Flashcards
5 Spinal Reflexes
Flashcards do conjunto (45)
- 1What is a lower motor neurone?a motor neurone that has its cell body in the ventral horn of the spinal cord (axons innervate striated muscle of the body) or brainstem (axons innervate striated muscle of the brain)
- 2What is an upper motor neurone?neurone that has its cell body in the motor cortex or brainstem that sends axons down the spinal cord in descending tracts to synapse on the cell bodies and dendrites of LMNs
- 3What are the main functions of UMNs that have cell bodies in the brainstem?postural reflexes and basic movements
- 4Where else may UMNs have their cell bodes?basal ganglia
-initiation of movement, suppression of unwanted movement
cerebellum
-motor performance and error detection
^output regulates the activity of UMNs
-cerebellum = excite
-basal ganglia = inhibit
^balance is key
-all send info back to primary motor cortex via thalamus - 5The LMN has three main types of synaptic input. What are these?descending tracts in spinal cord from UMNs
local interneurons (cells with all their processes inside the CNS)
local sensory nerve fibres via reflexes
-motor axon travels in the spinal nerve of the same spinal segment - 6What is the pyramidal system?UMN cell bodies project directly from motor cortex via corticospinal tract to LMNs
-essential for planning, initiating and directing voluntary movement - 7What is the extra-pyramidal system?UMN cell bodies in brainstem project to LMNs in spinal cord
-brainstem neurons regulated by motor cortex via corticobulbar tract
-evoluntionarily older - postural control - 8What is a reflex?involuntary motor action triggered by a sensory input
-have motor programs stored in synaptic connections between sensory, output and interneurons in one or two spinal cord segments - 9What may interneurons be?excitatory - produce EPSPs
or
inhibitory - produce IPSPs - 10What is a motor unit? What is meant by the term 'innervation ratio'? Explain the benefit and drawback of the arrangement of motor unitsa motor unit = LMN + fibres it innervates
each LMN either innervates a small amount (extra-ocular eye muscles, precisely regulated) or large amount (gastrocnemius, less precisely regulated) of muscle fibres
=innervation ratio
if LMN was to be damaged, adjacent neurone takes over control of denervated fibres
-means you have fewer, larger units with less precise control
different motor units helps muscles produce movements appropriate for the circumstance e.g. marathon runner, slow units adapted for prolonged exercise - 11What is a spinal cord segment?distance between two spinal nerves
- 12What is a myotactic reflex? Explain this in simple terms. What is meant by the term 'homonymous' reflex?monosynaptic
-tendon tap
-muscle stretch
-activates muscle contraction via activation of intrafusal and extrafusal fibres
-reflex prevents rapid muscle stretch and returns muscle back to original length
stretch of a certain muscle e.g. quadriceps, activates same muscle to contract - 13What are the two types of LMNs?alpha
-innervate extrafusal fibres
-large
gamma
-innervate intrafusal fibres
-smaller - 14Why may the stretch reflex need to be performed on both sides?stretch reflexes are ipsilateral
- 15Deep tendon reflexes may be used to assess specific muscles, joints and spinal levels. Give examples of thissupinator (wrist) C5-C6
biceps (elbow) C5-C6
triceps (elbow) C7
quadriceps (knee) LL3-L4
gastrocnemius (ankle) S1 - 16Why may these reflexes be difficult to suppress?there is a direct connection between the sensory input (muscle spindle afferent) and motor neurone
- 17Explain the concept of reciprocal inhibition? What kind of reflex is this?tendon tap activates the extensor to contract
and
activates flexor to relax
-achieved via action of inhibitory interneurone, hence polysnaptic reflex - 18What is a muscle spindle? What is it often called and why? What input does it provide?receptor that mediates the tendon reflexes
often called proprioceptor as responds to movements of the body rather than external stimuli
provides sensory input to spinal cord about length and rate of change (velocity) of length of the muscle - 19How is a muscle spindle activated?stretch of muscle also stretches muscle spindle and activates the 1a sensory afferent
-spindles spontaneously active at rest so stretch increases their firing rate
-muscle spindle = muscle length detectors - 20When the patellar tendon is tapped, what brings about the 'twitch' in the muscle?tendon tapped
burst of AP in several muscle spindles in muscle
lots of AP acting on dendrites of motor neurones of quadriceps
spatial and temporal summation on motor neurones
-motor neurones each fire a single AP
-produces a twitch - 21What does the muscle spindle consist of?modified skeletal muscle fibres in a capsule- intrafusal fibres
-all the contractile tissue is at ends leaving centre without actin/myosin but full of cell bodies and mitochondria
-central region has no connective tissue so easily stretched
