Neuronal Communication

4 changes in external environment organism may need to respond to.

1. Humidity 2. Temperature 3. Light 4. Sudden/new sound

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4 changes in internal environment organism may need to respond to.

1. Temperature 2. Cell pH 3. Blood glucose concentration 4. Water potential

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Why is coordination needed?

Because many cells and systems do not work in isolation e.g. RBCs do not work in isolation need to be constantly produced by haematopoietic stem cells . To maintain homeostasis. Cell signalling

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How does cell signalling work? How does this occur locally + over large distances.

Communication between cells where on cell releases a chemical which attaches to receptors on a target cell. Neurones are used locally (neurotransmitters). Over large distances hormones e.g. ADH

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Name the 3 parts of a neurone. Briefly describe them.

1. Cell body: contains nucleus, cytoplasm + lots of mitochondria and ER to produce neurotransmitters. Axon: elongated fibre, cylindrical, impulse away from the cell body. Dendron. Short extensions which branch into dendrites, impulse to cell body.,

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What are 3 types of neurone?

Sensory, relay and motor.

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Describe where they transmit impulses.

Sensory: from receptor cell to relay/ motor neurone. Relay: between the motor neurones and sensory neurones. Motor: between the relay/ sensory neurone to the effector.

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Describe in terms of axons and dendrons the 3 types of neurone.

Sensory: one axon, one dendron. Relay: many axons and many dendrites which form dendrons. Motor: many dendrites and one axon.

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Reflex arc.

Stimulus, receptor cell, sensory neurone, relay neurone, motor neurone, effector (gland or muscle), response

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Label a sensory neurone.

Draw.

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What cells create the myelin sheath and how? State a positive.

Schwann cells which wrap around the axon creating an insulating double phospholipid bi-layer, due to the insulating properties off the myelin sheath the impulse is transmitted much faster.

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How does the myelin sheath achieve a faster pace of transmission.

The impulse jumps between the nodes of Ranvier because the myelin is insulating and the impulse cannot travel here.

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What are the 2 main features of receptors?

1. Act as a transducer converting stimulus energy into a nervous impulse. 2. Only detect one type of stimulus.

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In terms of a sensory receptor what does transducer mean?

It converts stimulus energy into a nervous impulse.

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What are the 4 types of receptor? What is their stimulus?

1. Mechanoreceptor:mechanical pressure + movement. 2. thermoreceptor: heat. 3. Chemoreceptor: chemicals. 4. Photoreceptor: light.

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For each sensory receptor give an example + corresponding sense organ.

1. Mechanoreceptor: Pacinian corpuscle- skin. 2. Thermoreceptor: End-bulbs of krause- tongue. 3. Chemoreceptor: olfactory receptor. 4. Photoreceptor: cone cells- eye.

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Receptors act as a transducer, when receptors convert the stimulus energy into a nervous impulse what is the known as?

A generator potential.

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What do pacinian corpuscles detect? Describe the structure.

Mechanical pressure, the end of the sensory neurone is located in the centre of the pacinian corpuscle which is surrounded by layers of connective tissue with gel in between each layer.

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What is the name of the specialised sodium channels present in the pacinian corpuscle?

Stretch-mediated sodium ion channels.

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What is the value of the resting potential of a neurone?

-70mV

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What is a nervous impulse?

An action potential which is propagated along a neurone to the end of another neurone.

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What is the period of time known as when the axon cannot be excited again. How does this happen?

The refractory period, the sodium gated ion channels remain closed and cannot be opened to create an action potential.

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Why is the refractory period so important?

It ensures that impulses are unidirectional (prevents propagation backwards). Prevents action potentials OVERLAPPING.

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Define saltatory conduction.

The propagation of an action potential along a myelinated neurone via the nodes of Ranvier.

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Why is saltatory conduction faster than regular propagation?

This is because impulses jump between the nodes of Ranvier so depolarisation can only occur here (no myelin), as opening ion channels and Na+ diffusing down takes time, limiting the number of times this happens makes it much faster.

