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Biology Alevel > Neuronal Communiation > Flashcards

Neuronal Communiation Flashcards

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1
Q

What are neurones and nerves?

A

Specialised cells of nervous system which carry electrical impulses around body

Bundle of neurones = NERVE

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2
Q

Features fund in all types of neurone?

A

Axon
Cell body - contains nucleus/other cellular structures
Axon terminal - end of axon , contain many nerve endings
These nerve endings allow neurones to connect to many other neurones /receive impulses from them , forming network for easy communication

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3
Q

What is meant when some neurones are myelinated? How is it beneficial?

A

Axon is INSULATED by a myelin sheath , with small uninsulated sections along its length —> NODES OF RANVIER
Myelin sheath made of specialised cells —> Schwann cells

So electrical impulses don’t travel down whole axon- jump from one node to next , reducing time wasted transferring impulse from 1 cell to another

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4
Q

Why does impulse travel more slowly non myelinated neurones ?

A

Axon is uninsulated so impulse travels along entire length of axon
- travels more slowly

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5
Q

3 types of neurone and function?

A

Sensory : carry impulses from RECEPTORS —> CNS (brain or spinal chord)
Relay : found within CNS and connect SENSORY —> MOTOR NEURONES
Motor: carry impulses from CNS —> EFFECTORS

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6
Q

Structure of 3 types of neurone?

A

Motor : large cell body at one end that lies in SPINAL CHORD/BRAIN
- nucleus in cell body
- highly branched dendrites extending from cell body —> large SA for axon terminals of other neurones when communicating

Relay : short, high branched axons and dendrites

Sensory: cell body that branches off middle of cell
- single long dendron carries impulses TO cell body /axon that carries impulse AWAY from cell body

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7
Q

What is a stimulus and a receptor cell?

A

Stimulus: Detectable change in internal/external environment of an organism

Receptor cells respond to a stimulus
- they are transducers - convert energy from one form into energy in an electrical impulse within sensory neurone

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8
Q

What are pacinian corpuscles ?

A

Found at ends of sensory neurone axons - made of layers of membrane around end of neurone separated by a gel
- gel between layers contain sodium ions (na+)

Section of axon surrounded by layers of membrane contain stretch-mediated sodium ion channels - OPEN when SUFFICIENT PRESSURE APPLIED
- allows Na+ to flow into neurone - electrical potential difference across axon membrane established - GENERATOR POTENTIAL

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9
Q

What is resting potential?

A

In a resting axon (not transmitting impulses) , INSIDE of axon always has NEGATIVE electrical potential compared to OUTSIDE
- this potential difference is usually -70mV inside axon

Sodium potassium pumps* - actively transport USING ATP , 3Na+ ions OUT of axon and 2 K+ ions INTO axon

Differential membrane permeability - membrane not as permeable to Na+ ions - channels mainly closed- so cant diffuse back in —> CREATES SODIUM ION ELECTROCHEMCIAL GRADIENT
K+ ION CHANNELS are mainly open so membrane permeable to K+ ions - diffuse back OUT axon down electrochemical grad (HIGH —> LOW)

  • More NEGATIVE inside neurone - increase ELECTROCHEMICAL GRAD
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10
Q

2 factors contributing to establishing/maintaining resting potential?

A
  • Active transport of sodium ions and potassium ions
  • Differential membrane permeability
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11
Q

What are action potentials caused by?

A

Rapid movement of sodium and potassium ions across the membrane of axon

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12
Q

What are voltage gated channel proteins?

A

Channel proteins in axon membrane that changes shape to allow sodium and potassium ions to pass through
- open and close depending on voltage (electrical potential) across axon membrane
Closed when *axon membrane at resting potential

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13
Q

Stage 1 of an action potential?

A

STIMULUS (electrical impulse/chemical change to membrane of neurone)
- triggers Na+ ion channels in membrane to open —> Na+ ions diffuse into neurone down ELECTROCHEMICAL GRADIENT
When large enough stimulus detected by neurone, RESTING POTENTIAL —> ACTION POTENTIAL

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14
Q

Stage 2 of an action potential?

