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A-levels > Biology- Internal / External Stimuli, Receptors and Nervous System > Flashcards

Biology- Internal / External Stimuli, Receptors and Nervous System Flashcards

1
Q

Define Taxis

A

A simple response where the direction is determined by the direction of the stimulus.
Positive taxis - Move towards stimulus
Negative taxis - Move away from stimulus

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2
Q

Define Kinesis

A

A response in which the organism does not move to or away from the stimulus (non-directional)

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3
Q

Define tropism

A

The growth movement of a part of a plant in response to a directional stimulus.

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4
Q

Define Transducers

A

Convert energy from one form to another.

E.g Rod and cone cells convert light energy into electrical energy of a nerve impulse.

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5
Q

Define Retinal convergence

A

Where many/several rod cells are connected to one bipolar neurone.

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6
Q

Define Generator potential

A

The depolarisation of a membrane of a receptor cell as a result of a stimulus.

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7
Q

Define visual acuity.

A

The clarity of vision dependent on optical and neural factors.

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8
Q

What are Rod cells and where are they located?

A
  • Photoreceptor cells located in the retina of the eye
  • Contain Rhodopsin (protein pigment) which absorb light
  • Rod cells are stimulated by light at a range of varying intensities (often a lower light intensity)
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9
Q

What are Cone Cells and where are they located?

A
  • Photoreceptor cells located in the retina of the eye
  • Contain iodopsin (protein pigment) whcih absorbs light.
  • Cone Cells are stimulated by light at a higher light intensity.
  • Responsible for coloured vision.
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10
Q

What is the role of a Transducer?

A

Role of a transducer is to convert the change in some form of energy by the stimulus into a form( nerve impulse) that can be understood by the body.

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11
Q

What are Pacinian Corpuscles?

A

A mechanoreceptor found on the skin.

Stimulus —-> Mechanical Pressure

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12
Q

What are Baroreceptors?

A

Mechanoreceptors located in the Carotid sinus and aortic arch.
Stimulus —-> Detect changes in blood pressure stimulates by stretching.

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13
Q

What is Chemo receptors?

A

Detect changes in chemical concentrations

In carotid sinus, They detect a change in the partial pressure of O2 and CO2.

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14
Q

How can chemo receptors detect a change in pH?

A

As the partial pressure of CO2 increases the pH of blood plasma decreases (more acidic)
H2O + CO2 —-> H2CO3 (Carbonic acid)
H2CO3 —-> H+ + HCO3-
Hydrogen ion concentrations increases so acidity decreases.

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15
Q

What is bleaching?

A

Rhodopsis —-Light energy —> Retinal + Opsin

Retinal - causes polarisation to be changed (generator potential = depolarised)
Rhodopsin can be regenerated using ATP + Darkness

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16
Q

Define Resting Potential

A

The difference in charge maintained across the membrane of the axon of a neurone when not stimulated.
At rest the outside of the membrane is more positive than inside.
-70mv charge.

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17
Q

How is Resting Potential achieved?

A

The sodium potassium pump pumps out 3Na+ and brings in 2K+ ions across the axon membrane. This creates a membrane potential. Furthermore the membrane is more selectively permeable to K+ ions than Na+ ions so K+ ions diffuse out of the cell. This creates a larger positive potential out of the cell than inside.

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18
Q

Define Depolarisation

A

Temporary reversal of electrical charges on the cell surface membrane of a neurone that takes place when a nerve impulse is transmitted.

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19
Q

What causes the depolarisation of the membrane?

A

Stimulus affects the Na+ ion channels
so they open
causing them to depolarise

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20
Q

What are the steps in the depolarisation of a membrane?

A

1) Stimulus causes more Na+ channels to open
2) Na+ diffuse into the cell down a concentration gradient.
3) This changes the voltage causing the membrane to become more selectively permeable to Na+ ions and therefore more voltage gated Na+ channels to open which allows more Na+ to diffuse in.
4) Positive feedback loop when more and more Na+ ion channels open.
5) Once charges flip (+40 mv) then Na+ ion channels close and repolarisation begins.

