Physiology Flashcards
Functions of Skeletal muscle
Maintainposture, purposeful movement, resp movements, heat production, contributes to metabolism
Skeletal muscle features
Striated and voluntary (innervated by somatic nervous system), no gap junctions, neurogenic initiation (acteylcholine neurotransmitter @ neuromuscular junction), calcium entirely from SR
Cardiac muscle features
striated and involuntary (autonomic)
Smooth muscle
unstriated and involuntary (autonomic)
Motor unit
a single alpha motor neuron and all the skeletal muscle fibres it innervates
Precision > ….
Power
Fine movements have …
fewer fibres per motor unit (10 or so)
Powefful movements have …
more fibres per motor unit (100s -1000s)
Breakdown of muscle
Muscle > Muscle fibre > Myofibril > Sarcomere
Sarcomere contains …
Myocin and actin (actin slides over myocin)
Actin is …
thin and light
Myocin is …
thick and dark
skeletal muscle consists of …
parallel muscle bundled by connective tissue (fibres suually exteend entire length of muscle)
Sarcomeres are found….
between two Z lines (
Sarcomeres contain four zones
A band, H zone, M line and I band
How calcium is released in skeletal muscles…
In fibres Ca2+ is released from the lateral sacs of the SR when the surface action potential spreads down the transverse tubules (T-tubules)
ATP is needed:
- during muscle contraction (to power cross bridges)
- During relaxation to release cross bridges and to pump Ca2+ back into SR
Skeletal muscle tension is dpendent on
number of muscle fibres contracting and the tension developed by each contracting muscle fibre (depends on frequency of stimulation and summation of contractions)
In skeletal muscle the duration of action potential is …
much shorter than the resulting twitch
Stronger contractions can be achieved by …
summating twitches through repetitive fast stimulation of skeletal muscle
Tetanus
muscle fibre stimulated so rapidly that it has no oppurutnity to relax (e.g. lock jaw)
Why can’t cardiac muscle tetanus
it has too long a refractory period
Increasing frequency of stimulation of skeletal muscle causes
stonger contraction
Maximal contraction can be achieved when
the muscle is at its optimal length before the onset of contraction
Isotonic contraction
used for body movements and moving objects. Tension remains constant as the muscle changes
Isometric contraction
used for supporting objects in fixed positions and maintain body posture. Muscle tension develops at constant muscle length.
Slow oxidative
type 1 = slow contraction, high reisstance to fatigue, low work aerobic e.g. walking
Fast oxidative
type IIa = fast contraction, average resistance to fatigue, aerobic and anaerobic e.g. jogging
Fast-glycolytic
type IIx = fast contraction, low resistance, to fatigue, anaerobic, short term high intensity e.g. jumping
reflex action
stereotyped response to a specific stimulus
stretch reflex
a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle.
Muscle spindle
sensory receptor in muscle stretch (afferent neurons increase firing to motor units)
example of stretch reflex
tendon hammer on patellar tendon (checks femoral nerve L3, L4)
causes of imapired skeletal muscle function
intrinsic disease of muscle
diseae of NMJ
disease of lower motor neurons which supply muscle
disruption of input to motor nerves (e.g. MND)
Genetic causes of intrinsic muscle disease
Congenital myopathies (reduced contractility of musles) Chronic degeneration (e.g. muscular dystrophy) Abnormalities in membrane ion channels (e.g. myotonia)
Acquired causes of intrinsic muscle disease
inflammatory myopathies (polymositis)
Non-inflammatory (fibromyalgia)
Endocrine (cushing syndrome, thyroid disease)
Toxic (alcohol, statins)
Symptoms of muscle disease
muscle weakness, delayed relaxation post voluntary contraction (myotonia), muscle pain (myalgia), msucle stiffness
Invx in neuromsucular disease
Electromyography (EMG) [electrodes detect muscular activity] > Nerve conduction studies (done with EMG, checks function of peripheral nerves) > Muscle enzymes (CK) > Inflammatory markers (CRP, Plasma Viscocity) > Muscle Biopsy
