Lecture - Physiol 1 Nerves and Neurons

Question 1

What can you say about neutron size and shape?

Answer 1

They vary with function

Question 2

Parts of a neuron - describe what they look like etc

Dendrite
Nucleus 
Cell body (soma)
Axon
Node of Ranvier
Myelin
Nerve terminals (synaptic boutons)

Answer 2

Dendrite: Usually input-end but that’s conventional view - as discussed before, it can release neurotransmitters

Nucleus is within the cell body

Axons goes away from the cell body

Node of Ranvier: Have these through the length of it and AP jumps from node-to-node

Myelin: And wrapped by different glial cells and create myelin

Synaptic boutons: Branches and have synaptic endings (boutons - release neurotransmitter) and either side of each of these would be a muscle fibre

Question 3

Peripheral nerve - describe what these look like etc

• Spinal cord
• Cell body of sensory and motor neuron
• Dorsal and ventral root
• Nerve

Answer 3

Look at the diagram

Sensory axon goes through the dorsal root and motor axon goes through ventral

Inside the spinal cord, have interneurons and all

Sensory axon: Touch, temp, pain and once gets past threshold then sends AP though and straight past body and relrease nurotransmitter into spinal cord. Doesnt have to be myelinated or can be

Neuron doesnt necessarily have to have dendrite like this one doesnt seem to

Question 4

Peripheral nerve - what does a cross section look like?

Answer 4

Go look at slide 6 lol

Question 5

What’s the functional classification of axons in nerves and how are they classified?

Answer 5

Without opening up a body, you can classify the axons. There are two nomenclatures:

1. ABC system
2. I-IV system

“A’ or I:
Myelinated, largest, fastest (have alpha, beta, gamma and I think that’s theta)

“B” or II-III
Slower, mostly autonomics (parasym and sym fibres)

“C” or IV
Slowest

So you put electricity through these wires and one side of the nerve becomes positive so sodium channels open and then you get AP and then all these axons in nerve that have been activaed will conduct down and you’ll record. On the graph, you’ll get various peaks and the first peak is A, second B and third C. Under A peak, have multiple smaller peaks (alpha, beta, gamma and something - all in the A peak)

Question 6

SO neutrons and muscles use electrochemical gradients for receiving and generating signals. But how is the RMP set up?

Answer 6

Measure voltage different between inside and outside. Originally no voltage difference but then stab into it and you get a voltage difference across membrane

As I understand this, you have high K+ conc inside cell so it leaves the cell and creates a negative charge inside the cell. This negative charge pulls some K+ back in since they are positive. There is a balance between the leaving and the pulling. But RMP isn’t at the equilibirum of K+ because some Na+ leaks in (or some other small imbalances) every now and then which makes it more positive

Question 7

How do gates membrane ion channels work?

Answer 7

“Gated” ion channels􀀁
=
Controlled changes in selective permeability to ions
=
Changes in membrane potential􀀁
=
Signaling in nervous system􀀁

Question 8

What’re the three types of gates channels?

Answer 8

1. Voltage gated:
   -Especially important in action potential. Other v.g. channels for K, Ca. 􀀁
   N.B. some voltage gated K channels are also sensitive to intracellular ions, e.g. Ca, Na􀀁
   -Membrane voltage change here leads to change in protein shape (as a response) and ion channel opens and you get ions flowing through
   -Na channel: Even though voltage holding it open, it can only transietnly conduct (open very very short time) bc too long open = too much sodium gets in (since too high of a driving force fr sodium to come in) so AP have such a short duration and thus have a refractory period
2. Mechanically gated ion channels:
   - Physical stimuli leads to membrane deformation and then pore opens
   - Eg touch or auditory receptors
3. Chemically (ligand) gated
   - eg synapses, olfaction, taste, pain.
   - have two types: direct (nicotinic) and indirect (muscarinic)

Directly gated: very fast operating, ligand binds to part of ion channel and then it opens in response to chemical signal

Indirect gated: Eg in parasympathetic endins in ANS

Or call it metabotropic (operates by remote control aka activate something and then the ion channel)

So the ion channel responds to comthing like G protein