The Synapse

Question 1

Neurons will synapse with what types of cells in the:
CNS
PNS

Answer 1

CNS: nerve cells (other neurons)
PNS: Other neurons or EFFECTOR CELLS (such as glands, or muscle cells)

Question 2

Myoneural or neuromuscular junctions refer to what?

What is an effector cell of a neuron?

Answer 2

A synapse between a neuron and a muscle cell.
An effector cell of a neuron is a non-neuron which elicits responses to stimuli emmited through synapses with neurons (e.g. muscle cell, gland)

Question 3

What type of nerve is the vagus nerve, what effect does it do?

Answer 3

It is a cranial nerve (parasympathetic nerve). It causes a slowing of the heart.

Question 4

What experiment did Auto Loewi perform to discover the chemical nature of some synapses?

Answer 4

He had two hearts, one still connected to the vagus nerve, suspended in baths with a pump which could circulate fluid between the baths.
With the pump off only the one connected to the vagus nerve slowed.
With the pump on both hearts slowed, indicating something diffusible, in our case acetylcholine.

Question 5

What is necessary for electrical coupling of cells?

How is this accomplished?

Answer 5

Cells must be roughly equal in size and joined by a contact area of low electrical resistance.
Gap junctions (cells spaced 2 nanometers apart)

Question 6

What is the structure of a gap junction?

Answer 6

Six proteins called connexins for a hemichannel (hemi = half, channel = channel)
Two hemichannels form a gap junction when docked together.

Question 7

Where are gap junctions localized?

Answer 7

Gap junctions allow for quick dispersal of a signal unmodified between many cells. Examples:
In cardiac cells this allows the heart to beat in unison.
In smooth muscle cells, like those of the uterus, this allows contractions to occur to in unison.
The brain, where it is uncertain what they do.
Neuroglial cells where it is believed they allow exchange of Ca2+ and other ions.

Question 8

Are gap junctions adaptable systems?

Answer 8

Yes. The amount of gap junctions between cells can be changed to alter the conductivity.
They can also interact functionally with chemical synapses.

Question 9

What keeps post-synaptic and pre-synaptic vesicles together?

Answer 9

CAMs (cell adhesion molecules)

These act like velcro to hold the synapses right where they need to be.

Question 10

Why do synapsis act as one way gates?

Answer 10

There are only receptors for the neurotransmitter on side (post-synaptic). there is also, in theory, only production of neurotransmitter on one side.

Question 11

What triggers the release of neurotransmitter into the synaptic cleft?

Answer 11

You know its the sweet release of Ca2+ into the pre-synaptic cell. Let me explain. The action potential depolarizes the cell, opening voltage gated Ca2+ channels, which enables a flood of Ca2+ in, which leads to release of neurotransmitter by fusing of synaptic vesicles remarkably quickly.

Question 12

What is a terminal bouton?

How large is the synaptic cleft?

Answer 12

It is what idiots call the presynaptic endings (the end of axons).
Only 10 nms!

Question 13

What is the name of the protein complex which holds vesicles near the membrane walls?

Answer 13

SNARE complex

Question 14

Which protein complexes with Ca2+ and then the SNARE complex?
What does this lead to?

Answer 14

Synaptotagmin

Fuses the vesicles through a mechanism not entirely understood and releases their contents into the synaptic cleft.

Question 15

Which two SNARE proteins are complexed with the plasma membrane?

Answer 15

Syntaxin and SNAP-25

Question 16

Which SNARE protein is complexed with the vesicle membrane?

Answer 16

Synaptobrevin-2

Question 17

Voltage-gated channels:

Ligand-gated channels (chemically regulated channels):

Answer 17

Channels will be depolarizing or hyperpolarizing

Voltage-gated channels: Located primarily on the axon
Ligand-gated channels: Located predominately on the dendrites

Question 18

Graded changes:

• EPSP (Excitatory Post-Synaptic Potential):
• IPSP (Inhibitory Post-Synaptic Potential):

Answer 18

EPSP: Caused by an influx of Na+ (or any other cation)
IPSP: Caused by an influx of Cl- (or any other cation)

Question 19

How are EPSPs/IPSPs transmitted?

Answer 19

Cable properties

Question 20

Tell me the story of synaptic transmission:

Answer 20

An EPSP will build up to high enough levels in the dendrite or axon that the cable properties transmit to the initial axon segment. There the cable properties will start an action potential, which will conduct either by saltatory or normal conduction to the terminal bouton of the axon which will synapse with another cell 10 nm apart (its dendrite). SNARE is already prepped here, holding vessicles near the membrane. Ca2+ influx will result from the from the change in voltage. Ca2+ will complex with Synaptotagmin which will complex with the SNARE proteins (Two in the plasma membrane: Syntaxin, and SNAP-25, and one in the vessicle membrane: synaptobrevin-2) this results in the neurotransmitter entering the synaptic cleft. This will then diffuse to the next cell, and bind to ligand gated channels, causing a EPSP or IPSP which may result in an action potential. The number of impulses will convey strength of the stimuli, as well as the recruitment of neurons which have higher thresholds.

Question 21

Acetylcholine:
When is it always excitatory?
Where can it be excitatory or inhibitory?

Answer 21

ACh is excitatory for some neurons in the CNS and by somatic motor neurons in the neuromuscular junction.
At autonomic nerve endings ACh can be either excitatory or inhibitory.

Question 22

Acetylcholine receptors:
Nicotinic:
Muscarinic:

Answer 22

Nicotinic: are always excitatory and are used in the skeletal muscles. (nicotine is a poison which stimulates nicotinic receptors)
Muscarinic: can (muscurine is a poison which stimulates muscurinic receptors)

Question 23

Nicotinic ACh receptors:

Location:

Answer 23

Location: Autonomic ganglia, Skeletal muscle fibers, certain regions of the brain (addiction to nicotine)

Question 24

Muscarinic ACh receptors

Location:

Answer 24

Location:
Cardiac cells of the heart, smooth muscles, of particular glands and the brain. (It is therefore involved in the digestive system and cardiovascular system)