Week 6- Muscle Flashcards
Smooth muscle
- NO STRIATIONS, INVOLUNTARY
- found in most hollow organs
- FUNCT: move food, urine, reproductive tract secretions
- controls diametre of respiratory passage ways& blood vessels
- nerve supply is AUTONOMIC
Cardiac muscle
- STRIATED, INVOLUNTARY
- short and branched
- linked to eachother at intercalated discs
- ONLY IN HEART: moves book and maintains BP
- autorhythmic due to pacemaker cells
- uses AEROBIC RESPIRATION almost exclusively
→ large mitochondria make it resistant to fatigue
→ very vulnerable to interruptions in O2 supply
skeletal muscle
- STRIATED, VOLUNTARY
- contains skeletal muscle tissue → muscle cells.
- long cylindrical cells - MULTINUCLEATE
- contains blood vessels → O2 & glucose supply, waste removal
- nerves→coordinate muscle contraction
- contains connective tissue
skeletal muscle- connective tissue
Epimysium: covers whole muscle belly
Perimysium: surrounds bundle of muscle cells → fascicles
Endomysium: thin areolar connective tissue around each cell → allows room for capillaries & nerve files
muscle tissue - function
- generating a force caled MUSCLE TENSION → basic funct.
- MOVEMENT, POSTURE, STABILITY (joints & support tissue
- guard entrance & exits → sphincters
- maintain body temp → generate heat
- provide nutrient reserve
- regulate flow of materials through hollow organs
Skeletal muscle - fibre structure
- formed by FUSIOIN of embryonic MYOBLAST giving multiple nuclei
- MYOFIBRIS: most abundant , made of contractile proteins
- SARCOLEMMA: plasma membrane
- the SARCOPLAMIC RETICULUM (sr) surrounds the myofibrils & stores & releases CALCIUM IONS
- SARCOPLASM (cytoplasm) willed w/ MYOFIBRILS, GLYCOGEN ( energy storage) & MYOGLOBIN (O2 storage)
- other organelles (mitochondria, packed between myofibrils
TRANSVERSE TUBULES (T-TUBULES) : deep inwards extension of sarcolemma that surround each myofibril - form a tunnel-like network within fibre, continuous w/ exterior of cell → filled with ECF
TERMINAL CISTERNAE:
- Enlarged sections of SR found → edge of Sr meet T-T
- flanking each T-Tubule
Two terminal cisternae & their corresponding T-T form a triad
Myofibril - structure
Made of hundreds- thousands of MYOFILAMENTS consist of 1 or more of:
- CONTRACTILE PROTEINS: generate tension
- REGULATORY PROTEINS: dictate when fibre may contract
- STRUCTURAL PROTEINS: maintain proper myofilament ALLIGNMENT & FIBRE STABILITY
3 types of MYOFILAMENTS:
- Thick
- Thin
- Elastic: hastitin → resists excessive stretching force
myofibril structure - thick filament
Composed of contractile protein MYOSIN
- each myosin has GLOBULAR HEADS at each endlinked by INTERTWINING TAILS
- each head has an active site that binds w/ ACTIN
bundle of ~300 myosin molecules
TITIN consist of huge , springy protein flank thick filaments, ancor it to the Z line & prevent over stretching
myofibril structure - thin filament
Compost of ACTIN, TROPOMYOSIN & TROPONIN
- multiple actin subunits to form the 2 intertwining strands in the functional fillament, each bead-shape actin has an active site that binds w/ the MYOSIN HEADS
- TROPOMOSIN: REGULATORY PROTEIN that twists around ACTIN, covering up active sites
- TROPONIN: small REGULATORY PROTEIN that HOLDS binding troposmyosin in place & assists w/ contraction. has CA2+ sites
NEBULIN: holds F-actin strands together
motor unit
- functional unit comprising of motor neurons & all the muscle fibres it innervates
- when contract together → weak contraction, wide area, provide stability to sustain long-term contraction as motor units take turns resting
- RECRUITMENT: inc in muscular tension by increasing no. of motor units
- MUSCLE TONE: resting tension
neuromuscular junction
The specialised SYNAPSE where a motor neuron communicates w/ a MUSCLE FIBRE
Components:
- axon terminal
- synaptic cleft
- motor end plate: specialised region of muscle fivre plasma membrane whpse FOLDED surface has many LIGAND GATED Na+ CHANNELS
neurotransmiter: ACETYLCHOLINE - excitatory
- causes opening of sodium channels & commencement of action potential along the sarcolemma and t-tubules
REPOLARISATION OCCURS WHEN K+ CHANNELS OPEN: causing K+ efflux, returning end plate potentioals to ~-85mV
Skeletal muscle - contraction
- EXCITATION PHASE: when AP signals the release of ACh from the axon terminal into synaptic cleft, ACh binds to ligand-gated channels into synaptic cleft
- EXCITATION-CONTRACTION COUPLING: link between stimulus & contraction
- CONTRACTION PHASE: when Ca2+ ions bind troponin which pulls tropomyosin away from actins active site, CROSS BRIDGE CYCLE BEGINS
contraction - coupling
- an END-PLATE POTENTIAL leads to opening of VOLTAGE gated Na+ channels in the sarcolemma surrounding the motor end plate, which triggers an AP
- the AP signals the terminal cisternae to open VOLTAGE GATED cA2+ CHANNELS releasing Ca2+ from SR into cytosol
contraction - preparation
contraction cycle begins w/ arrial of CALCIUM IONS
actin binding sites are exposed:
- calcium ions bind to TRPOPNIN
- corformational change results in tropomyosin being moved out of the way
relaxation
2 components:
- motor neuron action potentials STOP signalling for the release of ACETYLCHOLINE from axon terminals.
- calcium ions are actively pumped (ATP needed) back into the SR terminal cisternae
