case 3

Question 1

sensation

Answer 1

detection of stimuli via sensory organs

Question 2

transduction

Answer 2

process by which sense organs convert energy from environment into neural activity.

Question 3

sensory coding

Answer 3

axons code info from sense organs by anatomical or temporal coding

Question 4

psychophysics

Answer 4

study of relation between physical characteristics of stimuli and sensation they produce. used to measure absolute and difference threshold.

Question 5

perception

Answer 5

our interpretation of what is represented by sensory input. recognition of objects sound, occurs unconciously.

Question 6

gestalt principles

Answer 6

adjacency/proximity principle. similarity. good continuation, law of closure. common fate

Question 7

attention

Answer 7

allocation of awareness to stimuli. shifting attention compromises disengagement shifting and focus.

Question 8

walls or the orbit

Answer 8

lateral:zygomatic, sphenoid. thickets wall.
Medial: ethmoid, lacrimal, maxilla, sphenoid
Superior: frontal sphenoid
Inferior: maxilla, zygomatic and palatine.

Question 9

ligaments of the eye

Answer 9

medial check expansion of MR, prevents over action, lateral check and suspensory ligament prevents downward displacement.

Question 10

eyelids

Answer 10

when open called palpebral fissure. angles known as L and M commisures-lacrimal caruncle cont sebacious gland and sudoriferous gland. superficial to deep: epidermis, dermis, subcutaneous tissue, fibres of the orbicularis oculi muscle, a tarsal plate, tarsal glands, and conjunctiva. associated with superior tarsus is levator palpebrae superioris which raises eyelid.loss of function leads ptosis. tarsal g;ands secrete fluid to keep eyelids adhering to each other. infection causes chalazion. palprebral and bulbar conjunctiva. over sclera is vascular

Question 11

lacrimal apparatus

Answer 11

gland-ducts-canal-lake-sup/inf punctum-sup/inf canaliculi-sac-blinking orbicularis oculi forces fluid into nasolacrimal duct. opens into inf nasal meatus.

Question 12

fibrous tunic

Answer 12

superficial layer. sclera and cornea. at junction canal of schlemm. sclera mostly collagen and fibroblasts. cornea helps focus light onto retina. recieves O2 from outside.

Question 13

Vascular tunic

Answer 13

choroid ciliary body and iris.choroid highly vasculated provide nutrients to retina, also contain melanocytes cause appear dark absorbs stray light rays. ciliary muscles and process, secrete aqueous humour, zonular fibres atach lens, contract bulge so zonular fibres shorten and lens widens-near vision. relax zonular fibres lengthen lens thinner. Iris contains radial and circular muscles. amount melanin determines eye colour.

Question 14

lens

Answer 14

Lens capsule – it is a thin, transparent, hyaline membrane surrounding the lens.
 Anterior epithelium – it is a single layer f cuboidal cells, which lies deep to the anterior capsule.
 Lens fibres – these form the main bulk of the lens and are arranged compactly as nucleus and cortex of the lens.
o Nucleus is the central part which contains the oldest fibres.
o Cortex is the peripheral part which comprises the youngest fibres. Proteins – crystallins – in the cells of the lens, make up the refractive media of the lens. These proteins are arranged like the layers of an onion. The refractive media is transparent and lacks blood vessels.

Question 15

anterior cavity

Answer 15

ant and post chambers. AH nourishes lens and cornea. from ciliary processes into post chamber through pupil to ant chamber drains in canal of shlemm. 90min. glaucoma when disrupted.
vitrous cavity-vitrous body like jelly. mostly water and collagen. helps suspend lens keep retina in place maintaqin shape.

