Neurones & Synaptic Transmission

Question 1

Types of neurones

Answer 1

Sensory neurones:
Carry messages away from the PNS to the CNS

Relays neurones:
Connect the sensory neurones to the motor or other relay neurones

Motor neurones:
Connect CNS to effectors e.g. muscles, glands

Question 2

Role of neurones

Answer 2

• transmitting signals electrically and chemically
• provide the nervous system with its primary communication.

Question 3

Structure of neurone

Answer 3

• cell body inside the nucleus, contains genetic material of the cell
• dendrites branch off from the cell body, carry nerve impulses from neurones to cell body
• axon covered in fatty myelin sheath, protects the axon and speeds up electrical transmission of impulse
• myelin has nodes of ranvier that segment it, speed up the transmission of the impulse, force it to jump across the axon.
• terminal buttons, communicate with the next neurone across the synapse

Question 4

Location of neurones

Answer 4

• cell bodies of motor neurones in CNS but they have long axons, form part of the of PNS
• sensory neurones are located outside of the CNS, in the PNS in clusters called ganglia

Question 5

Electrical transmission - the firing of a neurone

Answer 5

• when neurone is in resting state, the inside is -tively charged compared to the outside
• when it is activated by stimulus, the inside becomes +tively charged for split second causing an action potential to occur.

Question 6

Synaptic transmission - chemical transmission

Answer 6

• neurones communicate via neural networks
• each neurone is separated by synapses
• signals between neurones are transmitted chemically across the synapse
• when the electrical impulse reaches the pre-synaptic terminal, triggers the release of neurotransmitters from synaptic vesicles

Question 7

Neurotransmitters

Answer 7

• N.T crosses the gap, taken up by the postsynaptic receptor site on the dendrites of the next neurone
• chemical message is converted back to an electrical impulse, the transmission begins again
• each N.T has specific molecular structure that fits to the postsynaptic receptor site
  E.g. acetylcholine is found where a motor neurone meets a muscle, cause muscle to contract

Question 8

Excitation and inhibition

Answer 8

• N.T either excitory or inhibitory effect on neurones
• inhibitory = neurone becomes -tively charged and less likely to fire e.g. serotonin
• excitatory = increasing +tive charge, more likely to fire e.g. adrenaline

Question 9

Summation

Answer 9

• whether a postsynaptic neurone fires is decided by summation
• excitatory or inhibition are summed: if net effect on the postsynaptic neurone is inhibitory then the P.S.N is less likely to fire.
• if the net effect is excitatory, more likely to fire, more positively charged.
• once the electrical impulse is creates it travels down the neurone
• the action potential is only triggered if the sum of the excitatory and inhibitory signals at any time reaches the threshold.