Neuronal communication

Question 1

What are sensory receptors for? (2)

Answer 1

Detecting changes in its environment (1) and converting the stimulus into a nervous impulse (1)

Question 2

What does it mean when sensory receptors are referred to as ‘transducers’? (1)

Answer 2

They convert stimuli into nervous impulses (1)

Question 3

Each sensory receptor is specific to a single type of stimulus. Describe the stimuli and an examplery sensory organ attached to each of these types of sensory receptors (8) :

• Mechanorecptor
• Chemoreceptor
• Thermoreceptor
• Photoreceptor

Answer 3

• Mechanorecptor; pressure and movement, skin. (2)
• Chemorecptor; chemicals, nose/tongue. (2)
• Thermoreceptor; heat, tongue/skin. (2)
• Photoreceptor; light, eyes. (2)

Question 4

Order the following components (1) : relay neurone, effector, sensory neurone, motor neurone, receptor

Answer 4

Receptor -> sensory neurone -> relay neurone -> motor neurone -> effector (1)

Question 5

Schwann cells produce membranous layers that grow around the axon of neurones (myelin sheath). What is the purpose of this? (2)

How does it work?

Answer 5

Acts as an insulating layer (1). Myelinated neurones conduct electrical impulses at a faster rate (1).

Works by gaps in the mylelin sheath called nodes of Ranvier (1). The electrical impulse ‘jumps’ from node to node (1).

Question 6

The resting potential of an axon is -70mv. Describe how this is maintained. (6)

Answer 6

• Sodium-potassium pumps (carrier proteins) are in the membranes of neurones. (1)
• Pumps use ATP to actively transport 3 sodium ions out and 2 potassium ions in. (1)
• More positive ions outside axon than inside/maintains electrochemical gradient. (1)
• The membrane contains channel proteins that allow potassium and sodium ions to move through by facilitated diffusion. (1)
• The protein channels are less permeable to sodium ions (1), resulting in potassium ions diffusing out (down the concentration gradient) at a faster rate than the diffusion of sodium ions into the axon. (1)

Question 7

Fill in the blanks about producing an action potential (9) :

Stimuli cause ___ ion channels to open, allowing the ions to diffuse ___ the electrochemical gradient. Once the potential ___ has reached a certain threshold, the neurone is said to be de___ and an action potential is generated. As the inside of the axon becomes less ___, more channels open (___ feedback). Once the p.d has reached around 30mv the sodium ___-gated channel proteins close, while potassium channels open (___ feedback). As potassium ions diffuse out the axon and sodium ions are prevented from diffusing in, ___ occurs.

Answer 7

• Sodium (1)
• Down (1)
• Difference (1)
• Depolarised (1)
• Negative (1)
• Positive (1)
• Voltage (1)
• Negative (1)
• Repolarisation (1)

Question 8

Following depolarisation, potassium voltage-gated channels are slow to close. What does this result in?

Answer 8

Hyperpolarisation/the p.d becomes lower than the resting potential (1), as too many potassium ions diffuse out the axon (1)