Neuronal Communication TLOs

Question 1

Describe the basic
functions of the following neuron parts:

• Cell body,
• Axon
• Dendrites
• Axon terminal
• Synapse
• Myelin sheath

Answer 1

Cell Body: Carrier’s genetic information, maintains neuron structure and provides energy

Axon: To carry nerve impulses away from the body

Dendrites: to receive signals from other neurons, to process these signals, and to transfer the information to the soma of the neuron.

Axon terminal: important in cell to cell communication through the neurotransmitters it releases into the synaptic cleft

Synapse: Transmit nerve impulses between two nerve cells (neurons) or between a neuron and muscle cell.

Myelin Sheath: Surround and insulate the axon, increasing the speed of signals

Question 2

Explain what neuronal membrane potentials are and the ‘Na/K pump’ movement of ions in maintaining the resting membrane potential

Answer 2

At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.

The Sodium-Potassium pump is the most important mechanism that keeps the resting membrane potential. For every 3 Na pumped out of a neuron, 2 K are pumped in.

Question 3

What are Leak and Voltage Gated Channels?

Answer 3

Leak Channels - passive diffusion depends on electrochemical driving force different channels & numbers for different ions

Voltage-Gated Channels
open and close depending on membrane voltage - different for different ions

Question 4

Explain the action potential (AP) and describe the movement of ions and channels/ pump occurring during the different phases of an AP

Answer 4

An Action Potential is the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.

A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Sodium has a positive charge, so the neuron becomes more positive and becomes depolarised.

It takes longer for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the depolarisation. Also at about this time, sodium channels start to close. This causes the action potential to go back toward -70 mV (a repolarization). The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.

Question 5

Describe the different types of synapses (chemical and electrical) and describe the principles of chemical synaptic transmission

Answer 5

Electrical:

• Very fast
• Bidirectional
• Not as common in mammals

Chemical:

• Unidirectional
• Many neurotransmitter mediators