1

Chapter 6 – Muscular System

BIO 105

What do all these muscle types have in common?

1. Muscles are excitable

2. Muscles have the ability to contract.

3. Muscles are extensible.

4. Muscles are elastic.

Organization of skeletal muscle

The muscles that we use for locomotion are attached to bones by __________.

2

Muscle origins and insertions

(a) Flexion

The relaxed triceps

is stretched.

The biceps contracts

and pulls the forearm

up, flexing the arm.

Origin of muscle:

attachment of muscle to less moveable bone

Insertion of muscle:

attachment of muscle to more moveable bone

extension

(b) Extension

The triceps contracts and

pulls the forearm down,

extending the arm.

The relaxed biceps

is stretched.

Structure of skeletal muscle

3

skeletal muscle

(c) A diagram and

electron micrograph

of a myofibril

(d) A sarcomere, the contractile unit of a skeletal muscle, contains actin and

myosin myofilaments.

Z line

Z line

Z line

Actin

Myosin

One sarcomere

One sarcomere

Thick & thin myofilaments Skeletal muscle contraction

Sliding filament model – muscle contracts

when actin filaments slide along the myosin filaments, increasing the degree of

overlap between actin and myosin, and

thus shortening the sarcomere.

4

5

6

What stimulates skeletal muscle

contraction?Neuromuscular Junction

Amyotrophic Lateral Sclerosis (ALS)

Degeneration of the motor neurons that control skeletal muscle.

7

Muscular Dystrophy

Progressive degeneration

of skeletal muscle fibers

Motor Units and RecruitmentTypes of Skeletal Muscle Fibers

Slow - twitch

• Slow speed of contraction

• Slow to fatigue

• Many mitochondria & blood vessels

Fast - twitch

• Fast speed of contraction

• Fast to fatigue

• Fewer mitochondria & blood vessels

8

A muscle twitch is a single contraction-

relaxation cycle that occurs in a muscle fiber in response to a

single action potential.

Where does this wealth of ATP come from?

1. ATP stored in muscle cells

2. The breakdown of creatine phosphate

3. Cellular respiration

4. Fermentation

9

How does aerobic vs. anaerobic exercise affect your muscles?

• Aerobic exercise facilitates the

development of new blood vessels, more mitochondria, cardiac & respiratory

improvement

• Anaerobic exercise increases muscle size