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A-Level EDUQUAS Biology > Component 3: Nerves > Flashcards

Component 3: Nerves Flashcards

1
Q

How are are responses in mammals processed?

A

In mammals, responses to many external and internal stimuli involve the reception of of information and its transfer from a receptor to an effector via the nervous system or as hormones via the blood

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2
Q

What does the structure of the human central nervous system include?

A

The brain, spinal cord and the peripheral nervous system

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3
Q

Label the parts of a transverse section through a spinal cord

A
  • central canal
  • grey matter
  • white matter
  • dorsal root
  • ventral root
  • sensory neurone
  • dorsal root ganglion
  • relay neurone
  • motor neurone
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4
Q

What are the steps in the reflex arc?

A

Stimulus -> Receptor -> Sensory Neurone -> Relay Neurone -> Motor Neurone -> Effector -> Response

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5
Q

Describe the nervous system in a hydra

A
  • Nerve Net
  • Ganglion cells is the only type of nerve cell
  • cell process lengths are short
  • axons are unmyelinated
  • conduction speed of 5m/s^-1 (slow)
  • impulse from stimulation point can travel in both directions
  • limited number of stimuli that can be detected by sensory receptors
  • limited number of effectors
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6
Q

Give ways in which the nerve net in Hydra differs from that of that of the nervous system of a vertebrate

A
  • axons have no myelin insulation
  • limited number of effectors
  • no central nervous system
  • action potential can be carried in more than one direction along neurone
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7
Q

What are the parts of the motor neurone?

A
  • Dendrite(s)
  • Cell Body
  • Nucleus
  • Axon
  • Myelin Sheath
  • Schwann Cell
  • Node of Ranvier
  • Pre-synaptic knob
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8
Q

What is the function of the dendrite?

A

thin extensions which carry the impulses towards the cell body

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9
Q

What is the function of the axon?

A

long cytoplasmic extension which transmits away from the cell body

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10
Q

What is the function of the Schwann cells?

A

cells which surround axon and insulate them

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11
Q

What is the function of the myelin sheath?

A

schwann cells grow around the axon to form thin multi-layered fatty sheath, acts as an electrical insulator that speeds up transmission along the axon

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12
Q

What is the function of the Nodes of Ranvier?

A

areas along the axon where the myelin sheath is missing

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13
Q

What is the function of the cell body?

A

part of the neurone which contains the nucleus, RER, numerous mitochondria and other cell organelles

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14
Q

What is a reflex action?

A

Rapid reaction to stimulus which is involuntary

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15
Q

What is the reflex arc?

A
  • pathway taken by a nerve impulse during a reflex action
  • the co-ordinator is the spinal cord
  • it is for protection (survival) of the organism from dangerous situations
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16
Q

Why are ‘giant’ squid axons important?

A
  • giant axons are big enough to connect electrodes too
  • microelectrodes are used to stimulate the axon and a cathode ray oscilloscope is used to measure the potential difference across the membrane
17
Q

What is the nerve impulse?

A
  • a nerve impulse is the movement of ions in and out the axon membrane
  • based on the movement of Na+ and K+ ions across the membrane of the axon
18
Q

What are the 4 types of transport proteins in the axon membrane?

A
  • a Na+/K+ pump which requires ATP
  • voltage-gated Na+ channels (sometimes open/shut)
  • voltage-gated K+ channels (sometimes open/shut)
  • K+ channels (always open and make membrane more permeable)
19
Q

Describe what is happening in the neurone at resting potential

A
  • At rest the Na+/K+ pump actively transports 3 Na+ ions out axon for every 2 K+ ions it actively transports in
  • Makes concentration gradients for the ions
  • Some K+ ions may diffuse out down a concentration gradient through the K+ channels (won’t be many)
  • Over time this will make the inside of the axon negatively charged compared to the outside
  • The potential difference (difference between the inside and outside of axon) is -70mV (resting potential)
  • The membrane is said to be polarised (outside axon has more positive ions than inside the axon, negative)
20
Q

What is action potential?

A

rapid, fleeting change in potential difference across the membrane is called an action potential

21
Q

Describe what is happening in the neurone at depolaristation?

A
  • Stimulation of axon (brief reversal in pd from -70mV to +40mV) causes voltage gated Na+ channels to open
  • When channels open Na+ rapidly diffuses into axon down an electrochemical gradient
  • This depolarises the axon (makes the inside more positive)
  • If it reaches -55mV it creates a threshold change, soall gated Na+ channels will open, Na+ rushes in (down conc gradient) and the potential difference rises to +40mV
  • axon membrane is said to be depolarised
22
Q

Describe what is happening in the neurone at repolarisation?

