lecture exam 3

Tendon

Dense connective tissue cord that attaches muscle to bone (or occasionally to another muscle) and transmits the force of contraction.

Origin (Muscle)

The usually proximal, relatively fixed attachment point of a muscle to a bone.

Insertion (Muscle)

The usually distal, more movable attachment point of a muscle to a bone.

Sarcomere

The contractile unit of striated muscle; shortens during muscle contraction.

Biceps brachii

Two-headed arm muscle that flexes the elbow and supinates the forearm.

Triceps brachii

Three-headed arm muscle that extends the elbow joint.

Serratus anterior

‘Boxer’s’ or ‘hugging’ muscle that protracts and rotates the scapula; also helps elevate ribs when scapula is fixed.

Lever

A rigid bar (bone) that moves on a fixed point when a force is applied to overcome a load.

Effort

The force applied to a lever—supplied by muscle contraction.

Fulcrum

The pivot point of a lever system; typically a joint.

Load (Resistance)

The weight or force that is moved by a lever—often the weight of the body segment or an external object.

First-class lever

Lever with fulcrum between effort and load (e.g., atlanto-occipital joint when nodding).

Second-class lever

Lever with load between fulcrum and effort (e.g., plantar-flexion at the ball of the foot when standing on tiptoe).

Third-class lever

Lever with effort between fulcrum and load (e.g., elbow flexion by biceps brachii).

Fascicle

Bundle of skeletal muscle fibers surrounded by perimysium.

Parallel fascicular arrangement

Fascicles run alongside the long axis of the muscle; produces large range of motion (e.g., sartorius).

Fusiform muscle

Spindle-shaped muscle with expanded belly and tapered ends (e.g., biceps brachii).

Circular muscle

Fascicles arranged in concentric rings that close an opening (e.g., orbicularis oris).

Triangular (Convergent) muscle

Broad origin with fascicles converging toward a single tendon (e.g., pectoralis major).

Pennate muscle

Short fascicles attach obliquely to a central tendon, resembling a feather.

Unipennate

Pennate muscle with fascicles inserting into one side of the tendon (e.g., extensor digitorum longus).

Bipennate

Pennate muscle with fascicles inserting into both sides of a central tendon (e.g., rectus femoris).

Multipennate

Pennate muscle with several tendons and multiple rows of fascicles (e.g., deltoid).

Agonist (Prime mover)

Muscle chiefly responsible for producing a specific movement.

Antagonist

Muscle that opposes or reverses the action of an agonist.

Synergist

Muscle that assists a prime mover by adding extra force or reducing undesirable movements.

Plantar aponeurosis

Thick band of connective tissue spanning the sole of the foot from calcaneus to toes.

Plantar fasciitis

Inflammation or micro-tearing of the plantar aponeurosis, producing heel or sole pain.

Compartment syndrome

Painful condition caused by rising pressure within a fascial compartment, compromising blood flow and nerve function.

PRICE protocol

First-aid approach: Protection, Rest, Ice, Compression, Elevation—used to manage acute musculoskeletal injuries.

NSAID (Non-steroidal Anti-inflammatory Drug)

Medication such as ibuprofen or aspirin that reduces pain, fever, and inflammation without steroid hormones.

Skeletal Muscle Tissue

Voluntary, striated muscle attached to bones or skin; fibers are long, multinucleated cells responsible for body movements.

Cardiac Muscle Tissue

Involuntary, striated muscle of the heart composed of single-nucleated cells connected by intercalated discs to pump blood.

Smooth Muscle Tissue

Involuntary, non-striated, spindle-shaped muscle found in walls of viscera and blood vessels; moves substances via peristalsis.

Striations

Alternating light and dark bands in skeletal and cardiac muscle created by orderly arrangements of actin and myosin.

Intercalated Disc

Specialized junction containing gap junctions and desmosomes that electrically and mechanically link adjacent cardiac muscle cells.

Gap Junction

Protein channel connecting cytoplasm of two cells, allowing rapid ion flow and electrical communication (e.g., in cardiac muscle).

Spindle-shaped Cell

Cell that tapers at both ends and bulges in the middle; typical of smooth muscle fibers.

Peristalsis

Rhythmic, wave-like contractions of smooth muscle that propel contents through tubular organs (e.g., intestines).

Contractility

Property of muscle to shorten and generate pulling force.

Extensibility

Ability of muscle tissue to be stretched or lengthened without damage.

Elasticity

Ability of muscle to return to its original length and shape after contraction or extension.

Electrical Excitability

Capacity of muscle and nerve cells to respond to ionic imbalances (primarily Ca2+ and Na+) with action potentials.

Calcium Ion (Ca²⁺)

Divalent cation stored in the sarcoplasmic reticulum that triggers muscle contraction when released.

Sodium Ion (Na⁺)

Monovalent cation that moves through T-tubules and initiates action potentials in muscle fibers.

Actin

Thin filament protein that interacts with myosin to produce muscle contraction and forms part of striations.

Myosin

Thick filament motor protein whose heads bind actin and hydrolyze ATP to generate force during contraction.

Myoblast

Embryonic muscle precursor cell that differentiates and fuses to form muscle fibers.

