Module 5, Chapter 13 - Neuronal Control

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Give 4 examples of internal and 4 examples of external environments organisms must respond to

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1

Give 4 examples of internal and 4 examples of external environments organisms must respond to

Internal: blood glucose concentration, internal temperature, water potential, cell pH; external: humidity, external temperature, light intensity, new or sudden sound

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2

Why is coordination required (give an example)

Cells are specialised for different functions, so must work with different types of cells, organs and tissues to carry out complex functions (eg: red blood cells must be replenished with haematopoietic stem cells, and red blood cells are required by muscle cells to transport oxygen)

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3

What is homeostasis

The maintenance of a stable equilibrium in the conditions in the body

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4

What two systems are used in cell signalling, how do the systems work and when are they used (describe one, then the other)

Nervous system: electrical signals are transferred between neurones at synapses using a neurotransmitter, used for rapid or local responses; hormonal system: signals are released using hormones, which bind the the receptors of the specific target organ cells, used for long-distance, more long term effect responses

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5

What is the role of a neurone

To transmit electrical impulses around the body to detect stimuli and initiate responses

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6

What is the cell body and what are its features (why does it have these features)

Part of a neurone containing the nucleus surrounded by cytoplasm; lots of endoplasmic reticulum and mitochondria (to synthesise neurotransmitters)

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7

What are dendrons, what are their features and what is their role

Small extensions from the cell body; the extensions divide into smaller branches called dendrites; responsible for transmitting electrical impulses across the cell body

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8

What are axons, what are their features and what is their role

Singular, elongated nerve fibres; often very long, cylindrical in shape, consist of a narrow region of cytoplasm surrounded by a plasma membrane; transmit electrical impulses away from the cell body

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9

What is the role of a sensory neurone and what are its features

To transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain; single long dendron leading to cell body, followed by long axon leading away from cell body

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10

What is the role of a relay neurone and what are its features

To transmit impulses between neurones, eg: sensory neurone to a motor neurone; many short dendrons and singular short axon

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11

What is the role of a motor neurone and what are its features

To transmit impulses from a relay or sensory neurone to an effector; many short dendrons and singular long axon

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12

What is the role of the myelin sheath and how is it generated

Acts as an electrical insulator to allow electrical impulses to be transmitted between them much faster; Schwann cells produce many layers of membrane by growing around the axon many times

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13

What is a node of Ranvier and how does it affect electrical impulse transmission

Gaps in the myelin sheath; electrical impulse jumps from one node to the next, allowing impulses to be transmitted much faster

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14

What are the two features of sensory receptors

They are specific to a single type of stimulus; they are transducers, so convert a stimulus into a nervous impulse (generator potential)

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15

For each of the 4 types of sensory receptors, state their name, stimulus, example of one, and example of a sense organ they are located in

Mechanoreceptor, pressure and movement, Pacinian corpuscle, skin; chemoreceptor, chemicals, olfactory receptor, nose; thermoreceptor, heat, end-bulbs of Krause, tongue; photoreceptor, light, cone cell, eye

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16

What is the Pacinian corpuscle and what is the special feature of a neurone ending in it

Specific sensory receptors that detect mechanical pressure; the sodium ion channel is stretch-mediated, so when the channel changes shape due to pressure, they open

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17

What are the steps for how a Pacinian corpuscle converts mechanical pressure into a nervous impulse

Initially, stretch mediated sodium channels are closed so there is a resting potential. When pressure is applied, the membrane changes shape so the sodium channels open to allow sodium to diffuse into the neurone. This causes the membrane to become depolarised, creating a generator potential which initiates an action potential, which passes along the neurone.

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18

How is a resting potential generated

Sodium-potassium pumps actively transport 3 sodium ions out of the membrane for every 2 potassium ions they move into the axon. As potassium ion channels are open and sodium ion channels are closed, only potassium ions are able to diffuse across the membrane, creating an imbalance of charge: negative inside, positive outside.

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19

Give the definition of depolarisation and the definition of repolarisation

A change in potential difference from negative to positive in a neurone; a change in potential difference from positive to negative in a neurone

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20

What is a resting potential and what is an action potential (give the value for this)

The potential difference across the membrane of a neurone when not transmitting an impulse (-70mV); the change in potential difference across a neurone membrane when stimulated (+40mV)

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21

How is an action potential generated

Energy transferred by stimulus opens some of the voltage-gated sodium ion channels, causing sodium ions to quickly diffuse down electrochemical gradient into the membrane. The change in charge stimulates more sodium ion channels to open, causing more sodium ions to diffuse through faster, meaning the axon becomes depolarised.

