Download Human Anatomy & Physiology I

Chapter 10
Central Nervous
System, Spinal
Nerves, and Cranial
Nerves
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End of Chapter 10
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Spinal Cord Structure: Protection and
Coverings
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Vertebrae
Spinal meninges
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Three layers of connective tissue
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Dura mater
Arachnoid mater
Pia mater
Continuous with cranial meninges
Cerebrospinal fluid (CSF)
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Spinal Meninges and Spaces
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Epidural space: between vertebrae and dura
mater
Dura mater- tough ,dense connective tissue
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Arachnoid mater: resembles spider’s web
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Extends into subarachnoid space
Subarachnoid space
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Extends to vertebra S2 (well beyond spinal cord)
CSF circulates in this space
Pia mater: thin, delicate layer
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Adheres to surface spinal cord (and brain)
Contains blood vessels
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Spinal
Meninges
and Spaces
Copyright 2010, John Wiley & Sons, Inc.
Gross Anatomy of Spinal Cord
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Extends from medulla of brain to L2 vertebra
Cauda equina (horse’s tail)
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Left and right halves partially separated by
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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
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Points of origins of nerves to upper and lower limbs
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Gross
Anatomy of
Spinal Cord
Copyright 2010, John Wiley & Sons, Inc.
Internal Structure of Spinal Cord
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Gray matter forms “H” (or “butterfly”)
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Three horns on each side; sites of cell bodies
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Posterior gray horns: contain sensory neurons
Anterior gray horns: contain somatic motor neurons
Lateral: contain autonomic motor neurons
White matter (surrounds gray “H”)
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Consists of white columns
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Posterior, anterior, and lateral columns
Contain tracts (bundles of axons)
Sensory tracts: ascending to brain
 Motor tracts: descending from brain
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Internal Structure of Spinal Cord
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Spinal Nerves
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31 pairs
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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
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Dorsal root: made of axons of sensory neurons
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Dorsal root ganglion: swelling containing cell bodies of
sensory neurons
Ventral root: composed of axons of motor neurons
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Both somatic motor and autonomic motor
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Spinal Nerve Composition
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Formed by 2 spinal nerve roots
Are mixed:
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Formed from dorsal root (sensory) and ventral
root (motor) root
Connective tissue coverings
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Individual axons wrapped in endoneurium
Axons grouped in fascicles wrapped in
perineurium
Outer covering = epineurium
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Spinal Nerve Composition
Copyright 2010, John Wiley & Sons, Inc.
Distribution of Spinal Nerves
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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
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Called intercostal nerves
Supply abdominal muscles, skin of chest and
back, and muscles between ribs.
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Plexuses
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Cervical plexus
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Supplies posterior head, neck, shoulders, and
diaphragm
Important nerves: phrenic to diaphragm
Brachial plexus
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Supplies upper limbs + some neck and shoulder
muscles
Important nerves: radial, ulnar, axial, median to
arm, forearm, hand
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Plexuses
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Lumbar plexus
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Supplies abdominal wall, external genitalia, and
part of lower limbs
Important nerves: femoral (to anterior thigh:
quads)
Sacral plexus
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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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Spinal
Cord
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Spinal Cord Functions
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Pathways for nerve impulses within tracts
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Ascending (sensory). Example: spinothalamic
Descending (motor). Example: corticospinal
Reflexes: fast, involuntary sequences of
actions in response to stimuli
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Can be simple (withdrawal) or complex (learned
sequence such as driving car)
Levels
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Spinal (reflex arc): simple
Cranial: more complex
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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
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Example of Reflex Arc: Patellar Reflex
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Brain: Major Parts
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Brain stem: continuous with spinal cord
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Diencephalon: superior to brain stem
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Surface covered with gray matter: cortex
Deep to cortex is cerebral white matter
Cerebellum: posterior and inferior
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Thalamus, hypothalamus, and pineal gland
Cerebrum: largest part and most superior
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Medulla oblongata, pons, midbrain
Means “little brain”
Cranial meninges: dura mater, arachnoid
mater, and pia mater
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Brain: Major Parts
Copyright 2010, John Wiley & Sons, Inc.
Brain: Major Parts
Copyright 2010, John Wiley & Sons, Inc.
Brain Blood Supply and Blood-Brain
Barrier
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Requires 20% of the body’s O2 supply
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Requires continuous glucose supply
Protected by blood-brain barrier
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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
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Cerebrospinal Fluid (CSF)
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Formed in the 4 ventricles of brain
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Lateral (#1 and 2)  3rd  4th ventricle
Formed in choroid plexuses
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Pathway
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By filtration and secretion of blood plasma
In specialized capillary networks (covered by ependymal
cells) in walls of ventricles
Through 4 ventricles  central canal of spinal cord
and within subarachnoid space 
Reabsorbed through arachnoid villi into blood in
superior sagittal sinus
Cushions brain and provides nutrients
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Cerebrospinal
Fluid (CSF)
Copyright 2010, John Wiley & Sons, Inc.
