Unit 4

The Muscular System

Muscle Cells

There are 3 types of muscle cells– Cardiac, Smooth, and Skeletal

All muscles can contract (shorten)When muscles contract, part of the body moves

Cardiac Muscles

Striated, tubular, and branchedHave one nucleus per cellContract involuntarilyFound in the walls of the heart

Smooth Muscles

Non-striated, arranged in sheetsHave one nucleus per cell Contract involuntarily, and can sustain prolonged contractions

Smooth Muscles

Found in the walls of internal organs (cavities and tubes) such as:– Blood vessels, iris of the eye,

internal organs such as the stomach, intestines, uterus, and esophagus for peristalsis

Skeletal Muscles

Striated and tubularHave many nuclei per cellAttached to the bones of the skeleton

Skeletal Muscles

Contract voluntarily, controlled consciously by the nervous systemDue to structure and having many nuclei they are referred to as fibres

Compare the muscle types!Type Structure Voluntary/

Involuntary?Location

in the Body

Cardiac

Smooth

Skeletal

Type Structure Voluntary/ Involuntar

y?

Location in the Body

Cardiac Tubular, arranged in a branched network, striated, one nucleus per cell

involuntary Heart

Smooth Long, tapered, arranged in sheets, non-striated, one nucleus per cell

involuntary Walls of digestive system, blood vessels, other internal organs

Skeletal Tubular, very long, striated, many

nuclei per cell.

voluntary Attached to the bones of

the skeleton,

Muscle ContractionMuscles contract they shorten!Muscles can only pull they cannot pushMuscles that permit movement are found in pairs, as each muscle in the relaxed state needs an opposite muscle to stretch it.Antagonistic muscles- pairs of muscles that work against each other to make a joint move

Muscle contraction – bundle of fibres

Skeletal muscles consist of many bundled muscle fibres held together with connective tissueMuscle fibre consists of: – Myofilaments a thread of

contractile proteins found within muscle fibres

Muscle Contraction - bundles of fibres

Two types of Myofilaments– Thick filament – fine myofilament

composed of bundles of protein called myosin. Each myosin molecule consists of two polypeptide chains wrapped around each other. Binds to actin

Two types of MyofilamentsThin filament – fine myofilament composed of strands of protein called actin. Consist of globular actin proteins. Binds to myosin

Myofilament ContractionFour steps:1. The myosin head is attached to actin

Myofilament Contraction

2. The myosin head flexes, advancing the actin filament

Myofilament Contraction

3. The myosin head releases and unflexes, powered by ATP.

Myofilament Contraction

4. The myosin reattaches to actin farther along the fibre

Sliding Filament Model

Actin is anchored in the striated muscle tissue called the Z-LineSince it is ‘anchored’ like this, when actin moves it drags the Z-line with it, toward the myosinThis causes the entire muscle to contract

Sliding Filament ModelThe heads of the two ends of the myosin filament are orientated in opposite directions. When the heads attach to the actin, they bend toward the centre of the myosin.

Sliding Filament ModelAs one end of the myosin filament draws the actin filament and its attached Z line toward the centre, the other end of the myosin filament does the same

Sliding Filament ModelBoth Z lines move toward the centre, and contraction occurs