Chapter 14 - response to stimuli Flashcards
Define stimulus
A detectable change in the internal or external environment of an organism that leads to a response in the organism
Where are many receptor cells found?
Ears, eyes, mouth, nose, skin
What do receptor cells do?
They monitor their environment for changes and send this information to the CNS
What do effector cells do?
They receive an electrical impulse from a motor neurone to initiate a response
What are the advantages of an organism responding to a stimulus?
Have a greater chance of surviving to pass on their advantageous alleles to the next generation
How many stimuli are a receptor specific to?
1
What are the 2 types of methods of communication, and which is specific only to animals?
Chemical
Electrical - only animals
Summarise the sequence of events in nervous or chemical control
Stimulus –> sensory receptor cells –> sensory neurone –> relay neurone –> CNS –> relay neurone –> effector cells –> response
What is a taxis?
A directional response to an external stimulus
List 4 common environmental taxi
Thermotaxis
Chemotaxis
Hydrotaxis
Phototaxis
What is a positive taxis?
Movement towards the stimulus
What is a negative taxis?
Movement away from the stimulus
What is a kinesis?
A nondirectional response where an organism doesnt move away from or to the stimulus but instead increases speed or rate of turning
What response does an organism have in kineses?
Speeding up or increasing rate of turning
Define tropism
The directional growth (by cell elongation and cell division) in response to a stimulus
What is positive phototropism? what is the advantage of this?
Movement of something (eg shoots) towards light energy in order to find light for photosynthesis
What is negative phototropism? what is the advantage of this?
Movement of something (eg roots) away from light energy in order to maximise mineral and water absorption
What is positive gravotropism? what is the advantage of this?
Movement of something (eg roots) with the direction of gravity in order to maximise mineral and water absorption
What is negative gravotropism? what is the advantage of this?
Movement of something (eg shoots) against the direction of gravity in order to find light for photosynthesis
What is positive
hydrotropism? what is the advantage of this?
Movement of something (eg roots) towards the water in order to absorb more water
What is negative hydrotropism? what is the advantage of this?
Movement of something (eg shoots) away from water in order to find light energy for photosynthesis
What is a growth factor?
A plant hormone
why is it better to not call a growth factor a hormone?
The chemical is not only made in one particular organ, like hormones, but can be made throughout the plant.
The chemical stimulates growth of particular cells to cause a directional effect, whereas hormones have a large range of jobs.
explain the process of positive phototropism in flowering plants
- Cells in tip produce IAA which is then transported down the shoot
- IAA moves from light to shaded side
- concentration of IAA is higher on shaded side
- IAA activates proton pumps which lowers pH, which then activates enzymes to break down bonds on the cell wall to allow water to enter the cell and make it turgid, causing the cells to elongate
- The shaded side of the shoot elongates more than the light side so the plant bends towards the light
How does IAA cause elongation of cells?
IAA activates proton pumps which lowers pH, which then activates enzymes to break down bonds on the cell wall to allow water to enter the cell and make it turgid, causing the cells to elongate
In shoots does IAA stimulate or inhibit cell growth?
stimulate
In roots does IAA stimulate or inhibit cell growth?
inhibit
Explain the process of positive gravitropism in roots
- tip of root produce IAA which is then passed along the root
- gravity influences the movement of IAA from the upper side of roots to lower side
- This means that there is a greater concentration of IAA on the lower side than the upper side
- IAA inhibits growth of cells in roots, so cells on lower side elongate less than upper side
- there is more growth on upper side, causing the root to bend downwards towards the force of gravity
Define reflex arc
An automatic nervous response without the requirement to think
What is the central nervous system comprised of?
Brain and spinal cord
What are the 2 types of nervous system?
Central nervous system
Peripheral nervous system
What are the 2 types of peripheral nervous system?
sensory and motor neurones
What are the 2 types of motor neurones?
Voluntary nervous system
Autonomic nervous system
What are the 2 types of autonomic nervous system?
sympathetic nervous system
Parasympathetic nervous system
What is the peripheral nervous system?
A nervous system made up of pairs of nerves that originate from either the brain or spinal cord
What is the voluntary nervous system?
carries nerve impulses to body muscles - conscious control
What is the involuntary nervous system?
Carriers impulses to glands and smooth muscles and is involuntary control
What is the sympathetic nervous system?
The system that controls the fight or flight response and energy consumption
What is the parasympathetic nervous system?
The system that controls energy conservation
List 4 advantages of reflex arcs
involuntary (absence of decision making process) and fast - short diffusion pathway with few synapses
protect the body from harm
List 4 stimuli that the skin can identify
Pressure,
vibration,
heat
pain
What does an energy transducer do?
Convert energy from a stimulus into a frequency of impulses which are sent down the to CNS to be processed
What does the pacinian corpuscle respond to?
