Spinal refleses

Question 1

what is the name for receptor that mediates muscle tendon reflexes? [1]

what is basic structure? ^ [1]
what is inside them? [1]

Answer 1

what is the name for receptor that mediates muscle tendon reflexes? [1]
muscle spindle or proprioceptor

what is basic structure? ^ [1]
stretch receptor inside a CT sheath
inside = special muscle fibres called intrafusal muscle fibres

Question 2

what are intrafusal and extrafusual motor neurons? [2]

Answer 2

Extrafusal muscle fibers: comprise the bulk of muscle and form the major force-generating structure. found outside

Intrafusal muscle fibers are buried in the muscle, and they contain afferent receptors for stretch, but they also contain contractile elements.

Question 3

how are sensory afferents activated via muscle spindle? [1]

The main sensory nerve fibre from the muscle spindle is called WHAT? [1]

Answer 3

how are sensory afferents activated via muscle spindle? [1]
Stretch of the muscle also stretches the muscle spindle and activates the muscle spindle sensory afferents.

The main sensory nerve fibre from the muscle spindle is called a Ia afferent [1]

Question 4

what is muscle spindle morphology like?

• where do u find contractile apparatus? [1]
• what is actin, myosin and mito like here? [1]

Answer 4

In intrafusal fibres all the contractile apparatus is at the ends

This leaves the centre of the fibre without actin or myosin but full of cell bodies and mitochondria.

The Ia sensory afferents coil around the centre region. When it is stretched they are deformed and fire action potentials

Question 5

what is the difference between AP of stretched and unstretched muscles? [1]

what is the name for this? ^ [1]

Answer 5

what is the difference between AP of stretched and unstretched muscles? [1]
unstretched muscles are still firing AP. even though theyre at rest. However, stretched muscles increase their rate of AP firing

what is the name for this? ^ [1]
muscle length detectors

Question 6

describe the effect of tapping petalla tendon [3]

Answer 6

• induces a burtst of AP in some muscle spindles of muscle fibre [1]
• acts on dendrites of motor neurons in spinal cord [1]
• motor neurones are activated and cause twitch [1]

Question 7

what are the two types of motor neurone that exist on muscle spindle? [2]

what do they react to? [2]

Answer 7

what are the two types of motor neurone that exist on muscle spindle? [2]

- a motor neuron: innervate force-generating extrafusal muscle fibers at neuromuscular junctions

- y (gamma) motor neuron: stimulates contraction of the intrafusal fibres and prestretches their centers. keeps the sensitivity of muscle spindles; contraction of the infrafusal muscle fibres maintains muscle tension

Question 8

what would happen if during muscle contraction, only a motor neurons were only activated?

Answer 8

what would happen if during muscle contraction, only a motor neurons were only activated?
- only extrafusul muscle fibres would contract: the muscle spindle would become slack and no AP are fired.

what happens when both a & y are activated?
- intra & extra-fusal muscle fibres contract: tension is maintained in the muscle spindle

Question 9

how are gamma and alpha motor neurones activated? [2]

Answer 9

how are gamma and alpha motor neurones activated? [2]

alpha motor neuron: due to activation of la muscle spindle afferent

gamma motor neuron: due to descending input from motor cortex to gamma motor neuron (not reflexively activated by the muscle spindle affernets)

Question 10

what is the name of the second major proprioceptor in the muscle? [1]

what is ^ activated by? [1]

what is role? [2]

Answer 10

what is the name of the second major proprioceptor in the muscle? [1]
Golgi Tendon Organ

what is ^ activated by? [1]
muscle tension (not length)

what is role? [2]

• *provides CNS with information of degree of muscle tension**
• *prevents XS tension on the muscle**

Question 11

describe golgi tendon organ signal pathway [2]

is this pathway excitatory or inhbitory? [1] - which NT does it use

what would GTO do if you lift weight too heavy for you? [1]

Answer 11

describe golgi tendon organ signal pathway [2]
- disynaptic (interneurone) connection to its own motorneurons

is this pathway excitatory or inhbitory? [1]
glyinergic inhibitory neurone

what would GTO do if you lift weight too heavy for you? [1]
GTO would switch off muscle by powerful inhib action

Question 12

what comprises a motor unit? [3]

Answer 12

what comprises a motor unit? [3]​

• neuronal cell body (in lamina IX) of ventral horn of spinal cord
• motor axon
• set of muscles it innervates - although this can vary: (<10 to > 1000 muscle firbre)

Question 13

how do we change force of contraction of motor neuron? [1]

how do you do fine control of force v full power of force? [1]

Answer 13

how do we change force of contraction of motor neuron? [1]
increase or decrease force of contraction by recruiting more or fewer motor neurones

how do you do fine control of force v full power of force? [1]
fine control: active fewer small motor units
large power: recruit large motor units

