Muscle Tissue Anatomy & Physiology

These flashcards cover the anatomy and physiology of skeletal muscle tissue, including gross and microscopic structure, characteristics, and the components of the neuromuscular junction.

Excitability

The ability to respond to a stimulus by changing electrical membrane potential.

Conductivity

Involves sending an electrical change down the length of the cell membrane.

Contractility

Exhibited when filaments slide past each other, enabling the muscle to cause movement.

Extensibility

The ability of muscle tissue to be stretched.

Elasticity

The ability of a muscle to return to its original length following a lengthening or shortening.

Fascicle

A bundle of muscle fibers (muscle cells) within a whole muscle.

Epimysium

A layer of dense irregular connective tissue that wraps the entire whole muscle.

Perimysium

Dense irregular connective tissue that wraps a fascicle and houses many blood vessels and nerves.

Endomysium

A delicate layer of areolar connective tissue wrapping an individual muscle fiber for electrical insulation and capillary support.

Tendon

A cordlike structure composed of dense regular connective tissue that attaches muscle to bone.

Aponeurosis

A thin, flattened sheet of dense irregular tissue used for muscle attachment.

Deep fascia

Dense irregular connective tissue superficial to the epimysium that separates individual muscles and binds those with similar functions.

Superficial fascia

Areolar and adipose connective tissue superficial to deep fascia that separates muscles from the skin.

Sarcoplasm

The cytoplasm of a muscle fiber containing typical organelles plus contractile proteins.

Myoblasts

Embryonic cells that fuse together to form multinucleated skeletal muscle fibers.

Satellite cells

Undifferentiated myoblasts that remain in muscle tissue to assist in support and repair of fibers.

Sarcolemma

The plasma membrane of a muscle fiber, containing voltage-gated ion channels for electrical conduction.

T-tubules

Transverse tubules that extend deep into the muscle cell and contain voltage-sensitive calcium channels.

Sarcoplasmic reticulum

An internal membrane complex similar to smooth ER that stores calcium ions within the muscle fiber.

Terminal cisternae

Blind sacs of the sarcoplasmic reticulum that serve as specialized reservoirs for calcium ions.

Triad

A structure formed by two terminal cisternae with a T-tubule positioned in between them.

Myofibrils

Bundles of myofilaments surrounded by the sarcoplasmic reticulum, with hundreds to thousands residing in a single cell.

Thick filaments

Contractile protein filaments consisting of bundles of $200$ to $500$ myosin molecules.

Thin filaments

Contractile protein filaments composed of twisted strands of actin, which include G-actin monomers with myosin binding sites.

Tropomyosin and Troponin

Regulatory proteins associated with thin filaments that help control muscle contraction.

Sarcomere

The functional repeating unit of myofilaments, composed of overlapping thick and thin filaments.

Z discs

Specialized proteins at both ends of a sarcomere that serve as anchors for thin filaments.

I bands

Light-appearing regions of a sarcomere that contain only thin filaments and are bisected by the Z disc.

A band

The dark-appearing central region of a sarcomere containing the entire length of the thick filaments and overlapping thin filaments.

H zone

The central portion of the A band where only thick filaments are present; it disappears during maximal contraction.

M line

A protein meshwork structure at the middle of the H zone that serves as the attachment site for thick filaments.

Connectin

A protein extending from the Z disc to the M line that stabilizes thick filaments and has springlike properties for passive tension.

Dystrophin

A protein that anchors myofibrils to sarcolemma proteins; its deficiency or defect causes muscular dystrophy.

Myoglobin

A protein within muscle cells that stores oxygen for use in aerobic ATP production.

Motor unit

A single motor neuron and all the muscle fibers it controls.

Neuromuscular junction

The specific location where a motor neuron innervates a muscle fiber, typically at the mid-region of the fiber.

Synaptic knob

The expanded tip of a motor neuron axon that contains synaptic vesicles filled with acetylcholine (ACh).

Synaptic cleft

A narrow, fluid-filled space separating the synaptic knob from the motor end plate.

Motor end plate

A specialized region of the sarcolemma with numerous folds and ACh receptors.

Acetylcholinesterase

An enzyme residing in the synaptic cleft that breaks down acetylcholine (ACh) molecules.

Resting Membrane Potential (RMP)

The electrical charge across the sarcolemma when the muscle fiber is at rest, which is approximately $-90\,mV$.

Duchenne muscular dystrophy (DMD)

A hereditary disease caused by defective dystrophin, leading to damaged sarcolemma, muscle atrophy, and eventually death, usually by age $30$.

Myasthenia Gravis

An autoimmune disease where antibodies bind to ACh receptors, leading to their removal, decreased muscle stimulation, and rapid fatigue.