A change in pressure
How do pacinian corpuscles respond to changes in pressure?
- Pressure energy causes compression in the corpuscle,
- which is then transferred through gelatinous material to the receptor.
- The pressure causes deformation of the neurone and its membrane
- Stretch mediated sodium channels within the membrane respond to pressure by opening to sodium ions.
- when the channels are closed, there is a negative charge within the neurone, and the outside is positive.
- when channels are open and the sodium ions can enter by facilitated diffusion, building up a large charge created a generator potential.
- When this reaches the threshold an action potential is generated
- Which is passes down the sensory neurone to the brain.
describe the stretch mediated sodium channel
A special type of sodium channel that changes its permeability to sodium when it changes shape.
Summarise the sequence of events by which pressure on a Pacinian corpuscle leads to the creation of the generator potential:
When there is a change in pressure, the Pacinian corpuscle undergoes deformation, leading to stretching of sodium channels, allowing the facilitated diffusion of sodium ions into the neurone, leading to the depolarisation of the corpuscle, creating a generator potential
Do rod cells share a single bipolar sensory neurone, or have its own?
share
Do cone cells share a single bipolar sensory neurone, or have its own?
own
What is the impact of multiple receptor cells sharing a bipolar cell?
Greater chance that the threshold value is exceeded and a generator potential is triggered.
Lower visual acuity because of summation of light energy- only 1 impulse is made regardless of how many cells are stimulated
What is the impact of each cell linking to an individual bipolar cell?
Lower chance to exceed threshold because only 1 source of energy
higher visual acuity because light energy is not summated
What is the pigment found in rod cells?
rhodopsin
What is the pigment found in cone cells?
iodopsin
How many types of iodopsin are there?
3
what happens when light falls on the pigments?
The light energy breaks down the pigment, creating an action potential
Which cell needs more energy to break down its pigment? which pigment is it?
Cone cells - iodopsin
Where are cone cells found in high concentrations?
Fovea
Where are rod cells found in high concentrations?
peripheral
which sensory cells are found in the optic nerve?
None
Can light be perceived in the fovea?
Yes
Can light be perceived in the optic nerve?
No
Can rod cells create colour vision?
No
Can cone cells create colour vision?
Yes
What is the sinoatrial node?
An area of the heart muscle in the right atrium that controls and coordinates the contraction of the heart
What is the atriovetricular node?
A group of cells that lie between the atria and cause a delay of a wave of electrical excitation between the ventricles along the perkinje tissue
What is the purkinje fibre?
A series of specialised muscle fibres that spread impulses from the AVN along ventricular walls, causing ventricular systole.
What is the bundle of His?
a bundle of specialised muscle fibres which conduct the wave of electrical excitation through the atrioventricular septum to the base of the ventricles
What are chemoreceptors?
Receptors found in the wall of the carotid arteries that are sensitive to changes in pH caused by changes in CO2 concentration and therefore influence frequency of impulses to the brain
What are pressure receptors?
receptors that operate within the walls of the carotid arteries and the aorta that control the heartrate in the body by changing the nervous impulses sent to the brain
What is the part of the brain responsible for autonomic responses in the body?
The medulla oblongata
Explain the action of chemoreceptors in increasing heartrate
chemoreceptors detect an increase in pH due to increases CO2 levels and therefore send an increased frequency of impulses to the cardioacceloratory centre of the medulla oblongata.
More impulses are sent to the SAN from the brain via the SYMPATHETIC nervous system
Rate of electrical impulses initiated by the SAN inctrases
Rate of contractions increases
Heart rate increases
Explain how chemoreceptors decrease heartrate
Level of CO2 drops as more is being removed by higher blood flow
pH returns to normal
fewer impulses are sent to the medulla oblongata
fewer impulses sent to the SAN
Fewer impulses initiated by SAN
Rate of heart contractions decreases
Explain how baroreceptors deal with high blood pressure
When blood pressure increases, baroreceptors increase the frequency of impulses sent to the cardioinhibitory centre of the medulla oblongata, and more impulses are sent to the SAN via the PARASYMPATHETIC nervous system, causing the release of a hormone which reduces heart rate by inhibiting transmission of impulses
Rate of impulses initiated by the SAN decreases
rate of heart contractions decreases
heart rate decreases
Explain how baroreceptors deal with low blood pressure
When blood pressure decreases, baroreceptors increase the frequency of impulses sent to the cardioacceleratory centre of the medulla oblongata which is responsible for increasing heart rate
More impulses are sent to the SAN via the sympathetic nervous system, causing the release of a hormone which increases heart rate by increasing transmission
of impulses.
Rate of electrical impulses initiated by the SAN increases
Rate of heart contractions increases
Blood pressure increases.
