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2014-03-12 04:14:00
ch 13 exam
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  1. PNS
    peripheral nervous system: provides links from and to world outside body
  2. what are the PNS neural structures outside the brain
    • sensory receptors
    • peripheral nerves and associated ganglia
    • efferent motor endings
  3. sensory receptors
    • specialized to respond to changes in environment (stimuli)
    • activation results in graded potentials that trigger nerves impulses
    • sensation (awareness of stimulus) and perception (interpretation of meaning of stimulus occur in brain
  4. sensation
    awareness of stimuli
  5. perception
    interpretation of meaning of stimulus
  6. how are receptors classified
    • based on type of stimulus they detect
    • location in body
    • structural complexity
  7. what are the different types of receptors (5) classified by stimulus type
    • mechanoreceptors
    • thermoreceptors
    • photoreceptors
    • chemoreceptors
    • nociceptors
  8. mechanoreceptors
    respond to touch, pressure, vibration, and stretch
  9. thermoreceptors
    sensitive to changes in temperature
  10. photoreceptors
    respond to light energy (e.g. retina)
  11. chemoreceptors
    respond to chemicals (e.g. smell, taste, change sin blood chemistry)
  12. nociceptors
    sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)
  13. what are the three receptors classified by location
    exteroceptors, interoreceptors, and proprioceptors
  14. exteroreceptors
    • respond to stimuli arising outside body
    • receptors in skin for touch, pressure, pain, and temp
    • most special sense organs
  15. interoreceptors
    • respond to stimuli arising in internal viscera and blood vessels
    • sensitive to chemical changes, tissue, stretch, and temp changes
    • sometimes cause discomfort but usually unaware of their workings
  16. proprioceptors
    • respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
    • inform brain of one's movements
  17. classification of receptors by receptor structure
    general senses and special senses
  18. general senses
    • tactile sensations (touch, pressure, stretch, vibration) temp, pain, and muscle sense
    • modified dendritic endings of sensory neurons
  19. special senses
    vision, hearing, equilibrium, smell, and taste
  20. what are the two types of classifications of general senses
    nonencapsulated (free) or capsulated
  21. nonencapsulated nerve endings
    • free
    • abundant in epithelia and connective tissues
    • most nonmyelinated, small-diametered group C fibers; distal endings have knoblike swellings
    • respond mostly to temp. and pain; some to pressure-induced tissue movement; itch
  22. are thermoreceptors general senses or special senses
    • general senses;
    • cold receptors (10-40 C) in superficial dermis
    • heat receptors (32-48 C) in deeper dermis
    • outside those temperature ranges the nociceptors activated and it is perceived as pain
  23. are nociceptors capsulated or unincapsulated
    • unencapsulated
    • player in detection (vanillioid receptors); ion channel opened by heat, low pH, chemicals (things like red pepper=capsaicin)
    • respond to pinching, chemcials from damaged tissue, capsaicin
  24. what are other noncencapsulated dendritic endings
    light touch receptors: tactile (merkel) discs, hair follicle receptors
  25. what are examples of encapsulated dendritic endings
    • all mechanoreceptors in connective tissue capsule
    • tactile corpuscles: discriminative touch
    • lamellar corpuscles: deep pressure and vibration
    • bulbous corpuscles: deep continuous pressure
    • muscle spindles: muscle stretch
    • tendon organs: stretch in tendons
    • joint kinesthetic receptors: joint position and motion
  26. survival depends on what
    • sensation: awareness of changes in the internal and external environment
    • perception: the conscious interpretation of those stimuli
  27. sensory integrations
    • somatosensory system: part of the sensory system serving body wall and limbs
    • receives inputs from exteroceptors, proprioceptors, and interoceptors
    • input relayed toward head, but processed along way
  28. what are the levels or neural integration in sensory systems
    • receptors level: sensory receptors
    • circuit level: processing in ascending pathways
    • perceptual level: processing in cortical sensory areas
  29. processing at the receptors level
    • to produce a sensation
    • receptors have specificity for stimulus energy
    • stimulus must be applied in receptive field
    • transduction occurs (stimulus changed to graded potential; generator or receptor potential)
