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MBBS II MSS > L32 - Somatic and Autonomic Reflexes > Flashcards

L32 - Somatic and Autonomic Reflexes Flashcards

1
Q

List the 5 components of a typical reflex arc?

A
  1. Receptor– detects the stimulus
  2. Sensory neuron– transmits sensory (afferent) impulse from receptor to CNS
  3. Integration center – CNS interprets sensory information & coordinates the events in response to the stimuli
  4. Motor neuron – transmits motor (efferent) impulses from CNS to effector
  5. Effector– muscle or gland respondsto the instruction of motor neuron
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2
Q

Difference between monosynaptic and polysynaptic reflexes?

A

0 interneuron = monosynaptic: afferent fibers directly connect to efferent motor neurons, fastest

1 interneuron = disynaptic

> =1 interneuron = polysynaptic

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3
Q

Give examples of monosynaptic and polysynaptic reflexes?

A

Mono = stretch reflex

Poly = cough reflex, flexion reflex

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4
Q

Give examples of reflexes processed in the brain vs spinal cord?

A
  • spinal cord (spinal reflexes) e.g. withdrawal from pain

* brain (cranial reflexes) e.g. startle reflex to turn head

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5
Q

Give examples of reflexes orchestrated by skeletal and smooth muscles?

A
  • skeletal muscles (somatic reflexes) e.g. withdrawal from pain
  • smooth muscles or glands (autonomic reflexes) e.g. pupillary light reflex
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6
Q

All reflexes are inborn and innate. T or F?

A

False

  • inborn (innate reflexes) e.g. withdrawal from pain
  • learned (acquired reflexes) e.g. stepping on the brake when red traffic light appears
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7
Q

List examples of somatic reflexes?

A

Stretch reflexes:

  • Patellar reflex (knee-jerk reflex)
  • Biceps and Triceps reflex
  • Ankle-jerk reflex

Golgi tendon reflex

Flexor reflex (withdrawal reflex)

Crossed extensor reflex

Superficial cord reflex

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8
Q

List examples of autonomic reflexes?

A

Defecation reflex

Micturition reflex

Pupillary light reflex

Chemoreceptor reflex

Baroreceptor reflex

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9
Q

Define the receptor for stretch reflexes?

A

Muscle spindle -

Monitor how much (length) and how fast (rate) the change in muscle length

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10
Q

Describe the afferent innervation of muscle spindles?

A

Intrafusal muscle fibers:

1) Type Ia fibers form annulospinal primary endings on Nuclear bag fibers and nuclear chain fibers
2) Type II fibers form Flower spray endings on nuclear chain fibers

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11
Q

Compare the 2 types of muscle fibers in a skeletal muscle spindle?

A

Extrafusal fibers: contractile
Efferent: alpha* motor neurons (efferent)

Intrafusal fibers: has both receptive and contractile regions
Afferent = Ia and II sensory nerve fibers
Efferent = gamma* motor neuron

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12
Q

Compare the sensory information that triggers type Ia and II fibers at intrafusal muscle fibers?

A

Type Ia = sensitive to amount (static) + rate (dynamic) of stretch

Type II = Sensitive to amount (static) of stretch

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13
Q

Describe the efferent innervation of intrafusal muscle fibers?

A

Gamma motor neurons: innervate nuclear bag fibers and nuclear chain fibers

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14
Q

Describe the firing of intrafusal muscle fibers under muscle stretch and contraction?

A

Stretch:

  • Activate muscle spindle
  • Increase rate of AP firing at Ia fibers

Contraction:

  • Reduces tension in muscle spindle
  • Decrease rate of AP firing in Ia fibers
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15
Q

List the sequence of events in Patellar reflex?

A
  1. Tapping the patellar tendon
  2. Quadriceps stretched = Intrafusal muscle spindle activated
  3. Afferent impulses in Ia sensory neuron
  4. Monosynaptic (spinal cord) = no interneuron
  5. Impulses in alpha motor neuron to extrafusal muscle + suppress antagonist muscle
  6. Homonymous muscle contracts
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16
Q

Difference between tonic and phasic stretch reflex?

A

Tonic = maintaining muscle length by isometric contraction, mainly by static muscle stretch, type II fibers

Phasic = Transient contraction in reflex

17
Q

Describe how patellar reflex triggers antagonistic actions in two muscles?

A

Quadriceps stretch = trigger Ia afferent fiber:

1) Stimulate alpha motor neuron to quadriceps for contraction
2) Stimulate Ia Inhibitory interneuron to hamstring muscles = flexor relaxation

> > reciprocal inhibition

18
Q

Describe the function of alpha-gamma co-activation?

A

Maintain Ia fibers response during reflex contraction:

  • Alpha motor neuron cause extrafusal muscle to contract and shorten
  • Intrafusal muscle spindle becomes slack and Ia fibers cannot monitor muscle length
  • Gamma motor neuron contracts to tighten intrafusal muscle&raquo_space; restore Ia fiber responsiveness
19
Q

Describe how UMN lesion results in splasticity?

A

UMN lesion cause loss of inhibition of gamma motor neurons

> > more gamma activity = more intrafusal muscle fiber contraction

> > Increase sensitivity of muscle spindles

> > Increase alpha motor neuron activity and muscle tone

> > hyperactive stretch reflex

20
Q

Describe how LMN lesion or impaired reflex arc causes hyporeflexia?

