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Flashcards in spinal mech of motor control Deck (31)
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1
Q
  • PRIMARY ENDINGS (Group Ia fiber)
A
  • Sensory innervation of muscle spindle

–> one per muscle spindle

–> found on BOTH NUCLEAR BAG and CHAIN fibers

–> Shows both DYNAMIC (firing pattern signals RATE of muscle stretch/rate of change) and STATIC RESPONSE (firing pattern signals amount of stretch or muscle length

2
Q

Secondary ending (group II fibers)

A
  • Sensory innervation of muscle spindles
  • Found on NUCLEAR CHAIN fibers ONLY (also static nuclear bag)
  • SHOWS STATIC RESPONSE ONLY
  • firing rate gives info about muscle length but does NOT emphasize changes in muscle length
3
Q

Motor innervation of muscle spindle

A
  • Gamma efferent fibers = provide fusimotor drive to muscle spindle
  • Gamma-dynamic fibers = end on dynamic nuclear bag
  • Gamma-static fibers = end on nuclear chain fibers and static nuclear bag
  • Skeletofusimotor fibers = some motorneurons innervate BOTH extrafusal and intrafusal fibers (sometimes called beta-innervation)
4
Q

describe ALpha motor neurons

A
  • extrafusal motor neurons
  • Large-caliber
  • heavily myelinated = rapid speed
  • Responsible for initiating contraction
5
Q

Gamma motor neurons

A
  • INtrafusal motor neurons
  • Slender
  • Lightly myelinated = less rapid transmitting
  • control skeletal muscle by adjusting tension
6
Q

explain function of COACTIVATION of alpha and gamma motorneurons

A
  • When extrafusal muscle fibers contract, the muscle shortens and muscle spindles would become unloaded (not able to sense small lengthening of the muscle)
  • To prevent unloading, gamma motor neurons are activated and they make intrafusal fibers contract causing any small lengthening of the muslce can be sensed immediately
  • Ia fibers normally facilitate alpha motor neurons during muscle contraction. this facilitation would be lost if muscle spindles became unloaded during msucle contraction
7
Q

describe static response to muscle spindle

A
  • Firing pattern signals amount of stretch of muscle length
  • Type Ia and Type II fibers
8
Q

describe the dynamic response of muscle spindle

A
  • firing pattern signals rate at which muscle is being stretched or rate of change in muscle length
  • Type Ia ONLY
9
Q

describe the role of gamma motorneurons in controlling spindle response

A
  • the firing rate of muscle spindle afferents depends on both muscle length and the level of gamma activation of the intrafusal muscle fibers
  • when the nervous system interprests the signals fro muscle spindles it must take into account the amount of fusimotor drive gamam neurons
10
Q

describe the stretch reflex (myotatic reflex0

A
11
Q

describe PHASIC stretch (myotatic) reflex

A
  • Type Ia fibers synapse directly on alpha motor neuron of homonoymous and synergist muscles
  • Initiated by tapping on tendon of muscle with reflex hammer
  • Demonstrates evidence of LMN vs UMN problems
12
Q

describe TONIC stretch (myotatic) reflex

A
  • Type Ia fibers synapse directly on alpha motor neurons of homonymous and synegist muscles
  • Type II fibers synpase directly on alpha motor neurons of homonymous muscles
  • INTIATED BY passively bending a joint
  • Patients with SPASTICITY, the stength of reflex in spastic muscles depends on the speed of muscle stretch

–> faster the stretch, the stronger the reflex (tonic reflex is exagerated in parkinsonism)

13
Q

describe reciprocal innervation in spinal cord and how it is related to stretch reflex

A
  • group Ia fibers excite homonymous muscles (agonist muscles) and its synergist (flexors)
  • Group Ia fiber collaterals end on Ia inhibitory interneurons that act on antagonist muscles (extensors)
14
Q

Define Muscle tone and relation to myotatic reflex

A
  • Resting tone = slight tension that can be felt in relaxed muscles (properaly measured by testing the TONIC STRETCH REFLEX)
  • if subject is deeply relaxed should be no EMG activity in muscle but many subjects cannot relax that much
15
Q