Satellite Cell

Muscle stem cell located between sarcolemma and endomysium; fuses with fibers for growth and repair.

Muscle Fiber

Individual skeletal muscle cell; long, cylindrical, multinucleated, and packed with myofibrils.

Fascicle

Bundle of muscle fibers surrounded by perimysium within a whole muscle.

Endomysium

Delicate connective tissue sheath surrounding each individual muscle fiber.

Perimysium

Connective tissue layer encasing each fascicle of muscle fibers.

Epimysium

Dense connective tissue wrapping the entire muscle and continuous with tendons.

Tendon

Cord of dense regular connective tissue that anchors muscle to bone and is continuous with endo-, peri-, and epimysium.

Sharpie’s Fibers

Collagen fibers that embed tendons into periosteum, securing muscle attachments to bone.

Myofibril

Long, rod-like organelle inside muscle fibers composed of repeating sarcomeres; responsible for contraction.

Sarcolemma

Plasma membrane of a muscle fiber, invaginated to form T-tubules.

Sarcoplasmic Reticulum (SR)

Modified smooth ER in muscle fibers that stores and releases calcium ions for contraction.

Transverse (T) Tubule

Invagination of the sarcolemma that conducts action potentials deep into the muscle fiber.

Terminal Cistern

Enlarged end sacs of the sarcoplasmic reticulum that abut T-tubules and hold concentrated Ca²⁺.

Sarcomere

Smallest contractile unit of a myofibril, spanning from one Z-line to the next; contains overlapping actin and myosin.

Dystrophin

Cytoskeletal protein that anchors sarcomeres to the sarcolemma; mutations lead to muscular dystrophy.

Myo- / Sarco- Prefixes

Word roots indicating a relation to muscle (e.g., myofibril, sarcolemma).

Dense Regular Connective Tissue

Tissue with parallel collagen fibers providing great tensile strength; forms tendons and ligaments.

Mitochondrion

Organelle that produces ATP; abundant in muscle fibers to meet high energy demands.

Sarcomere

The smallest contractile unit of a myofibril, spanning from one Z disc to the next Z disc.

Thick Filament

Bundle of myosin molecules that appears dark and forms part of the A band.

Thin Filament

Filament made of actin molecules; interacts with myosin during contraction.

Myosin

Motor protein composing thick filaments; each molecule has a tail and a head that pulls on actin.

Actin

Globular protein that polymerizes into thin filaments and contains binding sites for myosin heads.

Myosin Head

Projection on a myosin molecule that attaches to actin and performs the power stroke.

Myosin-Binding Site

Specific location on an actin molecule where a myosin head attaches during contraction.

Zone of Overlap

Region in a sarcomere where thick and thin filaments overlap; enlarges during contraction.

Sliding Filament Theory

Model stating that muscle contraction occurs as thin filaments slide past thick filaments, shortening the sarcomere.

I Band

Light band containing only thin filaments; shortens during contraction.

A Band

Dark band containing the entire length of thick filaments, including overlap with thin filaments.

H Zone

Central area within the A band that contains only thick filaments and no overlap.

M Line

Middle line of a sarcomere where thick filaments are anchored; defines center of the H zone.

Z Disc (Z Line)

Zig-zag protein structure that anchors thin filaments and marks sarcomere boundaries.

Tropomyosin

Long regulatory protein that winds around thin filaments and blocks myosin-binding sites on actin.

Troponin

Regulatory protein that holds tropomyosin in place over actin's binding sites.

Dystrophin

Protein that anchors the sarcomere to surrounding structures, maintaining alignment.

Titan

Elastic protein that connects the Z disc to the M line, stabilizing and recoiling the sarcomere.

Nebulin

Protein that wraps around thin filaments, helping to align and stabilize them.

Myomesin

Protein that forms the M line and links thick filaments together.

Alpha-Actinin

Protein in the Z disc that binds actin filaments, helping to anchor them.

Fascicle

Bundle of muscle fibers surrounded by perimysium.

Epimysium

Connective tissue sheath that surrounds the entire muscle.

Perimysium

Connective tissue layer that wraps around and separates fascicles.

Endomysium

Thin connective tissue surrounding each individual muscle fiber.

Muscle Fiber

Single skeletal muscle cell; contains many myofibrils and multiple nuclei.

Sarcolemma

Plasma membrane of a muscle fiber.

Myofibril

Rod-like bundle of contractile proteins inside a muscle fiber, composed of repeating sarcomeres.

Sarcoplasmic Reticulum

Specialized endoplasmic reticulum that stores and releases calcium for contraction.

T Tubules

Extensions of the sarcolemma that penetrate the cell and transmit action potentials throughout the fiber.

Sliding Filament Mechanism

Process where thick (myosin) and thin (actin) filaments slide past one another, shortening the sarcomere and causing muscle contraction.

Myosin

Motor protein that forms thick filaments; its heads bind actin, hydrolyze ATP, and generate the power stroke.

Actin

Protein that forms thin filaments; contains binding sites for myosin heads.

Troponin

Regulatory protein that binds Ca²⁺, changes shape, and moves tropomyosin off actin’s binding sites.