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22

How does an axon repolarise after depolarisation - include steps before hyperpolarisation

When the potential difference reaches +40mV, the voltage-gated sodium ion channels close and voltage-gated potassium ion channels open. Potassium ions diffuse out of the axon down the electrochemical gradient (and sodium ions diffuse out using the sodium-potassium pumps)

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23

What is hyperpolarisation and how does the system reach the resting potential from it

When the inside of the axon is more negative than the resting potential; voltage-gated potassium ion channels close and potassium-sodium pumps transfer potassium ions back into the membrane

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24

How does the action potential propagate itself along the axon

The depolarisation of a region of membrane stimulates the opening of voltage-gated sodium ion channels further down the membrane. The sodium ions are attracted to the negative regions ahead, causing them to diffuse further down the axon to cause further depolarisation.

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25

What is the refractory period, how does it occur and why is it important

A period of time when a region of the axon can’t be excited again; the voltage-gated sodium ion channels remain closed to prevent diffusion of sodium ions; prevents the propagation of the action potential in the wrong direction.

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26

What is saltatory conduction, why is it faster and why is it more energy efficient

A process where the action potential jumps from one node of Ranvier to the next; opening/closing of channels and movement of ions takes time, and the process means depolarisation of the axon only occurs at the nodes, so there are now fewer places this is required; less sodium-potassium pumps are required, which use active transport

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27

What factors apart from myelination increase speed of action potential and why

Bigger axon diameter: there is less resistance to flow of ions in the cytoplasm; increased temperature: ions will diffuse faster (after 40 degrees Celsius, proteins denature so this is no longer the case)

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28

What is the threshold value and how does it affect nerve impulse transmission

The level of stimulus required for an action potential to be generated; if a stimulus does not reach this value, the action potential will not be generated

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29

How does the size of stimulus affect action potential

The larger the stimulus, the more frequent action potentials are generated

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30

What is the synaptic cleft, presynaptic neurone and the postsynaptic neurone

The gap which separates the axon of one neurone from the dendrite of the next neurone; the neurone along which the impulse has arrived; the neurone which receives the neurotransmitter

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31

What is the synaptic knob and what are its features

The swollen end of the presynaptic neurone; contains many mitochondria and endoplasmic reticulum to synthesise neurotransmitters

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32

What are the synaptic vesicles and what are neurotransmitter receptors

Vesicles containing neurotransmitters which fuse with the synaptic membrane and release contents into synaptic cleft; receptor molecules which neurotransmitter molecules bind to in the postsynaptic membrane

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33

What are excitatory neurotransmitters and give an example of one

Neurotransmitters which cause the depolarisation of the postsynaptic neurone and can trigger an action potential; acetylcholine

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34

What are inhibitory neurotransmitters and give an example of one

Neurotransmitter causing the hyperpolarisation of the postsynaptic neurone to prevent an action potential being triggered; GABA

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35

How are impulses transmitted across synapses

Depolarisation of presynaptic neurone causes voltage gated calcium ion channels to open and calcium ions diffuse into presynaptic knob. This causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters by exocytosis. Neurotransmitters diffuse across the synaptic cleft and bind to receptor molecules on the postsynaptic membrane. Sodium ion channels open, so sodium ions diffuse into the postsynaptic neurone, triggering an action potential.

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36

For Cholinergic synapses, state the neurotransmitter they use, where they are commonly found, the result once they reach a receptor cell, how the neurotransmitter is broken down and what happens to the products of this

Acetylcholine; CNS of vertebrates and neuromuscular junctions (where a motor neurone and muscle cell reach); muscle cells contract; hydrolysed by acetylcholinesterase; taken into the presynaptic knob to be reform acetylcholine to be used again

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37

Why are synapses important (give 3 reasons)

Ensure impulses are unidirectional; allow a single impulse to be transmitted to multiple neurones at multiple synapses; multiple impulses can be transmitted to a single neurone to give one response

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38

What is summation

Build up of sufficient levels of neurotransmitter in a synapse to trigger an action potential

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39

Where does spatial summation take place and how is an action potential triggered in this scenario

