Topic 6 - Response To A Stimuli Flashcards
What is a stimulus?
- a detectable change in the internal or external environment of an organism.
- examples: changes in temperature, light intensity, or chemical concentrations.
What is a receptor?
- a specialised cell or organ that detects stimuli.
- examples: rods and cones in the eye detentions light, or baroreceptors in blood vessels detect pressure changes.
What is a response?
- A reaction to a stimulus.
- may involve movement or physiological changes.
What is the relationship between receptors coordinators and effectors?
- Receptor detects the stimulus
- Coordinator processes information
- Effector carries out the response such as muscles contracting or glands releasing hormones
What is tropism?
Directional growth in response to a stimulus.
Example: phototropism; grows towards light
What is taxes?
Directional movement in response to a stimulus.
Example: Positive phototaxis in moths.
What is kinesis?
Non-directional movement where the speed or frequency of turning depends on the intensity of the stimulus.
Example: Woodlice move faster and turn less in dry conditions to find a damp environment.
What is phototropism?
- growth in response to light
- shoots: positively phototrophic (grows towards light).
- roots: negatively phototrophic (grows away from light).
What is gravitropism?
- growth in response to gravity.
- shoots: negatively gravitropic (grows upwards, against gravity.
- roots: positively gravitropic (grows downwards, with gravity).
what is indoleacetic acid?
A growth factor called an auxin produced in the shoot and root tips of flowering plants. IAA distribution controls tropism by influencing cell elongation.
What does it mean about the distribution of IAA if the shoot is illuminated equally from all sides?
- IAA is evenly distributed.
- Cells in the zone of elongation grow at the same rate, causing straight growth upwards.
What does it mean about the distribution of IAA if the shoot is only illuminated on one side?
- IAA moves to the shaded side of the shoot.
- Cells on the shaded side elongate faster, causing the shoot to bend towards the light.
What happens to IAA in the roots?
- IAA accumulates on the lower side due to gravity.
- In roots, IAA inhibits growth, so cells on the upper side elongate faster.
- This causes the root to bend downwards, into the soil.
What happens to IAA in the shoots?
- IAA also accumulates on the lower side, but in shoots, IAA promotes growth.
- Cells on the lower side elongate, causing the shoot to bend upwards, against gravity.
Where is IAA produced?
The tips of shoots and roots.
What is the role of IAA?
Controls cell elongation in response to environmental stimuli like light and gravity.
What does uneven IAA distribution cause?
Uneven cell growth, leading to the plants response.
What does IAA cause in the roots?
IAA inhibits elongation, causing differential growth.
What does IAA cause in the shoots?
IAA promotes elongation of cells.
How does IAA move?
Diffusion and active transport to the area where it is needed.
What are the 2 differences between taxis and kinesis?
Movement is directional - movement is non-directional
Stimulus determines direction - stimulus affects movement rate and direction changes
What is a reflex arc?
The pathway taken by nerve impulses during a reflex action. Reflexes are rapid, automatic responses to a stimulus that help protect the body from harm by bypassing conscious thought.
What is the pathway of a reflex arc?
- Stimulus: a change in the environment
- Receptor: detects the stimulus and generates a nerve impulse
- Sensory neurone: Transmits the impulse from the receptor to the spinal cord.
- Relay neurone: Found in the spinal cord, relays the impulse from the sensory neurone to the motor neurone.
- Motor neurone: transmits the impulse from the spinal cord to the effector
- Effector: A muscle or gland that produces a response.
- Response: the action taken to avoid. Harm.
What are external stimuli?
- Examples: Light, sound, temperature, chemicals.
- Animals may move towards beneficial stimuli (positive response) or away from harmful ones (negative response).
- Example: A moth flying towards light (positive phototaxis).
What is internal stimuli?
- Examples: Changes in blood glucose levels, hunger, or dehydration.
- Internal stimuli trigger movements that maintain homeostasis.
- Example: An animal moving to find water when dehydrated.
What is predation of danger?
- Animals may move to escape predators or environmental hazards.
- Example: A rabbit running away from a fox.
What is nervous system coordination as a mechanism of movement?
- stimuli are detected by receptors
- nerve impulses travel to the central nervous system where decisions are made
- motor neurones send signals to effectors to create movement
What is hormonal control as a mechanism for movement?
Hormones like adrenaline can prepare the body for movement in response to danger.
What is the skeletal and muscular systems role in moment?
Muscles contract to generate force, moving bones via the skeletal system.
What is the pacinian corpuscle?
Touch receptor that detects pressure and vibration.
What is the retina?
light-sensitive layer at the back of the eye, responsible for detecting light and converting it into electrical signals sent to the brain via the optic nerve. It contains specialised photoreceptor cells called rods and cones.
What are rods?
- photoreceptor cells
- selcialise for low light (scotopic) vision
- do not detect colour (monochromatic vision)
- found mainly in the periphery of the retina.
- contain the pigment rhodopsin, which breaks down in the presence of light to initiate a nerve impulse.
What are cones?
