Week 4: Micro-neuroanatomy - neurons, neurotransmitters and action potentials

Question 1

Sensory neurons

Answer 1

those which transmit information from sensory receptors in the body to the brain for further processing.

Question 2

Motor neurons

Answer 2

involved with transmitting information from the brain to muscles and organs in the body, with instructions for them on how to function.

Question 3

Interneurons

Answer 3

those which simply transmit information from one neuron to another neuron.

Question 4

Neuron Structure (Draw up diagram)

Answer 4

Soma or Cell body: important processing of the neuron occurs.

Nucleus: Contains a copy of all your DNA

Dendrites: receive information from other neurons.

Axon: responsible for transmitting electrical signals from the cell body through to the “terminal buttons”

Terminal Buttons: where information is conveyed to other neurons.

Myelin Sheath: a white fatty substance produced by subtypes of glial cells to insulate the electrical signal that is transmitted through the axon.

Nodes of Ranvier: parts of the axon that are unmyelinated, where an important process called the “action potential” occurs.

Synapse/ Synaptic Cleft – tiny space between terminal button and dendrites

Question 5

Types of Neurons

Answer 5

Unipolar Neuron

Bipolar Neuron ( important role in the visual system )

Multipolar Neuron ( most common type of neuron in the brain )

Pseudo-Unipolar Neuron ( observed as the long sensory and motor neurons which traverse the entire length of your body. )

Question 6

Grey and White Matter

Answer 6

Grey matter comprises of cell bodies and dendrites of neurons, whilst the white matter are the myelinated axons of neurons.

Question 7

Intra-neuronal communication

Answer 7

the type of communication that occurs within neurons, called ‘intra-neuronal communication”, involves the communication of electrical information.

Question 8

Ion

Answer 8

An ion is a molecule or chemical that has a charge. That charge can be positive or negative. A positively charged ion is called a “cation”, whilst a negatively charged ion is called an “anion”.

Question 9

Diffusion

Answer 9

is the passive movement of a substance from an area of high concentration to low concentration.

Question 10

Electrostatic pressure

Answer 10

the passive attraction of oppositely charged ions, and repulsion of similarly charged ions.

Question 11

Semi-Permeable

Answer 11

meaning that some things can pass through the cell membrane, whilst others cannot.

This “semi-permeability” of the cell membrane is made possible by the opening and closing of different ion channels located in the membrane which can allow certain ions to pass through easily, while preventing the passage of other ions.

Question 12

Resting state of Neuron

Answer 12

At rest, that is, when the neuron is not being stimulated, the intracellular space has an overall negative charge and the extracellular space has an overall positive charge.

Question 13

Membrane Potential

Answer 13

overall negative charge inside the neuron relative to the outside of the neuron.

The membrane potential when a neuronal cell is at rest, known as the “resting membrane potential”, has a value of approximately -70 millivolts (mV).

Question 14

Depolarisation and Hyperpolarisation.

Answer 14

If the effect of a manipulation causes the inside of the cell to become more positive and less negative, it is said to have caused the membrane potential to “depolarise”. A manipulation causing the membrane potential to depolarise is considered an “excitatory signal” or “excitatory potential”.

If the effect of a manipulation causes the inside of the cell to become more negative and less positive, it is said to have caused the membrane potential to “hyperpolarise”. A manipulation causing the membrane potential to hyperpolarise is called an “inhibitory signal” or “inhibitory potential”.

Question 15

graded potentials

Answer 15

Excitatory postsynaptic potentials (EPSPs) and Inhibitory postsynaptic potentials (IPSPs) which are received by a neuron (via the dendrites and cell body).

Question 16

The Action Potential

Answer 16

Communication through the axon that occurs via an electrical signal, and is the ‘firing’ or the ‘not firing’ of a neuron.

Instead of a graded response, an action potential is an “all-or-nothing” process. It either happens or it doesn’t happen.

Question 17

Threshold of excitation

Answer 17

A threshold of excitatory stimulation at the axon hillock that will trigger the action potential to occur, and thus fire the neuron.

This threshold is met when the excitatory effect reaches approximately between -55 to -65mV through depolarisation.

Question 18

The refractory period

Answer 18

When there is a short period of temporary hyperpolarization

Question 19

Action potentials at the nodes of Ranvier

Answer 19

The reason for the action potentials occurring at the nodes of Ranvier is that each node can act like a booster for the signal telling it to continue travelling along the axon. This form of communication is called “saltatory communication”. You get the excitatory signal being boosted at each node of Ranvier, with passive conduction of the signal between each of the nodes underneath the myelin.

Question 20

The synapse

Answer 20

-synapse / synaptic cleft: space between neurons where chemical communication occurs

-pre-synaptic neuron: the neuron located before the synapse; is the neurons sending the signal

-post-synaptic neuron: the neuron located after the synapse; is the neuron receiving the signal

-neurotransmitters (NTs): specialised chemicals released into the synapse; allow for chemical communication between neurons to occur

-synaptic vesicles: contain neurotransmitters; will descend down the terminal button and fuse with the cell membrane to release neurotransmitters into the synapse

Question 21

The lock-and-key principle

Answer 21

Specific neurotransmitters will bind to specific receptor sites based on their shape. That is, the molecular structure of one type of neurotransmitter, such as Dopamine, will only be able to bind to a receptor that can receive the specific structure of a dopamine molecule, such as a Dopamine receptor.

(Not in a goal-directed manner)

Question 22

Clearing the synapse

Answer 22

One way that excess neurotransmitter is removed is by re-uptake sites in the presynaptic neuron.

Another way is by having enzymes located in the synapse that break down neurotransmitters for them to be recycled.

Finally, some excess neurotransmitters will simply float out of the synapse and off into the ether.

Question 23

Neurotransmitters

Answer 23

the chemicals which are released into the synapse by the pre-synaptic neuron

Glutamate: Excitatory neurotransmitter that has a role in memory and learning
GABA: Inhibitory neurotransmitter
Dopamine: Activates reward pathways in our brain
Serotonin: involved in the regulation of sleep, mood, and arousal.
Acetylcholine (ACh): involved with learning memory, as well as movement and muscle coordination.
Endorphins: play a role in reducing pain and increasing mood.