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How is saltatory conduction more energy efficient?

Repolarisation, moving Na+ against the concentration gradient out of the axon using the Na-K pump uses ATP due to active transport. As this can only happen at the nodes of Ranvier less ATP is used.

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State and explain 2 other factors which reduce the speed at which an action potential travels.

1. Axon diameter: wider= faster due to less resistance for ions in the cytoplasm. 2: Temperature: generally higher= faster up until 40 degrees when channel proteins denature.

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What is meant by the all or nothing principle?

Stimulimust reach a certain level before they can initiate an action potential, this is called the threshold value. However for any stimulus over the threshold value the size of the impulse created will always be the same.

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How does the size of the stimulus affect the action potential created?

The larger the stimulus the more frequent the action potentials.

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What is the junction between 2 neurones called?

A Synapse.

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What chemicals allow an impulse to be carried across a synapse?

Neurotransmitters.

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Name the 6 main parts of a synapse.

Presynaptic neurone, postsynaptic neurone, synaptic cleft, synaptic vesicle, neurotransmitter receptors, synaptic knob.

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Define synaptic cleft.

The gap between the axon of one neurone and the dendrite of the next.

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presynaptic neurone.

The neurone along which the impulse has travelled.

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Postsynaptic neurone.

The neurone which receives the impulse in the form of a neurotransmitter.

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Synaptic knob.

The swollen end of the presynaptic neurone containing lots of mitochondria and ER for the production of neurotransmitters.

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Synaptic vesicles.

Vesicles in the presynaptic neurone containing neurotransmitters which fuse with its membrane to be released into the cleft.

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Neurotransmitter receptors.

Receptor molecules on the post synaptic neurone which neurotransmitters bind to.

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What are the 2 types of neurotransmitter, what do they do?

Excitatory: trigger an action potential by depolarising the post synaptic neurone if the threshold value is reached. Inhibitory: prevent an action potential by the HYPERPOLARISATION of the post-synaptic neurone preventing an action potential.

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Give an example of each type of neurotransmitter.

Excitatory: acetylcholine. Inhibitory: GABA (gamm-aminobutyric acid)

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Describe how synaptic transmission occurs. (1 of 2)

1.Action potential reach end of presynaptic neurone. 2. Causes Ca 2+ channels to open. 3. Ca 2+ fuse onto presynaptic knob= causes synaptic vesicles to be released=exocytosis of neurotransmitter after fusion with knob Into cleft.

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Describe how synaptic transmission occurs. (2 of 2)

4. Neurotransmitter binds to receptors on postsynaptic neurone. 5. Causes Na+ channels to open = action potential propagated along dendron of postsynaptic neurone.

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What neurotransmitter do cholinergic responses use?

Acetylcholine.

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What enzyme hydrolyses acetylene choline?

Acetylcholinesterase.

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what is acetylcholine broken down into?

Ethanoic acid and choline.

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describe what happens ton acetylcholine when its broken down.

Acetyl choline is hydrolysed into ethanoic acid and choline by acetylcholinesterase. It detaches from the neurotransmitter receptors and diffuses back across the synaptic cleft into the presynaptic knob of the presynaptic neurone where its reformed.

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State and explain 3 roles of synapses.

1.Impulses=unidirectional: due to receptors they can only travel from presynaptic to postsynaptic neurone. 2. Means an impulse from one neurone can be transmitted to multiple= simultaneous responses. 3. Many neurones to 1= single response.

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What are the two types of summation regarding neurones?

Spatial and temporal,

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What is meant by summation (neurones).

Initial amount neurotransmitter not large enough reach threshold value and trigger an action potential. However, neurotransmitter can build up at a synapse so eventually there is enough to reach the threshold value and initiate an action potential.

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Explain spatial summation.

Neurotransmitter from multiple presynaptic neurones builds up at one postsynaptic neurones, each releasing a small amount of neurotransmitter until threshold value is reached.

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Explain temporal summation.

