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Biology > Nervous Coordination > Flashcards

Nervous Coordination Flashcards

1
Q

Neurones

A

Neurones are SPECIALISED CELLS, they are adapted to their function which is to carry electrical impulses from one part of the body to another.

There are different types of neurone: sensory neurone, relay neurone, motor neurone

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2
Q

The structure of a motor neurone

A
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3
Q

Schwann cells

A

Surround peripheral nerves and form myelin sheath

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4
Q

How a resting potential is established

A

resting potential = -70mV
* active transport/pumping of sodium (ions across membrane);
* out of neurone/higher concentration outside;
* differential permeability to K+ and Na+;
* Membrane more permeable to K+ ions;

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5
Q

How a nerve impulse is transmitted

A

the membrane potential goes form –70mV to + 40mV in a short period of time

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6
Q

Depolarisation

A

Depolarisation = -55mV
* The high concentration of positive ions inside the cell is the ACTION POTENTIAL (+40mV)

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7
Q

Repolarisation

A

Repolarisation = -70mV

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8
Q

Hyperpolarisation

A
  • The K+ ion channel proteins remain open longer than needed to reach resting potential, making the inside of the cell even more negative to about -90mV. (hyperpolarisation)
  • The sodium potassium pump restores the resting potential back to -70mV
  • K+ channel goes from open to leaky to make more positive
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9
Q

The potential across the membrane is reversed when an action potential is produced.

Describe how.

A
  • Sodium ion gates / channel (proteins) open;
  • Na+ (rapidly) diffuse in;
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10
Q

The All or Nothing response

A
  • An action potential will only occur when the membrane is stimulated so that all the local Na+ voltage-gated channel proteins open.
  • The minimum intensity of stimulus is called the THRESHOLD
  • Sub-threshold no action potential will occur
  • Above the threshold a full-size action potential is given regardless of the increase in the size of the stimulus
  • This is the ALL OR NOTHING LAW
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11
Q

The Refractory period

A

the time taken to restore the resting potential
- avoid waste of ATP - cause neuronal stress

  • (Refractory period) limits number of impulses per second/frequency of nerve impulses;
  • Maximum frequency of impulse transmission
  • Period of time between threshold and resting membrane potential.
  • When maximum frequency reached/exceeded, no further increase in information
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12
Q

Impulse transmission along the axon

A

Action potential’s act as a stimulus to adjacent polarised areas of the membrane and this causes the action potential to be passed along

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13
Q

Factors affecting speed of conduction of impulses: Myelin sheath and saltatory conduction

A
  • The impulse travels by jumping from one node of Ranvier to the next node of Ranvier
  • This is known as SALTATORY conduction
  • It occurs because myelin sheath provides electrical insulation along axon and depolarisation can only occur at the nodes of Ranvier
  • The electrical impulse depolarise the next node and the impulse is passed along by jumping form node to node
  • This INCREASES the rate of transmission as depolarisation only occurs at the nodes / less of the axon membrane needs to be depolarised.
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14
Q

Factors affecting speed of conduction of impulses: Temperature

A
  • Higher temperatures increase the Kinetic energy so increases rate of diffusion of ions therefore increasing the rate of conduction
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15
Q

Factors affecting speed of conduction of impulses: Axon diameter

A
  • The larger the axon diameter the greater the speed of conductance as larger membrane surface area means there is an increases the number of channel proteins
  • So less resistance to flow of ions;
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16
Q

How the cholinergic synapse works

A
  1. In a cholinergic synapse the enzyme acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid using water to break the ester bond.
  2. Choline and ethanoic acid diffuse back across the synaptic cleft and are transported across the presynaptic neurone membrane.
  3. ATP released by mitochondria is used to resynthesise acetylcholine which is then stored in vesicles inside the presynaptic neurone.
17
Q

Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane.