Role of co-contraction

A
  • Co-contraction of muscles at a joint means that both PRIME MOVERS at a joint and its ANTAGONISTS are contracted simultaneously
  • THIS ACTION STIFFENS JOINT
  • USEFUL when precision and joint stabilization are important
16
Q

define reciprocal innervation

A
  • yeiled RECIPROCAL INHIBITION
  • Group Ia fibers excite homonymous muscles (agonist muscles) and its synergists
  • Group Ia fibers colalterals end on Ia inhibitory interneurons (inhibit antagonist muscles (reciprocal inhibiton)
17
Q

define homonymous muscles

A

the working muscle of the motor unit (flexors)

18
Q

define agonist muscls

A
  • muscles that perform the same/similar function to the homonymous muscles (flexors)
19
Q

Define synergist muscles

A
  • muscles that perform the same/similar function to homonymous muslces (same as agonist muscles)
20
Q

antagonist muscles

A
  • muscles that perfrom the opposite function to the homonymous muscles
21
Q

define hypertonia

A
  • exagerated reflex
  • several differnt types; most common is spasticity
22
Q

define atonia

A
  • no muscle tone (found during spinal shock)
23
Q

define hypotonia

A
  • weak reflex
  • found with purse pyramidal tract lesions and cerebellar lesions
24
Q

define spasticity

A
  • motor disorder
  • caused by brain truama, spinal cord injury, multiple sclerosis
  • Characterized by:

–> velocity-dependent increase in tonic stretch reflexes (resistance to tonic stretch increase as speed of stretch increases

–> increase in muscle tone (type of hypertonia)

  • SPASTICITY IS MORE PROMINENT IN ANTIGRACITY MUSCLES
  • exagerated phasicc stretch reflexes, babinski sign, clonus, clasp-knife reflex
25
Q

define fusimotor neuron

A
  • gamma motor neuron
26
Q

describe the golgi tendon organ

A
  • innervated by Ib fibers
  • Activated by TENSION (measures MUSCLE FORCE or TENSION)
  • Increased firing = increased tension
27
Q

describe the GTO reflex

A
  • REFLEX ARC for GROUP Ib REFLEX:

–> increased tension (force) on muscle increases firing in Ib fibers

–> Ib fibers synapses on inhibitory interneuons which inhibits alpha motor neurons to homonymous muslces resulting in decreased muscle tension (increased tension causes muscles to be inhibited)

–> conclusion: GTO FEEDBACK mechanisms monitors and maintains muscle force (opposite of myotatic reflex)

28
Q

describe flexor withdrawal reflex

A
  • stimulated leg will be withdrawn/flexed away from painful stimulus
  • see drawing
29
Q

Describe the corssed extension reflex

A
  • commissural neurons will cross to affect the contralateral side/extensor muscles

–> stimulated leg (side with pain) will flex to withdraw

–> opposite leg will extend to support (the cross extension reflex)

  • SEE DRAWNING
30
Q

Compare and contrast the output of muscle spindles and golgi tendon organ during muscle contraction and passive muscle stretch

A

MUSCLE SPINDLE

  • Passively stretched = INCREASED AFFERENT ACTIVITY
  • Actively stretched = DECREASED afferent activity

GTO OUTPUT

  • Passively stretched = DECREASED afferent activity
  • Actively stretched = INCREASED afferent acitivity
31
Q

describe clasp-knife reflex

A
  • Most easily domenstrated in the knee extensor of spastic patients
  • clinician tries to quickly bend the patient knee
  • resistance to flexion seems to build up gradually and then at a certain point, resistance suddenly decreases
  • the hyperactive stretch reflexes of the spastic patient causes the increase in resistance to stretch found in the knee extensors
  • the sudden DECREASE is the clasp-knife phenomenon
  • the biceps is an anti-gravity muscle in humans and the clasp-knife reflex can demonstrated in the spastic biceps when you try to extend the elbow