6A Response to Stimuli Flashcards
Define a stimulus
change in the internal/external environment
What detects a stimulus?
receptors
What do effectors do? Give examples of effectors
bring about a response to stimuli eg. muscle cells and cells in glands
What is the simple difference between the central nervous system and the whole nervous system?
CNS= brain and spinal cord, coordinates info
NS= made up of all the neurons in the body. 3 main types are sensory, relay and motor
Simply describe what happens during a reflex action
- receptors in a sense organ detect a stimulus
- electrical impulses are sent along sensory neurons to the CNS
- the CNS sends electrical impulses to an effector along a motor neuron
- the effector then responds accordingly
Describe simply what a synapse is
- the connection between 2 neurons
- nerve signal is transferred by chemicals called neurotransmitters which diffuse across the gap
- these chemicals set off a new electrical signal in the next neuron
What are auxins?
- plant growth hormones
- they control growth at the tips of shoots and roots
- they move around the plant in solution
- they stimulate growth in shoots and inhibit growth in roots
What is a taxis?
- a directional response to a stimulus
- eg. a woodlouse moving away from a light source which increases its chance of surviving predation
What is a kinesis?
- a non-directional response to a stimulus
- eg. woodlouse moving slowly in humid conditions which leaves them in humid conditions for longer so less water loss and increased survivability
What is a tropism?
- directional response to a stimulus by a PLANT
Describe phototropism
- directional response too light
- positively phototropic = grows towards light
- negatively phototropic = grows away from light
Describe gravitropism
- directional response to gravity
- positively gravitropic = grows towards gravity/downwards
- negatively gravitropic = grows away from gravity/upwards
Describe the tendancies of plant roots
- positively gravitropic
- negatively photoropic
Describe the tendancies of plant shoots
- negatively gravitropic
- positively phototropic
What is indoleacetic acid?
- IAA
- a type of auxin of flowering plants
- can diffuse into nearby cells or can be carried in the phloem
How is IAA responsible for phototropism?
- diffuses to shady side of plants and encourages cell elongation so plant bends towards light (SHOOTS)
- in ROOTS it inhibits cell elongation so the root grows away from the light
How is IAA responsible for gravitropism?
- diffuses to the underside of shoots and roots
- in the shoots this encourages upward growth because it elongates the cells on the underside
- in shoots it inhibits cell elongation in the underside cells so it encourages downward growth
Give an example of receptors
- rods and cones
- photoreceptors in the eyes
- allow for the detection of light
What does the CNS consist of?
brain and spinal cord
What does the PNS consist of?
- the autonomic section and the voluntary section
What does the autonomic section of the PNS consist of?
- sympathetic response (fight or flight)
- parasympathetic response (rest or digest)
Compare and contrast the nervous system and the endocrine system
- nervous is fast, endocrine is slow
- nervous is short-lasting, endocrine is long-lasting
- nervous is electrical, endocrine is chemical
- nervous is a localised area, endocrine is a generalised area
- nervous travels via neurons, endocrine travels in bloodstream
What is the summary order of a reflex arc?
- stimulus
- receptor
- sensory neuron
- CNS (relay neuron)
- motor neuron
- effector
- response
What do receptors detect?
- a single type of stimulus
- eg. change in light, temp or pressure
Describe what is happening with a receptor when it is resting
- there’s a difference in electrical charge between the inside and outside of the cell
- imbalance in charge is due to the differing concs of ions
- this is resting potential
At rest, which part of the cell is more negatively charged?
- the inside is more negatively charged
What do changes in electrical charge create?
- voltage
- the changes in charge are small so we use millivolts as the unit
What are generator potentials?
- small changes in voltage across cell membranes
- receptor detects stimulus, membrane becomes excited
- this means ions can move into the cell more easily
- the influx of ions causes a voltage change
What is an action potential?
- when the generator potential is large enough an action potential is triggered
- an action potential is an electrical impulse that travels down the neuron
- a certain voltage must be reached for this to happen
What is the threshold potential?
- the certain voltage value that must be reached for the action potential to be sent down the neuron
Are action potentials variable in size or always the same?
