CENTRAL NERVOUS SYSTEM

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CENTRAL NERVOUS SYSTEM
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SUBDIVISIONS OF BRAIN

• 1. telencephalon
• surface gray - cerebrum cortex
• deep gray - basal nuclei
• white matter
• 2. diencephalon
• epithalamus
• thalamus
• hypothalamus

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SUBDIVISIONS OF BRAIN

• 3. mesencephalon
• corpora quadrigemina
• cerebral peduncles
• substantia nigra
• red nucleus
• 4. metencephalon
• cerebellum
• pons
• 5. myelencephalon
• medulla oblongata
• olive

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MENINGES

• a. dura mater
• double layer over most of brain
• outer periosteal layer
• inner meningeal layer
• separate by _______________ which empty into the
  internal jugular veins
• single layer over spinal cord
• epidural space between dural sheath and spinal
  cord

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MENINGES

• b. arachnoid
• middle cob-web layer
• separated from dura mater by subdural space
• some feel this my be an artifact
• separated from pia mater by subarachnoid space
• 2 spaces contain __________fluid
• subarachnoid space is much larger
• arachnoid villi
• c. pia mater
• inner most delicate areolar connective tissue

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THREE VENTRICLES

• 1. lateral ventricles
• in each cerebral hemisphere
• 1st two ventricles fuse to form the lateral
  ventricles
• connected to third ventricle by _______________
  foramen
• 2. 3rd ventricle
• between left and right halves of the thalamus
• connected to 4th ventricle by mesencephalic
  (cerebral) __________
• 3. 4th ventricle
• between inferior brain stem and the cerebellum
• connects to the spinal canal in the spinal cord

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CEREBROSPINAL FLUID

• components
• very different from plasma
• low in proteins
• pH is lower
• K, Ca, HCO3 and glucose are lower
• Na is about the same

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CEREBROSPINAL FLUID

• functions
• a. Buoyancy
• human brain weighs about 1500 g in air but 50 g
  when suspended in CSF
• b. Protection
• protects brain from striking the cranium
• c. Chemical Stability
• provides means of rinsing metabolic wastes from
  CNS and regulating its chemical environment

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CEREBROSPINAL FLUID

• formation
• formed in the _______________
• in roofs of the ventricles
• volume 100 - 160 ml
• produce about 500 ml per day
• 160 mm pressure

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CEREBROSPINAL FLUID

• pathway
• produced in roofs of all ventricles
• lateral ventricle --gt interventricular foramen
  --gt 3rd ventricle --gt cerebral aqueduct --gt 4th
  ventricle --gt (central canal of spinal cord) --gt
  subarachnoid space --gt arachnoid villi --gt dural
  sinus

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CEREBROSPINAL FLUID

• lumbar puncture
• between L3 and L4
• CSF from __________ space
• spinal tap 3-9 ml
• myelogram
• epidural and spinal blocks
• into the epidural space
• steroids and anastethetics

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BLOOD SUPPLY

• one - two minute interruption of blood may weaken
  cells
• brain constitutes 2 of adult body weight,
  receives 15 of blood and consumes 20 of bodys
  oxygen and glucose
• 4 minute interruption of blood, brains cells have
  permanent injury
• lysosomes release enzymes to break down brain
  cells
• brain cells
• _____ stored oxygen like myoglobin
• _____ energy reserves in the form of
  carbohydrates (glycogen) or lipids

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BLOOD BRAIN BARRIER

• normal capillary bed is very permeable
• Two different barriers
• 1. blood brain barrier
• capillary bed has tight junctions
• protoplasmic __________ cover capillary and
  release chemicals that control the permeability
  of the endothelium
• 2. Blood-CSF barrier
• ependymal cells in choroid plexus have _______
  junctions

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BLOOD BRAIN BARRIER

• blood brain barrier
• pass easily
• water, glucose
• lipid soluble substances - oxygen, carbon
  dioxide, caffeine, nicotine, heroin, and
  anesthetics
• pass slowly
• sodium, potassium, chloride, creatinine, and
  urea
• do not pass
• proteins, most antibiotics
• neurotransmitters, formed elements