    • graded potentials must reach threshold for action potential
  30. processing at receptor level for general sense receptors
    graded potential called generator potential

    stimulus -> generator potential in afferent neuron -> action potential
  31. processing at receptor level in special sense organs
    stimulus -> graded potential in receptor cell called receptor potential -> affects amount of neurotransmitter released -> neurotransmitters generate graded potentials in sensory neuron
  32. adaptation of sensory receptors
    • adaptation is change in sensitivity in presence of constant stimulus
    • receptor membranes become less responsive
    • receptor potentials decline in frequency of stop
  33. what are the two types of adaptation of sensory receptors
    • phasic (fast adapting) receptors: signal beginning or end of stimulus; e.g. receptors for pressure touch, smell
    • tonic receptors: adapt slowly or not at all; e.g. nociceptors and most proprioceptors
  34. processing at the circuit level
    • pathways of three neurons conduct sensory impulses forward to appropriate cortical regions;
    • first order sensory neurons, second order sensory neurons, and third order sensory neurons
  35. first order sensory neurons
    conduct impulses from receptors level to spinal reflexes or second order neurons in CNS
  36. second order sensory neurons
    transmit impulses to third order sensory neurons
  37. third order sensory neurons
    conduct impulses from thalamus to the somatosensory cortex (perceptual level)
  38. processing at the perceptual level
    • interpretation of sensory input depends on specific location of target neurons in sensory cortex;
    • aspects of sensory perception: perceptual detection, magnitude estimation, spatial discrimination
  39. perceptual detection
    ability to detect a stimulus (requires summation of impulses)
  40. magnitude estimation
    intensity coded in frequency of impulses
  41. spatial discrimination
    identifying site or pattern of stimulus (studied by two point discrimination test)
  42. what are the main aspects of sensory perceptions
    • feature abstraction: identification of more complex aspects and several stimulus properties
    • quality discrimination: ability to identify submodalities of a sensation (e.g. sweet or sour tastes)
    • pattern recognition: recognition of familiar or significant patterns in stimuli (e.g moldy in piece of music)
  43. perception of pain
    • warns of actual or impending tissue damage (protective action)
    • stimuli include extreme pressure and temp, histamine (inflammation), K+, ATP, acids, and bradykinin
    • impulses travel on fibers that releases neurotransmitters glutamate and substance P
    • some pain impulses are blocked by inhibitory endogenous opioids (endorphins)
  44. pain tolerance
    • all perceive paint at same stimulus intensity
    • pain tolerance varies
    • sensitive to pain means low pain tolerance, not low pain threshold
    • genes help determine pain tolerance, response to pain medications
  45. homeostatic imbalance
    long-lasting/intense pain -> hyperalgesia, chronic pain, phantom limb pain
  46. visceral pain
    • stimulation of visceral organ receptors
    • felt as vague aching, gnawing, burning
    • activated by tissue stretching, ischemia, chemicals, muscle spasms
  47. referred pain
    • pain from one body region perceived from drifferent region
    • visceral and somatic pain fibers travel in same nerves; brain assumes stimulus from common somatic region
    • e.g. left arm pain during heat attack
  48. structure of a nerve
    • cordlike organ of PNS
    • bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue
    • connective tissue coverings (endo, peri, epineuriums)
  49. three types of connective tissue coverings in a nerve
    • endoneurium: loose connective tissue that encloses axons and their myelin sheaths
    • perineurium: coarse connective tissue that bundles fibers into fascicles
    • epineurium: tough fibrous sheath around a nerve
  50. classified nerves according ot direction transmit impulses
    • mixed nerves: both sensory and motor fibers; impulses both to and from CNS
    • sensory (Afferent): impulses only toward CNS
    • motor (efferent) nerves: impulses only away from CNS
  51. what are the four different types of fibers in mixed nerves
    • somatic afferent
    • somatic efferent
    • visceral afferent
    • visceral efferent
  52. peripheral nerves classified as
    cranial or spinal nerves
  53. ganglia associated with afferent nerve fibers
    dorsal root ganglia
  54. ganglia associated with efferent nerve fibers
    autonomic ganglia
  55. the process if peripheral axon is damaged
    • axon fragments spreads distally form injury
