salters nuffield Topic 8

1) Centeral nervous system. - Brain and spinal cord.

2) Peripheral nervous system consists of...

• sensory nerves, carry info from receptors to CNS.
• Motor nerves. Carry commands from CNS to Effectors.

Peripheral nervous system sub-divided into...

1) Somatic nervous system - voluntary, stimulates skeletal muscle.

2) Autonomic nervous system - Involuntary stimulates smooth muuscle cardiac muscle and glands.

Autonomic nervous system subdivided into...

1) Sympathetic - Prepares body for fight or flight response.

2) Prepares body for rest and digest

Always within CNS. (axon extends out)

Conducts impulses from CNS to effectors.

Can have very long axons i.e. leg.

AKA effector neurones.

Carry impulses from sensory cells to CNS.

Found in CNS

Large number of connections with other nerve cells.

AKA connector neurines and interneurones.

Surrounded by myelin sheath made up of scheann cells.

Sheath affects speed of nerve impulse transmission.

1) Receptors detect stimulus and generate nerve impulse.

2) Sensory neurones conduct nerve impulse to CNS along sensory pathway.

3) Sensory neurones enter spine through dorsal route.

4) Sensory neurone synapses with relay neurone.

5) Relay neurone synapses with motor neurone which leaves the spine through ventral route.

6) Motor neurone carries impuls to effector, resulting in response.

1) High light strikes photoreceptors in reina

2) Nerve impulse passes along optic nerve to midbrain.

3) Impulses sent from co-ordinator cells along parsympathetic motor neurones to circular musscles.

4) Circular muscle contract radial muscles relax.

5) Pupil constrict less light enters.

The distibution of ions inside and outside an axon is unequal.

this is acheived by the action of the Na+/k+ Pumps.

1) Na+/k+ pump creates concentation gradient. across membrane.

2) K+ diffuse out of cell down concentration gradient.(outside +ve inside -ve)

3) Electrical graient pulls K+ back into cell.

4) At - 70mV two gradients counteract and no net movement of K+ ions.

1) Depolarisation...

• Change in potential difference leads to flow of Na+ into cell.
• Depolarisation increases and more Na+ channels are opened and more Na+ flow in.
• Inside of cell becomes more positive than ouside. (rising phase on oscilliscope)
• Example of positive feedback. A change encourages further change of the same sort.

2) Repolarisation...

• After 0.5 ms Na+ gates spontaneously close.
• K+ channels open and K+ Flow out of cell. (down concentration gradient.)
• Inside of cell becomes more negative than outside. (falling phase on oscilliscope.)

3) Restoring resting potential...

• Inside of cell is more negatibve than resting potenial. (hyperpolarisation.)
• Closing K+ channels restores resting potential.
• Pottasium ions diffuse into axon.