6 Responding to Change- Nervous Communication

Question 1

How can organisms increase their chance at survival?

Answer 1

By detecting a change & responding accordingly

Question 2

Where can organisms detect changed in?

Answer 2

-External environments (eg temp of surroundings)
-Internal environments (eg blood glucose conc)

Question 3

What are the 3 steps in coordinating a response?

Answer 3

-Stimulus; change in environment
-Receptors; detect change in environment
-Effectors; initiate response

Question 4

How do plants respond to change,why?

Answer 4

-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

Question 5

What is phototropism?

Answer 5

Growth in response too direction of light:

-Shoots positively phototropic= grow towards light
-Roots negatively phototropic= grow away from light

Question 6

What is gravitropism?

Answer 6

Growth in response to direction of gravity:

Shoots negatively gravitropic= grow upwards, away from gravitational pull
Roots positively gravitropic= grow downwards, towards gravitational pull

Question 7

What is Indoleacetic acid (IAA)?

Answer 7

Type of auxin controlling tropic response in plants

Question 8

How can IAA be transported and what does this result in for its distribution?

Answer 8

-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

Question 9

What is the process of a shoot bending towards light?

Answer 9

-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

Question 10

What is the process of a shoot bending away from the gravitational pull?

Answer 10

-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

Question 11

What is the process of roots bending towards the gravitational pull?

Answer 11

-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

Question 12

What are tactic responses (taxes)? + give example

Answer 12

-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

Question 13

What are kinetic responses (kinases)? + give example

Answer 13

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

Question 14

What are reflex responses and what to they do?

Answer 14

-Automatic, quick, unconscious responses to a stimulus
-Often help organism respond quickly to harmful stimulus like heat

Question 15

What is a reflex arc and which 3 neurones does it involve?

Answer 15

-Pathway of neurones involved in a reflex response
-3 neurones; sensory, relay and motor

Question 16

What are the steps involved in a reflex arc?

Answer 16

-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

Question 17

What are the 2 features of receptors?

Answer 17

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

Question 18

What is the Pacinian Corpuscle?

Answer 18

-A mechanoreceptor found in skin
-These respond to changes in pressure to establish a generator potential

Question 19

What is resting potential and what occurs during it?

Answer 19

The corpuscle consists of concentric rings of connective tissue that surrounds a sensory neurone
When corpuscle isn’t stimulated—> at resting state

-Resting state- charge inside neurone= more negative than (-70mV), as there’s more Na+ ions outside neurone than inside
-Difference in charge across cell membrane= potential difference

Question 20

What occurs when pressure is applied to the Pacinian corpuscle?

Answer 20

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

Question 21

How is the generator potential established?

Answer 21

-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

Question 22

How is an action potential produced?

Answer 22

If the generator potential reaches threshold level (approx -50mV), an action potential is produced in the sensory neurone

Question 23

What are rod and cone cells and what do they both do?

Answer 23

2 main (photo)receptors in the human eye
Both respond to photons of light

Question 24

What are the differences with rod and cone cells?

Answer 24

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.

Question 25

What happens when light is detected and how is a generator potential established?

Answer 25

-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

Question 26

What is the role of the bipolar neurone in the process of light being converted to electrical impulses?

Answer 26

-Each photoreceptor synapses (forms junction) w/ a relay neurone (bipolar neurone)
-Each bipolar neurone synapses w/ a sensory neurone (ganglion cell)
-Axons (long, extended cell body of nerve) of ganglions leave eye via optic nerve to send signal to brain

Question 27

Why are there differences in sensitivity to light in rod and cone cells?

Answer 27

-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)

Question 28

What is spatial summation and what does it result in?

Answer 28

-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

Question 29

What does cardiac muscle do with every heartbeat, and what allows it to do so?

Answer 29

-The cardiac muscle contracts & relaxes w/out stimulation by nerves
-Cardiac muscle is myogenic; self-stimulating

Question 30

What is the Sinoatrial node (SAN) and its purpose?

Answer 30

-Located in wall of right atrium
-Acts as pacemaker by transmitting waves of electrical activity along walls of atria at regular intervals

Question 31

What causes the atria to contract and what does this result in?

Answer 31

-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

Question 32

Why does the electrical impulse need to pass through the Atrioventricular node (AVN) and what happens?

Answer 32

-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)

Question 33

Why do the ventricles contract and what does this cause?

Answer 33

-As waves of electrical activity pass along Purkyne fibres, ventricles contract together
-Blood is forced out vertices & out of heart

Question 34

What are the 2 main receptors involved in controlling heart rate and what do they do when stimulated?

Answer 34

-Chemoreceptors & baroreceptors
-When stimulated, they send a signal to a region in brain (medulla oblongata)

Question 35

What are chemoreceptors sensitive to and where are they found?

Answer 35

-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

Question 36

What are baroreceptors sensitive to and where are they found?

Answer 36

-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)

Question 37

What is the role of the medulla oblongata and its sub-regions?

Answer 37

-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)

Question 38

How is high blood detected and what is the response to it?

Answer 38

-Detected by baroreceptors
-Impulses are sent from medulla along parasympathetic neurones to SAN
-Acetylcholine (neurotransmitter) is released
-Heart rate slow down, blood pressure decreases

Question 39

How is low blood pressure detected and what is the response to it?

Answer 39

-Detected by baroreceptors
-Impulses sent from medulla along sympathetic neurones—> SAN
-Noradrenaline (neurotransmitter) released
-Heart rate rises, blood pressure increases

Question 40

How is low CO²/high O² detected and what is the response to it?

Answer 40

-Detected by chemoreceptors
-Impulsed sent from medulla along parasympathetic neurones—> SAN
-Acetylcholine (neurotransmitter) released
-Heart rate slows, CO² levels increase/O² levels decrease

Question 41

How is low O²/high CO² detected and what is the response to it?

Answer 41

-Detected by chemoreceptors
-Impulses sent from medulla along sympathetic neurones —> SAN
-Noradrenaline (neurotransmitter) released
-Heart rate rises, O² levels decrease/CO² levels decrease