Where a number of presynaptic neurones connect to one postsynaptic neurone; each presynaptic neurone releases neurotransmitters to reach threshold levels

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40

How is an action potential triggered in temporal summation

A single presynaptic neurone must produce high frequency action potentials to release enough neurotransmitters to trigger an action potential

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41

What does the CNS and PNS consist of

Brain and spinal cord; all neurones connecting CNS to the body (sensory and motor neurones)

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42

Which part of the nervous system is the somatic nervous system a subdivision of, what control is it under and where does it carry impulses (where from)

PNS; conscious; skeletal muscles (sense organs)

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43

What part of the nervous system is the autonomous nervous system a subdivision of, what control is it under, where does it carry impulses (where from), and what can it be split into

PNS; subconscious; glands, smooth muscle and cardiac muscle (internal receptors); sympathetic motor and parasympathetic motor system

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44

What part of the nervous system controls “fight or flight” responses and give an example of a neurotransmitter it uses

Sympathetic motor system; noradrenaline

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45

What part of the nervous system gives relaxing responses and give an example of a neurotransmitter it uses

Parasympathetic motor system; acetylcholine

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46

What is the name of each lobe of the cerebrum and what does each control

Frontal lobe: motor function, problem solving, judgement, behaviour, personality; parietal lobe: sensory information, spatial awareness, perception; occipital lobe: integration of visual stimuli ; temporal lobe: listening, language perception and communication, memory formation

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47

What is the function of the cerebrum and what does it do

Controls voluntary actions (eg: learning, memory, personality, conscious thought); receives sensory information, interprets it using previous experiences and sends impulses to produce an appropriate response

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48

What is the function of the cerebellum and how does it work

Controls unconscious functions (eg: posture, balance, non-voluntary movement); receives information from organs of balance in ears and tone of muscles and tendons, and relays this to areas involved in motor control

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49

What is the function of the medulla oblongata (give examples)

Used in autonomic control such as reflex actions (ventilation, heart rate) and other unconscious actions such as swallowing, coughing

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50

What is the hypothalamus and give 3 of its functions

Regulatory centre for temperature and water balance; controls complex patterns of behaviour such as feeding, sleeping; monitors composition of blood plasma; produces hormones

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51

What is the function of the pituitary gland, state the name of both sections of it, what they do, and an example of a hormone produced by each (what is this hormone used for)

Produces hormones to control most glands in the body; anterior pituitary produces 6 hormones eg: FSH (involved in growth and reproduction hormones); posterior pituitary stores and releases hormones produced by the hypothalamus eg: ADH (involved in urine production)

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52

What is the general path for a reflex arc - mention cells involved (what does each part do)

Receptor (detects stimulus and creates action potential), sensory neurone (carries impulse to spinal cord), relay neurone (connects sensory neurone to motor neurone in spinal cord), motor neurone (carries impulse to effector to carry out a response)

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53

What is the stimulus for the knee-jerk reflex, how does it stimulate the nervous system and what is the response

Leg tapped below kneecap; initiates reflex arc which causes extensor muscle on thigh to contract. Relay neurone also inhibits motor neurone of flexor muscle to cause it to relax; leg extends once

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54

What could be the cause of a lack of knee jerk reflex, what is the possible cause with multiple oscillations and what is the reflex used for

Nervous problems; sign of a cerebellar disease; maintain posture and balance

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55

What are the steps for the blinking reflex

Cornea of eye is stimulated, sensory neurone passes impulse to relay neurone in lower brain stem, impulse sent along motor neurones to eyelids to close simultaneously

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56

What is the importance of the blinking reflex, when is it stimulated (what type of reflex is this), what is the test of the reflex used for

To protect the eye from damage; cornea is touched (corneal), sounds greater than 40-60Db, bright light (optical) (overall cranial reflex); test if lower brain stem is functioning (a failure of this means someone is brain dead)

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57

How do reflexes increase chance of survival

As brain is not involved, the brain has space to deal with more complex responses; present at birth so provide immediate and unlearnt protection; much faster; many control everyday actions such as digestion

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58

What are skeletal muscles responsible for, what is the fibre structure, what type of control are they under, how are they arranged and why, how long is the length and speed of contraction

Movement; striated, multinuclear, tubular; voluntary; regularly so muscles can contract in one direction; short length, rapid speed

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59

What are cardiac muscles responsible for, how are they myogenic, what is the fibre structure, what type of control are they under, how are they arranged and why, how long is the length and speed of contraction

