Week 3 - Neuroanatomy 2

Question 1

What are schwann cells?

Answer 1

similar to function of oligodendrocytes but in Peripheral Nervous System, can guide axonal regeneration

Schwann cell wraps around the axon with the myelin.

Question 2

What are oligodendrocytes?

Answer 2

A glial cell that helps to myelinate the neurons in the CNS.

Question 3

What are astrocytes?

Answer 3

The largest glial cell that is shaped like a star. It provides structural integrity, helps in creating the blood brain barrier (seal off capillaries) and helps to detect pH shifts to release ATP for enhancement of breathing.

Question 4

What is a microglia?

Answer 4

A glial cell in the CNS responsible for responding to injury or disease.
Anti-inflammatory response. e.g. after stroke
It rapidly activates to stop pathogens and works to eliminate excess neurotransmitters.

Question 5

Describe the relationship between glial cells, myelin sheath and action potential.

Answer 5

Oligodendrocytes form myelin on axons to facilitate high-speed transmission via saltatory conduction on the nodes of Ranvier (gaps between the myelin sheath generating action potential).

Perinodal astrocytes are in contact with the axon at nodal regions. between the myelin sheath.

Question 6

Afferent neuron what is it? and what types of neurons are usually afferent?

Answer 6

Moving away from a central organ or point.
Messages from receptors to the brain or spinal cord.
Unipolar neurons. (Sensory neurone)

Question 7

Efferent neuron what is it? and what types of neurons are usually efferent?

Answer 7

Moving toward a central organ or point.
Messages from the brain or spinal cord to the muscles/organs.
Usually multipolar neurons. (motor neurone)

Question 8

What are interneurons?

Answer 8

Relays message from sensory neurone to motor neurone in the spinal cord
Make up the brain and spinal cord

Question 9

What are the roles of ribosomes in the neurons?

Answer 9

Ribosomes are involved in the production of proteins. Specifically, ribosomes are the site of protein production, whereby messenger RNA (mRNA) is used to code the sequence of sub-units that make up the protein

The ribosomes and endoplasmic reticulum are utilised to generate proteins - in the case of neurons, the neurotransmitters.

Question 10

What is the role of mitochondria in the neuron?

Answer 10

Mitochondria synthesises ATP, a molecule responsible for energy/fuel in the cell. it has its own DNA and is capable of mitophagy which is a process of discarding waste mitochondria and replacing it with new ones through autophagy.

Question 11

What is the role of Golgi complex in the neuron?

Answer 11

A system of membranes that packages proteins (=neurotransmitters) into vesicles for use.

Question 12

What are microtubules in the neuron?

Answer 12

Microtubules are abundant in neurons, occupying axons and dendrites as paraxially aligned arrays. These microtubule arrays provide a structural backbone for axons and dendrites that allows them to acquire and maintain their specialized morphologies

It helps to transport the packaged neurotransmitters down the axon for release.

Question 13

What is the function of terminal buttons?

Answer 13

The terminal buttons are located at the end of the neuron and are responsible for sending the signal on to other neurons.

The terminal buttons also collect the NT in the vesicles, while they await release.

Question 14

What is the process of neuronal degeneration in Alzheimer’s dementia? what are the neuropathological changes associated with this disease?

Answer 14

Cerebral atrophy in Alzheimer’s disease:
Neuronal death
external surface of the brain with widened sulci and narrowed gyri, mostly over the frontal and parietal regions.

Diagnosis associated with
Poor new learning
Changed personality
Language deficits

Question 15

What are amyloid plaques? and which chromosomal structure may be related to the cause of these plaques?

Answer 15

“Cellular trash” mostly found in areas where there are many synapses. The synapses then degenerate.
Plaques contain an amino acid peptide protein core: beta-amyloid (ß-amyloid)
Mostly in frontal and temporal regions and around hippocampus

ß-amyloid is coded on chromosome 21, same as Down’s syndrome; people with Down’s often show dementia-like symptoms after 30 years – so chromosome 21 may be responsible

Question 16

What are neurofibrillary tangles? and which layers of the neocortex can these tangles be observed?

Answer 16

Look like twisted ropes within swollen cell body.
Consist of “tau” proteins that accumulate, creating tangles through brain (incl. layers III and V of cortex)

Layer 3: Loosely packed stellate cells; intermediate-sized pyramidal cells.
Layer 5: very large pyramidal cells; a few loosely packed stellate cells.

Question 17

How does membrane potentials work in the neuron? what are the important ions and what are the two methods of intracellular exchange of ions?

Answer 17

Membrane potentials work through voltage-gated ion channels which are made of proteins. The four important ions Na+, K+, Cl- and other Protein- are dispersed in and out of the cell. These ions are either transported or diffused.

Question 18

How does saltatory conduction work?

Answer 18

Saltatory conduction is the conduction of action potentials in myelinated axons.

Passive conduction (instant and decremental) along each myelin segment to next node of Ranvier
New action potential generated at each node
Instant conduction along myelin segments results in faster conduction than in unmyelinated axons

Question 19

What are the three parts of the synapse?

