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Human Physiology > C3 - The Nervous System > Flashcards

C3 - The Nervous System Flashcards

1
Q

Describe synapses

A

Small gap junctions between 2 nerve cells where impulses pass by diffusion of a neurotransmitter.

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2
Q

Define nervous impulse

A

Transmission of a change in pot along a nerve fibre associated w/ the movement of Na+ ions.

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3
Q

Define the dendrite

A

Thin extensions that carry impulses towards the cell body.

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4
Q

Define the axon

A

Long membrane-covered cytoplasmic extension, that transmits impulses away from cell body.

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6
Q

What’s the function of the 3 types of neurones?

A

S = Carries impulse from receptor to CNS

M = Carries impulse from CNS to effector

R = Carries impulse along CNS

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7
Q

Define voltage gated channel

A

One in which opens or closes in response to a particular voltage across the membrane

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8
Q

Define the Schwann cells

A

Cells which surround + support peripheral neurones

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9
Q

Define the myelin sheath + its function

A

== Schwann cells grown around the axons to form a multi-layered fatty sheath.

Acts as an electrical insulator that speeds up transmission along the axon because impulse jumps from 1 node of ranvier to the next

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10
Q

What only has a myelin sheath?

A

Vertebrates

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11
Q

Define the Nodes of Ranvier

A

Areas along the axon where the myelin sheath thins

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13
Q

Define the cell body

A

Part of the neurone that contains nucleus, RER, mitochondria and other cell organelles

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15
Q

What are the 2 main parts of the nervous system?

A

PNS - peripheral nervous system

CNS - central nervous system

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16
Q

Explain the CNS

A

Brain + spinal cord

Processes info provided by a stimulus

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17
Q

Explain the PNS

A
  • Somatic NS (so pairs of nerves that originated in the brain or spinal cord + their branches)

Sensory + motor neurones

  • Autonomic NS which unconsciously controls the functions of internal organs
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18
Q

Where is the Hydra’s nerve net?

A

In its ectoderm

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19
Q

What does the nerve net in Hydra do?

A

Connects sensory photoreceptors + touch sensitive nerve cells in body wall + tentacles.

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20
Q

What is the nerve net made of?

A

Simple nerve cells w/ short extensions joined together + branching w/ multiple synapses.

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21
Q

Why is the transmission of impulse slow in a nerve net?

A

Lack of myelin sheath

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22
Q

What directions do the impulses travel in?

A

Hydra - Both

Human - One

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24
Q

What can’t the Hydra’s nerve net do?

A

Detect the direction of a stimulus.

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25
Q

What are the 2 types of cells in a nerve net?

A

Ganglion cells = providing connections in many directions.

Sensory cells = detecting stimuli

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26
Q

How many stimuli can be detected by sensory receptors ?

A

Hydra - Limited

Human - Many

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27
Q

How many effectors do Hydra + humans have?

A

Hydra - 1 = tentacles

Humans - lots = muscles + glands

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28
Q

Define reflex arc

A

Pathway travelled by the nerve impulses during a reflex action.

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29
Q

What are the 2 types of reflexes?

A

Spinal

Cranial

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30
Q

Define cranial reflex

A

Pathways travelled by the nerve impulses during a reflex action through cranial nerves and the brainstem.

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31
Q

Define the spinal reflex

A

Info may be transmitted to brain, but it’s the spinal cord, not brain, that’s responsible for the integration of sensory information and a response transmitted to motor neurones.

Most reflexes

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32
Q

Define resting potential

A

p.d between inside + outside of membrane, when a nerve impulse is NOT being conducted

Typically -70mV, the inside is -ive due to accumulation of more Na+ outside cell than K+ inside.

Membrane is said to be POLARISED

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33
Q

How long are the axons in the 3 types of neurones

A

Sensory - Short

Motor - Long

Relay - Short

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34
Q

Where is the location of the cell body in the 3 types of neurones

A

Sensory - Dorsal root ganglion

Motor - Grey matter

Relay - Grey matter

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35
Q

How is the myelin sheath formed?

A

Schwann cells become associated w/ axons + dendrons during embryonic development.

These surround axon to form myelin sheath made of many layers of myelin or phospholipid bilayers.

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36
Q

Why is the white matter white and the grey matter grey?

A

White = Myolinated due to phospholipids in myelin sheath

Grey = Many nuclei + cell bodies found there

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37
Q

What is the name given for the cells that partially cover neurones?

A

Schwann cells

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38
Q

What is the name given to the material which the cells produce to cover the axon?

A

Myelin

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39
Q

What fluid does the spinal canal contain?

A

Cerebral spinal fluid

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40
Q

What does the white matter contain?

A

Ascending fibres that carry action potential to the brain.

Descending fibres which carry action potential from the brain.

