Muscle Tissue Structure, Physiology, and Mechanics

Comprehensive practice flashcards in fill-in-the-blank style covering muscle tissue properties, sarcomere anatomy, neuromuscular excitation-contraction coupling, energy metabolism, muscle mechanics, and smooth/cardiac muscle physiology.

The ability of muscle to be passively stretched is called __________.

extensibility

The ability of a muscle membrane to conduct an action potential along its length is called __________.

conductivity

The spring-like ability of muscle to return to its resting length is called __________.

elasticity

A skeletal muscle contains connective tissue sheaths, blood vessels, arteries, __________ , and muscle fibers.

nerves

From smallest to largest, the organizational hierarchy is __________ → muscle fiber → __________ → whole skeletal muscle.

Myofibril; fascicle

From superficial to deep, the connective tissue coverings are __________ → Perimysium → Epimysium.

Endomysium

The cordlike connective tissue structure attaching muscle to bone is a __________.

tendon

The broad, flat connective tissue sheet that attaches a muscle to a bone or another muscle is an __________.

aponeurosis

Neurons that stimulate skeletal muscle contraction are called __________ neurons.

motor

Skeletal muscle fibers have many nuclei because embryonic muscle cells (__________ ) fuse together.

myoblasts

The calcium-storing membranous network surrounding myofibrils is the __________ reticulum.

sarcoplasmic

Inward extensions of the sarcolemma that transmit electrical signals deep into the fiber are __________.

transverse tubules (T-tubules)

Enlarged calcium reservoirs of the sarcoplasmic reticulum are called __________ __________.

terminal cisternae

Thick filaments are composed primarily of the protein __________.

myosin

The three major proteins associated with thin filaments are __________ , __________ , and __________.

actin, tropomyosin, and troponin

The protein found in thick filaments but not thin filaments is __________.

myosin

Each thick filament contains approximately __________ myosin molecules, each with two heads and two intertwined tails.

$200$ to $300$

The long cylindrical contractile organelles found by the hundreds or thousands in a muscle fiber are __________.

myofibrils

The dark band of a sarcomere is the __________ band.

A

The protein attachment boundary for thin filaments is the __________ disc.

Z

The lighter central region containing only thick filaments in a relaxed sarcomere is the __________ zone.

H

The light band containing thin filaments but no thick filaments is the __________ band.

I

Myosin heads bind to active sites located on __________.

actin

One sarcomere extends from one __________ disc to the next __________ disc.

Z; Z

The oxygen-binding protein inside muscle cells is __________.

myoglobin

A typical skeletal muscle cell contains approximately __________ mitochondria (select from 3, 30, 300, or 3,000).

$$300$$

Mitochondria and myoglobin support __________ respiration.

aerobic

Muscle cells store carbohydrate for rapid energy access in granules of __________.

glycogen

A motor unit consists of one __________ neuron and all the __________ fibers it controls.

motor; muscle

Fibers belonging to the same motor unit are generally __________ throughout much of the muscle rather than confined to a single fascicle.

dispersed (scattered)

The narrow gap between a motor neuron terminal and a muscle fiber is the synaptic __________.

cleft

Acetylcholine (ACh) is stored in synaptic __________.

vesicles

When an action potential reaches the motor neuron terminal, calcium enters through __________ -gated calcium channels.

voltage

ACh is released when vesicles fuse with the presynaptic membrane by __________.

exocytosis

ACh binds to receptors on the muscle fiber’s motor __________ __________.

end plate

The neurotransmitter initiating skeletal muscle excitation and ultimately calcium release is __________.

acetylcholine (ACh)

Calcium binds to the regulatory protein __________ on the thin filament.

troponin

The end plate potential results largely from __________ ions entering the muscle fiber, making its interior more __________.

sodium ($Na^+$); positive

The muscle action potential travels across the __________ and down the __________.

sarcolemma; T-tubules (transverse tubules)

During action potential repolarization, __________ -gated __________ channels open.

voltage; potassium ($K^+$)

In the crossbridge cycle, ATP hydrolysis to ADP and inorganic phosphate provides energy to __________ the myosin head.

cock (reset)

During the power stroke, the __________ head pulls a __________ filament toward the sarcomere center.

myosin; thin

For relaxation, ACh receptor channels close and calcium-release channels in the __________ __________ close.

sarcoplasmic reticulum

During relaxation, cytosolic calcium concentration __________; calcium dissociates from __________; and __________ again covers myosin-binding sites on actin.

decreases; troponin; tropomyosin

As crossbridges stop forming, muscle __________ helps restore resting length.

elasticity

Transferring phosphate from creatine phosphate to ADP supplies __________ ATP and does __________ require oxygen.

$1$; not

Glycolysis occurs in the __________ and does not directly require __________.

cytosol (cytoplasm); oxygen ($O_2$)

The net ATP yield of glycolysis per glucose molecule is __________ ATP.

$$2$$

During an approximately 60-second sprint, ATP comes primarily from phosphate transfer and __________.

glycolysis

Oxidative muscle fibers are generally __________ in color and __________ -resistant.

red; fatigue

Slow-twitch fibers have a __________ extensive capillary supply than fast-twitch fibers.

more

An intermediate muscle fiber is a fast-twitch, __________ fiber.

oxidative (fast oxidative-glycolytic)

The excitation–contraction coupling events before measurable tension rises occur during the __________ period of a twitch.

latent

The period when crossbridges detach and tension declines is the __________ period.

relaxation

Increasing stimulus intensity recruits additional motor units; this process is called __________.

recruitment

Increasing stimulus __________ (not intensity) produces wave summation.

frequency

Muscle tone results from __________ nervous system activity and helps __________ joint position.

involuntary; stabilize

During an isometric contraction, muscle length __________ change.

does not

The most prevalent skeletal muscle fiber category identified in the exam is __________ -twitch fibers.

fast

An elevated concentration of inorganic __________ may contribute to muscle fatigue by disrupting contraction-related processes.

phosphate ($P_i$)

Loss of muscle size after inactivity is called __________.

atrophy

The muscle type with one nucleus, thick and thin filaments, and no Z discs is __________ muscle.

smooth

Uterine smooth muscle growth during pregnancy involves both __________ (increase in cell size) and __________ (increase in cell number).

hypertrophy; hyperplasia

The latchbridge mechanism that maintains tension efficiently is characteristic of __________ muscle.

smooth

In smooth muscle, calcium binds __________, which activates myosin light-chain __________.

calmodulin; kinase

Smooth muscle contraction is regulated in part by the __________ nervous system.

autonomic

After being stretched for a prolonged time, smooth muscle can adapt by __________.

relaxing (stress-relaxation response)

Smooth muscle whose cells are stimulated individually is called __________ smooth muscle.

multiunit

The most abundant smooth muscle type is __________ -unit, also known as __________ smooth muscle.

single; visceral

In single-unit smooth muscle, neurotransmitters are released from autonomic neuron __________ at __________ junctions.

varicosities; diffuse

Striated, branching, Y-shaped muscle cells connected by intercalated discs are __________ muscle cells.

cardiac

The smooth muscle type with relatively independent innervation resembling motor-unit organization is __________ -unit smooth muscle.

multiunit