Download Human Anatomy & Physiology I

Central Nervous System, Spinal
Nerves, And Cranial Nerves
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Unit 1
Chapter 10
Spinal Cord Structure
Protection and Coverings
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• Spinal cord in vertebral cavity-
Surrounded by bone
• Wrapped in meninges• Spinal cord meninges are
continuous with brain meninges
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3 layers of connective tissue
Spinal Meninges
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• Epidural space lined with fat
• Dura mater- tough ,dense connective tissue
Extends to 2nd sacral vertebra
Well beyond spinal cord
• Arachnoid mater- collagen and elastic fibers
• Subarachnoid space• Pia mater- transparent layer
adheres to surface of brain & spinal cord
Contains blood vessels
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cerebral spinal fluid circulates in this space
Figure 10.1
• runs to 2nd lumbar vertebra
• Roots of spinal nerves for lumbar,
sacral & coccygeal nerves in
vertebral cavity before leaving =
Cauda Equina
• Enlargements: cervical & lumbar
Include nerves for upper & lower limbs
• Each spinal segment gives rise to a
spinal nerve – 31 pairs
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Gross Anatomy Of Spinal Cord
Figure 10.2
Internal Structure Of Spinal
Cord
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• Two grooves- left & right halves
Anterior median fissure & posterior
median sulcus
• Gray matter- 3 horns on each side
• Anterior- somatic motor
neurons
• Posterior- sensory neurons
• Lateral- autonomic motor
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Anterior, posterior, lateral
Internal Structure Of Spinal
Cord (cont)
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• White matter- organized into columns
Anterior, posterior & lateral white columns
• Each column contains one or more tracts
having a common destination
• Sensory = ascending tracts
• Motor = descending tracts
Carry information down spinal cord
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Carry information toward brain
Figure 10.3
Spinal Nerves
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Contains Cell bodies of sensory neurons
• Ventral root- axons of somatic &
autonomic motor neurons
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• Serve particular area of body
• Contain 2 bundles of axons = roots
• Dorsal root- only sensory axons
• Swelling called dorsal root ganglion
• Named and numbered according to
level of vertebra they emerge from
• C1-8, T1-12, L1-5, S1-5 & 1
coccygeal
• C1 from above atlas
• Rest through intervertebral foramina
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Spinal Nerves (cont)
• Roots unite to form nerve at
foramina
• Mixed sensory & motor axons
• Each axon wrapped in
endoneurium
• Axons grouped in fascicles wrapped
in perineurium
• Outer covering = epineurium
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Spinal Nerve Composition
Figure 10.4
• After leaving vertebra nerves branch
• Some join with axons from neighboring
nerves to form plexuses
• Names then relate to area they are in or
region innervated
• Spinal nerves T2-T11 do not form
plexuses= intercostal nerves
Supply abdominal muscles, skin of chest &
back and muscles between robs.
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Distribution Of Spinal Nerves
Plexuses
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e.g. ilioinguinal, femoral, obdurator nerves
• Sacral plexus- buttocks, perineum &
lower limbs
e.g. Gluteal, sciatic & pudendal nerves
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• Cervical plexus- posterior head, neck,
shoulders & diaphragm
• Brachial plexus-upper limbs & some
neck & shoulder muscles
• Lumbar plexus- abdominal wall,
external genitals & part of lower limbs
Figure 10.2
• Routes signals along pathways
• Gray matter integrates signals
• Reflex = fast involuntary sequence of
actions in response to a stimulus
• Inborn reflex e.g. withdrawal reflex
• Can also have learned reflexes,
e.g. driving skills
• Can be spinal or cranial integration
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Spinal Cord Functions
Reflex arc (patellar reflex)
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1. Sensory receptor- responds to stimulus
Tap below patella
2. Sensory neuron- to dorsal horn & brain
3. Integrating center- e.g. single synapse
4. Motor neuron- from center to effector
Via ventral horn
5. Effector- responder (muscle or gland)
Patellar reflex- rectus femoris contracts
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Sensory to motor neurons
Figure 10.5
Brain-major parts
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• Brain stem- continuous with spinal cord
Medulla oblongata, pons, midbrain
• Diencephalon- above brain stem
Thalamus, hypothalamus & pineal gland
• Cerebrum- at top and largest part
• Cerebellum- back of brain stem
Means “little brain”
• Cranial meninges- dura mater, arachnoid mater
& pia mater
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Surface covered with gray matter- cortex
Beneath is cerebral white matter
Figure 10.6a
Figure 10.6b
Brain blood supply
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• Requires ~20% body’s oxygen supply
4 min lack => permanent damage
Allows lipid soluble materials: O2, CO2, alcohol,
anesthetic agents but controls entry of other
materials
• Created by tight capillaries and glial cells
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• Requires continuous glucose supply
• Protected by Blood-brain barrier
Cerebral Spinal Fluid (CSF)
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• Circulates through ventricles of brain and
the subarachnoid space.