A

DEPOLARISATION
Threshold of -55mV is reached , an action potential is stimulated and so:

Voltage-gated sodium ion channels in the axon membrane open
Sodium ions pass into the axon down the electrochemical gradient (high conc -> low conc)
- inside of the axon is - , attracting the + charged sodium ions
The movement of sodium ions reduces the potential difference across the axon membrane as the inside of the axon becomes less negative – depolarisation
Depolarisation triggers more channels to open, allowing more sodium ions to enter and causing more depolarisation - positive feedback
The action potential will reach a potential of around +30mV

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15
Q

Stage 3 of an action potential?

A

REPOLARISATION
Once pd reached 30mV , all Na+ voltage gated channel proteins CLOSE in this section , stopping further diffusion of Na+ into axon
K+ ion voltage gated channel proteins in this section OPEN —> diffusion of K+ OUT of axon (DOWN CONC GRAD)
- returns pd to Normal (-70mV)- REPOLARISATION /example of negative feedback

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16
Q

Stage 4 of an action potential?

A

HYPERPOLARISATION
K+ ion channels are slow to close so too many K+ ions diffuse out of neurone - hyperpolarisation
- pd across this section of axon membrane is more negative than normal resting potential

17
Q

Stage 5 of action potential?

A

Once the K+ ion voltage gated channel proteins are closed , the SODIUM-POTASSUM PUMP restores resting potential
- sodium ion channel proteins in this section of membrane become responsive to depolarisation again

18
Q

How are action potentials transmitted along an axon?

A

An action potential triggered —> depolarisation* of that section of the axon - sodium ions channels open at that point
Na+ ions can diffuse ACROSS membrane into neurone
Na+ ions diffuse sideways along neurone, away from area of high conc —> movement of charged particles is LOCAL CURRENT
Local current causes slight depolarisation further along neurone, causing voltage gated Na+ channels to OPEN - cause FULL DEPOLARISATION along neurone (bc more Na+ ions flood in)
The previous section of the axon is in the repolarisation stage (the Na+ channels are closed and K+ channels are open) and is unresponsive
- makes the action potentials discrete events/ the impulse can only travel in one direction

19
Q

What is the all or nothing principle?

A

An impulse is only transmitted from receptor to sensory neurone , if the initial stimulus is sufficient to increase membrane potential ABOVE threshold potential

Stronger stimulus = increased frequency of impulses

20
Q

What is the refractory period?

A

When both Na+ and K+ channels are CLOSED
- when this occurs, this section of the axon membrane is in a period of recovery and is unresponsive

21
Q

Importance of refractory period?

A
  • ensures action potentials are discrete events —> stopping from merging into one another
  • ensures that ‘new’ action potentials are generated ahead (further along axon) as region behind is recovering from the action potential that has just occurred
  • impulse can only travel in one direction - for the successful /efficient transmission of nerve impulses
  • minimum time between action potentials
  • determining max frequency at which impulses are transmitted along neurones
22
Q

What is the speed of conduction and what is it determined by?

A

How quickly the impulse is transmitted along a neurone

Determined by:
Myelination
Diameter of the axon
Temperature

23
Q

How does myelination affect speed of conduction?

A

Unmyelinated neurones —> speed is very SLOW
- Bc depolarisation must occur along whole membrane of axon

When myelin is present —> increases SPEED
- action potentials can only occur at the nodes of ranvier (uninsulated section of axon)
Presence of Schwann cells mean action potentials ‘jump’ from one node to next —> SALTATORY CONDUCTION - allow impulse to travel much faster

24
Q

How does diameter affect speed of conduction ?

A

Thicker axons - impulse conducted at higher speed
- as axon membrane will have larger SA for diffusion of ions , increasing rate of diffusion through channels - INCREASE RATE of DEPOLARISATION/ACTION POTENTIALS

Axons with larger diameter also have greater volume of cytoplasm (contains ions) - reduce electrical resistance so action potential can push into next section faster

25
Q

How does temperature affect the speed of conduction?