Brain Stem: Medulla Oblongata
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Most inferior part of brainstem
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White matter connects spinal cord and other parts
of brain
Contains vital nuclei
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Cardiovascular center
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Medullary rhythmicity area
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Regulates heart rate, blood pressure
Adjusts respiratory rhythm
Other sensory and reflex motor areas
Cranial nerves VIII-XII attached here
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Brain Stem: Pons
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Serves as a “bridge”
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Connects medulla to midbrain and above
Contains ascending and descending tracts
Connects left and right sides of cerebellum
Contains nuclei
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Motor relays from cerebrum to cerebellum
Helps control breathing
Cranial nerves V-VIII attached here
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Brain
Stem
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Brain Stem: Midbrain
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Connects pons to diencephalon
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Large tracts: cerebral peduncles
Nuclei:
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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
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Scanning eye movements
Responses to visual stimuli
Inferior colliculi: responses to auditory input
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Reticular Formation
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Netlike arrangement of gray and white matter
Contains ascending and descending tracts
Ascending part = reticular activating system
(RAS)
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Carries sensory pathways to cerebral cortex
Helps maintain consciousness
Helps induce sleep
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Reticular Formation
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Diencephalon
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Thalamus: major sensory relay center
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Hypothalamus: lies inferior to thalamus
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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
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Controls sleep, biological clock
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Diencephalon
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Cerebellum
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Location: posterior to medulla and pons,
inferior to cerebrum
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Attached to brain stem by cerebellar peduncles
Structure:
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Two cerebellar hemispheres
Cerebellar cortex: gray matter
Tree-like appearance (seen in sagittal section) of
white matter and gray nuclei
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Cerebellum
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Functions
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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.
Cerebrum: Structure
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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
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Cerebrum: Structure
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Each hemisphere has 4 lobes
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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
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Globus pallidus, putamen, caudate nucleus
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Cerebrum
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Cerebrum
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Limbic System
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Ring of structures on inner border of
cerebrum and floor of diencephalon
Called “emotional brain”: plays primary role in
pain, pleasure, anger, affection and in
behavior
Involuntary activity related to survival
Important in memory development
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Limbic System
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Functional Areas of Cerebral Cortex
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Specialized areas in specific regions 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.
Sensory Areas
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Primary somatosensory area: postcentral
gyrus
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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.
Motor Areas
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Located anterior to central sulcus
Primary motor area: precentral gyrus
Broca’s speech area
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Interacts with premotor area and primary motor
area to regulate breathing and speech muscles
Is in left hemisphere in 97% of persons
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Association Areas
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Adjacent to sensory and motor areas and
connected via association tracts
Integrate and interpret information
Examples
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Somatosensory association area
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Posterior to primary somatosensory area
Integrates sensation: exact shape and texture of object
compared with stored memories
Wernike’s area: left temporal, parietal lobes
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Interprets meaning of speech: words  thoughts
Right hemisphere adds emotional content
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Cerebrum: Functional Areas
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Somatic Sensory Pathways
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Relay sensory information from periphery to
cerebral cortex
3 neurons in each pathway
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Cell body #1 in dorsal root ganglion
Cell body #2 in spinal cord or brain stem
Cell body #3 in thalamus; axon extends to
cerebral cortex (somatosensory area in
postcentral gyrus)
Most sensory input to right side of body
reaches left side of brain (and vice versa)
Copyright 2010, John Wiley & Sons, Inc.
Somatic Sensory Pathways
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Posterior column - medial lemniscus pathway
senses
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Fine touch: body location, texture, size
Proprioception: position and motion of body parts
Vibrations: fluctuating touch stimuli
Spinothalamic pathways
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Anterior and lateral spinothalamic tracts
Relay impulses for pain, tickle, itch, hot, and cold
sensations
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Somatic
Sensory
Pathways
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Somatic Motor Pathways
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Signals come from
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Upper motor neurons: via corticospinal tracts
Basal ganglia: help with muscle tone
Cerebellum: coordination
Sensory neurons or interneurons via reflexes
Impulses activate lower motor neurons
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Cell bodies in anterior gray of spinal cord
Axons  ventral root  spinal nerve  muscle 
voluntary movements
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Somatic Motor
Pathways
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Somatic Sensory and Motor Pathways
Interactions Animation
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Somatic Sensory and Motor Pathways
You must be connected to the internet to run this animation.
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Lateralization
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Brain controls opposite side of the body: all
sensory and motor pathways cross in CNS
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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
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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.
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
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Cranial Nerves
VI. Abducens: motor—control of eye
movements
VII.Facial: mixed
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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
IX. Glossopharyngeal: mixed
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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)
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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 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.
Aging
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Rapid brain growth during first few years of
life
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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:
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Decline in brain mass
Fewer synaptic contacts brain function
Some decrease in brain function
Copyright 2010, John Wiley & Sons, Inc.