Response To Stimuli Flashcards
(43 cards)
Stimulus
Detectable change in the environment
detected by cells called receptors
Nervous system structure
Central nervous system = brain and spinal cord
peripheral nervous system = receptors, sensory and motor neurones
Simple reflex arc
Stimulus (touching hot object)
-> receptor
-> sensory neurone
-> coordinator (CNS / relay
neurone
-> motor neurone
-> effector (muscle)
-> response (contraction)
Importance of simple reflexes
Rapid - short pathway only three neurones & few synapses
autonomic- conscious thought not
involved - spinal cord coordination
protect from harmful stimuli
Tropism
Response of plants to stimuli via growth
can be positive (growing towards stimulus) or negative (growing away from stimulus)
controlled by specific growth factors (IAA)
Specific tropisms
Response to light - phototropism
response to gravity - gravitropism
response to water - hydrotropism
Indoleacetic acid
Type of auxin (plant hormone) controls cell elongation in shoots
inhibits growth of cells in roots made in tips of roots / shoots
can diffuse to other cells
Phototropism in shoots
Shoot tip produces IAA
diffuses to other cells
IAA accumulates on shaded side of shoot
IAA stimulates cell elongation so plant bends towards light
positive phototropism
Phototropism in roots
Root tip produces IAA
IAA concentration increases on
lower (darker) side
IAA inhibits cell elongation
root cells grow on lighter side
root bends away from light
negative phototropism
Gravitropism in shoots
Shoot tip produces IAA
IAA diffuses from upper side to lower side of shoot in response to gravity
IAA stimulates cell elongation so plant grows upwards
negative gravitropism
Gravitropism in roots
Root tip produces IAA
IAA accumulates on lower side of root in response to gravity
IAA inhibits cell elongation
root bends down towards gravity and anchors plant
positive gravitropism
Taxis
Directional response by simple
mobile organisms
move towards favourable stimuli (positive taxis) or away from unfavourable stimuli (negative taxis)
Kinesis
When an organism changes its speed of movement and rate of
change of direction in response to
a stimulus
if an organism moves to a region
of unfavourable stimuli it will
increase rate of turning to return
to origin
if surrounded by negative stimuli,
rate of turning decreases - move
in straight line
Receptors
Responds to specific stimuli stimulation of receptor leads to
establishment of a generator potential - causing a response
pacinian corpuscle
rods
cones
Pacinian corpuscle
Receptor responds to pressure changes
occur deep in skin mainly in fingers and feet
sensory neurone wrapped with layers of tissue
How pacinian corpuscle detects pressure
When pressure is applied, stretch-mediated sodium ion channels are deformed
sodium ions diffuse into sensory neurone
influx increases membrane potential - establishment of generator potential
Rod cells
Concentrated at periphery of retina
contains rhodopsin pigment
connected in groups to one bipolar cell (retinal convergence)
do not detect colour
Cone cells
Concentrated on the fovea
fewer at periphery of retina
3 types of cones containing different iodopsin pigments
one cone connects to one neurone
detect coloured light
Rod and cone cell differences
Rod - more sensitive to light, lower visual acuity, allow monochromatic
vision (black and white)
Cone - less sensitive to light, higher visual acuity, allow colour vision
Visual acuity
Ability to distinguish between separate sources of light
a higher visual acuity means more detailed, focused vision
Why rods have high sensitivity to light
Rods are connected in groups to one bipolar cell
retinal convergence
spatial summation
stimulation of each individual-
cell alone is sub-threshold but because rods are connected in groups more likely threshold potential is reach
Why cones have low sensitivity to light
One cone joins to one neurone
no retinal convergence / spatial
summation
higher light intensity required
to reach threshold potential
Why rods have low visual acuity
Rods connected in groups to one bipolar cell
retinal convergence
spatial summation
many neurones only generate 1
impulse / action potential ->
cannot distinguish between
separate sources of light
Why cones have high visual acuity
One cone joins to one neurone
2 adjacent cones are stimulated, brain receives 2 impulses
can distinguish between separate sources of light
