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Biology Noor > 13.11 Nervous Coordination > Flashcards

13.11 Nervous Coordination Flashcards

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1
Q

What does the nervous system involve?

A
  • Detection of stimuli by receptors
  • Transmission of nerve impulses by neurons
  • Response by effectors
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2
Q

Types of neurones

A
  • Sensory neuron
  • Relay neuron
  • Motor neuron
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3
Q

Structure of (motor) neurone

A
  • Dendrites
  • Cell body
  • Nucleus
  • Axon
  • Myelin sheath
  • Nodes of Ranvier
  • Schwann cell
  • Terminal end branch
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4
Q

Function of nucelus

A

Found in the cell body and contains the DNA which codes for neurotransmitters

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5
Q

Function of dendrites

A

Extensions of the cytoplasm of the cell body receiving chemical signals from other neurons at the postsynaptic membrane

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6
Q

Function of cell body

A

Contains the nucleus and groups of ribosomes needed to synthesise neurotransmitters

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7
Q

Function of axon

A

Long extension of the cytoplasm that transmit impulses away from cell body towards the terminal ends

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8
Q

Function of myelin sheath

A

Formed as Schwann cells grow around the axon
provide electrical insulation
Speeds up transmission

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9
Q

Function of Schwann cells

A

Surround peripheral nerves and forms myelin sheath
K+ and Na+ ions cannot diffuse through

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10
Q

Function of terminal end branch

A

Connect to other neurons or effectors

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11
Q

How is resting potential established and maintained?

A
  • High conc of Na+ on outside of neuron
  • High conc of K+ on the inside of the neuron
  • Many Na+/K+ pumps that move 3 NA+ out and 2K+ in
    via ATP hydrolysis
  • Na+ voltage gated channel proteins are closed
  • Na+ pumped out cannot diffuse back in
  • K+ channel proteins are leaky/mainly closed
  • K+ can diffuse back out

Net result= more positive on outside than inside

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12
Q

How a nerve impulse is transmitted?

A
  • Resting potential maintained until membrane is stimulated
  • Action potential is where the membrane reaches a threshold and becomes depolarised
  • An action potential is the reversal of the resting potential
  • -70mV to 40mV
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13
Q

Process of depolarisation

A
  • Stimulus causes membrane to become more permeable to Na+ ions
  • Na+ channel proteins are open if threshold reached
  • Higher conc of Na+ outside the cell
  • Na+ ions rapidly diffuse into the cell via FD
  • Higher conc of Na+ inside the cell reverses action potential
  • Inside is more positive
  • K+ voltage-gated channel proteins remain closed
  • High conc of + ions is action potential
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14
Q

Three types of nerve impulses

A

Resting potential
Depolarisation
Repolarisation
(Hyperpolarisation)

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15
Q

Process of repolarisation

A
  • Once the internal potential reaches +40mV
    Na+ ion voltage gated channel proteins close
  • K+ voltage gated channel proteins open
  • More K+ ions inside than outside
  • K+ ions diffuse out down a conc gradient
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16
Q

Process of hyperpolarisation

A
  • K+ ion channel proteins remain open longer than needed to reach action potential
  • Inside of the cell more negative to -90mV
  • Sodium potassium pump restores the resting potential back to -70mV
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17
Q

The all or nothing principle

A

Above the threshold the full sized action potential is given regardless of the increase in the size of the stimulus

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18
Q

Refractory period

A

Time taken to restore the resting potential potential

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19
Q

What is the impulse transmission along the axon

A

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

20
Q

Saltatory conduction

A

Impulse travels by jumping from one Node of Ranvier to the next Node of Ranvier
To increase the rate of transmission

21
Q

Factors affecting the speed of conduction of impulses

A
  1. Myelin sheath and saltatory conduction
  2. Temperature
  3. Axon diameter
22
Q

How does temperature affect the rate of transmission?

