Physiology: Skeletal Muscle Physiology Flashcards
What is tetanus?
Maximal sustained contraction of a muscle fibre that results from repeated stimulations so close together than the fibre does not have time to relax between stimuli
What are 𝛾-motor neurons?
Efferent (motor) supply of muscle spindles
Describe the structure of skeletal muscle
Parallel muscle fibres (skeletal muscle cells) bundled by connective tissue
What causes the striation of skeletal muscle?
Alternating dark bands (myocin) and light bands (actin)
Define isometric contraction
Muscle tension develops at constant muscle length
Define isotonic contraction
Muscle tension remains constant as the muscle length changes
What is excitation-contraction coupling?
The process whereby surface action potential results in activation of the contractile structures of the muscle fibre via Ca2+
What are slow oxidative (type I) muscle fibres?
Aerobic fibres used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking
What is electromyography?
Electrodes detect frequency and amplitude of muscle fibre action potentials
What is the Z-line of a sarcomere?
The sarcomere is found between two Z lines - connect the thin filaments of 2 adjoining sarcomeres
What is isometric contraction used for?
Supporting objects in fixed positions and maintaining body posture
What is the A-band of a sarcomere?
Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
Where do Ca2+ ions bind to in the sliding filament theory of muscle contraction?
Troponin (on actin filaments)
What is a muscle spindle (intrafusal fibres)?
Collection of specialised muscle fibres which act as sensory receptors for the stretch reflex
What is the sliding filament theory?
Muscle tension is produced by sliding of actin filaments on myocin filaments
Which muscle type is non-striated and involuntary?
Smooth muscle
How is muscle tension from contraction transmitted to bone?
Via the elastic components of muscle
What are fast glycolytic (type IIx) muscle fibres?
Anaerobic fibres used mainly used for short-term high intensity activities e.g. jumping
What is the optimal length of skeletal muscle?
The resting length of a skeletal muscle is approximately its optimum length
What is ATP required for in the generation of muscle tension?
Contraction (powers cross bridges) and relaxation (release of cross bridges and to pump Ca2+ back into SR)
Define a sarcomere
The functional unit of muscle
What is the function of 𝛾-motor neurons?
Adjust tension in muscle spindles to maintain sensitivity during contraction, when the muscle shortens
Which muscle type is striated and voluntary?
Skeletal muscle
What are fast oxidative (type IIa) muscle fibres?
Use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging
What are nerve conduction studies?
Determine the functional integrity of peripheral nerves
What is a reflex action?
Stereotyped response to a specific stimulus - simplest form of coordinated movement
How does a skeletal muscle’s function affect the number of muscle fibres per motor unit?
If a muscle serves fine movements, it will have fewer fibres per motor unit, and vice versa
What triggers the release of Ca2+ in skeletal muscle?
Action potential reaches T-tubules
What are annulospiral fibres?
Sensory nerve endings of muscle spindles
What is Ca2+ required for in the generation of muscle tension?
Cross bridge formation
Define myotonia
Delayed reaction after voluntary contraction
How do Ca2+ ions allow the formation of cross-bridges in the sliding filament theory of muscle contraction?
Bind to troponin which moves tropomyosin aside to uncover the cross-bridge binding sites on the actin, allowing myosin to bind
Which muscle type is striated and involuntary?
Cardiac muscle
What is the H-zone of a sarcomere?
Lighter area within middle of A-band where thin filaments don’t reach
When a skeletal muscle fibre receives an action potential, where will Ca2+ be released from?
The lateral sacs of the sarcoplasmic reticulum
What are reflex pathways used for in a clinical context?
To identify lesions in the motor system e.g. knee jerk (stretch reflex)
What is the I-band of a sarcomere?
Consists of remaining potion of thin filaments that do not project in the A-band
What is the M-line of a sarcomere?
Extends vertically down the middle of A-band within the centre of H-zone
What is a twitch?
A single contraction of a muscle fibre following a single stimulation
What are T-tubules in skeletal muscle?
Extensions of the surface membrane that dip into the muscle fibre
What is isotonic contraction used for?
Body movements and moving objects
Define a motor unit
A single alpha motor neuron and all the skeletal muscle fibres it innervates
Describe the structure of a myofibril
Actin and myocin arranged into sarcomeres
Where are muscle spindles found?
In the belly of muscles, run parallel to ordinary muscle fibres
What usually attaches skeletal muscles to the skeleton?
Tendons
Define myalgia
Muscle pain
