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Paper 3 - Bio > The nervous system > Flashcards

The nervous system Flashcards

1
Q

State the components of a nervous response.

A
  • Receptors.
  • Effectors.
  • Nervous system or hormones transfer info from receptors to effectors.
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2
Q

What is the CNS?

A

Brain and spinal cord.

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3
Q

What is the PNS?

A

Pairs of nerves that originate from the CNS and carry nerve impulses into and out of the CNS.

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4
Q

What is the dorsal root?

A
  • One of two roots that emerges from the spinal cord.
  • Travels to the dorsal root ganglion.
  • Sensory neurons enter the spinal cord via the dorsal root.
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5
Q

What is the ventral root?

A
  • One of two roots that emerges from the spinal cord.

- Motor neurons leave the spinal cord via the ventral root.

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6
Q

What is a reflex?

A

A rapid, automatic response to a sensory stimulus by the body. It serves as a protective mechanism.

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7
Q

Outline a simple reflex arc.

A

Stimulus - receptor - sensory neuron - relay neuron (in CNS) - motor neuron - effector - response.

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8
Q

How does a reaction differ from a reflex?

A
  • Reaction is voluntary and coordinated by the brain.

- Reflex is non-voluntary and does not involve the brain.

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9
Q

What is a nerve net?

A
  • Simplest form of nervous system found in Cnidarians.

- Consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli.

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10
Q

State the three types of functional neurons.

A
  • Sensory
  • Relay
  • Motor
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11
Q

State the function of a sensory neuron.

A

Carries nerve impulses from the receptors to the CNS via the dorsal root.

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12
Q

State the function of a motor neuron.

A

Carries nerve impulses from the CNS to the effectors via the ventral root.

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13
Q

Describe the structure of a motor neuron.

A
  • Short dendrites carry impulses from CNS to cell body.
  • Cell body found at one end of neuron.
  • Long axon carries impulses from cell body to effectors.
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14
Q

State the function of a relay neuron.

A
  • Located in the spinal cord.

- Links the sensory neuron to the motor neuron.

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15
Q

What is the function of dendrites?

A
  • Short, branched extensions of the cell body.

- Receive nerve impulses from other neurons.

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16
Q

Describe the cell body.

A

The region of the neuron that contains the organelles, notably the nucleus and the rough endoplasmic reticulum.

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17
Q

What is the function of the axon?

A

A long fibre that conducts nerve impulses away from the cell body.

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18
Q

What are axon terminals?

A

Branched endings of an axon that approach the muscle fibre.

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19
Q

What is a synaptic end bulb?

A

The end of an axon that is bulbous shaped contains synaptic vesicles filled with neurotransmitters.

20
Q

Describe the additional features of a myelinated neuron.

A
  • Schwann cells: wrap around axon, involved in electrical insulation, phagocytosis and nerve regeneration.
  • Myelin sheath: made from myelin-rich membranes of Schwann cells.
  • Nodes of Ranvier: small gaps between neighbouring Schwann cells where there is no myelin sheath.
21
Q

Define action potential.

A

The temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse.

22
Q

What is resting potential?

A

Potential difference (voltage) across a neuron membrane when not stimulated (-70 mV).

23
Q

How is resting potential established?

A
  • Membrane more permeable to K+ than Na+.
  • Sodium-potassium pump actively transports 3 Na+ out of the cell and 2K+ into the cell.
  • Organic phosphates and large protein anions remain in cytoplasm.
  • Establishes electrochemical gradient: cell contents more negative than extracellular environment.
24
Q

Name the stages of an action potential.

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarization
  4. Return to resting potential
25
Q

What happens during depolarisation?

A
  1. Stimulus causes a change in the voltage across an axon membrane, opening voltage-gated Na+ channels.
  2. Na+ diffuse into the axon.
  3. Potential difference across membrane becomes more positive, membrane depolarises.
26
Q

What happens during repolarization?

