Saturday, January 17, 2015

Synaptic transmission {physio}

T/F: The dendrites of a neuron have a threshold potential which, if exceeded, could initiate an action potential within the shaft of the dendrite.

True, although this threshold is far higher than at the axon hillock so it is never exceeded.

Why does the axon hillock have the lowest threshold potential?

It is the region with the highest number of voltage-gated sodium channels

What two ways can an EPSP become strong enough to initiate an AP?

Spatial summation (recruit more excitatory neurons with a stronger stimulus)
Temporal summation (add multiple EPSPs close together)

T/F: Inhibitory neurons located on dendrite shafts decrease the strength of local EPSPs while inhibitory neurons located near the axon hillock decrease the strength of the collective EPSP of the cell.

True

A measure of the change in EPSP strength compared to the original EPSP.

Synaptic strength (efficacy)

What is the principle difference between axo-somatic inhibitory synapses and axo-axonic inhibitory synapses?

Axo-somatic inhibitory synapses act by lowering the strength of the graded potential, making it harder to reach threshold. Axo-axonic inhibitory synapses act downstream of the AP and act to limit the amount of neurotransmitter release.

What is a major function of axo-axonic inhibition in the various sensory pathways?

It serves to filter out "noise" allowing the subject to focus on the important stimulus more efficiently. For example, random noise in a room when you are having a conversation.

The process of filtering out sensory "noise"

Habituation

What is the principle axo-axonic inhibitory neurotransmitter?

GABA

GABA inhibits via two receptors. What are they and how do they cause inhibition?

GABAb: close Ca++ channels and/or open K+ channels
GABAa: open Cl- channels

**think "a" is first letter, so it's the most simple. Only one ion.

These cells in the CNS "fine-tune" muscle responses.

Renshaw cells

A motorneuron sends ACh to _________ receptors at the NMJ while simultaneously sending ACh to _________ receptors on Renshaw cells.

Nicotinic (ionotropic); muscarinic (metabotropic)

Interneurons in the motor pathway use _________ as the primary inhibitory neurotransmitter.

Glycine

Motor axons are _________ while motor neuron axon collaterals are _________.

Myelinated; unmyelinated

Muscarinic receptors on Renshaw cells are blocked by this compound.

Atropine

T/F: Muscarinic Renshaw cell receptors increase K+ conductance.

False. They decrease K+ conductance

Norepinephrine, dopamine, seratonin are synthesized in the _________ of a neuron. They are neither __________ nor __________.

Terminal bouton; excitatory nor inhibitory

These are minor CNS neuromodulators that are synthesized in the soma and transported to the boutons.

Neuropeptides. Substance P (burning sensation) and enkephalin (opiate action)

Increasing/decreasing K+ conductance changes the __________ of action potentials.

Frequency (or duration)

T/F: A larger synaptic head tends to produce a stronger EPSP.

True. The larger head allows for more receptors.

T/F: Mentally retarded children will exhibit a larger number of dendritic spines in their neurons early on.

True. But these are largely immature and eventually disintegrate, leading to a lowered number of spines in adulthood (Slide 17, lecture 08)

T/F: Sanel has less LTP going on in his hippocampus than in Rick Hill's hippocampus.

:-)

What induces a LTP to form?

A strong, short stimulus

Describe the steps of LTP.

1) Activation of NMDA receptors, Ca++ flows in
2) Ca++ binds to calmodulin, activates PKC
3) More AMPA receptors are recruited to the plasma membrane, increasing synaptic strength
**Additionally, the phosphorylation state of existing AMPA receptors can be changed to modulate their activity

T/F: Genetic actin defects lead to mental retardation.

True. Actin is used to anchor AMPA receptors during LTP/LTD. A problem in this process will lead to decreased cognitive abilities.

T/F: Now that you understand the molecular basis of cognitive pathways, studying moderately over long periods of time is better than studying a lot over a short period of time.

True!

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