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157 Cards in this Set
- Front
- Back
inflammatory pain
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pain resulting from long-term changes in nociceptor sensitivity to stimuli
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neuropathic pain
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irritation of conducting fibers of nociceptors
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central pain
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pain resulting from abnormal activity of neurons of the anterolateral system
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what is collectively true of inflammatory pain, neuropathic pain and central pain?
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often persist and are hard to treat
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Why do sensitized receptors respond more vigorously to stimuli than normal?
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b/c their threshold for activation is lowered
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why is a warm shower or a gentle pat on sunburned skin painful?
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b/c nociceptors in that area are SENSITIZED
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2 types of abnormality of stimulus detection
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hyperalgeisa
allodynia |
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2 primary causes of nociceptor sensitization
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noxious stimuli cause release of toxic soup of chemicals from cells/tissues in vicinity of injury
axon reflex - neuroendocrine function of nociceptors |
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substances released by cells in vicinity of injury, in response to noxious stimuli
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bradykinin
histamine PGs serotonin K+ |
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which cause of nociceptor sensitization is primarily responsible for arthritis pain?
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toxic soup release
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axon reflex
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impulses that propagate centrally along sensory axons can depolarize terminal branches and cause release of other mediators from receptor endings
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what increases the blood flow that causes further receptor sensitization, edema and reddening of skin?
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axon reflex
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4 endogenous agents that activate nociceptors
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K+
serotonin (5-HT) bradykinin histamine |
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3 endogenous agents that sensitize nociceptors
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PGs
LTs Substance P |
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3 pharmalogical approaches to managing hyperalgesia from inflammatory/arthritic pain
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block initial sensitization fo nociceptor endings with NSAIDs
block release of substance P from nociceptors that can sensitize neighboring receptors (eg: topical anesthetic creams, like capsaicin) impede impulse conduction in afferent nerves with Lidocaine |
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how do NSAIDs work?
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inhibit PG formation by inhibiting COX
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how do capsaicin creams work?
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depleting substance P from nociceptor nerve endings
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how does Lidocaine work?
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blocks voltage-gated Na+ channels and has generalized anesthetic, not analgesic effects
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central component to sensitization mediating inflammatory/arthritis pain involves what NT?
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glutamate
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which two excitatory amino acid channels does glutamate released from nociceptors act on?
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AMPA
NMDA |
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What normally blocks NMDA?
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Mg2+
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What happens when Glu opens AMPA channels?
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Glu --> AMPA opens --> membrane potential depolarized --> NMDA channels become unblocked --> additional depolarization
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repeated activation of C fibers causes...
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a "wind up" or successive increase in repsonsiveness of dorsal horn neurons as NMDA channels lose their Mg2+ block and become activated
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central pain
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severe condition caused by damage to anterolateral system or its targets
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phantom limb pain is a form of what kind of pain?
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central pain
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phantom sensations
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sensations, including pain, emanating from the amputated limb
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phantom pain may be caused by...
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hyperactive neurons in the AL system from an imbalance between excitatory and inhibitory input following deafferentiation
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referred pain results from...
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activation of nociceptors
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referred pain
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condition in which pain following injury to an internal organ (by activation of visceronociceptors) is perceived as coming from other areas on body surface
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cause of referred pain
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convergence of somatic and visceral nociceptive inputs to DORSAL HORN SPINOTHALAMIC TRACT neurons
stimulus detection and condition are normal, but localization is faulty |
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what two afferent types converge to cause referred pain?
where do they converge? |
nociceptive visceral afferents and afferents innervating specific somatic areas converge
on same anterolateral system projection neuron |
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Radicular pain
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pain of neural, NOT sensory, originn
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radicular pain arises from mechanisms that BYPASS ____
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radicular pain arises from mechanisms that bypass the normal activation of nociceptors
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2 causes of MECHANICAL radicular pain
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sciatica (herniated intervertebral disc)
spinal stenosis |
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4 categories of radicular pain
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mechanical
increase in nerve excitability w/ ectopic impulse initiation inflammation or irritation of chronically injured peripheral nerves ectopic impulses propagating peripherally, releasing neuroactive agents that sensitize its neighbors |
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which ganglia are particularly sensitive to mechanical compression
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dorsal root ganglia
especially following ischemia |
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only link between nervous system and skeletal muscles
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motor neurons
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Sherrington's "final common path"
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motor neurons serve as the only link between the nervous system and skeletal muscles
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lower motor neurons, aka:
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spinal motor neurons
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brainstem and cortical motor neurons, aka:
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upper motor neurons
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upper motor neurons influence the activity of _____, via _____
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upper motor neurons influence the activity of lower motor neurons via descending projections
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nuclei and laminae in which spinal motor neurons are located?
