Neurophysiology Neurophysiology

Membrane Potential

How is the Resting Membrane Potential Changed?

Changes in Membrane Potential

• From -70 mV to +30 mV

Channels and Changes in the Membrane Potential

Chemically Gated Channels Chemically Gated Channels

Voltage-Gated Channels Voltage-Gated Channels

When these gates are opened, ions move down their electrochemical gradient!When these gates are opened, ions move down their electrochemical gradient!

How are Graded Potentials Different from Action Potentials?

Only occur in ‘excitable membranes’Muscle cells Neurons Axon Hillock

Graded potentials may turn into action potentialsSummation

○ Temporal and Synaptic

Comments Strength does not decreaseSelf propagating

Only occur in ‘excitable membranes’Muscle cells Neurons Axon Hillock

Graded potentials may turn into action potentialsSummation

○ Temporal and Synaptic

Comments Strength does not decreaseSelf propagating

Propagation(fig. 11.13)

Propagation(fig. 11.13)

ThresholdsThresholds

Ion channels - openNeuron cannot respond to another stimulus Na+ channels must close first!

○ Resets normal polarized state

Types AbsoluteRelative

Pre-Synaptic and Post-Synaptic Activity

• Depolarization waves– Moves towards the synapse

• Conduction speed depends on – Diameter of axon– Myelination

• Nerve Fiber Types– Group A, B, C

Saltatory Conduction

When the Nerve Transmission Reaches the Synapse

Electrical Synapse – less common; coordinate neuron activity between neurons; ions move through gap junctions; most abundant in embryonic tissue; brain find stereotyped movements (hippocamus); glial cells of CNS

Chemical Synapses – ions flow between channels; Neurotransmitters are released

Chemical Synapse

At the Synapse

Summation

• Neurons of CNS – neuronal pools – Integrate incoming information

• Neurons of CNS – neuronal pools – Integrate incoming information

1. Discharge zone 2. Facilitated zone 1. Discharge zone 2. Facilitated zone

Neural Circuits