neurons and synaptic transmission

• neurons are cells that are specialised to carry neural information throughout the body.
• there are three types of neurons: 1. sensory neurons 2. motor neurons 3. relay neurons
• neurons typically consist of a cell body, dendrites and an axon
• dendrites receive signals from other neurons or sensory receptors
• the cell body is the control centre of the neuron
• in many nerves there is an insulating layer that forms around the axon- the myelin sheath. this allows nerve impulses to transmit more rapidly along the axon
• sensory neurons carry nerve impulses from sensory receptors to the spinal cord and brain
• relay neurons allow sensory and motor neurons to communicate with each other
• motor neurons form synapses with muscles and control their contractions
• synaptic transmission refers to the process by which a nerve impulse passes across the synaptic cleft from one neuron (presynaptic) to another (postsynaptic)
• a synapse is a conjunction of the end of the axon of one neuron and the dendrite or cell body of another
• neurotransmitters are chemical substances that play an important part in the workings of the nervous system by transmitting nerve impulses across a synapse
• STAGE 1- when an action potential travels down the axon of the presynaptic neuron, it reaches the axon terminal
• STAGE 2 - vesicles containing neurotransmitters fuse with the membrane of the axon terminal and release their contents into the synaptic cleft
• stage 3 - the released neurotransmitters diffuse across the synaptic cleft and bind to receptor sites on the postsynaptic neuron's dendrites
• stage 4 - this binding causes ion channels in the postsynaptic neuron's membrane to open or close, leading to changes in the electrical charge of the postsynaptic neuron
• stage 5- re-uptake- the neurotransmitter is then taken up again by the presynaptic neuron, where it is stored and made available for a later release
• neurotransmitters can be classified as either excitatory or inhibitory in their action
• excitatory neurotransmitters increase the likelihood that the postsynaptic neuron will fire an action potential
• inhibitory neurotransmitters decrease the likelihood that the postsynaptic neuron will fire an action potential
• Excitatory Postsynaptic Potential (EPSP): If the ion channels allow positive ions (like sodium, Na⁺) to enter, making the inside of the neuron more positive and likely to fire an action potential.
• Inhibitory Postsynaptic Potential (IPSP): If the ion channels allow negative ions (like chloride, Cl⁻) to enter, making the inside of the neuron more negative and less likely to fire an action potential.