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Component 3 Part 2 Eduqas Biology A Level > Nerves > Flashcards

Nerves Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Dendrites

A

Thin extensions which carry the impulses towards the cell body.

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2
Q

Axon

A

Long membrane-covered cytoplasmic extension, which transmits impulses away from the cell body.

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3
Q

Schwann cells

A

Cells which surround and support peripheral neurones

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4
Q

Myelin sheath

A

Schwann cells grow around axons to form this multi-layered fatty sheath. Acts as an electrical insulator that speeds up transmission along the axon. Humans have both myelinated and unmyelinated nerve cells.

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5
Q

Nodes of Ranvier

A

Areas along the axon where the myelin sheath thins

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6
Q

Cell Body

A

Part of the neurone which contains the nucleus, RER, numerous mitochondria and other cell organelles

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7
Q

Sensory Neurone

A

Relays messages from the receptors to the brain or the spinal cord - moves away from central organ or point…?

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8
Q

Interneurone

A

Relays messages from the sensory neurone to the motor neurone. Makes up the brain and spinal cord.

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9
Q

Motor Neurone

A

Relays messages from the brain or spinal cord to the muscles and organs - moves towards a central organ or point…?

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10
Q

What is saltatory conduction?

A

Conduction that jumps between the Schwann cells to the nodes of Ranvier. It is faster.

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11
Q

Reflex Arc

A

pathway travelled by the nerve impulses during a reflex action.

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12
Q

Reflex Action

A

rapid, involuntary response to a stimulus. Most are spinal reflexes - information may be transmitted to the brain but it is the spinal cord, not the brain, that is responsible for the integration of sensory information and a transmitted response.

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13
Q

What are the subsections of the nervous system?

A

CNS and peripheral (NS)

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14
Q

What are the two parts of the CNS?

A

brain and spinal cord

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15
Q

what does the peripheral nervous system do?

A

controls organs and muscles

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16
Q

What are the subsections of the peripheral nervous system?

A

Autonomic and Somatic

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17
Q

What does the autonomic PNS do?

A

controls self-regulated action of internal organs and glands

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18
Q

What does the somatic PNS do?

A

controls the voluntary movements of skeletal muscles

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19
Q

What are the two types of autonomic peripheral nervous system?

A

Sympathetic (arousing) and Parasympathetic (calming)

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20
Q

What is the reflex arc (or arc for any voluntary response)?

A

Stimulus -> Receptor -> Co-ordinator -> Effector -> Response

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21
Q

Example of stimulus

A

Environmental change

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22
Q

Example of Receptor

A

Specialised cells

23
Q

Example of co-ordinator

A

brain / spinal cord

24
Q

Example of effector

A

muscles/ glands

25
Q

Example of response

A

change to stimulus

26
Q

Experiments with neurones…?

A

Microelectrodes can be used to stimulate the axon and cathode ray oscilloscopes can be used to measure potential difference across the membrane

27
Q

How is potential difference across the membrane actually determined?

A

By the potential difference between the tissue fluid and the axon cytoplasm.

28
Q

What axons can be used in experiments and why?

A

Squid axons, as these are large enough to attach electrodes to them.

29
Q

Nervous system in simple organisms, e.g. hydra?

A

Nerve net system that consists of simple nerve cells with short extensions that branch out in a number of different directions, joining to each other with multiple synapses. It connects photoreceptors with touch-sensitive nerve cells in the body wall and tentacles.

30
Q

Why do hydra only have a nerve net?

A

They don’t need a complex nervous system to succeed as they have little need for directional response to a stimulus and few sensory cells.

31
Q

Describe nerve cells in hydra

A

Only one type of short cells, no myelin sheath so conduction speed is slow. Direction of impulse happens in both directions (humans only one way) and a limited number of stimuli can be detected. There is a small number of effectors.

32
Q

What is a ‘local circuit’ in regard to an axon?

A

A local circuit is a local flow of electrical current, usually caused by the influx of Na+ ions (the action potential).

33
Q

What is propagation?

A

The movement of a series of local circuits along an axon…?

34
Q

How do human neurones compare in length?

A

sensory & motor long, relay is short

35
Q

How do human neurones compare in location of the cell body?

A

Sensory neurones have their cell bodies in the dorsal root ganglion, whereas the motor and relay neurones have theirs in the grey matter.

36
Q

What are the 4 proteins involved in nerve impulse transmission?