Question 14

which of the following are all or nothing AP:

sensory
motor

Answer 14

which of the following are all or nothing AP:

sensory - constant rate of firing ongong
motor

Question 15

what is tetanus or tetanic contraction of motor unit? [1]

Answer 15

smooth contraction due to high frequency of AP creating movement (as opposed to lots of small twitches)

how healthy muscles work

Question 16

what happens to motor neurons if you have neuronal loss? [2]

Answer 16

what happens to motor neurons if you have neuronal loss? [2]
death of motor neurons causes remaining axons to sprout peripherally to innervate muscle fibres that had lost their motor neuron

causes overall increase in motor unit size & therefore reduced fine motor control

Question 17

what is a homonymous reflex? [1]

what is reciprocal inhibition? [1]

Answer 17

what is a homonymous reflex? [1]
a reflex in which stimulation of a muscle produces a contraction of the same muscle (e.g. patella tendon reflex)

what is reciprocal inhibition? [1]
(during non-homonymous reflexes) same tendon tap that activates reflex also inhibits the antagonist muscle via inhibitory interneurone (e.g. activates extensor, inhibits flexor)

Question 18

what underpins the vast majority of reflexes? [1]

Answer 18

patterns of synaptic connections between inputs, outputs and interneurones in the dorsal and ventral grey matter of spinal cord

Question 19

how does your body respond to activation of painful stimulus in small myelinated nociceptor afferent?

can you stop this reflex? why?

Answer 19

afferent sensory acts on interneurons in spinal cord: normally 2/3 excitatory interneurones between pain afferent input and flexor motor neuron (polysynaptic)

because a flexion relfex involves several interneurones, it can be suppressed by the brain

Question 20

Suppose you step on a nail. A flexion reflex withdraws you foot from the injury. When this occurs the crossed extensor reflex occurs. what is this [3]

Answer 20

branches of the afferent nerve fibres cross from the stimulated side of the body to the controlateral side of the spinal cord.

causes extensors in the opposite leg to contract, to take extra weight of body when you stand on one limb.

At the same time, signals travel up the spinal cord and cause contraction of the contralateral muscles of the hip and abdomen to shift the body’s centre of gravity over the extended leg.

Question 21

to maintain posture, muscle tone is constantly doing what? [1]

why are monosynpatic reflexes particularly active in postural muscles and leg extensory muscles? [1]

Answer 21

to maintain posture, muscle tone is constantly doing what? [1]
muscle tone is constantly finely adjusted by muscle fibres contracting in relays

why are monosynpatic reflexes particularly active in postural muscles and leg extensory muscles? [1]
need for maximum postural stability: faster feedback response the quicker the corrective muscle balance. without = fall over

Question 22

how many synaptic contacts from muscle spindle la nerve fibres do motor neurone dedrites have? [1]

how many synapses need to be active to make motor neurone fire? [1]

what regulates this system? [1]

Answer 22

how many synaptic contacts from muscle spindle la nerve fibres do motor neurone dedrites have? [1]
loads ! dozens / hundreds

how many synapses need to be active to make motor neurone fire? [1]
at least two firing simultaenously to go above threshold

​what regulates this system? [1]
interneurones

Question 23

what are the three different outputs from motor cortex? [3]

are they from upper motor neurone or lower motor neurone ?

Answer 23

what are the three different outputs from motor cortex? [3]

pyramidal system: these tracts originate in the frontal lobe, carrying motor fibres to the spinal cord via corticospinal tracts. upper motor neurone

extrapyramidal system: These tracts originate in the brain stem, carrying motor fibres to the spinal cord. upper motor neurone

spinal cord: has lower motor neurones in ventral horn that project out via peripheral nerve to muscles

Question 24

explain how your descending motor acitivity and muscles spindles work together to hold up and object in your flexed arm

Answer 24

descending activity and msucle spindles

• initial input from descending axons of forebrain (via corticospinal tract) activates bicep motor neurones
• feedbak from streched bicep muscle spindles adds to motor neurone synaptic input
• together, keep arm in desired position
• after while, get fatigue in bicep means it contracts less strongly. starts to stretch and arm starts to droop.
• this stretch of the muscle increases the AP firing from the muscle spindles to spial cord. this increases synaptic input to motor neurones. causes arm to move back to desired position

Question 25

what is muscle tone? [1]

what is the difference between upper and lower motor injury?

Answer 25

what is muscle tone? [1]
slight resistance of contraction in muscles when they are passively moved

what is the difference between upper and lower motor injury? [1]
lower motor neurones = tone is reduced or absent. CNS or PNS. inactivated muscles
upper motor neurones = tone is increased - get spasticity. CNS only. aggrivated muscles

Question 26

which structures are involved in upper motor neurone lesions?
which structures are involved in lower motor neurone lesions?

Answer 26

which structures are involved in upper motor neurone lesions?
motor cortex, corticospianl tract, other motor tracts

​which structures are involved in lower motor neurone lesions?
spinal or brain stem, a motor neurones, peripheral motror neurones