The Nervous System Flashcards
(25 cards)
What is the axon hillock?
The commencement point of an action potential
What is a Golgi stain?
A silver salt taken up by neurons that shows the structure and network of the discrete cells
What is the soma of a neuron?
The cell body containing the metabolic centre of the neuron
What is the all or none principle?
Action potentials are always the same amplitude and always result in the same change in charge
What are the steps of an action potential?
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
What occurs at the neural synapse?
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
What do postsynaptic neurotransmitter receptor proteins contain?
Binding component: Binds to neurotransmitter
Ionophore component: Opens an ion channel or activates a second messenger system
What do second messenger activators do?
Allow prolonged changes in the activity of neurons e.g. Memory
How does diameter size of a neuron affect transmission speed?
Larger diameter = faster transmission speed
What is a type A neuron?
A myelinated neuron with fast transmission speed
What is a type B neuron?
An unmyelinated neuron with slow transmission speed
What are the two types of summation and what do they involve?
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
What are the four ways in which neuronal activity is modulated?
Presynaptic inhibition/facilitation
Neuronal fatigue
Modulation of molecular machinery
Environmental changes
How does presynaptic inhibition modulate neuronal activity?
Influx of chloride ions decreases the ability of calcium channels to open
How does presynaptic facilitation modulate neuronal activity?
Prolonged opening of calcium channels results in increased neurotransmitter being released
How does neuronal fatigue modulate neuronal activity and what does it protect against?
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.
How does modulation of molecular machinery modulate neuronal activity?
Activation of second messengers alters the cell threshold, excitatory properties, firing pattern and organisation of synaptic connections
How do environmental changes modulate neuronal activity?
Acidosis: Decreases neuronal activity
Alkalosis: Increases neuronal activity
Hypoxia: Leads to unconsciousness
What are neuronal pools and what are the five different types?
Groups of neurons with a special organisation.
Diverging signal, converging signal, lateral inhibition, reverberating circuits and continuous signalling
What is a diverging signal and what is its function?
A signal that enters a neuronal pool and excites more neurons leaving the pool, causing amplification and separation into multiple tracks
What is a converging signal and what is its function?
A signal from multiple units that unites to excite a single neuron, allowing amplification and summation e.g. the rod photoreceptor pathway
What is lateral inhibition and what is its function?
An incoming signal that excites in some directions and inhibits in others, blocking lateral spread of signals and increasing contrast
What are reverberating circuits and what are their function?
Positive feedback circuits that re-excite input of the same circuit allowing repetitive discharge for long periods
What is continuous signalling and what is its function?
Intrinsic neuronal excitability: Membrane potential is high enough for continuous firing
Reverberating circuit: Not fatigued, modulated in either direction
