muscle Flashcards
what are skeletal muscles responsible for
-voluntary movement of bones that underpins locomotion
-control of inspiration by contraction of diaphragm
-skeletal-muscle pump which helps with venous blood return to the heart
-sheath in muscle is called epimyosin
-the fascicle is surrounded by a sheath called peremyosin
-muscle cell is surrounding by endomyosin sheath
-myofibrils are involved in the contraction of skeletal muscles
-myofibrils are made up of many sarcomere
-thick and thin filaments (myofilaments) are mainly myosin and actin
what is the skeletal muscle structure
-skeletal muscle is striated in appearance
-I band only contains actin- the light band
-the light band is isotropic (how they react to polarised light)
-A band is dark and anisotropic
-as sarcomere contracts, actin is pulled inwards so I band becomes smaller, in the A band their is overlapping of actin and myosin filaments
-large number of different proteins working together in the sarcomere
-nebulin is a protein in sarcomere which is linked around actin fibres
-titin is a protein in the sarcomere and they send length and state of the sarcomere
-between the Z disk is the sarcomere unit where actin is attached to the sarcomere
how do skeletal muscle initiate contraction
-release of ACh at the neuromuscular junction initiates an action potential in the plasma membrane of muscle fibre
-wave of depolarisation passes along the sarcolemma and through the T-tubule network to reach interior of the cell
-In skeletal muscle, the endoplasmic reticulum is specialised and known as the sarcoplasmic reticulum
-the T tubule runs near two areas of the SR forming a triad
-depolarisation triggers an increase in intracellular calcium
steps in the cross-bridge formation and contraction of the sarcomere
1) ATP binds to myosin head, causing dissociation of the actin-myosin complex
2) ATP is hydrolysed causing myosin heads to return to their resting conformation
3) a cross-bridge forms and the myosin head binds to a new position on the actin
4) a phosphate is released
5) a conformational change in the myosin head causes a power stroke. the filaments slide past each other
6) ADP released
-release of Ca2+ triggers this muscle contraction due to cross-bridges forming
-process is dependent on ATP and ATP phosphorylation
summation in skeletal muscle
-increasing frequency stimulation
-summation is when before the muscle relaxes completely, the next action potential occurs
-at highest frequency (50Hz) there is no chance for the Ca2+ to be taken back up into the stores therefore Ca2+ is always around which causes constant muscle contraction
slow oxidative muscle fibres (type 1)
-rely on oxidative phosphorylation
-fatigue resistant
-red in colour
-metabolism is oxidative
-low glycogen content (doesn’t need much glycogen for energy as already has ATP from oxidative phosphorylation)
-ATP synthesis is aerobic
-high in mitochondria
-muscles are soleus
fast oxidative muscle fibres (IIa)
-fatigue resistant
-red in colour
-metabolism is oxidative
-glycogen content is abundant (main source of energy)
-ATP synthesis is aerobic
-higher mitochondria levels than slow oxidative fibre
-muscles are gastrocnemius
fast glycolytic (IIx/IIb)
-fatigable
-white in colour
-metabolism is glycolytic
-high in glycogen
-ATP synthesis is anaerobic
-mitochondria is few
-muscle type is biceps branchii (gets fatigued quickly, high reserves of glycogen for production of ATP
-lack myoglobin
what’s the difference between fast and slow muscle fibres
-slow fibres are half the diameter of fast fibres and take longer to contract after nerve stimulation
-fast fibres take 10 msec or less to contract
-slow example is soleus
-fast example is eye muscles
what does isometric mean
-muscle fixed at length, tension generated but no change in length
what does isotonic mean in muscle regards
-muscle stimulation causes a change in length
what’s botulinum toxin
-linked to food poisoning
-clostridium botulinum
-muscle weakness, paralysis leading the death
-endoproteinase that cleave proteins required for exocytosis of ACh in autonomic nervous system
-1st symptom is dry mouth and double vision, 2 nd symptom is gastrointestinal , 3rd is paralysis of limbs and respiratory muscles
-clinical use is treatment of strabismus (cross eye)
some neuromuscular junction and inhibitors
-neuronal Na+ channel for tetrodotoxin and saxitoxin
-K+ channel for dendrotoxin
-ACh release for tetanus toxin and botulinum toxin
-acetylcholinesterase for DFP and physostigmine
-AChR channel for ACh, nicotine, tubocurarine and abungarotxin
-muscle Na+ channel for tetrodotoxin, saxitoxin and micro conotoxin
-Ca2+ channel for 1-conotoxin
what’s cardiac muscle like
-specific to the heart
-cardio myocytes are also striated like skeletal muscles
-myocytes are shorter and more branched than skeletal muscles and they are joined together at intercalated disks
-there is electrical couple (between different cardiac muscle cells) between adjacent myocytes at the intercalated disks by ,eats of the gap junction
-action potential initiated at the pacemaker curled in the SAN and the propagates between cells via the gap junction
-repolarisation and depolarisation can occur
