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biology sem 2 > Nerves > Flashcards

Nerves Flashcards

1
Q

What are neurones?

A

specialised cells that allow communication between different parts of the body in the form of nerve impulses

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2
Q

what are the characteristics of neurones?

A
  • excitable (can detect/respond to stimuli)
  • conductive (transmit nerve impulses/action potentials)
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3
Q

what are the three types of neurones?

A
  • sensory
  • intermediate/relay
  • motor
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4
Q

what do sensory neurones do?

A

Transmit nerve impulses from receptors to the central nervous system (brain/spinal cord)

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5
Q

what do intermediate/relay neurones do?

A

Found inside CNS (brain/spinal cord) and transmit impulses to and from other neurones

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6
Q

what do motor neurones do?

A

Transmit nerve impulses from CNS to an effector

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7
Q

what is the difference between nerves and neurones?

A

Nerves are collections of neurons that are joined together by connective tissue.

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8
Q

what are reflex arcs?

A

A reflex arc is a pathway along which nerve impulses are passed from a receptor to effector without involving any conscious thought.

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9
Q

How do nerve impulses transmit?

A
  • neurones transmit impulses as electrical signals
  • These signals are brief changes in the distribution of electrical charges across the plasma membranes of neurones
  • The change in electrical charge is caused by the movement of sodium ions and potassium ions across the plasma membrane
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10
Q

what is the resting potential?

A
  • Before an impulse can be generated in a neurone there must be a negative charge across the neurone membrane
  • the membrane is said to be polarised
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11
Q

how is the resting potential created?

A
  • There is a protein pump in the neurone plasma membrane – called a sodium/potassium pump
  • It pumps sodium ions out of the cell and potassium ions into the cell
  • This is an active process as the ions are pumped against their concentration gradient and requires ATP
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12
Q

How much Na+ is pumped out for every K+ pumped in?

A

3 Na+ are pumped out for every 2 K+ pumped in

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13
Q

what happens to the Na+ and K+?

A

Some of the Na+ and K+ then diffuse back across the membrane but more K+ diffuses across than Na+

This leads to more positive ions outside compared to inside creates a potential difference across the membrane -65mV

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14
Q

what is the action potential?

A

Action potentials are a brief reversal of the resting potential across the cell membrane of a neurone

-They cause a potential difference across the membrane

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15
Q

What potential difference does the action potential cause?

A

+40mV

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16
Q

what does an action potential show?

A

what happens at one particular point in an axon membrane

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17
Q

what is the function of a neurone?

A

to transmit action potentials across the whole length

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18
Q

what does an action potential across the axon cause?

A

triggers the production of an action potential just next to it

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19
Q

action potential formation step 1

A

The membrane is polarised with a resting potential of -65mV on the inside compared with the outside

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20
Q

action potential formation step 2

A

Sodium ion channels open and some sodium ions diffuse into the cell

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21
Q

action potential formation step 3

A

The membrane depolarises and the inside becomes less negative compared with the outside and reaches a threshold value of -50mV

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22
Q

action potential formation step 4

A

Voltage gated sodium ion channels open and many sodium ions flood in. The inside of the cell becomes positive compared with the outside of the cell

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23
Q

action potential formation step 5

A

The potential difference across the membrane reaches +40mV . The cell is depolarised

