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NAS > Reflexes > Flashcards

Reflexes Flashcards

1
Q

What is a reflex

A

Stereotyped - predictable
Involuntary - autonomic response
Rapid

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2
Q

Clinical relevance of reflexes

A

Testing reflexes
Pupillary reflex - construction of pupil in response to bright light under ANS
deep tendon reflex - SNS

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3
Q

General functions of reflexes

A

Protective - limb withdrawal/ cough reflex
Postural control - walking. No conscious activity
Homeostasis - blood glucose/ pressure

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4
Q

Components of reflex arc

A

Sensory receptors
Afferents
Integration centre CNS
Efferent neurones
Effectors

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5
Q

Importance of sensory receptors in reflex arc

A

Detect stimuli
Generate AP

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6
Q

Importance of CNS in reflex arc

A

Interneurones in CNS - where info from a sensory neurone is passed to motor neurone
Can be excitatory and inhibitory

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7
Q

Where are interneurones found

A

Spinal cord
Brain stem nuclei
Enteric NS - control of gut

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8
Q

Does reflex arc work in isolation

A

No works with the rest of ns

Impulse sent to muscle to remove it from hot object but impulses also sent to the brain which cause u to feel pain

Brain can also override reflexes e.g. choose to hold hand close to hot

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9
Q

Where do somatic/ autonomic reflexes normally operate from

A

most somatic reflexes operate via spinal cord whereas most autonomic reflexes operate via the brain stem nuclei

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10
Q

What is modulation

A

Interneurones produce output depending on the inputs they receive

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11
Q

Importance of efferent neurones in reflex arc

A

Called motor neurones - somatic reflexes
Called efferent neurones - ANS
Innervate effectors by passing on AP from interneurones/ sensory neurones

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12
Q

What are simple stretch reflexes

A

Required for adjusting posture
Adjust degree of skeletal muscle contraction
Sensory receptors - proprioceptors (mechanoreceptors)
Monitor state of skeletal muscle

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13
Q

Two examples of proprioceptors

A

Muscle spindles
Golgi tendon organs

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14
Q

Where are muscle fibres found

A

Within all skeletal muscles

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15
Q

What are muscle spindles

A

Specialised set of muscle fibres
Made up of nerve endings of sensory axons wrapped around muscle fibres
If there is change in muscle fibres, the nerve endings can detect change

There is a direst synapse between the sensory neuron and the motor neurone: no interneurons and no modulation potentials in between

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16
Q

What is a monosynaptic reflex

A

One neurone to neurone synapse
No NMJ

17
Q

Mechanism 1 of simple stretch reflex mediated via muscle spindle when lifting heavy weights

A

Opposes sudden change in muscle length

(Refer to diagram if confused)
Muscle is stretched and elongated which stretches the muscle spindle
Generates AP which travels down sensory neurone to spinal cord
At synapse the sensory neurone will release excitatory NT
Excites the motor neurone - AP travel along the motor neurone via ventral root
AP gets to NMJ the alpha motorneurone releases ACh
Leads to skeletal contraction
Contraction prevents damage

Mechanism allows us to pick up heavy objects

18
Q

Mechanism 2: knee jerk reflex

A

Myotatic reflex

Antagonistic muscle pairs - quadriceps and hamstrings

Tendon being hit causes stretching of the quadriceps muscle - stretching - activates muscle spindle
Cause AP to be sent to spinal cord via sensory neurone
Sensory neurone releases excitatory NT (ACh)
Alpha motor neurone stimulated causing contraction of quadricep
Excitatory NT - interneurone - inhibitory NT causing hamstring to relax
Simultaneous contraction and relaxation allow extension of the knee

19
Q

Where is the muscle spindle fibre (sensory receptor) present in the knee jerk reflex

A

In quadricep

20
Q

Sensory neurone in knee jerk reflex connects to

A

Motor neurone
Interneurone - which then connects to another motor neuroen

21
Q

How to stimulate knee jerk reflex

A

Tapping below the patella
Hit tendon

22
Q

What are Golgi tendon organs

A

Receptors in tendons (muscle to bone)
Amongst collagen fibres are nerve endings of sensory neurones which form Golgi tendon organ
Interneurone btw afferent and efferent neurone
Described as polysynpatic

23
Q

Polysnypatic reflex

A

withdrawal reflex is polysynaptic, meaning that, in addition to the sensory and motor neurons, this response utilizes interneurons which pass signals between the sensory and motor neurons, ultimately creating multiple synaptic connections.

24
Q

Difference between monosynaptic and polysynpatic

A

Monosynaptic reflex: ↑ A reflex that only contains one space for an action potential to travel between a sensory and motor neuron.
Polysynaptic reflex: ↑ A complex reflex that contains many connections between neurons.

25
Q

Mechanism of Golgi tendon organ

A

Muscle stimulated by heavy weight so muscle contracts
Tendon pulled due to increase in muscle contraction
Collagen fibres in tendon straighten and lightly compress the nerve ending and GTO activated
Reaches threshold - AP down sensory axons
Excitatory NT - interneurone - inhibitory output
Prevents activation of motor neurone
Decreases muscle activity so decreases less

Reverse myotatic reflex - more muscle activity results in less muscle activity after reflex

26
Q

Importance of Golgi tendon organ reflex

A

Prevents damage due to overwork of muscles - stops contraction e.g. weightlifting
Fine control of muscle tension - tiny adjustments to muscle activity e.g. when writing

27
Q

Mechanism when someone walking and steps on smth sharp (crossed extensor flexor)

A

Causes leg to lift:
Nociceptors activated in skin
AP to dorsal horn of spinal cord via sensory neurone
Sensory neurone branches
One branch to brain allows pain experience
Other branches:
Excitatory NT - interneurone - excitatory output - activates alpha motor neurone - causes right hamstring contraction
Excitatory NT - interneurone - inhibitory output - deceases right quadricep activity (relaxation)

If person walking lifting leg will cause them to fall so need stabilisation in the other leg:
Excitatory NT - interneurone - excitatory output - alpha motorneurone - left quadriceps contraction
Excitatory NT - interneurone - inhibitory output - left hamstring relaxation

Refer to diagram on lecture

NAS (17 decks)

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