BIOL 2101 SKELETAL MUSCLE HISTOLOGY AND PHYSIOLOGY LAB QUIZ

What are the functions of skeletal muscle?

1. Pulling on bones to produce movement at the joints

2. Posture

3. Supporting and protecting soft tissues of abdome + pelvis

4. Controlling entrances and exits of digestive + urinary systems

5. Producing heat to maintain internal body temp

6. Reservoir for amino acids

Tendon

1. Bundle of dense reg CT located at ends of muscle

2. Contains collagen fibers

3. Attaches muscle to bone

Aponeurosis

A broad sheet tendon

Fascicle

Bundle of muscle of fibers within a muscle; surrounded by perimysium

Muscle fiber

Single multinucleate muscle cell wrapped in endomysium

Endomysium

CT layer that encases individual muscle fibers within fascicle; contains capillaries and neurons associated with its muscle fiber

Perimysium

Fibrous CT rich in collagen + elastin that divides muscle into fascicles;  contains nerves and bv

Sarcomere

The functional unit of a myofibril that extends from one Z disc to the next; overlapping thick and thin filaments slide past each other to produce contraction

What are the components of a sarcomere?

I band, A band, H zone, M line, Z disc

I band

Light region of each band that contains only thin filaments

A band

Dense central region that contains thick and thin filaments

H zone

Lighter region around M line that contains only thick filaments

M line

Connects thick filaments tail to tail in the center of sarcomere

Z disc

End line of sarcomere; thin filaments are anchored to it

Troponin

Causes muscle contractions by binding Ca+ 

Tropomyosin

Covers myosin bindind sites on the actin filaments

Actinin

Connects actin filaments to Z disc

Titin

Responsible for passive elasticity of muscle fiber

Dystrophin

Protects muscle fibers against damage during contraction

Thick myofilament

Composed primarily of myosin; creates banded pattern within sarcomere

Thin myofilament

Composed primarily of actin; creates banded pattern within sarcomere

Sarcoplasmic reticulum

Tubular network wrapped around each myofibrl; contains high Ca2+ concentration; Ca2+ is released into muscle fiber when depolarized to trigger muscle contraction

Myofibril

Subunit of muscle fiber that consists of a series of sarcomeres; appears banded under microscope due to arrangement of myofilaments

Mitochondria

Produce ATP to power muscle contraction

Transverse tubule

Continuous with sarcolemma; forms network through muscle fiber; carries wave of depol throughout muscle fiber 

Sarcolemma

Plasma membrane of muscle fiber

Neuromuscular junction

Point at which a branch of motor neuron connects with a single muscle fiber

Each muscle fiber has _____ NMJ

ONE

What is the result of ACh receptors in the sarcolemma binding to sodium channels?

Sodium influx results in depol of muscle fiber (AP); AP then spreads through the sarcolemma eventually leading to muscle contraction

Axon of motor neuron

Branch of efferent motor neuron that transmits AP to muscle fiber

Axon terminal

Distal portion of a motor neuron; arrival of AP causes calcium influx; calcium influx causes migration of synaptic vesicles to the neuromuscular interface

Synaptic vesicles

Located at tip of axon terminal; contan ACh; fuse with plasma membrane of axon terminal to release ACh into synaptic cleft

Synaptic cleft

Narrow space between axon terminal and motor end plate; contains AChE to break down ACh into acetic acid and cholin

Motor end plate

Specialized region of sarcolemma; forms muscle side of neuromuscular junction

What are the two requirements for contraction of a skeletal muscle to occur?

Stimulation by a motor neuron at NMJ and energy in the form of ATP

Sliding Filamement Theory

1. Motor neuron depolarizes sarcolemma at motor end plate

2. Wave of depol spreads throughout muscle fiber, causing release of Ca2+ from SR

3. Ca2+ triggers cross-bridges to form between thick and thin filaments

4. Cross-bridges move to pull thin filaments toward center of sarcomere

5. Z lines are brought closer together, increasing zone of overlap between thick and thin filaments

The state of being contracted continues until…

1. Motor neuron ends its stimulation of the motor end plate, causing Ca2+ to return to the SR; cross-bridge formation loses its trigger and stops

2. Or aerobic respiration is not able to supply sufficient ATP; cross-bridge movement cannot continue

Individual muscle cells are called…

muscle fibers

Each muscle fiber is a bundle of ___________

myofibrils

Myofibrils consists of a series of smaller units called ___________

sarcomeres

The _____ filaments are the least dense

THIN

The A band consists of…

Zone of overlap and H zone

What happens when the sarcomere is fully contracted?

Z disc closer together; I band and H zone disappear; zone of overlap increases; no change in size of A band

Cross-bridge formation

1. Myosin head (thick filament) attaches to actin (thin filament)

2. Working stroke- the myosin head pivots and bends, pulling the thin filament toward the midline (rigor mortis)

3. ATP attaches to the myosin head, causing it to detach from the actin filament

All-or-none principle

Individual muscle fibers contract to 100% of their ability or not at all

Graded muscle contraction

The recruitment of only the number of muscle fibers necesssary to accomplish a particular task

Twitch

Quick muscle contraction in response to a single stimulus

Threshold stimulus

Minimum stimulus that is capable of producing a muscle twitch

What are the components of a single twitch?

latent phase, contraction phase, and relaxation phase

Latent phase

Lag time between nerve stimulation and the beginning of a muscle contraction

Contraction phase

Muscle fibers are shortening; tension is being developed

Relaxation phase

Muscle fibers are returning to resting length; tension decreases

Individual twitches

Low rate of stimulation that produces isolated muscle twitches

Summaation

Increased rate of stimulation; individual twitch peaks are still visible; next twitch occurs before muscle returns to resting length; each twitch produces more force until maximum force is reached

Tetanus

High rate of stimulation; produces a smooth sustained contraction; max sustained force a muscle is capable of

Fatigue

High rate of stimulation contains until muscle is no longer physiologically capable of contracting; primarily due to depletion of ATP stores when CV system is unable to deliver sufficient oxygen to meet ATP production demands of muscle