BIO 211 & 212 Muscle and Skeleton Overview

Flashcards covering skeletal systems, connective tissues, muscle types, sarcomere structure, and the mechanisms of muscle contraction.

Exoskeleton

A hard external shell composed of chitin and $CaCO_3$ where muscles pull from the inside against the rigid shell.

Hydrostatic Skeleton

A fluid-filled body cavity that uses pressure and antagonistic muscles for movement, found in organisms like earthworms and jellyfish.

Endoskeleton

Internal bones and cartilage where muscles attach to bone via tendons, typical of vertebrates.

Bone

A connective tissue made of calcium phosphate and a collagen matrix that provides rigid support, leverage, and protection.

Cartilage

A connective tissue consisting of a chondroitin and collagen matrix used for flexibility and shock absorption.

Tendon

A dense collagen structure that connects muscle to bone.

Ligament

A dense collagen structure that connects bone to bone, such as the ACL or MCL of the knee.

Flexion

Movement that results in a decrease in joint angle, moving the limb inward.

Extension

Movement that results in an increase in joint angle, moving the limb outward.

Antagonistic pairs

Muscle groups consisting of a flexor and an extensor that work together since muscles only pull and never push.

Skeletal Muscle

Voluntary, striated muscle attached to bones that is multinucleate and contains myofibrils and sarcomeres.

Cardiac Muscle

Involuntary, striated, and branched muscle found in the heart wall that contains intercalated discs.

Smooth Muscle

Involuntary, non-striated muscle found in hollow organs like the gut and vessels that propels substances and forms sphincters.

Z-disc

The boundaries of a sarcomere that anchor thin filaments and move closer together during muscle contraction.

I band

The region of the sarcomere that contains thin filaments (actin) only and shortens during contraction.

A band

The region of the sarcomere containing overlapping thick (myosin) and thin (actin) filaments that stays the same length during contraction.

H zone

The central region of the sarcomere containing thick filaments (myosin) only, which disappears during contraction.

M line

The center of the myosin filaments within a sarcomere that stays the same during contraction.

Actin

The protein that makes up the thin filaments and contains active sites for myosin binding.

Tropomyosin

A thin filament protein that blocks binding sites at rest to prevent contraction.

Troponin

A thin filament protein that binds $Ca^{2+}$ to initiate the movement of tropomyosin.

Myosin

A motor protein and the primary component of thick filaments, featuring a head that binds to actin.

Rigor Mortis

The stiffening of muscles $3-4$ hours after death caused by a lack of ATP, which leaves myosin stuck to actin.

Muscle Fiber

One giant multinucleate cell packed with myofibrils.

Myofibril

Repeating sarcomeres arranged end-to-end within a muscle fiber.

Sarcomere

The basic functional unit of muscle microanatomy organized from Z-disc to Z-disc.

Power stroke

The step in the sliding filament model where $ADP$ and $P_i$ are released, causing myosin to pull actin and move Z-discs closer.

T-tubules

Structures that carry action potentials deep into the interior of a muscle fiber.

Sarcoplasmic reticulum (SR)

An organelle that serves as a storage site for $Ca^{2+}$, with walls loaded with $Ca^{2+}$ pumps.

Motor Unit

The combination of one neuron and all of the muscle fibers it innervates.

Size principle of recruitment

The recruitment order of motor units starting from small fibers for fine movement to large fibers for powerful movement.

Neuromuscular Junction (NMJ)

The site where an action potential arrives at a motor neuron terminal, triggering the release of ACh and subsequent muscle contraction.