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Edexcel Biology B A-level > 9.2 The Mammalian Nervous System > Flashcards

9.2 The Mammalian Nervous System Flashcards

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1
Q

Name the 2 main divisions of the nervous system.

A

Central nervous system (CNS)
Peripheral nervous system (PNS - all neurons that are not part of the CNS)

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2
Q

Describe the central nervous system.

A

Comprised of brain and spinal cord
Specialised system of nerve cells processes stimuli and propagates impulses

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3
Q

Name the 2 main divisions of the PNS.

A

Voluntary (under conscious control)
Autonomic (not under conscious control)

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4
Q

Name the 2 main divisions of the autonomic nervous system.

A

Sympathetic
Parasympathetic
They act antagonistically to regulate response of effectors e.g., heart rate

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5
Q

Describe the sympathetic nervous system.

A

Usually stimulates effectors (coordinates fight-or-flight response)
Neurotransmitter noradrenaline
Ganglia are located near CNS

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6
Q

Describe the parasympathetic nervous system.

A

Usually inhibits effectors (coordinates rest/digest response)
Neurotransmitter acetylcholine
Ganglia located far from CNS

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7
Q

Describe the structure of the spinal cord.

A

Cylindrical bundle of nerves fibres runs from brain stem to lower back - surrounded by spinal vertebrae
Consists of nerve tissue
Grey matter - H-shaped region contains neurons
White matter - myelinated axons

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8
Q

What is the function of the cerebellum?

A

Controls execution of movement
Possible role in cognition

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9
Q

What is the function of the medulla oblongata?

A

Controls a range of autonomous functions including breathing and heart rate

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10
Q

What is the function of the cerebrum?

A

Uppermost part of the brain that is organised into lobes which control voluntary functions

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11
Q

What is the function of the hypothalamus?

A

Includes anterior pituitary gland
Involved in thermo and osmoregulation

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12
Q

What is resting potential?

A

Potential difference across neuron membrane when not stimulates - about -70mV in humans

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13
Q

How is resting potential established?

A
  1. Membrane is more permeable to K+ than Na+
  2. Sodium-potassium pump actively transports 3Na+ out of cell and 2K+ into cell
    Establishes electrochemical gradient
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14
Q

Name the stages in generating an action potential.

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarisation
  4. Return to resting potential
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15
Q

What happens during depolarisation?

A
  1. Stimulus —> facilitated diffusion of Na+ into cell down electrochemical gradient
  2. P.D across membrane becomes more positive
  3. If membrane reaches threshold potential (-50mV) voltage gated Na+ channels open
    Significant influx of Na+ ions reverses P.D to +40mV
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16
Q

What happens during repolarisation?

A
  1. Voltage gated Na+ channels close and voltage gated K+ channels open
  2. Facilitated diffusion of K+ ions out of cell down their electrochemical gradient
  3. P.D across membrane becomes more negative
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17
Q

What happens during hyperpolarisation?

A
  1. Overshoot when K+ ions diffuse out of= P.D becomes more negative than resting potential
  2. Refractory period: no stimulus is large enough to raise membrane potential to threshold
  3. Voltage gated K+ channels close and sodium-potassium pump re-establishes resting potential
18
Q

Explain the importance of the refractory period.

A

No action potential can be generated in hyperpolarised sections of membrane:

  1. Ensures unidirectional impulse
  2. Ensures discrete impulses
  3. Limits frequency of impulse transmission
19
Q

How is an action potential propagated along an unmyelinated neuron?

A
  1. Stimulus leads to influx of Na+ ions - first section of membrane depolarised
  2. Local electrical currents cause sodium voltage-gated channels further along membrane to open - meanwhile the section behind begins to depolarise
  3. Sequential wave of depolarisation
20
Q

Describe the structure of a motor neuron.

A

Cell body: contains organelles & high proportion of RER
Dendrons: branch into dendrites which carry impulses towards cell body
Axon: long, unbranched fibre carries nerve impulse away from cell body

21
Q

Describe the additional features of a myelinated motor neuron.

A

Schwann cells: wrap around axon many times
Myelin sheath: made from myelin-rich membranes of Schwann cells
Nodes of Ranvier: very short gaps between neighbouring Schwann cells where there is no myelin sheath

22
Q

Explain why myelinated axons conduct impulses faster than unmyelinated axons.

A

Saltatory conduction: impulse jumps from one node of ranvier to another - depolarisation cannot occur where myelin sheath acts as electrical insulator
So impulse does not travel along whole axon length

23
Q

Describe the structure of a synapse.

