Anatomy unit 5 skeletal and muscular systems bone injury notes
Muscular System : Unit 3.1
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Transcript of Muscular System : Unit 3.1
Muscular System: Microanatomy and Physiology
EHS Unit 3 Day 1
Goals
• Identify key structures in the microscopic anatomy of skeletal muscles.
• Discuss the process of muscle contraction.
Muscular System Overview
• This is the term for the collective skeletal (voluntary) muscles. There have three functions.
– Allow movement (works with???)
– Give shape to the body, posture and compresses the vital organs.
– Generates heat to regular temperature (what other system regulates temp??)
Characteristics of Muscle Tissue
• Excitability– Able to respond to impulse from nerve cell
• Contractility– Able to shorten in length to produce movement.
• Extensibility– Ability to stretch beyond resting length.
• Elasticity– Ability to return to resting length after contracting
or stretching.
Structure of a Skeletal Muscle
• Made of of Myocytes
– Myocytes are long, cylindrical cells with multiple nuclei.
– Sarcoplasm is the special cytoplasm of muscle cells that contains myoglobin (carries oxygen) and glycosomes (stores energy).
– These cells are also filled with fibers called myofibers.
Myofibrils
• These contain the contracting units of the muscle. – They are banded.
– The space from one Z band to the next is a sarcomere.
– Bands are created by the pattern of Myosin (thick) and Actin (filaments)
– During muscle contraction, the sarcomere shortens from both ends:
The Process of Muscle Contraction
• Occurs in Stages:
1. Nerve Stimulus and Release of ACh at Neuromuscular Junction
2. Generation of Action Potential Across Sarcolemma (muscle cell membrane)
3. Muscle Fiber Contraction
4. Relaxation
Nerve Stimulus
• An impulse originating in the central nervous system travels through the peripheral nervous pathway to the neuromuscular junction.
– At the synapse, the nerve releases ACh (acetylcholine), a neurotransmitter.
– ACh receptors in the muscle bind with the ACh molecules.
– ACh cases Ion channels to open, allowing for generation of action potential.
Action Potential
• This is the term for the electrical impulse that travels along the muscle unit. – It is generated by the movement of ions across the
sarcolemma.
– The movement of K+ and Na+ ions create this. (A wave of depolarization followed by repolarization)• When stimulated, ACh opens ion gates which allow Na+
to move in rapidly. (Depolarization)
• Once ACh is broken down, Na+ gates close and K+ gates open, allowing potassium to move out of the cell.
Fiber Contraction
• The action potential stimulates the release of calcium ions in the cell.
– Calcium allows the myosin heads to bind to the actin strands.
– ATP and phosphate are then used to produce the contractions (the myosin pulls in a rowing motion towards the middle of the sarcomere)
Relaxation
• Following contraction, the cell must return to it’s original shape.
– ATP is used, broken into ADP and phosphate.
– Ca+ ions are returns to their location.
– Actin and Myosin return to original location.
– Relaxation is a necessary break in the contraction cycle, because ions need to return to original location, ATP and Oxygen need to be replenished.
Aerobic Vs. Anaerobic Contraction
Aerobic
• Requires oxygen
• Uses stored ATP
• Then, used direct phosphorylation of ADP when exertion increases.
Anaerobic
• When oxygen is depleted and ATP or ADP production cannot keep up with demands (prolonged or extremely intense exercise) .
• Generates energy via glycolysis.
• Produces lactic and pyruvate acids as waste products.
Muscle Fatigue
• This occurs when the muscle can no longer respond to nerve stimulus.
– With prolonged exercise, acids (waste products) build up in the cell and prevent the contraction mechanism from working.
– This can also be caused by severe electrolyte imbalance that prevents generation of action potential. (What do we say we need if we have cramps?)