Micro- Nueroanatomy

Question 1

Functions of neurons

Answer 1

Neurons can be classified by their function at a broad level this includes sensory neurons, motor neurons and internuerons.

Sensory neurons transmit information from sensory receptors in the body to the brain for further processing

Motor neurons do the opposite they transmit information from the brain to muscles and organs instructing them on how to function.

Sensory and motor neurons can be very long sometimes spanning the entire length of the body for example a sensory receptor in you big toe is attached to a single sensory neuron that travels the entire length of the body through the spinal cord to your brain.

Interneurons simply transmit information from one neuron to another these make up the majority of the neurons in the brain.

Question 2

Structure of a typical neuron

Answer 2

Soma or cell body
Where all important processing of the neuron occurs inside the cell body is the nucleus which contains a copy of all you DNA it is the control house of all instructions for how the neurone is structured and needs to function

Dendrites feed into the cell body, they receive information from other neurons the complexity of this is enormous with 100s or 1000s of communicative inputs from other neurons feeding into the dendrites.

Extending from the cell body is the axon with the area connecting the two being called the axon hillock. The axon is responsible for transmitting electrical signals from the cell body through to the terminal buttons.

Terminal buttons is where the information is conveyed to other neurons

Most of the axon is covered by myelin a white fatty substance produced by subtypes of glial cells. It insulated the electrical signal the entire axon is not covered by myelin these interspersed sections are called nodes of Ranvier

With the axon hillock nodes of ranvier are the sections of the axon where action potential occurs the process that propagated an electrical signal allowing information to be transmitted to dendrites of the next cell.

Neurons do not interact through direct contact there is a tiny gap between terminal buttons and dendrites this gap is called synapse which is where chemicals are released from terminal buttons to communicate a new signal to the dendrites of the next neuron

Question 3

Classifying Neurons by structure

Answer 3

Common way to classify via structure is based on how many projections that are extending from the cell body. There are four different types including unipolar neuron, bipolar neuron, multipolar nuerons and psuedo-unipolar neurons

Unipolar: only one projection can be dendrite or axon

Bipolar: most important in visual system has two projections

Multipolar: prototypical neuron most common type in brain.

Pseudo-unipolar: although only having one projection it still comprised of both dendrites and axon typically the long sensory and motor neurons

Question 4

Structure seen through brain

Answer 4

Grey matter comprises of cell bodies and dendrites of cell bodies whilst the white matter are the myelinated axons of neurons. The cell body is where all the information processing occurs the grey matter is located in the outside of the brain in the cerebral cortex. The white matter is cromprised if enormous networks of myelinated axons mainly about transmission of information from different grey matter areas. The corpus callosum is entirely white same with the spinal cord as these are both functions of transmitting information

Question 5

Neuronal communication

Answer 5

The process of Neuronal communication can be broken up into three broad steps.
Step A: within neuron communication dendrites and cell bodies receive input from nearby neurons a form of electrical communication

Step B: within neuron communication process by which information travels from axon hillock along the Axon to the terminal buttons a form of electrical communication

Step C: between neuron communication process by which a signal reaching the terminal buttons causes the release of a chemical signal across the synapse communicating with nearby neurons a form of chemical communication

Question 6

Intra neuronal communication

Answer 6

Involves the communication of electrical information.

Question 7

Diffusion

Answer 7

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

Question 8

Electrostatic pressure

Answer 8

Is a passive attraction of oppositely charged ions and repulsion’s if similar charged ions

Question 9

Inside and outside a brain cell

Answer 9

An important feature of the cell membrane is that it is semipermeable meaning some things can pass through the membrane whilst others can’t. This is made possible through the opening and closing of different ion channels which allow certain ions to pass through easily while preventing others. At rest the intercellular space has an overall negative charge and the extra cellular space has an overall positive this is due to some large negative molecules in the cell that can’t leave. This is called membrane potential testing membrane potential is -70mV

Question 10

Changing membrane potential

Answer 10

If certain ion channels open and allowed for certain positively charged ions to move wherever they wanted they would be attracted to the inside the cell due to its negative charge (diffusion) the membrane potential will become more positive (-68mV or -66mV)
When other types of channels were to open and close the cell can become more negative (-74mV or -79mV)

Question 11

Depolarisation

Answer 11

If the manipulation effect make the cell more positive then the membrane potential has depolarised. This manipulation is considered an excitatory signal or excitatory potential.