A

Increase in temp
Increase in kinetic energy
Increase in the rate of diffusion
Increase the rate of conduction

23
Q

How does axon diameter affect the rate of transmission

A

The larger the axon diameter, the greater the speed of conductance
Larger membrane surface area - increase in number of channel proteins

24
Q

Most synapses are…

A

cholinergic- use acetylcholine neurotransmitter

25
Q

Why are most impulses unidirectional?

A

From pre-SN to post-SN
Vesicles containing neurotransmitters only produced in pre-SN
AND
Neurotransmitter receptor proteins only found on membrane of the post-SN membrane.

26
Q

Process of synaptic transmission

A
  • Action potential arrives
  • Voltage gated Ca2+ channel opens
  • Ca+ ion diffuse into the synaptic knob (presynaptic neuron) via facilitated diffusion
  • Vesicles fuse with presynaptic membrane to release acetylcholine via exocytosis
  • Acetylcholine diffuse down conc gradient, across cleft and bind to receptors on post-SN
  • Na+ channels open allowing Na+ into postsynaptic neuron
  • If membrane potential reaches threshold= membrane becomes depolarised and action potential occurs and spreads along axon membrane of post SN
  • K+ channels open allowing K+ out into the cleft
    enzyme acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid using water to break the ester bond
27
Q

Types of neurotransmitters

A

Excitatory
Inhibitory

28
Q

Type of inhibitory neurotransmitter

A

GABA

29
Q

How do inhibitory neurotransmitters work

A
  • Resting potential= hyperpolarized
  • Less likely to reach threshold in the postsynaptic membrane and generate action potential
30
Q

What is the neuromuscular junction?

A

A synapse between a motor neuron and a muscle cell
uses acetylcholine which binds to receptors

31
Q

Adaptations to muscular junctions that differentiate them from synapses

A
  1. Lots of folds, increase in surface area for more enzymes
  2. More receptors
  3. Always triggers a response
32
Q

Summation

A

Build-up of neurotransmitters within the synapse

33
Q

Two types of summation

A

Spatial
Temporal

34
Q

Process of spatial summation

A
  • Different neurons converge at a single synapse
  • Action potentials arrive from several different neurons
  • Release of enough neurotransmitter to reach threshold and cause an action potential
35
Q

Process of temporal summation

A
  • Only one presynaptic neuron
  • Impulses arrive in rapid succession giving a cumulative effect
  • Sufficient to depolarise the post synaptic neuron
36
Q

How do excitatory neurotransmitters work

A

Cause action potential in post SN by making resting potential LESS negative
LESS sodium ions required to reach threshold

37
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 / Na+ (actively) moved out along whole length of axon in non-myelinated;
38
Q

Describe how a resting potential is maintained in a neurone.

A
  • 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;
39
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;
40
Q

SYNAPSE:

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);
  • (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
  • Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
  • (Acetylcholine attaches) binds to receptors on the postsynaptic membrane;
  • Sodium ions enter (postsynaptic neurone) leading to depolarisation;
41
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/depolarisation of membrane) causes Ca2+ channel (proteins) to open;
  • Ca2+ enter by (facilitated) diffusion;
  • Causes (synaptic) vesicles to fuse with (presynaptic) membrane;
42
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;
43
Q

Describe how the speed of the conduction could be increased in a neurone.

A
  • Axon is myelinated;
  • So shows saltatory conduction/impulses jump from node of Ranvier to node of Ranvier;
    OR
  • Axon has a larger diameter;
  • So less resistance to flow of ions;
43
Q

Myelination affects the rate of conduction of a nerve impulse. Explain how.

A
  • Impulse jumps from node of Ranvier to node of Ranvier / depolarisation only at node of Ranvier;
  • Fewer jumps / depolarisations to travel length of axon;
44
Q

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

A
  • Acetylcholine not broken down / stays bound to receptor;
  • Na+ ions (continue to) enter / (continued) depolarisation / Na+ channels (kept) open / action potentials;
44
Q

Describe what is meant by the term refractory period

A
  • (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/ all (higher) stimuli seem the same;

Biology Noor (30 decks)

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