6 Responding to Change- Nervous Communication Flashcards
How can organisms increase their chance at survival?
By detecting a change & responding accordingly
Where can organisms detect change in?
-External environments (eg temp of surroundings)
-Internal environments (eg blood glucose conc)
What are the 3 steps in coordinating a response?
-Stimulus; change in environment
-Receptors; detect change in environment
-Effectors; initiate response
How do plants respond to change,why?
-Plants aren’t mobile organisms so can’t move to avoid harmful environments
-They regulate growth in response to direction stimuli, which are called tropisms
What is phototropism?
Growth in response too direction of light:
-Shoots positively phototropic= grow towards light
-Roots negatively phototropic= grow away from light
What is gravitropism?
Growth in response to direction of gravity:
Shoots negatively gravitropic= grow upwards, away from gravitational pull
Roots positively gravitropic= grow downwards, towards gravitational pull
What is Indoleacetic acid (IAA)?
Type of auxin controlling tropic response in plants
How can IAA be transported and what does this result in for its distribution?
-Can be transported over short distances (diffusion/active trans) & longer distances (in phloem) around plant
-This causes an uneven distribution of IAA, and a directional growth occurs
What is the process of a shoot bending towards light?
-Shoots= positively phototropic
-If shoot—> exposed to uneven light source, IAA is transported to more shaded part
-Higher conc of IAA in shaded part—> causes cells in shaded area to elongate
-Cell elongation= shoot bends towards light
What is the process of a shoot bending away from the gravitational pull?
-Shoots= negatively gravitropic
-If shoot—> exposed to uneven gravitational pull, IAA transported to underside (closer to gravity pull)
-High conc of IAA—> cells in underside elongates
-So, shoot bends away from gravitational pull
What is the process of roots bending towards the gravitational pull?
-Roots= positively gravitropic
-If root—> exposed to uneven gravitational pull, IAA= transported to underside (closer to gravity pull)
-Higher conc of IAA in underside—> inhibits cell elongation on lower side
-Root bends towards gravitational pull
What are tactic responses (taxes)? + give example
-Stimulus= positively/negatively directional, like light
Eg- woodlice move away from light source
-Dark environments like under stones= favourable for woodlice for protection from predators
-Ability to detect direction of light + move away helps woodlice locate more favourable habitat
What are kinetic responses (kinases)? + give example
Stimulus= non-directional, like humidity
Eg woodlice move more slowly, turn less in high humidity but opposite in low humidity
-Damp environments= favourable for woodlice, reduce water loss
-Woodlice detect drier environment—> move more, increases chance they’ll find more favourable enviro
-Woodlice detect damper environment—> move less, ensures they stay in more favourable enviro
What are reflex responses and what to they do?
-Automatic, quick, unconscious responses to a stimulus
-Often help organism respond quickly to harmful stimulus like heat
What is a reflex arc and which 3 neurones does it involve?
-Pathway of neurones involved in a reflex response
-3 neurones; sensory, relay and motor
What are the steps involved in a reflex arc?
-Detection; Thermoreceptors in skin detect heat stimulus
-Sensory neurone carries impulse from thermoreceptors to relay neurone in spinal cord
-Relay neurone carries impulse to motor neurone
-Motor neurone carries impulse to effectors (like muscles in arm)
-Response; arm moves away from hot object
What are the 2 features of receptors?
Specificity; receptors only respond to specific stimuli, eg- light, temp, pressure
Generator potential; Receptors connect w/ sensory neurones. When stimulated, the receptor creates a generator potential in sensory neurone, eg. where stimulation of receptor causes generator potential= Pacinian corpuscle
What is the Pacinian Corpuscle and what does it mean consist of?
-A mechanoreceptor found in skin
-These respond to changes in pressure to establish a generator potential
-Consists of concentric rings of connective tissue that surrounds a sensory neurone
What is resting potential and what occurs during it?
When Pacinian corpuscle isn’t stimulated—> at resting state
-Here, charge inside neurone= more negative than outside (-70mV), as there’s more Na+ ions outside neurone than inside
-Difference in charge across cell membrane= potential difference
What occurs when pressure is applied to the Pacinian corpuscle?
When pressure is applied to the Pacinian corpuscle, the rings of connective tissue apply pressure on sensory neurone, which has stretch mediated Na+ channels; normally restrict movements of Na+ ions
Applied pressure—> Na+ channels open
How is the generator potential established?
-Na+ ions flood into sensory neurone through open Na+ channels
-Now, there’s more Na+ ions inside neurone than out
-Charge inside neurone—> more positive than out, so potential difference has been changed
-The generator potential has been established
How is an action potential produced?
If the generator potential reaches threshold level (approx -50mV), an action potential is produced in the sensory neurone
What are rod and cone cells and what do they both do?
2 main (photo)receptors in the human eye
Both respond to photons of light
What are the differences with rod and cone cells?
