L2: Neural signaling

How are electrical signals moved between neurons?

Synapse

Synaptic gap

Effector

Examples of effector cells

• Skeletal muscle fibers (centres, gland cells)

• Carry out the effect/response to a stimulus

Does a signal pass in one direction or both directions across a typical synapse?

One direction

What is the role of neurotransmitters?

• Brains and neurons systems are able to communicate

• Neurotransmitters are related from the presynaptic membrane into the synaptic cleft

• This is a critical process that allows neurons to transmit signals to other neurons or effector cells

• this enables how brains processes information, control our movement

Mechanism of synaptic transmission occurring at a presynaptic cell, including depolarization, calcium ions, exocytosis and diffusion

1. Depolarization

• An action potential arrives at a presynaptic terminal, causing depolarization of the membrane

2. Calcium ion influx

• Depolarization opens voltage-gated calcium channels then calcium ions diffuse into the presynaptic terminal down their electrochemical gradient

3. Exocytosis of neurotransmitters

• The rise in intracellular calcium triggers synaptic vesicles to move and fuse with the presynaptic membrane, releasing neurotransmitters by exocytosis

4. Diffusion across the synaptic cleft

• Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane, initiating a response

What ion functions as a chemical signal triggering exocytosis of neurotransmitters from a presynaptic cell?

Calcium ions trigger exocytosis of neurotransmitters in the presynaptic cell

Mechanism of synaptic transmission occurring at a post-synaptic cell including neurotransmitters, diffusion, receptors, gated ion channels, threshold potential and action potential

1. Neurotransmitter release and diffusion

• Neurotransmitters released from the presynaptic cell to the post-synaptic membrane

2. Binding receptors

• They bind to specific receptors, usually ligand-gated ion channels

3. Opening of gated ion channels

• Binding open channels allowing ions (Na+,K+,Cl-) to move and change the membrane potential

4. Post-synaptic potential

• EPSP: Na+ influx depolarizes the membrane

• IPSP: Cl- influx or K+ efflux hyper polarizes the membrane

5. Threshold and action potential

• If depolarization reaches the threshold potential, voltage-gated sodium channels open, triggering an action potential in the post-synaptic neuron

What neurotransmitter is used as the neurotransmitter in many synapses, including neuromuscular junctions?

Acetylcholine

Outline the digestion of acetylcholine by acetylcholinesterase in the synapse

• Acetylcholine is released into the synaptic cleft from the presynaptic neuron

• It binds to receptors on the post-synaptic membrane triggering a response

• Acetylcholinesterase present in the synaptic cleft rapidly breaks down acetylcholine

• Acetylcholine is hydrolyzed into choline and execrate

• Choline is reabsorbed into the presynaptic neuron to be reused in acetylcholine synthesis

• This breakdown, terminates the signal and prevents continuous simulation