Motor control lab

Question 1

What is a stretch reflex?

Answer 1

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

Question 2

Describe the stretch reflex arc

Answer 2

A monosynaptic reflex arc

Question 3

How does a stretch reflex occur?

Answer 3

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

Question 4

How can stretch reflexes be elicited?

Answer 4

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

Question 5

What are muscle spindles?

Answer 5

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

Question 6

Describe the stretch reflex

Answer 6

• 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

Question 7

Where does a motor neuron axon extend?

Answer 7

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

Question 8

What is an ipsilateral reflex?

Answer 8

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

All monosynaptic reflexes are
ipsilateral.

Question 9

How does the stretch reflex prevent injury?

Answer 9

Preventing the overstretching of muscles

Question 10

How is muscle tone maintained?

Answer 10

• 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

Question 11

What is the function of proprioceptors in the joints?

Answer 11

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

Question 12

How is information from proprioceptors received in the brain?

Answer 12

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

Question 13

what are muscle spindles?

Answer 13

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

Question 14

Where are muscle spindles most predominant?

Answer 14

In the muscles of the limbs

Question 15

Describe the muscle spindle structure

Answer 15

• 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

Question 16

Describe the arangement of muscle spindles

Answer 16

Interspersed among most skeletal muscle fibers and aligned parallel to them

• more plentiful in muscles that produce fine movements

Question 17

Which muscles do not contain any muscle spindles?

Answer 17

the muscles of the middle ear

Question 18

What are gamma motor neurons?

Answer 18

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.

Question 19

What are golgi tendon organs?

Answer 19

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

Question 20

What is the importance of golgi tendon organs?

Answer 20

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

Question 21

What happens when a tendon reflex is initiated?

Answer 21

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

Question 22

What types of joint kinaesthetic receptors are there?

Answer 22

• free nerve endings
• ruffini corpuscles
• pacinian corpuscles
• articular ligaments

Question 23

Which joint kinaesthetic receptors respond to pressure?

Answer 23

• free nerve endings

- ruffini corpuscles

Question 24

What do pacinian corpuscles respond to?

Answer 24

acceleration and deceleration of joints during movement

Question 25

What do articular ligaments respond to?

Answer 25

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

Question 26

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

Answer 26

Grouped according to conduction velocity - A - B - C

Question 27

How are A axons further categorised?

Answer 27

- Aalpha - Abeta - Agamma - Adelta

Question 28

What are the features of C axons?

Answer 28

unmyelinated

Question 29

What are the features of B axons?

Answer 29

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

Question 30

Describe the axons of nociceptors

Answer 30

- small myelinated Adelta | - unmyelinated group c

Question 31

How can you work out the diameter of an axon?

Answer 31

only if conduction velocity if known (and vice versa) Using Hursh's conversion factor

Question 32

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

Answer 32

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

Question 33

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

Answer 33

- 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

Question 34

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

Answer 34

- 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