- photoreceptor
- specialised for colour vision and sharp detail.
- function best in bright light
- found mainly in the fovea, the central part of the retina
- contain the pigment iodopsin, which is sensitive to different wavelengths
What is the fovea?
- a small depression in the centre of the retina
- contains a high concentration of cones but no rods
- responsible for sharp, central vision.
What is the blind spot?
- the point where the optic nerve leaves the retina
- contain no photoreceptor cells, so it cannot detect light
What are bipolar cells?
Connect photoreceptors to ganglion cells.
What are ganglion cells?
Their axons form the optic nerve, carrying signals to the brains.
How does the retina process light?
- Light enters the eye through the pupil and is focused by the cornea and lens onto the retina.
- Photoreceptor cells absorb light, breaking sown their pigments and generating a generator potential.
- The electrical signal is transmitted through bipolar cells to ganglion cells.
- The optic nerve carries the signal to the visual cortex of the brain for processing.
What are the differences between rods and cones?
Very sensitive to dim light - require bring light
Monochromatic - colour vision
Peripheral retina - central retina
Many rods share one bipolar cell - each cone has its own connection to the brain
What are the adaptions in rod and cone cells in dark and light?
Dark adaption: Rhodopsin in rods regenerates, allowing better vision in low light
Light adaption: cone cells adjust to bright light.
Why is the heart myogenic?
Initiate its own contractions without external nervous input.
What is the role of the SAN in the control of the heartbeat?
Sinoatrial node:
- Located in the wall of the right atrium, the SAN acts as the pacemaker of the heart.
- It generates a wave of electrical excitation that causes the atria to contract simultaneously, pushing blood into the ventricles.
What is the role of the AVN in the control of the heartbeat?
Atrioventricular node:
- Located between the two atria.
- There is a delay at the AVN, ensuring the ventricles contract only after the atria have fully emptied.
What is the role of the bundle of his in the control of the heartbeat?
- The electrical impulse is passed from the AVN to the Bundle of His, located in the septum of the heart.
- The Bundle of His conducts the impulse to the apex of the heart.
What is the role of the purkinje fibres in the control of the heart beat?
- The impulse is transmitted from the apex upwards through Purkyne fibres, which spread throughout the walls of the ventricles.
- This causes the ventricles to contract from the apex upwards, efficiently emptying the heart by pushing blood into the aorta and pulmonary artery.
What variables are adjusted in response to the heart rate?
External variables like carbon dioxide concentration and blood pressure. These changes are detected by specialised receptors and regulated via the nervous system.
What is the effect of pH and carbon dioxide?
- High levels of carbon dioxide lower blood pH because CO2 reacts with water to form carbonic acid.
- Chemoreceptors in the carotid arteries, aorta, and medulla oblongata detect this change.
- The chemoreceptors send impulses to the medulla oblongata, specifically to the cardioacceleratory centre.
- The medulla sends more frequent impulses via the sympathetic pathway to the sinoatrial node (SAN).
- This increases the heart rate, pumping blood faster to the lungs to expel CO2 and restore pH levels.
What do baroreceptors detect?
Baroreceptors in the carotid sinus and aorta monitor blood pressure.
What happens if blood pressure is too high?
- Baroreceptors send more frequent impulses to the medulla, activating the cardioinhibitory centre.
- Impulses are sent via the parasympathetic pathway to the SAN, slowing heart rate and lowering blood pressure.
What happens if blood pressure is too low?
Baroreceptors send fewer impulses, prompting the medulla to stimulate the sympathetic pathway, which increases heart rate.
What is the autonomic nervous system?
Part of the peripheral nervous system, responsible for regulating involuntary actions such as heart rate, digestion, and respiration. It operates without conscious control and ensures the body maintains homeostasis.
What is the sympathetic nervous system?
- Prepares the body for “fight or flight” responses during stress or emergencies
- Increases heart rate, dilates pupils, and inhibits digestion.
- Neurotransmitter: Noradrenaline.
What is the parasympathetic nervous system?
- Promotes “rest and digest” activities to conserve energy and maintain normal functions.
- Decreases heart rate, constricts pupils, and stimulates digestion.
- Neurotransmitter: Acetylcholine.
What are dendrites?
Conduct impulses towards the cell body.
What are axons?
Transmit impulses away from the cell body.
What is the myelin sheath?
Insulates axons, increasing the speed of action potential conduction.
What is a neuron?
Specialised nerve cell that play a key role in transmitting impulses.
What is the resting potential?
In the resting state, the neurone membrane is polarised:
- Outside: Positively charged due to high sodium ion concentration.
- Inside: Negatively charged due to large anions and fewer positive ions.
This polarity is maintained by the sodium-potassium pump which actively transports 3 Na⁺ out and 2 K⁺ in.
What is cardiac output?
The volume of blood pumped by the heart in one minute. It is a measure of the efficiency of the cardiovascular system in delivering oxygen and nutrients to tissues.
Formula for cardiac output
Cardiac output = heart rate x stroke volume
