Chapter 14 - Response to Stimuli Flashcards
What is a stimulus?
A stimulus is a change in the internal or external environments of an organism
How are stimuli detected in organisms?
By receptors, which are each specific to one type of stimulus
What are the differences between neuronal and hormonal responses?
Nervous responses are very quick and localised because the response is sent along the neurone and releases a chemical messenger directly onto the cell, resulting in a localised, short-lived and quick response. Hormones however are distributed through the blood and therefore have a much slower response, however their response is much more widespread and lasts longer
Why are responses so important?
Without animals being able to respond effectively to stimuli their chance of survival is lowered.
What is Indoleacetic acid (IAA)?
IAA is a plant growth hormone that, in the meristem will oppose the direction that the light hits the plant, which causes the opposite side of the plant to grow more quickly, stretching the plant towards the light. However in the roots it has the opposite effect, and slows the growth process resulting in the IAA moving to the bottom of the root and therefore the top grows faster and curves downwards.
What are taxes in organisms?
A taxis is a simple repsonse as a result of a stimulus where the organisms will either move directly towards to stimulus (positive taxis) or directly away from the stimulus (negative taxis)
What are the stages of a reflex arc?
Stimulus -> receptor -> Coordinater -> effector -> response
What is a kinesis?
A kinesis is where an animal receives a stimulus and moves in random directions and speeds. If the stimulus or conditions become more unfavourable, the organsims turns more often and moves faster, however if it moves into more favourable conditions it will slow down and turn less often
How is a pressure stimulus detected in a finger?
It is detected through a Pacinian corpuscle. This is the end of a sensory neurone with sacs of fluid around it. When a pressure is applied to the Pacinian corpuscle, stretch-mediated sodium channels open, allowing sodium ions to enter causing an action potenital. More pressure results in more channels opening which increases the frequency of action potentials, stronger response - this is known as a generator potential
What are the two main types of cells in the human eye?
The rod cells and the cone cells, with rod cells being considerably more numerous and tending to line the peripherary of vision
How do rod cells work?
They contain a pigment called rhodopsin which is easily broken down by low levels of light (resulting in black and white vision) and several rod cells are connected to one bipolar cell, which causes summation which means that each rod cell needs lower levels of stimulus to cause a visual response. However due to this summation, there is a quick level of adjustment to light but only low levels of visual acuity
How do cone cells work?
They are largely distributed around the fovea, and generally only one cone cell will go to each bipolar cell. There are three different types of cone cell which each contain a different type of iodopsin (their pigment) which provides colour vision, however it means high levels of light are required to induce an action potential. Due to the lack of summation, adjustment can be slow and requires high light intensity, but results in high visual acuity
What term is used to describe the heart?
It is myogenic, which means it is able to beat without the signalling of the brain
Where does the stimulation of the heart come from?
The SA (sinoatrial) node in the right atrium
How does the SA node cause a heartbeat?
It send a wave of electricasl activity over the heart, causing the atriums to pump before the eave reaches the atrioventricular (AV) node, which delays the wave before sending it down the bundle of His, preventing it from going into the ventricles top-down. When it reaches the apex of the heart, the wave will travel up the Purkyne fibres, which causes the ventricles to contract.
