stimulus + receptors Flashcards
what is a stimulus?
change in the internal or external
environment, such as light, temperature etc..
differences between electrical impulse response vs hormone response
impulse:
specific to one target cell only
as it releases neurotransmitter directly onto it, producing a response that is usually rapid, short-lived and localised.
hormone:
bind to complementary binding sites of protein receptors on target cells and produce responses that are usually slow, long-lasting and widespread.
what is a tropism?
a directional growth response of a PLANT to a stimulus.
describe production of IAA in shoot tips vs root tips in response to light + gravity
shoot tips:
1. IAA is produced in the shoot tip + diffuses to the lower/shaded side of the
shoot, increasing its concentration.
2. Stimulates cell elongation so cells on lower/shaded side elongate more than the cells on the light side.
3. Causes directional growth towards light and away from gravity (upwards) for photosynthesis- positive phototropism, negative gravitropism
root tips:
1. IAA is produced in the root tip + diffuses towards shaded side, increasing
its concentration.
2. Inhibits cell elongation so the cells on shaded side elongate less than the cells on the upper side/ light side.
3. Causes directional growth away from light and towards
gravity (downwards)- negative phototropism, positive phototropism
interpret the data
interpret the data
interpret the data
interpret the data
what is kinesis?
Non-directional movement to a stimulus. It involves increasing/decreasing random movements,
including speed of movement and the rate at which it changes direction.
give example of kinesis
Woodlice move faster when the humidity is low and change direction less (less non-directional
random movements).
Woodlice move slower when the humidity is high and change direction more (more non-directional random movements). Woodlice are more likely to stay in favourable conditions (high
humidity)
what is a taxis?
directional movement to a stimulus
give example of taxis
Earthworms move away from light- negative phototaxis
* More chance of survival as move into soil
o More likely to find food/ mate
o More likely to avoid predators
o Less likely to dehydrate
which 2 divisions is the nervous system controlled?
- CNS (Central Nervous System)– the brain and the spinal cord
- Peripheral nervous system- nerves that originate from brain or spinal cord that cover the rest of the
body
which 2 divisions can the peripheral nervous system be divided into?
- Voluntary nervous system- which is under voluntary control (conscious).
- Autonomic nervous system- it is involuntary (subconscious control).
what is a reflex?
rapid, involuntary response to a stimulus.
chain of events in a reflex arc
stimulus-receptor-sensory neurone-intermediate neurone-motor neurone-effector-response
why are reflex actions important?
- Rapid – due to short pathway and only 3 synapses (slowest part of nerve impulse)
- Inate - Do not have to be learned, (effective from birth)
- Prevent damage to tissues.
- Help escape from predators
- Have a role in homeostasis (maintaining internal conditions)
- Involuntary / automatic – don’t require brain, but impulses are sent to the brain which can override
reflex if necessary - Allows food / mates / suitable conditions to be found
stimulus of receptors leads to what
a generator potential
where are pacinian corpuscles found?
mainly in skin
draw a pacinian corpuscle
how do pacinian corpuscles cause a generator potential
- Pressure on the skin causes the lamellae to become deformed+ stretch mediated sodium ion channels open in the membrane of the sensory neurone.
- Sodium ions diffuse into the axon, causing depolarisation forming a generator potential.
- The greater the pressure on the pacinian corpuscle the more sodium ion channels open, the more sodium ions diffuse in and the larger the depolarisation.
- If the generator potential reaches threshold, action potentials are created and nerve impulses pass along the sensory neurone membrane.
- The frequency of impulses relates to the intensity of the stimulus – the greater the pressure (stimulus) the more frequent impulses
describe rods in the retina
- found mainly at the periphery (less at the fovea).
- they do not allow colour vision
- contains the pigment rhodopsin (cannot distinguish different wavelengths of light)
- higher sensitivity to light (stimulated in low light
intensities) - have low visual acuity, this means the image has a
poor resolution.
describe cones in the retina
- present mainly in the fovea (where the lens focuses the light)
- Contains the pigment iodopsin
- they allow colour vision as there are 3 different types of cone cell, each with an iodopsin which responds to different wavelengths of light. Blue sensitive, green sensitive and red sensitive cone cells.
- Lower sensitivity to light (only stimulated in high light
intensities) - they have high visual acuity with a higher resolution.
how do rod/cones detect light
Light causes the pigment (rhodopsin or iodopsin) to break down (bleach) causing depolarisation and a generator potential. If the
generator potential reaches threshold, action potentials are transmitted to the brain forming an image.
