Nerves and Stimuli

Nerve Cells

Nerve Cells

axon

myelin

Action Potential

Action Potential

Cytosol Extracellular fluid

Na+

15 mM

K+

150 mM

Cl-

120 mMA-

100 mM

Na+

150 mM

K+

5 mM

Cl-

10 mM

-70 mV

negative

Action Potential

Sodium (Na+) ion

Potassium (K+) ion

Sodium channel

Potassium channel

Activation gate

Inactivation gate

Action Potential

3. Depolarization opens most Na+ activation channels. Influx of Na+ makes inside of cell +ve.

4. Inactivation channels close & block Na+ influx.Activation gates on K+ channels open & K+ ions leave making cell more -ve.

5. Some K+ channels are still open, allowingK+ ions to escape and making the cell more -ve.As the K+ gates close, the cell returns to its resting state.

1. Resting state - activation gates on K+ and Na+ channels are closed.

2. Stimulus opens activation gates on some Na+ channels. Influx of Na+ and depolarization.

Synaptic Junctions

Chemoreceptors

Hamster - taste bud Moth antenna

Mechano- and chemoreceptors

Thermoreceptors

Photoreceptors

Photosensitive cells - Planaria

Compound eye - Arthropods

Nerve cells, stimuli and behaviour

Tail flip response in crayfish

Tail flip response in crayfish

Lateral Giant interneuron (LGI)

a. Correlation between nerve firing and response

LGIStimulating electrode

Recording electrode

Tactile stimulation

b. LGL is sufficent for response

LGIStimulating electrode

Recording electrode

Tactile stimulation

LGIStimulating electrode

Recording electrode

Tactile stimulation

c. Hyperpolarizing nerve

Tail flip

Tail flip

No tail flip

Peripheral Processing of Stimuli

Worm-catching Toads

Central Processing

Optic Tectum of a Toad

Central Pattern Generators (Motor Pattern Generators)

Nerves and Stimuli

1. Structure of nerves

2. Polarity of a nerve cell

3. Transmission of an action potential

4. Peripheral filters

5. Central filters

6. Motor pattern generators