L32 - Somatic and Autonomic Reflexes

Question 1

List the 5 components of a typical reflex arc?

Answer 1

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

Question 2

Difference between monosynaptic and polysynaptic reflexes?

Answer 2

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

1 interneuron = disynaptic

> =1 interneuron = polysynaptic

Question 3

Give examples of monosynaptic and polysynaptic reflexes?

Answer 3

Mono = stretch reflex

Poly = cough reflex, flexion reflex

Question 4

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

Answer 4

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

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

Question 5

Give examples of reflexes orchestrated by skeletal and smooth muscles?

Answer 5

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

Question 6

All reflexes are inborn and innate. T or F?

Answer 6

False

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

Question 7

List examples of somatic reflexes?

Answer 7

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

Question 8

List examples of autonomic reflexes?

Answer 8

Defecation reflex

Micturition reflex

Pupillary light reflex

Chemoreceptor reflex

Baroreceptor reflex

Question 9

Define the receptor for stretch reflexes?

Answer 9

Muscle spindle -

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

Question 10

Describe the afferent innervation of muscle spindles?

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Type II = Sensitive to amount (static) of stretch

Question 13

Describe the efferent innervation of intrafusal muscle fibers?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

List the sequence of events in Patellar reflex?

Answer 15

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

Question 16

Difference between tonic and phasic stretch reflex?

Answer 16

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

Phasic = Transient contraction in reflex

Question 17

Describe how patellar reflex triggers antagonistic actions in two muscles?

Answer 17

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

Question 18

Describe the function of alpha-gamma co-activation?

Answer 18

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

Question 19

Describe how UMN lesion results in splasticity?

Answer 19

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

Question 20

Describe how LMN lesion or impaired reflex arc causes hyporeflexia?

Answer 20

Decrease in muscle tone due to efferent neuron damage

Unable to coordinate reflex arc = Hypoactive stretch reflex

Question 21

Summarize the functions of muscle stretch reflex?

Answer 21

• 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

Question 22

Name the receptor for muscle tension?

Answer 22

Golgi tendon organ: detects tension

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

Question 23

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

Answer 23

Golgi tendon organ

Question 24

Describe the innervation of Golgi tendon organ?

Answer 24

Afferent innervation by Type Ib fibers:

unmyelinated endings wrap around collagen fibers of Golgi tendon organ

Question 25

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

Answer 25

1. Extrafusal muscle contraction >> 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 >> reduce activity in alpha motor neuron >> homonymous muscle relax b) Excitatory interneurons >> increase activity in alpha motor neuron >> Antagonist muscle contract

Question 26

Function of golgi tendon reflex?

Answer 26

Prevent injury by over-contraction/ excessive loading of muscles Regulate tension of muscle during contraction

Question 27

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

Answer 27

1) Nociceptor activation: A-delta and gamma pathway to spinal cord 2) Polysynaptic coordination: a) Excitatory interneurons >> motor neurons >> ipsilateral flexor muscle contracts b) Reciprocal innervation: inhibitory interneurons >> motor neurons >> ipsilateral antagonistic extensor muscle relaxes 3) Withdraw leg from stimulus (knee flexes)

Question 28

List the sequence of events in crossed extensor reflex?

Answer 28

1) Nociceptor stimulated on one leg >> 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

Question 29

Give one example of superficial cord reflex?

Answer 29

Plantar reflex = normal (Babinski reflex = abnormal in adult, normal in babies) Stroke sole of foot from heel to toes = inward flexion of sole, toes

Question 30

Describe the coordination involved in the plantar reflex?

Answer 30

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

Question 31

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

Answer 31

``` 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

Question 32

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

Answer 32

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

Question 33

List the sequence of events in the Defacation reflex?

Answer 33

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

Question 34

List the sequence of events in the micturition reflex?

Answer 34

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

Question 35

Tract the brain structures involved in the pupillary light reflex?

Answer 35

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

Question 36

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

Answer 36

- 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

Question 37

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

Answer 37

 L2-L4 for knee jerk reflex  L5-S1 for plantar reflex S1-S2 = ankle jerk

Question 38

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

Answer 38

C5-C6 = biceps reflex C7-T1 = Triceps reflex