14 - Response to Stimuli Flashcards
stimulus
detectable change in the internal or external environment of an organism that leads to a response in the organism
receptors
detect stimuli
effectors
produces response (eg. muscle, gland)
coordinator
directs the response brought about by the effector
taxis
a response in which the organisms direction of movement is determined by the direction of the stimulus
positive taxis
towards stimulus
kinesis
a response in which the organism doesn’t move towards or away from a stimulus, but instead changes the speed at which it moves and the rate at which it changes direction
its rate of turning and movement will increase on entering an unfavourable environments as this raises its chances of quickly returning to a favourable environment
tropism
growth of a plant in response to a directional stimulus, involves plant growth factors (hormones)
tropism in plant shoots
display positive phototropism and negative gravitropism
tropism in plant roots
display negative phototropism, positive gravitropism and hydrotropism
IAA
indoleacetic acid, a plant growth factor
stimulates elongation of cells in shoots, inhibits elongation of cells in the root
process of phototropism in the shoots
cells in the tip of the shoot produce IAA, which is then transported down the shoot
IAA is initially distributed evenly through all regions of the shoot
light causes IAA to move to the shaded side of the shoot
greater concentration of IAA builds up on shaded side than the light side
IAA causes elongation of cells, so cells on shaded side elongate more quickly than cells on light side
so shoots bend towards light
CNS
central nervous system
consists of brain and spinal cord
PNS
peripheral nervous system made up of pairs of nerves which originate from either the brain or spinal cord divided into: sensory neurones motor neurones
sensory nerurones
carry nerve impulses from receptors towards CNS
motor neurones
carry nerve impulses from CNS to effectors
subdivided into:
voluntary nervous system - carries nerve impulses to body muscles
autonomic nervous system - carries nerve impulses to glands, smooth muscle and cardiac muscle
reflex arc
receptor detects stimulus and generates nerve impulse in the sensory neurone
sensory neurone passes nerve impulses to CNS
coordinator (relay neurone) links the sensory neurone to the motor neurone in the CNS
motor neurone carries nerve impulse from CNS to effector
effector produces response
pacinian corpuscle
respond to mechanical changes in pressure
a transducer - converts one form of energy into another
sensory neurone, the ending surrounded by layers of connective tissue with viscous gel between
functioning of the pacinian corpuscle
in its resting state, the stretch mediated sodium channels around the neurone are too narrow to allow sodium ions to pass along them
therefore the membrane has resting potential
when pressure is applied to the pacinian corpuscle, it is deformed and the membrane around its neurone becomes stretched
stretching widens the sodium channels and sodium ions are able to diffuse into the neurone
this creates an action potential (nerve impulse)
rod cells
produce b&w images because cannot distinguish between different wavelengths of light
many connected to a single sensory neurone in the optic nerve
used to detect light at very low intensity
to create a generator potential pigment in the rod cells must be broken down, low intensity light provides enough energy for this
gives low visual acuity (not sharp images)
cone cells
3 different types which respond to a different range of wavelengths of light
produce coloured images
often have their own separate bipolar cell connected to a sensory neurone in the optic nerve
respond to high light intensity, otherwise generator potential cannot be created
autonomic nervous system
divided into:
sympathetic - stimulates effectors and so speeds up activity, responsible for fight or flight response
parasympathetic - inhibits effectors and so lows down activity, controls activities under normal resting conditions
cardiac muscle
a myogenic muscle (contraction is initiated from within the muscle itself)
sinoatrial node
SAN - where the initial stimulus for contraction of the heart originates
group of cells located in the wall of the right atrium
contraction of the heart
- wave of electrical excitation spreads out from the SAN across both atria, causing them to contract
- the atrioventricular septum is non-conductive tissue ans so prevents the wave crossing to the ventricles
- the wave of excitation enters the atrioventricular node AVN which is located between the atria
- the AVN conveys a wave of electrical excitation between the ventricles along the bundle of His
- the bundle of His conducts the wave through the septum to the base of the ventricles
- causes the ventricles to contract quickly at the same time
medulla oblongata
region in the brain which controls changes to heart rate
has a centre which increases heart rate (via sympathetic nervous system) and a centre which decreases heart rate (via the parasympathetic nervous system)
chemoreceptors
found in the wall of the carotid arteries (arteries supplying the brain)
sensitive to changes in the pH of the blood (causes by changes in CO2 concentrations)
pressure receptors
found in the walls of the carotid arteries and aorta
sensitive to changes in blood pressure
process of control by chemoreceptors
high concentration of CO2 lowers the pH of the blood
chemoreceptors detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate
increased blood flow caused by a raised heart rate leads to more CO2 being removed by the lungs
CO2 concentration returns to normal
pH returns to normal and so frequencies of impulses decreases and heart rate returns to normal
receptors respond only to…
specific stimulus
stimulation of a receptor leads to…
the establishment of a generator potential
