Anatomy Exam 3

Joints, muscle tissues, skeletal muscle

Fascicle

A bundle of muscle fibers surrounded by perimysium that makes up skeletal muscle tissue. This layer contains the blood vessels and nerves.

Epimysium

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

Perimysium

Dense irregular connective tissue that wraps indivdual fascicles and houses major neurovascular bundles.

Endomysium

Areolar connective tissue that wraps individual fibers to provide electrical insulation, capillary support, and binding of neighboring cells.

Aponeuroses

Thin, flattened sheets of dense irregular connective tissue used for muscle attachment.

Deep Fascia

Connective tissue that separates and binds different muscles together while housing nerves and lymph vessels.

Myoblasts

Embryonic cells that fuse into a single large multinucleated cell to form a muscle fiber.

Satellite cells

Myoblasts that do not fuse during development and remain in the periphery to assist in support and repair.

Sarcolemma

The plasma membrane of a muscle fiber containing T-tubules that conduct electrical signals deep into the cell.

Sarcoplasmic Reticulum (SR)

An internal membrane complex designed for ion storage, acting as the cell's Calcium bank.

Triad

A structural hallmark consisting of one T-tubule flanked by two terminal cisternae (blind sacs of the SR).

Calmodulin and Calquestrin

Storage proteins used by the Sarcoplasmic Reticulum to maintain high internal concentrations of Calcium.

Sarcomere

The functional unit of skeletal muscle contraction, defined as the distance from one Z-disc to the next.

Thick Filaments

Bundles of Myosin molecules, each featuring two intertwined tails and two heads with actin-binding and ATPase sites.

Thin Filaments

Two strands of Actin (G-actin globules) containing myosin binding sites along with the regulatory proteins Tropomyosin and Troponin.

Tropomyosin

A string-like protein that covers the myosin-binding sites on actin when the muscle is at rest.

Troponin

A globular protein attached to tropomyosin. When calcium binds here, it pulls tropomyosin off the binding sites, allowing contraction to begin.

Z-Discs

anchor thin filaments; The zigzag boundaries of a single sarcomere that mark the edges of sarcomeres in skeletal muscle.

I-Bands

Light regions of the sarcomere containing only thin filaments; they narrow or disappear during contraction.

A-Band

Dark region, has thin and thick filaments; the length remains constant during contraction.

H-Zone

The center of the A-band containing only thick filaments; it disappears during contraction.

M-Line

The protein attachment site in the exact center of the thick filaments.

Connectin

A protein extending from Z-disc to M-line that provides springlike passive tension and maintains structural integrity.

Dystrophin

A protein that anchors myofibrils to sarcolemma proteins.

Motor Unit

A single somatic motor neuron and all the muscle fibers it innervates.

Synaptic Knob

The end of a motor neuron that releases ACh into the synaptic cleft to stimulate muscle contraction.

Acetylcholinesterase

The enzyme residing in the synaptic cleft that acts as a molecular off switch by breaking down Acetylcholine.

Motor End Plate

The folded region of the sarcolemma packed with Acetylcholine (ACh) receptors.

Resting Membrane Potential (RMP)

The electrical state of a fiber at rest, typically $-90\,mV$.

End-plate Potential (EPP)

A local electrical change caused by Acetylcholine binding to receptors and opening chemically gated channels.

Depolarization

The phase where voltage-gated $Na^+$ channels open, shifting the membrane potential to $+30\,mV$.

Repolarization

The phase where $Na^+$ channels close and $K^+$ channels open, letting $K^+$ flow out to return the cell to $-90\,mV$.

Power Stroke

myosin head pulls the thin filament toward the M-line (ADP and Pi are released).

Myasthenia Gravis

An autoimmune disease where antibodies attack Acetylcholine receptors, leading to decreased stimulation and rapid fatigue.

Myoglobin

A unique protein used strictly for internal oxygen storage within muscle fibers.

Creatinine Phosphate

A high-energy molecule that acts as the cell's emergency cash by donating a phosphate group to instantly replenish ATP.

Synaptic Cleft

The fluid-filled gap where the enzyme Acetylcholinesterase resides.

Crossbridge Cycle (Mechanical Action)

The series of events that occur when myosin heads attach to actin filaments, pull them toward the center of the sarcomere, and detach, leading to muscle contraction.

Sliding Filament Theory

The theory that explains muscle contraction through the sliding motion of actin and myosin filaments past one another, leading to shortening of the sarcomere.

Acetylcholine (ACh)

A neurotransmitter released into the synaptic cleft to bind to receptors on the motor end plate, triggering muscle contraction.

Acetylcholinesterase (AChE)

An enzyme that breaks down acetylcholine in the synaptic cleft, terminating the signal for muscle contraction.

Arthrology

The study of joints.

Fibrous Joint

A joint where bones are held together by dense connective tissue and lacks a joint cavity, such as sutures or gomphosis.

Cartilaginous Joint

A joint where bones are joined by hyaline or fibrocartilage and lacks a joint cavity.

Synovial Joint

A joint where bones are joined by ligaments with a fluid-filled joint cavity separating the bone surfaces; classified as diarthroses.

