3.6.1 Response to stimuli Flashcards
Describe how electrical impulses control the cardiac cycle (start at the SAN)
How does atrial contraction occur ?
Depolarisation at the SAN generated an electrical impulse that spreads across the right and left atria
Why can’t the wave of electrical impulse pass directly from the atria to the ventricals?
There is a band of non conducting collagen tissue preventing this
Why is there a delay before the impulse is conducted from the AVN to the ventricles ?
It ensures that the atria have finished contracting and have emptied and the ventricles have filled with blood before they contract
What are the Purkyne fibres?
Large specialised muscle fibres that conduct impulses rapidly to the apex of the ventricles
What is the Bundle of His?
The right and left bundles of fibre are collectively known as the Bundle of His
Why do the ventricles contract from the bottom up ?
This ensures the blood is pushed into the aorta and pulmonary artery
What controls the rate of breathing ?
Ventilation centres in the medulla oblongata in the brain
What happens when the level of carbon dioxide in the blood increases during exercise ?
the pH of the blood decreases
Where are chemoreceptors and what do they do ?
Aortic bodies and carotid bodies that are sensitive to changes in blood pH and send impulses to the medulla oblongata
What happens if chemoreceptors detect a decrease in blood pH?
They send nerve impulses to the medulla oblongata which sends more frequent nerve impulses via the sympathetic NS to the intercostal muscles and diaphragm. This increases the rate and depth of breathing
Why does the cardiac output increase during exercise?
The heart rate and stroke volume increase
Which part of the brain controls the heart rate ?
The cardiovascular centre in the medulla oblongata
How does the cardiovascular centre control the heart rate ?
It controls the rate at which the SAN fires electrical impulses
What are baroreceptors and how are they stimulated?
pressure receptors in the aortic and carotid bodies which are stimulated by high and low pressure
How are chemoreceptors involved in heart rate?
They monitor the oxygen level in the blood and also carbon dioxide and pH
What is the sympathetic nervous system?
Gets the body ready for action. Stimulates effectors - e.g. increases the heart rate during exercise
What is the parasympathetic nervous system?
Calms the body down. It’s the rest and digest system which helps to decrease the heart rate after exercise
What is the response of the SAN when there is high blood pressure ?
SAN fires impulses less frequently to slow heart rate and reduce blood pressure back to normal
What is the response of the SAN when there is low blood pressure ?
SAN fires impulses more frequently to increase heart rate and increase blood pressure back to normal
What is the response of the SAN when there is high blood oxygen or low CO2 or high pH levels ?
SAN fires impulses less frequently to decrease heart rate and return oxygen, carbon dioxide and pH levels back to normal
What is the response of the SAN when there is low blood oxygen or high CO2 or low pH levels ?
SAN fires impulses more frequently to increase heart rate and return oxygen, carbon dioxide and pH levels back to normal
What factors affect rate of breathing ?
temperature, exercise, hormones, CO2 and O2 conc, pH
What is a tropism?
A plants growth response to a directional stimulus
What is positive tropism ?
Growth towards the stimulus
What is negative tropism ?
Growth away from the stimulus
What are the three types of cones ?
Red sensitive, green sensitive and blue sensitive
What is a reflex action ?
Rapid and automatic, short lived response to a stimulus
What is a stimulus?
A change in the internal or external environment
What is the light sensitive pigment in rods ?
rhodopsin
Describe the structure and the function of the rods
Found mainly in peripheral parts of retina, only give information in black and white, work and dim and bright light. 2 or 3 receptors can be attached to one neurone.
Describe the structure and the function of the cones
Found packed together in fovea, give information in colour , work only in bright light, 1 receptor is connected to 1 neurone
Describe the structure of the motor neurones
Many short dendrites carry nerve impulses from the CNS to the cell body. One long axon carries nerve impulses from the cell body to effector cells
Describe the structure of the relay neurones
Many short dendrites carry nerve impulses from sensory neurones to the cell body. an axon carries nerve impulses from the cell body to motor neurones
Describe the structure of the sensory neurones
One long dendron carries nerve impulses from receptor cells to the cell body which is located in the middle of the neurone. One short axon carries nerve impulses from the cell body to the CNS
What is a sensory neuron?
Transmit electrical impulses from receptors to the central nervous system
What is a relay neuron?
Found in the CNS. transmit electrical impulses from the sensory neurones to the motor neurones
What is a motor neuron?
The cell body is always in the CNS and the axon extends out, conducting electrical impulses from the CNS to the effectors
Describe the medulla oblongata
At base of brain near top of the spinal cord. Automatically controls breathing rate, heart rate and blood pressure
What are auxins ?
Growth factors that stimulate growth of shoots by cell elongation. This is where the cell walls become lose and stretchy, so the cells get longer. They inhibit growth in the roots though
What is an important auxin that is produced in the tip of shoots in flowering plants ?
Indoleacetic acid (IAA)
How does IAA move around the plant to control tropisms ?
It moves around the plant by diffusion and active transport over short distances and via the phloem over long distances
Describe how IAA is involved in phototropism
IAA moves to the more shaded parts of the shoots and roots, so there’s uneven growth. IAA causes cells to elongate and the shoot bends towards the light. IAA inhibits growth in roots so the root bends away from the light
Explain how auxin causes phototropsim
