BIOS 1300 Lab 7: Muscular Tissue and Axial Musculature Comprehensive Study Guide

Vocabulary practice flashcards covering muscular tissue organization, histology, contraction physiology, orthopedic tests, and axial muscles.

Fusiform

Describing a muscle that is tapered at both ends and wider in the middle, resembling the shape of a spindle. This structure allows for efficient force generation and movement.

Parallel

muscle fibers are arranged in the same direction, allowing for greater range of motion but less power compared to other muscle fiber arrangements.

Triangular

A muscle shape characterized by a broad origin and a narrow insertion, resembling a triangle. This structure allows for a strong contraction while maintaining a lighter weight.

Unipennate

A type of muscle arrangement where the muscle fibers are oriented at a single angle, attaching to one side of the tendon, resembling a feather.

Bipennate

A type of muscle arrangement where the muscle fibers are oriented at two angles, attaching to both sides of the tendon, resembling a double feather.

Multipennate

A type of muscle arrangement where the muscle fibers are oriented at multiple angles, attaching to the tendon in a way that resembles multiple feathers.

Circular

A type of muscle arrangement where the muscle fibers are organized in a circular pattern around an opening, allowing for contraction and control of the opening's diameter.

Main Functions of the Muscular System

Produce movement

Maintain body posture and position

Stabilize Joints

Generate Heat

Muscle attachment types

Direct, Fleshy, Tendon, and Aponeurosis

Direct Muscle Attachment

A type of muscle attachment where the muscle fibers are directly attached to the bone or perichondrium of cartilage, allowing for a strong connection and movement.

Fleshy (indirect) Muscle Attachment

A type of muscle attachment where the muscle fibers insert onto other soft tissues

Tendon (indirect) Muscle Attachment

A type of muscle attachment in which the muscle fibers connect to the bone through a rope-like structure made of dense connective tissue, providing stability and facilitating movement.

Aponeurosis (indirect) Muscle Attachment

A type of muscle attachment where the muscle fibers are attached to a broad, flat sheet of connective tissue, enabling force transmission over a wide area.

Epimysium

The outermost dense connective tissue sheath wrapping the entire exterior of a skeletal muscle, extending into the tendon

Perimysium

The intermediate layer of connective tissue sheath that partitions muscle fibers into bundles called fascicles

Endomysium

The deepest, innermost layer of connective tissue that wraps around each individual muscle fiber or cell located directly exterior to the sarcolemma.

Sarcolemma

The specialized plasma membrane of a muscle cell/fiber that conducts and propagates electrical action potentials for contraction.

Myofibril

A rodlike contractile organelle composed of bundles of myofilaments organized into repeating sarcomeres arranged end to end.

Sarcomere

functional unit of a muscle extending from one $Z$-disc to the adjacent $Z$-disc.

Striations

The alternating microscopic light ($I$-bands) and dark ($A$-bands) bands that impart a banded or striped appearance to skeletal and cardiac muscle fibers.

Z-disc (Z-line)

The protein disc serving as the structural anchor line for thin (actin) filaments that marks the lateral boundaries of an individual sarcomere.

M-line

The central structural protein anchor line in the middle of the sarcomere that cross-links thick (myosin) filaments.

A-band

The dark striation band spanning the entire length of the thick filaments, including the outer zones where thick and thin filaments overlap.

I-band

The light striation band centered on the $Z$-disc that consists exclusively of thin (actin) filaments.

H-zone (H-band)

The pale central region within the $A$-band that contains thick (myosin) filaments only, with no overlapping thin filaments when the sarcomere is relaxed.

Myosin

The contractile protein that makes up thick filaments, featuring two golf club-shaped heads that twist together to form cross-links to pull thin filaments toward the $M$-line.

Actin

The primary contractile protein of thin filaments containing specific binding sites for myosin heads to attach during muscle contraction.

Tropomyosin

A regulatory protein strand wrapped along thin filaments that blocks the myosin-binding sites on actin when a muscle fiber is relaxed.

Troponin

A globular regulatory protein complex bound to tropomyosin that binds calcium ions ($\text{Ca}^{2+}$), causing a conformational change that moves tropomyosin away from actin binding sites.

Triad

1 T-tubule and 2 Terminal cisternae

Sarcoplasmic Reticulum

An elaborate smooth endoplasmic reticulum network running longitudinally along the muscle fiber that stores and releases calcium ions ($\text{Ca}^{2+}$) during contraction.

Terminal Cisternae

Enlarged end-sacs of the sarcoplasmic reticulum that flank transverse tubules and act as major calcium storage reservoirs.

Transverse (T) Tubules

Tubular invaginations of the sarcolemma located at the $A$-band/$I$-band junctions, filled with extracellular fluid, that rapidly propagate electrical signals into the muscle fiber interior.

