Section 6- Response to stimuli Flashcards
What do vertebrates have that provide rapid, automatic responses to stimuli?
Reflex arcs
What is the process of stimulus to response?
Impulse passes across a synapse to a relay neuron
Across another synapse
Travels to an effector via the motor neuron
Effector initiates the response
What are tropisms?
Growth response in a plant
Reponses are controlled by specific control factors
What is an example of a specific growth factor that controls tropisms?
Auxins
Indole acetic acid (IAA)
What is a photoropism?
Growth of a plant towards or away from light
What is the process of positive phototropism?
Grow towards lights
IAA is produced in shoot tip and diffuses into the growing region
In presence of light is moves to the dark side
IAA disrupts hydrogen bonds between microfibrils in cellulose allowing cells to elongate and divide
Leads to unequal growth
What is gravitropism?
Plants response to gravity
What is the process of positive gravitropism?
Grow towards gravity
IAA made in the tips of the roots diffuses into the growing region
Dense organelles amyloplasts sink to the bottom of the roots
Moves IAA with them
IAA inhibits growth causing the root to bend downwards
What are amyloplasts and when are they used?
Storage vesicles of starch
Sink to bottom of roots during positive gravitropism
What is an example of a positive and negative phototropism?
Positive: Shoots of plant growing towards lights
Negative: Roots growing away from the light
What is a taxis?
Directional movement responses to a directional stimulus
What is an example of a positive phototaxis?
Moth flying towards light
What would be an example of a negative phototaxis?
Worm burrowing underground
What is a kineses?
A kinetic response is a non-directional response
How does the strength of a stimulus affect the rate of movement?
Bigger stimulus causes the animal to move faster
Make more frequent turns
What is the kinesthetic response when an organism is in favourable conditions?
Organism slows down and turns less frequently
Increases chances of remaining in favourable environment
What is the difference between taxis and kinesis?
Taxis is a directional movement response to a directional stimulus
Kinesis is a non-directional response
What is the Pacinian corpuscle?
Pressure receptor found in the skin tissue of mammals
One of many receptors in the skin that each detect just one stimulus
What does the Pacinian corpuscle consist of?
Series of plasma membranes that enclose the end of a sensory neurone
Membranes are called lamellae
Within the final lamellae are lots of sodium ions
In lamellae and the axon membrane are stretch-mediated carrier proteins for sodium ions
What happens when pressure is applied to the lamellae in the Pacinian corpuscle?
The membranes become distorted
Carrier proteins open allowing sodium ions to move by facilitated diffusion into the axon
Potential difference (voltage) is altered across the membrane = GENERATOR POTENTIAL
In the Pacinian Corpuscle, the bigger the stimulus…
The more stretch-mediated carrier proteins open
More sodium ions enter the axon by facilitated diffusion, so the change in potential difference is larger
In the Pacinian Corpuscle, if the generator potential is big enough to pass through the threshold
Then an ‘action potential’ (nerve impulse) will be generated
How is the cardiac cycle controlled?
- Impulse starts in SinoAtrial (SA) node
- Impulse travels through atria walls
- Both atria contract
- Cardiac impulse reaches Atrioventricular (AV) node
- Impulse spreads down Bundle of His
- Impulse spreads around ventricle walls through purkinje fibres
- Causes ventricles to contract
What is the SinoAtrial (SA) node and where is it located?
Pacemaker
Located at top of right atrium
What does the Atrioventricular (AV) node do?
Helps delay the impulse to allow the atria to finish their contraction before ventricles contract.
Where is the Bundle of His located?
The septum
Why does the impulse in the heart need to be delayed?
Ensures enough time for blood to pass through and valves to close
What does myogenic mean?
Can create its own impulse
What 2 sections is the autonomic nervous system split into?
Sympathetic = fight or flight
Parasympathetic = rest and digest
What is the medulla oblongata and what does it contain?
Contains the cardioregulatory centre
It receives information from chemoreceptors and baroreceptors
What happens when there is a decrease in blood pH?
