Nervous SystemCNS

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Nervous System-CNS

• Chapter 11

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Meninges-Dura Mater

• 3 protective layers that separate soft tissue of
  brain and spinal cord from bone
• 1. dura mater-tough mother
• Outer periosteal layer and inner meningeal layer
  (periosteal layer is only in the cranial)
• Separated in places by dural sinuses which
  collect blood and empty into jugular vein
• Falx cerebelli-separates 2 hemispheres of
  cerebellum
• Falx cerebri-separates 2 hemispheres of cerebrum
• Tentorium cerebelli-separates occipital lobes
  from cerebellum

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Layers of the meninges
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Meninges continued

• 2. arachnoid mater-spider web like layer
• No blood vessels
• 3. pia mater-delicate mother
• Contains nerves, blood vessels and is attached to
  brain and spinal cord

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Spaces between layers

• Epidural space-fat, blood vessels, and areolar
  CT, get epidural in this space in spinal cord for
  childbirth
• Called a potential space
• Subdural space-also a potential space, blow to
  head may cause blood to accumulate here
• Subarachnoid space-filled with cerebrospinal
  fluid (CSF)

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Ventricles

• Lateral ventricles ---interventricular foramen
  3rd ventricle cerebral aqueduct 4th
  ventricle central canal of spinal cord
• Ventricles are lined with ependymal cells which
  cover a network of capillaries called choroid
  plexus (500 ml of CSF produced daily)
• ventricles are filled with CSF, about 160 ml are
  present at a time due to reabsorption
• 40 of CSF is formed in subarachnoid space, 30
  by ependymal lining of ventricles, and 30 by
  choroid plexuses
• Absorbed by arachnoid villi and mixes with blood
  in the sagittal sinus

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Blood Brain Barrier

• Brain is 2 of body weight, uses 20 of oxygen
  and glucose, and 15 of blood
• A 10 second interruption of blood flow can cause
  loss of consciousness
• 4 minutes-6 minutes without blood (oxygen) can
  cause permanent brain damage
• BBB strictly regulates what substances can enter
  and which cant
• Glucose, water, and lipid soluble substances (O2,
  CO2, alcohol, nicotine, caffeine, anesthetics)
  can enter
• BBB absent in 3rd and 4th ventricle so brain can
  monitor fluctuations in important ions and gases

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Spinal Cord

• Functions
• Conduction-white matter tracts conduct
  information up and down the cord
• Reflexes-involuntary stereotyped response to
  stimuli

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Spinal Cord-Anatomy

• Rope like bundle nervous tissue extending from
  foramen magnum to first lumbar vertebrae
• 1.8 cm wide by 45 cm long (adult)
• 31 pairs of spinal nerves
• Longitudinal groove on anterior surface is
  anterior median fissure
• Longitudinal groove on posterior surface is
  posterior median sulcus (PMS)

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Cross section

• Gray matter in shape of butterfly
• Dorsal or posterior horn-receive input from
  sensory receptors
• gray commissure with central canal in middle
• Lateral gray horn-T, L, and S only, regulate
  smooth muscle, cardiac muscle, glands
• Anterior or ventral horn-provide nerve impulses
  for contraction of sk. Muscle (motor)
• Dorsal root ganglia-cell bodies here
• White matter is columns or funiculi (anterior,
  lateral, posterior)
• Denticulate ligaments are extensions of pia mater
  that anchor the spinal cord laterally

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Anatomy of Cord continued

• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
• Cervical enlargement and lumbar enlargement
• Conus medullaris- end point
• Filum terminale-attaches to coccyx as anchor
• Cauda equina (horse tail), bundle of nerve roots

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Cross section of cord-links

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Spinal tracts

• Ascending carry sensory
• Descending carry motor
• Many fibers have decussation and cross over in
  cord or medulla oblongata
• Contralateral from neck down-right brain controls
  left side, and visa versa
• Ipsilateral in head and neck-right brain controls
  right side

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Tracts continued

• Ascending tracts are often named spino _____
• Awareness is often a 3 neuron pathway
• First order neuron detects stimulus and transmits
  signal to brain or spinal cord
• Second order neuron continues to thalamus
  (gateway)
• Third order neuron carries signal the rest of the
  way to the sensory region of the cerebral cortex

