Neuronal Communication Module 5.1.3

Question 1

What is a description and function of dendrons and dendrites?

Answer 1

-Dendrons split into smaller dendrites
-They carry nerve impulses towards the cell body

Question 2

What is a description and function of the axon?

Answer 2

-Elongated nerve fibres which can be short or long depending on the type of neuron
-Carry nerve impulses away from the cell body

Question 3

What is a transducer?

Answer 3

-A cell that can convert one form of energy into another

Question 4

What is the structure and function of a sensory neuron?

Answer 4

-They have short dendrites and one long dendron carries action potential from receptor cells to the cell body
-One short axon then carries the action potential to the CNS
-Specialized cells and transducers
-Each sensory receptor only responds to one type of stimulus

Question 5

What is the structure and function of motor neurones?

Answer 5

-Short dendrites carry action potential from CNS to a cell body
-One long axon then carries cell body to effector cells

Question 6

What are the structural differences between a motor and sensory neuron?

Answer 6

-Sensory neuron has short dendrites and long dendrons whereas motor neuron only has short dendrites
-Sensory neuron has a short axon whereas motor neuron has a long axon

Question 7

What is the structure and function of Relay neurones?

Answer 7

-Short dendrites that carry action potential away from sensory neurones to cell body
-One axon carries action potential to motor neurones

Question 8

What are the four main types of sensory receptors, their stimulus and an example of an organ they belong to?

Answer 8

1. Mechanoreceptor- Pressure and movement- Skin
2. Chemoreceptor- Chemical- Nose
   3.Thermoreceptor- Heat- Tongue
   4.Photoreceptor- Light- eye

Question 9

What is the membrane of a sensory receptor-like when not being stimulated?

Answer 9

-There is a difference of charge between the inside and outside of the cell, the inside is negatively charged relative to the outside

Question 10

What is a generator potential?

Answer 10

-When a stimulus is detected the receptor cell changes permeability ions move into and out of the cell via pumps and channels
-Ions carry a charge so there is a change in potential difference, this change due to a stimulus is a generator potential

Question 11

What will happen if a stimulus is too small?

Answer 11

-A smaller stimulus will produce a smaller movement of ions across the membrane
-This causes a smaller change in potential difference across the membrane and the threshold level isn’t reached so there is no action potential

Question 12

When is an action potential triggered and what is it?

Answer 12

• If the generator potential is big enough
  -An action potential is a nerve impulse that travels along a neuron

Question 13

What is the Pacinian Receptor?

Answer 13

-Sensory receptor, found in the skin
-Contains Mechanoreceptors that detect mechanical pressure and vibration

Question 14

What happens when pressure is applied to the Pacinian Corpuscle?

Answer 14

-Stretch mediated sodium channels in the membrane of the neurone change shape and sodium ions diffuse across the membrane into the neurone.
-This creates a generator potential and if it reaches the threshold potential an action potential is triggered

Question 15

Why do you not constantly receive electrical impulses from the corpuscles?

Answer 15

-The corpuscles only respond to changes in pressure so when it is constant they stop responding therefore you don’t receive mundane electrical impulses

Question 16

How do neurones set up a resting potential?

Answer 16

1. Sodium-potassium pumps pump more sodium out of the cell and they can’t diffuse back in as they aren’t permeable to the membrane
2. Potassium inside the cell due to the pump can diffuse back out through potassium pumps
3. As a result the cell is negative inside the cell as there are more positive ions outside the membrane

Question 17

Describe the propagation(spread) of an action potential down the axon?

Answer 17

1. First region becomes depolarised and sodium ions are attracted to the negative ions in the next region so diffuse sideways
   2.Process continues creating a wave of depolarisation as the first area becomes repolarised.

Question 18

What is the refractory period and why is it important?

Answer 18

-After an action potential the neurone cannot become excited straight away
-This is important as it ensures action potentials don’t overlap and are unidirectional

Question 19

What are the two stages of the refractory period?

Answer 19

-Absolute refractory period: nothing happens
-Relative refractory period: during this period another action potential can only be initiated if stimulus is more intense than normal threshold.

Question 20

What is the difference between myelinated and non-myelinated neurones?

Answer 20

-The axon of myelinated neurones are covered in a myelin sheath made of layers of plasma membrane, non-myelinated do not have these

Question 21

Describe saltatory conduction in myelinated neurones?

Answer 21

1. Sodium and potassium ions cannot diffuse through the myelin sheath, and the neurone is only permeable at the nodes of Ranvier
2. This allows the depolarisation to ‘jump’ from node to node, the sodium ions can also diffuse rapidly, making conduction faster.

Question 22

Why is saltatory conduction more efficient?

Answer 22

-It saves time and energy because every time a channel opens it takes time for ions to move it also requires ATP so reducing the number of times a membrane is repolarised it reduces energy.

Question 23

What are two factors that affect the speed of action potentials?

Answer 23

-Axon diameter: bigger the axon diameter the faster the impulse due to less resistance for diffusion of ions
-Temperature: the higher the temperature the faster the nerve impulse up until the temperature at which proteins begin to denature

Question 24

What is the difference in action potentials between a large and small stimulus?

Answer 24

-The size of the stimulus does not determine the size of the action potential instead it determines the number of action potentials in a given time

Question 25

How does the brain determine the intensity of a stimulus?

Answer 25

-From the frequency of action potentials, the higher the frequency the higher the intensity.

Question 26

What are the key features of a synapse?

Answer 26

-Synaptic cleft: gap between axon terminal of a neurone and dendrite of another
-Presynaptic neurone: neurone where the impulse arrives
-Postsynaptic neurone: neurone that receives neurotransmitter
-Synaptic vesicle: contains neurotransmitters
-Neurotransmitter receptors: where the neurotransmitter binds to on the postsynaptic neurone

Question 27

What are the two types of neurotransmitters?

Answer 27

-Excitatory: result in depolarization of a postsynaptic neurone and if a threshold is reached an action potential is triggered
-Inhibitory: hyperpolarize the postsynaptic neurone, preventing an action potential

Question 28

What is synaptic divergence and synaptic convergence?

Answer 28

-Synaptic divergence: when one neurone connects to many neurones, electrical impulse can be lessened
-Synaptic convergence: when many neurones connect to one, electrical impulse can be amplified

Question 29

What is spatial summation?

Answer 29

-When a number of presynaptic neurones connect to one postsynaptic neurone. They all release neurotransmitters which build up to a high enough level for an action potential

Question 30

What is temporal summation?

Answer 30

-When a single presynaptic neurone releases neurotransmitter as a result of an action potential several times, this builds up neurotransmitters in the synapse until a sufficient amount is present to trigger an action potential.

Question 31

How can drugs, poisons and toxins affect synapses?

Answer 31

-They can inhibit the enzyme that breaks down the neurotransmitter, or the release of neurotransmitters
-Some chemicals are the same shape of Neurotransmitters so can mimic their actions or block the receptors so they can’t bind