkinson disease
Red nuclei: help coordinate movements
Origin of cranial nerves III and IV (control eye
movements)
Superior colliculi: nuclei involved in



Scanning eye movements
Responses to visual stimuli
Inferior colliculi: responses to auditory input
Copyright 2010, John Wiley & Sons, Inc.
(D) Reticular Formation



Netlike arrangement of gray and white matter
Contains ascending and descending tracts
Ascending part = reticular activating system
(RAS)



Carries sensory pathways to cerebral cortex
Helps maintain consciousness
Helps induce sleep
Copyright 2010, John Wiley & Sons, Inc.
(D) Reticular Formation
Copyright 2010, John Wiley & Sons, Inc.
(D) Types of Sleep
Rapid Eye Movement
(REM)
• Some areas of brain active
• Heart and respiratory rates
irregular
• Dreaming occurs
Slow Wave
• Person is tired
• Decreasing activity of
reticular system
• Restful
• Dreamless
• Reduced blood pressure and
respiratory rate
• Ranges from light to heavy
• Alternates with REM sleep
11-40
Copyright 2010, John Wiley & Sons, Inc.
(D) What If You Stopped Sleeping?

http://www.youtube.com/watch?v=nNhDkKAv
xFk
(2) Diencephalon

Thalamus: major sensory relay center


Hypothalamus: lies inferior to thalamus







Also motor, autonomic, and consciousness
functions
Control of pituitary and hormone production
Works with ANS regulating many viscera
Involved with feelings and behavior patterns
Regulation of eating, drinking, fluid levels
Control of body temperature
Regulation of circadian rhythms, sleep, waking
Pineal gland: secretes melatonin

Controls sleep, biological clock
Copyright 2010, John Wiley & Sons, Inc.
(2) Diencephalon
11-32
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(2) Diencephalon
Copyright 2010, John Wiley & Sons, Inc.
(3) Cerebrum: Structure







Cerebral cortex
Internal white mater
Deep gray nuclei
Surface folds of cerebral cortex: Gyri
Grooves between gyri: Sulci
Longitudinal fissure: divides cerebrum into
left and right hemispheres
Hemispheres connected by Corpus collosum
Copyright 2010, John Wiley & Sons, Inc.
(3) Cerebrum: Structure

Each hemisphere has 4 lobes





Frontal, parietal, temporal, occipital
Central sulcus separates frontal, parietal
Precentral gyrus anterior to sulcus: primary motor
area
Postcentral gyrus: primary somatosensory area
Deep gray nuclei: basal ganglia

Globus pallidus, putamen, caudate nucleus
Copyright 2010, John Wiley & Sons, Inc.
(3) Functions of Cerebrum
• Interpretation
• Storing memory
• Retrieving memory
• Reasoning
• Center for intelligence and personality
11-21
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(3) Limbic System


Ring of structures on inner border of
cerebrum and floor of diencephalon
Called “emotional brain”: primary role in



Pain, pleasure, anger, affection and behavior
Involuntary activity related to survival
Important in memory development
Copyright 2010, John Wiley & Sons, Inc.
(3) Limbic System
Consists of
• Portions of frontal lobe
• Portions of temporal lobe
• Hypothalamus
• Thalamus
• Basal nuclei
• Other deep nuclei
11-34
Copyright 2010, John Wiley & Sons, Inc.
(3) Limbic System
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(3) Cerebrum
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(3) Cerebrum
Copyright 2010, John Wiley & Sons, Inc.
(3) Functional Areas of Cerebral Cortex



Sensory areas receive input  perception
Motor areas  initiate movements
Associative areas  complex integration:
memory, emotion, reasoning, judgment
Copyright 2010, John Wiley & Sons, Inc.
(3) Sensory Areas

Primary somatosensory area: postcentral
gyrus





Input includes: touch, proprioception, pain, itching,
tickle, temperature
Primary visual area: occipital lobe
Primary auditory area: temporal lobe
Primary gustatory (taste) area: base of
postcentral gyrus
Primary olfactory (smell) area: medial aspect
of temporal lobe
Copyright 2010, John Wiley & Sons, Inc.
(3) Sensory Areas
11-25
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(3) Sensory Areas
11-26
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(3) Motor Areas