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Ascending Tracts

• Fasciculus gracilis- carries signals for deep
  touch, vibration, and position and movement of
  lower limbs and trunk
• Fasciculus cuneatus- same sensory signals as
  above, but begins at T6
• Spinothalamic tract- signals for pain, temp,
  pressure, light touch, tickle, and itch
• Spinocerebellar tract- signals for proprioception
  (coordination of muscle movement) from limbs and
  trunk

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Descending Tracts

• Named for part of brain for point of origin and
  end in spinal
• Corticospinal tracts-carry motor signals from
  cortex for precise, finely coordinated limb
  movement
• Reticulospinal tracts-control muscles of upper
  and lower limbs and help maintain posture
• Rubrospinal tracts-muscle coordination of limbs
  (more developed in other mammals)
• Tectospinal tracts-movement of head and eyes in
  response to visual stimuli

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Reflexes

• Automatic, subconscious response to a stimulus
• Somatic reflexes are also called spinal reflexes
• 5 parts of a reflex arc
• Receptor
• Afferent nerve fiber
• Interneuron (integrate info)
• Efferent nerve fiber
• Effector (skeletal muscle)
• See clinical application 11.2

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Stretch reflex

• When muscle is stretched it responds by fighting
  back and contracts
• Stretch reflex feeds back to both prime movers,
  synergists, and antagonists
• This helps stabilize joints by balancing tension
  in extensors and flexors
• Keeps you from being jerky
• Knee jerk reflex is a monosynaptic reflex and
  show reciprocal inhibition too (antagonists are
  inhibited)

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Withdrawal reflex

• Protective
• Is a flexor reflex that results in quick
  withdrawal by contraction of the flexor muscles
• Sustained contraction is by parallel
  after-discharge neuron pool and is a
  poly-synaptic reflex arc
• Usually accompanied by crossed extensor reflex,
  branches of afferent nerve fibers cross o other
  side of cord and stimulate muscle on other side
  (extensors are usually stimulated)

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Brain

• Divided into 3 major portions
• no pain receptors, malnutrition affects
  development of brain in infants
• Cerebrum-about 80-85 of volume
• Has 2 hemispheres separated by a longitudinal
  fissure
• Gyri (convolutions) are thick folds separated by
  shallow grooves called sulci
• Deeper grooves are fissures
• A corpus callosum connects the left and right
  hemipheres
• click for sagittal section of brain

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Continued

• Cerebellum
• Also has gyri, sulci, and fissures
• Is the second largest area (10) of volume
• Has over 50 of the neurons found in the brain
• Processes information very quickly
• Transverse fissure separates it from cerebrum
• Anatomy of the Brain - Cerebellum

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Continued

• Brainstem is composed of
• Midbrain
• Pons
• Medulla oblongata
• Brain Basics
• Note diencephalon provides a connection between
  the cerebrum and brain stem

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Cerebrum

• Extensive folding of gyri gives cerebrum
  extension surface area
• Lissencephaly is a condition where the brain is
  smooth
• 5 lobes frontal, parietal, temporal, occipital,
  and 5th is called insula
• Central sulcus-separates frontal from parietal
  lobes
• lateral sulcus-separates frontal from temporal
• Parieto-occipital sulcus-separates parietal from
  occipital

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White Matter tracts

• 3 types of tracts
• 1. projection tracts connect higher to lower
  centers vertically
• 2. commissural tracts connect one hemisphere to
  another through commissures (corpus callosum is
  largest)
• 3. association tracts connect different regions
  within the same hemisphere

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Basal Nuclei

• Masses of neural cell bodies buried deep in white
  matter lateral to thalamus
• Also called basal ganglia
• Receive input from cerebral cortex and provide
  output to motor portions of cortex
• Control subconscious contractions of sk. muscle,
  like arm swinging while walking
• Help regulate initiation and termination of
  movements
• Include caudate nucleus, putamen
• globus pallidus-regulates muscle tone
• Lentiform nucleus-putamen and globus pallidus
  together
• Corpus striatum-putamen and caudate nucleus

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Limbic System-emotional brain

• Loop of cortical structures surrounding corpus
  callosum and thalamus involved in memory,
  emotion, and smell
• Amygdala (emotion) and hippocampus (memory)
• Fornix leads to mammillary bodies of hypothalamus
  which are olfactory (smell)
• Cingulate gyrus-arches over corpus callosum