Question 12

Depolarisation

Answer 12

If the manipulation effect make the cell more positive then the membrane potential has depolarised. This manipulation is considered an excitatory signal or excitatory potential.

Question 13

Hyperpolarisation

Answer 13

If the manipulation effect causes the cell to become more negative the cell membrane potential had hyperpolarisrd. This manipulation is called an inhibitory signal or inhibitory potential

Question 14

Graded potential

Answer 14

A neuron will receive input from nearby neurons via its dendrites and cell body the inputs cause either an excitatory or inhibitory signal. Excitatory and inhibitory signals received by a neuron are called graded potentials. The signals are graded based on how strong they are. The stronger the signal the more the signal will be conducted through the dendrites and cell body and the more the signal will get through. If there is a stronger excitation potential then neuron will depolarise. In contrast if there is more inhibitory potential the neuron will hyperpolarisr
Graded potentials can cancel each other out the sum of these graded potential get a net effect and this would either be excitatory or inhibitory determining what the neuron should do
All graded potentials converge at the axon hillock where it’s determined whether the electrical signal will continue

Question 15

Action potential

Answer 15

Communication through the axon occurs via an electrical signal called an action potential. An all or nothing process. It is responsible for the electrical communication from the axon hillock, through the axon to the terminal buttons.

Question 16

Graded potentials and the threshold of excitation

Answer 16

For an action potential to occur a neuron needs to reach a certain threshold of excitatory stimulation at the axon hillock to trigger the action potential. This threshold is called the excitation threshold which is between -55 + -65mV. The converging graded potentials need to cause the membrane potential to depolarise and shift from -70mV to -55 or -65mV.

Question 17

The action potential: polarisation

Answer 17

Once the threshold is reached a massive depolarisation of the membrane potential occurs with the membrane potential reaching 0mV and then to a temporary positive charge or 40mV. Eventually the opening and closing of the ion channels will cause the ions to begin returning to their normal state through repolarisation as the membrane potential returns to -70mV. At certain point hyperpolarisation will take place before finally returning to resting state

Question 18

The refractory period

Answer 18

The short period of hyperpolarisation is called the refractory period. During this period the ion channels become unable to open and allow ions to move across the membrane no matter how much excitatory stimulation is given. This is important as it ensure an action potential can only flow in one direction. An action potential will continue to trigger further action potentials as it acts as a depolarising stimulus for other areas of the cell membrane. The refractory period stop the signal from going the opposite direction

Question 19

Action potential at the nodes of ranvier

Answer 19

It starts at the axon hillock and is passively conducted down the axon insulated by myelin and then pops up at the first node of Ranvier and then acts as an excitatory trigger for another action potential at the next node of ranvier and so on until it is propagated along the terminal buttons. This occurs at each node as it acts like a booster for the signal telling it to continue travelling. This is called saltatory communication maintaining the right conditions for the action potential to occur requires energy and input from the cell. Only requiring action potential at the nodes of ranvier is an efficient saver of resources of neurons.

Question 20

The synapse

Answer 20

Presynaptic neuron: neuron before the synapse sending the signal

Postsynaptic neuron the neuron after the synapse receiving the signal

Neurotransmitters: specialised chemicals released into the synapse allow for chemical communication between neurons

Synaptic vesicles: contain neurotransmitters will descend down from the terminal button and fuse with the cell membrane to release neurotransmitters into the synapse

Question 21

Neurotransmitters

Answer 21

Are synthesised by the neuron and once synthesised they are stored in the terminal buttons in small vesicles. When the electrical signal reaches the terminal button the signal will trigger these vesicles to move towards the cell membrane once they merge with the membrane and release the transmitter into the synapse

Question 22

The lock and key principle

Answer 22

Once neurotransmitters are released from their vesicles into the synapse we moved from electrical communication to chemical communication. The neurotransmitters released from one neuron must travel across the synapse and bind to the receptors in the second neuron. Not any neurotransmitters can bind with any receptor, specific neurotransmitters will bind to specific receptor sites based on shape. Known as the lock and key principle as the process is like finding a key to fit into the lock of the neurotransmitter (key) does not fit and bind with the receptor site (lock)