Rod cells;
-Highly sensitive to light
-Low visual acuity
-Highly numerous
-Evenly distributed on retina, absent in fovea
-Use pigment called rhodopsin, detects light + dark
-Monochromatic; detects only 1 wavelength of light
Cone cells;
-Less sensitive to light
-High visual acuity
-Fewer cells than rod cells
-Distributed mainly at single point in retina (fovea)
-Use pigment called lodopsin, detects colour
-Trichromatic; divided into 3 types, respond to diff wavelengths of light either red, blue or green.
What happens when light is detected and how is a generator potential established?
-Light is absorbed by pigments (rhodopsin/iodopsin) in photoreceptor cells
-A change in membrane permeability of pigments is induced
-Na+ ions flood into cell, generator potential is established
-If it reaches the threshold, a nerve impulse flows along a bipolar neurone
What is the role of the bipolar neurone in the process of light being converted to electrical impulses?
-Each photoreceptor synapses (forms junction) w/ a relay neurone called a bipolar neurone
-Each bipolar neurone synapses w/ a sensory neurone called a ganglion cell
-Axons (long, extended cell body of nerve) of ganglions leave eye via optic nerve to send signal to brain
Why are there differences in sensitivity to light in rod and cone cells?
-Differences in sensitivity to light—> due to diff in how rod & cone cells connect to bipolar neurones
-Each cone cell synapses w/ single bipolar neurone
(Sufficient light must stimulate cone cell to generate an action potential in bipolar neurone)
-Several rod cells synapse w/ same bipolar neurone
(Light stimulating a single rod cell may not be sufficient to generate an action potential in bipolar neurone)
What is spatial summation and what does it result in?
-Several rod cells synapse w/ same bipolar neurone
-So, cumulative stimulation of 1+ rod cell can make an action potential in bipolar neurone —> this is spatial summation
-Results in retinal convergence—> several rod cells generate signal in single sensory neurone
What does cardiac muscle do with every heartbeat, and what allows it to do so?
-The cardiac muscle contracts & relaxes w/out stimulation by nerves
-Cardiac muscle is myogenic; self-stimulating
Heartbeat process 1; What is the Sinoatrial node (SAN) and its purpose?
-Located in wall of right atrium
-Acts as pacemaker by transmitting waves of electrical activity along walls of atria at regular intervals
Heartbeat process 2; What causes the atria to contract and what does this result in?
-Electrical waves from SAN cause right & left atria to contract together
-Blood from the right atrium is forced into the right ventricle & blood from the left atrium into the left ventricle
Heartbeat process 3; Why does the electrical impulse need to pass through the Atrioventricular node (AVN) and what happens?
-Waves of electrical activity cant pass from atria to ventricles due to collection of non-conducting tissue
(Creates delay to ensure atria= empty before ventricles begin to contract)
-Electrical activity passes through AVN to bundle of His, a collection of conducting tissue transmitting electrical activity to apex (bottom) of heart & around ventricle walls along fibres (Purkyne fibres)
Heartbeat process 4; Why do the ventricles contract and what does this cause?
-As waves of electrical activity pass along Purkyne fibres, ventricles contract together
-Blood is forced out vertices & out of heart
What are the 2 main receptors involved in controlling heart rate and what do they do when stimulated?
-Chemoreceptors & baroreceptors
-When stimulated, they send a signal to a region in brain (medulla oblongata)
What are chemoreceptors sensitive to and where are they found?
-Sensitive to changes in CO² concentration, if high—> heart rate increases
-Found in aortic body; wall of aorta
-Found in carotid body; wall of carotid artery in neck
What are baroreceptors sensitive to and where are they found?
-Sensitive to changes in blood pressure—> if increases, so does heart rate
-Found in walls of various arteries but particularly in carotid sinus (wall of carotid artery)
What is the role of the medulla oblongata and its sub-regions?
-When stimulated, chemoreceptors & baroreceptors send signal to the medulla oblongata, a brain region
-Region in medulla modifying heart rate= cardiovascular centre, w/ 2 regions;
-Cardio-inhibitory & cardio-acceleratory centre
-Nervous impulses= sent from these centres along automatic nervous system to sinoatrial node (SAN)
Control of heart rate; How is high blood pressure detected and what is the response to it?
-Detected by baroreceptors
-Impulses are sent from medulla along parasympathetic neurones to SAN
-Acetylcholine (neurotransmitter) is released
-Heart rate slow down, blood pressure decreases
Control of heart rate; How is low blood pressure detected and what is the response to it?
-Detected by baroreceptors
-Impulses sent from medulla along sympathetic neurones—> SAN
-Noradrenaline (neurotransmitter) released
-Heart rate rises, blood pressure increases
Control of heart rate; How is low CO²/high O² detected and what is the response to it?
-Detected by chemoreceptors
-Impulsed sent from medulla along parasympathetic neurones—> SAN
-Acetylcholine (neurotransmitter) released
-Heart rate slows, CO² levels increase/O² levels decrease
Control of heart rate; How is low O²/high CO² detected and what is the response to it?
-Detected by chemoreceptors
-Impulses sent from medulla along sympathetic neurones —> SAN
-Noradrenaline (neurotransmitter) released
-Heart rate rises, O² levels increase/CO² levels decrease
