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REFLEX.MCQ
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1993-08-06
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D:Created 14.49 06/08/1993
D:Subject : Physiology
D:Topic : Reflexes
D:Level : Moderate
D:
D:Authors : Department of Physiology
D: The University
D: Leeds LS2 9NQ
I:MCQ SB 1
G:3
G:1:Dental Students
Q:1,2,3,4,5,6,7,8
G:2:Medical Students
Q:1,2,3,4,5,6,7,8
G:3:Science Students
Q:1,2,3,4,5,6,7,8
T:A
L:2
#:1
G: 10464 1 2 3
S:1
:The myotatic reflex:
B:N:5
B:1:T:1
:is mediated by muscle spindle primary afferent fibres
B:2:F:1
:is a polysynaptic reflex
B:3:T:1
:is mediated by Golgi tendon organs
B:4:T:1
:exhibits reciprocal innervation
B:5:F:1
:in quadriceps femoris has a latency of about 50 msec in man
F:6
:The myotatic (stretch) reflex is a monosynaptic reflex which utilises
:muscle spindle afferents; these give off axon collaterals in the cord to
:excite interneurons that inhibit the motoneurones of antagonistic
:muscles (reciprocal innervation). The reflex time for the quadriceps
:muscle in man is 20-25 msec. Golgi tendon organs are not involved in the
:stretch reflex.
E:------
#:2
G: 10464 1 2 3
S:1
:The main features of a polysynaptic reflex are:
B:N:5
B:1:F:1
:it involves only one segment of the spinal cord
B:2:F:1
:no afterdischarge
B:3:T:1
:delayed conduction time
B:4:T:1
:it is elicited by cutaneous afferents
B:5:F:1
:few opportunities for facilitation of occlusion
F:6
:Polysynaptic reflexes, such as the flexor (withdrawal) reflex commonly
:involve many segments of cord; the polysynaptic nature of the pathway
:increases the conduction time (relative to the monosynaptic reflex),
:offers opportunities at every synapse for facilitation or occlusion, and
:is commonly associated with after discharge. Flexor reflexes are
:elicitable by stimulation of small diameter cutaneous afferents.
E:------
#:3
G: 10464 1 2 3
S:2
:In a quadriplegic patient with a complete spinal transection at
:the sixth cervical segment, the following reflexes would be present:
B:N:5
B:1:T:1
:reflex hypertension during bladder distension
B:2:T:1
:reflex slowing of the heart during hypertension
B:3:F:1
:reflex diminution of sympathetic tone during hypertension
B:4:T:1
:reflex relaxation in the stomach
B:5:T:1
:hyperactive tendon jerks
F:9
:Spinal reflexes such as the tendon jerks and the cardiovascular
:reflexes elicited from the bladder would be exaggerated in this
:situation. Reflexes that depend of vagal afferents and efferents will be
:present in the quadriplegic; these reflexes include receptive relaxation
:in the stomach, and reflex vagal bradycardia. The component of the
:baroreceptor reflex vagal bradycardia. The component of the
:baroreceptor reflex mediated by the sympathetic efferents will however
:be absent because links between the medulla and the sympathetic outflow
:are sectioned.
E:------
#:4
G: 10464 1 2 3
S:1
:Consider spinal reflexes:
B:N:5
B:1:F:1
:there is a delay of about 1.5 msec at each synapse
B:2:T:2
:stimulation of a dorsal root causes electrical activity in ventral
:roots
B:3:F:2
:stimulation of a ventral root causes electrical activity in dorsal
:roots
B:4:T:2
:antidromic activation of ventral roots can inhibit alpha
:motoneurones
B:5:F:3
:facilitation of the response to electrical stimulation of a muscle
:nerve can be induced by a preceding stimulus to the same nerve when the
:two stimuli are separated by 50 msec
F:7
:The synaptic delay is about 0.5 msec.
:Reflex arcs conduct in only one direction - from dorsal roots to ventral
:roots but the response of alpha motoneurones can be facilitated or
:inhibited, by temporal or spatial summation and by pre- or post synaptic
:inhibition respectively. Temporal summation has a time course similar to
:that of the EPSP i.e. about 15 msec. Renshaw cells are responsible for
:recurrent inhibition of alpha motoneurones.
E:------
#:5
G: 10464 1 2 3
S:1
:Tapping the tendon of a muscle:
B:N:5
B:1:F:1
:excites Golgi tendon organ afferents
B:2:T:1
:produces a reflex contraction in that muscle
B:3:F:1
:excites gamma motor axons
B:4:T:1
:excites primary muscle spindle afferents
B:5:T:2
:causes a reflex inhibition of alpha motoneurones innervating
:antagonistic muscles
F:1
:No explanation available.
E:------
#:6
G: 10464 1 2 3
S:1
:The receptors responsible for the knee jerk reflex lie:
B:N:5
B:1:F:1
:in skin
B:2:F:1
:between adjacent muscle fibres
B:3:F:1
:at the motor end plate
B:4:F:1
:in the fascia
B:5:T:1
:the patellar tendon
F:1
:No explanation available.
E:------
#:7
G: 10464 1 2 3
S:7
:Hoffmann described the electrical changes recorded from human
:calf muscles (using surface electrodes) following electrical stimulation
:of their motor nerves. At low stimulation voltages,a wave of activity
:occurred at about 20-25 msec (the H-reflex). At higher voltages a
:response (the M-response) occurred with a latency of about 10 msec and
:increased in size as the H-response decreased to zero amplitude.
:Consider these responses:
B:N:5
B:1:F:2
:the H-reflex resulted has a long latency due to activation of slowly
:conducting fibres
B:2:T:2
:the H-reflex resulted from stimulation of low threshold muscles
:afferents
B:3:F:1
:the H-reflex resulted from stimulation of skin afferents
B:4:T:1
:the M-response was due to direct activation of alpha motoneurones
B:5:F:2
:the electrical threshold of Ia afferents is greater than that of alpha
:motoneurones
F:7
:The H-reflex is due to excitation of Ia afferents, whose threshold is
:less than that of motoneurones; the response at around 25 msec is due
:to a monosynaptic reflex. Increased intensities of stimulation bring in
:an earlier wave of activity due to direct excitation of alpha
:motoneurones. The H-reflex diminishes because centrifugal activity in
:the efferents collides with antidromic activity in the same nerve axons
:that give rise to the M-response.
E:------
#:8
G: 10464 1 2 3
S:1
:The following reflexes are present in spinal animals:
B:N:5
B:1:T:1
:flexor reflex
B:2:F:1
:Hering-Breuer reflex
B:3:T:1
:intestino-inhibitory reflexes
B:4:F:1
:tonic neck reflexes
B:5:T:1
:crossed extensor reflex
F:9
:The flexor and crossed extensor reflexes are two components of the
:withdrawal response during noxious stimuli, and are present in spinal
:animals. The intestino-intestinal inhibitory reflexes are sympathetic
:reflexes elicited by gut distension and depend upon a spinal reflex
:pathway. The Hering-Breuer reflex is initiated by lung inflation and
:depends on a vagal afferent pathway. Tonic neck reflexes depend on
:afferents from muscles and joints at the top of the neck which enter the
:cord in the upper four cervical dorsal roots. The tonic neck reflex
:pathways through the brainstem reticular formation.
E:------
::