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Wjec A Level Biology > 3.8 The Nervous System > Flashcards

3.8 The Nervous System Flashcards

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1
Q

Hormonal control

A

Endocrine response
Changes things more slowly
Long-term response
Relies upon chemicals being carried by the blood

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2
Q

Nervous control

A

Nervous response
Rapidly
Short term response
Relies upon information carried by neurones

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3
Q

What does the nervous system consist of

A

Central nervous system
Peripheral nervous system

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4
Q

What does the CNS consist of

A

Brain and spinal cord

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5
Q

What does the PNS consist of

A

Spinal nerves and cranial nerves

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6
Q

Order of how a stimulus gets a response

A

Stimulus
Detector
Coordinator
Effector
Response

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7
Q

What is a stimulus

A

Change in environment

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8
Q

What does a detector have and do

A

Contains cells that detect stimuli
Converts energy from one form to an electrical impulse

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9
Q

What is an effetor

A

Something that brings about a response
Muscle or gland

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10
Q

Order of neurones

A

Sensory
Relay
Motor

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11
Q

Describe a reflex arc

A

Rapid
Protective
Involuntary

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12
Q

How does a reflex arc occur

A
  1. Receptor detects a stimulus
  2. A nerve impulse is initiated and transmitted through a sensory neurone to the spinal cord
  3. The impulse crosses a synapse into a relay neurone in the grey matter
  4. The impulse is transmitted through the relay neurone to a motor neurone across a synapse
  5. The motor neurone transmits the impulse to an effector
  6. Effector makes the response
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13
Q

What is a hydra

A

A nerve net that consists of simple nerve cells of one type that have short extensions and connect with other nerve cells in a net like structure which branches in several different directions

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14
Q

Compare cnidarian nerve net and mammalian nervous system

A

• A cnidarian consist of 1 type of simple neurone whilst a mammalian has 3 neurones
• nerve nets are unmyelinated whilst nervous systems are myelinated so mammals have a faster impulse transmission
• nerve nets have short-unbranched neurones whilst nervous systems have long, unbranched neurones
• nerve nets have impulses transmitted in both directions whilst the nervous system is unidirectional

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15
Q

Function of the cell body

A

Contains granular cytoplasm with ribosomes for protein synthesis. DNA is present within a nucleus and acts as the site for transcription

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16
Q

Function of the axon

A

Carries the impulse away from the cell body

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17
Q

Function of the myelin sheath

A

Surrounds the axon providing electrical insulation resulting in a faster impulse transmission

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18
Q

Function of Schwann cell

A

Surrounds the axon and forms the myelin sheath

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19
Q

Function of Nodes of Ranvier

A

Gaps in the myelin sheath between the Schwann cells that are approximately 1 um wide where the axon membrane is exposed. They allow faster nerve impulse conduction

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20
Q

Function of axon endings

A

Secrete a neurotransmitter which results in depolarisation of the adjacent neurone

21
Q

Function of synaptic end bulbs

A

Swelling found at the end of an axon where a neurotransmitter is synthesised

22
Q

What is the membrane at resting potential

A

Polarised

23
Q

Resting potential value

A

-70 mV
The axoplasm is negative in relation to the outside of the cell

24
Q

How is resting potential brought about

A

• a sodium potassium pump using ATP actively transports 3 Na+ out of the neurone and 2 K+ into the neurone
• K+ channels are leaky and K+ pass out of the axoplasm by facilitated diffusion
• Na+ channels are closed so Na+ remain outside of the neurone
• larger proteins and organic phosphates in the cytoplasm are negatively charged

25
Q

What is happening to the nerve cell at resting potential

A

It is not transmitting an impulse

26
Q

Potential difference of an action potential

A

+40mV

27
Q

What happens during an action potential

A

When the threshold level is reached all the Na+ channels open and Na+ rapidly diffuse into the cell causing an influx of Na+.