    • macrophages clean dead axon; myelin sheath intact
    • axon filaments grow through regeneration tube
    • axon regenerates; new myelin sheath forms
  56. which type of CNS cell bears growth inhibiting proteins that prevent CNS fiber regneration
  57. which type of cell blocks axonal regrowth
  58. ventral roots
    contain motor (efferent) fibers from ventral horn motor neurons.  fibers innervate skeletal muscles
  59. doral roots
    contain sensory (afferent) fibers from sensory neurons in dorsal root gnaglia and conduct impulses form peripheral receptors
  60. doral root and central roots unite to form what
    • spinal nerves
    • which emerge form vertebral column via intervertebral foramina
  61. dermatome
    area of skin innervated by cutaneous branches of single spinal nerve
  62. hilton's law
    any nerve serving a muscle that produces movement at joint also innervates joint and skin over joint
  63. review of innervation of skeletal muscle
    • takes palce at neuromuscular junction
    • neurotransmitter acetylcholine released when nerve impulse reaches axon terminal
    • ACh binds to receptors, resulting in: movement of Na+ and K+ across membrane, depolarization of muscle cell, an end plate potential, which triggers an action potential (muscle contraction)
  64. steps when a nerve impulse reaches a neuromuscular junction (6 steps)
    • action potential arrives at axon terminal of motor neuron
    • voltage gated Ca2+ channels open. Ca2+ enters axon terminal moveing down its electrochemical gradient
    • Ca2+ entry causes ACh to be released by exocytosis (a neurotransmitter)
    • ACh diffuses across the sympatic cleft and binds to its receptors on the sarcolemma
    • ACh binding opens ion channels in the receptors that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle fiber. ¬†More Na+ ions enter than K+ ions exit, which produces a local change in the membrane potential called the end plate potential
    • ACh effects are terminated by its breakdown in the synaptic cleft by acetylcholinesterase and diffusion away from the junction
  65. which is slower, visceral motor responses or somatic responses
    visceral motor
  66. acetylcholin and norepinephrine act indirectly via second messengers during
    innervation of visceral muscle and glands
  67. branches form syanpses en passant via varicosities during
    innervation of visceral muscle and glands
  68. levels of motor control
    • segmental level
    • projection level
    • precommand level
  69. what are the main parts of motor control
    cerebellum and basal nuclei are the ultimate planners and coordinators of complex motor activities
  70. segmental level
    • lowest level of motor hierarchy
    • reflexes and automatic movements
    • central pattern generators: segmental circuits that activate networks of ventral horn neurons to stimulate specific groups of muscles
    • controls locomotion, and specific, often repeated motor activity
  71. projection level
    • consists of upper motor neurons that initiate direct pyramidal system to produce voluntary skeletal muscle movements and the brain stem motor areas that oversee indirect extrapyramidal system to control reflex and CPG controlled motor actions
    • projection motor pathways send info to lower motor neurons and keep higher command levels informed of what is happening
  72. precommand level
    • neurons in cerebellum and basal nuclei
    • regulate motor activity
    • precisely start or stop movements
    • coordinate movements with posture
    • block unwanted movements
    • monitor muscle tone
    • perform unconscious planning and discharge in advance of willed movements
    • cerebellum: acts on motor pathways through projection areas of brain stem; acts on motor cortex via thalamus to fine tune motor activity
    • basal nuclei: inhibit various motor centers under resting conditions
  73. spinal cord is all about reflexes, true or false
  74. two types of reflexes
    inborn (intrinsic) and learned (acquired)
  75. inborn (intrinsic) reflexes
    • rapid, involuntary, predictable motor response to stimulus
    • e.g. posture, control visceral activities
    • can be modified by learning and conscious effort
  76. learned (acquired) reflexes
    • result form practice of repetition
    • e.g. driving skills
  77. components of a reflex arc
    • receptor: site of stimulus action
    • sensory neuron: transmits afferent impulses to CNS
    • integration center: either monosynaptic of polysynaptic region within CNS
    • motor neuron: conducts efferent impulses from integration center to effector organ
    • effector: muscle fiber or gland cell that responds to efferent impulses by contracting or secreting
  78. functional classification of reflexes
    • somatic reflexes: activate skeletal muscles
