Response To Stimuli Flashcards
What is the basic sequence of response
Stimulus Receptor Coordinator Effector Response
Define stimulus
Detectable change to environment
Define Effector
Cells that produce response
Define receptors
Cells that detect stimulus
What are the types of response in motile organisms
Taxis
Kineses
Describe taxis
Directional movement
In relation to stimulus
+ve is towards
-ve is away
Examples of taxis
+ve phototaxis of algae
+ve chemotaxis of bacteria to glucose
Describe kinesis
Changes to speed
Changes to rate of turns
Random and non-directional movement
Explain how kinesis works
Once in unfavourable conditions = many turns
Much time in unfavourable conditions= less turns and faster movement
Types of movement in Non-motile organisms
Tropism
Examples of tropism
Geotropism
Gravitropism
Phototropism
Use of tropism in shoots
+ve phototropism = more light for Photosynthesis
-ve geotropism= grows up towards light
Use of tropism in roots
+ve geotropism= grows down for support
+ve hydrotropism= water for Photosynthesis
-ve phototropism = grows down towards light
What chemicals are involved in tropism
Plant growth factors
What is the difference between plant growth factors and hormones
Made by cells throughout plant
May have effect on nearby cells
What does IAA stand for
Índoleacetic acid
Give examples of plant growth factors
Auxins
IAA
How does IAA work
Controls cell elongation in flowering plants
Describe how phototropism occurs in shoots
IAA produced in shot tip Travels down both sides evenly at first IAA accumulates on shaded side Increase IAA conc causes cells to elongate faster than on light side Shoot grows towards light
What theory explains how IAA works
Acid growth hypothesis
Describe the acid growth hypothesis
IAA attaches to cell membrane
More H+ are Transported in cell wall
Decreased PH causes microfibrils to be stretched
More plasiticity= elongated
What is the response to touch called
Thigmotropism
Describe the effect of IAA on roots
Produced in tip
Diffuse down sides evenly
Accumulate on lower side due to gravity
IAA inhibits elongation
Upperside grows quicker than lowerside
Grows down
What is the spinal cord made up of
Pairs of motor and sensory neurons entering and leaving
Intermediate neurons within
What is the coordinator in a reflex arc
Intermediate neuron
Why are reflex arcs important
Prevent tissue damage
Allow brain to carry out more complex responses
Very quick
Don’t have to be learnt
Why are reflexes so quick
Very few neurons involved
What are the features of receptors
Specific to one stimulus
Transducers (convert energy from one form to another)
What must occur for an action potential to be generated
Generator potential must exceed threshold
What do pacinian corpuscles respond to
Mechanical pressure
What is a graded response
Where increase in stimulus causes increase in generator potential frequency of action potentials
Describe the structure of the pacinian corpuscles
Neuron end with ending surrounded by layers of connective tissue with viscous gel between layers
Describe what occurs what pressure is applied to a pacinian corpuscles
Layers of tissue deform
Neuron membrane is stretched causing strech mediated sodium ion channel to open
Na+ Diffuse in
Membrane is de polarised
Generator potential created
If exceeds threshold then action potentials produced
What is an action potential
Nervous impulse
Describe why pacinian corpuscles have a graded response
Larger pressure= Larger deformity of membrane = Larger polarisation = Larger generator potential= increase frequency of action potentials
What receptors are present in the eye
Rods and cones
Where are Rod cells found
At periphery only
Describe and explain the visual acuity of rod cells
Low visual acuity due to retinal convergence (multiple rod cells conected to same bipolar neuron and ganglion cell)
Describe and explain the sensitivity to low light intensity of rod cells
Very sensitive due to summation
Generator potentials added up due to retinal convergence so more likely to surpass threshold
Describe and explain visual acuity of cone cells
High because each cone cell is attached to one neuron
Describe and explain the sensitivity to low intensities of light in cone cells
Poor
No retinal convergenc so larger stimulus need to surpass threshold
Are Rod or cone cells more abundant
Rod
How many types of rod cells are there
One
How many types of cone cells are there
3 Red Blue Green Light detection
Where are cone cells found
Mainly at fovea some at periphery
What parts of the nervous system control heart rate
Periphery nervous system
Autonomic
Sympathetic and parasympathetic
Define myogenic
Initiated within the muscle
Describe how a heart beat is started
Wave of electrical excitement starts from SAN
Move across atria walls causing contraction
AVseptum prevents waves entering ventricles
After delay wave eminates from AVN down bundle of his and purkinji fibres
Ventricles contract from apex up
What does SAN stand for
Sino atrial node
Where is the SAN
Right atrium wall
What does AVN stand for
Atrioventricular node
What is the AV septum
Non conductive tissue seperating atrium and ventricles
Where is the AVN found
Right atrium walls
Where are chemo receptors found
Carotid artery walls
What do chemo receptors respond to
Changes in PH
Describe how chemo receptors respond to decreased PH
Chemo receptors increase frequency of nervous impulses to accelatory centre in medulla oblognata
Increase in waves down Sympathetic nerves
More electrical waves emitted from SAN
Increased heart rate and blood flow
Carbon dioxide concentration decreases
PH increases
What is the alternative name for pressure receptors
Baro receptors
Where are pressure receptors found
Carotid artery walls
And aorta
What are carotid arteries
Arteries leading to brain
How do pressure receptors respond to increased blood pressure
More impulses to inhibitory centre in medulla oblognata
More pulses via parasympathetic nerves
Less waves from SAN
Reduced heart rate
How do barorecptors respond to decreased blood Pa
More impulses to accelatory centre in medulla oblognata
More pulses via sympathetic nerves
More waves from SAN
Increased heart rate