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41
Q

What does a thicker neurone mean in regards to flow of impulse?

A

Thicker = less resistance

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42
Q

How is the resting potential achieved?

A

Na/K pumps maintain conc of an uneven distribution of Na+ + K+ ions across the axolemma (membrane).

— 3Na+ out + 2 K+ in = Requires ATP but NOT simultaenous

Membrane is more permeable to k+ ions than Na+ due to protein channels for K+ ions. = They can diff out of axon due to conc grad created by Na+/K+ pump ⬆️ the +ive charge outside.

Anion (large protein molecules COO-) + organic phosphates (ATP4-) concentrations are higher inside neurone.

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43
Q

How can you reach threshold potential?

A

Any stimulation of an axon causes some Na+ channels to open temporarily.

Some Na+ ions diff down electrochemical + conc grad back into axon.

== ⬇️ p.d across membrane

If reduction is great enough it will reach threshold potential in which voltage gated channels open.

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44
Q

Why is AT needed in the maintenance of a resting potential

A

Because the neurone membrane is impermeable to the entry of sodium ions

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45
Q

When must an action potential be generated?

A

Before an impulse can be established + transmitted

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46
Q

How is the action potential generated?

A

Energy of stimulus causes some VOLTAGE-GATED Na+ channels in axon membrane to OPEN.

(BIGGER stimulus = MORE channels open)

This ⬆️ in permeability of membrane to Na+ ions allow them to RAPIDLY DIFF INTO axon down their electrochemical + conc gradients.

So then, the -ive charge of -70mV inside axon becomes charge of +40mV.

== Cell membrane becomes DEPOLARISED.

Once pot inside cell is +40mV, Na+ channels CLOSE.

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47
Q

GENERATION OF ACTION POTENTIAL

What must the stimulus be?

A

Above a certain minimum value = threshold stimulus

AND produced a maximum of all or no response in the neurone.

48
Q

GENERATION OF ACTION POTENTIAL

Where might the stimulus come from?

A

External environment i.e light or pressure changes

Internal environment i.e chaining blood temp or pH

49
Q

Describe what happens in REPOLARISATION

A

Voltage gated K+ channels open + K+ ions quickly diff out of axon down electrochemical + conc gradients.

Cell becomes less +ive inside as more diffuse out + membrane is REPOLARISED.

50
Q

Briefly describe the propagation of an impulse in a MYELINATED neurone

A

Electrons of the local currents jump from one Node of Ranvier to the next.

51
Q

What is the refractory period?

A

Time after a stimulus has established an action potential before a second stimulus can set up another action potential.

52
Q

Define reflex action

A

Rapid, involuntary response to a stimulus

53
Q

What must have occurred before a second action potential can arise?

A

Enough potassium outflow from the neurone

54
Q

In how many directions can synapses conduct impulses?

A

1

55
Q

What are the consequences to electrons of the local currents jumping from one Node of Ranvier to the next in a myelinated neurone

A

Gain or loss of ions is restricted to nodes and so Na/K pumps have to expend less energy in recovery.

Saltatory conduction greatly ⬆️ speed at which impulses travel.

56
Q

What is the jumping conduction called?

A

Saltatory conduction

57
Q

What do inhibitory synapses do?

A

Won’t transmit signal so stimulation of inhibitory neurone will lead to the stopping of activity under control.

58
Q

Is any energy lost in transmission of an impulse?

A

NO

59
Q

What are the tough protective membranes called that surround the brain + spinal cord?

A

meninges

60
Q

Describe HYPERPOLARISATION

A

More K+ ions diff out than NA+ in, so p.d across membrane = more -ive than resting pot = membrane hyper polarised. (-90mV)

Refractory period occurs.

61
Q

What is an excitable cell?

A

One in which the potential across the membrane can be altered.

62
Q

How is the p.d across the membrane restored after hyper polarisation?

A

Na/K pump pump:

k+ ions IN
Na+ ions OUT

== restores ion balance of resting pot.

63
Q

What does the reversal of pot after Hyperpolarisation set up?

A

Local currents as Na+ ions move laterally through axon.

64
Q

How is an impulse carried along the neurone after an action potential has been generated?

A

Once impulse is made, local current is set up.

The lateral flow of some Na+ towards -ive area causes Na+ channels to open + depolarisation occur. = AP moves down neurone.

65
Q

Where is local current set up?

A

Between area of AP + resting area next to it.

66
Q

What is the absolute refractory period?

A

Time in which another stimulus given to the neurone (no matter how strong) will not lead to a second action potential.

Lasts around 1ms.

67
Q

When might you get a stimulus but no action potential generated?

A

When intensity of stimulus is below certain threshold value.

68
Q

Does an ⬆️ in the intensity of a stimulus give a greater action potential?