    • autonomic (visceral) reflexes: activate visceral effectors (smooth or cardiac muscle or glands)
  79. spinal reflexes
    • integration center in spinal cord
    • effectors are skeletal muscles
  80. stretch and tendon reflexes
    • to smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding:
    • length of muscle: form muscle spindles
    • amount of tension in muscle: from tendon organs
  81. functional anatomy of muscle spindles
    composed of 3-10 modified skeletal muscle fibers (intrafusal muscle fibers) wrapped in connective tissue capsule
  82. intrafusal fibers
    • noncontractile in central regions (lack myofilaments)
    • two types of afferent endings: anulospiral endings and flower spray endings
  83. anulospiral enedings
    • primary sensory endings
    • endings wrap around spindle; stimulated by rate and degree of stretch
  84. flower spray endings
    • secondary sensory endings
    • small axons at spindle ends; respond to stretch
  85. what are the two ways muscle spindles are excited
    • external stretch of muscle and muscle spindle
    • internal stretch of muscle spindle
  86. what does a stretch cause
    it causes increased rate of impulses to spinal cord
  87. the stretch reflex
    • maintains muscle tone in large postural muscles and adjusts it reflexively
    • causes muscle contraction in response to increased muscle length (stretching)
  88. how stretch reflexes work
    • stretch activates muscle spindle
    • sensory neurons synapse directly with motor neurons in spinal cord
    • motor neurons cause stretched muscle to contract
    • all stretch reflexes are monosynaptic and ipsilateral
  89. recipricol inhibition
    • fibers synapse with interneurons that inhibit motor neurons of antagonistic muscles
    • e.g. patellar reflex, stretched muscle (quads) contract and antagonists (hamstrings) reflex
  90. positive reflex reactions indicate
    • sensory and motor connections between muscle and spinal cord intact
    • strength of response indicates degree of spinal cord exciteability
  91. stretch reflexes are hypoactive or absent if
    peripheral nerve damage or central horn injury
  92. stretch reflexes are hyperactive if
    there are lesions of corticospinal tract
  93. events of which muscle stretch is damped
    • 1. when stretch activates muscle spindles, the associated sensory neurons transmit afferent impulses at higher frequency to the spinal cord
    • 2. the sensory neurons synapse directly with alpha motor neurons, which excite extrafusal fibers of the stretched muscle. sensory fibers also synapse with interneurons that inhibit motor neurons controlling antagonistic muscles
    • 3a. efferent impulses of alpha motor neurons cause the stretched muscle to contract, which resists of reverses the stretch
    • 3b. efferent impulses of alpha motor neurons to antagonist muscles are reduced (recipricol inhibition)
  94. the tendon reflex
    • polysnaptic reflexes
    • helps prevent damage due to excessive stretch
    • important for smooth onset and termination of muscle contraction
    • produces muscle relaxation (lengthening) in response to tension
  95. steps in the tendon reflex
    • 1. quadriceps strongly contracts. tendon organs are activated
    • 2. afferent fibers synapse with interneurons int he spinal cord
    • 3a. efferent impulses to muscle with stretched tendon are damped. muscle relaxes, reducing tension
    • 3b. efferent impulses to antagonist muscle cause it to contract
  96. flexor reflex
    • initiated by painful simulus
    • causes automatic withdrawal of threatened body part
    • ipsilateral or polysnaptic
    • protective; important
    • brian can override (e.g. stick for blood)
  97. crossed extensor reflex
    • occurs with flexor reflexes in weight-bearing limbs to maintain balance
    • consists of ipsilateral withdrawal reflex and contralateral extensor reflex
    • e.g. step barefoot on broken glass
  98. superficial reflexes
    • elicited by gentle cutaneous stimulation
    • depend on upper motor pathways and cord level reflex arcs
    • plantar reflex and abdominal reflex
  99. plantar reflex
    • superficial reflex
    • test integrity of cord from L4-S2
    • stimulus: stroke lateral aspect of sole of foot
    • response: downward flexion of toes
    • damage to motor cortex or corticospinal tracts > abnormal response =babinski's sign
    • normal in infants til 1 year due to incomplete myelination
  100. abdominal reflexes
    • superficial reflex
    • test integrity of cord from T8-T12
    • cause contraction of abdominal muscles and movement of umbilicus in response to stroking of skin
    • vary in intensity from one person to another
    • absent when corticospinal tract lesions present