When several action potentials occur over a short period of time at one presynaptic neurone so neurotransmitter builds up until threshold value is reached.

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What are the 2 types of nervous system? What do they consist of?

The CNS (central): brain and spinal cord only. The PNS: all neurones connecting rest of body to CNS.

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What are the 2 systems the nervous system is functionally broken down into? Briefly explain.

The autonomic and somatic nervous systems. Somatic= everything under conscious, voluntary control e.g. moving a muscle. Autonomic= everything involuntary, subconscious, CONSTANT e.g. heart beat + digesting food.

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Draw a diagram to show how nervous system is organised.

CNS + PNS= somatic and autonomic= sympathetic + parasympathetic.

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What is the autonomic nervous system broken down into?

The sympathetic and parasympathetic nervous system.

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Briefly explain with regards to responses how to sympathetic and parasympathetic nervous systems work.

The sympathetic nervous system increases a response e.g. heart rate or breathing rate. Parasympathetic generally decreases a response.

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Name the 5 main parts of the brain.

Cerebrum, cerebellum, medulla oblongata, hypothalamus, pituitary gland.

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State the function of the cerebrum and cerebellum.

Cerebrum: voluntary actions= learning, memory and personality. Cerebellum= involuntary action such a posture + balance.

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State the function of the medulla oblongata, hypothalamus and pituitary gland.

Medulla oblongata: AUTONOMIC CONTROL e.g. heart rate and breathing rate. Hypothalamus: regulatory centre for water potential + temperature. Pituitary gland: releases hormones e.g. ADH + FSH.

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Why is the cerebrum highly convoluted?

Increases SA.

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How is the cerebrum broken down? Which sides of the body do they control?

The left and right cerebral hemispheres with the outside being referred to as the cerebral cortex. The left cerebral hemisphere controls the right and the right cerebral hemisphere controls the left side allowing us to judge depth and perspective.

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Explain how the propagation of an action potential occurs.

1. Stimulus causes change in sensory receptor. 2. Triggers action potential. 3. 1st region=depolarised (+40mV). 4. Acts a stimulus for the depolarisation of next region. 5. Wave of depolarisation along axon. 6. The Na+ in axon= attracted -ve ahead.

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Explain how the pacinian corpuscle converts a mechanical pressure stimulus into a nervous impulse. (1 of 2)

1. Resting state, stretch-mediated sodium ion channels are too narrow for Na + to pass through into the neurone (resting potential= -70mv) 2. Pressure causes a change in shape membrane surrounding the neurone and Na+ channels widen.

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Explain how the pacinian corpuscle converts a mechanical pressure stimulus into a nervous impulse. (2 of 2)

3. Sodium ions diffuse into the neurone. 4. Na+ cause depolarisation (=40mV) 5. Results in generator potential which creates an action potential which is propagated along the sensory neurone.

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How is a resting potential in a neurone created? (1 of 2)

3 x Na+ = actively pumped out. 2x K+ = actively pumped out. Actively transported by the sodium-potassium pump. Sodium and potassium gated ion channels which allow diffusion of Na+ and K+ but Na+ gated are normally closed preventing its movement.

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How is a resting potential in a neurone created? (2 of 2)

Therefore, more +ve outside than inside creating a resting potential of -70mV.

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Explain how an action potential is created. (1 of 2)

1. Resting potential (-70mV) K+ X3 = actively in. Na+ x3 = actively out. K+ channels open and Na+ channels closed. 2. Stimulus energy triggers so Na+ gated channels to open= Na+ diffuse into axon down the electrochemical gradient.

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Explain how an action potential is created. (2 of 2)

3. Positive feedback = more Na+ channels open. 4. Until P.D reaches +40mV. 5. Na+ channels close, K+ open. 6. K+ diffuse out down electrochemical gradient= hyperpolarisation. 7. K+ channels close, sodium-potassium pump = 3 Na+ out= repolarisation.

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What 3 main things does the hypothalamus control?