A

NO.

AP is always +40mV

Instead, frequency of AP ⬆️.

69
Q

What is the ‘All or nothing law”?

A

Nervous impulse is either initiated or not + is always the same size.

Allows the AP to acts as a filter, preventing minor stimuli setting up nervous impulses so that the brain isn’t overloaded with info.

70
Q

What are the 3 major factors that affect the speed of conduction of a nerve impulse?

A

Temperature

Diameter of axon

Myelination

71
Q

FACTORS AFFECTING SPEED OF CONDUCTION

Explain temperature

A

⬆️ temp = ⬆️ KE = ⬆️ Ion movement.

⬆️ temp = ⬆️ rate of respect = ⬆️ production of ATP - needed for NA/K pump

72
Q

Why do birds + mammals transmit nervous impulses more quickly and have faster responses than all other groups of animals??

A

Because they are homeothermic taxa.

73
Q

FACTORS AFFECTING SPEED OF CONDUCTION

Explain diameter of axon

A

Greater diameter = ⬆️ Na+ ions flow through axon = ⬆️ impulse speed.

Less resistance from cytoplasms to the flow of ions.

74
Q

How big are the diameters of human non-myelinated axons?

A

0.2-1.5 micrometers.

75
Q

How does the squid compensate for very low temperature in regards to speed of impulse conduction?

A

Giant axons w/ diameter up to 1mm.

76
Q

Compare the speed of impulses along myelinated neurones + non-myelinated

A

M = 100m/sec

Um=1-3m/sec

77
Q

How does saltatory conduction work?

A

AP at NofR causes Na+ ions to move into axon.

Na+ ions diff to areas of -ive charge further down con towards insulated axon.

VG Na+ channels ONLY present at NofR so a new AP only occurs at the next Nof R….

78
Q

What are the 2 classes of synapse?

A

Electrical - 3nm across

Chemical - 20nm gap (too big for nervous impulse to jump). so branches of axons lie close to dendrites of other neurone but don’t touch. Impulse is transmitted by neurotransmitter.

79
Q

Describe the process of synaptic transmission

A

AP arrives at axon terminal - synaptic knob which ⬆️ membranes permeability to Ca+ ions.

So, Ca+ ions diff in down conc grad.

Causes synaptic vesicles to move towards presynaptic membrane until they fuse w/ it + release acetylcholine into synaptic cleft by exocytosis.

Acetylcholine mol. diff across cleft to post-synaptic membrane to then bind to receptors on postsynaptic membrane.

Ligand-gated Na+ protein channels OPEN = Na+ diff into dendrite of postsynaptic neurone.

AP is generated in postsynaptic memb. - Depolarisation.

Cholinesterase breaks down acetylcholine in protein receptor = choline + acetate.

Na+ channels in postsynaptic membrane close - no more AP.

Choline + acetate diff back to presynaptic mem.

Energy from mitochondria is used to resynthesise acetylcholine + package into vesicles.

80
Q

What are the neurotransmitters in synaptic transmission?

A

Acetylcholine molecules

81
Q

What’s the difference between voltage gated channels + ligand gated channels?

A

VG = open in response to voltage

LG = open in response to a ligand (some chemical signal) binding to them.

82
Q

What would happen if acetylcholine remained in the synaptic cleft?

A

Would constantly initiate new impulse in post-synaptic membrane + so impulses wouldn’t be distinct.

83
Q

How is it ensured that acetylcholine doesn’t remain in synaptic cleft? (3)

A
  • Direct uptake of acetylcholine into pre-synaptic neurone so none left in cleft to bind to post synaptic receptor.
  • AT of Ca+ ions out of synaptic knob so no more exocytosis of acetylcholine occurs.
  • Hydrolysis of acetylcholine
84
Q

How do neurones transmit impulses in only 1 direction?

A
  • Depolarisation happens behind AP + so depolarisation could not happen at that point.
  • Synaptic vesicles only occur at s. knob of the pre-synaptic neurone.
  • Neurotransmitter receptors only occur on post-synaptic membrane.
85
Q

What are the functions of synapses? (7)

A

Transmit info between neurones across the junctions.

Flow of impulses in 1 direction = precision in nervous system.

Protects response system from overstimulation.

Filter out low-level stimuli

Allows acclimatisation

Convergence

Integration + divergence

86
Q

FUNCTIONS OF SYNAPSES

Explain Integration + divergence

A

Impulse travelling down a neurone may reach a synapse which has several post synaptic neurones all going to different locations.

i.e sensory neurone detects a ⬇️ in temp so diverges impulse to:

  • neurone — shiver
  • neurone — hairs
  • neurone — vasoconstriction
87
Q

FUNCTIONS OF SYNAPSES

Explain convergence

A

Several presynaptic neurone might converge to 1 postsynaptic neurone.