• 4 ventricles: 2 lateral, third & fourth
• Formed in choroid plexuses
• Flows through ventricles then from 4th to
central canal of spinal cord & subarachnoid
cells
Reabsorbed through arachnoid villi into superior
saggital sinus
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= Specialized capillary networks in wall of
ventricles covered by ependymal cells
Figure 10.7
Brain Stem- Medulla
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• Medulla Oblongata- inferior part of
brainstem
white matter extending between spinal cord &
other parts of brain
• several nuclei: cardiovascular center
(heart rate)
(respiratory rhythm)
• Other sensory & reflex motor areas
Some related to cranial nerves
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• Medullary rhythmicity area
Brain Stem- Pons
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• Pons (bridge)- nuclei & tracts
• Ascending & descending tracts
• Nuclei – motor relays from cerebrum
to cerebellum , respiration & cranial
nerves V, VI, VII, VIII
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Connect left & right of cerebellum
Figure 10.8
Brain Stem- Midbrain
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• Connects pons to Diencephalon
• Nuclei = substantia nigra, red
nuclei, cranial nerves III & IV
• Superior colliculi – nuclei involved
in tracking visual stimuli
• Inferior colliculi – auditory input
& startle reflex
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Large tracts = cerebral peduncles
(motor)
• Netlike arrangement of gray and
white mater
• Ascending part = Reticular
Activating System (RAS)
• Projects to cerebral cortex & helps
maintain consciousness
• Inactivation => sleep
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Reticular formation
Figure 10.9
Diencephalon
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• Thalamus- critical relay for sensory
input
Transmits motor information from cerebellum & basal
nuclei to cerebrum
Control of ANS-regulation of many activities
Control of pituitary and hormone production
Regulation of emotional & behavior patterns
Regulation of eating & drinking
Control of body temperature
Regulation of circadian rhythms & states of
consciousness
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• Hypothalamus- important for
homeostasis
Figure 10.10
Cerebellum
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• Two cerebellar hemispheres
• Cerebellar cortex –gray matter
• Tree like white matter & nuclei
• Attached to brain stem via cerebellar
peduncles
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Posterior to medulla and pons, below
cerebrum
Cerebellar function
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• Gets wide range of sensory input
• Compares with programmed motor
activity from cerebral cortex
• Smoothes & coordinates complex
activities
• Regulates posture & balance
• Required for skilled motor activities
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• Cerebral cortex
• Internal white mater
• Deep gray nuclei
• Surface folds = gyri
• Grooves between = sulci
• Longitudinal Fissure- divides it
into left & right hemispheres
• Connected by corpus collosum
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Cerebrum- Structure
Cerebrum- Structure (cont)
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• Each hemisphere has 4 lobes
Frontal, parietal, temporal, occipital
Precentral gyrus anterior to sulcus= primary
motor area
Postcentral gyrus = primary sensory area
• Deep gray = basal nuclei (basal ganglia)
Globus palladus, putamen, caudate nucleus
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• Central sulcus separates frontal &
parietal
Figure 10.11a
Figure 10.11b
Limbic System
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• Ring of structures on inner border of
cerebrum and floor of diencephalon
• “emotional brain” – pain , pleasure,
anger, affection, docility
• Involuntary activity related to
survival
• Important in memory development
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Figure 10.12
• Specialized areas anatomically
located
• Sensory areas receive input and
responsible for perception
• Motor areas- initiate movements
• Associative areas- complex
integration: e.g. memory, emotion,
reasoning, etc.