Synarthroses

Immobile joints, such as fibrous or cartilaginous joints like skull sutures.

Amphiarthroses

Slightly mobile joints, such as intervertebral joints.

Diarthroses

Freely mobile joints; this category includes all synovial joints.

Mobility and Stability Relationship

An inverse relationship where more stable joints (like skull sutures) are less mobile, and more mobile joints (like the shoulder) are more unstable.

Articular Capsule

A double-layered capsule in synovial joints consisting of an outer fibrous layer for strength and an inner synovial membrane.

Synovial Membrane

The inner layer of the articular capsule composed primarily of areolar connective tissue that produces synovial fluid.

Joint Cavity

The space between bones in a synovial joint containing synovial fluid.

Synovial Fluid

A viscous, oily substance that lubricates articular cartilage, nourishes chondrocytes, removes waste, and acts as a shock absorber.

Articular Cartilage

Hyaline cartilage on bone surfaces that reduces friction and absorbs compression; it is avascular and lacks a perichondrium.

Perichondrium

A sheath of dense irregular connective tissue that surrounds most cartilage, helping maintain its shape.

Extrinsic Ligaments

Ligaments that are separate from the articular capsule.

Intrinsic Ligaments

Thickenings of the articular capsule itself.

Bursae

Fibrous, saclike structures containing synovial fluid that alleviate friction between bones, ligaments, or tendons.

Tendon Sheaths

Elongated bursae that wrap around tendons where friction is excessive, commonly found in the wrist and ankle.

Subluxation

A partial or incomplete dislocation where the bone is not completely displaced.

Shoulder Joint

A ball-and-socket joint formed by the head of the humerus and the glenoid cavity of the scapula; it has the greatest range of motion but is the most unstable.

Elbow Joint

A hinge joint where the trochlear notch of the ulna articulates with the trochlea of the humerus.

Hip Joint

A freely movable ball-and-socket joint formed by the head of the femur and the acetabulum of the pelvic girdle.

Sternoclavicular Joint

A saddle joint formed by the manubrium of the sternum and the sternal end of the clavicle.

Plane Joint

A uniaxial joint with flat articulating surfaces that allow bones to slide past one another, such as intercarpal joints.

Hinge Joint

A uniaxial joint where a convex surface fits into a concave depression, moving like a door hinge; examples include the elbow and knee.

Pivot Joint

A uniaxial joint where a rounded bone surface fits into a ring formed by a ligament and another bone, allowing rotation on an axis; example is the neck joint.

Condylar (Ellipsoid) Joint

A biaxial joint characterized as a 'stick in a hole,' such as the metacarpophalangeal (MP) joints.

Saddle Joint

A biaxial joint where articular surfaces resemble a person sitting on a horse, such as the sternoclavicular joint

Ball-and-Socket Joint

A multiaxial joint in which a ball rests within the cup of a second bone; examples include the shoulder and hip joints.

flexion

decreasing the angle between bones

extension

increasing the angle between bones

abduction

the movement of a limb away from the midline of the body

adduction

the movement of a limb toward the midline of the body

synchondroses

a type of cartilaginous joint in which bones are joined by hyaline cartilage,immbole immobile

syndesmosis

a type of fibrous joint where bones are connected by a ligament or an interosseous membrane, allowing limited movement.

symphysis

a type of cartilaginous joint where bones are joined by fibrocartilage

menisci

crescent-shaped cartilage in the knee

uniaxial synovial joints

plane, pivot and hinge joints

biaxial synovial joints

condylar/ellipsoid and saddle joints that allow movement in two planes.

multiaxial synovial joints

ball and socket joints

Tetanus

spastic paralysis; blocks inhibitory neurotransmitters, causing overstimulation. A serious bacterial infection affecting the nervous system, often resulting in muscle stiffness and spasms.

botulism

a condition caused by a toxin that inhibits the release of acetylcholine, leading to muscle weakness and paralysis.

fibrosis

As we age, muscle mass is often replaced by dense irregular connective tissue, decreasing flexibility.

T-tubules (Transverse tubules)

Invaginations of the sarcolemma that carry electrical signals into the cell.

terminal cisternae

Swollen ends of the sarcoplasmic reticulum that store calcium ions and release them during muscle contraction.

Crossbridge Formation

The process where myosin heads attach to actin filaments during muscle contraction, facilitating tension development.

Release (CBC)

ATP binds to the myosin head, causing it to detach from actin.

Reset (CBC)

myosin heads return to their original position after detaching from actin, preparing for the next contraction cycle.

Immediate Supply (Phosphate Transfer)

Uses molecules like creatine kinase to transfer phosphate to ADP.

Short-term Supply (Glycolysis)

anaerobic process in the cytoplasm that breaks down glucose into pyruvate, yielding a net of 2 ATP per glucose molecule.

Long-term Supply (Aerobic Cellular Respiration)

Occurs in the mitochondria and requires oxygen. This is the most efficient pathway, producing approximately 30 to 38 ATP per glucose molecule.

Extensibility

capacity to be pulled out to a greater length

Elasticity

ability to return to the original starting length once the tension is released