Response to stimuli Flashcards
What is a stimulus?
A detectable change in the internal or external environment of an organism that leads to a response in the organism
What does the central nervous system consist of?
CNS consists of brain and spinal cord
What does the peripheral nervous system consist of?
Sensory nervous system and motor nervous system
What does the motor nervous system consist of?
Voluntary nervous system and autonomic nervous system
What does the voluntary nervous system do?
Carries impulses to body muscle, under voluntary control
What does the sensory nervous system do?
Carries nerve impulses from receptors to CNS
What does the autonomic nervous system do?
Carries nerve impulses from CNS to glands, cardiac and smooth muscles
What is the spinal cord?
A column of nervous tissue that runs along the back and lies inside the vertebral column for protection
What are the four types of receptors?
Photoreceptors, chemoreceptors, thermoreceptors and mechanoreceptors
What is the Pacinian Corpuscle and where is it found?
Mechanoreceptor, deep in the skin, typically on fingers, soles of feet and external genitalia
They are also found in joints, tendons and ligaments where they enable an organism to know which joints are changing direction
What’s the structure of a Pacinian Corpuscle?
Single sensory neurone in the centre, surrounded by layers of connective tissue with a viscous gel between the tissue layers
What type of sodium channel is in the plasma membrane of PC?
Stretch-mediated sodium channel
When does the PC have a resting potential?
In its normal resting state, when the sodium channels are too narrow to allow sodium ions to pass through
When are the sodium channels of PC widened?
When pressure is applied, it becomes deformed and the membrane around the neurone stretches
When is a generator potential produced?
When the sodium ions move into the PC
What does the generator potential do?
Creates an action potential (nerve impulse) that travels to CNS
What is the order of cells inside the retina?
Ganglion cells, bipolar neurones then rod and cone cells
How are rod and cone cells acting as transducers?
Conserving light energy into electrical energy of a nerve impulse
How many rod cells are there in each eye?
120 million roughly
Can rod cells distinguish between different wavelengths of light?
No, meaning they can not identify colour
Where are rod cells dense or absent?
Greater density at the periphery and absent at the fovea
What are rod cells used for?
Detect low light intensity, so are used to see in the dark or dim lighting
Why are multiple rod cells connected to a single bipolar cell?
Much greater chance of threshold for generator potential being exceeded
What must happen for a generator potential to be created in rod cells?
Pigment Rhodopsin must be broken down
Why do rod cells give poor visual acuity?
Multiple neurones are stimulated in other bipolar cells but only one impulse is received by the brain
How many types of cone cells are there?
Three, each respond to a different wavelength of light, meaning we can see colour
How many cone cells are there in each eye?
Around 6 million
Why do cone cells only respond to high light intensity?
Each cell is connected to a single neurone
What pigment do cone cells contains?
Iodopsin, each type contains a specific iodopsin
Why do cone cells need high light intensity?
They require higher amounts of energy to create generator potential
Why do cone cells give good visual acuity?
Each connected to a single bipolar cell, so if 3 are stimulates then 3 signals are received
Where are cone cells most dense or absent?
Most dense at the fovea and they are not found in the periphery
What are the two divisions of ANS?
Parasympathetic nervous system and sympathetic nervous system
What does the sympathetic nervous system do?
Stimulates effectors to speed up any activity, controls effectors when we exercise strenuously or experience powerful emotions and helps us cope in stressful situation by heightening our awareness and preparing us for activity (fight or flight)
What does the parasympathetic nervous system do?
Inhibits effectors and slows down any activity, control activities under normal resting conditions and helps to conserve energy and replenish the body’s reserves
What is SAN?
Sinoatrial node, control heart rate (pacemaker)
How is heart rate controlled?
A wave of electrical activity spreads out from the SAN, causing both atria to contract. The wave enters the AVN, which conveys a wave between the ventricles across purkyne tissue (bundle of His). The wave is conducted through the AV septum to the base of the ventricles where the wave is released causing the ventricles to contract quickly at the same time
What is AVN?
Atrioventricular node, a group of cells, which lies between the atria
What is Purkyne tissue?
A series of specialised muscle fibres, collectively called a Bundle of His
What centre of the brain controls the changes to heart rate?
Medulla oblongata
What does increasing and decreasing HR involve?
Increasing: SAN and sympathetic nervous system
Decreasing: SAN and parasympathetic nervous system
Where are chemoreceptors found?
In the wall of carotid arteries
What detection causes chemoreceptors to send signals?
Sensitive the changes in pH, resulting from changes in CO2 concentration
What do chemoreceptors do when PH is lowered?
Increase frequency of nerve impulses to the centre of medulla oblongata in control of increasing heart rate
What are baroreceptors and where are the found?
Pressure receptors, found in the walls of the carotid arteries and the aorta
When do baroreceptors operate?
When blood pressure is too high or low
What do baroreceptors do when blood pressure is too high?
Transmit more nerve impulses to the centre of the medulla oblongata in control of decreasing heart rate
What happens when the centre decreasing HR receives more impulses?
Centre send impulses via the parasympathetic nervous system to the SAN which decreases HR
What happens when blood pressure is too low?
Receptors transmit more nerve impulses to the centre in the medulla oblongata that increases the HR, this centre sends impulses via the sympathetic nervous system to the SAN which increases the rate at which it beats
What is a taxis?
A form of simple response where the direction is determined by the direction of the stimulus
How are taxes classified?
Positive or negative
What is kinesis?
Simple form of response in which the organism does not move towards or away from a stimulus, instead it changes the speed at which it moves and rate at which it changes direction
What happens if an organism moves considerable distance into an unfavourable environment?
The rate of changing direction may slow so it moves in a long straight line
What’s an example of kinesis?
Wood lice lose water form their body when in a dry environment , they move more rapidly and change direction which increases their chances of returning to damp conditions
What is IAA?
Indoleacetic Acid is a plant growth factor that controls plant elongation
How does IAA control phototropism?
Cells in root tip produce IAA, light causes IAA to move to shaded side of the plant and the cells on shaded side elongate more due to more IAA
Where does IAA accumulate in gravitropism?
Lower side on horizontal growth
