Neuronal communication Flashcards
What are sensory receptors for? (2)
Detecting changes in its environment (1) and converting the stimulus into a nervous impulse (1)
What does it mean when sensory receptors are referred to as ‘transducers’? (1)
They convert stimuli into nervous impulses (1)
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
- Mechanorecptor; pressure and movement, skin. (2)
- Chemorecptor; chemicals, nose/tongue. (2)
- Thermoreceptor; heat, tongue/skin. (2)
- Photoreceptor; light, eyes. (2)
Order the following components (1) : relay neurone, effector, sensory neurone, motor neurone, receptor
Receptor -> sensory neurone -> relay neurone -> motor neurone -> effector (1)
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? (2)
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).
The resting potential of an axon is -70mv. Describe how this is maintained. (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)
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.
- Sodium (1)
- Down (1)
- Difference (1)
- Depolarised (1)
- Negative (1)
- Positive (1)
- Voltage (1)
- Negative (1)
- Repolarisation (1)
Following repolarisation, potassium voltage-gated channels are slow to close. What does this result in?
Hyperpolarisation/the p.d becomes lower than the resting potential (1), as too many potassium ions diffuse out the axon (1)
What does ‘refractory period’ refer to? (2)
The period of time starting from repolarisation (1) and ending once the resting potential is established again (1)
Describe the transmission of a nerve impulse along the axon. (3)
- Depolarisation moves in one direction across the axon. (1)
- Depolarisation of one section of the axon triggers sodium channels to open further down the axon. (1)
- The previous section of the axon is in the repolarisation stage (sodium channels closedm potassium channels open). (1) This makes it unresponsive. (1)
What is the all or nothing principle? (2)
The stimulus must depolarise the receptors beyond the threshold level to trigger the sensory neurone to transmit a nervous impulse. (1)
No matter how strong the stimulus, the size of the action potential is the same (however, stimulus strength may affect frequency). (1)
State two purposes of the refractory period. (2)
- Ensuring action potentials are discrete events/prevents them from merging. (1)
- Prevents current from travelling backwards. (1)
- Ensures that impulse travels in one direction. (1)
- Determines the frequency at which impulses can be transmitted across an axon. (1)
Explain saltatory conduction. (4)
- It is the transmission of nervous impulses in myelinated neurones. (1)
- In the sections of the axon surrounded by a myelin sheath, depolarisation cannot occur. (1)
- Action potentials only occur at the nodes of Ranvier. (1)
- The attraction between sodium ions and the negative potential difference at the next node of Ranvier produces a localised electrical circuit. (1)
- This induces the opening of sodium voltage-gated channels at the next node, causing the nervous impulse to ‘jump’. (1)
How does diameter of an axon affect the speed of conduction? (3)
How does temperature affect the speed of conduction? (2)
- Thicker axons have a greater speed of conduction. (1)
- The axon membrane has a larger surface area over which diffusion of ions can occur. (1)
- Therefore, the rate at which action potentials and depolarisation occurs is higher. (1)
- There is less electrical resistance in the cytoplasm of wider axons. (1)
- Colder temperatures mean potassium and sodium ions have less kinetic energy in facilitated diffusion. (1)
- Rate of diffusion, therefore, is slower. (1)
Define ‘synapse’. (1)
The junction where two neurones meet (1)
