Stimuli, Responses, Reflexes Flashcards
Taxes
A response in which the whole body moves towards a favourable directional stimuli or away from an unfavourable one
Keneses
A response where an organism changes the speed at which it moves and the rate at which it changes direction as a result of a stimuli
Tropism
Growth of part of a plant in response to a directional stimuli
Phototropism
Cells in tip of shoots produce IAA which is evenly transported down shoot
Light causes movement of IAA from light to shaded side
IAA conc. on shaded side > on light side
IAA promotes cell elongation in shaded side more than light side
So shoot grows towards light
Gravitropism
Cells in tip of roots produce IAA which is evenly transported along root
Gravity causes movement of IAA from upper side to lower side
IAA conc. on lower side > on upper side
IAA inhibits cell elongation in lower side more than upper side
So root grows downwards
Role of IAA + Experiment !!!!!!!!!!!
Removed Tip: No response shows tip detects stimuli or causes response or both
Covered tip: No response shows tip detects stimuli
Central and Peripheral Nervous System
CNS: mad up of the brain and spinal chord
PNS: made up of a pair of nerves that originate form the brain or spinal chord, contains sensory and motor nervous system
Voluntary and Autonomic Nervous System
Both part of motor nervous system
Voluntary: carries nerve impulse to muscle cells under conscious control
Autonomic: carries nerve impulses to smooth muscle, cardiac muscle and glands subconsciously
Reflex Arc
Stimulus
Receptor
Sensory Neurone
Intermediate Neurone in CNS
Motor Neurone
Effector
Response
Structure of Pacinian Corpuscle
A single neurone ending with stretch mediated sodium channels.
Neurone ending surrounded by layers of connective tissue with viscous gel between
Capillary runs along base layer of the tissue.
All in a capsule
Pacinian Corpuscle Response to Stimuli
Pressure applied to Pacinian corpuscle.
Deformed and so the membrane of the neurone is stretched.
This widens and opens the sodium ion channels and sodium ions diffuse into the neurone.
This depolarises the neurone and thus creates a generator potential
When the generator potential is large enough it triggers an action potential that passes down the neurone.
Rods
Black and White. More rods than cones. Evenly distributed around periphery but not in fovea
Many rod cells to a single bipolar neurone
Detect low intensity light due to summation as many rod cells are used to reach the threshold for the generator potential to be created.
Low visual acuity as many rods to one neurone so less information sent to the brain so lower resolution images.
Generator potential created by breaking down pigment rhodopsin
Cones
Three types, each detect different range of wavelengths of light (red, blue and green). Located mainly in fovea.
Each cone cell to a single bipolar cell and one sensory neurone.
High visual acuity as more information sent so higher resolution images
Lack of summation therefore harder to reach threshold for generator potential therefore only respond to high light intensity.
Generator potential created by breaking down pigment iodopsin
Pathway of light stimuli to brain
Photoreceptor
Bipolar neurone
Ganglion cell of optic nerve
Brain
Control of Heart Rate
Sinoatrial node, located in wall of right atrium, sends a wave of electrical activity to both atria.
Both atria contract, atrioventricular septum prevents wave reaching ventricles.
Wave reaches atrioventricular node, in wall between atria, which sends a wave of electrical activity between the ventricles down Purkyne tissue in bundle of His which releases the wave at the apex.
Both ventricles contract
Sympathetic vs Parasympathetic Nervous System
Sympathetic: stimulates effectors in stressful conditions. (increases heart rate)
Parasympathetic: inhibits effectors to maintain normal conditions. (decreases heart rate
Chemoreceptors for heart rate
CO2 is acidic so high conc. means low pH of blood.
Detected by chemoreceptors in wall of carotid arteries and aorta.
Increase in frequency of nerve impulses to the centre in medulla oblongata that increases heart rate.
Increase in frequency of nerve impulses to the sinoatrial node via sympathetic nerve
Increase in electrical waves form sinoatrial node
Increase in heart rate
CO2 removed from blood, pH returns to normal
Baroreceptors for heart rate
Blood pressure too high.
Detected by pressure receptors in wall of carotid arteries and aorta.
Increase in frequency of nerve impulses to the centre in medulla oblongata that decreases heart rate.
Increase in frequency of nerve impulses to the sinoatrial node via parasympathetic nerve
Decrease in electrical waves form sinoatrial node
Decrease in heart rate
Blood pressure decreases to normal.
