Structure & function of neurons & synaptic transmission

Question 1

What is the nervous system (micro level)?

Answer 1

• Cells relay info around brain & nervous system
• Uses electrical impulses & NT’s
• Electrical impulses travel from end of a neuron to the other
• Process results in release of a NT (chemical)
• If the NT’s are not functioning properly - affects our behaviour

Question 2

What is the structure of a neuron?

Answer 2

• Cell body includes a nucleus (contains genetic material of cell)
• Branch like structures are dendrites, they carry impulses from other neurons towards cell body (receiver)
• Axon carries impulses away from cell body down length of neuron
• Axon covered in myelin sheath, protects the axon & speeds up electrical impulse
• Myelin sheath segmented by nodes of Ranvier, they speed up transmission of impulse by forcing it to jump across axon gaps
• End of axon are terminal buttons, they communicate with next neuron in the chain across a synaptic gap using NT’s

Question 3

What type of neuron does not have a myelin sheath?

Answer 3

• Relay neurons

Question 4

What are the 3 types of neuron?

Answer 4

1. Sensory (unipolar)
2. Relay (multipolar)
3. Motor (multipolar)

Question 5

Sensory neuron description & role?

Answer 5

• Carries messages from PNS to CNS
• Only purpose is to transmit messages (unipolar)

-Notifies brain about internal & external environment by processing info from 1/5 sensory receptors (e.g. eyes, ears etc)
- Info converted into neural impulses
- Impulses made into sensations so we react

• Long dendrites & short axons

Question 6

Relay neuron description & role?

Answer 6

• Most common type of neuron in CNS
• Allow sensory & motor neurons to communicate & connect
• e.g. carry nerve impulses between neurons
• Only carry nerve impulses from one part of CNS to another
• Relay neurons only found in brain, spinal cord & visual system (eyes)
• Short dendrites & short axons (short & stubby)

Question 7

Motor neuron description & role?

Answer 7

• Carry impulses from CNS to effectors (muscles & glands)
• Multipolar as they send & receive info from many sources
• Form synapses & when stimulated release NT’s to trigger a response
• Strength of effector movement depends of rate of nerve impulses

Question 8

Outline the process of synaptic transmission?

(7 parts)

Answer 8

1. Dendrite picks up NT message & sends an electrical impulse (action potential) through cell body, along axon to the terminal buttons
2. Action potential arrives at terminal buttons it needs to be transferred to next neuron
   - It must cross synaptic gap (between pre & post synaptic neuron)
3. End of terminal buttons are synaptic vesicles (contain NT’s)
   - These will convert impulse into NT’s transferred to next neuron
4. As impulse travels to the neuron end reaching synaptic vesicle, they release NT that crosses synaptic gap
5. NT diffuses across the synaptic gap binding to specialised receptors on surface of the next neuron’s dendrites
   - Receptor recognises type of NT & matches it to particular cell (dopamine recognises dopamine)
6. Once next cell is activated, receptor molecules produce an excitatory (increasing further impulses) or inhibitory effect (decreases further impulses) at a post synaptic level
7. Synaptic transmission completed in a fraction of a second through re-uptake
   - Whereby the NT is recycled by the pre-synaptic neuron

Question 9

Where does synaptic transmission take place?

Answer 9

• The synapse from the pre-synaptic membrane & post-synaptic membrane
• Area in between the neurons

Question 10

Define a NT?

Answer 10

• Chemicals released from the end of brain cells (neurons)
• Chemicals allow neurons to communicate
• When neuron releases NT, receptors of post-synaptic neuron pick up this ‘message’ & relay this (electrical impulse) to the next neuron

Question 11

Explain excitatory & inhibitory effect in synaptic transmission?

Answer 11

• Excitation: post-synaptic neuron creates positive charge & make neuron more likely to fire
• Rise in action potential increases activity
• Inhibition: post-synaptic neuron creates negative charge & make neuron less likely to fire
• Fall in action potential decreases activity

Question 12

What is summation in synaptic transmission?

Answer 12

• Excitation & inhibition are summed (added together)

Question 13

Examples of excitatory NT’s?

Examples of inhibitory NT’s?

Answer 13

• Excitatory:
• Glutamate
• Epinephrine
• Dopamine
• Inhibitory:
• GABA
• Serotonin
• Dopamine

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