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lamina IX
somatic motor nuclei |
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alpha motor neurons
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motor neurons that innervate extrafusal muscle fibers
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what type of synapse(by NT) is the NMJ?
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cholinergic
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motor unit
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a single alpha motor neuron and all the muscle fibers it innervates
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the nervous system acts only on ____
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motor units
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nervous system controls muscle contraction by varying which 2 things?
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rate coding: regulating motor neuron FIRING RATE
recruiting motor units |
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size of motor unit depends on...
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number of muscle fibers innervated
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sense organs innervating muscles and tendons provide ______ to _____ neurons
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sense organs innervating muscles and tendons provide PROPRIOCEPTIVE SENSORY INPUT to VENTRAL HORN MOTOR NEURONS
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two types of sensory fibers innervating muscle spindles
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Group Ia - signal both velocity & length
Group II - signal length only |
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GTOs contribute to ______
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fine adjustments in muscle force needed during voluntary movements
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only sensory receiver to receive efferent connections from the nervous system
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muscle spindles
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efferent innervation from nervous system to muscle spindles is through ____ fibers
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gamma motor neurons
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gamma motor neurons regulate...
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gamma motor neurons regulate the sensitivity of muscle spindles during movement
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type of neuron thought to play a role in the development of spasticity after spinal cord injuries
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gamma motor neurons
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alpha-gamma coactivation
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during muscle contraction, the nervous system fires gamma motor neurons at the same time as alpha motor neurons
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alpha-gamma coactivation preserves...
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proprioceptive input to the nervous system during movement by keeping muscle spindles from going slack during extrafusal muscle contraction and no longer providing information about muscle length
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2 types of spinal reflexes
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tendon reflexes
flexor - crossed extension reflex |
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2 types of tendon reflexes
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stretch reflex
inverse myotactic reflex |
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stretch reflex, aka: ____ or _____
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stretch reflex, aka: myotatic or monosynaptic reflex
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what nerves mediate stretch reflex
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Group Ia afferents innervating muscle spindles
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what activates stretch reflex
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tapping any large tendon
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best known example of stretch reflex
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patellar tendon reflex
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sequence of events in stretch reflex
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tap patellar tendon --> stretch spindle --> excite sensory endings --> impulses conducted along afferent axons to motor neurons --> motor neurons excite quadriceps motor neurons --> contraction of muscle
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reciprocal inhibition
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one group of muscles is excited while the antagonist muscles are inhibited
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function of reciprocal inhibition
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prevents reflexive contraction of the antagonist muscles
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what reflex counteracts muscle stretch during contraction or passive, fatigue-produced muscle lengthening (e.g.: when standing)
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length-maintaining reflex (type of tendon reflex)
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inverse myotatic reflex regulates
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muscle tension and stiffness
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inverse myotatic reflex is activated by which neurons?
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group Ib fibers innervating GTOs
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which has a higher threshold, stretch reflex or inverse stretch reflex?
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inverse stretch reflex
(not activated by tendon tap) |
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sequence of events in inverse myotatic reflex
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stretch tendon --> excite GTOs --> impulses conducted to inhibitory interneurons --> inhibit motor neurons that innervate muscle attached to tendon
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autogenic inhibition
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muscle group inhibited by its own sensory input
muscle tension leads to inhibition of motor neurons |
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which reflex helps maintain posture during standing
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inverse myotatic reflex
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flexor-crossed extension reflex controls _____ and involves ____ spinal segments
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MUSCULATURE acting around MULTIPLE JOINTS
and involves SEVERAL spinal segments |
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which reflex is polysynaptic?
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flexor-crossed extension reflex
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flexor-crossed extension reflex, aka:
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withdrawal reflex
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protective function of flexor-crossed extension reflex
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automatically withdraws limb from noxious stimulus and transfers weight to opposite limb
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what structures initiate the flexor-crossed extension reflex?
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A-delta nociceptors
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mechanism of flexor-crossed extension reflex
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nociceptive input to the Al system is relayed to excitatory and inhibitory interneurons that synapse on the ipsilateral and contralateral flexor and extensor motor neurons
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sequence of events in flexor-crossed extension reflex
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painful stimulus --> excite flexor motor neurons --> rapid withdrawal of limb away from harmful object --> excite contralateral extensors and inhibit contralateral flexors to enable opp. limb to support body weight.