Answer 19

1. Presynaptic terminal (terminal buttons)
   With vesicles containing neurotransmitters
   And receptors for re-uptake
2. Junction / gap (synaptic cleft)
   Where the neurotransmitters ‘float’ briefly after release
3. Post-synaptic terminal (dendrites)
   with receptors for the neurotransmitters

Question 20

What is presynaptic facilitation and inhibition? and what are axoaxonic synapse?

Answer 20

Presynaptic inhibition is a phenomenon in which an inhibitory neuron provides synaptic input to the axon of another neuron (axo-axonal synapse) to make it less likely to fire an action potential. Presynaptic inhibition occurs when an inhibitory neurotransmitter, like GABA, acts on GABA receptors on the axon terminal.

Question 21

What are the four different small molecule NT and the large molecule NT?

Answer 21

Glutamate
GABA
Acetyl Choline
Norepinephrine

Large: Substance P

Question 22

How are small molecules in the neurons packaged, synthesised and stored?

Answer 22

Synthesized in cytoplasm of the terminal button,
packaged in vesicles by the Golgi complex
Vesicles stored in clusters next to pre-synaptic membrane, waiting for the trigger to be released.

Question 23

How are large molecules in the neurons packaged, synthesised and stored?

Answer 23

all neuropeptides
Assembled in the cell body by ribosomes;
packaged by Golgi complex
transported to the axon terminal via microtubules

Question 24

What are the three main amino acid NTs? and where is it usually observed?

Answer 24

Usually found at fast-acting directed synapses in the CNS
1. Glutamate – Most prevalent excitatory neurotransmitter in the CNS

2. GABA (γ – aminobutyric acid)
   Synthesized from glutamate
   Most prevalent inhibitory neurotransmitter in the CNS
3. Aspartate and glycine

Question 25

What are the two main monoamine NTs? and where is it usually observed?

Answer 25

Effects tend to be diffuse – non-directed
1. Catecholamines – synthesized from tyrosine
Dopamine
Norepinephrine
Epinephrine
2. Indolamines – synthesized from tryptophan
Serotonin
Melatonin

Question 26

What is the synthesis pathways of dopamine and adrenaline?

Answer 26

Tyrosine -> L-Dopa -> Dopamine -> Norepinephrine (noradrenaline) -> Epinephrine (Adrenaline). (-> = enzyme).

Question 27

What is an example of a large molecule?

Answer 27

Neuropeptides:

Endorphins:
“Endogenous opioids”
Produce analgesia (pain suppression)
Receptors were identified before the natural ligand was

Question 28

What are the two types of receptors on post-synaptic membrane?

Answer 28

Ionotropic receptors – associated with ligand-activated ion channels

Metabotropic receptors – associated with signal proteins and G proteins

Question 29

What is an ionotropic receptor?

Answer 29

neurotransmitter binds and an associated ion channel opens or closes, causing a Post-Synaptic Potential (PSP)
If Na+ channels are opened an Excitatory PSP occurs (EPSP)
If K+ channels are opened an Inhibitory PSP occurs (IPSP)

Question 30

What is an metabotropic receptors?

Answer 30

Effects are slower, longer-lasting, more diffuse, and more varied
1. neurotransmitter 1st messenger binds.
2. G protein subunit breaks away.
3. Ion channel opened/closed OR a 2nd messenger is synthesized.
4. 2nd messengers may have a wide variety of effects

Question 31

What are the seven steps in NT action?

Answer 31

1. NTs are synthesised from precursors under the influence of enzymes (Tryptophan, Tyrosine etc.)
2. NT’s are stored in vesicles
3. NTs that leak from their vesicles are destroyed by enzymes
4. Action potentials cause vesicles to fuse with the presynaptic membrane and release their NT into the synapse.
5. released NTs bind with autoreceptors and inhibit subsequent NT release.
6. binds to postsynaptic receptors
7. Nts are deactivated by either reuptake, diffusion or enzymatic degradation.

Question 32

What is an agonist and give three examples of pharmacological agonists?

Answer 32

increase or facilitate activity

Cocaine – catecholamine agonist
Blocks reuptake – preventing the activity of the neurotransmitter from being “turned off” – increases alertness but also heart rate, blood pressure

Benzodiazepines – GABA agonists
Binds to the GABA molecule and increases thebinding of GABA – drowsiness, slurred speech, confusion

Physostigmine – Ach agonist:
inhibits Acetylcholinestrase (Ache), which breaks down Ach, so enhances neuromuscular transmission

Question 33

What is an antagonist and give two examples of pharmacological antagonists?

Answer 33

decrease or inhibit activity.

Atropine – ACh antagonist
Binds and blocks muscarinic receptors
Many of these metabotropic receptors are in the brain
High doses disrupt memory

Curare – ACh antagonist
Bind and blocks nicotinic receptors, the ionotropic receptors at the neuromuscular junction
Causes paralysis
Treated with physostigmine