Motor control lab Flashcards

1
Q

What is a stretch reflex?

A

a stretch reflex causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle

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2
Q

Describe the stretch reflex arc

A

A monosynaptic reflex arc

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3
Q

How does a stretch reflex occur?

A

by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron

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4
Q

How can stretch reflexes be elicited?

A

by tapping on the tendons attached to muscles at the elbow, wrist, knee and ankle joints

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5
Q

What are muscle spindles?

A

sensory receptors in the muscle that monitor changes to the length of the muscle

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6
Q

Describe the stretch reflex

A
  • slight stretching of the muscle stimulates muscle spindles
  • muscle spindles generate nerve impulses that propagate along a somatic sensory neuron through the dorsal root of the spinal nerve and into the spinal cord
  • In the cord (integrating center), the sensory neuron makes an excitatory synapse with and activates a motor neuron in the ventral gray horn
  • If impulse is strong enough, impulses will arise in the motor neuron and propagate along its axon to the muscle
  • Acetylcholine is released at the neuromusculor junction, triggering APs to contract the muscle
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7
Q

Where does a motor neuron axon extend?

A

extends from the spinal cord into the anterior root and through peripheral nerves to the stimulated muscle

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8
Q

What is an ipsilateral reflex?

A

sensory nerve impulses enter the spinal cord on the same side from which motor
nerve impulses leave it.

All monosynaptic reflexes are
ipsilateral.

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9
Q

How does the stretch reflex prevent injury?

A

Preventing the overstretching of muscles

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10
Q

How is muscle tone maintained?

A
  • large-diameter motro neurons innervate typical skeletal muscle, while smaller diameter motor neurons innervate smaller specialised muscle fibers within the muscle spindles
  • This allows regulation from the brain
  • By adjusting how vigorously a muscle spindle responds to stretching, the brain sets an overall level of muscle
    tone
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11
Q

What is the function of proprioceptors in the joints?

A

Sensors that provide information about joint angle, muscle length, and muscle tension, (i.e position of the limb in space)

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12
Q

How is information from proprioceptors received in the brain?

A

APs reach the cerebellum and transmits this into information allowing adjustment and fine tuning of coordination

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13
Q

what are muscle spindles?

A

found in skeletal muscle and provide information about changes in muscle lengths and participate in stretch reflexes

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14
Q

Where are muscle spindles most predominant?

A

In the muscles of the limbs

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15
Q

Describe the muscle spindle structure

A
  • Each muscle spindle consists of several slowly adapting sensory nerve endings that wrap around specialized
    muscle fibers, called intrafusal muscle fibers (intrafusal = within a spindle).
  • A connective tissue capsule encloses the sensory nerve endings and intrafusal fibers and anchors the spindle to
    the endomysium and perimysium
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16
Q

Describe the arangement of muscle spindles

A

Interspersed among most skeletal muscle fibers and aligned parallel to them

  • more plentiful in muscles that produce fine movements
17
Q

Which muscles do not contain any muscle spindles?

A

the muscles of the middle ear

18
Q

What are gamma motor neurons?

A

These motor neurons terminate near both ends of the intrafusal fibers and adjust the tension in a muscle
spindle to variations in the length of the muscle.

E.g. when a muscle shortens, gamma motor neurons stimulate the ends of the intrafusal fibers to contract
slightly.

19
Q

What are golgi tendon organs?

A
  • also called neurotendinous receptors
  • located at the junction of a tendon and a muscle
  • provide information about changes in muscle tension
20
Q

What is the importance of golgi tendon organs?

A

They initiate tendon reflexes and protect tendons and associated muscles from damage due to excessive tension

21
Q

What happens when a tendon reflex is initiated?

A

When tension is applied to a muscle, the tendon organs generate nerve impulses that propagate into the CNS,
providing information about changes in muscle tension.

Tendon reflexes decrease muscle tension by causing muscle relaxation

22
Q

What types of joint kinaesthetic receptors are there?

A
  • free nerve endings
  • ruffini corpuscles
  • pacinian corpuscles
  • articular ligaments
23
Q

Which joint kinaesthetic receptors respond to pressure?

A
  • free nerve endings

- ruffini corpuscles

24
Q

What do pacinian corpuscles respond to?

A

acceleration and deceleration of joints during movement

25
Q

What do articular ligaments respond to?

A

contain receptors similar to tendon organs that adjust reflex inhibition of the adjacent muscles when excessive strain is placed on the joint

26
Q

What are the different groups of axons in the peripheral nerve?

A

Grouped according to conduction velocity

  • A
  • B
  • C
27
Q

How are A axons further categorised?

A
  • Aalpha
  • Abeta
  • Agamma
  • Adelta
28
Q

What are the features of C axons?

A

unmyelinated

29
Q

What are the features of B axons?

A

Thinly myelinated and are preganglion sympathetic and are therefore not found in peripheral nerves

30
Q

Describe the axons of nociceptors

A
  • small myelinated Adelta

- unmyelinated group c

31
Q

How can you work out the diameter of an axon?

A

only if conduction velocity if known (and vice versa)

Using Hursh’s conversion factor

32
Q

What events make up the monosynaptic circuit for the knee jerk reflex?

A

o Stimulus (tendon tap) stretches muscle
o activates muscle spindle receptors
o conduction along afferent (sensory) fibres (Ia afferent)
o transmission at synapses between Ia afferent and motoneurone
o conduction along efferent (motor) fibre
o neuromuscular transmission
o excitation contraction coupling
o twitch contraction of skeletal muscle

33
Q

Explain why vibrating tendons leads to errors in perception of joint angles

A
  • vibration distorts perception of static joint angle and movement and causes errors in the end point of movement
  • muscle spindle afferents are activated by vibration which evokes perceptual changes
  • bias in perception appears to be related to the difference between vibration and movement evoked activity in the muscle spindle afferents
34
Q

Describe a non-invasive method of demonstrating descending motor pathways connecting with muscles

A
  • magnetic stimuli (principle of electromagnetic induction) applies over the motor cortex and activates the corticospinal tract
    -APs produces in pyramidal neurons, which have long axons descending to the spinal cord
  • These descending motor fibres connect directly or indirectly with motorneurons and therefore when activated,
    twitch contractions are elicited in skeletal muscles