PSYC201 Week 3

Properties of reflexes that suggest special processes in the junctions of neurons

(1) Reflexes are slower than conduction along an axon.  

(2) Several weak stimuli presented at nearby places or times combine their effects.  

(3) When one set of muscles becomes excited, a different set becomes relaxed. 

Temporal summation is when…

repeated stimuli within a brief period of time combine their effects.

A graded depolarization is an…

excitatory postsynaptic potential (EPSP), this leads to positive sodium ions to flood into the neuron.  

A graded hyperpolarization is an…

inhibitory postsynaptic potential (IPSP, this leads to negative chloride ions flooding into the neuron. 

spacial summation would be if…

multiple stimuli from different areas were picked up by different sensory neurons however, their axons converged meaning the combined excitation was enough to reach the threshold. 

Exocytosis is…

A sudden release of neurotransmitters from the presynaptic neuron, these neurotransmitters then diffuse across the synaptic cleft to attach to receptors on the post synaptic neuron. 

Ionotropic effect is…

When a neurotransmitter binds to an ionotropic receptor, it twists the receptor just enough to open its central channel which is sized and shaped to only allow one type of ion to pass through. 

Metabotropic Effects is where…

Some receptors control metabolic effects, through a slower starting (but longer lasting) sequence of metabolic reactions unlike ionotropic. Neuromodulators are what affect these receptors. 

Autoreceptors are…

receptors on the presynaptic terminals that are sensitive to the neurotransmitter that they release. They respond to the released neurotransmitter by inhibiting further synthesis and release. 

A hormone is…

a chemical secreted by cells in one part of the body and conveyed by the blood to influence other cells.

The difference between hormones and neurotransmitters are…

A neurotransmitter is like a telephone signal: It conveys a message from the sender to the intended receiver.

Hormones function more like radio waves: They convey a message to any receiver tuned to the right station.

anterograde amnesia is…

The inability to form memories for events that happened after brain damage

retrograde amnesia is…

The loss of memory for events before the brain damage 

Hebbian synapses are…

Essential for many kinds of associative learning. Is a synapse that increases its effectiveness because of simultaneous activity in the presynaptic and postsynaptic neurons.

Long-term potentiation (LTP) is where…

One or more axons connected to a dendrite bombard it with a rapid series of stimuli. 

The burst of intense stimulation leaves some of the synapses potentiated (more responsive to new input) for minutes, days, or weeks.

What are three properties that make Long-term potentiation (LTP) an attractive 

candidate for a cellular basis of learning and memory?

specificity—If some of the synapses onto a cell have been highly active and others have not, only the active ones become strengthened. 

cooperativity—Nearly simultaneous stimulation by two or more axons produces LTP more strongly than does repeated stimulation by just one axon. 

associativity—Pairing a weak input with a strong input enhances later response to the weak input.

Long-term depression (LTD) is…

a prolonged decrease in response at a synapse, occurs for axons that have been less active than others. 

Depolarization is…

The cell becoming less negative 

Hyperpolarization is…

The cell becoming less negative so that it can return to its resting state after the overshot

Na+ channels open during an action potential because…

the cell has reached the threshold to open the channels, the Na+ ions flood in and as a result the inside of the cell becomes less negative (more positive). 

What happens to the Na+ channels at the peak of the action potential?

The channels will close and Na+ will stop flowing in.

After the action potential has reached its peak and has entered Repolarization what will occur?

K+ channels open, at first there is little flow of K+ out of the cell but the electrical gradient pushes K+ out of the cell more as the cell becomes less negative. 

What happens to the charge of the cell when the K+ ions leave during the Repolarization period?

When K+ moves out of the cell the inside becomes more negative again.

What restores the balance of K+ and Na+ to the cell after an action potential?

There is a sodium potassium pump that restores the balance. It takes potassium from the outside and brings it inside, and takes sodium from the inside and brings it to the outside. 

Action potential propagation is…

The sodium ion channels along the axon to the terminals. When the cell is activated and the first sodium ion channel is opened, as positive NA+ flow in, the membrane potential becomes less negative therefore the next channel opens up and so on. The cell depolarizes this then spreads to the next channel. 

Neuron refractory period is…

the period where during this phrase the sodium ion channels cannot open up anymore. (During reploarization the cell will eventually return to -60mV, this phase prevents to sodium channels from reopening and continuously firing.

The refractory period consists of two states which are…

Absolute refractory state

Relative refractory state

The Absolute refractory state is where…

The cell is not responsive at all to any stimuli and an action potential cannot open any channels

Relative refractory state is where…

If the cell is stimulated by a strong stimuli the channel can still open 

Saltatory conduction is…

The “jumping” of the action potential between nodes of Ranvier  

When action potential arrives at the terminal region what channels will open?

calcium channels

Two types of receptors:

Ionotropic

Metabotropic

Ionotropic receptors…

A receptor wherein a neurotransmitter comes, it binds and then opens up the channel.

Metabotropic receptors…

A receptor wherein a neurotransmitter binds then the structure changes and activates the G-protein. 

What effect does blockage of uptake in the storage have on neurotransmission?

It will decrease neurotransmission as no neurotransmitters can be released into the synapse

What effect does blockage of the reuptake inhibitor have on neurotransmission?

It will increase neurotransmission as more of the neurotransmitter is left in the synalitc cleft. 

What effect do Agonists have on neurotransmission?

They will enhance neurotransmission

What effect do Antagonist have on neurotransmission?

They will reduce neurotransmission

Direct synaptic communication…

neurotransmitters or drugs will bind to the receptors.

Indirect synaptic communication…

Does not bind to the receptor directly (could be blocking reuptake or vesicles) 

AMPA and NMDA are both excitatory inotropic receptors however, which receptor is blocked by a magnesium ion?

The NMDA receptor

If the weaker signal in the AMPA receptor is paired with a stronger signal what effect will that have on the NMDA receptor?

The AMPA is strong enough to push away the magnesium and now even with a weak stimulus both receptors are open and the action potential can be triggered as there is a flood of ions into the cell.