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24
Q

action potential formation step 6

A

The sodium ion channels close and the potassium ion channels open

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25
action potential formation step 7
Potassium ions diffuse out of the cell and the cell becomes repolarised and negative inside compared with outside
26
action potential formation step 8
The potential difference across the membrane becomes more negative than -65mV and the cell is said to be hyperpolarised
27
action potential formation step 9
The potassium channel closes and the sodium potassium pumps restore the resting potential of -65mV
28
what is the transmission of action potentials along a neurone: STEP 1
Temporary depolarisation of the membrane where the action potential is causes a “local circuit” to be set up between the depolarised region and the resting regions either side
29
what is the transmission of action potentials along a neurone: STEP 2
This depolarises regions next to the action potential and causes voltage gated sodium channels to open
30
what is the transmission of action potentials along a neurone: STEP 3
Sodium ions flood in A few milliseconds later potassium ions flood out Causes an action potential
31
What direction is the action potential usually transmitted?
in one direction, ahead of the previous action potential
32
why does the action potential only move in this direction?
Because the region behind an action potential takes time to recover from its own action potential and is temporarily incapable of generating a new one – refractory period
33
what does the speed of conduction of action potentials along a neurone depend n?
axon diameter myelination of neurone number of synapses involved
34
what does axon diameter do to the speed of conduction?
wider axons conduct faster
35
what does myelination of neurone do to the speed of conduction?
Myelinated neurones transmit impulses faster than non myelinated neurones
36
what does the number of synapses of neurone do to the speed of conduction?
more synapses = slower speed
37
what are some neurones surrounded by?
schwann cells which wrap themselves around the axon
38
what are gaps between schwann cells called?
Nodes of Ranvier
39
structure of neurones
40
what is myelin sheath made from?
lipids and proteins
41
what forms the myelin sheath?
node of reanvier and schwann cells. described as being myelinated
42
what is the role of myelin sheath
myelin insulates axons and increases speed of transmission of impulses
43
what can't flow through myelin sheath?
sodium and potassium
44
where does sodium and potassium flow across?
the membrane at the nodes of ranvier
45
what is saltatory conduction?
Action Potentials “jump” from one node to the next which is called saltatory conduction
46
what does saltatory conduction speed up transmission by?
50 times
47
what is a synapse?
a junction between 2 neurones
48
what is the synaptic cleft?
There is a very narrow gap of about 20nm between neurones called the synaptic cleft.
49
why are neurotransmitters used across synapses?
An action potential cannot cross the synaptic cleft so chemicals called neurotransmitters are used.
50
Synapses that use acetylcholine as the neurotransmitter...
called cholinergic synapses
51
Pre-synaptic neurone
neurone carrying the impulse before the synaptic cleft
52
post-synaptic neurone
neurone receiving impulse after the synaptic cleft
53
how are neurotransmitters made?
Neurotransmitters are made by the pre-synaptic neurone
54
how are neurotransmitters stored?
stored in synaptic vesicles at the end of the axon in the synaptic knob.
55
what does the membrane of the post-synaptic neurone have?
The membrane of the post-synaptic neurone has membrane receptors which have specific binding sites for neurotransmitters.
56
What happens at a cholinergic synapse? Stage 1
An action potential arrives at presynaptic membrane. Voltage gated calcium channels in the presynaptic membrane open, calcium ions enter the presynaptic neurone.
57
What happens at a cholinergic synapse? Stage 2
Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft.
58
What happens at a cholinergic synapse? Stage 3
Acetylcholine diffuses cross the synaptic cleft and binds to specific receptor sites in the post synaptic membrane.
59
What happens at a cholinergic synapse? Stage 4
Sodium channels open. Sodium ions diffuse into the postsynaptic membrane causing depolarisation, which may initiate an action potential.
60
What happens at a cholinergic synapse? Stage 5
Acetylcholinesterase is an enzyme that breaks down acetylcholine to choline & ethanoic acid. These products diffuse back into the presynaptic neurone where acetycholine is resynthesised using ATP from the mitochondria.
61
what is the roles of synapses?
- Ensure one way transmission of impulses - Acclimatisation: synapse becoming fatigued - Summation: amplification of low level signals - Involved in memory and learning - Increase possible range of actions in response to a stimulus
62
Roles of a synapse: Impulses are only transmitted in 1 direction.
- NT only produced in the PRE-synaptic neurone in VESICLES - NT binds to RECEPTORS only found on POST-synaptic membrane.
63
Roles of a synapse: can be excitatory or inhibitory.
Excitatory: presynaptic neurone releases NT which binds to specific/complementary receptors on post synaptic neurone that results in Na+ channels opening and Na+ enter post synaptic neurone which cause post synaptic neurone membrane to depolarise and AP generated in post synaptic neurone
64
Roles of a synapse - Summation
If the stimulus is weak there might not be enough NT released from ONE presynaptic neurone to allow threshold to be reached in post synaptic neurone to depolarise it/create an AP
65
Roles of a synapse Integration of communication – convergence or divergence
One post synaptic neurone generate AP in response to impulses from many presynaptic neurones – useful when several stimuli require one coordinated response Many post synaptic neurones generate AP in response to impulses from one presynaptic neurones – useful when one stimuli require many coordinated responses
66
Roles of a synapse - Acclimatisation.
Extensive repeated stimulation of the same synapse results in the synaptic bulb running out of the neurotransmitter (acetylcholine). This means the synapse is 'fatigued', so can no longer transmit the action potential.
67
Roles of a synapse – Memory and Learning
Create synapses between neurones to learn
68
what is the effect of nicotine at synapses?
similar in shape to Ach so fits in Ach receptors. Initiates action potentials. Large dose can be fatal.
69
what is the effect of botulinum toxin at synapses?
prevents release of Ach
70
what is the effect of Organophosphorous insecticides at synapses?
inhibits acetylcholinesterase so Ach not broken down so continuous action potentials on postsynaptic membrane
71
structure and function of non-myelinated neurones
- AP conducted at slower rate (0.5-10ms-1) - Has no Nodes of Ranvier - Not associated with Schwann cells therefore no myelin sheath - Found in CNS & in nerves controlling organs with no conscious control
71
structure and function of myelinated neurones
- AP conducted at faster rate (100-120ms-1) - Has Nodes of Ranvier every 1- 3mm. (Node is 2 - 3µm wide) - Associated with Schwann cells therefore myelin sheath - Found mainly in peripheral nervous system
72
what happens at the synapse?
- ACTION POTENTIAL arrives - Uptake of Ca2+ ions - Vesicles containingacetylcholine( a neurotransmitter) move and fuse with the PREsynaptic membrane - Acetylcholine released by exocytosis - Diffuses across synaptic cleft - Acetylcholine binds with SPECIFIC COMPLEMENTARY SHAPED RECEPTOR on POSTsynaptic membrane - Sodium ion channels open - Na+ floods in to presynaptic NEURONE by diffusion - Depolarises PRE SYNAPTIC membrane - Action potential initiated
73
what does Acetylcholinesterase split Ach into?
choline and ethanoic acid otherwise continuous action potentials would be fired. Choline goes back to the presynaptic neurone and combines with acetyl to form Ach again

biology sem 2 (7 decks)

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