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Question 1

Define an upper motor neurone

Answer 1

• Motor efferent fibres- Cell body in the motor region of the cerebral cortex or brainstem- Axons remain in the CNS and synapse with lower motor neurones

Question 2

Define a lower motor neurone

Answer 2

• Somatic motor efferent neurone- Cell body is found in Lamina IX of the spinal cord or in the cranial nerve motor nucleus- Axons directly supply skeletal muscles

Question 3

What are the two types of lower motor neurones?

Answer 3

Alpha and gamma

Question 4

Define a motor unit

Answer 4

Made up of:- an alpha motor neurone- all the muscle fibres that is suppliesThis is the minimum functional unit of the motor system

Question 5

What is a motoneurone?

Answer 5

A somatic efferent nerve which supplies skeletal muscles

Question 6

What do motoneurones do?

Answer 6

1. Bring about movements2. Set muscle tone

Question 7

Where do you find the two different subtypes of motoneurones?

Answer 7

UMN - CNS to LMNLMN - UMN to muscle

Question 8

Describe what alpha-motoneurones innervate and initiate

Answer 8

Innervate the extrafusal muscle fibres of skeletal muscle. It is directly responsible for initiating skeletal muscle contraction

Question 9

Describe what gamma-motoneurones innervate and initiate

Answer 9

Innervate intrafusal muscle fibres of muscle spindles and keep muscle spindles taut

Question 10

Define a muscle spindle

Answer 10

Connective tissue capsules that contain intrafusal muscle fubres

Question 11

How are the muscle spindles innervated?

Answer 11

Middle portion = afferent sensory neuronesEnd portion = efferent gamma-lower motoneurones

Question 12

Define a spinal reflex

Answer 12

A reflex is an involuntary, unlearned, repeatable autonomic reaction to a specific stimulus that does not require the brain.

Question 13

What are the components that make up the reflex arc?

Answer 13

A receptorAn afferent fibreAn integration centreAn efferent fibreAn effector

Question 14

How does stretching affect the action of the afferent sensory neurones in muscle spindles?

Answer 14

Stretching the muscle fibres increase the firing of the afferent sensory neurones. Therefore, shortening the muscle fibres causes a decrease in the firing rate.

Question 15

Why do gamma motoneurones innervate the intrafusal muscle fibres?

Answer 15

They prevent the muscle spindle from becoming slack when extrafusal fibres contract. The contraction of extrafusal muscles removes feedback from the sensory neurones, therefore there is no information provided to the motor centre regarding muscle length.

Question 16

Where do you find golgi tendon organs?

Answer 16

At the junction between the muscle and the tendon. They are innervated by sensory neurones.

Question 17

Define a reflex arc

Answer 17

The neuronal pathway that describes a relex

Question 18

What are golgi tendon organs composed of?

Answer 18

Network of collagen fibres inside a connective tissue capsule with a sensory axon that winds around the collagen

Question 19

What does the stretch reflex circuit connect?

Answer 19

A lower motor neurone with the afferents of the muscle-length sense organs.

Question 20

What happens when a tendon is stretched?

Answer 20

The firing rate of the sensory neurone increases.

Question 21

What happens to golgi organs when muscles contract?

Answer 21

The tension throughout the golgi tendon organ increases which leads to an increased inhibition on the alpha-lower motoneurones. This reduced firing of the sensory afferents and therefore decreasing the muscle contraction.

Question 22

Describe the golgi tendon organ reflex?

Answer 22

Acts as a protective mechanism, by controlling the tension of an active muscle. it does this by causing relaxation before the tendon tension becomes high enough to do any damage.

Question 23

Describe the process of the golgi tendon organ reflex

Answer 23

• Contracting muscle stretches golgi tendon organ- Afferent sensory neurone fires, synapsing with inhibitory interneurones in the spinal cord- Inhibitory interneurones redude alpha-LMN firing, reducing muscle contraction, preventing damage from over-contraction

Question 24

Where does the golgi tendon organ reflex act?

Answer 24

On the antagonising muscle, to allow for a reflex to occur and to prevent damage due to over contraction.

Question 25

Define muscle tone

Answer 25

The continuous, passive, partial contraction of all skeletal muscle. It is seen as a muscle’s resistance to passive stretch during resting state.

Question 26

Why do we have muscle tone?

Answer 26

Allows us to maintain body posture and hold our heads up straight.

Question 27

How is muscle tone produced?

Answer 27

Is produced by the tonic contraction by the muscles of lower motoneurones to their fibres.

Question 28

Why to muscles not get tired when they are constantly producing muscle tone?

Answer 28

The fibres contract randomly throughout the muscle. This gives sufficient tone yet prevents the muscle from getting tired.

Question 29

Describe the size principle for recruiting fibres for increasing muscle tone

Answer 29

Smaller motor units are recruited first and the larger motor units are recruited later.

Question 30

What nerve fibres give rise to the afferent response of the myotatic reflex?

Answer 30

Fast conducting, large myelinated axons (group 1a afferents)

Question 31

Describe what happens in the stretch reflex

Answer 31

Muscle is stretchedAP produced by the muscle spindle fibresThe afferent fibres directly synapse with alpha motoneurones in the spinal cord. Contraction of the muscle that was stretched occurs. The afferent neurone also synapses with an inhibitory neurones that synapses with the motoneurones that innervate the antagonistic muscle.

Question 32

Describe what happens in the withdrawal reflex

Answer 32

Noxious stimuli stimulate the nociceptorsAfferent impulses travel along the afferent fibres which directly synapse with alpha-motoneurones in the spinal cord. These are normally polysynaptic with 3/4 interneurones involved. This causes contraction of the ipsilateral flexor muscles, which causes the limb to be drawn away from the noxious stimuli.