Stimuli and Responses Flashcards
What is a stimulus?
- A change in the internal or external environment
What are receptors?
- A cell or proteins on cell membranes that detect a stimulus
What are effectors?
- Muscles or glands that bring about a response to a stimulus
What are sensory neurones?
- They transmit electrical impulses from receptors to the CNS (brain/ spinal cord)
What are relay neurones?
- They transmit electrical impulses between sensory and motor neurones
What are motor neurones?
- They transmit electrical impulses from the CNS to the effector
What 2 systems make up the nervous system?
- CNS
- Peripheral nervous system
What is the peripheral nervous system?
- Neurones that connect to the CNS and the rest of the body
What 2 systems make up the peripheral nervous system?
- Somatic nervous system
- Autonomic nervous system
What is the somatic nervous system?
- It controls the conscious activities
What is the autonomic nervous system?
- Controls the unconscious activities
What 2 systems make up the autonomic nervous system?
- Sympathetic nervous system
- Parasympathetic nervous system
What is the sympathetic nervous system?
- It prepares the body for action
- Flight or Fight system
What is the parasympathetic nervous system?
- Calms the body down
- Rest and digest system
What is a reflex?
- When the body responds to a stimulus without making a conscious decision
What happens in a reflex action?
- Information travels really fast from the receptors to the effectors
How are nervous responses localised, short lived and rapid?
- Neurotransmitters are secreted directly onto target cells
- Neurotransmitters are quickly removed once their job is done
- Electrical impulses are really fast, to react quickly to stimuli
How do plants respond to stimuli?
- Respond to light and grow towards it to maximise photosynthesis
- Respond to gravity and grow their shoots and roots in the right direction
What is tropism?
- Response of a plant to a directional stimulus
What is positive tropism?
- Growth towards the stimulus
What is negative tropism?
- Growth away form the stimulus
How do shoots respond to light and gravity?
- Shoots are positively phototropic and negatively gravitropic
How do roots respond to light and gravity?
- Roots are negatively phototropic and positively gravitropic
How does IAA work in phototropism?
- IAA moves to the most shaded side of the shoot which elongates the cells so the shoot bends towards the light
- IAA moves to the shaded side of the root so growth is inhibited, bending the root away from the light
How does IAA work in gravitropism?
- IAA moves to the underside of the shoot which elongates the cells making the shoot grow upwards
- IAA moves to the underside of roots where growth is inhibited so the root grows downwards
What does IAA stand for?
- Indoleacetic acid
What is taxes?
- When organisms move towards or away from a directional stimulus
What is kineses?
- When an organisms movement is affected by a non-directional stimulus
How do receptor cells communicate information via the nervous system?
- When the receptor is at resting rate, there is a difference in charge between the inside + outside. So there is voltage across the membrane
- When a stimulus is detected, the cell membrane is excited + becomes more permeable. The change in PD is due to a generator potential
- If the generator potential is big enough it will trigger an action potential, but only if it reaches the threshold
What are pacinian corpuscles?
- Pressure receptors
What happens when a pacinian corpuscle is stimulated?
- The lamallae become deformed and press on the sensory nerve ending
- This causes the sensory neurone’s cell membrane to stretch which deforms the sodium ion channels. They open and sodium ions diffuse into the cell creating a generator potential
- If the generator potential reaches the threshold, it triggers an action potential
What is a mechanoreceptor?
- A receptor that responds to changes in pressure
Where are photoreceptors found?
- They are found in the fovea of the retina
How do photoreceptors convert light to electrical impulses?
- Light enters the eye and hits the photoreceptors which is absorbed by the light-sensitive pigments
- Light causes a chemical change and alters the membrane permeability to sodium ions
- ## A generator potential is created and when the threshold is reached, a nerve impulse is sent along a bipolar neurone to the optic nerve
Where are rods mainly found?
- In the peripheral parts of the retina
Where are cones found?
- Packed in the fovea
Why are rods sensitive to light?
- There are many rods joined to one neurone , so many weak generator potentials combine to reach the threshold and trigger an action potential
Why are cones less sensitive?
- As one cone joins to one neurone, so more light is needed to reach the threshold and trigger an action potential
Why do rods have a low visual acuity?
- Due to the fact they have many rods joined to the same neurone, so 2 points close together can not be told apart
Why do cones have high visual acuity?
- Cones are close together and one cone joins to one neurone.