A
  • Depolarisation of presynaptic membrane;
  • Ca2+ channels open and calcium ions enter (synaptic knob);
  • synaptic vesicles fuse with presynaptic membrane and release acetylcholine
  • Acetylcholine diffuses across synaptic cleft
  • binds to receptors on the postsynaptic membrane;
  • Sodium ions enter postsynaptic neurone leading to depolarisation;
18
Q

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.

Describe how.

A
  • Nerve impulse causes Ca2+ channel (proteins) to open;
  • Ca2+ enter by facilitated diffusion;
  • Causes synaptic vesicles to fuse with presynaptic membrane;
19
Q

Describe how the inhibition of acetylcholinesterase affects the action of synapses.

A
  • Acetylcholine not broken down
  • Na+ ions (continue to) enter / (continued) depolarisation
20
Q

Synapses are unidirectional

A
  • Vesicles containing neurotransmitter are only found in presynaptic neurone
  • Receptors for neurotransmitter are only found on post synaptic neurone

The synapse will delay the impulse slightly.
Synapses prevent the impulse from going in the wrong direction.
Synaptic transmission is the same regardless of the neurotransmitter.

21
Q

The Neuromuscular junction

A

is a synapse between a motor neurone and a muscle cell. Neuromuscular junctions use acetylcholine which binds to nicotinic cholinergic (protein) receptors.

Neuromuscular junctions work in the same way as the cholinergic synapse but there are a few differences:
1. The postsynaptic membrane has lots of folds that form clefts. These clefts increase surface area so MORE acetylcholinesterase enzymes that hydrolyse acetylcholine at a faster rate.
2. The post synaptic membrane has more receptors than other synapses.
3. When a motor neurone fires an action potential, it always triggers a response in a muscle cell (this is not always the case for a synapse between two neurones).

22
Q
  1. Spatial summation (Eye)
A

Different neurones converge at a single synapse. Action potentials arrive from several different neurones at the synapse.
This causes the release of enough neurotransmitter to reach threshold and cause an action potential in the post-synaptic neurone

23
Q
  1. Temporal summation
A

In this case there is only one presynaptic neurone but the impulses arrive in rapid succession giving a cumulative effect which is sufficient to depolarise the post synaptic neurone

24
Q

Fatigue

A

If the rate of transmitter release is higher than the rate at which it is reformed, then it said to be fatigued. The presynaptic neurone cannot release enough neurotransmitter to generate an action potential in the post synaptic neurone until the transmitter is regenerated.

25
Q

Different types of neurotransmitters

A

Excitatory neurotransmitters cause action potential in post synaptic neurone by making the resting potential LESS negative, so less sodium ions are required to reach THRESHOLD.

Inhibitory neurotransmitters (e.g. GABA: opens Cl- channel proteins) affect different receptors on post synaptic neurone. The resting potential becomes hyperpolarised and the postsynaptic membrane is therefore less likely to reach the threshold value and generate an action potential.

26
Q

The binding of GABA to receptors on postsynaptic membranes causes negatively charged chloride ions to enter postsynaptic neurones.

Explain how this will inhibit transmission of nerve impulses by postsynaptic neurones.

A
  • (Inside of postsynaptic) neurone becomes more negative/hyperpolarised;
  • More sodium ions required (to reach threshold) OR Not enough sodium ions enter (to reach threshold);
  • For depolarisation/action potential;
27
Q

The effects of drugs on synapses:

A
  1. They can stimulate the nervous system by creating more action potentials in the post synaptic neurone- Excitatory effects.
    Drug may have similar shape to neurotransmitter and so bind to receptors on post synaptic membrane mimicking the effect of the neurotransmitter.
    Drug may cause an increase in the release of the neurotransmitter.
    Drug may inhibit enzyme that hydrolyses the neurotransmitter.
  2. They can create fewer action potentials in the post synaptic neurone and have an inhibitory effect.
    Drug may inhibit release of neurotransmitter or bind and block the receptors on the post synaptic membrane.
28
Q

As a neurone transmits an impulse, its rate of oxygen consumption increases.
Explain why.

A
  • ATP required for active transport;
  • Na+ (actively) moved out only at nodes in myelinated

Biology (29 decks)

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