Contraction Of Skeletal Muscle

Front 1

Actin and Myosin slide past each other, what is this Mechanism called?

Back 1

Sliding Filament Mechanism

Front 2

Over lap of myosin and actin:

Back 2

Dark Bands ( Anisotropic)

Front 3

No overlap of myosin and actin:

Back 3

Light Bands (Isotropic)

Front 4

If the sliding filament mechanism is correct, what does this then mean about the overlap of myosin and actin?

Back 4

There is more overlap of actin and myosin in a contracted muscle.

Front 5

A Sarcomere shortens when a muscle contracts but what other changes occur ?

Back 5

1. Isotropic bands (light) become narrower

2. Z-lines are lines that are adjacent to each other at the centre of an isotropic band, these become move closer together so the sarcomere shortens

3. The H-zone ( at the centre of each dark band there is this lighter region) becomes narrower

Front 6

Does the width myosin change when a muscle contracts?

Back 6

No because the width of this band is determined by the length of the myosin filaments. These filaments do not become shorter, this discounts the theory that muscle contraction is due to the filaments shortening.

Front 7

Describe structure of Actin

Back 7

Two long strands that twist around each other forming a helical strand

Front 8

Describe structure of Myosin

Back 8

Made of two types of protein :

1. Fibrous protein arranged in filament and made up of several molecules

2. A globular protein formed into two bulbous structures at one end.

Front 9

How do Actin and Myosin conjoin?

Back 9

Myosin forms thin threads that wand around actin filaments

Front 10

What supports the hypothesis that Actin and myosin slide past each other when a muscle contract?

Back 10

1. Changes seen in band patterns (more darker bands because actin and myosin overlap)

2. The Length of myosin doesn't change.

Front 11

What are the three processes sliding filament mechanism divided into?

Back 11

1. Muscle stimulation

2. Muscle Contraction

3. Muscle Relaxation

Front 12

Muscle stimulation 1:

Back 12

An action potential reaches many neuromusclular junctions , causing calcium ion channels to open and calcium ions to move into he synaptic knob.

Front 13

Muscle Stimulation 2:

Back 13

The Calcium ions cause the synaptic vessels to fuse with presynaptic membrane and release their acytelcholine into the synaptic cleft.

Front 14

Muscle Stimulation 3:

Back 14

Acetylcholine diffuses across the synaptic cleft and binds with the receptors on the post-synaptic neuron membrane, causing it to depolarize.

Front 15

Muscle contraction 1:

Back 15

The action potential travels deep into the fibre through a system of Tubules that branch throughout the sarcoplasm . These tubules are in contact with the endoplasmic recticulum of the muscle, which actively absorbed calcium ions from the sarcoplasm

Front 16

Muscle contraction 2:

Back 16

The action potential opens the calcium ion channels on the endoplasmic recticulum and calcium ions flood into the muscle down a diffusion gradient.

Front 17

Muscle Contraction 3:

Back 17

Calcium ions are released from the ENDOplasmic recticulum and these cause the tropomyosin molecules that where the blocking to the actin binding sites to move. The ADP molecule attached to the myosin heads means they are now in a state to bind to the actin filament, forming a cross bridge

Front 18

Muscle Contraction 4:

Back 18

Once attached to the actin filament, the myosin heads change their angle , pulling the actin filament along as they do so releasing a ADP molecule. The ATP molecule attaches to each myosin head , causing it to become detached from the actin filament .

Front 19

Muscle Contraction 5:

Back 19

The calcium ions then activate the enzyme ATPase , which hydrolysis ATP to ADP + PHOSPHATE which provides energy for the myosin head to return to its original position. The myosin is then attached to an ADP again and ready to move further along the actin filament.

Front 20

Muscle Relaxation 1:

Back 20

When the nervous stimulation ends the calcium ions are actively transported back into the endoplasmic reticulum using the energy from hydrolysis of ATP. The re-absorption of calcium ions causes the tropomyosin to block the binding site of the actin filament again. The muscle now relaxes.

Front 21

What is energy needed for in muscle contraction?

Back 21

1. The movement of myosin heads

2. The re-absorption of calcium ions into the endoplasmic reticulum by active transport.

Front 22

There is a constant need for oxygen in muscles to perfoum aerobic respiration to form ATP, as oxgen is being rapidly used up in muscles, how is ATP then generated without aerobic respiration?

Back 22

ATP is produced anaerobically , this is achieved using a chemical called phosphocreatine

Front 23

What is phosphoocreatine?

Back 23

It acts as a reserve in the muscles and stores phosphates needed to generate ATP