NS in muscle Flashcards Preview

MMB > NS in muscle > Flashcards

Flashcards in NS in muscle Deck (24):

Types of reflex

regulatory (vestibule-ocular/muscle-stretch)
protective (blink, gag, withdrawal)


Spinal cord arrangement

Sensory through dorsal horn
Motor from ventral horn
Proximal muscles closer to midline in ventral horn


Motor unit

Single alpha-motor neurone and muscle fibres it contacts, in smaller higher input resistance


Recruitment of motor units

Smaller motor units recruited first
Lower activation needed when stretch is optimum but more when it's over stretched


Muscle spindle composition

Intrafusal fibres attached to tendon and extrafusal fibres
1a fibres from annulospiral endings sensitive to fast changes
II fibres from flower spray endings, continuously fire in relation to static length
Have gamma motor neuron innervation as well as alpha, allows comparison of extra/intrafusal fibres (afferent discharge inc when e>i and vice versa)


Golgi tendon organ effect

Sends signals through 1b afferents which activate 1b inhibitory to relax muscle if load is too great (tension too high)


Muscle stretch reflex

Only monosynaptic reflex in NS
1a afferent responds to stretch, connects to alpha neuron for contraction


Reciprocal stretch reflex

1a afferents to 1a interneuron which causes relaxation of antagonist


Flexion reflex

Protective, nociceptors cause flexors to contract and inhibitory interneurons to relax extensors


Crossed extensor reflex

Accompanies flexion, 250ms after this contralateral limb extends


Inverse myotactic reflex

Golgi tendon organ activates 1b afferents when load increased, when load increases too much then homonymous muscle relaxes and antagonist contracts


Spindle in active contraction

Alpha motor neurones only activate extrafusal, spindle not stretched but gamma coactivation helps maintain spindle sensitivity


AChR change from embryonic to adult

Gamma subunit changes to epsilon in AChR on NMJ if innervated, otherwise changes back to gamma
Become clustered at nerve contact to muscle during development


Controlling contraction

Contraction strength by synchrony, recruitment and rate coding, asynchrony of motor unit activation for smoother muscle contraction


Tetanic contraction

Sustained muscular contraction, when there's repeated activation not all Ca++ has returned to SR so greater contraction occurs as more Ca++ released and more cross bridges formed


Force-velocity relationship

Slower contraction gives more time for cross-bridges to attach so stronger contraction


NMJ block in anaethetics

Tetanic contractions more selectively blocked than twitch, so larynx paralysed but not lungs at right conc with atracurium
Edrophonium is a cholinesterase blocker so ACh available again, atropine given as well to prevent muscarinic SEs


Iceberg effect of ACh

5x ACh needed is released from terminal, 75% of receptors need to be blocked for EPP to drop below threshold
Sometimes reappearance of blocker occurs due to edrophonium half-life being shorter than NMJ blocker, ACh given to counteract


Examples of muscle weakness through NMJ issues

Myasthenia gravis
NM block from venom
Nicotine insecticide poisoning AChR desensitisation


Cerebral palsy

UMN lesion leading to reduced recruitment, X-SA decrease, stiffer longer sarcomeres, predominance of MHC-1, spastic muscle tone usually with co-contraction


Record muscle activity

Electromyogram can measure action potentials summated, amplitude related to muscle fibres activated


Jendrassik's manoeuvre

Patient clenches + hooks flexed fingers together, raises lumbar spina neurones so high amplitude EMG


Hoffman reflex

Electrically stimulating a nerve will activate 1a afferents and activate a slightly quicker tendon tap
Also alpha motor neurones activated if amplitude is high enough causing M response before H reflex
In longer latency M response there's a refractory period in the alpha motor neurone so can't see H-reflex


Preference with internal and external stimulus for neurones

Larger diameter first for external stimulus, smaller for nervous activity