Skeletal system - Muscle Flashcards
What are the types of muscle?
- Skeletal
- Cardiac
- Smooth
Describe each type of muscle?
- Skeletal: movement of bone & body parts, voluntary
- Cardiac: heart only, develops pressure for arterial blood flow
- Smooth: grouped in walls of hollow organs, move material in GI & reproductive organs
What is excitability?
Ability to receive and respond to stimuli
What is contractility?
Ability to shorten when stimulated
What is extensibility?
Ability to be stretched
What is elasticity?
Ability to recoil to resting length
List the functions of the skeletal muscle
- Producing movement
- Maintaining posture & body position
- Supporting soft tissues
- Guarding body entrance & exits
- Maintaining body temp
- Storing nutrients
What is endomysium?
Loose connective tissue that surrounds individual muscle fibres
What is epimysium?
Dense irregular connective tissue surrounding entire muscle
What is perimysium?
Collagen & elastic fibres surrounding a group of muscle fibres called a fascicle
What do motor neurons do?
Stimulate muscle fibres to contract
What do capillary beds surrounding muscle fibres require?
Large amounts of energy
What is the sarcolemma?
cell membrane
What are myofibrils?
Cylindrical structures within muscle fibre
What are myofilaments?
Bundles of protein filaments
What is the difference between actin & myosin filaments?
Actin - thin
Myosin - thick
What is the sarcomere?
Smallest contractile unit of a muscle fibre
What is the difference between thick and thin filaments?
What does the Z disc do?
1) Thick - run the length of A band
2) Thin - run the length of I band & partway into A band
3) Z - coin shaped sheet that anchors the thin filaments & connects myofibrils to each other
What is tropomyosin?
An elongated protein winds along the groove of the F actin double helix
Troponin composed of 3 subunits (Tn-I, Tn-T, Tn-C), what do they bind to?
- Tn-I = binds to actin
- Tn-T = binds to tropomyosin
- Tn-C = binds to calcium ions
What is SR?
Sarcoplasmic reticulum
A single T-tubule & 2 terminal cisternae form a ?
triad
SR stores what when not contracting?
Ca 2+
After contraction, SR pumps the Ca 2+ back into?
SR
What is the neuromuscular junction (NMJ) ?
Skeletal muscles stimulated by somatic motor neurons
What is released from nerve fibre?
ACh
What are the components of the NMJ?
- Synaptic knob swollen end - contains ACh
- Motor end plate
- Synaptic cleft
List the 4 actions involved in muscle
- Excitation
- Excitation-contraction coupling
- Contraction
- Relaxation
Describe each action
- Excitation: nerve action potentials lead to action potentials in muscle fibre
- ECC: action potentials on sarcolemma activate myofilaments
- Contraction: shortening of muscle fibre
- Relaxation: return to resting length
What is the sliding filament theory?
Explains the relationship between thick & thin filaments as contraction proceeds
Cyclic process beginning with Ca release from SR. What does Ca bind to?
Troponin
What does ATP allow?
Release of cross bridge
ACh binds with nAChR in muscle membrane to allow what to enter?
Na+ ions
Na+ ions generate what?
Action pontential in sarcolemma
What happens when action potential cease?
Muscles stop contracting
What are the functions of ATP in the skeletal muscle contraction?
- Hydrolysis of ATP by myosin
- Binding of ATP to myosin
- Energises Ca 2+ pumps actively transport Ca 2+ back into SR
- Runs the Na+ K+ pump into sarcolemma
ATP for muscle contractions, produced from what 3 sources?
- Creatine phosphate ( 1 ATP per CP)
- Aerobic respiration (36 ATP per glucose)
- Anaerobic resp (Glycolysis) - breakdown of glucose to yield ATP & lactic acid
Velocity & duration of contraction influenced by what?
- Muscle fiber type
- Load
- Recruitment
How are skeletal muscle fibres classified?
- Speed of contraction
- Metabolic pathways for ATP synthesis
What are the 3 types of fibers?
- Slow oxidative fibers
- Fast oxidative fibers
- Fast glycolytic fibers
What affects influence of load?
↑ load - ↑ latent period, decrease contraction & duration
What is a muscle twitch?
Response of a muscle fibre to a single, brief threshold stimulus
What are the 3 phases of a muscle twitch?
- Latent period
- Contraction phase
- Relaxation phase
What is a motor unit?
Motor neuron & all the muscle fibres it supplies
List the motor unit ratios
Back muscles - 1:100
Finger muscles - 1:10
Eye muscles - 1:1
List components of smooth muscle
- More actin than myosin
- No sarcomeres
- Caveolae: indentations in sarcolemma
- Dense bodies instead of Z disks
List the groups of smooth muscle
- Longitudinal layer: muscle fibres run parallel to organ’s long axis
Circular layer: muscle fibres around circumference of organ
What is smooth muscle innervated by?
Autonomic nervous system (ANS)
What is a multiunit?
Cells/groups of cells act as independent units
What does Ca 2+ interact with to activate myosin?
Ca 2+ interacts with calmodulin + myosin light chain kinase (MLCK)
Phosphorylated cross bridges interact with _____ to produce _____
actin, shortening
_____ muscle _____ when intracellular Ca 2+ levels drop
Smooth
Relaxes
What is cardiac muscle?
Involuntary muscle found only in heart wall
What are fibers connected by?
- Intercalated discs (thickened cell membranes)
- Gap junctions that allow spread of action potentials
What does cardiac muscle not require?
Nerve stimulation nerve
Cardiac muscle has its own _______
intrinsic pacemaker (conduction system within cardiac muscle) - Initiates cardiac contraction (auto-rhythmicity)
What do intercalated discs with gap junctions do?
Transmit action potentials from one muscle to the next
What is the H zone?
Lighter midregion where filaments do not overlap
What is the M line?
Line of protein myomesin that holds adjacent thick filaments together
