neurones

what are the 3 types of neurones

sensory relay motor

describe the sensory neurone

transmits signal back from the skin/ muscle back to the CNS

describe the relay

This connects the sensory and motor neurones. They are found in the CNS. They have short dendrites and axons.

describe the motor

These are connected to the relay neurone and at the other end the effector.

what is an effector

muscle and glands

1. dendrites

2. nucleus

3. soma/ cell body

4. axon

5. scwann cells

6. node of Ranvier

7. myelin sheath

8. axon terminals

how can you identity which neurone is which

Neuron Type	Direction of Info	Key Structural Features	Location
Sensory	Receptors → CNS	Long dendrites, short axon, cell body in middle	PNS → CNS
Relay	Within CNS	Short axons & dendrites also don’t often have myelin sheath	CNS only
Motor	CNS → Muscles/Glands	Short dendrites, long axon, cell body at one end	CNS → PNS

reflex arch

stimulus, sensory neurone, relay(CNS), motor neurone, effector responds. At each synapse the electrical signal is converted into a chemical signal.

1. presynaptic neurone 

2. action potential 

3. transport protein (no key just on the diagram) 

4. vesicles with neurone transmitters 

5. postsynaptic neuron 

6. receptor / receptor sites 

7. synaptic cleft/ gap 

describe how messages get across a synapse

1. An electrical impulse travels down the axon into the presynaptic neurone this is know as an action potential

2. The electrical impulse stimulates the vesicles to merge with the membrane of the presynaptic neurone and release the neurone transmitters into the synaptic cleft.

3. The neurone transmitters diffuse across the gap reaching the postsynaptic neurone and binding to receptors on its surface.

4. To make an action potential fire the electrical charge has to reach a threshold.

5. when the neurone transmitters bind to the receptors they can either give and excitory or inhibitory response depending on the neurotransmitter.

6. excitory effect the electrical charge is more positive this is called depolarization. This happens when the receptors allow positively charged sodium ions enter the cell. This increases the likelihood that a new action potential will be fired. 

7. An inhibitory effect is when the cell become hyperpolarised (more negative) this happens when positive potassium ions released out of the cell making it negative. This decreases the likelihood that a new action potential will be fire 

8. The sum of all the exitory and inhibitory neurone transmitters and added up. If the sum meets threshold the action potential will fire this is called summation 

9. after this a process called reuptake occurs. This is when the neurotransmitters are reabsorbed into the presynaptic cell after transmitting a neural impulse. This happens at transport proteins and prepared the cell to fire again .