Topic 6.5: Neurons and Synapses Flashcards Preview

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Flashcards in Topic 6.5: Neurons and Synapses Deck (50):
1

Define neuron

Neurons are specialised cells that function to transmit electrical impulses within the nervous system

2

What is a dendrite?

Dendrites – Short-branched fibres that convert chemical information from other neurons or receptor cells into electrical signals

3

What is an axon?

Axon – An elongated fibre that transmits electrical signals to terminal regions for communication with other neurons or effectors

4

What is a soma?

Soma – A cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival

5

Define resting potential

A resting potential is the difference in charge across the membrane when a neuron is not firing

In a typical resting potential, the inside of the neuron is more negative relative to the outside (approximately –70 mV)

6

What is the sodium-potassium pump?

The sodium-potassium pump is a transmembrane protein that actively exchanges sodium and potassium ions (antiport)

7

How is a resting potential generated?

Sodium-potassium pump expels 3 Na+ ions for every 2 K+ ions admitted (additionally, some K+ ions will then leak back out of the cell)
This creates an electrochemical gradient whereby the cell interior is relatively negative compared to the extracellular environment (as there are more positively charged ions outside of the cell and more negatively charged ions inside the cell)

8

What is an action potential?

Action potentials are the rapid changes in charge across the membrane that occur when a neuron is firing

9

What are the 3 main stages of the action potentials?

Action potentials occur in three main stages: depolarization, repolarization and a refractory period

10

What is depolarization?

Depolarisation refers to a sudden change in membrane potential – usually from a (relatively) negative to positive internal charge

11

What is the first step of depolarization?

In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon

12

After In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon, what is the next step of depolarization?

As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium

13

As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium, what is the last step of depolarization?

The influx of sodium causes the membrane potential to become more positive (depolarisation)

14

What is repolarization?

Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge)

15

What is the first step of repolarization?

Following an influx of sodium, potassium channels open within the membrane of the axon

16

After Following an influx of sodium, potassium channels open within the membrane of the axon, what is the next step of repolarization?

As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium

17

After As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium, what is the last step of repolarization?

The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarisation)

18

What is the refractory period?

The refractory period refers to the period of time following a nerve impulse before the neuron is able to fire again

19

Describe the refractory period

In a normal resting state, sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential)
Following depolarisation (sodium influx) and repolarisation (potassium efflux), this ionic distribution is largely reversed
Before a neuron can fire again, the resting potential must be restored via the antiport action of the sodium-potassium pump

20

Define nerve impulses

Nerve impulses are action potentials that move along the length of an axon as a wave of depolarisation

21

What is the propagation of nerve impulses caused by?

Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential

22

Define synapses

Synapses are junctions between neurons and between neurons and receptor or effector cells

23

What is the first step of chemical transfer across synapses?

When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels

24

After When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels, what is the next step of chemical transfer across synapses?

Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane

25

After Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane, what is the next step of chemical transfer across synapses?

The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft

26

After The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft, what is the next step of chemical transfer across synapses?

Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels

27

After Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels, what is the next step of chemical transfer across synapses?

The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal

28

After The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal, what is the last step of chemical transfer across synapses?

The neurotransmitters released into the synapse are either recycled (by reuptake pumps) or degraded (by enzymatic activity)

29

Define neurotransmitter

Neurotransmitters are chemical messengers released from neurons and function to transmit signals across the synaptic cleft

30

What does the central nervous system consist of?

brain and spinal cord

31

What does the peripheral nervous system consist of?

peripheral nerves (cranial and spinal)

32

What is the function of the central nervous system?

integrative control center

33

What is the function of the peripheral nervous system?

communication between CNS and body

34

What is the function of the sensory neurons?

conducts signals from receptors to CNS

35

What is the function of the motor neurons?

conducts signals from CNS to effectors

36

What is the function of the autonomic nervous system?

controls involuntary responses

37

What is the function of the somatic nervous system?

controls voluntary movement

38

What is the function of the sympathetic division?

mobilizes body system; flight or fight responses

39

What is the function of the parasympathetic division?

conserves energy; rest and digest responses

40

Define stimulus

A stimulus is a change in the environment (either external or internal) that is detected by a receptor

41

Define effectors

Effectors are organs (either muscles or glands) that produce a response to a stimulus

42

Define response

A response is a change in the organism resulting from the detection of a stimulus

43

What is the first step of stimulus-response model?

A stimulus is detected by a receptor

44

After A stimulus is detected by a receptor, what is the next step of the stimulus-response model?

Receptors transform environmental stimuli into electrical nerve impulses

45

After Receptors transform environmental stimuli into electrical nerve impulses, what is the next step of the stimulus-response model?

These impulses are then transmitted via neurons to the central nervous system where decision-making occurs

46

After These impulses are then transmitted via neurons to the central nervous system where decision-making occurs, what is the next step of the stimulus-response model?

When a response is selected (consciously or unconsciously), the signal is transmitted via neurons to effectors

47

After When a response is selected (consciously or unconsciously), the signal is transmitted via neurons to effectors, what is the last step of the stimulus-response model?

effectors produce a response to stimulus

48

Define reflex

A reflex is a rapid and involuntary response to a stimulus, resulting from a simple signalling pathway called a reflex arc

49

What is the function of excitatory neurotransmitters?

Excitatory neurotransmitters trigger depolarisation, increasing the likelihood of a response

50

What is the function of inhibitory neurotransmitters?

Inhibitory neurotransmitters trigger hyperpolarisation, decreasing the likelihood of a response

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