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BLOOD BRAIN BARRIER

• not found
• portions of the hypothalamus
• posterior pituitary gland
• pineal gland
• choroid plexus
• by-pass bbb
• nasal sprays
• can travel up the olfactory nerve fibers

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MYELENCEPHALON

• medulla oblongata
• 3 cm long (1 inch)
• forms inferior part of brain stem
• lateral side - Olive
• contains inferior olivary nuclei
• communicates with the cerebellum

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MYELENCEPHALON

• three groups of nuclei (we will consider 2)
• 1. autonomic nuclei controlling visceral
  activities
• cardiac center
• vasomotor center
• two respiratory centers
• 2. relay stations along sensory or motor
  pathways
• nucleus gracilis and nucleus cuneatus
• sensory information crosses over
• decussation of pyramids
• descending motor tracts
• 2/3 of fibers cross over

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RETICULAR FORMATION

• brain stem
• medulla pons mesencephalon
• contains more than 100 clusters of neurons
• dispersed gray matter
• functions
• 1. Somatic motor control
• 2. Cardiovascular control
• 3. Pain modulation
• 4. Sleep and consciousness

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METENCEPHALON

• second largest part of the brain
• contains 50 of brains neurons
• two major areas
• a. cerebellum
• b. pons

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METENCEPHALON

• a. cerebellum
• composed of two cerebellar hemispheres connected
  by the vermis
• gray matter
• cortex contains huge and highly branched Purkinje
  cells
• can receive input from up to 200,000 synapses

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METENCEPHALON

• a. cerebellum
• white matter or arbor vitae
• superior cerebellar peduncles
• middle cerebellar peduncles
• inferior cerebellar peduncles

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METENCEPHALON

• a. cerebellum
• functions
• 1. adjusting the postural muscles of the body
• coordinates rapid, automatic adjustments that
  maintain balance and equilibrium
• 2. programming and fine-tuning movements
  controlled at the conscious and subconscious
  levels
• refines learned movement patterns

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METENCEPHALON

• b. pons
• links cerebellar hemispheres with mesencephalon,
  diencephalon, cerebrum and spinal cord
• contains
• nuclei involved with control of respiration
• nuclei and tracts that process and relay
  information heading to or from the cerebellum

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MESENCEPHALON

• also called midbrain
• contains
• gray matter
• 1. corpora quadrigemina
• 2. red nucleus
• 3. substantia nigra
• 4. reticular formation

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MESENCEPHALON

• contains
• white matter
• cerebral peduncles
• connect primary motor cortex with motor neurons
  in brain and spinal cord
• carry sensory information to thalamus

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MESENCEPHALON

• 1. corpora quadrigemina
• superior colliculus
• initiates reflex response to visual stimuli
• inferior colliculus
• initiates reflex response to auditory stimuli
• 2. red nucleus
• contains iron and many blood vessels
• controls posture

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MESENCEPHALON

• 3. substantia nigra
• darkly pigmented with melanin
• inhibits the activity of the cerebral nuclei by
  releasing dopamine
• associated with Parkinsons disease
• 4. reticular formation
• reticular activating system
• maintenance of consciousness

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DIENCEPHALON - THALAMUS

• structure
• two oval masses of nerve cell bodies
• 4/5 of diencephalon
• contains over 20 functionally separate nuclei
• functions
• gateway to cerebral cortex
• communicates cerebellum with the cerebrum
• nearly all sensory impulses pass through the
  thalamus
• passes only a small portion of arriving sensory
  information to cerebrum

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DIENCEPHALON -HYPOTHALAMUS

• components
• numerous nuclei
• nuclei --gt hormones
• preoptic areas --gt body temperature, sexual
  behavior
• mammillary bodies --gt controls feeding reflexes
  and processes motor information associated with
  eating, relays signals from limbic system to
  thalamus
• tuber cinereum --gt nerve tracts that carry
  hormones to the pituitary
• infundibulum --gt stalk that connects to posterior
  lobe of pituitary