A
  1. Membrane potential reaches +40mV.
  2. Voltage-gated Na+ channels close and voltage-gated K+ channels open.
  3. Facilitated diffusion of K+ ions out of cell down their electrochemical gradient.
  4. Potential difference across membrane becomes more negative, membrane repolarizes.
27
Q

What happens during hyperpolarization?

A
  1. ‘Overshoot’ when K+ ions diffuse out.
  2. Potential difference becomes more negative than resting potential.
  3. Membrane hyperpolarizes, preventing another impulse occuring.
28
Q

What is the refractory period?

A

The time period after an action potential during which further action potentials are prevented.

29
Q

Why is the refractory period important?

A

Ensures that action potentials can only be propagated in one direction.

30
Q

Describe the ‘all or nothing’ law.

A

Principle that states that all stimuli above a certain threshold value will generate the same size of action potential, regardless of the strength of the stimulus.

31
Q

State the factors affecting the speed of conduction of a nervous impulse.

A
  • Temperature
  • Axon diameter
  • Myelin sheath
32
Q

Explain why myelinated axons conduct impulses faster than unmyelinated axons.

A

Saltatory propagation: impulse ‘jumps’ from one node of Ranvier to another (depolarisation cannot occur where myelin sheath acts as electrical insulator). Therefore, impulse doesn’t travel along whole axon length.

33
Q

How does temperature affect the speed of conduction of nervous impulses?

A

The higher the temperature, the faster the speed of conduction.

34
Q

How does axon diameter affect the speed of conduction of nervous impulses.

A

The larger the diameter, the faster the speed of conduction.

35
Q

What is a synapse?

A

The junction between two nerve cells or a nerve cell and an effector.

36
Q

What is the function of synapses?

A
  • Electrical impulse cannot cross junction.
  • Neurotransmitters send impulses between neurons of from neurons to effectors.
  • Summation of sub-threshold impulses.
  • New impulses can be initiated in several different neurons for multiple simultaneous responses.
37
Q

Describe the structure of a synapse.

A
  • Presynaptic neuron ends in synaptic knob.
  • Synaptic knob contains a high concentration of mitochondria, endoplasmic reticulum and vesicles of neurotransmitter.
  • Synaptic cleft, 20-30 nm gap.
  • Postsynaptic neuron has complementary receptors to neurotransmitter (lingang-gated Na+ channels).
38
Q

What is the synaptic cleft?

A

A small gap between neurons across which a nerve impulse is transmitted via neurotransmitters.

39
Q

Describe synaptic transmission in the presynaptic neuron.

A
  1. Wave of depolarisation travels down presynaptic neuron, causing voltage-gated Ca2+ channels open.
  2. Ca2+ cause vesicles of acetylcholine to move towards and fuse with presynaptic membrane.
  3. Exocytosis of neurotransmitter (e.g. acetylcholine) into synaptic cleft.
40
Q

How do neurotransmitters cross the synaptic cleft?

A

Via simple diffusion.

41
Q

Describe synaptic transmission in the postsynaptic neuron.

A
  1. Acetylcholine diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane.
  2. Ligand-gated Na+ channels open.
  3. If influx of Na+ ions raises membrane to threshold potential, action potential is generated.
42
Q

How is the merging of impulses prevented during synaptic transmission?

A
  • Active transport of Ca2+ out of synaptic knob.
  • Role of cholinesterase.
  • Reabsorption of neurotransmitters.
43
Q

Describe the role of cholinesterase in synaptic transmission.

A
  • Hydrolyses acetylcholine in the postsynaptic neuron.

- Products diffuse back across the cleft.

44
Q

What is the effect of organophosphates on the transmission of impulses?

A
  • Act as cholinesterase inhibitors, preventing the hydrolysis of acetylcholine in postsynaptic neuron.
45
Q

What are organophosphates commonly found?

A

Component of insecticides.

46
Q

How do psychoactive drugs (e.g. amphetamine) affect the transmission of impulses?

A
  • Excitatory drugs stimulate the release of neurotransmitters such as noradrenaline.

Paper 3 - Bio (5 decks)

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