PM154 Lecture 9 - Nervous System Part 1 & 2: Neuron & Electrochemical Signalling

Learning objectives

• Define the role of the nervous system in human physiology.

• Identify the functional divisions of the nervous system.

  • Describe the functions of the central, peripheral and autonomic systems.

  • Describe the functions of the main structures within the nervous system (brain, spinal cord, peripheral nerves)

Part 2: Neurons and electronic signalling

Neuron: the soma

• Relatively large nucleus

• Very high demand for protein synthesis

• Many proteins packaged into vesicles and transported to axons

• Some organelles are more abundant in the soma and others in distal portions of axons and dendrites

Neuron: dendrites

• Number of dendrites present on a neuron varies

• Neurons often display elaborate dendritic arbores (i.e. complex braching networks)

• Can have spines - bumps that provide more surface area to relay electrical signals

Neuron: the axon

• signal goes from axon → terminal - termed as retrograde

Neuron: axon terminals and synapses

• Neurons are not continuous; each cell is a separate unit and forms a very close contact association with other nerve cells.

• The neuron sending the signal is referred to the presynaptic neuron

• The neuron receiving the signal is referred to as the postsynaptic neuron

• Lots of mitochondrion present for the energy needs of the nerve cells

Synaptic transmission

How do neurons conduct electricity?

• Ion concentration gradients across the cell membrane

• Voltage (electrical potential difference) across the membrane

• Membrane permeability

The neuronal action potential

• Transient reversal in the voltage across the axonal membrane

• Instigated by rapid change in permeability to Na+ ions and the resulting influx of positive current

• Terminated by K+ efflux and loss of positive current from the cell

Leak channel - always open

More potassium leaking out than sodium coming in