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21
Q

Define Action Potential

A

A change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nerve impulse passes.

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22
Q

Define Hyperpolarisation

A

Is a change in the cells membrane potential that makes it more negatively charged than it already is. (opposite to depolarisation)

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23
Q

Define Repolarisation

A

Return to the resting potential in the axon of a neurone after an action potential.

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24
Q

What is the Refractory Period?

A

The area/period of time where hyperpolarisation takes place and the membranes charge is brought back to rest.
Absolute R.P —> No action potential ever
Relative R.P —> Need a stimulus > normal threshold.

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25
Q

What are the stages in an action potential?

A

1) Initial depolarisation of membrane triggered by stimulus (cause generator potential)
2) Many generator potentials lead to overall depolarisation.
3) If generator potential reaches threshold then an action potential is generated.
4) positive feedback loop of Na+ channels opening
5) once action potential at +40 mv is established then repolarisation occurs but overshoots rest.
6) Hyperpolarisation brings charge back to rest.

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26
Q

What are the stages/steps or repolarisation?

A

1) once an action potential of +40 mv is established, after a delay Na+ ion channels close and more K+ channels open.
2) K+ ions diffuse out of the cell down concentration gradient so positive charge gets re-established outside of cell.
3) Charge is overshot however so charge is more positive outside of cell than at resting potential. The ions are in the wrong places and therefore must be re established via the sodium potassium pump.

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27
Q

How does hyperpolarisation restore the membranes charge to resting potential?

A

Since resting potential is overshot, and the ions are in the wrong places, the sodium potassium pump has to re-distribute Na+ and K+ ions back to their preferred environment and re-establish the -70 mv resting potential.

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28
Q

What is an impulse and how do they work?

A

A wave of depolarisation.

In an impulse local currents are set up which causes depolarisation to occur along an axon membrane.

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29
Q

Define Saltatory conduction

A

The Propagation of action potentials along myelinated axons from one node of ranvier to the next node.
Depolarisation leaps from region (node to node) since myelin acts as an electrical insulator.
This speeds up an impulse.

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30
Q

Where do action potentials occur in a neurone?

A

Along the axon membrane in unmyelinated axons.

At the nodes of ranvier in myelinated axons.

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31
Q

What is the central nervouse system made up of?

A

Brain and spinal chord

32
Q

What is the peripheral nervous system made up of?

A

Pairs of nerves that originate from either the brain or spinal chord.

33
Q

What are sensory neurones?

A

Neurones which carry electrical impulses from receptors towards the central nervous system.

34
Q

What are motor neurones?

A

Neurones which carry electrical impulses away from the central nervous system and towards the effectors.

35
Q

What is the voluntary nervous system.

A

Nerves/neurones which carry nerve impulses to body muscles and is under voluntary (conscious) control.

36
Q

What is the Autonomic nervous system?

A

Nerves/neurones which carry nerve impulses to glands, smooth muscle, cardiac muscle and is not under voluntary control (subconscious)

37
Q

What is the sympathetic nervous system?

A

This stimulates effectors and so speeds up any activity. Acts as an emergency controller. It helps us cope with stressful situations by heightening our awareness and preparing us for activity.
“Fight or flight response”

38
Q

What is the parasympathetic nervous system?

A

Inhibits effectors and so slows down any activity.

It controls activities under normal resting conditions.

39
Q

What is a reflex action?

A

An Involuntary response to a stimulus that bypasses the brain.

40
Q

What is a reflex arc?

A

The pathway of neurones involved in a reflex

41
Q

What are the 3 neurones involved in a reflex arc?

A

Sensory neurone
Relay neurone (intermediate)
Motor neurone

42
Q

Why are reflex actions important?

A
  • Protect us from danger
  • Fast due to short neurone pathway
  • Required no thinking.
43
Q

What is the process of a reflex arc?

