Nature of the nerve impulse

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Presentation transcript:

Nature of the nerve impulse

-Nerve impulse: electrochemical charge that travels along the nerve fibre. -Impulse speed varies: o Unmyelinated: approx 2m/sec o Myelinated: approx 18m/sec to 140m/sec (through saltatory conduction)  This is affected by: diameter of neuron or distance between nodes of ranvier impulse

-. Two types of electric charges, positive (Na+, K+) & negative (Cl-) - Two types of electric charges, positive (Na+, K+) & negative (Cl-). - Like charges repel, unlike attract. (caused by an ‘electrical force’) - When unlike charges get closer the force increases until they meet and release energy - When those forces are being separated (by a membrane or something else) they still have the potential to be pulled together (and release energy). This is called potential difference

- The potential difference between two places (when they are separated and when they come together) can be measured in Volts. - Regarding cells, if it is a cell membrane creating the potential difference then it is termed: membrane potential.

- Generally inside of axon is negatively charged and outside is positively charged. (inside of cell = -70 millivolts) When un-stimulated, Neuron is polarized as the inside is more negative than the outside. (This is described as ‘resting membrane potential’) The inside has 70 mv less potential electrical charge.

-. NOTE: Polarized= two sides have different charges o - NOTE: Polarized= two sides have different charges o Depolarized= polarity changes towards opposite o Hyperpolarized=polarity changes to become more intense

-. Refractory period: Period when membrane cannot be stimulated again - Refractory period: Period when membrane cannot be stimulated again. (approx 2.5 ms after stimulus) - All-or-none response: Once the 15mv stimulus occurs a full action potential response occurs. There is not half or weak response. (all or none) o Variety of stimulus is differentiated by number of nerve impulses (less/more) and the number of nerve fibres being stimulated. (shallow/deep)

Unmyelinated fibres One action potential provides the stimulus for an action potential to occur directly beside it. (creating a nerve impulse) The refractory period prevents the nerve impulse from going backwards. Myelinated fibres Ions can’t flow through the membrane where it is covered by the myelin sheath. It will only occur at the Nodes of Ranvier

Saltatory Conduction: jumping conduction between nodes Saltatory Conduction: jumping conduction between nodes. Transmission of Across a Synapse: Neurotransmitters: Special chemicals which are released from end of axon and attach to dendrite Chemical effect: eg caffeine, Benzedrine (stimulate) & anesthetics (depress)