-1a sensory afferent endings coil around centre region and detect when its stretched - 22As well as the 1a afferent fibre, the muscle spindle is also supplied with a motor neurone. What is this? Where do they get their input from?gamma motor neurone
-causes ends of intrafusal fibres to contract which puts tension on central portion of fibre (where 1a sensory afferent endings found) and stretches it so increases sensitivity of spindle to stretch
-information driven from supraspinal descending motor pathways
e.g. vestibulospinal, reticulospinal
-NOT REFLEXLY ACTIVATED BY MUSCLE SPINDLE AFFERENTS - 23Explain the benefit of the a-y co-activation principlewhen A innervated extrafusal fibres contract to shorten, Y fire to shorten intrafusal fibres at same rate so sensitivity of muscle spindle is maintained
-Y conduct AP slower than A so intrafusal fibres contract fractionally larger than extrafusal fibres, giving time for sensory systems to respond - 24What is the result of pathological increases in gamma activity?hyperactive tendon reflexes
- 25Muscle spindles don't exist to just provide a twitch of the muscle during a tendon tap. What else do they do?provide continuous feedback to motor neurones
continually adjust the motor neurone output during normal movement - 26Explain how muscle spindles are useful in the face of fatigue using an examplemuscles fatigue
-despite steady drive from brain via descending motor pathways, the longer the muscle is contracting the amount of contraction per muscle AP decreases
monosynaptic reflex form of negative feedback to maintain constant muscle length despite ongoing muscle fatigue - 27Why is the monosynaptic reflex easiest to elicit in leg extensor muscles (quadriceps and gastrocnemius)continuous feedback from muscle spindles in the spinal cord and high speed of AP conduction in the afferent and efferent nerves give tendon jerk reflex shortest possible delay time
- 28What is the Golgi Tendon organ? Where is it found? What is it activated by? What's a similarity between muscle spindles and GTOs?proprioceptor in muscle, found in muscle tendons
activated by muscle tendon
both muscle spindle and GTO activated when muscle is passively stretched but spindle switched off if muscle shortens back to original length - 29Explain how the GTO works. Draw a diagrammuscle tension increases
collagen fibres that contain 1b endings stretch
1b afferents fire
afferent synapse onto glycinergic inhibit interneurons
these in turn synapse onto alpha motoneurones of both homonymous and antagonist muscles
hence 'switches off' movement so muscles can relax - 30Explain the name given to the reflex involving Golgi Tendon organsincreased muscle tension causes negative feedback of homonymous muscle
-inverse myotactic reflex
to prevent further tension increase - 31Reflex withdrawal from a painful stimulus is mediated by...flexor muscles
- 32Why can a flexion reflex be suppressed by the brain?involves many interneurons so gives brain opportunity to override, mediate or control reflex
- 33Explain how a flexion and crossed extensor reflex workssensory afferents synapse onto interneurons ipsilaterally and contralaterally which supply flexor and extensor motorneurones
on the ipsilateral limb
-stimulation of flexor muscles
-inhibition of extensor muscles
=flexion reflex
on contralateral limb
-stimulation of extensor muscles
-inhibition of flexor muscles
-crossed extensor reflex - 34What is true of both flexion and crossed extensor reflexes?both activated by noxious stimuli
- 35In terms of muscle tone, what happens when LMNs and UMNs are damaged?LMN lesion
reduced or absent tone
-if absent = flaccid paralysis
UMN lesion
increased tone
-spastic paralysis = increased tone + exaggerated reflexes - 36UMN vs LMN lesions -possible locationCNS only
CNS or PNS - 37UMN vs LMN lesions -common causestrauma, ALS, infectious diseases
polio, tumour, trauma, alcoholism, diabetes - 38UMN vs LMN lesions -structures involvedmotor cortex or CS tract
spinal or brainstem Amotor neurones or peripheral motor axons - 39UMN vs LMN lesions -distributionnever individual muscles, always groups of muscles
segmental - limited to muscles innervated by damaged motoneurons or their axons - 40UMN vs LMN lesions -voluntary movementsparalysis or paresis especially of skilled movements
paralysis - 41UMN vs LMN lesions -muscle toneincreased, particularly in antigravity muscles
decreased - 42UMN vs LMN lesions -myotactic reflexeshyperactive or exaggerated
decreased or absent - 43UMN vs LMN lesions -cutaneous reflexessome abnormalities e.g. positive Babinski sign
decreased or absent - 44UMN vs LMN lesions -muscle bulkmay be slight atrophy
pronounced atrophy - 45UMN vs LMN lesions -classical descriptionspastic paralysis
flaccid paralysis
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- University Brain and Behaviour FlashCards sobre 5 Spinal Reflexes, criado por Ifeoma Ezepue em 01-04-2016.
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- Ifeoma Ezepue
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