Windows to the brain

Perception of stimuli Sense organs are our windows to the brain. They detect the changes that happen in the world around us. Our senses help us to learn, protect us from harm and have an affect on our emotions. What examples can you think of?

Mechanoreceptors Chemoreceptors Thermoreceptors Photoreceptors Stimulated by pressure/mechanical force. Touch. Arteries (blood pressure), stretch receptors in the lungs, proprioceptors in muscles, ligaments, tendons & joints (position of arms/legs), pressure receptors in inner ear (balance). Mechanoreceptors Chemoreceptors Thermoreceptors Photoreceptors Respond to chemical substances. Taste and Smell. Also monitors blood pH, pain receptors. Respond to temperature change. Warm (rise in temp.) and cold (drop in temp.) receptors. Respond to light. Sight. Rod cells respond to dim light (black and white vision). Cone cells respond to bright light (colour vision).

You need to be able to label and annotate this from memory. Task – pg. 466, fig. 16.3 Draw and label a diagram of the Human eye. You should include: sclera, cornea, conjunctiva, eyelid, choroid, aqueous humour, pupil, lens, iris, vitreous humour, retina, fovea, optic nerve and blind spot. You need to be able to label and annotate this from memory. Labels and functions

Part Function Iris Regulates size of pupil Pupil Admits light Retina Contains receptors for vision Aqueous humour Transmits light rays & supports eye ball Vitreous humour Rods Black and white vision in dim light Cones Colour vision in bright light Fovea Area of dense cones cells. Vision is most acute here Lens Focuses light rays Sclera Protects and supports eye ball Cornea Focusing begins here Choroid Absorbs stray light Conjunctiva Covers sclera & cornea – keeps eye moist Optic nerve Transmit impulse to brain Eye lid Protects eye

Does not work in the way you would expect The Retina Does not work in the way you would expect Light passes through the choroid to the photoreceptors (rod/cone cells) at the very back of the retina, the nerve signal goes back through the ganglion cells to the optic nerve.

Does not behave as you would expect!

Light enters the eye Focused on the photoreceptor cells of the retina (rods and cones) See fig. 16.4 pg. 467 Rod cells are very sensitive to light. Synapse with a bipolar neurone. Cone cells activated by bright light. Synapse with a bipolar neurone. Bipolar neurone cells which carry impulses from rod/cone cell to ganglion cell. Ganglion cells are the cell bodies of the optic nerve. Send impulses to the brain.

Rods Cones More sensitive to light, work well in dim light Less sensitive to light, work well in bright light Only one type of rod in the retina. Absorbs all wavelengths of visible light Three types of cone in retina. Sensitive to red, blue and green light Groups of rod cells send impulses to a single nerve fibre in the optic nerve. Impulse from single cone goes to a single nerve fibre in the optic nerve.

Hermann grid illusion What do you see? Why do you see it? You see grey in your peripheral vision – fewer light sensitive cells in this region compared to the centre of your retina (fovea) When you look directly at the grey areas, you are using the centre of the retina, with a high concentration of light sensitive cells. So you see white.

Edge enhancement When there is a strong contrast between colours – black and white. The theory is that light receptors in your eye ‘switch off’ neighbouring receptors. This makes the edges appear more distinct. Just like edge enhancement in images

Contralateral processing - see fig. 16.7, pg. 470 Contralateral (opposite side) processing is due to the optic chiasma. Nerve fibres from the right half of the visual field, converge at the optic chiasma and pass to the left side of the brain. Nerve fibres from the left half of the visual field, converge at the optic chiasma and pass to the right hand side of the brain. Information from contralateral processing eventually ends up in the visual cortex of the brain. This area must share information from both sides of the brain in order to see an image completely. Image received is inverted and reversed – brain must correct this. Cerebral cortex rebuilds image so we can see.

How can this be proved? Patients suffering brain lesions (some kind of damage). Lesion on the right (looking at the brain from above) would not recognise an object like a bucket. To such an extent they would argue that it is not a bucket. Lesion on the left would be able to describe the function of the bucket but not be able to name the object as a bucket. Both sides of the brain must work together in order for us to correctly see and interpret what something is. Our vision is information processing not just simply ‘seeing’.

Draw and label a diagram of the Human ear Pg.470 fig. 16.8 Your diagram should include: pinna, eardrum, bones of the middle ear, oval window, round window, semicircular canals, auditory nerve and cochlea. You do not have to draw this diagram from memory BUT you need to be able to label it and explain how sound is perceived by the ear. Include pinna, eardrum, bones of the middle ear, oval window, round window, semicircular canals, auditory nerve and cochlea.

Explain how sound is perceived by the ear, including the roles of the eardrum, bones of the middle ear, oval and round windows, and the hair cells of the cochlea.

The eye The ear Cataracts Glucoma Ear infection Retinal disorders Conjuctivitis Macular degeneration Diabetic retinopathy Amblyopia Strabismus The ear Ear infection Otitis Meniers disease Deafness Vestibular disorder Tinnitus Barotrauma In small groups chose one or two of these conditions, research and present to the group. Electronic notes must be available to share.