A
  1. Presynaptic neuron ends in synaptic knob - contains lots of mitochondria, endoplasmic reticulum & vesicles of neurotransmitter
  2. Synaptic cleft
    Postsynaptic neuron: has complementary receptors to neurotransmitter
24
Q

Explain the role of acetylcholine.

A

Causes muscle contraction at motor end plate
Causes excitation at preganglionic neurons
Causes inhibition at postganglionic neurons

25
Q

What happens to acetylcholine from the synaptic cleft?

A
  1. Hydrolysis into acetyl and choline by acetylcholinesterase
  2. Acetyl & choline diffuse back into presynaptic membrane
  3. ATP is used to reform acetylcholine from storage in vesicles
26
Q

What happens in the presynaptic neuron when an action potential is transmitted between neurons?

A
  1. Wave of depolarisation travels down presynaptic neuron, causing voltage-gated Ca2+ channels to open
  2. Vesicles move towards & fuse with presynaptic membrane
  3. Exocytosis of neurotransmitter into synaptic cleft
27
Q

How do neurotransmitters cross the synaptic cleft?

A

Via simple diffusion

28
Q

What happens in the postsynaptic neuron when an action potential is transmitted between neurons?

A
  1. Neurotransmitter binds to specific receptor on postsynaptic membrane
  2. Ligand-gated Na+ channels open
  3. If influx of Na+ ions raises membrane to threshold potential, action potential is generated
29
Q

What happens in an inhibitory synapse?

A
  1. Neurotransmitter binds to an opens Cl- channels on postsynaptic membrane & triggers K+ channels to open
  2. Cl- moves in & K+ moves out via facilitated diffusion
  3. P.D becomes more negative: hyperpolarisation so no action potential is generated
30
Q

How does nicotine work?

A

Absorbed in lungs - travels to brain via bloodstream
Similar shape to acetylcholine = bids to cholinergic receptors
Stimulant effect causes symptoms of sharpness & relaxation

31
Q

How does lidocaine work?

A

Absorbed through skin or injected
Blocks voltage gated Na+ ion channel = prevents postsynaptic neuron from depolarising
Prevents transmission of pain signals so acts as anaesthetic

32
Q

How does cobra venom work?

A

Blocks acetylcholine receptors on diaphragm = muscles cannot contract during inhalation
Disrupts normal breathing

33
Q

Name the 2 types of photoreceptor cells located in the retina.

A

Cone cells
Rod cells

34
Q

Where are rod and cone cells located in the retina?

A

Rod: distributed evenly around periphery but NOT in central fovea
Cone: mainly central fovea

No photoreceptors at blind spot where ganglion axon fibres form optic nerve

35
Q

Explain why rod cells do not generate action potentials in the dark.

A
  1. Na+ enters outer segment of red cell via on-specific cation channels - active transport of Na+ out of inner segment = rod cell is slightly depolarised
  2. Action potential = voltage gated Ca2+ channels open - triggers exocytosis of glutamate
  3. Glutamate acts as inhibitory neurotransmitter to hyperpolarisation bipolar neuron
36
Q

Explain how rod cells generate an action potential in the light.

A
  1. Rhodopsin pigment bleaches when it absorbs light & breaks down into opsin + retinal
  2. Opsin closes cation channels via hydrolysis - active transport of Na+ out of inner segment continues
  3. Rod cell becomes hyperpolarised - no glutamate is release, so no inhibitor signal
  4. Bipolar neuron depolarises
37
Q

Describe the pigments in rod and cone cells.

A

Rod: rhodopsin absorbs all wavelengths of light
Cone: 3 types of iodopsin which absorbs red, blue or green wavelengths of light

38
Q

Describe the visual acuity of rod and cone cells.

A

Rod: many told cells synapse with 1 bipolar neuron - low resolution
Cone: 1 cone cell synapse 1 bipolar neuron so there is no retinal convergence = high resolution

39
Q

Describe the light sensitivity of rod and cone cells.

A

Rod: very sensitive due to spatial summation of subthreshold impulses = vision in low-light conditions
Cone: less sensitive = vision in bright light

40
Q

Describe how light causes a change in the release of glutamate from rod cells.

A

Rhodopsin is involved
Retinal and opsin is formed from rhodopsin
Na+ channels are closed
Na+ is moving out of the cell
Stops glutamate/neurotransmitter release

41
Q

Explain the role of mitochondria in the functioning of rod cells.

A

Produces ATP
Needed for active transport of ions

Edexcel Biology B A-level (31 decks)

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