(5.3) Neuronal Communication

Question 1

What is the reflex arc?

Answer 1

Stimuli –> sensory receptor –> relay neurone –> motor neurone –> effector

Question 2

What is the central nervous system?

Answer 2

Brain and spinal cord

Question 3

Describe the structure of the sensory neurone

Answer 3

• Dendrites connecting to the dendron
• Shorter axon
• Cell body with nucleus outside of the CNS
• Axon Terminals connecting to the axon
• Myelinated sheath with nodes of Ranvier

Question 4

Describe the structure of a relay neurone

Answer 4

• short dendrites
• several divisions of the axon
• cell body with nucleus
• non-myelinated

Question 5

Why is the relay neuron non-myelinated?

Answer 5

It doesn’t need to transmit over long distances

Question 6

What creates a myelinated sheath?

Answer 6

Schwann cell

Question 7

Describe the structure of a motor neuron

Answer 7

• have cell body within the CNS
• long axon
• myelinated sheath
• axon terminals
• dendrites

Question 8

What is the function of a sensory neurone?

Answer 8

Carry an action potential from the sensory receptor to the CNS

Question 9

What is the function of a motor neurone?

Answer 9

Carry an action potential from CNS to an effector

Question 10

What is an effector?

Answer 10

A muscle or a gland

Question 11

What is the function of a relay neurone?

Answer 11

Connect a sensory and motor neurone and to conduct impulses within coordinated pathways

Question 12

How is a myelinated sheath created?

Answer 12

• Schwann cells are wrapped tightly around the neurone
• The sheath consists of several layers of cell membrane and thin cytoplasm
• prevents movement of ions across membranes - can only take place at the nodes of ranvier

Question 13

What is the structure of non-myelinated neurones?

Answer 13

• several neurones enshrouded in one schwann cell - loosely wrapped
• action potential moves along the neurone in waves rather than jumping over the nodes

Question 14

What are the advantages of myelination?

Answer 14

• transmit quickly
• carry over long distances
• more rapid response to stimuli

Question 15

How is a resting potential achieved and maintained?

Answer 15

• sodium and potassium ion pumps use ATP to pump 3 sodium ions out of the neurone and 2 potassium ions into the neurone
• sodium ion channels are kept closed but potassium ion channels are kept open
• potassium then tends to diffuse out
• large anions in the cell cytoplasm give the interior of the cell a negative potential
• cell membrane is then polarised
• potential difference is -60mV across the membrane

Question 16

Describe the process of an action potential

Answer 16

• The sodium ion channels in the plasma membrane open and sodium ions diffuse into the neurone
• The threshold of -60mV is then reached
• positive feedback then causes sodium ion voltage gated channels to open and more sodium ions to diffuse in
• a value of +40mV is then reached causing sodium ion voltage gated channels to close and potassium ion voltage gated channels to open after the action potential
• Potassium ions diffuse out of the neurone
• Hyperpolarisation occurs
• The potassium ion voltage gated channels close and the sodium potassium ion pumps restore the resting potential

Question 17

What is depolarisation during an action potential?

Answer 17

When the sodium ion channels in the plasma membrane open and sodium ions diffuse into the neurone

Question 18

What is repolarisation?

Answer 18

When the potassium ion voltage gated channels open and potassium ions diffuse out of the neurone

Question 19

What is hyperpolarisation?

Answer 19

When the potential difference overshoots

Question 20

Define sensory receptors

Answer 20

Specialised cells that can detect changed in our surroundings. Most are energy transducers.

Question 21

What is an energy transducer?

Answer 21

Convert one energy to another

Question 22

Describe the structure of the pacinian corpuscles

Answer 22

• rings of connective tissue
• abrobias
• sensory neurone fibre

Question 23

What are abrobias?

Answer 23

Cells that produce connective tissue

Question 24

How does the pacinian corpucles work?

