3.6.1 Stimuli Flashcards
What’s a stimulus
Change in internal or external environment of an organism, leads to a response
Why do organisms respond to stimuli
Increases chance of survival
What’s a receptor
Detects stimuli, each receptor is specific to a type of stimulus
What’s a coordinator
Links receptors and effectors, formulates a suitable response to a stimulus
What’s an effector
Produces a response
What’s are two types of response
Hormonal
Nervous system
What’s the sequence of a response to stimuli
Stimulus, receptor, coordinator, effector, response
Three types of simple responses to stimuli
Taxis
Kinesis
Tropism (plants)
What’s taxis
Organism responds directly to stimulus by moving towards (a favourable) or away from (an unfavourable) stimulus
eg earthworks move away from light
What’s kinesis
Organism changes the rate at which it moves/ rate it changes direction
In favourable conditions organisms turn lots to stay In that environment
In unfavourable conditions organisms turn less to help them move into a new favourable environment
What’s the central nervous system (CNS)
Brain and spinal cord
What’s the peripheral nervous system (PNS) and which nerves do they contain
Pairs of nerves that originate from the brain or spinal cord
Sensory neurones, carry nerve impulses from receptors towards the central nervous system
Motor neurones, carry nerve impulses from CNS to effectors
Two types of motor nervous system
Voluntary nervous system, nerve impulses are carried to body muscle, under conscious control
Autonomic nervous system, nerve impulses carried to glands/smooth muscle/Cardiac muscle, subconscious
What’s a reflex arc
The pathway of neurones involved in a reflex
What’s a reflex
A rapid and automatic response to a stimulus
Stages of a reflex arc
Stimulus eg heat from an object
Receptor eg Receptors on skin generates a nerve impulse in the sensory neurone
Sensory neurone, passes nerve impulse to spinal cord
Coordinator (relay neurone), connects sensory neurone to motor neurone in spinal cord
Motor neurone, carries nerve impulses from spinal cord to an effector eg muscle
Effector eg muscle in upper arm contracts
Response eg hand pulled away from hot object
Why is a reflex arc important
Involuntary, response is always the same
Protect body from harm, effective from birth
Fast, neurone pathway has one or two synapses, response is also automatic
What’s phototropism
Response of shoots to light
What’s gravitropism
The response of roots to gravity
What are specific growth factors
Regulate growth of shoots/roots in response to directional stimuli
Explain phototropism in plants
IAA evenly distributed through plant, Light causes movement of IAA to shaded side of plant, higher conc of IAA on dark side of shoot, cells on this side elongate more than the other side, shoot too bends towards light
Explain gravitropism in plants
IAA evenly distributed through roots, greater conc of IAA on lower side of root, IAA in roots inhibits elongation of cells on lower side, roots bend downwards towards gravity
What types of tropisms effect shoots and roots
Both tropisms effect both shoots and roots, IAA always inhibits cell elongation in roots
How does IAA elongate cells
H+ ions are actively transported from the cytoplasm into the cell wall, cells become more plastic allowing it to elongate
Two types of light receptors in the eye
Cone cells
Rod cells
How are rod cells connected to a sensory neurone and it’s impact on light sensitivity colour sensitivity and visual acuity
Many rod cells are connected to a single sensory neurone this is called retinal convergence, this allows for spatial summation, threshold value is reached, more sensitivity to light
Due to many rod cells sharing a single impulse the brain can’t differentiate between the separate sources of light, low visual acuity
Cannot distinguish differences in the wavelength of light
How are cone cells connected to a sensory neurone and it’s impact on visual acuity colour sensitivity and light sensitivity
Each cone cells connects to its own sensory neurone, no summation, not very sensitive to light
Each cell makes its own connection, where each sends its own SEPERATE impulse to the brain, brain can distinguish between two different light sources, high visual acuity
Each cell contains one of three different iodopsin pigments, each cell absorbs a different wavelength of light, colours depend on the proportion of each type that is stimulated
