Week 2 - topic 3

Question 1

Postsynaptic potential

Answer 1

alterations in the membrane potential (charge) of a postsynaptic neuron, produced by liberation of neurotransmitter at the synapse

Question 2

How do neurotransmitters cause PSP’s

Answer 2

• Neurotransmitters attach themselves to a binding site
• Lock and Key
• A chemical that attaches to a binding site (the correct key) is called a ligand
• Neurotransmitters don’t enter the cell, they bind to sites on receptor proteins

Question 3

Synaptic vesicle

Answer 3

• When an action potential goes down an axon to the terminal buttons, a small number of synaptic vesicles located just inside the presynaptic membrane fuse with the membrane and break open, spilling their contents into the synapse

Question 4

Postsynaptic receptor

Answer 4

a special protein molecule in the postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter

Question 5

Binding site

Answer 5

the location on the postsynaptic receptor that the neurotransmitter (or another ligand, like a drug) binds to

Question 6

Two types of neurotransmitter dependent ion channels

Answer 6

Ionotropic = direct
Metabotropic = indirect

Question 7

Ionotropic receptor

Answer 7

• a receptor that contains abinding site for a neurotransmitter and an ion channel that opens when a molecule of the neurotransmitter attaches to the binding site
• direct
• changes are faster to begin and shorter.

Question 8

Metabotropic receptor

Answer 8

• A receptor that contains a binding site for a neurotransmitter; activates an enzyme that begins a series of events that opens an ion channel elsewhere in the membrane of the cell when a molecule of the neurotransmitter attaches to the binding site
• indirect
• changes are slower to begin and last longer

Question 9

Postsynaptic potentials (PSP’s)

Answer 9

• Alterations in the membrane potential of a postsynaptic neuron, produced by the liberation of neurotransmitter at the synapse.
• The neurotransmitter does not determine whether the PSP is hyperpolarizng or depolarising
• The nature of the PSP is determined by the characteristics of the postsynaptic receptors - i.e. the type of neurotransmitter dependent ion channels that are opened
• > Hyperpolarization (inhibition/more negative)
• > Depolarization (excitation/more positive)

Question 10

Types of neurotransmitter dependent ion channels

Answer 10

Sodium (Na+)
Potassium (K+)
Chloride (Cl-)
Calcium (Ca2+)

Question 11

Sodium neurotransmitter dependent ion channel opens

Answer 11

Excitatory Postsynaptic Potential (EPSP)

• when the sodium binds to the sodium neurotransmitter dependent ion channel the channel opens allowing sodium to rush in and create a positive charge in the cell
• cell becomes depolarised

Question 12

Potassium neurotransmitter dependent ion channel opens

Answer 12

Inhibitory Postsynaptic Potential (IPSP)

• potassium leaves cell through the channel resulting in the cell becoming negatively charged
• cell becomes hyperpolarised

Question 13

Chloride neurotransmitter dependent ion channel opens

Answer 13

• > effect depends on the membrane potential
• if the neuron is at rest when the channel opens nothing happens, diffusion and electrostatic pressure keeps cell balanced
• if membrane has been depolarised the cell becomes neutralised as chloride ions rush into the cell and make cell more negatively charged again

Question 14

Calcium neurotransmitter dependent ion channels opens

Answer 14

EPSPs + more!

• similar to sodium ion channels
• calcium ions positively charged and mostly in extracellular fluid
• depolarised when the channel opens up, diffusion and electrostatic pressure allows positive ions to run into cell
• calcium binds with dendrites to activate enzymes to change cells biochemistry and structure

Question 15

Reuptake

Answer 15

• Reuptake occurs when a neurotransmitter that has been released into the synaptic cleft is rapidly removed by the terminal button.
• The process occurs via special transporter molecules on the presynaptic membrane that work a bit like a vacuum, sucking the neurotransmitter back up directly into the cytoplasm of the presynaptic cell

Question 16

Termination of postsynaptic potentials

Answer 16

• Once a neurotransmitter enters the synapse, receptor binding causes hyperpolarizations and depolarizations of the postsynaptic cell.
• But what happens to the neurotransmitter once it is released? It has to be cleaned up somehow - otherwise PSPs would go on forever!

There are two mechanisms which end PSPs:

• Reuptake
• Enzymatic Deactivation

Question 17

Enzymatic deactivation

Answer 17

• An enzyme is a molecule that controls a chemical reaction, combining two substances or breaking a substance into two parts. Enzymatic deactivation is the destruction of a neurotransmitter by an enzyme after it has been released.
• For example, one type of neurotransmitter found in the nervous system is called acetylcholine (ACh). After it is released into the synaptic cleft, the enzyme acetylcholinesterase (AChE) deactivates ACh by breaking it into choline and acetate

Question 18

Neural integration

Answer 18

• Following the opening of neurotransmitter dependent ion channels, at any given moment, a neuron might receive a number of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs).
• Neural Integration is the process by which the inhibitory and excitatory potentials summate and control the firing rate of a neuron (i.e. how often an action potential is triggered).

Question 19

Autoreceptors

Answer 19

Receptor molecules located on a neuron that respond to the neurotransmitter released by that neuron

• don’t open ion channels or produce changes in the cell’s membrane
• involved in the synthesis and release of transmitter molecules
• when auto receptor binds, inhibitory effect, decrease the rate of synthesis and release of neurotransmitter from the cell
• can also help increase rates of neurotransmitter production and release

Question 20

Axoaxonic synapses

Answer 20

• Synapses found on the axon
• Axoaxonic synapses influence the overall amount of neurotransmitter being released into the axodendritic synapse
• > Presynaptic inhibition decreases neurotransmitter released
• > Presynaptic facilitation increases neurotransmitter released

Question 21

Non-synaptic communication

Answer 21

• Neurotransmitters only travel a very short distance in the brain - synapses are tiny!
• So what are the other types of communication in the nervous system?
  1. Neuromodulators
  2. Hormone

Question 22

Neuromodulators

Answer 22

• Neuromodulators: a naturally secreted substance that acts like a neurotransmitter, except that it is not restricted to the synaptic cleft. Instead, neuromodulators can diffuse through the extracellular fluid. Most neuromodulators are peptides, which are chains of amino acids (building blocks of proteins).
• Neuromodulators are secreted in large amounts and diffuse across longer distances to modulate the activity of neurons in a particular part of the brain. They are involved in general behavioural states such as vigilance, fearfulness and sensitivity to pain

Question 23

Hormones

Answer 23

• Hormones: a chemical substance released by endocrine glands (e.g. the pancreas, thyroid gland) or other cells located in organs such as the stomach, brain and kidneys. Cells that release hormones release them into extracellular fluid.
• As you may already know, hormones are distributed through the bloodstream to impact the activity of various cells (including neurons). These cells contain special receptors either on the membrane or deep in the nucleus. Cells that have special receptors for particular hormones are called target cells for that hormone.
• Many neurons have hormone receptors, and hormones then influence behaviour and functioning by stimulating the neurons and changing their activity