6.5 Neurology

From MaritNy from Quizlet

What are the three basic components of all neurones?

1. Dendrites

2. Axon

3. Soma

What is the advantage and disadvantage of having a myelin sheath?

1. Faster electrical conduction

2. More space and energy required

What is the soma?

Cell body of a neuron, contains the *nucleus, organelles and essential metabolism*

Where does the axon propogate signals to and from?

Conducts impulses AWAY from the cell body (soma) to other neurones or effectors

What are dendrites?

Protoplasmic extensions that receive signals from other neurons, conducts impulses TOWARD the soma - NOT axon terminal (other )

What is the typical mammalian resting potential (charge difference when not excited) and which side of the cell is more negative?

70 milliVolts (inside is *more negative* than outside of cell)

Outline how the Sodium-Potassium pump, alongside two other components, maintain resting potential (3)

1. Three Na+ are actively expelled and two K+ are taken in, using ATP (making inside more negative)

2. Some K+ passively flows down Potassium leak channel, leaving the cell

3. Fixed anions within the cell help maintain more negative charge inside cell, too

What are the three names given to the stages of an action potential (firing/excitation)?

Depolarisation
Repolarisation
Refractory Period

Outline depolarisation

Sudden change from a relatively negative to positive membrane potential/inside of cell:

1. Mechnical Na+ channels are opened within axon membrane due to stimulus --> if enough Na+ then a ton more voltage Na+ channels open (threshold voltage)

2. Na+ passively diffuses back down its concentration gradient, into the cell

3. Membrane potential becomes more positive to +30mV

Outline repolarisation

Restoring a negative membrane potential (relative inner cell charge):

1. K+ channels open due to the large Na+ influx

2. K+ flows down its concentration gradient, out of the cell restoring negative membrane potential to about 80mV

What is the refractory period?

Absolute: depolarization + repolarization (Na+ channel must return to resting state)

RELATIVE: After repolarisation, we have a -80mV membrane potential and the K+ is outside and Na+ is now inside. Although another action potential CAN occur, even more Na+ needed to reach threshold voltage!)

The period where the *Sodium Potassium pump* reverses this and restores the potential to 70mV is called the refractory period [sometimes called hyperpolarisation]

Why is action potential propogation through a neuron regarded as a wave of depolarisation?

1. Ion channels in axon are voltage-gated (e.g. Na+)

2. Depolarisation of one axon segment triggers next segment's ion channels to open due to generation of local currents

i.e. If ion channels open in one section of the axon, this is enough to trigger the activation of ion channels in the next section

What is the treshold potential?

*55mV* is needed for LOADS OF voltage-gated ion channels to open and an action potential to *initiate* (all-or-nothing principle) - if Na+ channels are exposed to this, they will ALL open causing a massive influx during depolarisation

Outline the different parts of the oscilloscope trace of an action potential (ms agianst mV)

1. Resting potential (70mV)

2. Rising limb represents depolarisation: split into two parts as influx of Na+ increases rapidly past treshold voltage

3. Falling limb represents repolarisation to 80mV caused by K+ efflux

4. Refractory period is restoration back to baseline 70mV by Sodium-Potassium pump

What cells produces myelin (proteins and phospholipids)?

Oligodendrocytes (CNS) and Schwann cells (PNS)

What is saltatory conduction?

In *myelinated* neurones, action potential *jumps* between gaps in the myelin sheath called *nodes of Ranvier*

Using knowledge of saltatory conduction, explain why unmyelinated neurones are so slow

Action potentials must propogate sequentially along *ALL* sections of an axon instead of being conducted between nodes of Ranvier by myelin

What is the difference between white and grey matter?

White matter --\> Myelinated axons
Grey matter --\> Soma (cell bodies) and dendrites (as well as Schwann/support cells)

Outline how neurotransmitters are used for transferring the signal across synapses

1. Action potential causes opening of voltage-gated CALCIUM channels

2. Ca2+ ions diffuse into the cell and cause neurotransmitter vesicles to fuse together in cytoplasm

3. Exocytosis of neurotransmitters across synaptic cleft

4. Diffuse across synapse and bind to receptors on post-synaptic membrane

5. Open ligand-gatedsodium ion channels

6. Ion channels re-generate electrical impulse

What happens to neurotransmitter molecules after synaptic transmission?

Either recycled (reuptake pumps) or degraded (by enzymes)

Can neurotransmitters be both excitatory and inhibitory?

Yes - They can prevent a response! Inhibitory can open potassium or chlorine channels (the net graded potential with summation + interference has to be over threshold voltage for action potential to propagate)

What's the difference between the central and peripheral nervous system?

The central nervous system includes the brain and spinal cord, while the peripheral nervous system includes all of the nerves that branch out from the brain and spinal cord and extend to other parts of the body including muscles and organs

What's the difference between the somatic and autonomic nervous system?

The autonomic (non-voluntary) nervous system controls internal organs and glands, while the somatic nervous system controls muscles and movement. (voltunary)

What makes up the autonomic nervous system?

Sympathetic and parasympathetic

How is acetylcholine made?

Choline + Acetyl CoA (from mitochondria) \= acetylcholine (to be stored in vesicles until exocytosis)

Acetylcholine must be continually removed from the synapse (overstimulation causes paralysis) - how is this achieved?

*Acetylcholinesterase* (AChE) enzyme is released into synapse from either post or pre-synaptic cell

Broken down to Choline + Acetyl, and choline is recycled back to the presynaptic neurone

What do neonicitinoid pesticides do?

1. Bind to (more sensitive) acetylcholine receptors in insects

2. Neonictinoids cannot be broken down by acetylcholinesterase, so they lethally over-stimulate the neurone

Why have the EU restricted the use of neonictinoid pesticides?

1. Less bees and pollinators

2. Less birds (due to less pollinators)

In a post-synaptic neurone, outline how it is determined whether or not the neurone will fire?

1. Excitatory neurotransmitters (e.g. noradrenaline) cause depolarisation by opening ligand-gated sodium or calcium channels

2. Inhibitory neurotransmitters (e.g. GABA) cause hyperpolarisation by opening ligand-gated potassium or chlorine channels

3. The combined action of all neurotransmitters: neurone fires if there's more depolarisation than hyperpolarisation and a threshold potential is reached (55mV) - i.e. If threshold potential is reached via graded potentials, axon's voltage-gated ion channels open --> NEURON FIRE

EPSPs and IPSPs may summate/cancel each other out