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Science for Medicine > Reflexes > Flashcards

Reflexes Flashcards

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1
Q

What are reflexes?

A

Simple building blocks for movement.

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2
Q

What is the simplest type of spinal reflex?

A

Stretch reflex.

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3
Q

Where is the stretch reflex found?

A

All muscles.

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4
Q

What are examples of the stretch reflex?

A

Patellar tendon / knee jerk reflex.

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5
Q

What are reflex arc movements hardwired into?

A

Spinal cord.

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6
Q

How does the knee jerk/patellar tendon reflex work?

A

Sharp tap on inelastic patellar tendon
Force is transmitted to the elastic muscle fibres
Stretch activates sensory nerves in muscle spindle fibres
Increases the number of APs on afferent nerve
These project through dorsal horn into spinal cord
Divide and make various connections
Knee jerk = monosynaptic a-motorneurone response.

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7
Q

What type of synaptic response is the knee jerk reflex?

A

Monosynaptic acting on alpha-motor neurone.

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8
Q

What do monosynaptic responses directly affect?

A

Alpha motor-neurone; pulls to the initial area of stretch and causes rapid contraction of agonist muscle.

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9
Q

How are monosynaptic responses examples of negative feedback?

A

Muscle is stretched, stimulates muscle spindle fibres, causes reflex muscle contraction, muscle shortens to previous length.

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10
Q

What is the second type of synaptic reflex response?

A

Reciprocal inhibition.

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11
Q

What does reciprocal inhibition involve?

A

Due to lever systems, sensory muscles also come into contact indirectly and influence antagonist muscles to allow an antagonist relaxation mechanism.
This happens because spindle fibres activate inhibitory interneurones which decrease activation of alpha motor-neurones to the antagonist muscle and make it relax.

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12
Q

How does reciprocal inhibition allow?

A

Activation of inhibitory interneurones which decrease activation of alpha motor-neurones to the antagonist muscle.

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13
Q

What does activation of inhibitory interneurones do?

A

Decreases activation of alpha motor-neurones to the antagonist muscle which causes relaxation.

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14
Q

What type of synaptic reflex response do inhibitory interneurones play a role in?

A

Reciprocal inhibition.

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15
Q

What type of synaptic reflex response do only alpha motor-neurones play a role in?

A

Monosynaptic.

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16
Q

What is the third type of synaptic reflex response?

A

Spindle afferent firing up the dorsal column to the somatosensory cortex to tell the brain about muscle length.

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17
Q

Where do afferent spindle fibres fire up the dorsal column to in the third synaptic reflex response?

A

Somatosensory cortex

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18
Q

What does afferent firing through dorsal column to the somatosensory cortex do?

A

Brain is more informed about muscle length.

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19
Q

What happens in the inverse stretch reflex?

A

Caused by afferent nerves monitoring muscle tension. The muscle contracts and shortens which pulls on the tendon and the sensory nerves from the GTOs increase the firing of action potentials.

20
Q

What do afferent nerves in the Golgi Tendon Organs monitor?

A

Muscular tension.

21
Q

What increases the firing of APs in the Golgi tendon reflex?

A

Sensory nerves from the GTOs increase the firing of action potentials.

22
Q

What does increased firing of APs in the GTO cause?

A

Activation of inhibitory interneurones to the agonist muscle (decrease in contraction strength)
Activation of excitatory interneurones to antagonist muscle
Again, muscle tension info ascends in dorsal column to the somatosensory cortex.

23
Q

What does activation of inhibitory interneurones to the agonist muscle cause?

A

Decrease in contraction strength.

24
Q

What do GTO activated inhibitory interneurones act on?

A

Agonist muscle to cause a decrease in contraction strength.

25
Q

What do GTO activated excitatory interneurones act on?

A

Antagonist muscle.

26
Q

Why is the clasp-knife GT reflex protective?

A

Protective mechanism because it prevents muscle damage.

27
Q

What does greater tension in the tendon lead to?

A

A collapse in resistance.

28
Q

Why is the Golgi tendon reflex polysynaptic?

A

Disynaptic action of both inhibitory interneurone on agonist muscle and excitatory interneurone on antagonist muscle.

29
Q

What is the flexor (withdrawal) reflex?

A

Ipsilateral flexion in response to pain.

30
Q

What is the flexor/withdrawal reflex a reaction to?

A

Pain.

31
Q

What do flexor/withdrawal reflexes use information from?

A

Noiceptors- pain receptors in muscles/joints/skin.

32
Q

Are flexor / withdrawal reflexes polysynaptic and protective?

A

Yes.

33
Q

Why are flexor/withdrawal reflexes characterised by withdrawal?

A

Because in response to pain, they withdraw part of the body away from the painful stimulus and in towards the body (flexing the affected part).

34
Q

What do increased sensory action potentials from the pain receptors cause?

A

Increased activity in flexor muscle through excitatory interneurones
Antagonist muscles are inhibited by a variety of excitatory and inhibitory interneurones

35
Q

What would happen if you withdrew the limb during the withdrawal reflex and did nothing else?

A

You would fall.

36
Q

How is falling prevented in the flexor / withdrawal reflex?

A

The contralateral limb extends several excitatory interneurones which cross the spinal cord to excite the contralateral extensors.
At the same time, there is inhibition of the contralateral flexors through several interneurones.

37
Q

What does action on the contralateral limb allow in the flexor / withdrawal reflex?

A

Allows an upright posture to be upheld and prevents falling over which maintains the protective nature of the flexor reflex mechanism.

38
Q

Where does sensory information ascend to the brain within the flexor / withdrawal reflex?

A

Spinothalamic tract.

39
Q

Why is flexor/withdrawal spinal circuitry far slower?

A

Spinal cord circuitry for flexor/withdrawal and cross-flexor reflexes is far slower than the stretch reflex because one leg flexes but the other has to extend to stop you from falling so there is an increased load to think about.w

40
Q

Can reflexes be overridden?

A

Yes- although they are embedded as hardwires in the spinal cord, they can be overridden by voluntary input from the CNS.

41
Q

How is the GTO reflex overridden?

A

When holding something heavy and important, descending voluntary excitation of alpha motor neurones can override the inhibition from the GTOs and maintain contraction.

42
Q

How is the stretch reflex overridden?

A

Strong descending inhibition hyperpolarises alpha motor neurones and the stretch reflex cannot be evoked.

43
Q

Why are patients distracted during reflex testing in a clinical setting?

A

To prevent voluntary effects on the reflex response.

44
Q

Is the absence of a stretch reflex in an uncooperative patient always clinical evidence of peripheral nerve damage?

A

No- their unccoperativity could lead to voluntary effects on the reflex response.

45
Q

What does the activation of Y-motoneurones depend on?

A

Descending pathways.

46
Q

What does high Y-motoneurone activation of muscle spindles result in?

A

Causes muscles to become extremely resistant to the stretch reflex- described as spastic and has neurological condition link.

47
Q

Activation of muscle spindles from what causes extreme resistance to the stretch reflex?

A

Y-motoneurone.

Science for Medicine (19 decks)

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