Muscular Flashcards
Muscular system functions
- Produce Movement
- Maintain Posture and body position
- Regulating organ volume
- Moving substances in the body
- Heat production
Types of muscle
- Skeletal
- Cardiac
- Smooth
Skeletal
Attached to bone or skin
• Single, very long, cylindrical, multinucleate cells with obvious striations
Cardiac
Walls of the heart
• Branching chains of cells, uni- or binucleate, striations
Smooth
Unitary muscle in walls of hollow visceral organs
• Single, fusiform, uninucleate, no striations
Characteristics of muscle
1) Excitability (Irritability)
2) Contractility
3) Extensibility
4) Elasticity
Excitability
Ability to receive and respond to stimuli
Contractility
Ability to contract when stimulated
Extensibility
Ability to be stretched or extended
Elasticity
Ability to recoil to resting length
Origin
One end of the muscle is attached to a structure (usually bone) that remains stationary
Insertion
The opposite end of the muscle that is moved by the contraction
Tendon
Attach muscle to bone
Ligament
Attach bone to bone
Gaster/belly
The fleshy/meaty portion of the muscle that contracts
Antagonistic pairs
Skeletal muscles are arranged in opposing paird
Agonist
Contracts to cause an action
Antagonist
Stretches & yeilds to the action of the agonist
Synergist
Contract to stabilise intermediate joints
Fixator
Stabilise the origin of the agonist
Sarcolemma
Plasma membrane of a muscle cell
Sarcomere
Smallest contractile unit of a muscle fibre, repeating units of actin and myosin
Fascicle
A bundle of muscle fibres
Muscle fibre
Long, cylindrical cell with multiple nuclei just beneath the sarcolemma
Myofibril
Rod-like organelles with contractile proteins which make a muscle fibre
Transverse tubules (T-tubles)
Tiny invaginations of the sarcolemma that tunnel in from the surface toward the centre of each muscle fibre, carries action potential to myofibrils
Sarcoplasmic reticulum
Interconnecting tubules surrounding each myofibril which stores and release calcium when muscle fibre is stimulated
Sheaths of skeletal muscle from external to internal
1) Epimysium - surrounds the entire muscle
2) Perimysium - surrounds the bundles of fibres (fascicle)
3) Endomysium - surrounds individual muscle fibres
Crossbridges
Binding of myosin “heads” to actin
Sliding filament theory of muscle contraction
Crossbridges forming and pulling actin towards the centre of the sarcomere
Myosin
Thick filament with heads attached that have actin binding sites
Actin
Actin have sites for myosin to attach, that are blocked by tropomyosin
Tropomyosin
Blocks binding sites on actin so that myosin heads cannot form a crossbridge
Troponin
Locks tropomyosin in place
Crossbridge formation
Calcium released attaches to troponin, which releases its lock on tropomyosin. This opens the active sites of actin, allowing ATP to be used to form a crossbridge
Huxley sliding filament theory
Actin and myosin slide past each other during muscle contraction
Ratchet mechanism
Cross bridges are formed and broken several times to propel the actin filament towards the centre of the sarcomere
Muscle fibre contraction steps
1) Nerve stimulation
2) Action potential, an electrical current, must be generated in sarcolemma
3) Action potential must be propagated along sarcolemma
4) Intracellular Ca2+ levels must rise briefly
Somatic motor neurons
The nerve cells that stimulate a muscle to contract
Nerve impulse to the neuromuscular junction (synapse)
1) Action potential arrives at axon terminal
2) Voltage-gated calcium channels open and calcium enters the axon terminal
3) Synaptic vesicles then release their contents (acetylcholine) by exocytosis
4) Acetylcholine, a neurotransmitter diffuses across they synaptic cleft and binds to receptors in the sarcolemma
Nerve impulse
Motor neuron stimulate motor units which stimulate muscle fibre
In crossbridges calcium is the
Trigger
Potential propagation
- Once the muscle fibre is stimulated, an action potential is re-generated and is conducted along the sarcolemma and down the T-tubules to reach all of the myofibrils
- From the T-tubule, the impulse is transferred to the SR
- Causes calcium to ‘flood’ out of the SR
Excitation-contraction coupling steps
1) Action potential travels down the T-tubules which releases calcium
2) This triggers contraction by forming corssbridges
Muscle relaxation
Nerve impulse stops
1) Calcium channels close
2) ATP actively transports calcium back into the sarcoplasmic reticulum
3) Absence of calcium cause tropomyosin to clock myosin bind sites on actin
ATP regenerated through
- Direct phosphorylation by Creatine phospate (CP)
- Anaerobic respiration
- Aerobic respiration
Direct phosphorylation by Creatine phospate (CP)
Take phosphate from creatine phosphate, changing ADP to ATP
1 ATP per creatine phosphate
Anaerobic respiration
Breakdown of glucose in two stages;
1) Glycolysis
2) Lactic acid formation
No oxygen required, 2 ATP per glucose
Aerobic respiration
Breakdown of glucose in three stages; 1) Glycolysis, 2) Krebs Cycle 3) Oxidative phosphorylation Requires oxygen, 36 ATP per glucose
