Flashcards in Resting + Action Potentials and Receptors (Chapter 15) Deck (45)
What is a receptor cell?
- A cell that responds to a stimulus by initiating an action potential
- Transducers ∴ they convert energy in one form into energy in an electrical impulse in a neurone
Where are receptor cells often found?
In sense organs
What are chemoreceptors?
Specialised cells which detect a specific type of stimulus and influence the electrical activity of a sensory neurone e.g. those in the taste buds
What are (some) touch receptors?
The ends of sensory neurones
Describe the structure of the tongue
1) it is covered in many papillae (small bumps)
2) each papilla has many taste buds over its surface
3) within each taste bud are chemoreceptors
4) each chemoreceptor is covered with receptor proteins that detect the different chemicals from food or drink that dissolve in saliva
5) each receptor detects a different type of chemical, giving us a different sensation - five tastes: sweet, sour, salt, bitter and umami (savoury)
Describe how chemoreceptors in taste buds work
1) A chemical stimulus binds to a chemoreceptor, triggering Na+ to diffuse through highly selective channel proteins in the CSM of the microvilli, leading to depolarisation of the membrane - this increase in positive charge inside the cell is the receptor potential
2) if there is sufficient stimulation by Na+ inside the mouth, then the receptor potential becomes large enough to stimulate the opening of voltage-gated Ca2+ channels
3) Ca2+ enter the cytoplasm and stimulates the exocytosis of vesicles containing neurotransmitter from the basal membrane
4) the neurotransmitter stimulates an action potential in the sensory neurone that transmit impulses to the taste centre in the cerebral cortex of the brain
What are chemoreceptors in the tongue directly influenced by?
What happens when receptors are stimulated?
They are depolarised
What happens when there is a very weak stimulus for receptor cells?
The cells are not depolarised very much and the sensory neurone is not activated to send impulses
What happens where there is a stronger stimulus for receptor cells?
The sensory neurone is activated and transmits impulses to the CNS
What is the all-or-nothing law?
Neurones either transmit impulses from one end to the other or they do not
What happens if the receptor potential is below a certain threshold?
The stimulus only causes local depolarisation of the receptor cell
What happens if the receptor potential is above a certain threshold?
The receptor cell stimulates the sensory neurone to send impulses and action potentials are initiated in the sensory neurone
What do action potentials always have the same of and what does this mean?
- Action potentials always have the same amplitude
- ∴ if the intensity of the stimulus increases, the action potentials are produced more frequently, they do NOT become bigger