A

1) Arrival of stimulus at receptor
2) Activation of sensory neurone starting an impulse
3) Relay neurone allows CNS to process information
4) Activation of motor neurone
5) Effector cells contract initiating a response

44
Q

What is a synapse?

A

The junction between 2 neurones where neurotransmitters diffuse to pass on an impulse.

45
Q

Give some examples of neurotransmitters

A
  • Acetylcholine
  • Dopamine
  • Serotonin
  • Noradrenaline
46
Q

How is an impulse transmitted across a synapse?

A

1) Impulse arrives at synaptic knob/bulb
2) Causes membrane potential to change which opens Ca^2+ voltage gated channels
3) Ca^2+ diffuse rapidly into synaptic bulb
4) Ca^2+ cause vesicles containing neurotransmitters to move towards and fuse with presynaptic membrane.
5) Neurotransmitter is exocytosed from vesicles and diffuse across synaptic cleft.
6) Neurotransmitter binds to binding site of protein receptors (Na+ ion channels) causing them to open.
7) Na+ diffuse into post synaptic neurone and begin depolarisation causing and E.P.S.P or an I.P.S.P

47
Q

What do E.P.S.P and I.P.S.P stand for?

A

E.P.S.P - excitatory post synaptic potential

I.P.S.P - Inhibitory post synaptic potential

48
Q

What does E.P.S.P mean will happen?

A

Action potentials could form (if depolarisation exceeds threshold)
and therefore an impulse can be passed on through the post synaptic neurone.

49
Q

What does I.P.S.P mean will happen?

A

No action potential will happen due to hyperpolarisation and therefore will result in no impulse being passed on.

50
Q

Why does the synaptic bulb contain loads of mitochondria and SER?

A

Mitochondria - Active processes in action potentials and transmission of an impulse across a synapse.

SER - Synthesises lipids for phospholipid membrane of vesicles

51
Q

Why is a synapse uni-directional?

A

Impulses can only go in one direction due to no protein receptors being present in the pre synaptic membrane.
Neurotransmitters must be actively transported back out of the synaptic cleft and then repackaged in vesicles.

52
Q

What is summation?

A

The rapid build up of neurotransmitters in the synaptic cleft - Temporal summation
- Spartial summation

Happens due to low frequency action potentials often leading to the release of an insufficient concentration of neurotransmitters to trigger a new action potential in the post synaptic neurone.

53
Q

What is spartial summation?

A

Where 2 or more pre synaptic neurones release neurotransmitters into the synaptic cleft so the concentration is above threshold and an action potential can be triggered.
One neurone may not release enough neurotransmitters to get the concentration above threshold.

54
Q

What is temporal summation? (low frequency v high frequency action potential)

A

Low - Lead to neurotransmitters being broken down rapidly and therefore the concentration is below threshold and no action potential is triggered.

High - Lead to high release of neurotransmitters in a short amount of time so the concentration is above threshold and an action potential can be triggered.

55
Q

How does Axon diameter affect conduction velocity?

A
  • Increasing diameter increases nerve conduction velocity.
    Therefore a large axon means a larger membrane and therefore more ion channels for a greater influx of diffusion.
  • Increasing myelination (more myelin) means more ion channels are concentrated at the nodes of ranvier and therefore increasing conduction velocity.
56
Q

How does temperature affect conduction velocity?

A
  • As temperature increases the amplitude and duration of action potentials decreases.
  • As temperature decreases the resting potential is reduced (depolarisation) and this leads to the formation of an action potential.
57
Q

What do Chemoreceptors measure?

A

A change in the chemical concentrations or partial pressures of 02 and CO2 in the body.

58
Q

What do Baroreceptors measure?

A

A change in the blood pressure of the body.

59
Q

What and where are the SAN and AVN nodes in the body?

A

SAN (Sinoatrial Node) - Right atrium of the heart.

AVN (Atrioventricular Node) - Between the ventricles and the atria in the centre.

60
Q

What do the SAN and AVN nodes do?