- 2 action potentials are triggered and go to the brain so you are able to distinguish between 2 points
Distribution of rod cells
- Numerous
- Distributed evenly on the retina but not found on the fovea
Distribution of cone cells
- Less numerous than rod cells
- Distributed mainly at the fovea
How is heart rate controlled?
- Starts w/ SAN, found in right atrium. SAN sets the rhythm by sending out regular waves of electrical activity to atrial walls
- Causes right & left atria to contract at the same time, however collagen tissue prevents waves of electrical from being passed directly from atria to ventricles, so passed onto the AVN
- AVN responsible for passing waves of electrical activity to bundle of His, but there’s a delay before AVN reacts so that the atria empties before the ventricles contract
- Bundle of His is responsible for conducting waves of electrical activity between ventricles to apex of the heart + is split into the Purkyne tissue
- Purkyne tissue carries waves of electrical activity into muscular walls of right & left ventricles, causing them to contract simultaneously
What controls the rate of the SAN?
- Medulla oblongata of the brain
What are baroreceptors stimulated by?
- High and low blood pressure in the aorta and carotid arteries
Where are baroreceptors found?
- In the walls of various arteries especially carotid arteries
What are chemoreceptors stimulated by?
- By a change in oxygen level in the blood, carbon dioxide and pH in the aorta, carotid arteries and in the medulla
Where are chemoreceptors found?
- In the wall of the aorta
- In the wall of the carotid artery
How does the heart respond to high blood pressure?
- Baroreceptors detect high blood pressure, which send impulses to the medulla along the parasympathetic neurones.
- These secrete ACh which bind to receptors on the SAN
- This results in the heart rate slowing down
How does the heart respond to low blood pressure?
- Baroreceptors detect low blood pressure and send impulses to the medulla along the sympathetic neurones
- These secrete noradenaline which binds to receptors on the SAN
- This results in the heart rate speeding up
How does the heart respond high blood oxygen, low carbon dioxide or high pH level?
- Chemoreceptors detect the chemical change in the blood which sends impulses along the parasympathetic neurones
- These secretes ACh which binds to receptors on the SAN
- This results in heart rate decreasing
How does the heart respond low blood oxygen, high carbon dioxide or low pH level?
- Chemoreceptors detect the chemical change in the blood which sends impulses along the sympathetic neurones
- These secrete noradrenaline which binds to receptors on the SAN
- This results in the heart rate increasing
What is a reflex?
- A quick, automatic response to a stiumuli
What do thermoreceptors detect?
- Temperature
What does rhodopsin detect and where is it found?
- Light and dark
- Rod cells
What does lodopsin detect and where is it found?
- Colour
- Cone cells
How is a generator potential created by a photoreceptor cell?
- Light is absorbed by the pigments in rod and cone cells
- This changes the permeability of the membrane so Na⁺ flood in and a generator potential is generated
- If it reaches the threshold, a nerve impulses flows along the bipolar neurone
What is SAN and where is found?
- Sinoatrial node
- Wall of the right atrium
What is the role of SAN?
- Acts as a pacemaker by transmitting waves of electrical activity along the walls of the atria at regular intervals
What is AVN?
- Atrioventricular node
What is the bundle of His?
- A collection of tissue that transmits electrical to the apex of the heart around ventricle walls along the Purkyne fibres
What is the medulla oblongata?
- A region in the brain that modifies heart rate in the cardiovascular centre
What 2 regions are found in the cardiovascular centre?
- Cardio-inhibitory centre
- Cardio-acceleratory centre
What happens when blood pressure is too high?
- It is detected by baroreceptors
- The nerve impulse travels from the medulla along the parasympathetic neurones to the SAN
- This releases ACh
- Heart rate slows down, blood pressure decreases
What happens when blood pressure is too low?
- It is detected by baroreceptors
- Nerve impulse travels from the medulla down the sympathetic neurone to the SAN
- This releases noradrenaline
- Heart rate slows rises, blood pressure increases
What happens if there is low CO₂/ high O₂
- It is detected by chemoreceptors
- Nerve impulse travels from the medulla along parasympathetic neurones to the SAN
- ACh is released
- Heart rate slows down, CO₂ increases/ O₂ decreases
What happens if CO₂ is high/ O₂ low?
- Detected by chemoreceptors
- Nerve impulse travels from the medulla along the sympathetic neurone to the SAN
- Noradrenaline is released
- Heart rate rises, CO₂ decreases/O₂ increases
