stimulus and response 6a, 6b Flashcards
(33 cards)
What is a stimulus?
A detectable change in the internal or external environment.
What is a receptor?
A cell or protein that detects stimuli and converts it into an electrical impulse.
What is an effector?
A muscle or gland that brings about a response to a stimulus.
What is the role of the nervous system?
To detect stimuli, process information, and coordinate responses via electrical impulses.
What are the three types of neurones?
Sensory neurones: carry impulses from receptors to CNS
Relay neurones: connect sensory and motor neurones in the CNS
Motor neurones: carry impulses from CNS to effectors
What is a reflex?
A rapid, automatic response to a stimulus that does not involve conscious processing.
Why are reflexes important?
They protect the body from harm by providing fast responses.
Describe the reflex arc.
Stimulus → receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector → response
What are tropisms?
Growth responses of a plant towards or away from a stimulus.
What is phototropism?
Growth of a plant in response to light (e.g., shoots grow towards light).
What is gravitropism (geotropism)?
Growth of a plant in response to gravity (e.g., roots grow downward).
What is the role of auxins in tropisms?
Auxins (e.g., IAA) promote cell elongation in shoots and inhibit it in roots, creating curvature towards/away from stimuli.
What is resting potential?
The voltage across a neurone membrane at rest, around -70 mV (inside is more negative).
How is resting potential maintained?
By the sodium-potassium pump and K⁺ channels — 3 Na⁺ out, 2 K⁺ in.
What is an action potential?
A temporary reversal of membrane potential caused by ion movement across the membrane.
Describe the sequence of an action potential.
Stimulus opens Na⁺ channels
Depolarisation: Na⁺ floods in
Repolarisation: K⁺ channels open, K⁺ leaves
Hyperpolarisation: too much K⁺ leaves
Resting potential restored
What is the refractory period?
A short time when a neurone cannot fire again — ensures one-way transmission.
What is a synapse?
A junction between two neurones.
How is a signal transmitted across a synapse?
Impulse arrives → Ca²⁺ channels open
Vesicles release neurotransmitter (e.g. acetylcholine) into synaptic cleft
Neurotransmitter binds to receptors → Na⁺ channels open → new impulse
How is the signal stopped?
Enzymes break down neurotransmitter in the synaptic cleft.
What is spatial summation?
Multiple neurones release neurotransmitters to trigger one post-synaptic neurone.
What is temporal summation?
One neurone releases neurotransmitter repeatedly in a short time to exceed threshold.
How do stimulants affect synapses?
Increase neurotransmitter release or inhibit breakdown — heightening responses.
How do depressants affect synapses?
Reduce neurotransmitter activity — slowing responses.
