stimulus and response Flashcards
Stimulus
A detectable change in the internal or external environment that is detected by a receptor and elicits a response
Response
Is a reaction to a stimulus
Reflex
Is a rapid, innate, automatic response
How does the ability to respond to stimuli increase the chance of survival for an organism? [2]
- There is always a selection pressure favouring organisms with more appropriate responses
- Those organisms that survive have a greater chance of raising offspring and of passing their alleles to the next generation.
Reflex Pathway [10]
Stimulus
Receptor
Sensory Neurone
Synapse
Relay / Intermediate Neurone
CNS
Synapse
Motor Neurone
Effector
Response
Neurone [2]
- Long thin nerve fibre (axon)
- With a cell body, containing nucleus
Where is the relay neurone?
Within the CNS
Which takes longer, transport through axons or across synapses?
Synapse
Importance of Reflex Arc [5]
- Protect the body from harmful stimuli
- Effective from birth and do not have to be learnt
- Fast, as neurone
pathway short with very few synapses, important in withdrawal reflexes - Involuntary, don’t use the decision making powers of the brain, free to carry out more complex responses
- Some responses still sent to the brain, can sometimes over-ride the reflex if
necessary.
Receptor [3]
- The stimulus is always some form of energy
- e.g. heat, light, sound or mechanical energy
- All receptors convert the energy of the stimulus into a nerve impulse known as a generator potential
- Acting as a transducer
Examples of Receptors [4]
Skin
- pain, temperature, pressure
Eye
- light
Ear
- soundwaves
Nose, Tastebuds
- chemicals
Pacinian Corpuscle [3]
- Filippo Pacini
- Receptors are specific to one type
of stimulus only - Pacinian corpuscles are found throughout our skin and respond to change in mechanical pressure.
Pacinian Corpuscle Structure [3]
- A single nerve fiber is surrounded by a myelin sheath
- Which is surrounded by a capsule made of concentric rings of connective tissue (rings have nuclei)
- separated by gel
Pacinian Corpuscle Role [6]
- Pressure deforms the membranes and layers
- Causing stretch-mediated sodium ion channels to open
- Sodium ions diffuse through the layers to the neurone
- Causing the inside of the membrane to be relatively more positive compared to the outside
- Depolarising the membrane and creating a generator potential
- If the generator potential is big enough an action potential occurs
Label the eye [14]
Sclera
Choroid
Vitreous humour
Retina
Fovea
Optic disk/blind spot
Optic nerve
Ciliary muscle
Iris
Lens
Conjunctiva
Cornea
Aqueous humour
Suspensory ligaments
Sclera [3]
- The sclera is the white outer coating of the eye
- It is tough, fibrous tissue
- functions as the supporting wall of the eyeball, helps maintain eyeball shape, and protects it from injury
Choroid [2]
- The choroid is a dense network of blood vessels between the retina and the sclera
- supplies nutrition to the eye
Vitreous Fluid / Humour
- The vitreous humor provides nutrients to your eye and helps your eye keep its shape
Retina [4]
- A layer of photoreceptor cells within the eye
- captures incoming photons and transmits them along neuronal pathways
- as both electrical and chemical signals
- for the brain to perceive a visual picture
Fovea
- a small depression within the retina where visual acuity is the highest
Optic Disc [3]
- entry point for the major blood vessels that supply the retina
- has fewer photoreceptors
- making it the blind spot of the eye
Optic Nerve [2]
- an extension of the central nervous system
- transmits electrical impulses from the eyes to the brain
Ciliary Muscles [2]
- relaxes and contracts to change shape of lens
- important for moving the eyes as they place an image on the fovea to get maximum resolution
Iris [2]
- the colored part of the eye that surrounds the pupil
- It regulates the amount of light that enters the eye
Lens
- clear part of the eye behind the iris that helps to focus light and images on the retina
Conjunctiva
- thin, clear membrane that protects the eye
Cornea [3]
- clear window on the front of your eye
- made of tough, transparent tissue helps protect your eye
- keeps out dirt, germs and other particles and, also filters out some of the sun’s ultraviolet (UV) light.
Aqueous Humour [2]
- give the eye its shape
- nourishes the cornea and lens by supplying nutrition
Suspensory Ligaments
- series of fibers that connect the ciliary body of the eye with the lens, holding it in place
- contract and relax to change shape of the lens and adjust visual acuity
Photoreceptors [3]
- found in the retina
- there are two types: Rods and Cones
- act as transducers
Structure of Rod Cells [3]
DIAGRAM
How do Rod Cells work? [4]
- a number of rod cells are attached to a single bipolar cell creating a retinal convergence
- so there is a much greater chance that the threshold
value will be exceeded - this allows a generator potential to stimulate the bipolar cell and cause an action potential
- as a result, rod cells allow us to see in low light intensity, although only in black and white
Visual Acuity of Rod Cells [4]
- As many rod cells are joined to the same bipolar cells, only a single impulse will be stimulated
- This means that they cannot distinguish
between the separate sources of light that stimulated them - 2 dots close together will appear as a single blob
- Rod cells therefore have low visual acuity.
Structure of Cone Cells
DIAGRAM
Cone Cells
There are 3 types of cone cell, red sensitive, blue sensitive and green
sensitive
- Each responds
to different wavelengths of light
- Depending on the proportion of each type that is stimulated, we can
perceive images in full colour
How do Cone Cells work? [5]
- Cone cells contain the pigment (iodopsin)
- This requires a higher light intensity to be hydrolysed to create a generator potential
- Each cone cell usually has its own bipolar cell connected to a sensory neurone
- This means that often the generator potential is not exceeded
- As a result, cone cells only respond to high light intensity and not
to low light intensity
Visual Acuity of Cone Cells [2]
- As cone cells are attached to their own bipolar cell, if 2 adjacent cells are stimulated, the brain receives 2 separate impulses
- Cone cells give very accurate vision, they have good visual acuity
Photoreceptors at the Fovea [6]
- Light is focused by the lens on a point known as the fovea.
- The fovea therefore receives the highest intensity of light.
- Therefore cone cells, but not rod cells, are found at the fovea.
- The concentration of cone cells diminishes further away from the fovea.
- At the peripheries of the retina, where light intensity is at its lowest, only the rod cells are found
- As each receptor responds to different light intensities
Colour Blindness [3]
- These people lack red sensitive cones
- But the green sensitive cones are stimulated by the red light
- So all dots appear green
How many types of rod cell are there?
one
How many types of cone cell are there?
three
(red, green, blue sensitive)
How many rod cells are there?
Rod cells are more numerous than cones.
How many cone cells are there?
Cone cells are less numerous than rods
What is the distribution of rod cells in the retina?
More in periphery
What is the distribution of cone cells in the retina?
Fewer in periphery, concentrated in fovea
Describe rod cells sensitivity to light
High sensitivity
Describe cone cells sensitivity to light
Low sensitivity
What pigment is present in rod cells?
Rhodopsin
What pigment is present in cone cells?
Iodopsin