Located anterior to central sulcus
Primary motor area: precentral gyrus
Broca’s speech area


Interacts with premotor area and primary motor
area to regulate breathing and speech muscles
Is in left hemisphere in 97% of persons
Copyright 2010, John Wiley & Sons, Inc.
(3) Motor Areas
Frontal Eye Field
• Above Broca’s area
• Controls voluntary
movements of eyes
and eyelids
11-23
Copyright 2010, John Wiley & Sons, Inc.
(3) Association Areas




Adjacent to sensory and motor areas and
connected via association tracts
Integrate and interpret information
Provide memory, reasoning, verbalization,
judgment, emotions
Examples

Somatosensory association area
Posterior to primary somatosensory area
 Integrates sensation: exact shape and texture of
object compared with stored memories


Wernike’s area: left temporal, parietal lobes
Interprets meaning of speech: words  thoughts
 Right hemisphere adds emotional content

Copyright 2010, John Wiley & Sons, Inc.
(3) Association Areas
11-27
Copyright 2010, John Wiley & Sons, Inc.
(3) Association Areas
Frontal Lobe
• Concentrating
• Planning
• Problem solving
• Judging
Temporal Lobe
• Remember visual scenes
• Remember music
• Remember complex
patterns
Parietal Lobe
•Understanding speech
• Using words to
express thought
Occipital Lobe
• Combine visual images
with other sensory
experiences
11-28
Copyright 2010, John Wiley & Sons, Inc.
(3) Cerebrum: Functional Areas
Copyright 2010, John Wiley & Sons, Inc.
(3) Lateralization



Brain controls opposite side of the body: all
sensory and motor pathways cross in CNS
Left hemisphere important for spoken and
written language, numerical and scientific
skills, and reasoning
Right side more involved with spatial and
pattern recognition and emotional content
Copyright 2010, John Wiley & Sons, Inc.
(3) Hemisphere Dominance
• In over 90% of population, left hemisphere is dominant
Dominant hemisphere
• Speech
• Writing
• Reading
• Verbal skills
• Analytical skills
• Computational skills
Non-dominant
hemisphere
• Nonverbal tasks
• Motor tasks
• Understanding and
interpreting musical and
visual patterns
• Provides emotional and
intuitive thought processes
11-29
Copyright 2010, John Wiley & Sons, Inc.
(3) Memory




Process for storing and retrieving information
Involves structural and functional changes
Involves association areas, parts of limbic
system, and diencephalon
Skill memory also involves cerebellum and
basal ganglia
Copyright 2010, John Wiley & Sons, Inc.
(3) Memory
Short Term
• Working memory
• Closed circuit
• Circuit is stimulated over and
over
• When impulse flow stops, Long Term
• Changes structure and
memory disappears
function of neurons
• Enhanced synaptic
transmission
11-30
Copyright 2010, John Wiley & Sons, Inc.
Electroencephalogram (EEG)


Brain Waves – Electrical signals of nerve impulses
EEG




Records wave generated by neurons close to the
surface in the cerebral cortex
Detected by metal electrodes placed on forehead and
scalp
Used to study normal brain functions such as
changes that occur during sleep
Used to diagnosis variety of brain disorders

Epilepsy, tumors, metabolic abnormalities, sites of
trauma, and degenerative diseases
(4) Cerebellum

Location: posterior to medulla and pons,
inferior to cerebrum


Attached to brain stem by cerebellar peduncles
Structure:



Two cerebellar hemispheres
Cerebellar cortex: gray matter
Tree-like appearance (seen in sagittal section) of
white matter and gray nuclei
Copyright 2010, John Wiley & Sons, Inc.
(4) Cerebellum

Functions





Receives wide range of sensory input from
muscles, joints, tendons, eyes, inner ears
Compares actual movements with intended ones
Helps produce smooth, coordinated movements
Helps execute skilled motor activities
Regulates posture and balance
Copyright 2010, John Wiley & Sons, Inc.
(4) Cerebellum
11-41
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Brain Blood Supply and Blood-Brain
Barrier

