Section 6: Stimuli and responses Flashcards
1
Q
What is a stimulus?
A
- Detectable change in the internal/external environment of an organism that leads to a response
2
Q
What is a receptor?
A
- Detects stimulus, specific to 1 stimulus
3
Q
What is a co-ordinator?
A
- Formulates a suitable response to a stimulus
4
Q
What is an effector?
A
- Produces response to a stimulus.
- E.g muscle/gland
5
Q
What are the steps in a reflex arc?
A
- Stimulus - receptor - sensory neurone - co-ordinator - CNS/ Relay Neurone - motor neurone - effector - response
6
Q
What is the importance of a reflex arc?
A
- Rapid because only 3 neurones and few synapses
- Autonomic does not involve passage to the brain - does not have to be learnt
- Protect from harmful stimuli e.g escape from predators/ prevents damage to the body/tissues
7
Q
What is Taxes?
A
- Directional response by a simple mobile organism towards a stimulus (positive taxis) or away from a stimulus (negative taxis)
8
Q
What is Kinesis?
A
- Non-directional responses by simple mobile organism who change the speed of movement or the rate of direction change in response to a non-directional stimulus
9
Q
What is tropism and what is positive and negative tropism?
A
- Tropism - growth of a part of a plant in response to a directional stimulus
- Positive tropism - growth towards a stimulus
- Negative tropism - growth away from a stimulus
10
Q
What are growth factors?
A
- Move from growing regions e.g shoot tips/ leaves where they are produced to other tissues where they regulate growth in response to directional stimulus e.g auxins
11
Q
What does IAA do in roots and shoots?
A
- In roots, IAA inhibits cell elongation
- In shoots IAA promotes cell elongation
12
Q
How IAA promotes phototropism in shoots?
A
- Cells in tip of shoot produce IAA - transported down shoot
- IAA concentrates on shaded side
- Promotes cell elongation
- Shoot bend towards light
13
Q
How IAA results in gravitropism in roots?
A
- Cells in tips of shoot produce IAA - transported down shoot
- IAA concentration increases on the lower side of the root
- Inhibits cell elongation
- Root curves downwards towards gravity
14
Q
How is a generator potential produced?
A
- Mechanical stimulus e.g pressure deforms lamellae and stretch-mediated sodium ion channel
- Sodium ion channels open and sodium ions diffuse into the sensory neurone
- Greater pressure causes more channels to open and more sodium ions to enter
- Causes depolarisation, leading to a generator potential - if Generator potential reaches threshold it triggers an action potential.
15
Q
What does the Pacinian Corpuscle illustrate?
A
- Receptors only respond only to a specific stimulus (pressure)
- Stimulation of a receptor leads to establishment of a generator potential. When threshold is reached an action potential sent (all or nothing principle)
16
Q
What are some of the differences between rod and cone cells?
A
- Rods - more at periphery end . Cones - concentrated at fovea
- Rods - 1 type of rod containing 1 pigment. Cones - 3 types of cones containing different pigments
- Rods - connect in groups to 1 bipolar neurone. Cones - 1 cone joins 1 neurone
- Rods - Very sensitive to light. Cones - less sensitive to light
- Rods - Low visual acuity. Cones - high visual acuity
- Rods - Black and white (monochromatic). Cones - Colour (trichromatic)
17
Q
Why are rods more sensitive to light?
A
- Rods connected in groups to 1 bipolar neurone
- Spatial summation
- Stimulation of each individual cell connected in groups means threshold is more likely met
18
Q
Why do cones have a higher visual acuity?
A
- 1 cone joins to 1 neurone
- If 2 adjacent cone cells are stimulated, brain receives separate impulses
18
Q
Why do cones have a higher visual acuity?
A
- 1 cone joins to 1 neurone
- If 2 adjacent cone cells are stimulated, brain receives separate impulses
19
Q
Why do rods have a lower visual acuity
A
- Rods connected in groups to 1 bipolar neurone
- Spatial summation
- Many neurones only generate 1 impulse/ action potential, regardless of how many neurones stimulated
20
Q
How does cones allow for colour vision?
A
- 3 types of cones
- With different optical pigments that absorb different wavelengths
- Stimulation of different combinations gives a range of colour perception
21
Q
How is the heart stimulated
A
-
SAN sends out regular waves of electrical activity across both atria
- Causing right/left atria to contract simultaneously. Non-conducting tissue prevents wave crossing directly to ventricles
- Waves of electrical activity reaches AVN which delays impulse, allowing atria to fully contract and empty
- AVN passes wave of electrical activity to Bundle of His which conducts waves between ventricles to the apex of the heart where it branches into smaller fibres - Purkyne fibres
22
Q
Where are the baroreceptors and chemoreceptors located
A
- In the aorta and carotid arteries
23
Q
What are baroreceptors and chemoreceptors stimulated by
A
- Baroreceptors are stimulated by high/low blood pressure
- Chemoreceptors are stimulated by blood pH, CO2 conc, O2 conc
24
Q
What happens when there is a low BP
A
- Baroreceptors detect the low blood pressure
- More frequent impulses to the medulla
- More frequent impulses sent to SAN along sympathetic neurone
- Cardiac muscle contracts more frequently so heart rate increases
25
Q
What happens when there is high blood pressure
A
- Baroreceptors detect the high blood pressure
- More frequent impulses to medulla.
- More frequent impulses sent to SAN along parasympathetic neurone
- Less frequent impulses sent from SAN. Cardiac muscle contracts less frequently so heart rate decreases
26
Q
What happens when there is a high blood carbon dioxide concentration/ low pH
A
- Chemoreceptors detect the high carbon dioxide concentration
- More frequent impulses are sent to SAN along sympathetic neurone
- More frequent impulses sent to SAN - cardiac muscle contracts more frequently so heart rate increases
27
Q
What happens when there is a low blood carbon dioxide concentration?
A
- Chemoreceptors detect low blood CO2
- More frequent impulses sent to medulla
- More frequent impulses sent to SAN along parasympathetic neurone
- Less frequent impulses sent from SAN - cardiac muscle contracts less frequently - heart rate decreases.
28
Q
EXAM QUESTION: Increased intensity of exercise leads to an increased heart rate. Explain why (3)
A
- Oxygen/carbon dioxide detected by chemoreceptors/ pressure detected by baroreceptors
- Medulla/ cardiac centre involved
- More impulses to SAN/ along sympathetic nerve