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bottom line, what does withdrawal reflex produce?
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ipsilateral flexion & contralateral extension
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spinal reflexes are used as a diagnostic tool for evaluating what?
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motor system dysfunction
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spinal cord injury involving damage to descending pyramidal tract axons in the lateral funiculi produce _____
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"upper motor neuron signs"
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2 general categories of "upper motor neuron signs"
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spinal "shock" - initial flaccid paralysis of muscles below injury
spasticity - increased resistance of muscles to passive movement |
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4 types of spasticity
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hypertonia
hyperreflexia clasp-knife response clonus |
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hypertonia
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increased resistance to passive manipulation
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hyperreflexia
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exaggerated response to tendon tap
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clasp-knife response
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increased resistance to displacement of a joint - suddenly collapses like the closing of a pocket knife
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clonus
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repetitive alternating contraction of flexors and extensors, usu. at a distal joint (ankle)
often present with hypertonia and hyperreflexia |
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mechanisms underlying hypertonia and hyperreflexia
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excessive activation of gamma motor neurons from loss of descending inhibitory input
involves gamma loop pathway |
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gamma loop circuit
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gamma motor neuron --> intrafusal fiber --> Ia afferent --> alpha motor neuron --> extrafusal fibers
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intrafusal muscle fibers
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skeletal muscle fibers that comprise the muscle spindle and are innervated by gamma motor neurons.
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extrafusal muscle fibers
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innervated by alpha motor neurons
cause the muscle to contract |
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clasp knife response mediated by...
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autogenic inhibition from GTOs (inverse myotatic reflex)
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Sensory receptors that drive autonomic activity may originate from which three regions?
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viscera (visceral sensory)
body surface (somatic sensory) external environment (special sensory) |
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receptors of visceral afferents are usually located where?
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in the walls of hollow organs
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receptors located in organ walls are called ____
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intramural
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are mechanoreceptors in organs usually exposed to the organ lumen?
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no
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what type of receptors are sensitive to the following:
oxygen tension in aortic bodies pH in the stomach and duodenum |
chemoreceptors
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visceral pain is mediated by ____
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nociceptors in the walls of organs
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axons of spinal sensory neurons that mediate visceral pain usually travel along side _____
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sympathetic nerves
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3 components of most autonomic reflexes
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somatovisceral
viserosomatic viscerovisceral |
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what type of reflex is:
muscle movement eliciting reflex vasodilation |
somatovisceral
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what type of reflex is:
a strong intestinal contraction (usu. with pain) results in abdominal muscle contraction |
viscerosomatic
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what type of reflex is:
distention of one region of the intestin results in decreased motility in other regions of the intestine and changes in blood flow |
viscerovisceral
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basic visceral reflex arc consists of what 3 things?
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afferent, spinal sensory neuron
preganglionic neuron in the brainstem or intermediolateral region of spinal cord postganglionic neuron in an autonomic ganglion that innervates the effector organ |
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a reflex that involves spinal pathways may ascend to reach...
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higher centers in the brainstem or hypothalamus
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sympathetic innervation of pelvic organs originates in what region of the spinal cord?
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LUMBAR
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all autonomics are primarily release which NT?
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ACh
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in which nucleus of the spinal cord are preganglionic autonomic cell bodies found?
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intermediolateral nucleus
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pudendal nerve supplies what kind of innervation to which part of the urinary tract?
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pudendal nerve supplies SOMATIC innervation to the EXTERNAL URINARY SPHINCTER
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pelvic nerve supplies what kind of innervation to which part of the urinary tract?
effect? |
pelvic nerve supplies PARASYMPATHETIC innervation to the DETRUSOR MUSCLE of the bladder.
Causes the bladder to CONTRACT. |
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The hypogastric nerve supplies what kind of innervation to which part of the urinary tract?
effect? |
They HYPOGASTRIC nerve supplies SYMPATHETIC innervation to the DETRUSOR MUSCLE of the bladder.
Causes bladder relaxation during filling. |
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Fibers that provide principal excitatory input to bladder smooth muscle
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parasympathetic efferent fibers of pelvic nerves
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autonomic afferents innervating the bladder are sensitive to what 2 things?
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distention & pain
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sympathetic efferents of hypogastric nerves are
excitatory to _____ & inhibitory to ____ |
sympathetic efferents of hypogastric nerves are
excitatory to trigone muscle inhibitory to detrusor muscle |
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function of trigone
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signals brain that micturition threshold has been reached
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what occurs during the voiding phase of the micturition reflex?
