stimuli and response 3.6 Flashcards
what is a stimulus
a detectable change in the internal or external environment of an organism that leads to a response
function of receptors
detect stimuli
specific to one type of stimulus
detect information from inside body and the surroundings
function of coordinator
formulates a suitable response to stimulus
function of effector
produces a response
muscle or gland
how do hormones differ as an effector to muscles
relatively slow
found in both plants and animals
how do muscles differ as an effector to hormones
more rapid
found only in animals
summary of sequence of response
stimulus > receptor > coordinator > effector > response
what is taxis
a simple response whose direction is determined by the direction of the stimulus
what is positive taxis
moves towards stimulus
what is negative taxis
moves away from stimulus
what is kinesis
a response when an organism does not move towards or away from a stimulus. changes the speed at which it moves and the rate that it changes direction.
what is a tropism
direct stimuli that contribute to plant survival are responded to by positive or negative tropisms.
light tropism
phototrophic
gravity tropism
gravitropic
water tropism
hydrotropic
how does IAA bring about phototropism in plants
controls plant cell elongation
how does IAA affect root growth in response to light
high conc of IAA inhibits cell elongation in roots
cell elongation is greater on light side
roots are negatively phototropic
how does IAA affect root growth in response to gravity
IAA produced in root tip
greater conc of IAA builds up on the lower side of the root
cells on lower side elongate less causing root to bend downwards
how do shoots respond to gravity
greater conc of IAA on lower side increases elongation on lower side
shoots grow upwards away from gravity
IAA roots vs shoots
inhibits root elongation
stimulates shoot elongation
what is a sensory neurone
provides a sensory input
carries signals to the CNS from sensory organs
what is a motor neurone
provide a motor output
carry signals from the CNS that control activity of muscles and glands
what is the voluntary nervous system
controls involuntary movements by activating skeletal muscles
what is the autonomic nervous system
controls involuntary responses by influencing organs, glands, and smooth muscle
what is a reflex action
an involuntary response that is very rapid
not under control of the brain
protective, prevents damage to the body
order in reflex arc (8)
stimulus
receptor
sensory neurone
intermediate neurone
spinal chord
motor neurone
effector
response
difference between kinesis and taxis
kinesis is non directional
taxis is directional
difference between kinesis and tropism
kinesis in animals
tropism in plants
what is a traducer (sensory receptor is an example of a traducer)
detect one form of energy and convert it into electrical energy
what is a pacinian corpuscle made of
a single sensory neurone in the centre of a layer of tissues, each separated by gel
what happens when pressure is applied to skin around a pacinian corpuscle
changes the shape of the pressure sensitive sodium channels
causes them to open
name of the sodium channel in a pacinian corpuscle
stretch mediated sodium channel
what happens when sodium channels (in pacinian corpuscle) are opened
sodium ions diffuse in
membrane is depolarised and therefore produces a generator potential
this creates an action potential that is passed along the neurone
what are the two main light receptor cells
rods and cones
cone cells distribution
higher concentration in the fovea
rod cells distribution
spread evenly across retina but none in fovea
cone cells visual activity and why
high
each cone cell has a single connection to optic nerve
rod cells visual activity and why
low
several rod cells share a connection to the optic nerve
light intensity cone cells
sensitive to high light intensity
light intensity rod cells
sensitive to low light intensity
how many types of rod cells
1
how many types of cone cells
3
how many connections do rod cells have to bipolar cells
3:1
how many connections do cone cells have to bipolar cells
1:1
what pigment is broken down leading to a generator potential in cone cells
idopsin
how is an action potential produced in a rod cell
light shines on rhodopsin
pigment breaks down
creates a generator potential
this stimulates an action potential
why are multiple rod cells connected to a single bipolar cell
a threshold value has to be exceeded before a generator potential is made in a bipolar neurone. 3:1 makes this more likely
what is the consequence of many rod cells linking to a single bipolar cell
even if many rods detect light only a single impulse will be sent to the brain
brain cannot distinguish between separate sources of light
results in poor visual activity
consequence of each cone cell being attached to a single bipolar cell
if 2 cone cells stimulated then the brain receives 2 separate impulses
brain is able to distinguish between the 2 and so is able to resolve two dots close together
sympathetic nervous system
most dominant during stress and excitement
parasympathetic nervous system
most dominant during rest and sleep
