Neurons & Synaptic Transmission

Question 1

Info About Neurons

Answer 1

• They are nerve cells that vary in size (from less than a mm to up to 1m)
• They help nervous system communicate by transmitting signals electrically and chemically
• 100 billion in human nervous system, 80% of which are in the brain

Question 2

Sensory Neurons

Answer 2

• Carry messages from PNS and CNS
• Have long dendrites and short axons

Question 3

Relay Neurons

Answer 3

• Connect sensory neurons to the motor/other relay neurons
• Have short dendrites and short axons

Question 4

Motor Neurons

Answer 4

• Connect the CNS to effectors such as muscles and glands
• Have short dendrites and long axons

Question 5

Nucleus

Answer 5

• Control centre of a cell, which contains chromosomal DNA
• Is contained in cell body (soma)

Question 6

Dendrite

Answer 6

• Branch-like structure that receives the nerve impulse/signal from adjacent neurons

Question 7

Axon

Answer 7

• Where electrical signals pass along

Question 8

Myelin Sheath

Answer 8

• Insulates/protects the axon from external influences that might affect the transmission of the nerve impulse down the axon

Question 9

Nodes of Ranvier

Answer 9

• Segment myelin sheath + speed up the transmission of the impulse by forcing the neurotransmitter to ‘jump’ across the synapse (gap)

Question 10

Terminal Buttons

Answer 10

• Are at the end of the axon and communicate with next neuron in the chain across a synapse

Question 11

Electric Transmission - Firing Of A Neuron

Answer 11

• When a neuron is in a resting state, the inside of the cell is negatively charged compared to the outside
• When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur
• This creates an electrical impulse that travels down the axon towards the end of the neuron

Question 12

Synaptic Transmission

Answer 12

• Neurons communicate within groups known as neural networks
• Each neuron is separated by a synapse
• Signals WITHIN neurons are transmitted electrically while signals BETWEEN neurons are transmitted chemically across synapses
• When the electrical impulse reaches the end of the neuron (presynaptic terminal), it triggers the release of neurotransmitters from sacs called synaptic vesicles

Question 13

Synaptic Transmission Process

Answer 13

• An electrical impulse (action potential) travels along an axon
• This triggers the nerve-ending of a neuron to release neurotransmitters
• These diffuse across the synapse and bind with receptor molecules on the membrane of the next neuron
• The receptor molecules on the 2nd neuron bind only to the specific chemicals released from the 1st neuron
• This stimulates second neuron to transmit the electrical impulse

Question 14

Neurotransmitters

Answer 14

• Chemicals that are released from a synaptic vesicle into the synapse by neurons
• They affect the transfer of an impulse to another nerve or muscle
• These neurotransmitters are ‘taken back up’ into the terminal buttons of neurons through the process of reuptake OR are broken down by an enzyme

Question 15

Excitation & Inhibition

Answer 15

• Neurotransmitters have an excitatory/inhibitory effect on the neighbouring neuron
• Excitatory – They make it more likely the next neuron will fire (increasing positive charge)
• Inhibitory – They make it less likely the next neuron will fire (increasing negative charge)
• Summation is the combination of the result