Allowing signals from diff parts of body to create same response.

88
Q

FUNCTIONS OF SYNAPSES

Explain flow of impulses in 1 direction = precision in nervous system.

A

Because vesicles containing transmitter are only in presynaptic neurone + the receptor molecules are only on the post synaptic membrane.

89
Q

FUNCTIONS OF SYNAPSES

Explain acclimatisation

A

After repeated stimulation, a synapse might run out of the neurotransmitter.

i.e getting used to a smell or background noise.

90
Q

FUNCTIONS OF SYNAPSES

Explain Filter out low-level stimuli

A

Post-synaptic neurone doesn’t reach threshold stimulus + no AP is generated due to low levels of transmitter.

91
Q

How does the Action potential travel along an UNMYELINATED axon?

A

Influx of Na+ ions + depolarisation of membrane causes a local flow of ions (circuit). - This is due to the lateral flow of Na+ in the axon towards -ively charged regions.

Local current trigger the adjacent region of the axolemma to become more permeable to Na+ by opening the VG Na+ channels so causing a depolarisation in the next region.

The region of the membrane that has just depolarised is then non-responsive due to the inactivation of the Na+ channels so the region of depolarisation only moves in 1 direction.

92
Q

Explain Acetylcholinesterase

A

Enzyme that hydrolyses acetylcholine in the synaptic cleft into choline + ethanoic acid.

These diff back across synaptic cleft + ATP is used to reform neurotransmitter molecules + store them in vesicles.

93
Q

Where is Acetylcholinesterase released from

A

Cholinergic synapses - junction between a nerve and muscle

94
Q

What drugs and how can drugs INCREASE synaptic transmission?

A

Agonists / excitatory drugs

  • By mimicking the action of NT
  • By inhibiting the breakdown of NT in synaptic cleft
  • ⬆️ secretion of NT into synaptic cleft by exocytosis.
95
Q

AGONIST DRUGS

Explain how they mimic the action of neurotransmitters

A

By having the same shape + bind to LG receptors on post-synaptic membrane = initiating an AP in the post synaptic membrane.

96
Q

What drugs and how can drugs DECREASE synaptic transmission?

A

Antagonists / Inhibitory drugs

  • By mimicking the action of the NT, blocking the LG receptors on post synaptic membrane-no AP in the post synaptic membrane.
  • Preventing exocytosis of NT
  • Prevent Ca+ diff into synaptic knob
  • Prevent recycling/synthesis of NT
97
Q

Give 2 examples of psychoactive drugs

A

Cocaine

Cannabis

98
Q

How do psychoactive drugs affect the nervous system

A

Acts on CNS by altering brain function, causing temporary changes in perception, mood, consciousness + behaviour

Physical dependence may develop w/ sustained use.

May be excitatory or inhibitory drugs.

99
Q

Give an example of an excitatory/ agonist drug

A

Cocaine

100
Q

Give an example of an inhibitory/ antagonist drug

A

Morphine

101
Q

Define excitatory/ agonist drugs

A

Stimulate nervous system by creating more AP in post-synaptic membranes

102
Q

Define Antagonists / Inhibitory drugs

A

Inhibit the nervous system by creating fewer action potentials in post-synaptic membranes

103
Q

Explain Organophosphorus insecticides

A

Inhibits acetylcholinesterase

= Prolongs the effects of acetylcholine which remains in the synaptic cleft and causes repeated firing of the post-synaptic cell.

This results in repeated firing of the neurones at the neuromuscular junction resulting in permanent contraction of the muscle.

Results in paralysis and breathing stops.

104
Q

Briefly describe the reflex pathway

A

Stimulus

Receptor

(Sensory pathway)

CNS

(motor pathway)

Effector

Response

Fb

105
Q

Briefly describe what happened in the experiments w/ ‘Giant’ squid axons

A

Microelectrodes are used to stimulate the axon and the cathode ray oscilloscopes are used to measure the potential difference across the membrane

106
Q

FACTORS AFFECTING SPEED OF CONDUCTION

Explain myelination

A

Speeds up the rate of transmission by insulating the axon.

A myelinated nerve fibre only depolarises at nodes of Ranvier where resistance is low.

Voltage gated channels only occur here so this is where Na+ ions enter.

== AP jumps from node to node === SALTATORY CONDUCTION

107
Q

What does it mean that sensory receptors are transducers?

A

They detect energy in one form + convert it into electrical energy.

108
Q

What do excitatory synapses do?

A

Transmit signals from 1 cell to the next by establishing impulses in the post-synaptic membrane

109
Q

What can synapses be?

A

Excitatory

Inhibitory

== have an important homeostatic role

Human Physiology (16 decks)

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