Conduction of a Nerve Impulse
Human Biology (Year 12) - Nervous Transmission
What is a nerve impulse?
A nerve impulse is an electrochemical change that travels along the membrane of a neuron. Nerve impulses are transmitted rapidly, to allow for a rapid response to occur to any change in the internal or external environment.
What are the conditions in a neuron at rest?
A resting neuron is said to be polarised, as it has different charges on either side of the cell membrane
The exterior of the cell is positively charged due to the larger number of sodium ions present outside of the cell in comparison to the inside of the cell
The interior of the cell is negatively charged as it contains a low concentration of sodium ions and more negative organic molecules
There is also a concentration gradient present with a high concentration of potassium ions inside the cell compared to the outside
Due to these differences in charge, there is an electro-chemical difference or resting membrane potential (mV) of about -70 millivolts (-70mV)
The sodium-potassium pump uses ATP molecules to actively maintain this difference by removing sodium ions from inside the cell back and drawing potassium ions into the cells
The pump moves three sodium ions for every two potassium ions, and therefore there is a higher concentration of sodium outside compared to potassium inside
How is a nerve impulse generated? When a stimulus that is strong enough is detected by a neuron of at least 15mV to reach the threshold level of -55mV, a nerve impulse is generated in that neuron. This process is referred to as an 'all-or-none' response, and the stimulus triggers both chemical and electrical changes in the neuron.