Spinal Reflex

Question 1

What are the types of movement?

Answer 1

Reflex, rhythmic and voluntary.

Question 2

How does movement occur?

Answer 2

Initiated in the cerebrum, co-ordinated in the cerebellum for precision and transmitted by the brainstem and the spinal cord through the alpha motor neuron to the skeletal muscles.

Question 3

Where is automatic and reflex action generated?

Answer 3

Automatic and reflex action is generated by the brainstem and spinal cord.

Question 4

Where do sensory neurons enter the spinal cord?

Answer 4

In the dorsal horn of the grey matter

Question 5

Where do motor neurons leave?

Answer 5

In the ventral horn of the grey matter

Question 6

What are the cervical and lumbar enlargements?

Answer 6

Cervical enlargement: C3-T1
Lumbar enlargements: L3-S1
They contain the highest quantity of the ventral horn to control the body’s muscle

Question 7

How does sensation change from medial to lateral in the dorsal horn?

Answer 7

Most medial is the lower limbs and most lateral is the upper limbs

Question 8

How does motor control of muscles change from medial to lateral in the ventral horn?

Answer 8

In the cervical and lumbar enlargements; most medial is the trunk and limbs for posture, then the lateral aspect is the upper limbs for gait and fingers and toes for object manipulation

Question 9

What is the motor system?

Answer 9

Consists of the cerebral cortex and the muscles which are connected via the alpha lower motor neuron

Question 10

What does the brainstem control?

Answer 10

Head muscles

Question 11

What does the spinal cord control?

Answer 11

Muscles of the body

Question 12

What are the upper motor neurons?

Answer 12

Project from the cortex of the cerebrum and create descending tracts to synapse with lower motor neurons in the ventral horn of the spinal cord

Question 13

What are the lower motor neurons?

Answer 13

Exit the spinal cord at the ventral horn and project onto skeletal muscles to control movement

Question 14

What are alpha motor neurons?

Answer 14

Lower motor neurons part of the final common pathway. They are myelinated large diameter fast conducting which form neuromuscular junctions to control muscles in the body via acetylcholine release.

Question 15

How do impulses travel in the lower motor neuron?

Answer 15

Recevies input via dendrites which is integrated into the soma and summated in the axon hillock where it travels as an impulse down the axon to induce release of acetylcholine in the neuromuscular junction where it synapses with muscle fibres

Question 16

What are the inputs to the spinal motor neurons?

Answer 16

Sensation from muscle spindles and the skin eg the dorsal column and spinothalamic pathway, upper motor neurons and interneurones

Question 17

What is motor neuron disease and its treatment?

Answer 17

Degeneration of the alpha motor neurons which disrupts input between upper and lower motor neurones. Caused partly by glutamate

Question 18

What are the symptoms of motor neuron disease?

Answer 18

Muscle weakness with difficulty swallowing and breathing and muscle atrophy. Eye movements, cognition and sensation is preserved

Question 19

What is the reflex arc pathway?

Answer 19

Consists of the sensory afferent, motor efferent which is generally the alpha motor neuron and sometimes an interneurone.

Question 20

What is a reflex?

Answer 20

Unconscious muscle action induced by stimuli to the skin, muscle spindle or the joint (golgi tendon organs) which causes firing of the reflex arc pathway

Question 21

Why do we have reflexes?

Answer 21

To protect us from harm and co-ordinate muscle action in response to stimuli.

Question 22

What type of synaptic reflex is the reflex arc?

Answer 22

Generally mono-synaptic between the sensory afferent and motor neuron (usually alpha)

Question 23

What is a myotatic reflex?

Answer 23

Reflex of muscle concentric contraction in response to passive stretch caused by a weight load

Question 24

What is a muscle spindle?

Answer 24

Sensory receptor within muscle fibre that detects and controls length change. It consists of intrafusal muscle fibres, extrafusual muscle fibres, Ia sensory afferents and gamma motor neurons

Question 25

What are intrafusal muscle fibres?

Answer 25

Run parallel with extrafusal muscle fibres which detect changes in length

Question 26

What are the extrafusal muscle fibres?

Answer 26

Contract to change in length in response to alpha motor neurons

Question 27

What are Ia sensory neurons?

Answer 27

Wrapped around the intrafusal muscle fibres to communicate information about stretch to the alpha motor neurons in the ventral horn of the spinal cord. It enters the dorsal horn via dorsal root ganglion.

Question 28

What are gamma motor neurons?

Answer 28

Regulates the sensitivity of the muscle spindle to changes in length and allows contraction to occur following alpha motor neuron action inducing.

Question 29

Why are muscle spindles important?

Answer 29

Allows information about muscle stretching to be transmitted to the spinal cord and bypass the CNS via the monosynaptic transmission with alpha motor neurons

Question 30

Difference between alpha and gamma motor neurons?

Answer 30

Alpha motor neurons induce muscle contraction of the extrafusal muscle fibres. Gamma motor neurons regulate the sensitivity of the muscle spindle to changes in length and allows contraction in the intrafusal muscle fibres

Question 31

What is the knee jerk reflex?

Answer 31

When patella tendon is stimulated, it causes stretching of the quadricep which leads to Ia afferents firing and synapsing with alpha motor neurones to induce contraction via the extrafusal fibres.

Question 32

What are the muscle flexors?

Answer 32

Biceps and Quadriceps which have concentric contraction.

Question 33

What are the muscle extensors?

Answer 33

Hamstrings and triceps which have eccentric contraction

Question 34

What is reciprocal inhibition?

Answer 34

When a flexor is contracting, extensor that is simultaneously stimulated acts on inhibitory interneurons in the spinal cord ventral horn to prevent stimulation of alpha neuron to the extensor. This occurs for the flexor too.

Question 35

What is the inverse stretch reflex pathway?

Answer 35

When a load that is too heavy is added, it leads to forced relaxation of the muscle.

Question 36

What are the golgi tendons?

Answer 36

Stretch receptors between the muscle and the tendon and contain Ib afferents with a high threshold for stretch.

Question 37

What happens to golgi tendons during muscle contraction?

Answer 37

Muscle contracts due to stretch and the force generated acts on tendons. This causes too much tension collagen fibrils in the Golgi tendon organ to stretch and compress the stretch receptors that leads to firing of the Ib afferent to synapse with inhibitory interneuron to prevent firing of the alpha motor neuron to allow the muscle to relax and drop weight.

Question 38

What is the path of the flexor withdrawal reflex?

Answer 38

Stimuli of nociceptors such as stepping on a pin induces interneurons to activate two alpha motor neurones. On the affected leg, it causes contraction of the extensor to remove it from the stimuli and contraction of the flexor on the opposite leg to support our weight. Alongside this, inhibitory interneurons are activated for the flexor of the affected leg and the extensor of the opposite leg.

Question 39

What are central pattern generators?

Answer 39

Neural network of sensory, interneuron and motor neuron in the spinal cord and brainstem which generate oscillatory rhythmic action such as chewing, walking and running.