- always the same
- all or nothing principle
What are Pacinian corpuscles?
- mechanoreceptors found on the surface of the skin
What do Pacinian corpuscles do?
- they detect small vibrations or changes in pressure
- they contribute to the sensation of touch
- they contain sensory nerve endings that are surrounded by layers of tissue called lamellae
Describe the sequence of events that occur when the Pacinian corpuscle is stimulated.
- Pacinian corpuscle is stimulated and the lamellae become deformed
- the lamellae then press on the nerve ending, opening stretch-mediated sodium ion channels
- sodium ions diffuse into the cell through these ion channels which creates a generator potential
- if the generator potential exceeds the threshold potential then an action potential is triggered
Describe photoreceptors and where they are found
- found in the eye
- sensitive to changes in the eye
- as light enters the eye, photoreceptors are stimulated
- light enters through the pupil and light is focussed onto the retina
What are the 2 types of photoreceptors found in the eye?
- rods and cones
- rods are at the edge of the retina
- cones are at the centre of the retina
Which out of rods and cones are for colour and which is for general light?
- rod cells are very sensitive to changes in light
- they give a black and white image
- cone cells are less sensitive to light but offer coloured images
- there are 3 types of cone cell, each containing different optical pigments
Why are rod cells sensitive to light and how does this affect their function?
- several rod cells join to one sensory neuron
- this means that generator potentials can be combined to exceed the threshold potential and trigger an impulse
- helps in low light situations
Why do rod cells have low visual acuity?
- rod cells provide a low ability to tell 2 objects apart from one another when they’re close together
- many rods join to the same sensory neuron
- this means that the brain interprets these separate points as a single point
How are cone cells much less sensitive to light than rod cells?
- each cone cell is joined to a single sensory neuron
- more light is required to reach the threshold potential so it is harder to trigger an impulse
How do cone cells have a high visual acuity?
- each cone cell is attached to its own sensory neuron so the brain interprets impulses from each cone cell as separate
- this means that cone cells can offer much more visual detail than rod cells
How can the nervous system be divided?
- CNS and PNS
- PNS into somatic (conscious) and autonomic (unconscious)
- autonomic into sympathetic (fight or flight) and parasympathetic (rest and digest)
One word to describe the heart
- myogenic
- it can contract and relax without receiving signals from the nervous system
Describe the process of the heart beating
- heartbeat originates at the sinoatrial node (SAN)
- SAN has the ability to spontaneously produce an electrical impulse - SAN causes contraction in both atria
- a band of collagen (non-conductive tissue) prevents impulses directly passing to ventricles - impulses travel to the AVN which sends the impulse to the bundle of His
- there is a short delay first to allow the atria to contract and empty fully - bundle of His carries the impulse to the Purkinje fibres
- the conductive purkinje fibres carry the impulse from the apex of the heart up both the ventricles simultaneously
- both ventricles contract
What part of the body controls the heart rate?
- the brain
- more specifically, the medulla oblongata
Where are baroreceptors found?
- aorta
- carotid artery
What does the medulla do when coordinating a response for heart rate?
- the medulla coordinates a response when it receives impulses from the baro/chemo receptors via the sensory neurons
- it sends impulses to the SAN via the sympathetic or parasympathetic neurons depending on the required outcome
What is the difference between if the sympathetic or parasympathetic system is used to control heart rate?
- sympathetic = speeds up
- parasympathetic = slows down
What can the control of heart rate also be described as?
NEGATIVE FEEDBACK
- the body responds to a stimuli to bring it back to the norm
How is high blood pressure dealt with by the body?
- baroreceptor detects
- medulla sends an impulse through parasympathetic nervous system
- HR slows
- BP decreases
How is low blood pressure dealt with by the body?
- baroreceptor detects
- medulla sends an impulse through the sympathetic nervous system
- HR speeds up
- BP increases
How is a high blood pH dealt with by the body?
- chemoreceptor detects
- medulla sends an impulse through the parasympathetic nervous system
- HR slows
- pH decreases
How is a low blood pH dealt with by the body?
- chemoreceptor detects
- medulla sends an impulse through the sympathetic nervous system
- HR speeds up
- pH increases
