A3 Perception Flashcards
Define stimulus.
A change in the environment (internal or external).
What is the function of receptors in the brain?
Receptors detect stimuli and generate nerve impulses which are relayed to the brain and effector organs so an organism can respond accordingly.
What are four different types of sensory receptors?
1) Mechanoreceptors (mechanical pressure/movement). Eg. Pacinian corpuscles in the skin.
2) Chemoreceptors (chemicals). Eg. olfactory receptor neurons in the nose.
3) Thermoreceptors (temperature). Eg. receptors in the skin.
4) Photoreceptors (light). Eg. receptors in the retina.
How is pain sensed?
Damaged tissues release prostaglandins which stimulate the nociceptor pain neurons. These travel to the sensory area of the cerebral cortex and pain is transmitted.
Describe the structure of the human eye.
The outer layer: the schlera and cornea.
Middle vascular layer: the iris, ciliary muscles and choroid.
Inner retina: neurons and photoreceptor cells.
How is light receieved by the eye?
Light falls on the pigment epithelium of the retina at the back of the eye. This stimulates the photoreceptors (rods and cones) which convert the light stimuli into electrical nerve impulses. These impulses are transmitted from the bipolar cells to the ganglion cells which send messages to the brain via the optic nerve.
At the optic chiasma, impulses cross over to the opposite optic nerve then continue to the thalamus where optical information is processed. Images form in the visual cortex.
Describe the types of photoreceptors in the eyes.
- Rod cells.
These are specialised for vision in dim light. There is only one type so they cannot differentiate between different colours and they have low resolution. They are located at the periphery of the retina so are responsible for peripheral vision. - Cone cells.
These are specialised for vision in bright light. There are three different types of cone cells so they can differentiate between colours. They are found in the centre of the retina so are involved in visual focusing. They have high resolution.
Define contralateral processing.
When a stimulus is processed on the opposite side to where it was detected. Information from the right half of the visual field is detected by the left half of the retina and is processed by the left hemisphere.
What is colourblindness?
The inability or decreased ability to see colour or perceive colour difference. It occurs when one or more of the cone cells are in fewer numbers. It is normally caused by a sex-linked condition.
Eg. red-green colour blindness is the absence of red and green cones.
What is meant by trichromatic vision?
Normal colour vision. All three cone cells (red, green and blue) function correctly.
How is sound received by the ear?
Sound travels as pressure waves in the air, which travel down the auditory canal and cause the eardrum to vibrate. The eardrum transfers the vibrations via the bones of the middle ear (the ossicles) to the oval window of the cochlea. The vibration of the oval window causes fluid within the cochlea to be displaced – this displacement is detected by hair cells. The activation of these hair cells generates nerve impulses which are transmitted via the auditory nerve to the brain. The kinetic movement of the cochlear fluid (and stereocilia motion) is dissipated by the vibration of the round window.
What is the function of the middle ear?
The middle ear is an air-filled chamber that houses three small bones (collectively called the ossicles). The function of the ossicles is to amplify and transmit sound waves.
What is the function of the cochlea?
The cochlea is a fluid-filled spiral tube within the inner ear that converts sound vibrations into nerve impulses. The nerve impulse will be transmitted via the auditory nerve to the auditory centres of the brain.
What are cochlear implants used for?
Cochlear implants are used to stimulate the auditory centres of the brain in patients with non-functioning cochlea hair cells. Standard hearing aids are ineffective in deaf patients as they amplify sounds but do not bypass defective hearing structures.
Describe the structure of cochlear implants.
The external components (microphone, speech processor and transmitter) detect sounds, filter out extraneous frequencies and then transmit the signals to the internal parts. The internal components (receiver/stimulator) receive the transmissions and produce electrical signals via electrodes embedded in the cochlea. The electrical signals are then transferred via the auditory nerve to be processed by the brain, by-passing the non-functioning cochlea hair cells.
