Chapter 14 - Response to stimuli Flashcards
What is a stimulus?
A noticeable change in the external or internal environment that leads to a response
What are stimuli detected by?
Receptors
How many stimuli does each receptor detect?
1
What is the name of the molecule that generates a response?
Effector
Describe the sequence of events in the nervous system
Stimulus - receptor - coordinator - effector - response
What is a taxis?
A response whose direction is determined by the stimulus
What is a kinesis?
A response where the organism changes the speed at which it moves and direction
What is a tropism?
The growth of part of a plant in response to a directional stimulus
Why are plant growth factors not described as hormones?
They may be made throughout the plant, not just in organs
Some factors impact the tissues that release them rather than acting on a distant organ
What hormone controls plant cell elongation?
IAA
Describe how plants respond to unilateral light
Cells in the tip produce IAA, which is transported throughout the plant
Light causes the IAA to move to the unshaded region
A greater concentration of IAA builds up on the shaded region than the unshaded one
IAA causes the elongation of cells - cells on the shaded side grow more
This causes the tip to bend towards the light
What impact does IAA have on roots?
It inhibits cell elongation
Describe how plants respond to gravity
Cells in the root tip produce IAA, which is distributed throughout the root
It is transported to all sides of the root
Gravity means that a higher concentration of IAA gathers on the lower side
Cells on this side grow more slowly than those on the upper side
This causes the root to bend downwards
What happens as plant cells mature?
Their responsiveness to IAA decreases - they become more rigid
What is the Central Nervous System?
The brain and spinal cord
What is the Peripheral Nervous System?
Made of pairs of nerves that originate from the brain or spinal cord
What are the two neurones found in the peripheral nervous system?
Sensory and motor neurones
What do sensory neurones do?
Carry nerve impulses away from receptors towards the central nervous system
What do motor neurones do?
Carry nerve impulses away from the central nervous system to effectors
What two nervous systems is the motor nervous system divided into?
The voluntary and the autonomic nervous systems
What is the voluntary nervous system?
Carries nerve impulses to body muscles and is under voluntary control
What is the autonomic nervous system?
Carries nerve impulses to muscles and is not under voluntary control
Describe the process of a reflex arc
Stimulus Receptor Sensory neurone Coordinator Motor neurone Effector Response
Why are reflex arcs important?
Rapid
Instinctive
Short neurone pathway and few synapses
Don’t require input from the brain - prevents the brain from being overloaded
What do Pacinian Corpuscles respond to?
A change in pressure
What type of receptor is a Pacinian Corpuscle?
Sensory
How does a Pacinian Corpuscle act as a transducer?
Converts energy from the stimulus into nerve impulses that can be understood by the body (a generator potential)
Where are Pacinian Corpuscles found?
Deep in the skin, joints, ligaments and tendons
Describe the structure of a Pacinian Corpuscle
A single sensory neurone surrounded by layers of connective tissue with gel in between
How does a stretch-mediated sodium channel work?
In its resting state, the channels are too narrow for Na+ ions to pass through
When pressure is applied, it is deformed and the membrane surrounding the neurone stretches
This widens the channels so Na+ ions can diffuse into the neurone
The influx of ions depolarises the neurone and creates a generator potential
This creates an action potential along neurones to the CNS
How do rod and cone cells work as transducers?
Converting light energy into the electrical energy of an impulse
Why do rod cells only show us images in black and white?
They can’t distinguish between different wavelengths of colour
Why do rod cells allow us to see at low light intensity?
Many rod cells are connected to a single bipolar cell so there is a greater chance that the threshold value will be exceeded to produce a generator potential. This provides the energy to break down rhodopsin
What is a consequence of many rod cells linking to the same bipolar cell?
The light received by these cells will create just the one impulse and so rod cells can’t distinguish between two points of light
Why do cone cells only respond to high light intensity?
Each cell is connected to its own bipolar cell so the stimulation of a number of cone cells can’t be combined to exceed the threshold potential and break down iodopsin
What cells are found at the fovea?
Cone cells
What cells are found at the periphery of the retina?
Rod cells
What does stimulating the sympathetic nervous system result in?
An increase in activity
What does stimulating the parasympathetic nervous system result in?
A decrease in activity
Describe the sequence of events that cause the heart to beat
A wave of electrical impulses spread from the SAN across the atria, making them contract
A layer of non-conductive tissue stops this impulse reaching the ventricles
The impulse enters the AVN and travels along the Bundle of His to the base of the ventricles
This causes the ventricles to contract from the bottom up
What causes the heart rate to increase during exercise?
More respiration = more CO2 = lower pH
Chemo-receptors in the carotid artery detect this
Increases the frequency of impulse to the medulla oblongata
This increases the frequency of impulses via the sympathetic nervous system to the SAN
This causes the heart to beat more frequently so more CO2 is exhaled and the CO2 concentration returns to normal
What happens when blood pressure is too high?
Pressure receptors send impulses to the centre in the medulla that decreases heart rate
This centre sends an impulse through the parasympathetic nervous system to the SAN which decreases the heart rate
What happens when blood pressure is too low?
Pressure receptors send impulses to the centre in the medulla that increases heart rate
This centre sends an impulse through the sympathetic nervous system to the SAN which increases heart rate
