Muscle Tissue Ch 9 Flashcards
Skeletal Muscles
Organs that attach to and cover the skeleton
Have striations
Voluntary muscle
Cardiac Muscle
Only in heart
Striated
Involuntary
Smooth Muscle
In walls of hollow, visceral organs.
Nonstriated
Involuntary
4 Characteristics of Muscle Tissue
Excitability
Contractility
Extensibility
Elasticity
4 Major Muscle Functions
Movement
Posture
Stabilize joints
Generate heat
Additional functions of muscle
Protect internal organs
Form valves
Dilate and constrict pupils
Arrector pili in hair follicles
Nerve and blood supply
Generally 1 nerve, 1 artery, and 1 or more veins for each muscle.
3 Connective tissue sheaths of muscle
Epimysium: Surround whole muscle
Perimysium: Surrounds each fascicle
Endomysium: wispy sheath that surrounds each muscle fiber
Attachments
Direct: fleshy attachments, epimysium is attached directly to outside of bone or cartilage.
Indirect: more common, tissue extends beyond muscle as tendon or aponeurosis and anchors to bone or cartilage.
Insertion
The attachment at the movable bone
Origin
The attachment at the immovable or less movable bone.
Sarcolemma
Plasma membrane
Sarcoplasm
Cytoplasm of a muscle cell
Contains large amounts of glycosomes (glycogen) and myoglobin (oxygen).
Myofibrils
80% of cellular volume
rod-like cylinders that run the length of the cell
Sarcomere
smallest, contractile, functional unit of skeletal muscle.
Striations
Dark and light bands that wrap around the myofibril.
Dark:A bands
Light: I bands
Myofilaments
Smaller structures in sarcomeres: think and thin
Thick filaments
Central
Myosin (red)
Length of A band
Thin filaments
Lateral
Actin (blue)
Extend across I band into A band
Tropomyosin
rob-shaped protein, spiral around the actin core. Stabilize it and block myosin-binding sites.
Troponin
Globular-polypeptide complex
TnI: Inhibits, binds to actin
TnT: binds to tropomyosin, positions actin
TnC: binds calcium ions
Elastic filiments
Giant protein titin Extends from Z disc Forms thick filament core Holds think in place Helps muscle spring back
Sacroplasmic Reticulum
Interconnecting tubules surround each myofibril. Regulates calcium
T Tubules
Transverse, at each A band I band junction Increase muscle fibers surface area continuous with extra cellular space Encircle each sarcomere Ensures synchronized contraction
Terminal Cisterns
“end sacs”
Perpendicular cross channels at A-I band junctions
Involved in energy production
Triad Relationship
T tubules, SR and Terminal Cisterns.
T-tubules: act as voltage sensors
SR: gated channels through which terminal cisterns release Ca2+
Sliding filament model of contraction
During contraction thin filaments slide past thick so that the actin and myosin filaments overlap to a greater degree.
Neuromuscluar junction (NMJ)
or end plate, is a synapse between a muscle cell and neuron. Only one per each muscle fiber, located midway.
Acetylcholine
Neurotransmitter released into the synaptic cleft and open NA+ and K+ channels. Triggers action potential.
Achetylcholinestrase
enzyme that breaks down ACh and prevents continues muscle fiber contraction.
Excitation-Contraction Coupling (E-C)
- AP moves along sarcolemma & down T tubules
- Ca ions are released
- Ca bind to troponin & removes tropomysin
- Contraction begins
Cross bridge cycle
- Cross bridge forms, myosin head attached to actin
- Power stroke, myosin bends and pulls actin towards M line, low energy
- Cross bridge breaks, ADP attaches and weakens link
- Cocked position, myosin returns to high energy state.
Muscle tension
Isometric: load does not move
Isotonic: Load moves
Motor unit
One or more neurons and all the muscle fibers it supplies.
Muscle twitch
Muscles responce to single action potential
- Latent period:first few ms after stimulation
- Period of contraction: peak tension
- Period of relaxation: reentry of Ca into SR muscle tension returns to 0
Graded muscle response
Variations needed for proper control of muscle contractions
Muscle response to changes in stimulus frequancy
- Single stimulus =single twitch
- unfused tetanus wave/temporal summation: second contraction begins before the first begins
- Fused tetanus: no relaxation between frequencies.
Muscle response to changes in stimulus strength
- Sub-threshold: no response
- Threshold: contracts more and more as stimulus increases.
- Maximal: strongest & all motor unit muscles are recruited
Two Isotonic contractions
Concentric: muscle shortens and does work
Eccentric:muscle generates force as it lengthens.
Muscle tone:
Involuntary muscle contraction that maintains posture and protects joints.
3 ways to provide energy for contraction
- Direct phosphorylation
- Anaerobic pathway
- Aerobic pathway
Direct Phosphorylation
Coupled reaction of Creatine Phosphate and ADP
Uses no O2,
Creates 1 ATP
Lasts 15 seconds
Anaerobic pathway
Glycolysis & Lactic acid formation
No O2 needed
1 ATP per glucose
Lasts 30-40 seconda
Aerobic pathway
Cellular respiration
Uses O2
Produces 32 APT per glucose
Lasts hours
Muscle fatigue
Inability to contract.
For muscles to return to resting state:
- O2 reserves replenished
- Lactic acid converted to pyruvic acid
- Glycogen stores replaced
- ATP and CP replaces
Excess Postexercise Oxygen Consumption (EPOC)
Extra O2 the body needs to restore (Oxygen debt)
Heat production
40% of energy is converted into useful work and the rest is lost as heat.
Force of muscle contraction
- Number of muscles stimulated
- Size of fibers
- Frequency of stimulation
- Degree of muscle stretch
Muscle fiber types
Slow oxidative fibers
Fast oxydative fibers
Fast glycolytic fibers
Slow Oxydative Fibers
For endurance activities Contracts slowly Uses O2 Fatigue resistant small and red with many mitochondria and capillaries
Fast Oxydative Fibers
For Sprinting Contracts fast Mostly Aerobic red/pink, medium size Many mitochondria and capillaries
Fast Glycolytic Fibers
Short-term intense movements Fast contraction Anaerobic glycolysis Fast fatigue White, Large Few mitochondria and capilaries