Question 16

opthalmascope appearence of the eye

Answer 16

• Retinal blood vessels originate from the optic disk.
• The optic nerve fibres also exit the retina at the optic disk.
• Sensation of light can’t occur at the optic disk because there are no photoreceptors here, nor can it occur where the large blood vessels exit because the vessels cast shadows on the retina.
• Macula – this is yellow tissue at the centre of the retina, surrounding the fovea. It is for central vision. Besides it colour, the macula is distinguished by the relative absence of large blood vessels. The retinal blood vessels arc from the optic disk to the macula; this is also the trajectory of the optic nerve fibres from the macula en route to the optic disk. The absence of blood vessels improves the quality of central vision.
• Fovea – this is a dark spot about 2mm in diameter, at the centre of the retina. This is the thinnest part of the retina.
• The retina appears an orange colour because of this background colour is due to the choroidal circulation under the photoreceptor layer.

Question 17

refraction of the cornea

Answer 17

• The light rays entering the eye are parallel rays.
• The light rays that strike the curved surface of the cornea bend (as they enter the aqueous humor) so that they converge on the back of the eye; those that enter the centre of the eye pass straight to the retina.
• The distance from the refractive surface to the point where the parallel light rays converge is called the focal distance.
• The more curved the cornea, the shorter the focal distance.
• ‘Dioptre’ is the unit of the power of refraction
The cornea has a refractive power of 42 dioptres

Question 18

accommodation by the lens

Answer 18

• The lens has less refractive power (~12 dioptres) than the cornea (42 dioptres).
• The refraction supplied by the lens is adjustable, allowing objects at various distances from the observer to be brought into sharp focus.
• The additional focusing power is provided by changing the shape of the lens, a process called accommodation.
• The ciliary muscle forms a ring around the lens.
• For near vision, the ciliary muscle contracts and swells in size, thereby making the area inside the muscle smaller and decreasing the tension in the suspensory ligaments.
• The lens becomes rounder and thicker because of its natural elasticity.
• This increases the curvature of the lens, and thus its refractive power increases.
• For viewing distant objects, relaxation of the ciliary muscle increases the tension in the suspensory ligaments, and the lens is stretched into a flatter shape, and its refractive power is reduced.

Question 19

pupillary light reflex

Answer 19

• Narrowing the pupil reduces both spherical and chromatic aberration, leading to sharper images.
 Spherical aberration = it occurs due to the increased refraction of light rays when they strike a lens.
 Chromatic aberration = the effect produced by the refraction of different wavelengths of light through slightly different angles, resulting in a failure to focus.
• Reducing the size of the pupil also increases the depth of field—that is, the distance within which objects are seen without blurring.
• However, a narrowed pupil also limits the amount of light that reaches the retina, and, under conditions of dim illumination, visual acuity becomes limited by the number of available photons rather than by optical aberrations.

Question 20

visual field

Answer 20

• The visual field is the total amount of space that can be viewed by the retina when the eye is fixated straight ahead.
• The image of an object in the visual field is inverted on the retina.
• Binocular visual field is the visual field when both eyes are open.
• With only one eye open the field is uniocular and is restricted inwards by the nose.
• The most common visual field loss is due to glaucoma.

Question 21

route light passes

Answer 21

ganglion cell layer-inner plexiform-inner nuclear-outer plaxiform-outer nuclear-photo recepter segment-pigment epithelium. cell bodies are in the nuclear layer and ganglion layer. synapses are in the plexiform layers. photoreceptors are supplied by choroidal BV.

Question 22

direct and indirect synaptic interactions

Answer 22

 Direct synaptic interactions = photoreceptor cells > bipolar cells > ganglion cells > brain.
 Indirect synaptic interactions = photoreceptor cells > bipolar cells (+horizontal cells) > ganglion cells (+ amacrine cells) > brain.

Question 23

types of vision

Answer 23

• The contributions of rods to vision drops out nearly entirely in so called ‘photopic’ vision because their response to light saturates—that is, the membrane potential of individual rods no longer varies as a function of illumination because all of the membrane channels are closed.
 At the lowest levels of light, only the rods are activated – ‘scotopic’ vision.
 ‘Mesopic’ vision occurs in levels of light at which both rods and cones contribute.
• People who have lost cone function are legally blind.
• People who have lost rod function experience night blindness.