28
Q

What is the membrane described as during an action potential

A

Depolarised

29
Q

What is the all or nothing law

A

• The threshold level of the stimulus must be reached in order for an action potential to be generated
• the action potential is always the same size if the threshold level is reached
• a large stimulus will result in more impulses passing per second rather than a greater level of depolarisation

30
Q

Repolarisation

A

• return to resting potential from the action potential
• the Na+ channels close and K+ channels open
• the K+ leaves the axoplasm by facilitated diffusion and travel rapidly down their concentration gradient and potential difference falls quickly

31
Q

Hyperpolarisation

A

• slight overshoot of K+ leaving the neurone so electrical gradient reaches -80mV
• the K+ gates close and Na+/K+ pump re-establishes resting potential

32
Q

What is the refractory period

A

During an action potential and repolarisation further action potentials are not possible

33
Q

How does the refractory period keep the transmission along the axon moving in 1 direction

A

Part of the membrane immediately behind an action potential is still repolarising and cannot be stimulated to respond

34
Q

How does temperature affect the speed of conduction of a nervous impulse

A

A higher temperature increases the speed as the increased kinetic energy increases the rate of diffusion

35
Q

How does axon diameter affect speed of conduction of a nervous impulse

A

Larger diameter increases the speed and there is less leakage of ions from large axons due to larger volume to surface area ratio

36
Q

How does the myelin sheath effect the speed of conduction of a nervous impulse

A

It allows for saltatory propagation which increases the speed

37
Q

What is saltatory propagation?

A

The voltage gated ion channels are found only at the nodes of Ranvier and there is a myelin sheath between the nodes and act as a good electrical insulation so that the action potential can jump large distances from node to node

38
Q

Maximum speed of conduction for unmyelinated and myelinated neurones

A

Unmyelinated- 1m/s
Myelinated- 100m/s

39
Q

What is the only kind of animals that have a myelin shesth

A

Vertebrates

40
Q

What is a synapse

A

• a place where 2 neurones meet or where a motor neurone meets an effector
• is a gap between cells so transmission by ion transport across the membrane is not possible

41
Q

Functions of a synapse

A

• transmits information between neurones
• transmits information in 1 direction only
• acts as junctions
• filter out low-level stimuli
• prevent over stimulation of neurone and fatigue

42
Q

How does a synapse only transmit information in 1 direction

A

• vesicles are only found in the synaptic knob and the receptors are only found in the post-synaptic membrane

43
Q

Process of synaptic transmission

A
  1. Impulse arrives at the pre-synaptic knob
  2. Calcium channels open so Ca2+ ions diffuse rapidly into the pre-synaptic knob
  3. Ca2+ stimulate the vesicles of neurotransmitter (eg acetylcholine) to migrate to and fuse to the pre-synaptic membrane
  4. The neurotransmitter is released into the synaptic cleft by exocytosis which requires ATP
  5. Acetylcholine diffuses across the cleft and binds to receptors on the post-synaptic membrane causing sodium channels to open
  6. Na+ ions rush into the post-synaptic neurone by diffusion resulting in the depolarisation of the post-synaptic membrane. An action potential is initiated
  7. Acetyl cholinesterase splits the acetylcholine into ethanoic acid and choline, releasing them from the receptor, and sodium channels close and the products diffuse back across the cleft
  8. Products are reabsorbed into the pre-synaptic knob
  9. ATP is used to reform acetylcholine in the pre-synaptic knob
44
Q

How is the repeated depolarisation of the post synaptic neurone prevented

A

• hydrolysis of acetylcholine
• reabsorption of ethanoic acid and choline back into the pre-synaptic knob
• active transport of Ca2+ out of pre-synaptic knob which prevents the further exocytosis of neurotransmitter

45
Q

What happens if not enough acetylcholine is released

A

Not enough sodium channels open so post-synaptic membrane does not exceed the threshold of -55 mV so no action potential initiated

46
Q

What are the two main types of drugs

A

Antagonists and agonists

47
Q

How do antagonists work

A

• affect by preventing post-synaptic depolarisation
Eg cannabis, alcohol
• it can decrease action potentials in the post-synaptic membrane
• it prevents the exocytosis and so the release of the neurotransmitter
• it binds with receptors on the post synaptic membrane and blocks it
• it prevents Ca2+ entry into the presynaptic knob

48
Q

How do agonists work

A

• cause more post-synaptic depolarisation
Eg caffeine, cocaine, organophosphorous insecticide
• it acts as a cholinesterase inhibitor
• it mimics the neurotransmitter by linking to the receptors
• blocks the uptake back into the pre-synaptic knob which causes more exocytosis
• eventually it increases the number of receptors on post-synaptic membrane

Wjec A Level Biology (13 decks)

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