Lecture 10: Nervous System 2

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Questions and Answers

How is information coded in neurones?

In the form of action potentials (correct)

Through neurotransmitters release

Via direct cell-to-cell connections

By the number of dendrites

What is the main function of dendrites in a neurone?

Regulating body temperature

Receiving information (correct)

Producing energy

Transmitting information

Which fluid compartment occupies 66% of total body water?

Extracellular fluid

Intracellular fluid (correct)

Blood plasma

Interstitial fluid

What is the main function of the cell membrane?

Maintaining cell integrity Signup and view all the answers

How do substances with low lipid solubility cross cell membranes?

Through transmembrane transport proteins Signup and view all the answers

Where does the separation between intracellular and extracellular fluids occur?

By the cell membrane Signup and view all the answers

What is the major excitatory neurotransmitter that opens Na+ channels in the post-synaptic membrane?

Glutamate Signup and view all the answers

Which neurotransmitter can be both excitatory and inhibitory in the brain but is mainly excitatory in muscles?

Acetylcholine Signup and view all the answers

What is the main function of GABA, the major inhibitory neurotransmitter?

Causes IPSPs Signup and view all the answers

What process involves the addition of multiple EPSPs to reach the threshold for generating an action potential?

Temporal summation Signup and view all the answers

Which neurotransmitter undergoes reuptake into the presynaptic neurone or is broken down by enzymes?

Dopamine Signup and view all the answers

What is the function of myelin in nerve conduction?

Insulate axons to increase nerve conduction speed Signup and view all the answers

What does the Na-K ATPase pump do in terms of Na+ and K+ ions?

Pumps three Na+ out of the cell and two K+ into the cell Signup and view all the answers

Which type of fibre has the highest conduction velocity?

A-a Signup and view all the answers

Why is the membrane most permeable to K+ ions?

K+ ions move through leaky channels down their concentration gradient Signup and view all the answers

What happens when an action potential reaches the end of an axon?

Ca2+ moves in allowing neurotransmitter release Signup and view all the answers

What happens to the inside of the cell in terms of charge compared to the outside when equilibrium is reached?

It becomes negative Signup and view all the answers

Which fibre type is responsible for autonomic functions?

B Signup and view all the answers

What is the typical range of membrane potential in most cells?

$-90$ to $-50$ mV Signup and view all the answers

What percentage of myelin is composed of lipid?

80% Signup and view all the answers

What is the value of the threshold potential for action potential initiation?

$-55$ mV Signup and view all the answers

In saltatory conduction, the action potential jumps from one __________ to another, increasing the speed of nerve signals.

Node of Ranvier Signup and view all the answers

Why do all action potentials produce exactly the same electrical change?

Equilibrium between concentration and electrical gradients Signup and view all the answers

Study Notes

Na-K ATPase Pumps

Pump 3 Na+ out of the cell and take 2 K+ into the cell for each molecule of ATP, setting up an electrical gradient
Found in all parts of the body

Electrical Potential Across the Cell Membrane

The membrane is most permeable to K+ due to leaky K+ channels, allowing K+ to move down the concentration gradient
The membrane is less permeable to Na+
The inside of the cell becomes negative with respect to the outside
Equilibrium is reached when the concentration gradient is balanced by the electrical gradient
The membrane potential is -50 to -90 mV in most cells

Action Potential

Depolarisation: a rapid increase in the membrane potential above the threshold potential (-55 mV)
Repolarisation: a rapid decrease in the membrane potential back to the resting potential (-65 mV)
All action potentials produce exactly the same electrical change
A stronger stimulus does not produce a larger action potential

Neurotransmission

Neurotransmitters are released from the presynaptic neuron and bind to receptors on the post-synaptic membrane
Glutamate: major excitatory neurotransmitter that opens Na+ channels, causing excitatory postsynaptic potentials (EPSPs)
GABA: major inhibitory neurotransmitter that opens Cl- channels, causing inhibitory postsynaptic potentials (IPSPs)
Acetylcholine: can be excitatory or inhibitory in the brain, and excitatory in the muscle

Coding Information

One EPSP is not enough to produce an action potential; a bigger stimulus is needed
Summation: temporal and spatial summation of EPSPs can lead to an action potential

The Neurone

The basic structural unit of the nervous system
Each neuron is an individual cell that communicates at synapses
Consists of a single cell body with dendrites (receive information) and axons (transmit information)
Branch to communicate with many cells
Information is coded in the form of action potentials

Body Water and the Cell Membrane

Body water occupies two "compartments": intracellular fluid (ICF, 66% of total body water) and extracellular fluid (ECF, 33% of total body water)
The ICF and ECF are separated by the cell membrane
Cell membrane structure: phospholipid bilayer with phosphate heads (hydrophilic) on the surfaces and lipid tails (hydrophobic) centrally
Protein molecules are inserted into the bilayer

Myelinated Axons

Myelin: increases the speed of nerve conduction by insulating axons
Present around nerves in the central nervous system (CNS) and peripheral nervous system (PNS)
Composed of about 80% lipid

Fibre Types

A-a: 13-22 µm diameter, 70-120 m/s conduction velocity, motor neurons
A-b: 8-13 µm diameter, 40-70 m/s conduction velocity, touch, movement
A-g: 4-8 µm diameter, 15-40 m/s conduction velocity, touch, pressure
A-d: 1-4 µm diameter, 5-15 m/s conduction velocity, pain, pressure, temperature
B: 1-3 µm diameter, 2-14 m/s conduction velocity, autonomic
C: 0.1-1 µm diameter, 0.2-2 m/s conduction velocity, pain, touch, pressure, temperature

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Description

Test your knowledge on neurones, the basic structural unit of the nervous system, and action potentials with this quiz based on Paul Austin School of Medical Sciences content.