Muscles | Musculoskeletal System - Biology IB23

Muscle Functions

Allows force for bones to permit movements in animals, but also helps with:
- Heat Production
- Circulatory System
- Giving Birth
- Protection for Bone
- Digestive System

Antagonistic Pair

For opposite movement to be possible, there has to be a pair of muscles that exert force in opposite directions.

EX: Triceps and Biceps

Muscles Contraction and Relaxation

Muscles can only exert force when they contract and only lengthen one relaxed, and they’re limited to cause movement in only one direction.

Tendons

Muscle and bone attachment.

EX: Anchorage and Insertion

Types of Muscles

- Smooth Muscle
- Cardiac Muscle
- Skeletal Muscle

Smooth Muscle

- Spindle-shaped, non-striated, uninucleated fibers
- Occurs in walls of internal organs
- Involuntary

Cardiac Muscle

- Striated, branched, uninucleated fibers
- Occurs in the walls of the heart
- Involuntary

Skeletal Muscle

- Striated, tubular, multinucleated fibers
- Attached to the skeleton
- Voluntary

Skeletal Muscle Structure

Made up of multinucleated cells called muscle fibers, within each are myofibrils with a sarcoplasmic reticulum surrounding it. Mitochondria is found in between the myofibrils.

Sarcomeres

Myofibrils are made up of repeating sarcomeres that are light and dark bands which give a striated appearance. Each sarcomere can exert force and contract.

Sliding Filament Theory Definition

When muscle fiber contracts, they do not shorten, instead they slide over each other so the sarcomeres themselves shorten.

Sliding Filament Theory Steps

1. An acetycholine neurotransmitter reaches the muscle fiber over the synapse, Na+ enter and creates action potential.

2. Ca- ions are released from the sarcoplasmic reticulum in the muscle fiber.

3. Ca- ions bind with a protein, troponin, on the actin fibers causing the the shape to change and move the tropomyosin which exposes the actin binding sites.

4. Myosin heads attaches themselves onto the actin binding sites forming cross bridges making the heads move bringing in the sarcomere to the center.

5. ATP is used to break down the cross bridges, and the myosin heads will move onto the next acting binding sites which further pulls the sarcomere toward the center.

6. This continues until the Ca- ions disappear and the troponin-tropomyosin complex has fully covered the actin binding sites.