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Sliding Filament Theory

Muscle StriationsMuscle Striations



d) myofibril

Components of skeletal muscle

c) muscle fibre b) muscle fibre bundle a) Muscle belly

How do muscles contract?


The muscular system and the nervous system work together to signal and receive signals from the brain to allow for muscular contraction.

The link = neuromuscular junction


A muscle contraction results from a signal from a nerve impulse.

The electrical impulse travels down the neuron and body of the nerve to the neuromuscular junction.

(Where the nervous system and the muscle meet)

©Thompson Educational Publishing, Inc. 2003. All material is copyright protected. It is illegal to copy any of this material.This material may be used only in a course of study in which Exercise Science: An Introduction to Health and Physical Education (Temertzoglou/Challen) is the required textbook.

Neuromuscular JunctionNeuromuscular Junction

Sarcolemma

Axon

Receptor

Neurotransmitteracetylcholine (Ach)

Axon Terminal

Synaptic Cleft


Acetylcholine is released and receptors on the muscle fibers detect the chemicals presence and muscle contracts.

Within a motor unit (bundle of muscle fibers), all fibers contract at the same time or all fibers are relaxed = all or none principle


Neuromuscular JunctionNeuromuscular Junction

Sarcolemma

Axon

Receptor

Neurotransmitteracetylcholine (Ach)

Axon Terminal

Synaptic Cleft


The Motor UnitThe Motor Unit

Dendrites

Neuron cell body

Muscle fibres

Neuromuscular junction

Terminal branches

Axon hillock

Myelin sheathNeurolemma

Motor neuron

Direction of action potential

Motor end plate

How our muscle contracts once the message has been recieved


Muscle Structure

A muscle is a collection of many microscopic fibers.

Each muscle fiber consists of many small fibrils which are composed of even smaller protein filaments. (actin and myosin)

Myosin = thicker Actin = thinner When a muscle contracts/shortens the

finer/thinner actin filaments slide toward eachother and pass over the myosin filaments.


(a) At rest

Longitudinal section of myofibril


When a nerve impulse is received at the muscle (neuromuscular junction) it enters the interior of the fiber via a tuble.

The impulse causes the release of calcium ions (Ca++).

As a result, the myosin cross-bridges form a type of bond with selected sites on the actin filaments.

The Sliding Filament Theory

ATP is split and the energy released allows the acting filaments to slide toward each other. Consequently the muscle fiber shortens by about one third of its resting length.


The Sliding Filament TheoryThe Sliding Filament Theory


The Sliding Filament TheoryThe Sliding Filament Theory

Myosin crossbridges

Results in the sliding or overlap of the actin and myosin filaments Causes sarcomere to contract (muscle contraction)


In relaxation phase, the effect of the nerve impulse subsides, calcium ions are removed and the bond between myosin crossbrides and the actin filaments is broken.

Video

Contraction and Relaxation of muscle

Beef Muscle Contraction


Contractile Machinery:

Tendons, origin, insertion

In order for muscles to contract, they must be attached to the bones to create movement

Tendons: strong fibrous tissues at the ends of each muscle that attach muscle to bone

Origin: the point of attachment of the muscle to the bone that does not move

Insertion: the point of attachment of the muscle on the bone that moves


Muscle Fibre Types

Slow twitch fibres:

Slow Oxidative (Type I)

Fast twitch fibres: Fast Glycolytic (Type IIa) Fast Oxidative Glyc. (Type IIb)


A. Slow Twitch Fibres

Suited for repeated contractions during activities requiring a force

output of less than 20 to 25 percent of max force output

Examples: lower power activities, endurance events


B) Fast Twitch Fibres

Significantly greater force and speed generating capability than slow

twitch fibres

Well suited for activities involving high power

Examples: sprinting, jumping, throwing


Relative involvement of muscle fibre types in sport events.


Muscle Biopsy

Fast Twitch

(Type II Fibres)

Slow Twitch

(Type I Fibres)

Capillary Blood

Vessels


Muscle Teamwork Agonist (prime mover): - Muscle or group of muscles producing a desired effect

Antagonist: - Muscle or group of muscles opposing the action

Synergist: - Muscles surrounding the joint being moved

Fixators: - Muscle or group of muscles that steady joints closer to the body axis

so the desired action can occur


Bending or straightening of the elbow requires the coordinated interplay of the biceps and triceps muscles.

The triceps relaxes and the biceps contracts

The triceps contracts and the biceps relaxes

Agonist and Antagonist Pairs

sport books publisher1 sliding filament theory

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