Membrane Potentials, Synapses & Neurotransmitters

Question 1

List the excitable cells in human body

Answer 1

They are cells that can be electrically excited resulting in the generation of action potentials

• Neurons
• Muscle cells
• Some Endocrine cells (e.g. insulin secreting pancreatic β-cells)

Question 2

Describe the basis of electrical excitability and the membrane potential

Answer 2

Electrical excitability: Depolarization of the membrane above a certain threshold voltage triggers a spontaneous all-or-none response called an action potential.
Membrane potential: Electrical potential difference between the inside of the cell and the surrounding extracellular fluid. It codes and transmits information

Question 3

Explain the generation of action potentials

Answer 3

Firstly needs a stimulus. Ligand gated channels open with stimulation. Inflow of cations and lowers the membrane potential. Open the voltage-gated Na+ channels. Local depolarization of membrane occurs.
- Becomes less negative and more positive.

Question 4

Understand the effects of nerve diameter and myelination on conductance

Answer 4

Larger diameter = less resistance
Myelinated axons: Thicker, Fast transmitting information. Sharp pain, well localized
- Action potentials only produced in the exposed spaces of Ranvier’s nodes
Unmyelinated axons: Thinner, Slow pain, burning sensation, lingering pain. Chronic pain, poorly localized pain

Question 5

Synapse

Answer 5

– Synapse (between the cell originating and the cell receiving the signal)
– Only occurs between cells with the synapse
– Communication between neurons or between neuron and effectors (i.e. muscle cells)
1) Electrical synapse
2) Chemical synapses

Question 6

Neurotransmitter

Answer 6

Biologically active chemicals that transmit signals from a neuron to another neuron or target cell across a synapse.

1) Excitatory NTs: Influx of Na+ - Depolarisation –Action potential
2) Inhibitory NTs: Influx of Cl- - Hyperpolarisation –Difficult to reach threshold

Question 7

Understand the principle of anaesthetic function from a physiological point of view

Answer 7

Local anaesthetic – A drug which reversibly prevents transmission of the nerve impulse in the region to which it is applied, without affecting consciousness
› Lignocaine binds to voltage-gated Na+ channels in the peripheral nerve cell membrane and blocks the influx of Na+ (which is required to trigger an action potential)