A

Na+/K+ ion pump
K+ ion leakage channel
Na+ ion voltage-gated channel (sodium gated channel)
K+ ion voltage-gated channel (potassium gated channel)

37
Q

What do Na+/K+ ion pumps do?

A

pump out 3Na+ for every 2K+ in, using one molecule of ATP for active transport. They are always working, as long as ATP is available.

38
Q

What do K+ ion leakage channels do?

A

Allows K+ to ‘leak’ back out, along the concentration gradient - always open. They make the membrane more permeable to K+ than Na+.

39
Q

What do sodium/potassium ion voltage gated channels do?

A

Can open and close -> allows the ability to change the permeability of the membrane. Facilitates action potential to be sent through the axon.

40
Q

What is the resting potential?

A

The potential difference or voltage across the neurone cell membrane, where the neurone is at rest when it is not conducting another impulse.

41
Q

Describe polarisation

A

The sodium potassium pumps in the plasma membrane actively transport so that there is more of a positive charge outside the axon. the membrane is relatively impermeable to the sodium ions so they build up on the outside of the axon, but it is permeable to potassium ions from the channel proteins so they diffuse outside the axon. As a result the membrane is polarised. At this point, the pd across the membrane is called the resting potential and measures -70mV. The sodium and potassium gated channels finally close.

42
Q

What else in the axon helps the potential difference to be negative?

A

They cytoplasm also contains negatively charged proteins and inorganic phosphate ions.

43
Q

What is a nerve impulse in the axon membrane?

A

The movement of ions (Na+ and K+) into and out of the axon membrane, regulated by the changes of permeability in the membrane, resulting in the charges (and overall potential difference) inside and outside of the action changing.

44
Q

What is the resting potential?

A

Potential difference between the inside and outside of the axon membrane, WHEN A NERVE IMPULSE IS NOT BEING CONDUCTED.

45
Q

What happens in the resting potential?

A

The Na+/K+ pump actively transports 3 Na+ ions out of the axon per 2 K+ ions into the axon. This makes conc. gradients with a high concentration of Na+ outside the axon and a high concentration of K+ inside the axon. The K+ channels that are always open allow some K+ ions to diffuse back out, down the conc. gradient established by the pump. As a result, the outside ends up having more positive ions SO WE SAY THE INSIDE IS NEGATIVE AT A RESTING POTENTIAL OF 70mV. The membrane is said to be polarised = no nerve impulse.

46
Q

What is an action potential?

A

The rapid, fleeting change in potential difference across the membrane is called an action potential. This happens when stimulation of an axon results in a brief reversal in the potential difference across the membrane from -70mV to +40mV.

47
Q

What happens in an action potential?

A

Stimulation causes voltage-gated Na+ channels to open - the axon membrane becomes permeable to Na+. Na+ diffuses into the axon down the concentration and charge gradient (set previously in polarisation by the pump). The influx of sodium ions causes the inside to become more positive and the potential difference becomes +40mV. This is an example of positive feedback. THE MEMBRANE IS SAID TO BE DEPOLARISED.

48
Q

What is an electrochemical gradient?

A

The concentration and charge gradients combined create an electrochemical gradient for Na+ ions in depolarisation.

49
Q

What is meant by the axon having ‘reached the threshold’?

A

If enough Na+ ions diffuse through the channels that have opened due to the stimulus to increase the axon charge to -55mV, we say this. All the channels will then open and the ions will rapidly rush in.

50
Q

What is meant by the ‘all or nothing law’?

A

Either the membrane is depolarised or it is not. There is no such thing as a small or large stimulus. The need for a ‘threshold stimulus’ is part of this.

51
Q

What is a ‘threshold stimulus’?

A

A stimulus that opens enough Na+ channels to reach -55mV (the threshold).

52
Q

The greater the stimulus…?

A

The greater the frequency of action potentials.

53
Q

Repolarisation

A

A fraction of a second after depolarisation occurs, the voltage-gated K+ channels open, and the voltage gated sodium channels close. The membrane becomes more permeable to K+, which diffuse out of the axon, down their concentration gradient. This removal of positive charge starts to REPOLARISE the membrane.

54
Q

Hyperpolarisation

A

Due to so many K+ leaving the axon, the inside of the membrane briefly becomes even more negative than the normal resting potential - an overshoot called hyperpolarisation.

Component 3 Part 2 Eduqas Biology A Level (7 decks)

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