Neurological Reflexes

Question 1

What type of muscle fibres are there and how are they innervated?

Answer 1

Extrafusal - main group making up the contractile unit. These fibres are innervated by the α-motor neurones (11-16 μm diameter cells conducting at 60-80 m/s)

Intrafusal - A smaller number of gamma (γ) motor neurones (5 μm in diameter and conducting at 2-30 ms) innervate special intrafusal muscle fibres that are part of the MUSCLE SPINDLE

Question 2

What are the sensory units in the muscle?

Answer 2

Muscle spindles and Golgi tendon apparatus

Question 3

What is the purpose of the muscle spindle?

Answer 3

Convey information concerning changes in the length and tension of muscle fibres to the CNS.

Their function is to respond to the stretch of a muscle, and through reflex action, produce a stronger contraction to reduce the stretch.

Question 4

How does the golgi tendon organs function? How is it innervated?

Answer 4

Golgi tendon organs sense changes in muscle tension.

Each Golgi tendon organ is innervated by a single afferent type Ib myelinated axon.

Question 5

How is the muscle spindle innervated?

Answer 5

Motor: γ-motor neurones (comes mainly from the descending fibres of the facilitatory reticular formation)

Sensory:
1. type Ia fast myelinated nerve fibres transmitting sensory signals to the spinal cord at a velocity of 70 to 120 m/s - respond to the actual length of the intrafusal fibre and the rate of change in length.

2. Type II slow fibres have smaller diameter axons and slower conduction speeds - sense position

Question 6

How do the muscle spindle and golgi tendon differ in action?

Answer 6

• spindles facilitate activation of the muscle,

- neural input from Golgi tendon organ inhibits muscle activation

Question 7

What is the stretch reflex?

Answer 7

is a reflex muscle contraction in response to stretching force acting within the muscle.

It is a monosynaptic reflex, which provides automatic regulation of skeletal muscle length.

No interneurones involved in the reflex, nor is there any influence from the CNS

Question 8

What is the pathway of the stretch reflex?

Answer 8

The impulses from the muscle spindles travel via the sensory afferent nerve to the relevant segment of the spinal cord.

This synapses with an α-motor neurone in the spinal cord and increases α-motor neurone output.

This in turn causes the muscle fibres to contract and thus resist the stretching force.

Question 9

What is reciprocal inhibition?

Answer 9

sensory neurone also sends inhibitory signals, via interneurones, to the α-motor neurones supplying the opposing muscle across a joint, causing it to relax

Question 10

How does the withdrawal reflex differ from the stretch reflex?

Answer 10

is a spinal reflex intended to protect the body from damaging stimuli. Unlike the stretch reflex, it is polysynaptic.

Question 11

What is the pathway of the withdrawal reflex?

Answer 11

The withdrawal reflex can be described as a series of steps (Fig 1):

1. A noxious stimulus, such as heat or pain, excites the sensory nociceptor in the skin.
2. The signal travels through a primary sensory neurone, which enters the dorsal horn of the spinal cord and synapses with an interneurone.
3. The interneurone synapses with an α-motor neurone.
4. This α-motor neurone leaves via the ventral horn of the spinal cord and excites the flexor muscle, withdrawing the limb.