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Flashcards in NS in muscle Deck (24):
1

Types of reflex

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

2

Spinal cord arrangement

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

3

Motor unit

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

4

Recruitment of motor units

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

5

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)

6

Golgi tendon organ effect

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

7

Muscle stretch reflex

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

8

Reciprocal stretch reflex

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

9

Flexion reflex

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

10

Crossed extensor reflex

Accompanies flexion, 250ms after this contralateral limb extends

11

Inverse myotactic reflex

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

12

Spindle in active contraction

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

13

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

14

Controlling contraction

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

15

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

16

Force-velocity relationship

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

17

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

18

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

19

Examples of muscle weakness through NMJ issues

Myasthenia gravis
NM block from venom
Nicotine insecticide poisoning AChR desensitisation

20

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

21

Record muscle activity

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

22

Jendrassik's manoeuvre

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

23

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

24

Preference with internal and external stimulus for neurones

Larger diameter first for external stimulus, smaller for nervous activity