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Cerebral Cortex

• Orange peel around the cerebrum
• Contains 75 of all neuron cell bodies in nervous
  system
• Divided into functional areas and have been
  mapped
• brain map
• tutoral

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Sensory Areas of Cortex

• 1. Primary somatosensory area -parietal lobe in
  post central gyrus- receives impulses for pain,
  itch, tickle, touch, proprioception (joint and
  muscle position), and thermal sensation
• Functions to localize where the stimulus is
  coming from
• 2. Primary visual area- occipital lobe, receives
  impulses for vision, including shape, color, and
  movement of visual stimuli

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Sensory continued

• 3. primary auditory area- temporal lobe,
  receives information on characteristics of sound,
  like pitch and rhythm
• 4. primary gustatory area -base of postcentral
  gyrus in parietal lobe, receives information
  about taste
• 5. primary olfactory area- temporal lobe,
  receives information about smell

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Motor Areas

• Primary motor areas -precentral gyrus of frontal
  lobe, controls voluntary contractions of specific
  muscles on opposite sides of body
• Brocas speech area is anterior to primary motor
  cortex in frontal lobe, planning and production
  of speech, found in left frontal lobe in 97 of
  population

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Association Areas

• Integrate sensory experiences to generate
  meaningful patterns of recognition and awareness
• 1. somatosensory association area-receives input
  from primary somatosensory area, integrates and
  interpets sensations (stick hand in bag, you can
  tell what you are touching), stores memories of
  past experiences

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Association areas continued

• 2. prefrontal cortex-personality, intellect,
  complex learning skills, judgment, recall,
  conscience, intuition, etc
• 3. visual association area-occipital lobe next
  to primary visual area, relates past and present
  experience to help you recognize what you see
• 4. auditory association area-temporal lobe,
  allows you to recognize sound
• Note people born deaf or blind who suddenly get
  their missing sense restored must be taught what
  things are. If youve never heard a train
  whistle you wont know what it is.

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Association Areas again

• 5. Wernickes area -left temporal and parietal
  lobes, interprets meaning of speech by
  recognizing spoken words, lets you translate
  thought into words, areas in right hemisphere
  help add emotion to vocal communication
• 6. common integrative area-integrates all
  sensory data so you respond appropriately
• 7. premotor area-controls learned skills of a
  repetitious nature (typing)
• 8. frontal eye field area-frontal cortex,
  controls scanning movement of the eye (like for
  reading)

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Hemisphere lateralization

• Subtle differences in left and right hemispheres
• More pronounced in males than females
• Left hemisphere controls right side and visa
  versa
• Left hemisphere-reasoning, math/science, spoken
  and written language, use and understand sign
  language (in most people)
• Right hemisphere-music and art, spatial and
  pattern perception, recognition of faces and
  emotional content of language, generating mental
  images and comparing (touch, smell, sound, etc)

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Cognition

• Mental processes like awareness, perception,
  thinking, knowledge, memory
• Association areas of brain are concerned with
  integration of information between sensory and
  motor areas
• Lesions of brain will affect function
• Parietal lobe lesions -people lose awareness of
  one half of body (man shaves only half of face)
• Temporal lobe lesions -agnosia-(inability to
  recognize familiar objects) or prosopagnosia-(inab
  ility to recognize familiar faces)
• Frontal lobe lesions -personality and social
  behaviors are changed

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Brain Waves

• Rhythmic changes resulting from postsynaptic
  potentials in superficial layers of cerebral
  cortex
• Measured with EEG
• Used in studying normal brain function like sleep
  and consciousness and diagnosis
• 4 types of waves

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Waves continued

• 1. alpha waves-8-13 Hz, record in
  parieto-occipital area, awake and resting, eyes
  closed, disappear when sleeping, when open eyes,
  or engage in mental tasks like math
• 2. beta waves-14-30 Hz, frontal to parietal
  area, measured during mental activity and sensory
  stimulation and/or tension

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Waves

• 3. theta waves-4-7 Hz, normal in children and
  sleeping adults, indicate emotional stress or
  brain damage in awake adults
• 4. delta waves-3.5 Hz or less, slow waves, awake
  infants, deep sleep in adults

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Sleep

• Temporary state of unconsciousness
• Coma-state of unconsciousness from which a person
  cannot wake when stimulated
• 4 stages of sleep in first 30-45 minutes
• Stage 1-drifting, wake easily (alpha waves
  dominate)
• Stage 2-less easily aroused (sleep spindles
  appear on EEG)
• Stage 3-sleep deepens, muscles relax, vital signs
  drop, theta and delta waves appear
• Stage 4-vital signs lowest point, had to wake,
  slow wave sleep (delta waves dominate)

