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IB Biology HL New Syllabus 2025 > Nervous System > Flashcards

Nervous System Flashcards

SL & HL Content (77 cards)

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1
Q

What is the function of a sensory neuron?

A

Transmits impulses from receptors to the CNS.

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2
Q

What is the function of an interneuron?

A

Transmits impulses within the CNS.

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3
Q

What is the function of a motor neuron?

A

Transmits impulses from the CNS to effectors.

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4
Q

What is the function of dendrites?

A

Receive impulses from other neurons or receptors.

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5
Q

What is the role of the axon?

A

Conducts action potentials from cell body to axon terminals.

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6
Q

Define resting potential.

A

Electrical potential difference (~-70 mV) of a neuron not transmitting an impulse.

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7
Q

How does the sodium-potassium pump maintain resting potential?

A

Pumps 3 Na⁺ out and 2 K⁺ in using ATP.

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8
Q

What causes depolarization during an action potential?

A

Na⁺ enters the neuron via voltage-gated channels.

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9
Q

What causes repolarization during an action potential?

A

K⁺ exits the neuron via voltage-gated channels.

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10
Q

What is hyperpolarization?

A

Membrane potential becomes more negative than resting potential.

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11
Q

What is the threshold potential for triggering an action potential?

A

Approximately -55 mV.

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12
Q

What is a nerve impulse?

A

A propagated action potential along a neuron.

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13
Q

Define saltatory conduction.

A

Action potential jumps between nodes of Ranvier in myelinated axons.

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14
Q

Why is saltatory conduction faster?

A

Myelin insulates axon; fewer ion exchanges occur.

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15
Q

What are nodes of Ranvier?

A

Gaps in myelin where ion exchange occurs.

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16
Q

What is a synapse?

A

Junction between two neurons or a neuron and an effector.

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17
Q

What happens at the presynaptic membrane during neurotransmission?

A

Ca²⁺ enters, triggering exocytosis of neurotransmitters.

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18
Q

What does acetylcholine do at a neuromuscular junction?

A

Binds receptors, opens Na⁺ channels, initiates postsynaptic potential.

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19
Q

Define excitatory postsynaptic potential.

A

Na⁺ influx causes depolarization of postsynaptic membrane.

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20
Q

What is an inhibitory neurotransmitter?

A

Causes Cl⁻ or K⁺ influx, hyperpolarizing the postsynaptic membrane.

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21
Q

What is summation in neural signalling?

A

Combined effect of excitatory and inhibitory inputs on one neuron.

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22
Q

What correlation exists between axon diameter and impulse speed?

A

Positive correlation.

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23
Q

What correlation exists between animal size and impulse speed?

A

Negative correlation.

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24
Q

What are local currents?

A

Diffusion of Na⁺ ions causing depolarization ahead of the action potential.

