Chapter 3 Neuronal Communication

Question 1

What is a transducer?

Answer 1

A cell that converts one form of energy into another (sensory receptors convert energy to an electrical impulse)

Question 2

What are the sensory receptors that detect a change in light intensity?

Answer 2

Light sensitive cells in the retina (rods and cones)

Question 3

What are the sensory receptors that detect a change in temperature?

Answer 3

Temperature receptors in the skin and hypothalamus

Question 4

What are the sensory receptors that detect a change in pressure on the skin?

Answer 4

Pacinian corpuscles in the skin

Question 5

What are the sensory receptors that detect a change in sound?

Answer 5

Vibration receptors in the cochlea of the ear

Question 6

What are the sensory receptors that detect a movement?

Answer 6

Hair cells in the inner ear

Question 7

What are the sensory receptors that detect a change in length of muscle?

Answer 7

Muscle spindles in skeletal muscles

Question 8

What are the sensory receptors that detect a change in the air? (smell)

Answer 8

Olfactory cells in epithelium lining the nose

Question 9

What are the sensory receptors that detect chemicals in food?

Answer 9

Chemical receptors in taste buds on tounge

Question 10

What stimuli trigger a change from movement energy to electrical energy

Answer 10

• change in pressure on the skin
• change in sounds
• movement
• change in length of muscle

Question 11

What is a motor neurone?

Answer 11

Neurones that carry an action potential from the Central Nervous System to the effector

Question 12

What is a relay neurone?

Answer 12

Joins sensory neurones to motor neurones (no cell body)

Question 13

What is a sensory neurone?

Answer 13

Neurones that carry an action potential from the sensory receptor to the Central Nervous System

Question 14

What is a myelin sheath?

Answer 14

A fatty sheath made up of Schwann cells that is wrapped tightly around an axon. They prevent movement of ions across the neurone membrane so the action potential must ‘jump’ between the nodes of Ranvier, increasing the speed of conduction.

Question 15

What are nodes of Ranvier?

Answer 15

Gaps between the myelin sheath (1-3mm apart and 2-3μm long)

Question 16

How can non-myelinated neurones be associated with Schwann cells?

Answer 16

Several neurones may be enshrouded in one loosely wrapped Schwann cell.

Question 17

Which types of neurones can be myelinated?

Answer 17

Sensory and motor neurones

Question 18

What is an action potential?

Answer 18

A brief reversal of the potential across the membrane of a neurone causing a peak of +40mV compared to a resting potential of -60mV.

Question 19

Is the inside of the cell more negative or positive at resting potential?

Answer 19

More negative (-60mV)

Question 20

What is the path of an action potential to produce a response?

Answer 20

stimulus - receptor - CNS - effector - response

Question 21

What is the process of producing an action potential?

Answer 21

1. Resting potential :
   - polarised (Inside is more negative: -60mV)
   - Sodium Potassium Pump pumps 3 Na+ ions out and 2 K+ ions in.
   - Sodium channels are close
   - Some potassium channels are open allowing some K+ ions to leave
2. Depolarisation:
   - when stimulus is detected sodium channels open and Na+ enters, making it less negative
   - positive feedback causes voltage-gated sodium channels open
   - generator potential is produced (threshold of -50mV)
   - more positive inside the cell than outside
3. Repolarisation:
   - Sodium channels and sodium voltage gated channels close
   - Potassium channels and voltage gated channels open
   - K+ ions diffuse out the cell down the electrochemical gradient, making inside of cell more negative
4. Hyperpolarisation:
   - Too many ions have left the cell
   - sodium and potassium channels close
   - sodium-potassium pump restores resting potential

Question 22

What is a refractory period?

Answer 22

A period of time after an action potential where it is impossible to generate another action potential because the correct concentrations of ions are being restored. It ensures action potentials only travel in 1 direction.

Question 23

How can action potentials differ?

Answer 23

More frequent action potentials in stronger stimulus

Question 24

What effect do myelin sheaths have on the speed of transmission?

Answer 24

Saltatory conduction - Increases speed of transmission as action potential jumps between nodes of Ranvier due to local currents being elongated so more sodium diffuses along the neuron.

Question 25

How does an action potential diffuse across a membrane?

Answer 25

Depolarisation in the membrane creates electric fields. Depolarisation in one section opens voltage-gated sodium channels in the adjacent section, causing Na+ ions to enter, depolarising this section. Voltage-gated sodium channels in the first section close while potassium voltage-gated channels open, allowing K+ ions to leave so it can repolarise. This continues along the axon.

Question 26

What factors other than myelin can increase the speed of transmission?

Answer 26

• wider diameter
• shorter length

Question 27

What is a cholinergic synapse?

Answer 27

A synapse that uses acetylcholine as its neurotransmitter.

Question 28

What organelles are abundant in the terminal branch of a neurone?

Answer 28

• mitochondria (ATP to move vesicles)
• SER (package neurotransmitters into vesicles)

Question 29

What is the process of an action potential moving between neurones?

Answer 29

1. Action potential arrives at presynaptic bulb and Ca2+ channels open.
2. Calcium ions bind to synaptic vesicles containing neurotransmitters, causing them to move to the pre-synaptic membrane.
3. Vesicles bind with the membrane, releasing the neurotransmitters via exocytosis.
4. The neurotransmitters diffuse across the synaptic cleft and bind to receptors on the post-synaptic membrane.
5. Ligand-gated sodium ion channels open and an action potential is produced so the membrane is depolarised.

Question 30

What happens to acetylcholine after it has diffused across the synapse?

Answer 30

Acetylcholine is broken down into choline and acetic acid by the enzyme acetylcholinesterase (AChE). These products diffuse back into the synaptic bulb where ATP is used to recombine them and make acetylcholine.

Question 31

Where is acetylcholinesterase found?

Answer 31

Synaptic cleft

Question 32

What are excitatory post-synaptic potentials (EPSPs)?

Answer 32

Action potential producing depolarisation

Question 33

What are inhibitory post-synaptic potentials (IPSPs)?

Answer 33

Reduce effect of summation and prevent an action potential in the post synaptic neurone

Question 34

What is summation?

Answer 34

Occurs when the effects of several excitatory post-synaptic potentials (EPSPs) are added together

Question 35

What is temporal summation?

Answer 35

Several action potentials in the same pre-synaptic neuron. producing an action potential in the post-synaptic neurone.

Question 36

What is spatial summation?

Answer 36

Several different pre-synaptic neurones contribute to producing an action potential in one post-synaptic neurone.

Question 37

How can the immune system causes damage to the nervous system?

Answer 37

• Antigens on neurones activate the immune response
• Phagocytes can break down neurones/ schwann cells etc.