Neurotransmitters do not go directly across the synapse. They float through the space and if it reaches the post synaptic neuron and if it reaches a receptor it can bind to and if the receptor does not already have a neurotransmitter bound to it will only then the neurotransmitter bind and activate the receptor. Making it much slower than electrical communication

Question 23

EPSPs and IPSPs

Answer 23

Excitatory postsynaptic potentials (EPSPs) and Inhibitory postsynaptic potentials (IPSPs). When a neurotransmitter binds with a receptor one of these will occur by opening up ion chambers in the membrane that will change the membrane potential. Neurotransmitters can also bind to presynaptic neurons and provide feedback to tell the presynaptic neuron to stop releasing neurotransmitters

Question 24

Clearing the synapse

Answer 24

All excess neurotransmitters need to be removed from the synapse so the process can keep working. They can be removed by reuptake sites in the presynaptic neuron. Another way is by having enzymes located in the synapse that break down neurotransmitters for them to be recycled and some simply float off

Question 25

Importance of excitatory and inhibitory signals

Answer 25

It is important to have inhibitory and excitatory signals in the brain. Excitatory obviously fire the signal that allows transmission of information to continue to the next neuron. However you need to be able to stop neurons firing sometimes. Without inhibitory signals our brain would be uncontrollable excitation of nuerons all firing all of the time which is what a brain seizure is

Question 26

Different neurotransmitters

Answer 26

Neurotransmitters all work in slightly different ways to cause EPSPs and IPSPs. They form the basis of larger networks in our brain which are directly related to cognitions, emotions and behaviours. Neurotransmitters can be targeted by psychoactive drugs to treat mental disorders similarly to how addictive drugs affect neurotransmitters.
Six of the most common include glutamate, GABA, dopamine, serotonin, acetylcholine and endorphins.

Question 27

Glutamate

Answer 27

The most prevalent excitatory neurotransmitter in the nervous system and has been implicated in the pathophysiology of epilepsy and seizures. Also known to be important for memory and learning especially through a process called long term potentiation where synaptic connections between neurons that fire frequently together become stronger, making it important in reinforcing the strength of neuronal pathways in the brain

Question 28

GABA

Answer 28

Gamma amino butyric acid or GABA is the most prevalent inhibitory neurotransmitters. Alcohol directly influences of GABA neurons and networks by binding and activating the GABA receptor sites drinking alcohol can inhibit the frontal lobes that are meant to be controlling ur behaviour. Anaesthesia inhibits the nervous system to the point of basically shutting down and anxiety meds such as Valium and Xanax reduce brain activity in regions involved in making us anxious

Question 29

Dopamine

Answer 29

Famous for being the neurotransmitter that is activated in the reward pathways in our brain. Every drug of abuse releases extra dopamine. Dopamine is also involved in other things such as emotion, motivation, arousal and movement.

High levels of dopamine activity has been linked to schizophrenia and a similar presentation of people who use too much meth and coke. In contrast those with Parkinson’s have low dopamine and is the reason for motor tremor.

Question 30

Serotonin

Answer 30

Involved in sleep regulation, mood and arousal. Lowered serotonin is linked to depression. Some antidepressant called selective serotonin reuptake inhibitors block serotonin reuptake sites. Thus increasing the amount of serotonin available. Serotonin is highly implicated in emotions and empathy increased serotonin can inhibit aggression and antisocial behaviours. MDMA increases activity of serotonin and makes u feel more empathetic

Question 31

Acetylcholine

Answer 31

Is involved with learning memory as well as movement and muscle coordination. Has been linked to the pathophysiology of alzheimers disease and treatment aims to target acetylcholine activity

Question 32

Acetylcholine

Answer 32

Is involved with learning memory as well as movement and muscle coordination. Has been linked to the pathophysiology of alzheimers disease and treatment aims to target acetylcholine activity

Question 33

Endorphins

Answer 33

Play a role in reducing pain and increasing mood. Morphin and heroine increase activity of endorphins. The mimick endorphin molecules