SPINAL REFLEXES

Question 1

what are the 3 types of movement?

Answer 1

reflex, rhythmic and voluntary

Question 2

what is an alpha motor neurone?

Answer 2

large, multipolar lower motor neurones of the brainstem and spinal cord that innervate extrafusal muscle fibres of skeletal muscle and are directly responsible for initiating their contraction

Question 3

where are alpha motor neurones found? what do they release to contract muscle fibres?

Answer 3

in the ventral horn of the spinal cord. they release acetylcholine

Question 4

what are the 3 sources of input that spinal alpha motor neurones can receive input from?

Answer 4

sensory input from muscle spindles, skin, upper motor neurones in the brain and input from other spinal interneurones

Question 5

what forms the cervical and lumbar enlargements?

Answer 5

enlargement of the gray matter that contains the neural machinery necessary to operate the limbs.

Question 6

describe the somatotropic arrangement of grey matter in the spinal cord?

Answer 6

more medially are the axial motor neurones and more laterally are the neurone controlling the distal regions

Question 7

what are upper motor neurones?

Answer 7

Neurons in the cerebral cortex and brainstem whose axons remain in the CNS and which synapse on lower motor neurons directly or indirectly.

Question 8

what are lower motor neurones?

Answer 8

Neurons in the brainstem and spinal cord whose axons leave the CNS to synapse on muscle fibers

Question 9

what is motor neurone disease also known as?

Answer 9

Amyotrophic lateral sclerosis

Question 10

what is motor neurone disease?

Answer 10

Progressive degeneration of alpha motor neurons (upper from brain and lower from spinal cord)

Question 11

what is the pharmacological treatment of motor neurone disease?
what is the drugs mechanism of action?

Answer 11

Riluzole- it blocks glutamatergic neurotransmission which can slow the disease progression

Question 12

what are the chances of survival of motor neurone disease once the symptoms start?

Answer 12

most people live less than 3 years. 10% of people can live to 10 years

Question 13

what is a reflex?

what are their function?

Answer 13

An involuntary movement that occurs as a result of sensory stimulation and involves impulses travelling through a reflex arc.
They are important to protect the body from damage and to coordinate muscle activity.

Question 14

Outline the reflex arc pathway?

Answer 14

1. Receptor reacts to a stimulus
2. Afferent neurone transmits the impulse to the CNS
3. Information processing occurs in the CNS
4. Afferent neurone synapses with an interneuron which relays the information to an efferent neurone
5. The efferent neurone is the motor neurone which exits the CNS and delivers the signal to an effector (muscle or gland)
6. Effector produces a response

Question 15

what is a monosynaptic reflex?

what is a polysynaptic reflex?

Answer 15

monosynaptic= it involves a single synapse between muscles sensory fibres and alpha motor neurone.
polysynaptic= one or more interneurons connect afferent and efferent signals.

Question 16

what is the receptor in the stretch/myotatic reflex?

Answer 16

the muscle spindle fibres

Question 17

describe the structure of the muscle spindle fibres?

Answer 17

it runs parallel with the muscle and consist of intrafusal muscle fibres and extrafusal muscle fibres

Question 18

what is the structure of intrafusal muscle fibers?

what are they innervated by?

Answer 18

they have 1a afferents wrapped around them and are encapsulated by a connective tissue capsule
inverted by gamma motor neurones.

Question 19

what are extrafusal muscle fibres?

Answer 19

they comprise the bulk of the muscle and generate the force.

Question 20

describe the stretch/myotatic reflex?

Answer 20

when the muscle spindle is passively stretched, the 1a afferent neuron that is wrapped around the intrafusal muscle fibers within the muscle spindle sends its information into the dorsal horn of the spinal cord, synapses with an alpha motor neuron which then activates the extrafusal muscle fibers to contract.

Question 21

describe the function of the gamma motor neurone?

Answer 21

They regulate the sensitivity of sensory afferents to stretch

Question 22

what are the differences between alpha and gamma motor neurones?

Answer 22

Alpha motor neurons control muscle contraction involved in voluntary movement, whereas gamma motor neurons control muscle contraction in response to external forces acting on the muscle

Question 23

describe the knee jerk/patellar tendon tap reflex?

Answer 23

Use a hammer to tap patellar tendon beneath knee cap.
this stretches quadriceps muscle spindles (receptors) and activates the 1a muscle spindle
Impulses in the 1a afferents travel to the spinal cord and synapses with the motor neurons (efferent).
Motor neurons release acetylcholine which leads to contraction of the quadriceps by innervating the extrafusal muscle fibres- no interneurons
The afferents also stimulate an interneurons which inhibits the activity of the alpha motor neurones which supply the opposing muscle i.e. the hamstring

Question 24

what is the function of the knee jerk/patella reflex?

Answer 24

to allow us to maintain posture and balance

Question 25

what is the function of the inverse stretch reflex?

Answer 25

to prevent muscle and tendons from being damaged by regulating muscle tension

Question 26

where is the Golgi tendon organ found?

what is embedded within the collagen fibrils?

Answer 26

at the junction of the muscle and the tendon.

the 1b afferent dendrites

Question 27

describe the inverse stretch reflex?

Answer 27

Force generated acts directly on the tendon to increase tension of collagen fibrils in the Golgi organ and this causes compression of the intertwined sensory receptors and therefore increases activity of the 1b afferent. Afferent 1b sends its sensory information into the dorsal horn of the spinal cord which synapses with an inhibitory interneuron which inhibits the alpha motor neurone controlling the muscle contraction.

Question 28

what does it mean to say the inverse stretch reflex is a “very high threshold reflex”?

Answer 28

a large amount of stretch would require activation of the inverse stretch reflex.
only when tension is TOO MUCH would contraction cease to protect the muscles/tendons

Question 29

is the inverse stretch reflex monosynaptic or polysynaptic?

Answer 29

monosynaptic

Question 30

is the flexor withdrawal/crossed extensor reflex monosynaptic or polysynaptic?

Answer 30

polysynaptic

Question 31

describe the flexor withdrawal/crossed extensor reflex?

Answer 31

① Stepping on pin stimulates nociceptive cutaneous receptors
② Signal travels through afferent neuron to the lumbar spinal cord
③ here it synapses with 1->many interneurons
④ Interneurons synapse with alpha motor neurons
⑤ Alpha neuron flexes hamstring to bend knee, withdrawing stimulated leg
⑥ At the same time, another interneuron synapses with a different alpha motor neuron to inhibit the contraction of the extensor muscles.
⑦ Another 2 interneurons synapse with alpha motor neurones to cause the opposite in the other leg i.e. the flexor muscle will be inhibited and the extensor muscle with be activated= shifts weight to other leg.

Question 32

what is faster, monosynaptic or polysynaptic reflexes?

Answer 32

monosynaptic

Question 33

what is a central pattern generator?

Answer 33

which interconnected excitatory and inhibitory neurons produce an oscillating, rhythmic output in the absence of sensory feedback.

Question 34

what do central pattern generators do in locomotion?

Answer 34

they produce alternating flexion and extension of the limbs

Question 35

what are some examples of central pattern generators?

Answer 35

locomotion, chewing, swallowing, respiration, swimming

Question 36

what is the function of central pattern generators?

Answer 36

Automatic control of rhythmic movements important for survival