It is detected by the chemoreceptors
More action potentials sent to the acceleratory centre of the cardioregulatory centre of the medulla oblongata
More action potentials sent down sympathetic nervous system to sinoatrial node
Generates impulse at faster rate
What happens when an increase in blood pressure occurs?
Detected by barrow receptors
More action potentials sent to the acceleratory region of the cardioregulatory centre of the medulla oblongata
More action potenials sent down parasympathetic nervous to sinoatrial node
Less frequent impulses to be generated
What is the retina?
Located at the back of the eye
Tissue made entirely of receptor cells
What are the 2 different photoreceptor cells?
Cone cells
Rod cells
What are cone cells?
Provide colour vision in high light intensity
Mostly concentrated in the fovea where best vision is found
Provide high visual acuity
What are the 3 different types of cone cells?
Red sensitive
Blue sensitive
Green sensitive
What is the trichromatic theory of colour vision?
3 types of cone cells
Red sensitive
Blue sensitive
Green sensitive
What are rod cells?
Provide low visual acuity
Work in low light intensity
Lack colour perception
How do cone cells have high visual activity?
Each cone cell is connected to a single bipolar cell
This is connected to a single neuron in the optic nerve
When light strikes cone cell an action potential is triggered that tells brain exactly where light source is
(provided stimulus is intense enough to pass generator potential)
How to rod cells allow for low light vision?
Generator potentials can add together multiple rod cells that connect to 1 neuron
Allows low light vision
Brain cannot determine exactly where light source is
Visual acuity reduced
How does a Pacinian corpuscle produce a generator potential in response to a specific stimulus?
Pressure stretches membrane
Sodium ion gates open
Sodium ions enter causing depolarisation
Change in membrane potential
What is a stretch-mediated sodium channel?
Special type of sodium channel that changes its permeability to sodium when it changes shape
Why do brightly coloured objects often appear grey in dim light?
Only rod cells are stimulated by low light intensities
Rod cells cannot distinguish between different colour of light
Object is perceived only in a mixture of black and white
Why is it easier to see a star in the sky by looking slightly to the side of it rather than directly at it?
Looking at one side means light from star is focused toward the outer regions of the retina
Mostly rod cells
Stimulated by low light intensities so star is seen
What is the process by which by which sodium ions pass through the gated channels?
Facilitated diffusion
Why can’t we see colours in dim light?
Rod cells work in low light intensities, cone cells do not
They lack colour perception
If a constant stimulus is applied to a receptor it stops responding. Suggest the advantage of this.
Allows noticeable things to be identified
What are 2 stimuli that may result in a change of heart rate?
Blood pressure
Blood pH
How is a resting potential of -70mV maintained in the sensory neurone when no pressure is applied?
Membrane more permeable to K+ and less permeable to Na+
Na+ actively transported out and K+ in
How does applying pressure to the Pacinian corpuscle produce changes in membrane potential?
Applying pressure causes membrane to become distorted
Na+ channels in membrane open so Na+ moves in
Greater pressure move channels open
How is a membrane potential the same whether a medium or heavy pressure is applied?
All or nothing principle
Once passed threshold all Na+ channels open
What are advantages of a simple reflex?
Rapid
Protect against damage to body tissue
Doesn’t have to be learnt
What is saltatory comduction?
Schwann cells insulate axon
Depolarisation only occurs in nodes of ranvier
Faster than if entire length of membrane had to be depolarised
What controls a change in heart rate?
Medulla oblongata
How does stimulation of chemoreceptors during exercise results in a change in heart rate?
Increase in Co2 from respiration
Decrease in blood pH which is detected by chemoreceptors in carotid
More impulse to medulla oblongata
More impulses along sympathetic nervous system
to the SAN increasing heart rate
How does the connection of rod cells to neurons in the retina allow us to see objects in dim light?
Several rods have connections with one bipolar cell
Summation of generator potentials all together
Excess threshold
Individual generator potentials don’t exceed threshold
How does the refractory period ensure that nerve impulses are kept separate from one another?
No opening of Na+ voltage gated channels to allow influx of sodium ions causing depolarisation