What pigment do rod cells contain
Rhodopsin
What pigment do come cells contain
Iodopsin
How do the photoreceptors work
Rhodopsin in rod cells or iodopsin in cone cells absorb light, the pigment breaks down, if threshold value is reached (depends on light intensity) a generator potential is created,
Structure of the retina and its effect on visual acuity, sensitivity to light
Lens, focuses light onto retina
Retina, back of eye opposite pupil
Fovea- light focused by lens, highest light intensity, cone cells found here, NO rod cells, low sensitivity to light but high visual acuity
Rest of retina, low light intensity, only rod cells found, very sensitive to light, low visual acuity
Blind spot, no cells
What’s a pacinian corpuscle
A receptor
How does a pacinian corpuscle work
Specific to stimulus of mechanical pressure
Acts as a transducer to produce a generator potential, transducers mechanical energy into a generator potential (one for of energy converted into another)
Structure and function of a pacinian corpuscle
Single sensory neurone at centre of tissue layers, contain stretch mediated sodium channels
Capsule surrounds layers of tissue and gel
Tissue layers separated by gel
How is a generator potential established in a pacinian corpuscle
Resting state, stretch mediated Na+ channels are too narrow for Na+ to pass through
Pressure applied to corpuscle, deformed, membrane around neurone becomes stretched, widens Na+ channel, Na+ diffuses in
Membrane becomes depolarised, produces generator potential, which produces an action potential
What’s a property of a the heart
Myogenic, contraction is initiated from within the muscle itself
What cells are found in the right atrium of the heart
SAN, known as pacemaker, sets the Rhythm of stimulation
How is basic heart rate controlled
Wave of electrical excoriation spreads out from SAN across north atria, they both contract
A layer of non conductive tissue prevent this wave from crossing to the ventricles
The wave of excitation enters the AVN which lies between the atria
The AVN after a short delay conveys a wave of electrical excitation between ventricles along muscle fibres called the purkyne tissue, these tissues collectively form the bundle of his
The bundle of his conducts the wave through atrioventricular septum to base of ventricles, bundle branches into smaller fibres of purkyne tissue
Wave of excitation is released from purkyne tissue, causing ventricles to contract quickly, from the bottom of the heart upwards
Location of chemoreceptors
Found in wall of carotid arteries,
Role of chemoreceptors
Sensitive to changes in pH of the blood, result in changes to CO2 concentration, in a solution CO2 is acidic lowering pH
Blood has a higher than normal conc of CO2, pH is lowered
Chemoreceptors in wall of carotid artery and aorta detects this, increases frequency of nervous impulses to centre in medulla oblongata, increases heart rate
Centre increases frequency of impulses via sympathetic nervous system to SAN, increases rate of production of electrical waves by SAN, increases heart rate
Increases blood flow, more CO2 removed, CO2 conc returns to normal
pH in blood rises, chemoreceptors in wall of carotid artery and aorta reduce frequency of nerve impulses to medulla oblongata
Medulla oblongata reduces the frequency of impulses to SAN, reduced heart rate
What’s the location of pressure receptors
Found in walls of carotid artery and aorta
Role of pressure receptors
Higher than normal blood pressure
Pressure receptors transmit more nervous impulses to centre in medulla oblongata, decreases heart rate, centre sends impulses via parasympathetic nervous system to SAN, decreased heart rate
Lower blood pressure than normal
Pressure receptors transmit more nervous impulses to centre in medulla oblongata to increase heart rate, centre sends impulses via sympathetic nervous system to SAN increases heart rate
Why’s the autonomic nervous system
Controls involuntary activities of internal muscles or glands
Consists of sympathetic nervous system and parasympathetic nervous system
What’s the sympathetic nervous system
Stimulates effectors, speeds up activity, flight or fight response
What’s the parasympathetic nervous system
Inhibits effectors, slows down activity, conserves energy and replenished body’s reserves
Equation to calculate cardiac output
CO= R x V
CO- cardiac output
R-heart rate
V-stroke volume