Beating of the heart; they contract without need of the nervous system; branched uninuclear specialised striated; involuntary; cells branch and interconnect to allow simultaneous contraction; intermediate speed and length

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60

What are smooth muscles also known as, what is the fibre structure, what type of control are they under, how are they arranged and why, how long is the length and speed of contraction

Involuntary muscle; spindle-shaped, uninuclear, non-striated; involuntary; non-regular to allow different cells to contract in different directions; long length, slow speed

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61

What is the structure of muscle fibres (why is this present)

Made up of many embryonic muscle cells fused together (make muscles stronger); shared cytoplasm called sarcoplasm; shared membrane called sarcolemma; parts of sarcolemma fold inwards into T-tubules (help spread impulses through sarcoplasm so cells contract simultaneously);

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62

What are the modifications on some of the organelles in muscle fibres (why are these present)

Lots of mitochondria (to provide enough ATP for contraction); specialised ER - sarcoplasmic reticulum extends through muscle fibre and contains calcium ions required for muscle contraction

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63

What are myofibrils, where are they found and what proteins are they made up of (describe each protein)

Long cylindrical organelles made of protein and specialised for contraction lined parallel to each other; actin (thinner, two strands twisted around each other), myosin (thicker, long rod-shaped fibres with bulb shaped heads that project on one side)

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64

What is present in the light bands, dark bands and H-zone of a myofibril, what is a Z-line, sarcomere and H-zone

Light band: actin only; dark band: myosin and actin; H-zone: myosin only; line found at the centre of the light band; distance between two Z-lines and the functional unit of a myofibril;

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65

How does a sarcomere change when myofibrils contract

The light band and H-zone become narrower, the Z-lines move closer together as the sarcomere shortens

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66

How is the binding of myosin heads to actin prevented while muscles are relaxed and how is this then allowed in order for muscles to contract

Tropomyosin blocks actin-myosin binding sites and held in place by troponin; calcium ions bind to troponin, causing tropomyosin to change shape and free the binding sites

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67

How is the sarcolemma depolarised from the action potential in a motor neurone

The arrival of the action potential in the pre-synaptic knob stimulates calcium ion channels to open, so calcium diffuses into it, causing synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine. This binds to receptors on the sarcolemma, causing sodium ion channels to open to depolarise the membrane.

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68

What happens to acetylcholine after it has diffused across the neuromuscular junction (why does this happen)

Broken down by acetylcholinesterase into choline and ethanoic acid (to prevent muscle from being overstimulated), then the products diffuse into the neurone where they are recombined using energy

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69

What is a neuromuscular junction, and why are there many along the length of a muscle

The point where a motor neurone and skeletal muscle fibre meet; to cause all of the muscle fibre to contract simultaneously to increase the power of the contraction

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70

How does the depolarisation of the sarcolemma cause release of calcium ions into the sarcoplasm

The depolarisation spreads along the sarcolemma and through T-tubules, which are in contact with the sarcoplasmic reticulum. The SR has stored calcium ions actively absorbed from the sarcoplasm. This stimulates calcium ion channels to open, releasing of calcium ions.

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71

How does the release of calcium ions cause actin filaments to move (what is each part of the process called)

Calcium ions bind to troponin, causing tropomyosin to change shape and free actin-myosin binding sites (stimulation). Hinged myosin heads with an attached ADP group then bind to these sites to form an actin-myosin cross-bridge, which causes the myosin head to flex, moving the actin filament (attachment), which causes the ADP group to be released.

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72

How are myosin heads released from the actin-myosin binding sites (detachment) and reset to bind again

ATP binds to the myosin head, causing it to be released from the binding site. Calcium ions also bind to the myosin head, which stimulates ATPase to hydrolyse ATP to ADP + Pi. The energy released causes the myosin head to return to the original position

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73

What is anaerobic respiration used for and what are the issues with it

Alternative to aerobic respiration during short periods of high-intensity exercise in active muscles; pyruvate produced is converted to lactic acid, which can build up to cause muscle fatigue

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74

When is creatine phosphate used, how does it work, what is the advantage and disadvantage of using it, how is it replenished

Short bursts of vigorous exercise; acts as a reserve supply of phosphate to convert ADP directly to ATP; generates ATP rapidly, but is used up quickly; while the muscle is relaxed, it is regenerated from ATP

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