A

Colder conditions can slow down conduction
- less KE available for facilitated diffusion of K+ and Na+ ions during an action potential

26
Q

What is a synapse and what do they consist of?

A

Junction where 2 neurones meet

Consists of :
Presynaptic Knob
Synaptic cleft - small gap between 2 neurones
Postsynaptic membrane

27
Q

What are cholinergic synapses?

A

Synapses that use acetylcholine (ACh) as a neurotransmitter

28
Q

What is a neurotransmitter?

A

Chemical used as a signalling molecule between 2 neurones in a synapse

29
Q

How are electrical impulses transmitted across a synapse?

A
  1. Action potential arrives at synaptic bulb
  2. Voltage gated Ca+ ion channels OPEN /ions diffuse into synaptic bulb
  3. Ca+ ions cause synaptic vesicles to move to/fuse with PRE SYNAPTIC MEMBRANE
  4. Acetylcholine released by EXOCYTOSIS /diffuses across the cleft
  5. ACh bind to receptor sites on Na+ channels in POST SYNAPTIC MEMBRANE
  6. Na+ ion channels OPEN /ions diffuse across post synaptic membrane INTO post synaptic NEURONE —> DEPOLARISED so excitatory post-synaptic potential (EPSP) created or generator potential
  7. If sufficient generator potentials COMBINE the potential will reach threshold potential / new action potential created in POST SYNAPTIC NEURONE
  8. ACh molecules broken down /recycled —> stops Na+ channels staying open/stops permanent depolarisation of post synaptic membrane
    - ACETYLCHOLINESTERASE catalyses hydrolysis of ACh into ethanoic (acetic) acid + Choline
  9. Choline absorbed back into presysnaptic membrane / reacts with acetyl coenzyme A to form ACh ( USES ATP FROM RESPIRATION )- then packed into vesicles to repeat process
30
Q

Features of synapses ?

A

Unidirectionality: ensure 1 way transmission of impulses - neuron transmitters released on one side/its receptors on the other

Summation : when effects of multiple impulses are added together
- allows for effect of stimulus to be MAGNIFIED
- combination of different stimuli can trigger RESPONSE
- avoids nervous system from being overwhelmed by impulses - synapses are barrier/slow rate of transmission

31
Q

Why is single impulse sometimes insufficient to generate an AP in post synaptic neurone ?

A

Only small amount of ACh released into synaptic cleft
Only small no. Na+ ion channels are opened so insufficient no. Na+ ion pass through membrane
So threshold potential is NOT REACHED + ACh attached to receptors is broken down rapidly by acetylcholinesterase

32
Q

What is temporal and spatial summation?

A

Temporal: multiple impulses arrive within same PRE-SYNAPTIC NEURONE* + their effect is added together to generate an action potential

Spatial : action potentials arrive from several different pre-synaptic neurones

Both result in large amount of ACh released
- so large no. Na+ ions channels open + large no. Na+ ions pass through membrane
Therefore reaches threshold potential —> new AP GENERATED

33
Q

What do excitatory and inhibitory neurotransmitters do?

A

EXCITATORY: stimulate generation of an AP in POST SYNAPTIC NEURONE - by opening Na+ ion channels in post synaptic membrane causing DEPOLARISATION if threshold is reached

INHIBITORY: prevent generation of an AP in post synaptic neurone - open the K+ ion channels in post synaptic membrane - cause HYPERPOLARISATION of membrane

34
Q

What happens when neurones are subject to both excitatory and inhibitory synapses ?

A

Na+ ions enter cell body following stimulation by excitatory synapse
Stimulation of inhibitory synapses causes K+ ions to diffuse out of cell body
Cancels out effect of Na+ ions entering
Threshold potential is not reached so no AP generated

Biology Alevel (24 decks)

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