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REM sleep

• About 5 times per night you backtrack from stage
  4 to stage 1 and enter rapid eye movement stage
  or REM
• Vital signs increase, harder to arouse
• Wet dreams possible in this stage
• Dreams here, nightmares usually in stage 3 or 4
• Exhibit sleep paralysis so you dont act out
  dreams
• First one is 90 minutes after sleep starts,
  occurs again and again all night

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Diencephalon

• Thalamus
• Hypothalamus
• Optic tracts and optic chiasma
• Infundibulum-stalk that holds pituitary gland
• Posterior pituitary gland
• Mammillary bodies-relay station for reflexes
  related to smell
• Pineal gland

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Thalamus

• Sensory gateway for everything except smell
• 4/5th of diencephalon
• Intermediate mass connects right and left halves
  in most people
• Connected to limbic system

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Hypothalamus

• Hormone secretion that controls pituitary
• Integration center for ANS (heart beat, blood
  pressure, etc)
• Thermoregulation
• Food and water intake (satiety center and thirst
  center)
• Sleep and awake cycles (RAS)
• Memory
• Emotional behavior (anger, happiness, pleasure,
  sex drive, etc)

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Epithalamus-pineal gland

• Endocrine gland involved in biological rhythms
  and sleep cycle
• Melatonin hormone promotes sleepiness because it
  is released in the dark

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Brainstem

• Consists of midbrain, pons, medulla oblongata
• 1. Midbrain-cerebral aqueduct passes through and
  connects 3rd and 4th ventricles
• Contains cerebral peduncles-contains axons of
  both sensory and motor neurons
• Contains corpora quadrigemina
• 2 superior colliculi-visual reflex center
• 2 inferior colliculi-auditory reflex center

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Midbrain continued

• 2. Pons-bridge between midbrain and medulla
  oblongata
• Contains ascending and descending tracts
• Contains axons that connect left and right
  cerebellum
• Pneumotaxic area and apneustic area work with
  medullary rhythmicity center in medulla to help
  control breathing

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Midbrain continued

• 3. medulla oblongata-continuous with spinal cord
• Contains sensory and motor tracts
• Decussation of pyramids occurs here (90 of axons
  in left pyramid cross to right side and visa
  versa
• Cardiovascular center-rate and force of heartbeat
• Medullary rhythmicity center-rhythm of breathing
• Vasomotor center-diameter of blood vessels
• Vomiting, coughing, sneezing, swallowing reflex
  centers
• Olive-relay impulses about proprioception to
  cerebellum

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Reticular Formation

• Extends from lower diencephalon, brainstem, and
  into cord
• Contain ascending and descending tracts
• Portion is called reticular activating system
  (RAS) which is sensory axons projecting into
  cerebral cortex
• RAS helps maintain awareness, active during
  waking times
• Filters incoming sensory messages so we dont
  have overload (most is ignored quickly)

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Cerebellum

• 1/10 of brain mass, 50 of neurons
• Butterfly shaped, wings are hemispheres, body is
  vermis
• Anterior and posterior lobes separated by
  fissures
• These govern subconscious aspects of skeletal
  muscle movement
• Flocculonodular lobe on inferior surface governs
  equilibrium and balance

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Structures

• Has a cerebellar cortex of gray matter
• White matter tracts are arbor vitae (tree of
  life)
• Cerebellar nuclei within white matter give rise
  to axons that send impulses from cerebellum to
  other brain centers and spinal cord
• 3 paired cerebellar peduncles
• Superior-communication from cerebellum to
  midbrain and thalamus
• Middle-commands for voluntary movement from pons
  into cerebellum
• Inferior-sensory information from medulla to
  cerebellum and spinal cord

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Functions

• Monitor how well movements are being carried out
  (skilled movement)
• Incorrect movements are corrected by feedback
• Posture and balance also
• Walking the white line on the highway or other
  sobriety tests are focusing on cerebellum

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Clinical stuff to read

• Parkinsons Disease-p.410
• Note all green boxes!!
• Spinal cord injuries-p. 400
• Cerebral injuries-p. 408
• Sleep disorders-p. 413