Skeletal Muscle Structure & Function Flashcards
What are the 3 types of muscle?
Striated = skeletal and cardiac. Non-striated = smooth
Outline the features of skeletal muscle
Multinucleated, fused cells, attached skeleton, voluntary
Describe cardiac muscle
Branched uninucleated, heart only, intercalated disks, involuntary
Outline the characteristics of smooth muscle
Distinct cells, spindle shaped, wall of internal organs, involuntary
Define fasciculation
Small local involuntary muscle contractions and relaxation – may be visible under skin
Describe the structure, function and placement of circular muscles
Concentric fibres, act as sphincter to adjust opening, attach to skin/ligaments and fascia rather than bone e.g. orbicularis occuli/oris
What are the 3 main categories of parallel muscles?
Strap, fusiform, fan shaped
Describe a parallel strap muscle
Shape = belt, fibres run longitudinally to contraction direction
Outline a parallel fusiform muscle
Shape = wider in the centre, taper off at the ends
What is a parallel fan shaped muscle?
Shape = fibres converge at one end and spread over broad area at other end
What are the 3 types of pennate muscle and what distinguishes them?
Unipennate = all fascicles on same side as tendon.
Bipennate = fascicles on both sides of central tendon.
Multipennate = central tendon branches
What is the difference between a muscle origin and insertion?
Origin = greater mass and more stable during contraction. Insertion = tends to be moved by contraction, tends to be distal, may be bone/tendon/CT
What is compartment syndrome?
Trauma in one compartment (limbs divided into sections by fascia) = internal bleeding which exerts pressure on blood vessels and nerves
What role can a muscle assume in movement?
Agonist, antagonist, synergist (assists), neutralisers (prevents unwanted), fixator (hold part immobile)
Describe an isotonic contraction
Constant tension, variable muscle length: 1) concentric = shortens 2) eccentric = extended
Outline an isometric contraction
Constant length, variable tension
What is a first/second/third class lever?
First = load and effort on either side of the fulcrum (see-saw).
Second = load and effort on the same side, effort is furthest away (wheelbarrow).
Third = load and effort on the same side, load is furthest away (fishing-rod)
What is rigor mortis?
ATP depleted, myosin heads can’t detach
How any motor neurons innervate a single muscle fibre?
1
How many muscles fibres can a motor neuron innervate?
Many
What are the 3 main muscle fibre types?
Slow oxidative type I (many mitochondria),
fast oxidative type IIA (many mitochondria),
fast oxidative type IIX
What is the name given to sensory receptors located in intrafusal muscle fibres that detect change?
Proprioceptors
How is muscle force controlled?
Rate code = more AP the more force. Size = small motor neurons recruited before large
How is baseline tone maintained?
Healthy muscle never fully relaxed = retain tension and stiffness = tone
What is hypotonia?
Lack of skeletal muscle tone – symptom rather than a condition e.g. muscular dystrophies
Besides K+ leak channels, skeletal muscles fibres also have high conc of?
Cl- leak channels
What is myotonia?
Inability to relax muscle at will caused by mutations to chloride channel CLCN1, recessive or dominant
In skeletal muscle which ion provides the most conductance?
Cl-
What are the sources of ATP in muscle?
Short term stores ATP, creatine phosphate, glycolysis, oxidative phosphorylation
What causes acidosis?
Current thinking is that acidosis is not caused by lactate but other reactions like ATP hydrolysis
