Nervous system

Nerve net (hydra)

Have no CNS

ganglion cells provide connections in all direction

axons non myelinated

slow conduction speed

What does the nervous system do

Detect changes in environment and local environment and produce a response

What does the CNS comprise of

Brain + Spinal cord

Protected by meninges

2 divisions of the PNS + function

Somatic nervous system - voluntary actions

Autonomic nervous system (heart rate + breathing)

Sensory neurone

Carries impulse form receptor cells to co-ordinator

Relay neurone

Receive form sensory and relay to motor

Motor neurone

From coordinator to effector to bring a response

Dendrite

Carry impulse towards cell body

Axon

Transmits away from cell body

Schwann cells

Surround neurones and insulate

Myelin sheath

Made of many Schwann cells - acts as electrical insulator

Nodes of Ranvier

Areas on axon where myelin sheath is missing

Cell body

Contains nucleus + other cell organelles

What is the first stage of reflex action

Sensory neurone enters through dorsal root

What happens at the relay neurone + where

Neurotransmitter enters and creates action potential

In grey matter

How is the motor neurone used in reflex arc

Action potential transmitted out through the ventral root to produce a response at effector

What are the 4 types of axon transport proteins

Na+ / K+ pump

Voltage gated Na+ and K+ channels

K+ always open channels

Sodium / potassium pump

Uses active transport to move 3 Na+ out for every 2 K+ in

What happens to the cytoplasm of the axon due to Na+/K+ pump

Becomes more negatively charged due to 2 in, 3 out

Resting potential + charge

PD between inside and out of membrane when impulse is not being conducted

Due to the movement of ions the membrane is polarised and rests at -70mV

K+ always open channels at rest

Allows some K+ to diffuse back out down a conc. gradient

Action potential part 1 - Depolarisation

Stimulus causes opening of Na+ channel

Ions diffuse in across electrochemical + concentration gradient

If enough diffuse in and raise to -55mV all Na+ channels open and rapid diffusion of ions cause an action potential of +40mV

Action potential part 2 - Repolarisation

When PD reaches 40mV - Na+ close and K+ open

K+ rapidly diffuse out down concentration and electrochemical gradient

Action potential part 3 - Hyperpolarisation

Due to rapid diffusion out of K+ ions - axon becomes more negative at 90mV

K+ channels then close and Na+/K+ pump restarts and membrane become polarised again

All or nothing law

To cause depolarisation, stimulus must exceed threshold value

The action potential size is constant (40mV)