Copy of Lab 11 Mini Lesson Learning Guides

Homeostasis Role of Skeletal Muscle

Skeletal muscles maintain homeostasis by generating heat, enabling movement and posture, assisting in venous return of blood to the heart, and regulating metabolism and glucose uptake.

Hierarchy of Muscle Structure

Muscle (Organ) → Fascicle → Muscle Fiber (Cell) → Myofibrils → Sarcomeres → Myofilaments (Actin & Myosin).

Thick Filaments Composition

Made of myosin, with heads that form cross-bridges for contraction.

Thin Filaments Composition

Composed of actin, along with tropomyosin and troponin, which regulate contraction.

Z-line (Z-disk)

Boundaries of a sarcomere.

M-line

Center of the sarcomere, anchoring thick filaments.

A-band

Dark region containing thick filaments (myosin) and overlapping thin filaments.

I-band

Light region containing only thin filaments (actin).

H-zone

Region within the A-band that contains only thick filaments.

Titin

Elastic protein that helps with structural integrity.

T-Tubules

Extensions of the sarcolemma that transmit action potentials deep into the muscle fiber.

Sarcoplasmic Reticulum (SR)

Stores and releases calcium for muscle contraction.

Calcium's Role in Contraction

Calcium binds to troponin, causing tropomyosin to move and expose binding sites on actin, enabling myosin heads to bind actin.

Action Potential at Neuromuscular Junction

The arrival of action potential at the axon terminal of an alpha motor neuron triggers a sequence leading to muscle contraction.

End-Plate Potential (EPP)

Localized depolarization at the motor end plate which can trigger a full action potential if strong enough.

Botulinum toxin

Blocks ACh release leading to paralysis.

Curare

Blocks ACh receptors, preventing muscle contraction.

Organophosphates

Inhibit acetylcholinesterase, causing prolonged muscle contraction.

Succinylcholine

Mimics ACh but does not degrade quickly, leading to temporary paralysis.

Dihydropyridine Receptor (DHPR)

Voltage sensor in T-tubules, linked to RyR for calcium release.

Ryanodine Receptor (RyR)

Calcium release channel in the sarcoplasmic reticulum.

SERCA Pump

Pumps Ca²⁺ back into SR to stop contraction.

Sliding Filament Mechanism

Myosin heads bind actin, causing power stroke that moves thin filaments inward and shortens the sarcomere.

Rigor Mortis

Condition where myosin remains bound to actin due to lack of ATP after death, leading to stiff muscles.

Cytosolic Ca²⁺ Timing

Ca²⁺ rises quickly after action potential but slightly lags behind; its removal takes time leading to gradual muscle relaxation.

ATP Functions in Contraction

Energizes myosin for cross-bridge cycling, detaches myosin from actin, and powers Ca²⁺ pumps for relaxation.