Requires 20% of the body’s O2 supply



Requires continuous glucose supply
Protected by blood-brain barrier



4 min lack  permanent damage
Allows passage of lipid soluble materials: O2,
CO2, alcohol, anesthetic agents
But controls entry of most harmful materials
Created by tight capillaries and astrocytes
Copyright 2010, John Wiley & Sons, Inc.
Ventricles
• Interconnected cavities
• Within cerebral hemispheres
and brain stem
• Continuous with central canal
of spinal cord
• Filled with cerebrospinal
fluid (csf)
• 2 Lateral ventricles
• Third ventricle
• Fourth ventricle
• Cerebral aqueduct
11-4
Copyright 2010, John Wiley & Sons, Inc.
Cerebrospinal Fluid (CSF)

Formed in the 4 ventricles of brain

by choroid plexuses



Pathway



Specialized capillary networks (covered by ependymal
cells) in walls of ventricles
Through filtration and secretion of blood plasma
Through 4 ventricles  central canal of spinal cord
and within subarachnoid space  around the brain
Reabsorbed through arachnoid villi into blood in
superior sagittal sinus
Cushions brain and provides nutrients
Copyright 2010, John Wiley & Sons, Inc.
Cerebrospinal Fluid
(CSF)
Copyright 2010, John Wiley & Sons, Inc.
Objective:

Identify the 12 pairs of cranial nerves by
name and number and give the functions of
each
Cranial Nerves (Table 10.2)
I. Olfactory: special sensory—smell
II. Optic: special sensory—vision
III. Oculomotor: motor—control of eye
movements
IV. Trochlear: motor—control of eye movements
V. Trigeminal: mixed
 General
sensory: touch, pain, pressure, hot,
cold in face
 Motor: to muscles used for chewing
Copyright 2010, John Wiley & Sons, Inc.
Cranial Nerve V
11-49
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Cranial Nerves
VI. Abducens: motor—control of eye
movements
VII.Facial: mixed


Special sensory (taste) from anterior of tongue
Motor to muscles of facial expression, tear
glands, and some salivary glands
VIII.Vestibulocochlear: special sensory—ear
Copyright 2010, John Wiley & Sons, Inc.
Cranial Nerves VI and VII
11-50
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Cranial Nerves
IX. Glossopharyngeal: mixed


Sensory for posterior of tongue, pharynx, and
palate; blood pressure
Motor to pharyngeal muscles (swallowing),
salivary gland (parotid)
Copyright 2010, John Wiley & Sons, Inc.
Cranial Nerves
X. Vagus: mixed (the major parasympathetic
nerve)


Sensory from pharynx, ear, diaphragm,
visceral organs in thoracic and abdominal
cavities
Motor to palatal and pharyngeal muscles
(swallowing and voice); to viscera in thoracic
and abdominal cavities
Copyright 2010, John Wiley & Sons, Inc.
Cranial Nerve X
11-52
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Cranial Nerves
XI. Accessory: motor to voluntary muscles
including sternocleidomastoid and trapezius
(move head, shoulders)
XII.Hypoglossal: motor to tongue (swallowing
and speech)
Copyright 2010, John Wiley & Sons, Inc.
Objective:

Describe the effects of aging on the nervous
system
Aging

Rapid brain growth during first few years of
life



Due to increase in size of neurons and
proliferation of neuroglia
Increase in development of dendritic branches
and synaptic contacts
From early adulthood through old age:



Decline in brain mass
Fewer synaptic contacts brain function
Some decrease in brain function
Copyright 2010, John Wiley & Sons, Inc.
Life-Span Changes
• Over average lifetime, brain shrinks 10%
• Most cell death occurs in temporal lobes
• By age 90, frontal lobe has lost half its neurons
• Decreased levels of neurotransmitters
• Fading memory
• Slowed responses and reflexes
• Changes increase risk of falling
• Sleep problems common
11-71
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Clinical Application
Cerebral Injuries and Abnormalities
Concussion
Cerebral Palsy
• Brain jarred against cranium
• Motor impairment at
• Loss of consciousness
birth
• Temporary loss of memory
• Caused by blocked
• Mental cloudiness
cerebral blood vessels
• Headache
during development
• Recovery usually complete
• Seizures
Cerebrovascular Accident
• Learning disabilities
• Stroke
• Sudden interruption in blood flow
• Brain tissues die
11-72
Copyright 2010, John Wiley & Sons, Inc.