Week 9: Muscle Microanatomy and Histology

skeletal muscle

• striated

• voluntary contractions from nervous system

• acts on bone to produce motion

smooth muscle

• non- striated

• involuntary peristaltic

• lines the gi tract, respiratory tract, blood vessels of the circulatory system, urinary tract, and reproductive organs

• multinucleated

• vascularized and innervated

cardiac muscle

• striated

• branching fibers connected by intercalated discs; heart beat

• synchronized involuntary contraction

direct vs indirect attachment of smooth muscle

direct- straight attachment from muscle to bone via the periosteum or perichondrium

indirect - attachment via the tendon or apopneurosis (sheet of connective tissue)

label 1-6 of the composition of skeletal muscle

epimysium, fasicle, muscle fibers, endomysium, capillary, perimysium

describe epimysium, perimysium, and endomysium

epimysium- outermost sheath that surrounds the entire muscle

perimysium- surrounds a bundle of muscle fibers called a fasicle

endomysium- smallest sheat; surrounds a singular muscle fiber

fasicle

bundle of muscle cells with motor units

motor unit

a motor neuron and all the muscle fibers it innervates

muscle fiber

made up of myofibrils

myofibrils

rod shaped organelles with sarcomeres

sarcomeres

smallest unit of muscle

contractile unit of muscle of myosin and actin

myosin and actin

contractile proteins (myofilaments) that slide past each other to create muscle contraction

label and describe the Z disc, H zone, I band, A band, M line, and sarcomere

• Z disc- represent the edges of the sarcomere

• M line- represents the middle of the sarcomere

• A band- represents the length of myosin **never changes in length

• I band- represents the portion of actin that has no myosin overlap and contains only thin filaments ** will shorten when the muscle contracts

• H Zone- represents the portion of myosin that has no actin overlap and contains only thick filaments ** will shorten/disappear when muscle contracts

sliding filament theory

actin and myosin slide past each other during muscular activity to shorten the muscle causing contraction

sarcolemma

plasma membrane of a muscle cell

terminal cisternae and sarcoplasmic reticulum

calcium storage, release and uptake

t- tubule

allows action potential into muscle fiber

triad

t-tubule between two terminal cisternae

describe EC coupling

1. Acetylcholine released from the axon terminal binds to receptor on the sarcolemma

2. an action potential is generated and travels down the t-tubule

3. calcium is released from the SR in response to the change in voltage

4. calcium binds troponin; cross bridges form between actin and myosin

5. acetylcholinesterase removes acetylcholine from the synaptic cleft

6. calcium is transported back into the SR

7. tropomyosin binds active sites on actin causing the cross- bridge to detach

powerstroke

movement of the myosin head, bound to actin, towards the M-line of the sarcomere which pulls actin towards the center of the sarcomere, shortening the I-band, H-zone, and the entire sarcomere

describe the cross-bridge cycle

1. binding of actin to myosin

2. power stroke

3. rigor (myosin in low-energy form)

4. unbinding of myosin and actin

5. cocking of the myosin head (myosin in high-energy form)