Answer 24

• when pressure is applied the rings of connective tissue are deformed
• this pushes on the nerve ending opening the sodium ion channels meaning sodium ions diffuse into the sensory neurone creating a generator potential
• this activates the generator potential as the diffusion of sodium ions has reached a threshold (if enough sodium)

Question 25

How is a initiation failed?

Answer 25

the pressure is small that even though the sodium ion channels open the threshold is not reached meaning an action potential is not intiated also called the all or nothing law

Question 26

How are action potentials transmitted?

Answer 26

- sodium ion channels open (at point of action potential in neurone) - open sodium ion channels allow sodium to diffuse into the neurone - continues to diffuse sideways along the neurone called a local current (movement of charged particles) - local current causes a slight depolarisation further along the neurone causing voltage gated channels to open - open voltage gated channels causes further depolarisation along the neurone (action potential has been moved)

Question 27

What is the refractory period?

Answer 27

- After an action potential has taken place the sodium and potassium ions are in the wrong place - impossible to stimulate an action potential - restored by sodium and potassium ion pumps

Question 28

What is a saltatory conduction?

Answer 28

- sodium/potassium ions can't diffuse through the myelin sheath - diffusion occurs at the nodes of ranvier - local currents are elongated in myelinated neurones - sodium ions diffuse from one node to the next - action potential appears to jump - this is called a saltatory conduction

Question 29

How can the intensity of a stimulus be detected by the brain?

Answer 29

- The frequency of transmission - the more intense the stimulus is the more sodium channels open - this what causes the production of more generator potentials

Question 30

Define synapse

Answer 30

A junction between two or more neurones where the neurones can communicate

Question 31

Describe the structure of the post-synaptic membrane

Answer 31

- contains specialised sodium ion channels that respond to neurotransmitters - channels consist of 5 polypeptide molecules 2 of which have receptors for acetylcholine - receptor sites are complementary - when acetylcholine present in the synaptic cleft, binds to the 2 receptor sites and causes the sodium ion channels to open

Question 32

Describe the transmission across a synapse

Answer 32

- action potential arrives at the synaptic bulb - voltage-gated calcium ion channels open - calcium ions diffuse into the synaptic bulb - calcium ions cause the synaptic vesicles to move to and fuse with the pre-synaptic membrane - acetylcholine is released by exocytosis - acetylcholine molecules diffuse across the cleft and then bind to the receptor sites on the sodium ion channels in the post-synaptic membrane - sodium ion channels open and sodium ions diffuse across the post-synaptic membrane into the post-synaptic neurone - a generator potential or excitatory post-synaptic potential is created - if sufficient generator potentials combine then the potential across the post-synaptic membrane reaches the threshold potential - a new action potential is created in the post-synaptic neurones

Question 33

What are converging neurones and spatial summation?

Answer 33

- several pre-synaptic membranes converge on one post-synaptic neurone - allows action potentials from different parts of CNS to generate an action potential in post-synaptic membrane - Useful when multiple stimuli are warning of danger

Question 34

What are IPSPs?

Answer 34

- Inhibitory post-synaptic potential - several EPSPs (excitatory post synaptic potential) could be be prevented from producing an action potential because of one IPSP - reduce the effect of summation

Question 35

What are the main two IPSPs?

Answer 35

- GABA - Glycine

Question 36

What are divergent neurones?

Answer 36

- one pre-synaptic neurone diverges to several post-synaptic neurones - This allows one action potential to be transmitted to several parts of the CNS - Useful in the reflex arc as one part of the post-synaptic neurone elicit a response whilst another informs the brain

Question 37

What is one-way neurone transmission?

Answer 37

- synapses ensure that impulses are carried in the correct direction - only the pre-synaptic bulb contains vesicles of acetylcholine - if action potential starts half way along a neurone and ends at the post-synaptic membrane a response is not caused in the next cell

Question 38

How do synapses filter?

Answer 38

- synapses filter out unwanted low-level signals