The Nervous System

Question 0

What is the axon hillock?

Answer 0

The commencement point of an action potential

Question 1

What is a Golgi stain?

Answer 1

A silver salt taken up by neurons that shows the structure and network of the discrete cells

Question 2

What is the soma of a neuron?

Answer 2

The cell body containing the metabolic centre of the neuron

Question 3

What is the all or none principle?

Answer 3

Action potentials are always the same amplitude and always result in the same change in charge

Question 4

What are the steps of an action potential?

Answer 4

1) Depolarisation: Influx of Na+ causes inside of cell to become more positive
2) Absolute refraction: Na+ channels are inactivated and cannot reopen
3) Repolarisation: Efflux of K+ causes inside of cell to become less positive
4) Hyperpolarisation: Slow closing of the K+ channels causes an undershoot
5) Relative refraction: Larger depolarisation required to initiate a new action potential

Question 5

What occurs at the neural synapse?

Answer 5

1) Action potential activates the presynaptic neuron
2) Membrane is depolarised, opens Ca2+ channels
3) Ca2+ binds to vesicles
4) Vesicles bind to synaptic end feet and undergo exocytosis (release neurotransmitter)
5) Neurotransmitter binds to lygand-gated ion channels and opens them if threshold is reached

Question 6

What do postsynaptic neurotransmitter receptor proteins contain?

Answer 6

Binding component: Binds to neurotransmitter

Ionophore component: Opens an ion channel or activates a second messenger system

Question 7

What do second messenger activators do?

Answer 7

Allow prolonged changes in the activity of neurons e.g. Memory

Question 8

How does diameter size of a neuron affect transmission speed?

Answer 8

Larger diameter = faster transmission speed

Question 9

What is a type A neuron?

Answer 9

A myelinated neuron with fast transmission speed

Question 10

What is a type B neuron?

Answer 10

An unmyelinated neuron with slow transmission speed

Question 11

What are the two types of summation and what do they involve?

Answer 11

1) Spatial summation: Multiple terminals are excited simultaneously until the EPSP reaches threshold
2) Temporal summation: Rapid repeat firings at the terminals increases the EPSP until threshold is reached

Question 12

What are the four ways in which neuronal activity is modulated?

Answer 12

Presynaptic inhibition/facilitation
Neuronal fatigue
Modulation of molecular machinery
Environmental changes

Question 13

How does presynaptic inhibition modulate neuronal activity?

Answer 13

Influx of chloride ions decreases the ability of calcium channels to open

Question 14

How does presynaptic facilitation modulate neuronal activity?

Answer 14

Prolonged opening of calcium channels results in increased neurotransmitter being released

Question 15

How does neuronal fatigue modulate neuronal activity and what does it protect against?

Answer 15

Neurotransmitter stores are exhausted and the rate of postsynaptic discharge decreases, resulting in areas of the nervous system losing excitability. Protects against excessive neuronal activity.

Question 16

How does modulation of molecular machinery modulate neuronal activity?

Answer 16

Activation of second messengers alters the cell threshold, excitatory properties, firing pattern and organisation of synaptic connections

Question 17

How do environmental changes modulate neuronal activity?

Answer 17

Acidosis: Decreases neuronal activity
Alkalosis: Increases neuronal activity
Hypoxia: Leads to unconsciousness

Question 18

What are neuronal pools and what are the five different types?

Answer 18

Groups of neurons with a special organisation.

Diverging signal, converging signal, lateral inhibition, reverberating circuits and continuous signalling

Question 19

What is a diverging signal and what is its function?

Answer 19

A signal that enters a neuronal pool and excites more neurons leaving the pool, causing amplification and separation into multiple tracks

Question 20

What is a converging signal and what is its function?

Answer 20

A signal from multiple units that unites to excite a single neuron, allowing amplification and summation e.g. the rod photoreceptor pathway

Question 21

What is lateral inhibition and what is its function?

Answer 21

An incoming signal that excites in some directions and inhibits in others, blocking lateral spread of signals and increasing contrast

Question 22

What are reverberating circuits and what are their function?

Answer 22

Positive feedback circuits that re-excite input of the same circuit allowing repetitive discharge for long periods

Question 23

What is continuous signalling and what is its function?

Answer 23

Intrinsic neuronal excitability: Membrane potential is high enough for continuous firing

Reverberating circuit: Not fatigued, modulated in either direction

Question 24

What are the four types of gradual communication?

Answer 24

1) Modulation of the neuronal firing rate
2) Mechanical change e.g. pupil size
3) Neural adaptation
4) Background sensory intensity