1. complex patterns of behaviour such as feeding, sleeping + aggression. 2. Monitoring the composition of blood plasma, such as concentration of water and blood glucose. 3. Production of hormones.

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What are the names of the 2 parts of the pituitary gland? What hormones do these produce?

Anterior pituitary (front section) - 6x hormones including FSH. Posterior pituitary gland- stores + release hormones produced by the hypothalamus e.g. ADH.

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Where is the relay neurone located?

In the brain or spinal cord.

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What is the spinal cord?

a column of nervous tissue running up the back surrounded by the spine for protection.

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What type of reflex is the knee-jerk?

Spinal

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How is the knee-jerk reflex carried out? Explain how to response occurs.

Leg is tapped below the kneecap causing a kicking motion. Stretches the patellar tendon (stimulus), initiates reflex arc= extensor muscle contracts. Same time, relay neurone inhibits motor neurone forcing it to relax.

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What might the absence of/ multiple oscillations of the knee-jerk reflex indicate?

Absence= nervous problems. Multiple= cerebellar disease.

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What type of reflex is blinking?

Cranial

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When may the blinking reflex occur?

To prevent the invasion of a foreign body, bright light, if a sound over 40-60 dB is heard.

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Describe the reflex arc for the blinking reflex.

1. The cornea is stimulated by a foreign body. 2. Impulse is sent along sensory neurone. 3. Passes through the relay neurone in the lower brain stem. 4. Impulses are sent along branches of the motor neurone. 5. Both eyelids close- consensual response

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How fast is the blinking reflex?

0.1s

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Why is the corneal reflex done when a patient is unconscious?

To determine if they're brain dead.

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What are the 4 reasons the reflexes are important for survival?

Involuntary: do not have to go through conscious parts of the brain= prevents overload. Don't have to be learnt: immediate protection. Very fast: 1 our 2 synapses (slowest part of transmission). Many= everyday: upright/ digestion.

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What are the three types of muscle?

(SIC)Skeletal, involuntary (smooth), cardiac

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State if each type of muscle is striated.

Skeletal: striated. Involuntary: non- striated. Cardiac: specialised striated.

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State the type of control (voluntary or involuntary for each type of muscle).

Skeletal: voluntary. Cardiac: involuntary. Involuntary/ smooth: involuntary.

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Describe the arrangement, contraction speed and length for each type of muscle (1 of 2)

Skeletal: regular arrangement= contraction 1 direction, rapid contraction, short. Cardiac: cells branch + interconnect= simultaneous contraction, intermediate, intermediate.

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Describe the arrangement, contraction speed and length for each type of muscle (2 of 2)

Involuntary: no regular arrangement= different cells contract in different directions, slow, can remain contracted for a long time.

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Which type of muscles are multinucleated and uninucleated?

Skeletal: multinucleated. Cardiac: uninucleated. Involuntary: uninucleated.

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Skeletal muscles are made up of bundles of muscle fibres surrounded by a membrane, what is the name of this membrane?

The sarcolemma.

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Describe the structure of skeletal muscle. (1 of 2)

Composed of muscle fibres grouped together and enclosed by a membrane known as the sarcolemma. The muscle fibres are multinucleated + much longer than normal cells. They are formed form many embryonic cells fusing.

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Describe the structure of skeletal muscle. (2 of 2)

The fibres have a shared cytoplasm called the sarcoplasm. Parts of the sarcolemma fold inwards (T tubules)./ Lots of mitochondria for ATP for contraction. Sarcoplasmic reticulum produces Ca2+ for contraction.

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Why is it an advantage that skeletal muscle fibres are composed of embryonic cells fusing together?

Because this means there are no junctions between cells which would act as a point of weakness, so the muscle is stronger.

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What do the transverse or T tubules (inward folding of the sarcolemma) help do?

Ensures the whole fibre receives and impulse so It contracts at the same time.

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Muscle fibres contain many myofibrils: cylindrical organelle made of protein + specialised for contraction. What are the 2 types of protein these are composed of? Briefly describe them.