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25
What does an oscilloscope trace show?
Changes in membrane potential during action potentials.
26
How do neonicotinoids affect synaptic transmission?
Bind irreversibly to insect acetylcholine receptors, blocking transmission.
27
Why are neonicotinoids less toxic to humans?
Human receptors have a different shape and weaker binding.
28
How does cocaine affect dopamine signalling?
Blocks dopamine reuptake, causing prolonged stimulation.
29
What are nociceptors?
Pain receptors that open Na⁺ channels in response to stimuli.
30
How is pain perceived?
Action potential travels from nociceptor to brain.
31
What is consciousness in biological terms?
Emergent property from the interaction of neurons.
32
Why is the resting potential of a neuron negative despite the presence of positively charged ions?
Because there are more Na⁺ outside than K⁺ inside, and negatively charged proteins inside the cell contribute to the net negative charge.
33
What structural difference allows axons to transmit impulses more effectively than dendrites?
Axons are long single fibres adapted for directional, rapid transmission; dendrites are short and branched for receiving multiple inputs.
34
What two factors contribute most directly to establishing the resting membrane potential?
The sodium-potassium pump and the differential permeability of the membrane to K⁺ and Na⁺.
35
What is the role of ATP in maintaining the membrane potential of a neuron?
ATP provides energy for the sodium-potassium pump to actively transport ions against their concentration gradients.
36
Why is the action potential considered electrical in nature?
Because it results from the movement of charged ions (mainly Na⁺ and K⁺) across the neuronal membrane.
37
Explain why the movement of Na⁺ and K⁺ during an action potential is an example of facilitated diffusion.
The ions move through specific voltage-gated channels down their concentration gradients, without using ATP.
38
What structural adaptations increase the speed of nerve impulse conduction in large animals?
Larger axon diameter and myelination.
39
How do synapses ensure one-way transmission of impulses?
Neurotransmitter vesicles and receptors are only on the presynaptic and postsynaptic membranes respectively.
40
Why is the term "chemical synapse" used instead of "electrical synapse" in this context?
Because transmission occurs via neurotransmitters rather than direct ion flow through gap junctions.
41
What is the role of calcium ions in synaptic transmission?
Ca²⁺ enters the axon terminal upon depolarization, triggering vesicle fusion and neurotransmitter release.
42
Why does depolarization of the presynaptic membrane lead to calcium ion influx?
Voltage-gated calcium channels open in response to the change in membrane potential.
43
How does acetylcholine generate an excitatory postsynaptic potential (EPSP)?
It binds to receptors that open Na⁺ channels, leading to depolarization of the postsynaptic membrane.
44
How does neurotransmitter diffusion ensure specificity of synaptic transmission?
Neurotransmitters diffuse across the synaptic cleft and bind only to specific receptors on the postsynaptic membrane.
45
Why is a threshold potential necessary for initiating an action potential?
It ensures voltage-gated Na⁺ channels open, leading to a rapid depolarization.
46
What causes voltage-gated Na⁺ channels to close during an action potential?
When the membrane potential reaches approximately +30 mV.
47
At what point do voltage-gated K⁺ channels open during an action potential?
After the Na⁺ channels close, to begin repolarization.
48
How does local diffusion of Na⁺ inside the axon contribute to action potential propagation?
It depolarizes adjacent sections of the membrane, triggering threshold potential and continuing the signal.
49
What role do Na⁺ ions outside the axon play in local current propagation?
Their movement inward across the membrane sustains depolarization in the direction of the impulse.
50
How does an oscilloscope trace reflect changes in membrane potential during an action potential?
It shows a sharp rise (depolarization), a peak, and a fall (repolarization), then hyperpolarization.
51
What cellular event does the rising phase of an oscilloscope trace represent?
Influx of Na⁺ through voltage-gated sodium channels.
52
What cellular event causes the falling phase on an oscilloscope trace?
Efflux of K⁺ through voltage-gated potassium channels.
53
What effect do neonicotinoids have on cholinergic synapses in insects?
They bind irreversibly to acetylcholine receptors, blocking transmission and causing paralysis.
54
What is the physiological effect of dopamine accumulation in the synapse?
Prolonged stimulation of postsynaptic dopamine receptors, reinforcing reward pathways.
55
How do inhibitory neurotransmitters prevent action potentials?
By causing influx of Cl⁻ or efflux of K⁺, hyperpolarizing the membrane below threshold.
56
How does the balance of excitatory and inhibitory input determine postsynaptic response?
The summation of inputs must reach threshold to trigger an action potential; otherwise, it doesn’t fire.
57
What is the "all-or-nothing" principle in synaptic summation?
A postsynaptic action potential only occurs if the combined input reaches threshold potential.
58
How does capsaicin trigger pain perception in nociceptors?
It opens ion channels, allowing Na⁺ to enter and initiate an action potential.
59
What types of stimuli can open ion channels in nociceptors?
High temperatures, acids, and certain chemicals like capsaicin.
60
What type of ion channel is the nicotinic acetylcholine receptor?
A neurotransmitter-gated ion channel.
61
What is the difference between neurotransmitter-gated and voltage-gated ion channels?
Neurotransmitter-gated channels open in response to ligand binding; voltage-gated channels open in response to membrane potential changes.
62
How does binding of acetylcholine to its receptor change membrane potential?
It opens Na⁺ channels, causing an influx of positive ions and depolarization.
63
What is the functional consequence of a depolarized postsynaptic membrane?
It may reach threshold and initiate an action potential.
64
How does the spinal cord function in unconscious processing?
Integrates reflexes and automatic responses without involving the brain.
65
What is the pathway of sensory input to the central nervous system?
Sensory neurons transmit signals from receptors to the spinal cord or cerebral hemispheres.
66
How do motor neurons produce muscle contractions?
They carry impulses from the cerebral hemispheres to skeletal muscles, causing contraction.
67
What is a nerve?
A bundle of sensory and motor nerve fibres enclosed in a protective sheath.
68
What is a pain reflex arc?
An involuntary response involving a sensory neuron, interneuron in the spinal cord, and a motor neuron activating skeletal muscle.
69
What components are involved in a reflex arc for pain?
Sensory receptor → sensory neuron → interneuron → motor neuron → skeletal muscle (effector)
70
What is the role of the cerebellum?
Coordinates skeletal muscle contraction and maintains balance.
71
How does the hypothalamus regulate the endocrine system?
It sends signals to the pituitary gland to control hormone secretion.
72
What part of the brain coordinates heart rate response to sensory input?
The medulla oblongata.
73
How is heart rate adjusted following sensory input?
The medulla sends nerve impulses to the heart to change stroke volume and heart rate.
74
How is ventilation rate controlled by the nervous system?
Chemoreceptors send signals to the brainstem, which adjusts diaphragm and intercostal muscle activity.
75
Which parts of the digestive system are under voluntary nervous control?
Initiation of swallowing and egestion of faeces.
76
What is the role of the enteric nervous system (ENS)?
Controls involuntary peristalsis and coordinates gut motility between swallowing and egestion.
77
How does nervous signalling differ from hormonal signalling?
Nervous: fast, electrical, short-lasting, targeted. Hormonal: slow, chemical, long-lasting, widespread.

IB Biology HL New Syllabus 2025 (4 decks)

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