A
  • A fraction of a second later, voltage gated K+ channels open (voltage gated sodium channels close) and the membrane becomes more permeable to K+ which diffuse out of the axon down their concentration gradient
  • This removal of positive charge from the inside of the axon starts to repolarise the membrane
23
Q

Describe what is happening in the neurone at hyperpolarisation?

A
  • Due to so many K+ ions leaving the axon, the inside of the membrane briefly becomes even more negative than at normal resting potential
  • This overshoot is called hyperpolarisation
  • Then restores to resting potential
24
Q

What is the all-or-nothing law?

A
  • the action potential will only be generated by a stimulus if the depolarisation of axon membrane exceeds threshold value
  • threshold stimulus causes depolarisation of axon membrane and starts off an action potential in neurone
  • stimulus weaker than threshold value = no action potential
  • if stimulus intensity exceeds threshold and causes depolarisation, the action potential generated is always the same size and strength (!) no matter what size/strength of stimulus
  • however the greater the stimulus above the threshold value, the greater the frequency of the action potentials along axon (more often)
25
Q

What is the transmission (propagation) of a nerve impulse?

A

Once an action potential is set up in a neurone, it travels rapidly to the other end in a wave of action potentials.

The movement is due to local circuits set up by the action potential itself.

  • When the axon is stimulated, the voltage gated Na+ channels open and Na+ rushes in, depolarising the membrane.
  • This causes local circuits to be set up which make the Na+ channels in the next part of the membrane open and depolarises this next part of the membrane.
  • Behind the impulse K+ ions leave and start repolarisation (and then Na+/ K+ pump restarts to take membrane back to resting potential)
26
Q

What is the refractory period?

A
  • After an action potential, the voltage-gated Na+ channels are inactivated for a short time and cannot open to allow influx of Na+ into the membrane.

This is called the refractory period

27
Q

What does the refractory period prevent?

A
  1. An action potential being generated in the opposite direction.
  2. A second action potential being generated too close to the first – it limits the frequency of action potentials along a neurone.
28
Q

How does myelination affect the speed of nerve impulse?

A
  • Myelinated neurones transmit action potentials faster (100m/sec) than unmyelinated neurones (1-3m/sec)
  • Myelination insulates the axon (stops ions moving in or out of the membrane).
  • Depolarisation and action potentials only occur at the Nodes of Ranvier.
  • The result is that the impulse jumps from one node to the next, speeding up transmission. This is called saltatory conduction.
29
Q

How does the diameter of the axon affect the speed of the nerve impulse?

A

The greater the diameter of the axon, the lower the resistance to ion flow so the greater the speed of transmission.

30
Q

How does temperature affect the speed of the nerve impulse?

A
  • As temperature increases to 40o C, speed of transmission increases because generation of impulses involves active transport and requires ATP from respiration.
  • Anything that speeds up respiration rate also speeds up transmission of nerve impulses.
31
Q

What is grey and white matter made out of?

A

Grey matter contains cell bodies, white matter is mainly myelinated axons

32
Q

What are the two types of synapses?

A

Chemical and electrical

33
Q

What is the role of acetylcholinesterase?

A
  • an enzyme which hydrolyses acetylcholine in the synaptic cleft into choline and ethanoic acid
  • these diffuse back across the cleft and pre-synaptic membrane
  • ATP is used to reform the neurotransmitter molecules, storing them in vesicles (recycling of neurotransmitter)
34
Q

Where is acetylcholine released?

A

at cholinergic synapses neuromuscular junctions

35
Q

What are the function of synapses?

A
  1. transmit impulses between synapses
  2. ensures impulses pass in one direction only
  3. filter out low level stimuli (acclimatisation)
  4. summation
36
Q

What are the two types of summation?

A
  1. Temporal summation
    - a postsynaptic neurone may only be stimulated if there are frequent action potentials in the presynaptic membrane
  2. Spatial Summation
    - a postsynaptic neurone may only be stimulated if several pre-synaptic neurones receive stimulation
37
Q

Describe the process of a synaptic transmission

A
  • an action potential arrives at the end of the neurone
  • calcium ion channels open in the presynaptic membrane and calcium ions diffuse in
  • calcium ions fuse with vesicles containing neurotransmitter and neurotransmitter is released by exocytosis at presynaptic membrane
  • neurotransmitter enters the synaptic cleft and diffuses across the cleft
  • neurotransmitter binds to receptors on the postsynaptic membrane
  • sodium ion channels open and Na+ ions enter the postsynaptic neurone
  • if a threshold is exceeded the membrane depolarises
  • an action potential is generated
38
Q

What are 5 ways drugs can affect synapses?

A
  1. increasing number of impulses
  2. release neurotransmitter from vesicles with or without impulses
  3. block reuptake or block receptors
  4. produce more or less neurotransmitter
  5. prevent vesicles from releasing neurotransmitter

A-Level EDUQUAS Biology (24 decks)

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