A

SAN - Controls the pace/rate of heart contractions (controls heart rate)
AVN -Sends an impulse down a bundle of His to cause Ventricular Contraction.
- Has a delay to enable the atria to empty before allowing the ventricles to contract.

61
Q

Define Myogenic.

A

Refers to cardiac muscle:

Innate/natural rhythm of contraction so heart muscle will contract without external impulses.

62
Q

How do SAN and AVN nodes work?

A

1) SAN initiates a heartbeat/ starts a heart rate.
2) SAN sends an electrical impulse across atria causing atrial contraction.
3) AVN delays electrical impulses allowing the atria to empty before the ventricles contract.
4) AVN sends an impulse down the bundle of His to the purkyne firbres causing the ventricles to contract from base up.

63
Q

What does the Autonomic nervous system control?

A

Involuntary (subconscious) activities of the internal muscles

64
Q

What do the sympathetic and parasympathetic nervous systems do?

A

Sympathetic - Speeds up activity by stimulating effectors

Parasympathetic - Slows down activity by inhibiting effectors.

65
Q

What is the Medulla Oblongata?

A

Region of the brain which controls the heart rate by sending impulses to the SAN node via the sympathetic or parasympathetic nervous system.

66
Q

What prevents the impulse from the SAN node from crossing into the ventricles? (Just cross into atria)

A

A layer of non-conductive tissue

Atrioventricular septum

67
Q

What do the 2 centres in the Medulla Oblongata do?

A

One centre is linked to the SAN node via the sympathetic nervous system —> Increases the heart rate,
and the other centre is linked to the SAN node via the parasympathetic nervous system —> Decreases the heart rate.

68
Q

How do Chemoreceptors cause a change in heart rate?

A
  • Blood has higher than normal CO2 concentration so the pH is lower.
  • Chemoreceptors detect the change in blood pH and therefore send nerve impulses to the Medulla Oblongata.
  • This sends impulses via the Sympathetic nervous system to the SAN node to increase the heart rate.
  • Increase in heart rate means that more CO2 is removed from the body via the lungs and the CO2 concentration returns to normal.
  • These chemoreceptors detect this change and the process repeats to reduce the heart rate by sending a message from the Medulla Oblongata to the SAN node via the parasympathetic nervous system.
69
Q

How do Baroreceptors cause a change in blood pressure?

A
  • Baroreceptors detect blood pressure changes and therefore send more impulses to the Medulla Oblongata.
  • This sends impulses via the Sympathetic (to increase heart rate and therefore blood pressure) and parasympathetic ( to decrease heart rate and therefore blood pressure) Nervous system to the SAN node.
  • SAN node controls the heart rate to increase it and therefore blood pressure or decrease the heart rate and therefore blood pressure
70
Q

What is Auxin?

A

A plant growth hormone that stimulates cell elongation in shoots and inhibits cell elongation in the roots.

71
Q

Give an example of an Auxin and what does it do?

A

Indole Acetic Acid (IAA):

  • Apical dominance
  • Cell elongation in shoots
  • Inhibits cell elongation in roots
72
Q

Define Apical Dominance

A

Inhibits lateral growth

Enabling plants to control how they grow.

73
Q

Define Tropism.

A

The direction of growth is in response to the direction of a stimulus

74
Q

Define Meristem

A

A region of plant tissue found at the growing tips of shoots and roots
- consisting of actively dividing cells (via mitosis) forming new tissues.

75
Q

What affect does Auxin have on shoots and roots?

A

Shoots - Stimulates cell elongation.

Roots - Inhibits cell elongation.

76
Q

How does auxin cause shoots to bend towards the light?

A
  • Auxins (IAA) produced in tip move laterally to the darker side of the shoots.
  • Increased [Auxin] concentration so auxin diffuses down the darker side of the shoot.
  • More auxin molecules bind to the receptor sites of cells on the darker side of the the shoot in the zone for elongation.
  • Cell walls of shaded side remain flexible for longer.
  • Cell walls on shaded side elongate more than the light side causing shoot to curve and grow in direction of light.

A-levels (23 decks)

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