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destrusor muscle contracts
muscles of external urethral sphincter & pelvic floor muscles relax |
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what ends the filling phase?
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pressure reaches the micturition threshold
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where are reflex "centers" located?
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spinal cord & brain
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where is parasympathetic reflex center located?
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SACRAL spinal cord
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where are sympathetic reflex centers located?
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LUMBAR spinal cord
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spinal reflex centers are under the control of ____ centers
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SUPRASPINAL
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chain of command in micturition reflex
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cortical and diencephalic centers -->
brainstem centers --> sacral centers |
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effect of spinal shock on micturition
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no reflex emptying of the bladder
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neurogenic bladder
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any dysfunction of the bladder caused by a lesion of the nervous system
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where must the spinal cord be transected, given SCI, so that the spinal voiding reflex will operate?
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above the lumbar region
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transections above the lumbar region cause ______ bladder
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automatic, or uninhibited, bladder
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2 causes of automatic bladder
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spine transection above the lumbar region
Upper motor neuron region interrupting voluntary pathways to pontine micturition center |
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If sacral spinal cord is damaged, a ____ bladder results
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flaccid or atonic
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mechanism leading to flaccid bladder
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sacral spinal cord damage --> reflex pathway and preganglionic parasympathetic pathways damage --> loss of bladder contraction signal
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cystometrogram
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graphic record of pressure within bladder
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normal micturition threshold
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400-600 mL
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3 successive phases of male sexual response
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penile erection
emission of semen into posterior urethra ejaculation of semen from anterior urethra |
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start/stop points for male orgasm
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orgasm beings with or before emission and ends with the end of ejaculation
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Role of parasympathetic efferents in penile erection
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dilate cavernosal and helical arteries --> increased blood flow to lacunar spaces --> engorgement
engorgement --> compression of subtunical venules --> decreased blood outflow from penis --> further engorgement |
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activation of which nerves cause emission and ejaculation?
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sympathetic efferents in lower thoracic and upper lumbar cord become activated
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the sympathetic outflow that causes emission/ejaculation causes what sub-steps?
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contraction of smooth muscle in the epididymis, vas deferens, seminal vesicles and propstate
--> propulsion of semen into posterior urethra |
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ejaculation is what kind of reflex?
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spinal cord mediated
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what triggers the ejaculation reflex?
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excitation of afferents from pr0ostate and posterior urethra
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activation of somatic efferents during ejaculation causes...
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tonic-clonic contractions of bulbocavernosus and ischiocavernosus
and of pelvic floor muscles |
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afferents from which spinal regions participate in sexual reflex activation in the female?
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lumbar & sacral afferents
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what happens to the uterus during sexual arousal?
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uterus rises in the pelvis so that the cervix is moved away from the posterior wall of the vagina
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sensory innervation from the penis/clit is conveyed on which nerve?
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dorsal nerve of the clit/penis
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dorsal nerve of the clit is a branch of which nerve?
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pudendal nerve
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activation of parasympathetic efferent pathways in the female pelvis cause ____
& release ___, ____ and _____ |
activation of parasympathetic efferent pathways in the female pelvis cause VASODILATION
and release ACh, VIP & NO (vasodilatory substances) |
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Sympathetic postganglionic fibers with cell bodies in the _____ plexus innervate female genitalia and cause _____ & _____
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Sympathetic postganglionic fibers with cell bodies in the INFERIOR MESENTERIC PLEXUS innervate female genitalia and cause VASOCONSTRICTION and DETUMESCENCE
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are visceral afferent fibers myelinated?
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NO. Visceral afferent fibers are UNmyelinated.
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Visceral pain usually travels in ____ pathways.
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Sympathetic pathways.
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Autonomic dysreflexia
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acute syndrom of excessive, uncontrolled sympathetic output
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Autonomic dysreflexia is seen in patients who..
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have had spinal cord injury, usually at or above T6
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Spinal reflex pathways BELOW the level of the lesion remain intact, but ____ is interrupted.
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communication from the brain
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descending autonomic input to the autonomic preganglionic neurons is generally ____ (excitatory/inhibitory)
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inhibitory
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when descending inhibitory input is interrupted by SCI, autononic reflexes ...
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operate unopposed
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main findings of autonomic dysreflexia
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elevated BP
bradycardia |
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presenting symptoms of autonomic dysreflexia
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bilateral, pounding headache
sweating above level of injury nasal congestion, malaise and nausea |
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most common precipitating factors of autonomic dysreflexia symptoms
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full bladder or full rectum
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