Honors Anatomy & Physiology

3 types: 1. Skeletal striated & voluntary 2. Cardiac striated & involuntary 3. Smooth Smooth & involuntary

most attached to bone striations: see light & dark bands under microscope

found only in walls of heart chambers heart has a pacemaker that initiates each contraction called autorhymicity controlled by hormones & neurotransmitters

in walls of hollow organs attached to hair follicles some autorhythmic (wall of intestines) regulated by ANS motor neuron& hormones

1. producing body movements moving whole body or parts of body

2. stabilizing body position skeletal muscles stabilize joints & halp maintain body positions postural muscles hold sustained contractions (holding head up all day)

3. storing & moving substances w/in body storing: accompanied by sustained contractions of ringlike bands of smooth muscle called sphincters (hold material in organ) contraction/relaxation of smooth & cardiac muscle moves material thru bld vessels  heart  bld vessels

4. generating heat process called thermogenesis most of heat generated by muscle contraction maintains normal body temp of 37°C shivering: involuntary contraction of skeletal muscle increases heat production

1. electrical excitability ability to respond to certain stimuli by producing electrical signals called action potentials 2 main types stimuli: 1. autorhythmic electrical signals 2. chemical stimuli (neurotransmitters) released by neurons

2. contractility ability of muscle fibers to contract forcefully when stimulated by an action potential muscle fiber shortens & pulls on whatever it is attached to if force > resistance of object, movement occurs

3. extensibility ability of muscle tissue to stretch w/out being damaged smooth muscle fibers are stretched every time your stomach or bladder is really full

4. elasticity ability of muscle tissue to return to original length & shape after contraction or extension

fascia: sheet or broad band of fibrous CT that supports & surrounds muscles or other organs 2 layers: superficial & deep

2. 3 layers of CT extend from deep fascia  deeper into muscle tissue 1. epimysium: outermost layer, encircles entire muscle 2. perimysium: surrounds groups of 10 – 100 muscle fibers = a fascicle 3. endomysium: surrounds individual muscle fibers

3. tendon: extension of epimysium, perimysium, & endomysium beyond muscle that attaches the skeletal muscle to another structure (bone or another muscle)

hypertrophy: enlargement of existing muscle fibers ex: muscle growth in newborn hyperplasia: increase in # of muscle fibers ex: growth hormone causes increase in #s from childhood  adult fibrosis: replacement of muscle by fibrous scar tissue satellite cells: stem cells in muscle tissue; limited capacity

sarcolemma: plasma membrane sarcoplasm: cytoplasm myofibril: contractile organelles; thread-like structures; each extends length of muscle fiber

T tubules: (transverse) invaginations of sarcolemma into sarcoplasma; increasing surface area filled with interstitial fluid ensures action potentials excites all parts of muscle fiber

sarcoplasmic reticulum: (SR) endoplasmic reticulum that encircles individual myofibrils dilated end sacs called terminal cistern T tubule + 2 terminal cisterns = triad in relaxed muscle fiber SR stores Ca++ release of Ca++ triggers contraction

3 kinds proteins in myofibrils: 1. contractile proteins myosin make up thick filaments, golf-club shape (myosin head) actin  thin filaments 2. regulatory proteins tropomyosin & troponin: both in thin filaments 3. structural proteins ~12 different ones function in alignment, stability, elasticity, & extensibility of myofibrils

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1. ATP hydrolysis ATP attached to myosin head 2. attachment of myosin head to actin to form cross bridges 3. power stroke cross bridges rotate  center  slides thin filament past thick filament 4. detachment of myosin from actin ATP binds to myosin head & cross bridges released

somatic motor neurons innervate muscle fibers to contract

synapse: functional junction between 2 neurons or between a neuron & an effector (muscle or gland); may be electrical or chemical 1 st side of synapse: end of axon of motor neuron called synaptic end bulb then synaptic cleft (the space) lastly, motor end plate: part of sarcolemma that has receptors for neurotransmitter acetylcholine (ACh)

1. release of ACh 2. activation of ACh receptors 3. production of muscle action potential 4. termination of ACh activity

ACh stored in vesicles in synaptic end bulb action potential travels down axon  reaches synaptic end bulb  induces exocytosis of neurotransmitter from synaptic vesicles ACh diffuses across synaptic cleft toward motor end plate

2 molecules of ACh bind to ACh receptors embedded in sarcolemma  opens ion channel  allows Na+ diffuse across membrane

inflow Na+ makes inside of muscle fiber more + charged this change in membrane potential triggers a muscle action potential  propagates along sarcolemma  T tubules this causes SR to release Ca++  sarcoplasm  contraction

effect of ACh binding short because ACh is rapidly broken down by enzyme acetylcholinesterase (AChE)

@ midpoint of muscle fiber: muscle action potential propagate  both ends of fiber allows simultaneous activation & so contraction of all parts of muscle fiber

South American plant derivative causes paralysis by binding to & blocking ACh receptors on motor end plates curare-like drugs used in general anesthesia to relax skeletal muscles

disease caused by Clostridium botulinum  toxin that blocks exocytosis of synaptic vesicles so no ACh released so no muscle contraction toxin one of most lethal chemicals known causes death by paralyzing skeletal muscles: breathing stops when diaphragm & intercostal muscles stop contracting

“equal tension” force of contraction developed by muscle remains almost constant while muscle changes its length used for body movements & for moving objects 2 types: 1. concentric isotonic contraction 2. eccentric isotonic contraction

when tension generated is enough to overcome resistance of object being moved …muscle shortens & pulls on another structure (tendon) ….producing movement that reduces angle at a joint

tension exerted by the muscle resists movement of the load (whatever was lifted up) slowing the lengthening process

tension generated by the muscle is < tension needed to overcome resistance of the object muscle does not change its length

FQE FQE

same arrangement actin/myosin: striations muscle fibers branched *intercalated discs: unique to cardiac muscle autorhymicity alone: 75 bpm remains contracted x’s longer than skeletal muscle after 1 action potential due to prolonged delivery of Ca++ (SR + interstitial fluid larger & more #s of mitochondria

+thick & thin filaments but no T tubules & less SR so no striations

from mesoderm starts ~4 wks cardiac muscle forms tubes  bends & folds to form heart

spasm: sudden involuntary contraction of a single muscle is a large group of muscles

tic: an involuntary twitching by muscles that are normally under voluntary control

tremor: rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement

fasiculation: involuntary, brief twitch that is visible under the skin; occurring irregularly & not ass’c with movement seen in MS or ALS

fibrillation: spontaneous contraction of single muscle fiber that is not visible under skin but can be recorded by EMG (electromyograph) signals destruction of motor neurons

muscle strain: tearing of muscle due to forceful impact + bleeding +pain most often affect quadraceps femoris tx‘d RICE (rest, ice, compression ie a wrap, elevation)