Question 24

convergence

Answer 24

 Rod bipolar cells:
 These do not contact retinal ganglion cells.
 Instead, rod bipolar cells synapse with the dendritic processes of a specific class of amacrine cell that makes gap junctions and chemical synapses with the terminals of cone bipolar cells; these processes, in turn, make synaptic contacts on the dendrites of ganglion cells.
 Each rod bipolar cell is contacted by a number of rods, and many rod bipolar cells contact a given amacrine cell.
 Cone bipolar cells:
 Each retinal ganglion cell that dominates central vision (midget ganglion cells) receives input from only one cone bipolar cell, which, in turn, is contacted by a single cone.
makes rods better at detecting light.

Question 25

phototransduction

Answer 25

light stimulation leads to membrane hyperpolarisation. in the dark -30mV. steady influx Na. stimulated to open by cGMP. light stimulation activates G proteins which reduce cGMP. Na channels close hyperpolarising cell.
opsin and 11cis retinal are linked, absorption of light turns 11-cis to all trans retinal. activates opsin and its released. activates transducin conversion GTP to GDP by GTPase. hydrolyses cGMP. then turned to all trans retinol. termination of transducin occurs via GTPase.

Question 26

retinoid cycle

Answer 26

 The all-trans retinol is transported out of the outer segment and into the retinal pigment epithelium.
 Enzymes convert it to 11-cis retinal.
 After it is transported back into the outer segment, the 11-cis retinal recombines with opsin in the receptor disks to form rhodopsin.

Question 27

cones

Answer 27

trichromatic, red green blue. when all active see white. • Dichromacy is inherited as a recessive, sex-linked characteristic and exists in two forms:

1. Protanopia – blindness to red light so blue and green cones are used.
2. Deuteranopia – blindness to green light so blue and red cones are used.

Question 28

bipolar cells

Answer 28

 ON- and OFF-centre bipolar cells express different types of glutamate receptors.
o OFF-centre bipolar cells have ionotropic receptors (AMPA and kainate) that cause the cells to depolarize in response to glutamate released from photoreceptor terminals.
o ON-centre bipolar cells express a G-protein-coupled metabotropic glutamate receptor (mGluR6). When bound to glutamate, these receptors activate an intracellular cascade that closes cGMP-gated Na+ channels, reducing inward current and hyperpolarizing the cell.
horizontal cells release GABA. when light in surround will release GABA inhibiting bipolar cells.

Question 29

ganglion cells

Answer 29

M type and P type, P can transmit info about colour.
redvgreen bluevyellow. respond to wavelength centre and surround. • In this example, we will have a blue ON-centre and a yellow OFF-surround (B+Y-).
• Blue light drives blue cones that feed the receptive field centre.
• Yellow light activates both red and green cones that feed the surround.
• Diffuse blue light would be an effective stimulus for this cell with a dampened response.
• Yellow light on the surround would cancel the response.
• Diffuse white light too would cancel the response

Question 30

visual pathway

Answer 30

optic disc-optic nerve-then become myelinated-optic disc no photoreceptors blind spot-optic canal to optic chiasm,nasal side deccusate-optic tract-LGN-optic radiation through internal capsule, temporal radiation known as meyers loop, to cortex-calcarine fissure.

Question 31

secondary visual pathways

Answer 31

optic chiasm-superior colliculus: coordinates head and eye movement to visual targets.
Pretectum: coordinates pupillary light reflex. afferent terminate in pretectal nucleus pass to edinger westphal nucleus then project ciliary ganglion of oculomotor nerve causing constrictor pupillae muscles contract.
hypothalamus/suprachiasmatic nucleus: circadian cycle, project here express melanopsin.

Question 32

lateral geniculate nucleus

Answer 32

axons terminate in separate layers, so that individual geniculate neurons are monocular. right eye=layers 2,3,5 left eye=layers 1,4,6. Magnocellular layers in 1,2 recieve info from M type ganglion-location, Movement. (M for motion) go to 4Ca in cortex. layer 1 contralateral layer 2 ipsilateral eye
Parvocellular layers 3-6 recieve P type, detail of shape size and colour from red and green. go to 4Cb.
Kinocellular-from blue and yellow. go to layers II III of cortex called blobs.

