Nerves

Question 1

Name 6 sensory receptors and where they’re found

Answer 1

1. Light sensitive cells in the retina of the eye
2. Olfactory cells lining the inner surface of the nasal cavity
3. Taste buds in the tongue
4. Pressure receptors in the skin
5. Sounds receptors in the inner ear
6. Muscle spindles in muscles

Question 2

Name 3 types of neurone

Answer 2

1. Sensory neurone
2. Motor neurone
3. Relay neurone

Question 3

Where do sensory neurones carry action potentials to/from?

Answer 3

From a sensory receptor to the CNS

Question 4

Where do motor neurones carry action potentials to/from?

Answer 4

From the CNS to an effector

Question 5

Where do relay neurones carry action potentials to/from?

Answer 5

Between sensory and motor neurones

Question 6

What is a polarised membrane?

Answer 6

One that has a potential difference across it. This is the resting potential.

Question 7

What is depolarisation?

Answer 7

The loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.

Question 8

What is a generator potential?

Answer 8

A small depolarisation caused by sodium ions entering the cell.

Question 9

What is an action potential?

Answer 9

When the membrane is depolarised to a value of about +40mV. It’s an all or nothing response.

Question 10

What are the features of nerve cells that make them specialised?

Answer 10

• Very long - transmit signals over a long distance
• Gated ion channels to control the entry/exit of ions
• Sodium/potassium ion pumps that actively transport sodium and potassium ions
• Surrounded by a fatty sheath called the myelin sheath that insulates the neurone from electrical activity in nearby cells
• Many mitochondria in the cell body

Question 11

What is the resting potential?

Answer 11

The potential difference or voltage across the neurone cell membrane when the neurone is at rest. It is about -60mV inside the cell compared to outside.

Question 12

What is the sequence of events involved in generating an action potential?

Answer 12

1. The membrane is polarised to start (-60mV)
2. Depolarisation occurs - threshold value of -50mV reached
3. Influx of sodium ions via voltage-gated sodium ion channels
4. Action potential reached (+40mV)
5. Repolarisation
6. Hyperpolarisation - the potential difference overshoots slightly
7. Refractory period
8. Original potential difference restored

Question 13

What’s the refractory period?

Answer 13

A short time after the action potential when it is impossible to stimulate the cell membrane to reach another action potential.

Question 14

Why is the refractory period important?

Answer 14

It allows the cell to recover after an action potential and ensures that action potentials are only transmitted in one direction.

Question 15

What are local currents?

Answer 15

The movements of ions along the neurone. The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration.

Question 16

How does the myelin sheath affect the speed of action potential transmission?

Answer 16

The ionic exchanges that cause an action potential can only occur at the nodes of Ranvier. In myelinated neurones this means the local currents are elongated and sodium ions diffuse along the neurone from one node of Ranvier to the next. This is saltatory conduction, and it speeds up the transmission of the action potential..