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bio topic 6 > nervous control > Flashcards

nervous control Flashcards

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Biology 101 flashcards
1
Q

Give 3 functions of the nervous system

A
  • Communication
  • Coordination
  • To detect changes in the external and internal environments, evaluate this information and make appropriate responses
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2
Q

Compare the Nervous and Endocrine systems [5]

A

NERVOUS
Electrical impulses
Impulses pass via neurones
Fast transmission
Short-lived effect
Localised effect

ENDOCRINE
Chemical message
Chemicals move in bloodstream
Slow transmission
Long-lived effect
Widespread effect

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3
Q

Neurone

A

Nerves are bundles of neurones

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4
Q

Give 6 parts of the structure of a neurone

A

Cell Body
Dendrites
Axon
Schwann cells
Myelin sheath
Nodes of Ranvie

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5
Q

Cell body function [2]

A
  • contains a nucleus, large amounts of mitochondria and rough endoplasmic reticulum
  • is associated with production of proteins and is a neurotransmitter
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6
Q

Dendrites function

A

Multiple small fibres that carry nerve impulses towards the cell body

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7
Q

Axon function

A

A single long fibre that carries nerve impulses away from the cell body

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8
Q

Schwann cells

A

Are individual cells that surround the axon by wrapping around many times, protecting it and providing electrical insulation

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9
Q

Myelin sheath [3]

A
  • Forms the covering of axon
  • Made of membranes of the Schwann cells.
  • Rich in a lipid known as myelin
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10
Q

Nodes of Ranvier

A

Gaps between adjacent Schwann cells where there is no myelin sheath.

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11
Q

The Nerve Impulse [4]

A
  • Mainly involves the ions Na+, K+
    The impulse is determined by…
  • the potential difference across the membrane
  • the concentration of the ions in and around the neurone
  • the movement of ions across the axon membrane
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12
Q

What is Resting Potential? [2]

A
  • The inside of the axon membrane has a relatively more negative charge of -65mV, or resting potential
  • The neurone is polarised
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13
Q

Maintaining Resting Potential [6]

A
  • Our bodies use a lot of energy to keep resting neurones polarised

At the sodium-potassium pump in the neurone membrane:
- 3 Na+ move out for every 2 K+ that move in
- ATPase allows the hydrolysis of ATP
- 1 ATP is converted to ADP & Pi, releasing energy

  • The membrane also contains many permanently open potassium ion channels, and only a few sodium ion channels
  • This means that the membrane is 50x more permeable to K+ than Na+ so some K+ move out, down their concentration gradient
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14
Q

Action Potential [4]

A
  • An action potential refers to when an impulse passes along a neurone
  • A receptor that is stimulated sufficiently (creates a large enough generator potential) will cause a reversal of charges across the membrane
  • The charge alters from -65mV to +45mV
  • The membrane is depolarised.
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15
Q

An action potential is an all or nothing response…

A

Meaning unless the threshold value is reached the impulse will not occur

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16
Q

Action potential are the same size so size of stimulus depends on… [2]

A
  • More impulses in a time = larger stimulus
  • Neurones can have different threshold values. The brain can interpret the type of neurone and therefore the size of stimulus
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17
Q

When as impulse is received…

A

Depolarisation
Repolarisation
Overshoot or hyperpolarisation
Back to resting potential

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18
Q

Depolarisation [5]

A
  • This is the start of the action potential
  • The initial stimulus causes some of the voltage-gated Na+ channels in the membrane to open
  • Sodium ions enter the axon, diffusing down their concentration gradient
  • This causes more voltage-gated Na+ channels to open and more sodium ions to enter
  • The relative charge of the axon goes from -65mV to +45mV
19
Q

Repolarisation [6]

A
  • This is the continued process of action potential
  • A potential of +45mV causes the sodium ion voltage-gated channels to shut
  • The voltage-gated potassium ion channels open
  • Potassium ions move down their concentration gradient out of the axon
  • The potential difference across the membrane drops
  • Charge goes from +45mV to -65 mV
20
Q

Hyperpolarisation [4]

A
  • Movement of the potassium ions cause hyperpolarisation, where the membrane overshoots the resting potential of -65mV
  • The potential difference reaches -80mV
  • The voltage-gated potassium ion channels shut (meaning both channels are shut)
  • This point is also known as the refractory period when no further action potentials can take place
21
Q

The Refractory Period [2]

A
  • This is a short period of time that occurs when the neurone cannot be stimulated as it recovers from the previous stimulus
  • The voltage-gated sodium ion channels can’t open
22
Q

Why is the refractory period important? [3]

A
  • Ensures impulses can only travel in one direction
  • Allows separate impulses
  • Limits the strength of impulse
23
Q

When are the voltage-gated sodium ion channels open and closed?