Question 33

striate cortex

Answer 33

responce is tuned to orientation, orientation columns-vertical. In each column is simple cells-stationary bars certain orientation from monocular. Complex cells-respond to bars of light moving across receptive field. binocular.
layer 4 contains stellate cell.• Information from the upper visual field is mapped below the calacrine sulcus.
• Information from the lower visual field is mapped above the calacrine sulcus

Question 34

pupillary constriction and dilation

Answer 34

light generates AP on optic nerve, synapse on pretectal nucleus. EW nucleus to ciliary ganglion constrictor pupillae in iris constrict pupil.
Sympathetic preganglionic fibres to the eye (and face) originate in the hypothalamus, pass uncrossed through midbrain and lateral medulla, and emerge from the spinal cord at T1 (close to the lung apex) to form the superior cervical ganglion at C2.
Postganglionic fibres form a plexus around the carotid bifurcation.
dilater pupillae/radial to constrict.

Question 35

visual fields

Answer 35

• Superior Field = 60 degrees above the line of sight
• Inferior Field = 75 degrees below the line of sight
• Nasal Field = 60 degrees medial to the line of sight
• Temporal Field = 100 degrees lateral to the line of sight
• The superior field is limited by the frontal bone. It becomes restricted with ageing because the frontal bone depresses slightly and the eye ball is withdrawn into the orbit

Question 36

visual field defecits

Answer 36

deficits in chiasm, tract, radiation, cortex. anopia-defecit in visual field. Hemianopia-heteronymous-loss of half on different sides-binasal, bitemporal (optic chiasm),
homonymous-loss on same side (optic tract)
quadrantopia-one quarter (temporal radiation upper quarter, parietal lower)
macular sparring-cortex.

Question 37

myopia

Answer 37

 This can be caused by the corneal surface being too curved, or by the eyeball being too long.
 The image of distant objects focus in front of the retina, instead of on the retina.
use concave diverging lens

Question 38

hypermetropia

Answer 38

 This can be caused by the corneal surface not being curved enough, or by the eyeball being too short.
 The image of distant objects focus behind the retina, instead of on the retina.
use convex converging

Question 39

presbyopia

Answer 39

 This is the normal ageing of the lens which leads to a change in the refractive state of the eye.
 As the lens ages it becomes less able to alter its curvature and this causes difficulty with near vision.

Question 40

astigmatism

Answer 40

• Astigmatism is a condition in which the corneal surface is asymmetric: light is refracted differently along different axes – light is refracted to multiple areas of the retina.
• It may be myopic in one plane and hypermetropic or emmetropic in the other plane. cylindrical and spherical spectacle lenses.

Question 41

amblyopia

Answer 41

functional reduction in visual acuity. • Blindness can occur in the affected eye if amblyopia is not detected and treated before age 8.• Amblyopia results when there is persistent interference with the image from one eye but not the other.
• There are 3 causes:
 Strabismus can cause amblyopia because misalignment of the eyes results in different retinal images being sent to the visual cortex. Because the visual pathways are developed in adults, presentation of 2 different images results in diplopia rather than suppression of one image.
 Anisometropia (inequality of refraction in the 2 eyes, most often resulting from astigmatism, myopia, or hyperopia)
 Deprivation amblyopia is caused by obstruction of the visual axis at some point between the surface of the eye and the retina (eg, by a cataract),

Question 42

strabismus/squint

Answer 42

• If there is an imbalance in the extraocular muscles of the two eyes, the eyes will point in different directions1. Esotopia (convergent squint) – the directions of gaze of the two eyes cross, and the person is said to be cross-eyed.
2. Exotopia (divergent squint) – the directions of the gaze diverge, and the person is said to be wall-eyed.
usually congenital. can patch eye, prismatic glasses, surgery.