Book scanning of edexcel revision guide for UNIT 5 TOPIC 7 on Muscles


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5 Unit 5: Exercise and Coordination
Muscles and movement
Muscles, joints and movement
Bones can move in relation to one another at joints. Different types of joint allow
different degrees of movement. Ligaments are made of elastic connective tissue.
They hold bones together and restrict the amount of movement possible at a joint.
Tendons are cords of non-elastic fibrous tissue that anchor muscles to bones.
TOBONE cartilage
A typical synovial joint.
Skeletal muscles are those attached to bones and are normally arranged in
antagonistic pairs. This means that there are pairs of muscles which pull in opposite
directions. Flexors contract to flex, or bend a joint, e.g. biceps in the arm; extensors
contract to extend, or straighten a joint, e.g. triceps in the arm.
Remember that muscles can't
stretch themselves. It is the pull Each skeletal muscle is a bundle of millions of muscle cells called fibres. Each muscle
created by the contraction of the cell may be several centimetres long and contains several nuclei. It contains many
antagonistic muscle that stretches a myofibrils which are made up of the fibrous proteins actin (thin filaments) and
muscle when it is in a relaxed state. myosin (thick filaments). The cell surface membrane of a muscle cell is known as the
sarcolemma. The sarcoplasmic reticulum is a specialised endoplasmic reticulum
which can store and release calcium ions. The cytoplasm inside a muscle cell is called
the sarcoplasm. The specialised synapse (see page 63, Topic 8) between neurones
and muscle cells is called the neuromuscular junction.
The prefix myo- refers to `muscle'
The sliding filament theory of muscle
and sarco- to `flesh' (i.e. muscle) so contraction
specialist terms starting with myo-
or sarco- will refer to structures The functional unit of a muscle A one sarcomere
within muscles. fibre is called a sarcomere.
When the muscle contracts
the thin actin filaments move
between the thick myosin
filaments, shortening the length
of the sarcomere and therefore
myosin actin
shortening the length of the
The arrangement of actin and myosin
filaments in a sarcomere when relaxed
(A) and contracted (B).
44 Green Book 7.2 Orange Book 7.1

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Topic 7: Run for your life 5
Myosin filaments have flexible `heads' that can change their orientation, bind to actin
and hydrolyse ATP (using ATPase). Actin filaments are associated with two other
proteins, troponin and tropomyosin, that control the binding of the myosin heads to
the actin filaments.
When a nerve impulse arrives at a neuromuscular junction, calcium ions are released
from the sarcoplasmic reticulum and the following events take place that lead to the
contraction of the muscle.…read more

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Unit 5: Exercise and Coordination
Energy and the role of ATP in respiration
All living organisms have to respire. There are two different ways in which they do this
­ aerobic respiration (using oxygen) and anaerobic respiration (without oxygen).
Both of these processes make the energy stored in glucose available in the form of
ATP, to power metabolic reactions.…read more

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Topic 7: Run for your life 5
Anaerobic respiration allows animals to make a small amount glucose lactate pathway
of ATP. It is an inefficient process but it is rapid and can supply
muscles with ATP when oxygen is not being delivered quickly
enough to cells.
+2P i
2H reduced NAD NAD
Lactate forms lactic acid in solution which lowers the pH. This
can inhibit enzymes and, if allowed to build up, it can cause
muscle cramp.…read more

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Unit 5: Exercise and Coordination
Krebs cycle and the electron transport chain
In aerobic respiration, the pyruvate (from glycolysis) is completely oxidised into carbon
dioxide and water using oxygen.
Aerobic respiration takes place in two stages:
Many of the reactions involved in · First pyruvate is oxidised into carbon dioxide and hydrogen (accepted by the
respiration are redox reactions coenzymes NAD and FAD). This takes place in the matrix of the mitochondria
where one substrate is oxidised and involves the Krebs cycle.…read more

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Topic 7: Run for your life 5
Each molecule of the 2-carbon acetyl coenzyme A from the link reaction is used to generate:
· three molecules of reduced NAD
· one molecule of reduced FAD
· two molecules of CO2
· one molecule of ATP by substrate-level phosphorylation (synthesised directly
from the energy released by reorganising chemical bonds)
· one molecule of a 4-carbon compound, which is regenerated to accept an acetyl
group and start the cycle again.…read more

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Unit 5: Exercise and Coordination
RV 4
The heart, energy and exercise
non-conducting layer
in 2
heart wall between
atria and ventricles 4
LV The control of the cardiac cycle
RV 4
The impulse to contract originates within the heart itself from the sinoatrial node ­ the
Purkyne fibres
heart is said to be myogenic.…read more

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Topic 7: Run for your life 5
The heart rate can be affected by hormones (e.g. adrenaline) and nervous control. The
cardiovascular control centre in the medulla of the brain controls the sinoatrial
node via nerves. The sympathetic nerve speeds up the heart rate in response to falls
in pH in the blood due to CO2 and lactate levels rising, increases in temperature and
mechanical activity in joints.…read more

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Unit 5: Exercise and Coordination
Homeostasis is the maintenance of a stable internal environment, within a narrow
limit, of the optimum conditions needed by cells so they can function properly. A
homeostatic system therefore requires:
· receptors to detect the change away from the norm value (stimulus)
· a control mechanism that can respond to the information.…read more

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Topic 7: Run for your life 5
heat loss heat loss
centre in centre in
detected detected effectors effectors
hypothalamus hypothalamus
by receptors send by receptors sends send react sends react
impulses impulses
impulses impulses
mperature rises temperature rises temperature falls temperature falls
et point set point set point set point set point set point
(norm) (norm) (norm) (norm) (norm) (norm)
temperature falls temperature falls temperature rises temperature rises
detected by heat gain
detected by heat gain
effectors effectors
receptors centre in
receptors centre
react…read more


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