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© 2013 John Wiley & Sons, Inc. All rights reserved.
Chapter 10: Central Nervous System, Spinal Nerves, and Cranial Nerves
© 2013 John Wiley & Sons, Inc. All rights reserved.
Vertebrae Spinal meninges
3 layers of connective tissue Dura mater Arachnoid mater Pia mater
Continuous with cranial meninges Cerebrospinal fluid (CSF)
Spinal Cord Protection and Coverings
© 2013 John Wiley & Sons, Inc. All rights reserved.
External Cord Anatomy The spinal cord is located within the vertebral canal.
It is well protected. The vertebral ligaments, meninges, and CSF
provide additional protection. The meninges (e.g., dura,
arachnoid, pia) are three
layers of connective tissue
coverings that extend around
the spinal cord and brain.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Spinal cord extends from the medulla
oblongata, to the upper border of L2
(ending with
the conus medullaris). The roots of the
spinal nerves or
cauda equina, angle
down the vertebral
canal like wisps of
flowing hair.
External Cord Anatomy
© 2013 John Wiley & Sons, Inc. All rights reserved.
Internal Cord Anatomy
The gray matter of the spinal cord contains neuronal cell bodies,
dendrites, unmyelinated axons, axon terminals, and neuroglia.
On each side of the spinal cord, the gray matter is subdivided
into regions called horns. The white matter consists primarily of myelinated
axons of neurons and is organized into white columns.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Each spinal nerve (and cranial nerve) contains layers of protective connective tissue coverings. Individual axons, whether myelinated or unmyelinated, are wrapped in endoneurium. Groups of axons with their endoneurium are arranged in bundles,called fascicles, each of which is wrapped in perineurium. The superficial covering over the entire nerve isthe epineurium.
Peripheral Nerves
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Reflexes The pathway followed by nerve impulses that produce a
reflex is known as a reflex arc. Using the patellar reflex (knee jerk reflex) as an example, the basic components of a reflex
include:
1) sensory receptor,
2) sensory neuron,
3) integrating center,
4) motor neuron, and
5) effector.
© 2013 John Wiley & Sons, Inc. All rights reserved.
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• Reflexes
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The Human Brain The Human body uses only ~3 lbs. of tissue to process all
emotions, solve every equation, read every book, and take every breath
All these functions, and
many others, occur
within the 100 billion
neurons and 10 trillion
neuroglia that comprise
the human brain
© 2013 John Wiley & Sons, Inc. All rights reserved.
The human brain, compared to all other animals’
brains, is marked by the highest ratio of brain to
body size - thought to directly correlate with our
higher level of intelligence. Most of the expansion is manifest in man’s large cerebral
cortex. Especially expanded are the frontal lobes which are
associated with higher
(executive) functions such
as self-control, planning,
reasoning, and abstract thought.
The Human Brain
© 2013 John Wiley & Sons, Inc. All rights reserved.
Production and Flow of CSF CSF is a clear, colorless liquid that carries oxygen,
glucose, and other chemicals to neurons and
neuroglia and removes their wastes and toxic
substances. CSF circulates through the subarachnoid space
around the brain and spinal cord, and through
cavities called ventricles. The sites of CSF production are the choroid
plexuses.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Failure of CSF to form and drain normally results
in a buildup of pressure called hydrocephalus. Hydrocephalus occurs with congenital
abnormalities, head
injury, meningitis,
and episodes of
bleeding into
the brain.
Production and Flow of CSF
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial NervesCN I is the olfactory nerve (sense of smell).
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN II is the optic
nerve (sense of sight).
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CN III, IV, and VI innervate the extraocular muscles that allow us to move our eyes. CN III also supplies motor
input to our eyelid
muscles and
facilitates
pupillary
constriction.
Cranial Nerves
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN V is the trigeminal nerve (the major
sensory nerve of the face). It has three large
branches, each of
which supplies an
area of the face:ophthalmicmaxillarymandibular
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN VII is the facial nerve. It has 5 large
somatic branches which innervate the muscle
of facial expression. It also carries some taste
sensations (anterior 2/3 of tongue). Paralysis of CN VII is called Bell’s Palsy
and leads to loss of ability to close the
eyes and impairment of taste and
salivation.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN VIII is the vestibulocochlear nerve.
From the inner ear, the vestibular component carries information on balance, while the cochlear component enables hearing. Damage of CN VIII causes vertigo, ringing in
the ears, and/or deafness.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN IX is the glossopharyngeal nerve. This nerve
carries some taste sensations as well as ANS
impulses to salivary glands and the
mechanoreceptors of the carotid body and carotid
sinus (senses changes in BP).
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Cranial Nerves CN X is the vagus
nerve (“the wanderer”), which carries most of the parasympathetic motor efferents to the organs of the thorax and abdomen.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN XI is the spinal accessory nerve. This nerve
supplies somatic motor innervation to the Trapezius and Sternocleidomastoid muscles.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN XII is the glossopharyngeal nerve. This is a very
large nerve (a lot of resources) to be devoted solely to the tongue—it takes a lot more coordination than you might guess to chew, talk, and swallow without injuring our tongue.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Midbrain The midbrain connects the pons to the diencephalon.
The anterior part consists of a pair of large tracts called cerebral peduncles.
Midbrain contains nuclei (e.g., red nuclei, substantia nigra).
© 2013 John Wiley & Sons, Inc. All rights reserved.
Midbrain Red nuclei are reddish due to their rich blood supply and
iron. Axons from the cerebellum and cerebral cortex form synapses here and help coordinate muscular movements.
Nuclei of the substantia nigra are large and darkly pigmented. Loss of these neurons is associated with Parkinson’s disease.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cerebrum The cerebrum consists of the cerebral cortex (an outer rim
of gray), an internal region of cerebral white matter, and gray matter nuclei.
The cerebrum provides us with the ability to read, write, and speak; to make calculations and compose music; to remember the past and plan for the future; and to create.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cerebrum The cerebral cortex rolls and folds upon itself so that it
can fit into the cranial cavity. The folds are called gyri. The deep grooves between folds are fissures. The
shallow grooves are sulci.
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The longitudinal fissure separates the cerebrum into right and left halves called cerebral hemispheres.
The central sulcus separates the frontal and parietal lobes. The precentral gyrus is located
immediately anterior to the
central sulcus. The postcentral gyrus
is located immediately
posterior to the central
sulcus.
Cerebrum
© 2013 John Wiley & Sons, Inc. All rights reserved.
Cerebrum
Each cerebral hemisphere has four lobes that are named after the bones that cover them: frontal lobe, parietal lobe, temporal lobe, and occipital lobe.
© 2013 John Wiley & Sons, Inc. All rights reserved.
Encircling the upper part of the brain stem and the corpus
callosum is a ring of structures on the inner border of the
cerebrum and floor of the diencephalon that constitutes the
limbic system (limbic border). The limbic system is
sometimes called the
“emotional brain”
because it plays a
primary role in a
range of emotions,
including pain, pleasure,
docility, affection, and anger.
Limbic System
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• Somatic Sensory and Motor Pathways
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Lateralization Brain controls opposite side of the body:
all sensory and motor pathways cross in CNS Left side of the brain controls right side of body Right side of brain controls left side of body
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
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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
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Aging and the Brain 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 Some decrease in brain function
© 2013 John Wiley & Sons, Inc. All rights reserved.
End of Chapter 10
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