MSK 4 - Skeletal Muscle Flashcards Preview

CJ: UoL Medicine Semester Two (ESA2) > MSK 4 - Skeletal Muscle > Flashcards

Flashcards in MSK 4 - Skeletal Muscle Deck (51):

What are the three types of muscle?

- skeletal (striated)
- cardiac (striated)
- smooth (non-striated)


Give some characteristics of skeletal muscle?

- multinucleated
- fused cells
- attached to skeleton
- voluntary


Give some characteristics of cardiac muscle

- branched uninucleated
- heart only
- intercalated discs
- involuntary


Give some characteristics of smooth muscle

- distance cells
- spindle shaped
- wall of internal organs
- involuntary


What are the functions of skeletal muscle?

- movement
- posture
- joint stability
- heat generation


What is fasciculation?

Small, local, involuntary muscle contractions and relaxation. May be visible under skin.


What attaches a muscle to a bone?



What is the function of circular muscles?

They act as sphincters to adjust opening.


How are circular muscles arranged?

They have concentric fibres, and attach to skin, ligaments and fascia rather than bone. Eg. orbicularis oris, which is around the mouth


What are the three main categories of parallel muscles?

- Strap (fibres run longitudinally to contraction direction) eg. Sartorius
- Fusiform (wider and cylindrical shaped at centre) eg. Biceps brachii
- Fan-shaped (fibres converge at one end and spread over) eg. Pectoralis major


What is a pennate muscle?

One or more aponeuroses run through the muscle body from the tendon


Give an example of a multipennate muscle

Deltoid (this has central tendon branches)


What is the origin of a muscle?

A point on bone, typically proximal, which has greater mass and is more stable during contraction than the muscle's insertion


What is a muscle's insertion?

This is the structure (bone, tendon or connective tissue) that the muscle attaches to. Usually distal and moved by contraction.


What are compartments in limbs?

Limbs are divided into compartments by fascia - eg. The lower leg has four compartments


What is compartment syndrome?

When trauma in one compartment causes internal bleeding which exerts pressure on blood vessels and nerves.


What are the symptoms of compartment syndrome?

- deep constant, poorly localised pain
- aggravated by passive stretch of muscle group
- paresthesia (pins and needles)
- compartment feels tense/firm
- swollen shiny skin with bruising
- prolonged capillary refill time


How is compartment syndrome treated?

Fasciotomy, which can be covered by a skin graft


What are agonist muscles?

'Prime movers' - the main muscles responsible for a particular movement


What are antagonist muscles?

These oppose prime movers


What is the role of synergist muscles?

They assist prime movers. They cannot perform the movement alone, but their angle of pull assists


What is the role of neutraliser muscles?

They prevent the unwanted actions of a joint that would otherwise occur with an agonist


What is the role of fixators?

These act to hold a body part immobile whilst another body part is moving


What is the difference between isotonic and isometric contraction?

Isotonic - constant tension, variable muscle length

Isometric - constant length, variable tension, eg. hand grip


What is the difference between concentric and eccentric isotonic contraction?

Concentric - muscle shortens

Eccentric - muscle exerts a force while being extended eg. walking downhill


What are the three types of levers in the human body?

- first class lever "see-saw" (effort at one end, load at the other, fulcrum in the middle) eg. head

- second class lever "wheelbarrow" (effort at one end, fulcrum at other, load in middle) eg. standing on tip toes

- third class lever "fishing rod" (effort in middle, load at one end, fulcrum at other) eg. biceps in elbow flexion


What is the name given to what happens when ATP is depleted after death, causing myosin heads to be unable to detach?

Rigor mortis


What is a motor unit?

An alpha-motor neurone and the muscle fibres it innervates


True or false - muscle with less fibres are usually better at fine control, while muscles with more fibres are usually more powerful?



What are the three main muscle fibre types?

- slow type I
- fast type IIA
- fast type IIX

There are also several intermediates. Classification is based on myosin heavy chain expression.


Give some characteristics of Type I muscle fibres.

- slow oxidative
- aerobic, many mitochondria
- red colour
- high myoglobin levels
- fatigue resistant
- rich capillary supply
- first type to be recruited: standing, walking


Give some characteristics of type IIA muscle fibres

- aerobic, many mitochondria
- high myoglobin levels
- red-pink colour
- rich capillary supply
- moderate fatigue resistance
- second type to be recruited: walking, running


Give some characteristics of type IIX muscle fibres

- anaerobic glycolysis, few mitochondria
- low myoglobin levels
- white/pale colour
- poor capillary supply
- rapidly fatigable
- last type to be recruited: sprinting, jumping


What do intrafusal muscle fibres do?

They facilitate proprioception, allowing us to touch things accurately without watching our limbs


How are intrafusal muscle fibres innervated?

Two sensory neurones (type 1a and type 2), and gamma motor neurones


What does large-fibre sensory neuropathy cause?

Patients are unable to perform accurate movements without watching the affected limb


What is the size principle of muscle contraction?

Small motor neurones are recruited before large, so motor units mostly have fibres types:
Slow type I -> fast IIa -> fast IIx


What is it called when muscles cannot contact any further/faster?

Fused tetanus


Why are healthy muscle never fully relaxed (except in REM sleep)?

Baseline tone due to motor neuron activity and muscle elasticity


What is hypotonia?

A lack of skeletal muscle tone - this is a symptom rather than a condition. Most common in babies after birth, known as 'floppy baby syndrome'


Give some examples of conditions that can cause hypotonia

- muscular dystrophies
- spinal muscular atrophy
- Charcot-Marie-Tooth disease


Outline how the neuromuscular junction functions

- action potential opens voltage gated Ca2+ channels and triggers vesicle fusion and ACh release
- nACh channels open, Na+ flows into cell
- ACh rapidly broken down in synaptic cleft by AChE
- depolarisation opens voltage-gated Na+ channels in muscle cell
- action potential occurs


How is Ca2+ released into the muscle?

- voltage gated Ca2+ channels (DHP receptors) in the T-tubules release some calcium
- ryanodine receptors in SR are triggered by DHP receptors to allow rapid Ca2+ release


What does Ca2+ do once it is released into the muscles?

- Ca2+ binds to troponin, tropomyosin reveals actin binding sites for myosin heads
- relaxation is facilitated by Ca2+ being pumped back into the SR via Ca2+ pumps


Why is the resting membrane potential lower for skeletal muscle than other tissues?

Skeletal muscle has a high concentration of Cl- leak channels, so it is close to Nernst potential for Cl-


Give a disease caused by a channelopathy of the Cl- channel in skeletal muscle

Myotonia congenita


Give a disease caused by a channelopathy of the Na+ channel (alpha subunit) in skeletal muscle

Potassium aggravated myotonia, paramyotonia congenita, hyperkalemic periodic paralysis


Give a disease caused by a channelopathy of the Ca2+ channel (alpha 1s subunit) in skeletal muscle

Hypokalaemic periodic paralysis


What is myotonia congenita?

Inherited muscle stiffness which particularly occurs in the leg muscles. May be made worse by cold and inactivity.


What causes myotonia congenita?

Normally in skeletal muscle, Cl- ions help to bring the membrane potential back to baseline. In myotonia congenita this can't happen, so the muscles go into myotonia


What are the short term sources of ATP in muscle?

- stores of ATP in muscle fibre (very short term)
- creatine phosphate
- glycolysis
- oxidative phosphorylation

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