A

Voltage-gated sodium ion channels:
OPEN = depolarisation
SHUT = polarisation, repolarisation, hyperpolarisation

Voltage-gated potassium ion channels:
OPEN = repolarisation
SHUT = polarisation, depolarisation, hyperpolarisation

24
Q

Propagation of an Impulse in Unmyelinated Neurones

A

An action potential in one part of a neurone will stimulate an action potential in the next section

25
Q

Propagation of an Impulse in Myelinated Neurones [3]

A
  • The myelin sheath in made of lipid, an insulator
  • The action potential cannot move through the sheath
  • Saltatory conduction (jumping) takes place
26
Q

Saltatory Conduction

A

This results in the localised circuit forming between the nodes of Ranvier

27
Q

Give 3 factors affecting the speed of transmission

A
  • Temperature
  • Diameter of Neurone
  • Myelination
28
Q

Temperature [2]

A

temperature increases
- greater kinetic energy, faster transmission
temperature exceeds optimum
- proteins in the membrane denature, slower transmission

29
Q

Diameter [2]

A

Larger diameter = faster transmission
- It is easier to maintain concentration gradients in wider neurones than narrower
- There is less ‘leakage’ of ions

30
Q

Myelination [3]

A
  • Myelinated neurones conduct nerve impulses faster than non-myelinated neurones
  • because the action potential ‘jumps’ between the Schwann cells of the myelin sheath
  • and only needs to be conducted at the nodes of Ranvier
31
Q

Synaptic Transmission [7]

A
  • The action potential causes Ca2+ to diffuse into the synaptic knob
  • This causes vesicles of neurotransmitter to fuse with presynaptic membrane and, release the neurotransmitter into the synaptic cleft
  • Neurotransmitter diffuses across and attaches to receptors on the post-synaptic membrane
  • Ion channels open, causing depolarisation in post synaptic neurone
  • If depolarisation above threshold value then action potential is stimulated along the post synaptic axon
  • Neurotransmitter must be removed to prevent continual stimulation
  • The neurotransmitter, diffuses back, is broken down and is recycled

NEUROTRANSMITTER = acetylcholine

32
Q

1 - Calcium Channels Opening [3]

A
  • The incoming action potential causes depolarisation in the synaptic knob
  • This causes calcium ion channels to open
  • Calcium ions (Ca2+) diffuse into the synaptic knob
33
Q

2 - Neurotransmitter Release [2]

A
  • The influx of calcium ions causes synaptic vesicles to FUSE with the presynaptic membrane
  • This releases neurotransmitter into the cleft
34
Q

3 - Sodium Channels [3]

A
  • Neurotransmitter (acetylcholine) diffuses across the synaptic cleft
  • Neurotransmitter (acetylcholine) binds to the receptor site on the
    sodium ion channels, found on the post-synaptic neurone membrane
  • Sodium ion channels open
35
Q

4/5 - New Action Potential [2]

A
  • Depolarisation inside the postsynaptic neurone must be above a threshold value
  • If the threshold is reached a new action potential is sent along the axon of the post- synaptic neurone
36
Q

6 - Acetylcholinesterase [4]

A
  • Attachment of the acetylcholine to the receptor will keep the sodium ion channels open
  • This would mean an action potential would be continually stimulated
  • Acetylcholinesterase is a hydrolytic enzyme
  • Breaks up acetylcholine (the neurotransmitter) into acetyl (ethanoic acid) and choline
37
Q

7 - Remaking Acetylcholine [5]

A
  • ATP released by mitochondria is used to recombine acetyl (ethanoic acid) and choline thus recycling the acetylcholine
  • This is stored in synaptic vesicles for future use
  • More acetylcholine can be made at the SER
  • Sodium ion channels close in the absence of acetylcholine at their receptor sites
  • The synapse is now ready to be used again
38
Q

Features of Synapses

A

Unidirectionality
Inhibition
Summation

39
Q

Unidirectionality [2]

A
  • The impulse can only be sent from the presynaptic neurone to the postsynaptic neurone
  • This is due to the position of neurotransmitter vesicles and sodium ion channels
40
Q

Inhibition [5]

A
  • Some neurotransmitters stimulate chloride ion channels on the postsynaptic membrane to open and also potassium ion channels to open
  • Chloride ions (Cl-) diffuse INto the postsynaptic neurone
  • Potassium ions diffuse out
  • This hyperpolarises the neurone
  • This make it harder to achieve a action potential
41
Q

Types of Summation

A
  • Summation
  • Spatial Summation
  • Temporal Summation
42
Q

Summation [3]

A
  • Low frequency action potentials often release insufficient amounts of neurotransmitter to exceed the threshold in the postsynaptic neurone
  • Summation allows action potentials to be generated
  • This enables a build up of neurotransmitter in the synapse
43
Q

Spatial Summation [2]

A
  • A number of different presynaptic neurones share the same synaptic cleft
  • Together they can release enough neurotransmitter to create an action potential
    (multiple neurones)
44
Q

Temporal Summation [2]

A
  • A single presynaptic neurone releases neurotransmitter many times over a short period
  • If the total amount of neurotransmitter exceeds the threshold value an action potential is sent
    (1 neurone)

bio topic 6 (8 decks)

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