L32 - Somatic and Autonomic Reflexes Flashcards
List the 5 components of a typical reflex arc?
- Receptor– detects the stimulus
- Sensory neuron– transmits sensory (afferent) impulse from receptor to CNS
- Integration center – CNS interprets sensory information & coordinates the events in response to the stimuli
- Motor neuron – transmits motor (efferent) impulses from CNS to effector
- Effector– muscle or gland respondsto the instruction of motor neuron
Difference between monosynaptic and polysynaptic reflexes?
0 interneuron = monosynaptic: afferent fibers directly connect to efferent motor neurons, fastest
1 interneuron = disynaptic
> =1 interneuron = polysynaptic
Give examples of monosynaptic and polysynaptic reflexes?
Mono = stretch reflex
Poly = cough reflex, flexion reflex
Give examples of reflexes processed in the brain vs spinal cord?
- spinal cord (spinal reflexes) e.g. withdrawal from pain
* brain (cranial reflexes) e.g. startle reflex to turn head
Give examples of reflexes orchestrated by skeletal and smooth muscles?
- skeletal muscles (somatic reflexes) e.g. withdrawal from pain
- smooth muscles or glands (autonomic reflexes) e.g. pupillary light reflex
All reflexes are inborn and innate. T or F?
False
- inborn (innate reflexes) e.g. withdrawal from pain
- learned (acquired reflexes) e.g. stepping on the brake when red traffic light appears
List examples of somatic reflexes?
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
List examples of autonomic reflexes?
Defecation reflex
Micturition reflex
Pupillary light reflex
Chemoreceptor reflex
Baroreceptor reflex
Define the receptor for stretch reflexes?
Muscle spindle -
Monitor how much (length) and how fast (rate) the change in muscle length
Describe the afferent innervation of muscle spindles?
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
Compare the 2 types of muscle fibers in a skeletal muscle spindle?
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
Compare the sensory information that triggers type Ia and II fibers at intrafusal muscle fibers?
Type Ia = sensitive to amount (static) + rate (dynamic) of stretch
Type II = Sensitive to amount (static) of stretch
Describe the efferent innervation of intrafusal muscle fibers?
Gamma motor neurons: innervate nuclear bag fibers and nuclear chain fibers
Describe the firing of intrafusal muscle fibers under muscle stretch and contraction?
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
List the sequence of events in Patellar reflex?
- Tapping the patellar tendon
- Quadriceps stretched = Intrafusal muscle spindle activated
- Afferent impulses in Ia sensory neuron
- Monosynaptic (spinal cord) = no interneuron
- Impulses in alpha motor neuron to extrafusal muscle + suppress antagonist muscle
- Homonymous muscle contracts
Difference between tonic and phasic stretch reflex?
Tonic = maintaining muscle length by isometric contraction, mainly by static muscle stretch, type II fibers
Phasic = Transient contraction in reflex
Describe how patellar reflex triggers antagonistic actions in two muscles?
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
Describe the function of alpha-gamma co-activation?
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»_space; restore Ia fiber responsiveness
Describe how UMN lesion results in splasticity?
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
Describe how LMN lesion or impaired reflex arc causes hyporeflexia?
Decrease in muscle tone due to efferent neuron damage
Unable to coordinate reflex arc = Hypoactive stretch reflex
Summarize the functions of muscle stretch reflex?
- 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
Name the receptor for muscle tension?
Golgi tendon organ: detects tension
found at the junction between a group of EXTRAFUSAL fibers (muscle) and the tendon
Which is more sensitive to muscle contraction: golgi tendon organ or intrafusal muscle spindle?
Golgi tendon organ
Describe the innervation of Golgi tendon organ?
Afferent innervation by Type Ib fibers:
unmyelinated endings wrap around collagen fibers of Golgi tendon organ
List the sequence of events that occur in Golgi tendon reflex?
- Extrafusal muscle contraction»_space; increase muscle tension stretches the golgi tendon organ
- Golgi tendon organ increase firing rate through Type Ib sensory neuron
- 2 efferent effects through polysynaptic coordination:
a) Inhibitory interneurons»_space; reduce activity in alpha motor neuron»_space; homonymous muscle relax
b) Excitatory interneurons»_space; increase activity in alpha motor neuron»_space; Antagonist muscle contract
Function of golgi tendon reflex?
Prevent injury by over-contraction/ excessive loading of muscles
Regulate tension of muscle during contraction
List the sequence of events in flexor reflex (withdrawal reflex)?
1) Nociceptor activation: A-delta and gamma pathway to spinal cord
2) Polysynaptic coordination:
a) Excitatory interneurons»_space; motor neurons»_space;
ipsilateral flexor muscle contracts
b) Reciprocal innervation: inhibitory interneurons»_space; motor neurons»_space; ipsilateral antagonistic extensor muscle relaxes
3) Withdraw leg from stimulus (knee flexes)
List the sequence of events in crossed extensor reflex?
1) Nociceptor stimulated on one leg»_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
Give one example of superficial cord reflex?
Plantar reflex = normal
(Babinski reflex = abnormal in adult, normal in babies)
Stroke sole of foot from heel to toes = inward flexion of sole, toes
Describe the coordination involved in the plantar reflex?
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
Explain why infants exhibit the Babinski reflex but normal adults show plantar reflex to the same stimuli?
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
What neuro pathway is tested in the Plantar/ Babinski reflex?
Lesion of the corticospinal tract tested
Adult with lesion in the tract show Babinski reflex instead of normal Plantar reflex
List the sequence of events in the Defacation reflex?
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
List the sequence of events in the micturition reflex?
1) Stretch of bladder wall
2) Spinal reflex pathway: cause bladder contraction and internal sphincter relaxation
3) Supraspinal voluntary control relaxes external sphincter
Tract the brain structures involved in the pupillary light reflex?
1) Light activate Intrinsically photosensitive retinal ganglion cells
2) AP fired along optic nerve
3) synapse at pretectal nucleus (unilateral)»_space; then to Edinger- Westphal nucleus (bilateral)
4) Oculomotor nerve to pupillary constrictor muscles»_space; direct pupillary constriction + consensual light reflex
List the sequence of events in Chemoreceptor reflex to modulate BP?
- 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
Define the which reflexes are used to localize lumbar and sacral cord lesions?
L2-L4 for knee jerk reflex
L5-S1 for plantar reflex
S1-S2 = ankle jerk
Define which reflexes are used to test cervical and thoracic cord lesions?
C5-C6 = biceps reflex
C7-T1 = Triceps reflex