A

Decrease in muscle tone due to efferent neuron damage

Unable to coordinate reflex arc = Hypoactive stretch reflex

21
Q

Summarize the functions of muscle stretch reflex?

A
  • Gamma motorneurons:
    i) Alter sensitivity of muscle spindles
    ii) Alter activity of alpha motor neurons
  • Maintain muscle tone and control
  • Type Ia fibers convey sensory information to spinal cord and higher centers
22
Q

Name the receptor for muscle tension?

A

Golgi tendon organ: detects tension

found at the junction between a group of EXTRAFUSAL fibers (muscle) and the tendon

23
Q

Which is more sensitive to muscle contraction: golgi tendon organ or intrafusal muscle spindle?

A

Golgi tendon organ

24
Q

Describe the innervation of Golgi tendon organ?

A

Afferent innervation by Type Ib fibers:

unmyelinated endings wrap around collagen fibers of Golgi tendon organ

25
Q

List the sequence of events that occur in Golgi tendon reflex?

A
  1. Extrafusal muscle contraction&raquo_space; increase muscle tension stretches the golgi tendon organ
  2. Golgi tendon organ increase firing rate through Type Ib sensory neuron
  3. 2 efferent effects through polysynaptic coordination:
    a) Inhibitory interneurons&raquo_space; reduce activity in alpha motor neuron&raquo_space; homonymous muscle relax

b) Excitatory interneurons&raquo_space; increase activity in alpha motor neuron&raquo_space; Antagonist muscle contract

26
Q

Function of golgi tendon reflex?

A

Prevent injury by over-contraction/ excessive loading of muscles

Regulate tension of muscle during contraction

27
Q

List the sequence of events in flexor reflex (withdrawal reflex)?

A

1) Nociceptor activation: A-delta and gamma pathway to spinal cord

2) Polysynaptic coordination:
a) Excitatory interneurons&raquo_space; motor neurons&raquo_space;
ipsilateral flexor muscle contracts
b) Reciprocal innervation: inhibitory interneurons&raquo_space; motor neurons&raquo_space; ipsilateral antagonistic extensor muscle relaxes

3) Withdraw leg from stimulus (knee flexes)

28
Q

List the sequence of events in crossed extensor reflex?

A

1) Nociceptor stimulated on one leg&raquo_space; pain pathway to spinal cord

2) Polysynaptic coordination:
a) Ipsilateral leg flexor contract, extensor relaxes
b) Contralateral leg flexor relax, extensor contracts

3) Move painful foot away from stimulus + allow body weight to shift to non-stimulated leg

29
Q

Give one example of superficial cord reflex?

A

Plantar reflex = normal
(Babinski reflex = abnormal in adult, normal in babies)

Stroke sole of foot from heel to toes = inward flexion of sole, toes

30
Q

Describe the coordination involved in the plantar reflex?

A

1) Cutaneous stimulation of the foot plantar aspect
2) Efferent reflex response mediated by spinal cord + descending supraspinal control*** via corticospinal tract
3) Inwards flexion of toes and sole

31
Q

Explain why infants exhibit the Babinski reflex but normal adults show plantar reflex to the same stimuli?

A 
Plantar = Inwards flexion of toes and sole 
Babinski = Dorsiflexion of big toe and ankle + fanning out of toes

Infants have underdeveloped corticospinal tract = not complete superficial cord reflex

32
Q

What neuro pathway is tested in the Plantar/ Babinski reflex?

A

Lesion of the corticospinal tract tested

Adult with lesion in the tract show Babinski reflex instead of normal Plantar reflex

33
Q

List the sequence of events in the Defacation reflex?

A

1) Distension of rectum wall by feces in rectum activate stretch receptors

2) Spinal reflex pathway:
i) Contraction of rectum and sigmoid colon
ii) relax internal anal sphincter smooth muscle

3) Supraspinal voluntary control: external sphincter

34
Q

List the sequence of events in the micturition reflex?

A

1) Stretch of bladder wall
2) Spinal reflex pathway: cause bladder contraction and internal sphincter relaxation
3) Supraspinal voluntary control relaxes external sphincter

35
Q

Tract the brain structures involved in the pupillary light reflex?

A

1) Light activate Intrinsically photosensitive retinal ganglion cells
2) AP fired along optic nerve
3) synapse at pretectal nucleus (unilateral)&raquo_space; then to Edinger- Westphal nucleus (bilateral)
4) Oculomotor nerve to pupillary constrictor muscles&raquo_space; direct pupillary constriction + consensual light reflex

36
Q

List the sequence of events in Chemoreceptor reflex to modulate BP?

A
  • Chemoreceptors in carotid and aortic bodies sense low blood O2, low pH and high CO2
    2) Decrease parasympathetic stimulation/ increase sympathetic stimulation of heart and blood vessels
    3) Increase HR, Contractile force, Vasoconstriction
37
Q

Define the which reflexes are used to localize lumbar and sacral cord lesions?

A

 L2-L4 for knee jerk reflex

 L5-S1 for plantar reflex

S1-S2 = ankle jerk

38
Q

Define which reflexes are used to test cervical and thoracic cord lesions?

A

C5-C6 = biceps reflex

C7-T1 = Triceps reflex

MBBS II MSS (31 decks)

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