Nerve Physiology

Central Nervous System - Brain and Spinal Cord

Peripheral Nervous System - Peripheral nerves and AUTONOMIC

INFORMATION GOING TO THE CNS IS CARRIED IN SENSORY OF EFFERENT NERVES

INFORMATION EXITING FROM THE CNS IS CARRIED IN MOTOR OR EFFERENT NERVES

Some neurons are specialised, but all neurons recieve and transmit information as Nerve Impulses

DENDRITES recieve information from other cells

AXONS generate impulses

Information is transmitted to other cells at the AXON TERMINAL

Myelin Sheath is used for Insulation

Neurons may need to be very long and protected so they are packaged into nerves alongside blood vessels and wrapped in connective tissue

NERVE TRUNKS are packageing for the nerve and may contain MIXED NERVES

Neurons are excitable tissues and their impulses generate Action Potentials.

When they are not generating impulses they are said to be in resting state.

During resting state the fluid inside the cell is different from the outside of cell and there is a difference of charge =MEMBRANE POTENTIAL

INTRACELLULAR fluid is more negative than EXTRACELLULAR fluid

Sodium/potassium ATPase pump maintains difference in charge.

Information transfer only generated when sufficient stimulus is recieved = THRESHOLD STIMULUS

All or nothing response followed by ABSOLUTE REFRACTORY PERIOD = NO STIMULUS WILL INITIATE

RELATIVE REFRACTORY PERIOD = MORE STIMULUS NEEDED.

Action Potential occurs when the resting membrane potential becomes more positive = Permeability of cell membrane changes to certain ions = CONDUCTION CHANGES

NEURON stimulated

Increased membrane permeability to Sodium

Sodium moves into cell = DEPOLARISATION

Membrane potential increase potassium out = REPOLARISATION

Membrane potential below normal value = HYPERPOLARISATION

Action Potential starts at one end of axon down to axon terminal.

Adjacent sections depolarise die to current flow

speed = depend on neuron (myelinated or not)

Action Potentials only occur at weak points of the myelid called node of Ranvier. Not all axon depolarised.

Saltotory conduction jump.