1. Actin: thinner, 2 strands twisted around each other. 2. Myosin, thicker, long rod-shaped fibres with heads at one side.

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Myofibrils have alternating light and dark bands, explain their difference.

Light bands (I or isotopic bands) are lighter in colour because just actin (thinner) is present here and no overlap between myosin and actin. Dark bands (A or anisotropic)= thicker myosin filaments are present, the edges= darker overlap with actin.

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Describe the Z-line and H-zone of the myofibril and where they are found in the myofibril.

The Z-line is found at the centre of each light band, distance between Z-lines= sarcomere. When muscle contracts sarcomere shortens. H-zone= lighter centre of each dark band where only myosin is present, muscle contracts, H-zone shortens.

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What is the distance between 2 Z-lines know as?

The sarcomere.

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During contraction, the myosin filaments pull with actin filaments in towards the centre of the sarcomere. How does this affect the myofibril.

The light band becomes narrower (more overlap), the Z-lines moving closer together shortening the sarcomere, the H-zone becoming narrower (more overlap).

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Describe the structure a myosin filament.

Myosin filaments have globular heads that are hinged allowing them to move backwards and forwards. On each myosin head there are binding sites for ATP and actin. The tails of many myosin molecules are aligned to form a myosin filament.

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Describe the structure of an actin filament.t

Have binding sites for myosin heads (actin-myosin binding sites). Individual actin= 2 strands wrapped around each other.

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What protein is normally blocking myosin binding sites on actin filaments?

Tropomyosin.

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What protein holds tropomyosin on myosin binding sites on actin in place?

Troponin.

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When are the myosin binding sites on actin filaments blocked by tropomyosin and when are they not?

They are blocked when the muscle is in its resting state (relaxed) and not blocked when the muscle is stimulated to contract.

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What is it called when myosin heads bind to actin filaments?

Actin-myosin cross bridges.

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How is muscle contraction triggered?

When an action potential reaches a neuromuscular junction. (where a motor neurone and skeletal muscle fibre meet).

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(Not a question) There are many neuromuscular junctions along the length of the muscle to ensure all the fibres contract simultaneously.

If there was only one neurone muscular junction the contraction would not be as powerful and the would be much slower as the wave of contraction would have to pass along the whole muscle.

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What are muscle fibres supplied by a single motor neurone known as?

Motor units.

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Describe how an action potential stimulates the contraction of a muscle. (1 of 2)

1. Action potential reaches the neuromuscular junction. 2. Stimulates calcium ion channels to open 3. Ca 2+ diffuse into synaptic knob + cause synaptic vesicles to fuse with the presynaptic membrane

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Describe how an action potential stimulates the contraction of a muscle. (2 of 2)

3. Acetylcholine is released into the synaptic cleft and diffuse across attaching to postsynaptic receptors (the SARCOLEMMA). 4. This opens sodium ion channels and results in depolarisation. 5. Acetyl choline hydrolysed by acetylcholinesterase

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With regards to muscles why is it important acetylcholine left on receptors is hydrolysed into ethanoic acid and choline and returned to the presynaptic neurone?

To prevent over-stimulation.

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How is the energy for muscle contraction provided?

The hydrolysis of ATP into ADP and inorganic phosphate.

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State 2 reasons why ATP is required for muscle contraction?

1. Movement of myosin heads 2. Active absorption of the Ca 2+ by the sarcoplasm.

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What are the 3 main ways ATP is produced for muscle contraction?

1. Aerobic respiration 2. Anaerobic respiration 3. Creatine phosphate

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Summary of sliding filament: 1. Tropomyosin prevents myosin head attaching to the binding site of the actin molecule. (ADP) 2. Calcium ions from ER causes tropomyosin to pull away form binding site. (ADP). 3. Myosin head attaches binding site actin

4. Head of myosin changes shape + ADP released 5. ATP binds causing it to detach from actin filament. 6. Hydrolysis ADP to ATP= myosin to normal position. 7. Reattach + repeat.

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Neuronal Communication

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