The nervous system

The nervous system has two key parts

• your nervous system is what allows you to respond to changes in your environment 
• Receptors detect stimuli and effectors bring about a repsonse to a stimulus, effectors include muscle cells and cells found in the glands
• Receptors communicate with effectors via the nervous and endocrine system or both
• The Nervous system and Endcorine coordinate the response
• The nerovus system has two parts the CNS and PNS

• Neurons transmit information as electrical impulses around the body
• The cell body has dendrites that recieve and send information from other neurons 
• This information passes along the Axon in the form of an electrical impulse that ends up at a synaptic knob. The mylein Sheath insulates the axon to speed up nerovus transmission
• Theres  a small gap before the next neuron called a synapse 
• neurotransmitters are chemicals that are released from the synaptic knob. They pass across the synapse to pass on the signal to the dendrites of the next neuron 

Sensory neurons

• The nerve cells that transmit electrical impulses from the receptors to the CNS

relay neurons 

• The nerve cells that transmit electrical impulses between sensory nuerons and motor neurons

motor neurons 

• The Nerve Cells that transmit electrical impulses from the CNS to effectors 

A synapse is a junction between a neuron and the next cell 

• A synapse is the junction between a neuron and another neuron, or between a neuron and an effector cell 
• The tiny gap between the cells at a synapse is called the synaptic cleft 
• The presynaptic neuron - the one before the synapse has a swelling called a synaptic knob. This contains synaptic vesicles filled with neurotransmitters.
• When an electrical impulse reaches the end of a nueron , neurotransmitters are released into the cleft. They are then diffused and spread across the postsynaptic membrane and bind to specific receptors
• When they bind they might trigger impulses , casue muscle contraction or a hormone to be secreted 
• As receptors are only on postsynpatic membranes , impuleses are undirectional - only goes one direction 
• Neurotransmiters are removed from the cleft so the resposne doesn't keep happening - broken down by enzymes 

Excitatory 

• neurotransmitters increase the likelihood that an electrical impulse will be triggered

Inhibitory

• Neurotransmitters decrease the likelihood that an electrical impulse will be triggered in the postsynptic neuron

Acetycholine

• This excitatory neurotransmitter -involved in voluntary movement, memory, learning and sleep. Too much -linked to depression and too little may result in dementia 

Dopamine 

• Helps with movement attention and learning. Too much linked-schizophrenia , too little depression and parkinson's disease 

Noradrenaline

•  linked with adrenaline. Associated with 'flight or fight' response. Too much linked to schizophrenia and little in depression

Serotonin

• Is involved in emotion, mood, sleeping and eating. Too little is linked to depression

GABA

• GABA is an inhibitory neurotransmitter. Too little GABA is linked to anxiety disorders.