A.3 Perception of stimuli

Question 1

Diversity of stimuli

Answer 1

a wide range of stimuli can be detected by receptors in humans. Each receptor is specific to its stimuli and adapted to suit its function

Question 2

Olfactory receptors – sensing smell

Answer 2

Olfaction occurs inside the upper part of the nose.

Question 3

Receptor cells cilia which project into

Answer 3

the air in the nose. olfactory receptor proteins are located in the membrane of the cilia. Different olfactory receptors respond to different chemicals

Question 4

The combination of impulses reaching the brain allows us to

Answer 4

recognise many different types of smell

Question 5

Olfactory receptors – sensing smell (steps)

Answer 5

1. Odorants bind to receptors
2. Olfactory receptor cells are activated and send electric signals
3. the signals are relayed via converged axons
4. the signals are transmitted to higher regions of the brain

Question 6

The blind spot

Answer 6

the lens focuses light onto the retina (rod and cone cells) at the back of the eye which act as photoreceptors

when you focus on an object, light directly hits the fovea, a region of the retina with densely-packed rods and cones

Question 7

Mechanoreceptors respond to

Answer 7

mechanical forces and movements.

Question 8

Chemoreceptors respond to

Answer 8

chemical substances.

Question 9

Thermoreceptors respond to

Answer 9

heat

Question 10

Photoreceptors respond to

Answer 10

light

Question 11

Retina perception of light

Answer 11

1. light reflects off choroid and hits rods and cones
2. pigments in rod and cones break down
3. this stimulates an action potential
4. synapses pass impulses from photoreceptors to bipolar neurons and then to ganglia
5. ganglia carry the impulse via the optic nerve to the occipital lobe

Question 12

Rod cells

Answer 12

Many rod cells feed into one ganglion: all their action potentials are combined into a single impulse at the synapse. This means each ganglion has a large receptive field, but low acuity (low ability to detect differences).

Rod cells are activated in low light conditions, but ‘bleached’ in high light intensities.
They do not detect colour.

Rods are distributed throughout the retina.

Question 13

Cone cells

Answer 13

Cone cells feed into their own ganglion.
This gives a small receptive field for each ganglion, leading to high visual acuity – small differences are easily detected.

There are three types of cone cells, receptive to different wavelengths (red, green, blue). These are only active in sufficient light.

Cone cells are concentrated in the fovea.

Question 14

visual fields

Answer 14

range over which an eye can detect visual stimuli

Question 15

light from your left visual fields falls into the….

Answer 15

right side of the retina and vice versa

Question 16

stimuli from both left retinas are processed in the left visual cortex of the…

Answer 16

occipital lobe. therefore, both sides of teh brain process images from both eyes.

Question 17

visual cortex processes visual stimuli

Answer 17

images are focused by the cornea and lens
an inverted image is focused to the retina

both eyes send visual information from the inner halves of the retinas (nasal retinas) are crossed over

Question 18

optic tracts carry the visual nerve impulses to the…

Answer 18

visual cortex, in the occipital lobe, this is called contralateral processing

Question 19

contralateral processing

Answer 19

both sides of brain are responsible for processing information from both eyes

Question 20

Processing visual stimuli

Answer 20

perception of visual stimuli begins in retina, with edge enhancement.

retinal ganglia carry nerve impulses through the optic nerve to the brain

the nasal ganglia cross over at the optic chiasm
this means both sides of the brain process images from both eyes and is called contra lateral processing

the right side of the visual cortex processes images on both retinas (therefore both left visual fields)

Question 21

the visual cortext contructs images in the brian from the stimuli received. because the 2 eyes are apart the images are…

Answer 21

slightly different. this stereoscopic vision leads to the production of a 3D image

Question 22

inverted image that hits the retina is also

Answer 22

corrected

Question 23

The OPN1MW and OPN1LW genes are found at

Answer 23

at locus Xq28.

They are responsible for producing photoreceptive pigments in the cone cells in the eye. If one of these genes is a mutant, the pigments are not produced properly and the eye cannot distinguish between green (medium) wavelengths and red (long) wavelengths in the visible spectrum.

Question 24

Because the Xq28 gene is in a non-homologous region when compared to the Y chromosome,

Answer 24

red-green colour blindness is known as a sex-linked disorder. The male has no allele on the Y chromosome to combat a recessive faulty allele on the X chromosome.

Question 25

pinna

Answer 25

collection of sound waves

Question 26

eardrum

Answer 26

vibrated by air pressure changes due to sound waves

Question 27

middle ear bones

Answer 27

stimulated by ear drum, knock against each other and magnify sound (20X)

Question 28

semicircular canals

Answer 28

for balance

Question 29

oval windows

Answer 29

transmit vibrations from middle ear bones

Question 30

cochlea

Answer 30

tiny hairs responding to individual wavelengths of sound, generating AP

Question 31

auditory nerve

Answer 31

transmit nerve impulse from cochlea to brain

Question 32

eustachian tube

Answer 32

joins throat and sinus- for equalisation of pressure

Question 33

round window

Answer 33

dissipates vibrations (dampens “used” sound stimulus)

Question 34

how is sound perceived by the ears

Answer 34

eardrum/tympanic membrane is moved by sound waves;
eardrum causes movement of the bones of the middle ear;
bones of the middle ear (malleus, incus and stapes) amplify sound (by 20x);
bones of the middle ear on the oval window;
causing movement of fluid within the cochlea;
hair cells are mechanoreceptors;
different hair cells respond to different wavelengths/pitch of sound;
hair cells release a chemical neurotransmitter when stimulated;
sounds/vibrations are transformed into nerve impulses/action potentials;
carried by auditory nerve to brain;
round window releases pressure/dissipates sound;
this allows the fluid in cochlea to vibrate;

Question 35

How do cochlear implants work?

Answer 35

A cochlear implant is a surgically implanted device that helps to correct hearing loss associated with damaged cochlea hairs.
Its function is to generate electrical signals from sound vibrations and transmit them to your auditory nerve

Question 36

Detecting movement and maintaining balance

Answer 36

1. The three semi-circular canals, are at right angles to each other - they are each orientated in a different plane
2. Movement of the head causes the fluid in the canals, if the canal is aligned with the movement
3. Movement of the fluid is detected by hair cells in the cupula (wide base of each canal)
4. If the hairs are triggered they in turn stimulate nerve impulses which are transmitted to the brain by the Vestibular nerve
5. The brain deduces the direction of head movement from the combination of impulses