Internal + External Stimuli Detected & Lead to Response Flashcards
stimuli
a detectable change in the internal/external environment
receptor
a cell or organ that detects change in internal/external environment
coordinator
connects information between receptor and the appropriate effector
effector
a cell, tissue or organ that carries out a response
muscles and glands
response
a change brought due to a stimulus
plant growth factors and where are they produced
chemicals that regulate plant growth response to directional stimuli
produced in plant growing regions
diffuse from cell to cell/ phloem mass transport
positive phototropism in shoots
-cells in tip of shoot produce IAA, transported down the shoot
-light causes IAA to diffuse to shaded side of shoot tip
-greater concentration of IAA on shaded side
-as IAA causes elongation and greater concentration on shaded side, cells on this side elongate more.
-shaded side elongates faster than light side, causes shoot tip to bend towards light.
gravitropism in roots
-gravity causes IAA to accumulate in lower side of root
-IAA inhibits elongation in root cells
-cells on upper side of root grow faster relative to lower side causing root to bend downwards towards gravity
define taxis and kinesis and state their advantage
taxis-directional movement in response to external stimuli
kinesis-non-directional response to presence and intensity of external stimulus
-maintain mobile organism in optimum environment e.g. to prevent desiccation.
tropism
growth of part of a plant in response to directional stimulus
many organisms respond to temperature and humidity via kinesis rather than taxis. Why?
less directional stimuli; often no clear gradient from one extreme to another.
stages of reflex arc
receptor detects stimulus->sensory neuron-> relay neuron in CNS coordinates a response->motor neuron->response by effector
importance of reflex arc
-involuntary: doesn’t require a decision, frees brain from executing more complex decision
-protection: protects from potentially dangerous stimuli
-rapid response: neuron pathway short, very few synapses
autonomic nervous system
system that controls all involuntary activities of internal muscles and glands.
has 2 subdivisions: parasympathetic & sympathetic
difference between parasympathetic and sympathetic
parasympathetic: inhibits effectors so slows down activity, controls activity in normal resting conditions.
-concerned with conserving energy & replenishing body’s reserve
sympathetic: stimulates effectors so speeds up activity, involved in ‘fight or flight’ response.
-heightens awareness, helps cope in stressful conditions.
medulla oblongata and its function
located in brainstem and controls involuntary functions
function is transmitting signals between spinal cord and higher parts of brain-controls autonomic activities.
events that control basic heart rate
-SAN initiates wave of electrical energy- spreads across both atria, causes the atria to contract= atrial systole
-wave of excitation enters AVN-between atria
-AVN, after a short delay, conveys wave of electrical excitation between the ventricles along Purkyne tissue (bundle of His)
-Bundle of His conducts wave through atrioventricular septum to base of the ventricles, where bundle branches into smaller Purkyne fibres
-wave of excitation released quickly from Purkyne fibres, contracts quickly from apex upwards.
centres in medulla oblongata to mediate heart rate
-1 centre causes sympathetic nerve to release neurotransmitter noradrenaline-connects to SAN, increases heart rate
-2nd centre causes parasympathetic (vagus) nerve to release neurotransmitter acetylcholine, connects to SAN-decreases heart rate.
receptors involved in changing heart rate and their location
chemoreceptors: sensitive to changes in pH of the blood as a result of CO2 concentration
-found in wall of carotid artery and aortic body
baroreceptors: detects changes in blood pressure
-carotid body
how does body respond to increase in CO2 concentration
-higher CO2 concentration=production of carbonic acid-lowers pH of blood
-chemoreceptors detect & increase frequency of impulses to centre of medulla oblongata that increases heart rate + respiration rate
-centre increases impulses to SAN via sympathetic nervous system
-heart rate increases-rate of blood flow increases-rate of gas exchange increase so more CO2 removed
-pH of blood rises to normal , chemoreceptors reduce frequency, medulla oblongata reduces impulses to SAN=reduction in heart rate
