6A Stimuli and Response Flashcards
Myogenic
Contract and relax without receiving signals from nerves
How is the regular heartbeat maintained?
Through the pattern of contractions of the heart
SAN
Sinoatrial node
Where is the SAN?
In the wall of the right atrium
How does the SAN act like a pacemaker?
It sends out regular waves of electricity to the atrial walls
What prevents the wave of electricity in the heart from being passed from the artia to the ventricle?
Non-conducting collagen tissue
Where are the waves of electrical impulses transferred to from the SAN?
The AVN
AVN
Atrioventricular node
What does the AVN do?
It passes the electrical impulses to the bundle of His
What is the bundle of His?
In the heart, a group of muscle fibres that are responsible for conducting waves of electrical impulses between the ventricles to the apex (bottom) of the heart
What does the bundle of His split into?
Thinner muscle fibres in the left and right ventricle walls called Purkyne Tissue
What does the Purkne Tissue do?
Carries the waves of electrical impulses to the muscular walls of the right and left ventricles, causing them to contract simultaneously from the bottom upwards.
Why is there a slight delay before the AVN reacts?
To make sure the atria have emptied before they contract
What part of the brain unconsciously controls the rate at which the SAN fires ?
The medulla oblongata
What receptors deal with blood pressure?
Baroreceptors
What receptors detect the concentration of oxygen and carbon dioxide in the blood?
Chemoreceptors
If a high blood pressure is detected by the baroreceptors, what happens?
Impulses are sent to the medulla oblongata. The Medulla sends impulses down the parasympathetic neurones. They secrete acetylcholine (neurotransmitter) which binds to receptors on the SAN
If a low blood pressure is detected by baroreceptors, what happens?
Impulses are sent to the medulla, which sends impulses down the sympathetic neurones. These secrete noradrenaline (a neurotransmitter) which binds to receptors on the SAN
What happens if a high concentration of oxygen is detected by chemoreceptors?
Impulses are sent to the medulla, which sends impulses through the parasympathetic neurones. These secrete acetylcholine which binds to receptors on the SAN
What happens if a kow concentration of carbon dioxide is detected by the chemoreceptors?
Impulses are sent to the medulla, which sends impulses through the parasympathetic neurones. These secrete acetylcholine which binds to receptors on the SAN
What happens if a high pH is detected by the chemoreceptors?
Impulses are sent to the medulla, which sends impulses through the parasympathetic neurones. These secrete acetylcholine which binds to receptors on the SAN
What happens if a low concentration of oxygen is detected by the chemoreceptors?
Impulses are sent to the medulla, which sends impulses through the sympathetic neurones. These secrete noradrenaline which binds to receptors on the SAN
What happens if a high concentration of carbon dioxide is detected by the chemoreceptors?
Impulses are sent to the medulla, which sends impulses through the sympathetic neurones. These secrete noradrenaline which binds to receptors on the SAN
What happens if a low pH is detected by the chemoreceptors?
Impulses are sent to the medulla, which sends impulses through the sympathetic neurones. These secrete noradrenaline which binds to receptors on the SAN
Stimulus
A change in the environment that can be detected by an organism
Receptor
An organ specialised to detect a change in the internal or external environment
Taxis
A response that involves movement in a specific direction
Positive taxis
Movement towards a stimulus
Negative taxis
Movement away from a stimulus
Kinesis
Movement in random directions
Why is kinesis carried out?
To increase the chance of reaching different conditions more quickly. E.g Increasing speed and direction changes will increase the speed of a woodlouse finding a damp and dark region
What is an auxin?
A plant hormone
What is the auxin called that controls tropisms- (growth responses)
IAA
How does IAA effect parts of the plant?
Elongates the plant cells on the shoots so the shoot can bend or grow. Inhibits growth of the root cells
What is the reflex arc?
Stimulus, Receptor, Sensory Neurone, Intermediate Neurone, Motor Neurone, Effector, Response
What is the name for the pressure receptor in your skin?
Pacinian Corpuscle
What happens when a receptor is in its resting state?
There’s a voltage across the membrane (potential difference) as there is a difference in charge between the inside and the outside of the cell
Resting potential
When a receptor is at its resting state
What happens when a stimulus is detected by the receptor?
The membrane of the cell becomes more permeable and ions can move in or out of the cell (change in potential difference)
Generator potential
The change in potential difference of a cell due to a stimulus
Action potential
If the generator potential is big enough, an action potential is triggered, and sends an electrical impulse down the sensory neurone
How is the strength of the stimulus detected?
Action potentials are all one size, so it is the frequency of the action potentials that determine the strength
What type of receptors is the Pacinian Corpuscle?
Mechanoreceptors
Describe the structure of the Pacinian Corpuscle
Sensory nerve ending wrapped in lots of layers of connective tissue called lamellae
What happens when the Pacinian Corpuscle is stimulated?
The lamellae are deformed and press on the sensory nerve ending. This causes the sensory neurone’s cell membrane to stretch, deforming the stretch-mediated sodium ion channels. The channels open, and sodium ions can diffuse into the cell, creating a generator potential
How does light enter the eye?
Through the pupil. The amount of light is controlled by the iris
How are light rays focused onto the retina in the eye?
By the lens
Where are photoreceptors in the cell?
The retina, but mostly concentrated on the fovea
How are nerve impulses carried from the retina to the brain?
By the optic nerve
Where is the blind spot in the eye?
Where the optic nerve leave the eye because there are no photoreceptors present
How do photoreceptors convert light into electrical impulses?
Light hits the photoreceptors and is absorbed by light sensitive optical pigments. Light bleaches the pigments, causing a chemical change, and altering the membrane permeability to sodium ions. A generator potential is created, and if the threshold is reached, an impulse is sent along a bipolar neurone
Bipolar neurone
Connects photoreceptors to the optic nerve
What are the two types of photoreceptors in the eye?
Rods and Cones
Where are the rods found?
In the peripheral parts of the retina
Where are the cones found?
Packed together in the fovea
What colours can rods detect?
Only black and white (monochromatic)
What colours can cones detect?
Colour (trichromatic)
How many types of cone cells are there and what do the detect?
3 (trichromatic). One of each type- red sensitive, blue-sensitive, green-sensitive
How do you see different colours?
When the three different optical pigments in the cone cells are stimulated in different amounts
Why are rods more sensitive to light?
Many rods are attached to one neurone, so many weak generator potentials can combine into one to make the threshold and create an action potential
Why are cones less sensitive to light?
Only one cone is joined to one neurone, so more light is needed to generate a big enough generator potential and reach the threshold to make an action potential
Why do rods give a low visual accuracy?
Many rods are joined to the same neurone, so light from two points close together can’t be told apart
Why do cones give high visual accuracy?
Cones are close together and one cone joins to one neurone, so light from two points will trigger two action potentials
Somatic nervous system
Voluntary nervous system
Autonomic nervous system
Involuntary nervous system