Motor Unit

one nerve fiber and all the muscle fibers innervated by it; receives electrical signals

Neuromuscular Junction (NMJ)

The functional synapse between the synaptic end bulb of an axon terminal and the motor end plate of the sarcolemma on a skeletal muscle fiber.

Acetylcholine (ACh)

The neurotransmitter stored inside synaptic vesicles at the motor end bulb that binds ligand-gated cation channels on the motor end plate to initiate local depolarization.

Synapse

a cleft between motor neuron and motor end-plate

Motor End Plate

The specialized, pocketed region of the sarcolemma opposite the synaptic end bulb that contains approximately $30\text{ million}$ acetylcholine receptors.

Excitation-Contraction Coupling

The physiological sequence that couples an electrical action potential travelling across the sarcolemma and down $T$-tubules to the chemical release of $\text{Ca}^{2+}$ from the sarcoplasmic reticulum.

Sliding Filament Mechanism

The model of muscle contraction wherein myosin heads pull thin actin filaments inward toward the $M$-line, bringing $Z$-discs closer together and shortening the sarcomere without changing filament lengths.

Twitch Contraction

A brief, involuntary contraction of all muscle fibers in a single motor unit in response to a single nerve action potential or electrical stimulus.

Latent Period

The brief delay or lag phase between the initial application of an electrical stimulus and the onset of visible muscle force development.

Threshold Stimulus

The minimum stimulus intensity required to depolarize a motor unit sufficiently to produce a visible muscle twitch contraction.

Subthreshold Stimulus

A stimulus intensity that causes sensation but lacks sufficient voltage to elicit an observable twitch contraction.

Maximal Stimulus

The highest stimulus intensity beyond which no further increase in contraction force occurs, because all available motor units have been fully recruited.

Wave Summation

The additive physiological phenomenon where multiple stimuli are delivered before a muscle can fully relax, generating increased tension with each successive stimulus.

Unfused (Incomplete) Tetanus

A sustained muscle contraction produced by high stimulation frequency where partial relaxation occurs between successive twitches, allowing tension to build up in steps.

Fused (Complete) Tetanus

A smooth, sustained maximal contraction occurring at exceptionally high stimulation frequencies with zero relaxation between individual stimuli.

Treppe

The staircase or warm-up effect characterized by a progressive rise in twitch amplitude when consecutive stimuli of identical strength are applied to a rested muscle, caused by residual calcium buildup.

Muscle Fatigue

The physiological loss of muscle contractility and tension generation due to the depletion of intracellular energy stores during prolonged or repetitive stimulation.

Muscle Tone

The resting, involuntary basal state of partial muscle contraction that stabilizes joint positions, maintains posture, and defines muscle shape at rest.

Muscle Tension

load actively placed on the muscle that changes length, shape when in use

Frequency

the rate at which nerve impulses arrive at the NMJ can change, resulting in a change in tension of the muscle

Concentric Contraction

An isotonic contraction in which muscle tension exceeds resistance, causing the muscle to actively shorten while moving a load (e.g., the lifting phase of a bicep curl).

Eccentric Contraction

An isotonic contraction in which muscle tension is maintained while the muscle actively lengthens to control deceleration and act like brakes, protecting structures from damage.

Isometric Contraction

A muscle contraction where internal tension is produced without changing muscle length or moving a joint (e.g., pushing against an immovable wall or holding a plank).

TENS Unit

A transcutaneous electrical nerve stimulation device used clinically to modulate acute and chronic pain by stimulating cutaneous nerves, preventing pain signaling to the brain and promoting endorphin release.

Diaphragm

The primary muscle of respiration that originates on the sternum, lower ribs, and $L_1-L_3$ vertebrae, inserts onto its central tendon, and flattens upon contraction to increase thoracic volume during inspiration.

Muscles Associated w/Breathing

Diaphragm, External intercostals, internal intercostals, scalenes, transversus thoracis

Lachman's Test

An orthopedic physical examination test for anterior cruciate ligament ($\text{ACL}$) tears, performed with the patient supine and knee flexed to $30^\circ$ while applying an anterior translation force to the proximal tibia.

Posterior Drawer Test

An orthopedic test evaluating posterior cruciate ligament ($\text{PCL}$) integrity, performed by applying a posterior force to the proximal tibia with the patient's knee flexed to $90^\circ$.

Valgus Stress Test

An orthopedic clinical evaluation for medial collateral ligament ($\text{MCL}$) tears, performed by placing one hand on the lateral knee and applying valgus force to the medial malleolus with the knee slightly flexed.

Varus Stress Test

An orthopedic clinical evaluation for lateral collateral ligament ($\text{LCL}$) tears, performed by placing one hand on the medial knee and applying varus force to the lateral malleolus with the knee slightly flexed.

Anterior Drawer Test (Ankle)

An orthopedic clinical test evaluating tears in the anterior talofibular and calcaneofibular ligaments by applying anterior linear force to the calcaneus while stabilizing the malleoli with the ankle at $90^\circ$.