Neuronal Communication

• Sodium and potassium pump.
• For the 3 Na+ that leave, 2 K+ enter.
• This causes a high concentration of Na+ ouside, and low K+.
• Voltage gated channels.
• Sodium channels open.
• Sodium ions move into the neurone causing depolarisation.
• Until it reaches +40mV.
• This triggers sodium channels to close and potassium channels to open.
• Potassium ions then move out of the neurone causing repolarisation.
• There is a brief 'overshoot' causing hyperpolarisation and this also triggers the refractory period.
• More negative than resting potential due to this overshoot.
• Potassium channels then close.

Rods and cones / photreceptors detect light.

Taste buds / chemoreceptors detect chemicals.

Meissner's corpuscle / mechano receptors detects pressure / touch.

Ruffini's endings in skin / thermorecptors detect temperature changes.

Proprioreceptors detels mechanical displacement.

Hair cells detect movement.

Hair cells in cochlea detect sound.

Baroreceptors detect blood pressure changes.

Osmoreceptors detect changes in blood water potential.

• Action potential is recognised.
• Causes calcium channels to open.
• Calcium ions then enter.
• The calcium ions causes the vesicles to fuse with the membrane.
• Exocytosis release neurotransmitters into synaptic cleft.
• Neurotransmitters diffuse across and bind to receptors of post synaptic membrane.
• Sodium ion channels then open.
• If threshold value is reached then action potential is fired requiring ATP.

Sensory - from receptor to central nervous system (CNS).

Motor - from CNS to effectors (muscles and glands).

Relay - from sensory neurones and motor neurones.

• More postive ions outside the cell showing a difference in charge (polarised).
• At resting potential it is roughly -70mV.
• Membrane is not permeable to sodium ions so are moved out by sodium - potassium pumps and they can not come back in.
• Sodium - potassium pumps can move potassium ions into the cell, these are also permeable so can difuse back outside of the cell meaning it remains more positively charged outside.

Stimulus - Excites neurone cell membrane causing sodium ion channels to open.

Depolarisation - Once threshold is reached voltage gated sodium ion channels open.

Repolarisation - Sodium ion channels close and voltage gated potassium ion channels open meaning membrane is more permeable.

Hyperpolarisation - Potassium ion channels are slow to close so there is an 'overshoot' of too manyy potassium ions diffusing out.

Resting potential - Sodium potassium pumps return the membrane to its resting potential.

Synaptic divergence - One neurone connects to many neurones in order to diperse the impulse to different parts of the body.

Synaptic convergence - Many neurones connect to one neurone so information can be amplified (made stronger).

Spatial summation - Neurones converge so a small amount of neurotransmitter from each neurone can be enough altogether to reach a threshold to trigger an action potential.

Temporal summation - Two or more impulses arrive in quick succession from the same presynaptic neurone making action potential more likely because neurotransmitter is released into synaptic cleft.