BIOLOGY: Muscular System

Muscular System

Muscular System
- composed of muscle cells & tissues held together in bundles
- more than 600 muscles in our body
- 35 % of our weight

Properties

1.    Contractility – ability to become shorter/longer

2.    Extensibility – ability to be stretched

3.    Elasticity – ability to return to original form

4.    Irritability – stimulated by certain stimuli

Functions

1.    Allows us to stand upright

2.    Pumping of blood through Circulatory Sys.

3.    Moving of food through Digestive Sys.

4.    Breathing

5.    Movement

Skeletal
- enables voluntary movement of bones
- consists of densely packed groups of elongated cells known as muscle fibers
- contains more mitochondrion

1.    Neck muscles – hold the head up & move it in all directions

2.    Shoulder muscles – raise and lower the arms

3.    Triceps – straighten the arms
Biceps – bend the arms

4.    Abdominal muscles – move torso & help in breathing

5.    Thigh muscles – move lower leg

6.    Calf muscles – pull heel up & point toes

7.    Shin muscles – help move foot up & down, side by side

Smooth
- involuntary
- spindle-shaped cells with 1 nucleus each
- contracts in rhythmic waves to:
    a. propel food through digestive tract
    b. provide tension in the urinary bladder, blood vessels, uterus etc

Cardiac muscle
- found only in the heart
- drives blood through circulatory system
- connects to each other through specialized junctions known as intercalated disks

Structure of muscle

1.    Bundle – composed of many muscle fibers (40cm)

2.    Muscle fiber – is a single cell with many nuclei

3.    Myofibril – comprises muscle fiber

4.    Filaments – each myofibril has thick(myosin) & thin(actin) filaments

5.    Sarcomere – contractile unit of myofibril
- a unit of alternating thick & thin filament

6.    Sarcolemma – plasma membrane of muscle fiber

7.    Sarcoplasm – cytoplasm of 2 striated muscle cells

How do muscles work?

Antagonist – muscle that contracts to produce an action
Agonist – opposes the action

Flexion – Bent (BC, TR)
Extension – Straight (BR, TC)