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DIENCEPHALON -HYPOTHALAMUS

• functions
• subconscious control of skeletal muscle
  contractions
• control of autonomic function
• secretion of hormones
• production of emotions and behavioral drive
• regulation of body temperature
• food and water intake
• control of circadian rhythm
• memory

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DIENCEPHALON-EPITHALAMUS

• contains the pineal body producing the hormone
  _________________
• functions - lower vertebrates
• regulates reproductive cycles based on
  photoperiod
• functions of melatonin in humans
• regulation of day-night cycles
• jet lag
• onset of sleep

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TELENCEPHALON OR CEREBRUM

• components
• surface gray matter - neocortex
• 6 layers of nerve cell bodies
• deep gray matter - basal or cerebral nuclei
• white matter
• myelinated tracts
• features of cerebral cortex
• gyrus - fold in cortex
• sulcus - shallow groove
• fissure - deep groove

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CEREBRUM - WHITE MATTER

• forms three myelinated tracts
• 1. projection tracts
• to and from other parts of the brain such as the
  thalamus
• 2. association tracts
• within the same hemisphere
• 3. commissural tracts
• connects left and right hemispheres
• a. anterior and posterior commissures
• b. corpus callosum
• 4 billion impulses per second

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CEREBRUM - LOBES

• 1. Frontal
• voluntary control of skeletal muscle
• motivation, aggression, mood
• planning, social judgment, intelligence
• 2. Parietal
• major center for reception and evaluation of most
  sensory information
• excluding smell, hearing and vision
• including taste, touch, pressure, temperature,
  and pain
• 3. Occipital -- vision

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CEREBRUM - LOBES

• 4. Temporal
• smell and hearing
• memory, visual recognition, emotional behavior
• 5. Insula
• part of limbic system
• plays a role in understanding spoken language,
  taste, and in integrating sensory information
  from visceral receptors

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CEREBRUM - MOTOR AREASFRONTAL LOBE

• 1. Primary motor cortex
• controls precise voluntary contractions of
  skeletal muscle cells
• has pyramidal cells- origin of pyramidal tracts
• 2. Premotor cortex
• extrapyramidal tracts
• coordinates movement in sequence
• much of ones knowledge is stored here for
  controlling skilled movements
• 3. Brocas area
• controls speech
• 19/20 are in the left hemisphere

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CEREBRUM - SENSORY AREAS

• Primary sensory cortex
• parietal lobe
• touch, pressure, temperature, and pain
• Visual cortex
• occipital lobe
• Auditory cortex (sound)
• temporal lobe
• Olfactory cortex (smell)
• temporal lobe
• Gustatory cortex (taste??)
• insula and frontal lobe

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CEREBRUM - ASSOCIATION AREAS

• sensory and motor areas are connected to
  association areas
• regions of cortex that interpret incoming data or
  coordinate a motor response
• Association areas
• 1. Somatic sensory association area
• 2. Visual association area
• 3. Auditory association area

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CEREBRUM - GENERAL INTERPRETIVE OR WERNICKES
AREA

• description
• receive information from many association areas
  and direct complex motor activities
• perform complicated analytical functions
• forms one thought from other association areas
• meaning of written and spoken word
• found in temporal and parietal lobes
• only in left hemisphere

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CEREBRUM - FRONTAL AREA

• Frontal lobe
• origin of higher intellectual activities, will
  judgement, personality, long term memory
• prefrontal lobe or cortex
• coordinates information relayed from association
  areas of entire cortex
• abstract intellectual functions
• feelings of frustration, tension, and anxiety are
  generated at prefrontal cortex
• prefrontal lobotomy
• treated for a variety of mental illnesses,
  especially those associated with violent or
  antisocial behavior

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BRAIN LATERALIZATION

• generally left hemisphere contains general
  interpretive and speech centers and is
  responsible for language based skills
• premotor cortex is larger on the left side for
  right-handed people
• Left hemisphere - categorical hemisphere
• important for analytical tasks such as
  mathematical calculations and logical decision
  making
• more important in spoken and written language

