Neurons and Synaptic Transmission

Question 1

How many neurons/what are there basic function?

Answer 1

• 100 billion neurons (nerve cells) 80% of which are in the brain
• transmit signals electrically/chemically, provide nervous system with primary means of communication

Question 2

What are the Types of Neurons?

Answer 2

• Sensory Neurons
• Relay neurons
• Motor neurons

Question 3

How are Neurons Structured?

Answer 3

• Vary in size from less than a mm to up to a metre
• Cell body includes a nucleus (contains genetic material), dendrites protrude from cell body and carry nerve impulses from neighboring neurons to the cell body
• Axon carries impulses away from cell body down length of the neuron, covered in fatty layer of myelin sheath (protects axon and speeds up transmission)
• If myelin sheath was continuous would have reverse effect and slow down electrical impulses so has gaps called nodes of Ranvier, speed up transmission of impulse by forcing it to jump across gaps along the axon
• End of the Axon there are terminal buttons that communicate with next neuron in chain across the synapse

Question 4

Where are Motor, Sensory and Relay neurons located?

Answer 4

• Cell bodies of Motor neurons in CNS but have long axons which form party of PNS
• Sensory neurons locates outside CNS in PNS clusters known as ganglia
• Relay neurons make up 97% of all neurons and most are found within the brain and the visual system

Question 5

How does Electrical Transmission occur?

Answer 5

• When neuron resting inside of cell is negatively charged compared to outside, when activated by stimulus inside of cell becomes positively charged for a split second causing an action potential to occur. Creates electrical impulse that travels down the axon

Question 6

What is Chemical Transmission?

Answer 6

• Neurons communicate within neural networks, they are separated by synapses. Signals within are transmitted electrically but between are transmitted chemically
• When electrical impulse releases the pre-synaptic terminal it triggers release of neurotransmitters from synaptic vesicles

Question 7

What are Neurotransmitters?

Answer 7

• Chemicals that diffuse across the synapse to the next neuron in the chain. After crossing taken up by a postsynaptic receptor site on the dendrites of the next neuron (dendrites take signals away), here chemical message is transferred to an electrical impulse and process repeats
• One way system, each neurotransmitter has it’s own specific molecular structure that fits perfectly into a postsynaptic receptor site (lock and key) and some have specialist functions

Question 8

What are Excitation and Inhibition?

Answer 8

• Neurotransmitters have either an excitatory or inhibitory effect on receiving neuron. Either cause it to be positively (excitatory - more likely to fire e.g adrenaline) or negatively charged (inhibitory - less likely to fire e.g serotonin)
• if inhibitory inputs are higher than excitatory they can cancel out excitation and inhibit an action potential occurring

Question 9

What is Summation?

Answer 9

• the process of whether or not a postsynaptic neuron fired is called summation. The action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshhold

Question 10

What is the effect of inhibitory neurotransmitters on neurons?

Answer 10

• Stimulation of postsynaptic receptors by an inhibitory neurotransmitter result in inhibition of the postsynaptic membrane
• when an inhibitory neurotransmitter binds to the post-synaptic receptors it makes the post-synaptic cell less likely to fire