Central Nervous System, Spinal Nerves, And Cranial Nerves

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Central Nervous System, Spinal Nerves, And
Cranial Nerves

• Chapter 10

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Spinal Cord StructureProtection and Coverings

• Spinal cord in vertebral cavity-
• Surrounded by bone
• Wrapped in meninges-
• 3 layers of connective tissue
• Spinal cord meninges are continuous with brain
  meninges

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Spinal Meninges

• 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-
• cerebral spinal fluid circulates in this space
• Pia mater- transparent layer
• adheres to surface of brain spinal cord
• Contains blood vessels

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Figure 10.1
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Gross Anatomy Of Spinal Cord

• 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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Figure 10.2
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Internal Structure Of Spinal Cord

• Two grooves- left right halves
• Anterior median fissure posterior median sulcus
• Gray matter- 3 horns on each side
• Anterior, posterior, lateral
• Anterior- somatic motor neurons
• Posterior- sensory neurons
• Lateral- autonomic motor neurons

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Internal Structure Of Spinal Cord (cont)

• White matter- organized into columns
• Anterior, posterior lateral white columns
• Each column contains one or more tracts having a
  common destination
• Sensory ascending tracts
• Carry information toward brain
• Motor descending tracts
• Carry information down spinal cord

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Figure 10.3
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Spinal Nerves

• Serve particular area of body
• Contain 2 bundles of axons roots
• Dorsal root- only sensory axons
• Swelling called dorsal root ganglion
• Contains Cell bodies of sensory neurons
• Ventral root- axons of somatic autonomic motor
  neurons

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Spinal Nerves (cont)

• 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 Nerve Composition

• 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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Figure 10.4
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Distribution Of Spinal Nerves

• 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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Plexuses

• 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
• e.g. ilioinguinal, femoral, obdurator nerves
• Sacral plexus- buttocks, perineum lower limbs
• e.g. Gluteal, sciatic pudendal nerves

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Figure 10.2
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Spinal Cord Functions

• 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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Reflex arc (patellar reflex)

• Sensory receptor- responds to stimulus
• Tap below patella
• Sensory neuron- to dorsal horn brain
• Integrating center- e.g. single synapse
• Sensory to motor neurons
• Motor neuron- from center to effector
• Via ventral horn
• Effector- responder (muscle or gland)
• Patellar reflex- rectus femoris contracts

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Figure 10.5
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Brain-major parts

• Brain stem- continuous with spinal cord
• Medulla oblongata, pons, midbrain
• Diencephalon- above brain stem
• Thalamus, hypothalamus pineal gland
• Cerebrum- at top and largest part
• Surface covered with gray matter- cortex
• Beneath is cerebral white matter
• Cerebellum- back of brain stem
• Means little brain
• Cranial meninges- dura mater, arachnoid mater
  pia mater

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Figure 10.6a
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Figure 10.6b
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Brain blood supply

• Requires 20 bodys oxygen supply
• 4 min lack gt permanent damage
• Requires continuous glucose supply
• Protected by Blood-brain barrier
• 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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Cerebral Spinal Fluid (CSF)

• Circulates through ventricles of brain and the
  subarachnoid space.
• 4 ventricles 2 lateral, third fourth
• Formed in choroid plexuses
• Specialized capillary networks in wall of
  ventricles covered by ependymal cells
• 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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Figure 10.7
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Brain Stem- Medulla

• Medulla Oblongata- inferior part of brainstem
• white matter extending between spinal cord
  other parts of brain
• several nuclei cardiovascular center
• (heart rate)
• Medullary rhythmicity area
• (respiratory rhythm)
• Other sensory reflex motor areas
• Some related to cranial nerves

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Brain Stem- Pons

• Pons (bridge)- nuclei tracts
• Connect left right of cerebellum
• Ascending descending tracts
• Nuclei motor relays from cerebrum to cerebellum
  , respiration cranial nerves V, VI, VII, VIII

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Figure 10.8
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Brain Stem- Midbrain

• Connects pons to Diencephalon
• Large tracts cerebral peduncles (motor)
• 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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Reticular formation

• Netlike arrangement of gray and white mater
• Ascending part Reticular Activating System
  (RAS)
• Projects to cerebral cortex helps maintain
  consciousness
• Inactivation gt sleep

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Figure 10.9
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Diencephalon

• Thalamus- critical relay for sensory input
• Transmits motor information from cerebellum
  basal nuclei to cerebrum
• Hypothalamus- important for homeostasis
• 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
• Pineal gland- secretes melatonin

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Figure 10.10
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Cerebellum

• Two cerebellar hemispheres
• Posterior to medulla and pons, below cerebrum
• Cerebellar cortex gray matter
• Tree like white matter nuclei
• Attached to brain stem via cerebellar peduncles

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Cerebellar function

• 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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Cerebrum- Structure

• 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 (cont)

• 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 sensory area
• Deep gray basal nuclei (basal ganglia)
• Globus palladus, putamen, caudate nucleus

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Figure 10.11a
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Figure 10.11b
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Limbic System

• 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
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Function areas of Cortex

• 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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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 area base of postcentral
  gyrus
• Primary olfactory area- medial aspect of temporal
  lobe

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Motor Areas

• Mainly from anterior part of hemisphere
• Primary motor area- precentral gyrus
• Brocas speech area-
• interacts with premotor area primary motor area
  to regulate breathing and speech muscles

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Association Areas

• Adjacent to sensory motor areas
• connected with tracts- interpret information
• E.g. somatosensory association area
• Posterior to primary somatosensory area
• Integrates sensation- exact shape texture of
  object compares with stored memories
• Wernikes area- left temporal parietal lobes
• Interprets meaning of speech
• Right hemisphere adds emotional content

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Figure 10.13
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Sensory Pathways

• Relay information from periphery to cerebral
  cortex
• 3 neurons in each pathway.
• Posterior column- medial lemniscus pathway
• Fine touch- body location, texture, size
• Proprioception- position motion of body parts
• Vibratory sensations- fluctuating touch stimuli

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Figure 10.14a
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Sensory Pathways (cont)

• Spinothalamic pathways-
• anterior lateral spinothalamic tracts
• Relay impulses for pain, tickle, itch thermal
  sensations.

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Somatic Motor Pathways

• Signals converge on lower motor neurons
• Lower motor neurons stimulate muscles directly
• Input comes from
• Local interneurons- e.g. reflexes
• Upper motor neurons- corticospinal tracts
• Basal ganglia- help with muscle tone
• Cerebellum- coordination

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Figure 10.15
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Lateralization

• 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

• 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 Olfactory- special sensory
• II optic- special sensory -eye
• III oculomotor-Motor eye
• IV trochlear- motor eye
• V trigeminal- Mixed
• sensory around eyes upper mouth motor to
  chewing
• VI abducens- motor eye
• VII facial- mixed
• sensory to front of tongue motor to facial
• expression, lacrimal and some salivary glands

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Cranial Nerves

• VIII vestibulocochlear- special senses- ear
• IX glossopharyngeal-mixed
• Sensory for rest of tongue, pharynx palate,
  blood pressure
• Motor to pharyngeal muscles, parotid salivary
  gland
• X 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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Cranial Nerves (Cont.)

• XI Accessory-Motor to voluntary muscles including
  sternocleidomastoid and trapezius
• XII hypoglossal.- motor to tongue

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Aging

• 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