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BRAIN LATERALIZATION

• Right or representation hemisphere
• relates body to sensory environment
• can identify familiar objects by touch, smell,
  sight, taste or feel
• more for musical and artistic awareness

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CEREBRAL NUCLEI

• functions
• subconscious control of skeletal muscle tone and
  coordination of learned movement patterns
• do not initiate particular movements but proved
  general pattern and rhythm
• extrapyramidal tracts
• loss of function - Parkinsons disease
• leaves person with only crude motor activities
• movement of limbs stiff
• inhibits motor activities

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LIMBIC SYSTEM

• functions
• establishes emotional states
• links the conscious, intellectual functions of
  the cerebral cortex with the autonomic functions
  of the brain stem
• facilitates memory storage and retrieval
• makes you want to do complex tasks -- called
  motivational system

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SPINAL CORD

• general characteristics
• length - 45 cm (18 in)
• maximum width - 14 mm (0.55 in)
• enlargements
• cervical - C4 to T1
• lumbar - T9 to T 12

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SPINAL CORD

• general characteristics
• conus medullaris or medullary cone- 1st or 2nd
  lumbar
• terminal filum
• inferior tip of conus medullaris to 2nd sacral
  vertebra
• cauda equina
• appearance of horses tail from L2 to S5

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SPINAL CORD - MENINGES

• a. dura mater
• continuous with dura mater of brain
• between dura mater and wall of vertebral column
  is epidural space
• filled with areolar connective tissue and blood
  vessels
• b. arachnoid
• subdural and subarachnoid spaces

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SPINAL CORD - MENINGES

• c. pia mater
• adheres to surface of spinal cord and brain
• contains rich amount of blood vessels
• spinal cord is suspended in middle of dural
  sheath
• suspended by extensions of pia mater called
  denticulate ligaments
• protects cord against shock and sudden
  displacement

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SPINAL CORD - COMPOSITION

• gray and white matter is reversed from brain
• H of gray matter
• gray commissure
• central canal
• posterior or dorsal horns
• anterior or ventral horns
• lateral horns (thoracic and lumbar regions)
• dorsal root
• ventral root

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SPINAL CORD - WHITE MATTER

• a. ascending tracts - carry sensory information
• b. descending tracts - carry motor information

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REFLEX ARC

• not all sensory impulses carried to spinal cord
  enter one of the ascending tracts to the brain
• some synapse directly or through association
  neurons with motor neurons in the anterior horn
• called a reflex arc
• presence of spinal reflex arc makes possible
  automatic stereotyped reactions to stimuli
• at same time a reflex is occurring, information
  about stimulus is also transmitted to brain

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REFLEX ARC

• 1. receptor
• 2. sensory or afferent neuron
• 3. information processing - synapse
• monosynaptic
• polysynaptic
• 4. motor neuron
• 5. response - effector
• cardiac, skeletal or smooth muscle
• gland

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SPINAL REFLEXMONOSYNAPTIC REFLEXSTRETCH REFLEX

• results when a muscle is stretched to counteract
  the stretch
• slight stretching stimulates receptors in muscle
  called neuromuscular spindles or intrafusal
  fibers
• 3 to 10 specialized muscles cells (central area
  does not contract)
• once spindle is stretched sends impulses to
  dorsal horn where it synapses with efferent
  neurons called alpha motor neurons
• alpha motor neurons send impulse to muscle
  causing contraction

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SPINAL REFLEXMONOSYNAPTIC REFLEXSTRETCH REFLEX

• afferent neurons also synapse with inhibitory
  neurons
• inhibitory neurons synapse with efferent or motor
  neurons of the antagonistic muscles
• ex knee jerk reflex or patellar reflex
• maintaining balance - sends sends sensory
  impulses to cerebellum by away of the brainstem
  which integrates this information and relays it
  to the cerebral cortex