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Function areas of Cortex
Sensory Areas
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• Primary somatosensory areapostcentral gyrus.
• Primary visual area- occipital lobe
• Primary auditory area- temporal lobe
• Primary gustatory area – base of
postcentral gyrus
• Primary olfactory area- medial aspect
of temporal lobe
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input includes: touch, proprioception, pain,
itching, tickle, temperature
Motor Areas
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interacts with premotor area & primary
motor area to regulate breathing and
speech muscles
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• Mainly from anterior part of
hemisphere
• Primary motor area- precentral
gyrus
• Broca’s speech area-
Association Areas
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• Adjacent to sensory & motor areas
• connected with tracts- interpret
information
• E.g. somatosensory association area
• Wernike’s area- left temporal & parietal
lobes
Interprets meaning of speech
Right hemisphere adds emotional content
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Posterior to primary somatosensory area
Integrates sensation- exact shape & texture of
object compares with stored memories
Figure 10.13
Sensory Pathways
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Fine touch- body location, texture, size
Proprioception- position & motion of body
parts
Vibratory sensations- fluctuating touch
stimuli
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• Relay information from periphery to
cerebral cortex
• 3 neurons in each pathway.
• Posterior column- medial lemniscus
pathway
Figure 10.14a
Sensory Pathways (cont)
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• Spinothalamic pathways• anterior & lateral spinothalamic
tracts
• Relay impulses for pain, tickle, itch
& thermal sensations.
Somatic Motor Pathways
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Local interneurons- e.g. reflexes
Upper motor neurons- corticospinal tracts
Basal ganglia- help with muscle tone
Cerebellum- coordination
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• Signals converge on lower motor
neurons
• Lower motor neurons stimulate muscles
directly
• Input comes from:
Figure 10.15
Lateralization
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• Left gets input from & sends output
to right side of body and vice versa
• Left important for spoken & written
language, numerical & scientific
skills & reasoning
• Right more involved with spatial
and pattern recognition and
emotional content
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Memory
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• Process for storing & retrieving
information
• Involves structural & functional
changes
• Involves association areas, parts of
limbic system & diencephalon
• Skill memory also involves
cerebellum & basal ganglia
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Cranial Nerves (table 10.2)
•
•
•
•
•
I
II
III
IV
V
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Olfactory- special sensory
optic- special sensory -eye
oculomotor-Motor eye
trochlear- motor eye
trigeminal- Mixed
• VI
• VII
abducens- motor eye
facial- mixed
sensory to front of tongue & motor to facial
expression, lacrimal and some salivary glands
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sensory around eyes & upper mouth motor to chewing
Cranial Nerves
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• VIII vestibulocochlear- special senses- ear
• IX glossopharyngeal-mixed
Sensory for rest of tongue, pharynx & palate, blood
pressure
Motor to pharyngeal muscles, parotid salivary gland
vagus-mixed (major visceral nerve)
Sensory from pharynx, ear, diaphragm, visceral organs in
ventral cavity
Motor to palatal & pharyngeal muscles & organs in
ventral cavity
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• X
Cranial Nerves (Cont.)
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• XI Accessory-Motor to voluntary muscles
including sternocleidomastoid and trapezius
• XII hypoglossal.- motor to tongue
Aging
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• Rapid growth during first few years
• Size of neurons & proliferation of
neuroglia
• Increases development of dendritic
branches & synaptic contacts
• Decline in brain mass from early
adulthood on
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