Ch 15 pt 2) Special Senses Flashcards
1
Q
Functional Anatomy of Photoreceptors
A
Photoreceptors are modified nuerons with a cell body, synaptic terminal, and two segents
- Outer Segment) Light Reciving Area
- Has visual pigments (photopigments) which change chape as they absorb light
- Inner Segment) Joins the Cell body
- cilium) connects inner segment to outer segment
- Outer Fiber) connects cell body to inner segemnt
- Inner fiber) connects cell body to synaptic terminal of bipolar cells.
2
Q
Comparing Rod and Cone vision
A
- Rods) Very senative to Light
- Only has a single pigment so vision is in grey tones only
- Pathways of rods converge into one ganglion which causes fuzy, indisticnt images
- as many as 100 rods can synapse with one ganglion cell
- Cones) Require bright light to activate
- Have three pigments (red, green, blue) which allows for colored sight
- Detailed, high-resolution vision
- cones synapse with fewer ganglion than rods
3
Q
Color Blindess
A
- Cones lack one or more cone pigments
- Inhereted on X chromosome which makes it more common in males
- Most common type is red-green whrere red or green cones are absent
- red could appear green or vise versa.
4
Q
How do photoreceptors translate incoming light into electrical signals
A
- Retinal) Light absorbing molecule
- combines with one of four protiens (opsin) to form visual pigments
- Depending on type of oposin bound, the retinol will aborb diffrent wavlengths of light
- Opsins (four types)
- Rods) Rhodopsin
- Cones) Red, green and blue oposin,
- Cone wavlengths overlap allowing us to precieve color.
- Retinal Isomers (Retinal is bent until it absorbs light)
- Bent) 11-cis-retinal
- Straight) All-trans-retinal
5
Q
Phototransduction
A
- Process by which pigment captures of photon energy is converted into a graded receptor potential
- Capturing light
- Job of Deep Purple pigment Rhodopsin
- Three stepts of Rhodopsin formation and breakdown
- Pigment Synthesis) Opsin and 11-cis retinal combine to form rhodopsin in the dark
- Pigment Bleaching)When Rhodopsin absorbs light, 11-cis retinal strightens to All-Trans-retinal. retinal and opsin seperate
- Pigment Regenration) All-trans Retinal is converted back to 11-cis. Rhodopsin is regenrated,
6
Q
Light Transduction Reaction
A
- When Light Changes Oposin’s shape
- Light-Activated rhodopsin activated G-protien transudcin
- Transducin Activates PDE, which breaks down cyclic
GMP (cGMP)
- In dark
- cGMP holds cation channels of outer segment open: Na+ and Ca2+ enter and depolarize cell
- In light
- cGMP breaks down, channels close, cell hyperpolarizes;
- Hyperpolarization is signal for vision!
7
Q
Information Processing In the Retina
A
- Information is recived by photoreceptors.
- Photoreceptor cell will genereate a graded potentional
- Not an AP
- Light Hyperpolarizes photoreceptors which causes them to Stop releasing the inhibitor Glutamate to the Bipolar cells
- Bipolar cells depolarize (no inhibitior) which releases nuertoransmiter to ganglion cell
- Ganglion cells Generate and Transmit AP to optic nerve (II) to brain
8
Q
Light Adaption
A
- Moving from darkness to bright Light we see Glare
- Both rods and cones are stimulated at the time
- Pigments are broken down and Pupils constrict
- Visual activity improves over 5-10 mins
- Rods are turned off
- Retinal Sensitivity Decreases
- Cones and Nuerons rapidy adapt
9
Q
Dark Adaptation
A
- When moving from bright light to darkness we see blackeness
- Cones do not funciton in low light
- Bright light turns off Rod pigments and they need time to adjust
- Pupils dilate
- Rhodopsin will begin to accumilate so Rod sentivity increaes
- takes 20-30 mins
10
Q
Night Blindness
A
- Nyctalopia (night blindess) is a condition where rod funtion is seriouly hampered.
- Caused by vitiman A difiency
- Retinitis Pigmentosa) disiese that destroys rods
11
Q
Visual Pathways in the Brain
A
- Axons of Retinal Ganlion cells form the Optic Nerve
- Medial fibers of optic nerce cross over at Optic Chaisma
- Continue as Optic Tracts
- Each Optic Tract
- Contains Fibers from both lateral (temporal) and medial (nasal) aspects of the oppisit eye
- Each ceriries information from same half of visual field.
- Fibers of Optic Tracts continue on to Thalamus
- From the thalamus, thalamic nuerons project to the promary visual cortex in the occipital lobe
- Perception of images occurs here
12
Q
Depth Perception
A
Both eyes view images from slightly diffrent angles: visual cortex fuses images into a 3D image which leads to depth percetion
- Loss/Destruction of one eye elimanates depth perception.
13
Q
Visual Processing
A
- Retinal Cells split into input chnnels that include info about
- Color and brightess
- Angle, Direction, and speed of movment (of edges)
- Sudden chenges in brightness or color
- Ganglions pass info to the thalamus to be processed for depth perception.
- cone Imput is emphesized
- Primary Visual Cortex)
- Forms visual association areas
- Infor is also passed to other lobes where objects are identified and position in space is deteremined.
14
Q
Chemical Senes
A
- Senses of Smell (olfaction) and taste (gustation)
- Chemoreceptors) respond to chemicals in aqueous solutions
15
Q
Sense of Smell
A
- Olfactory Epithelium) Organ of Smell
- located in roof of nasal cavity
- Contains Olfactory Sensory Nuerons
- Supporting Cells) Support olfactory receptor cells
- Olfactory Stem Cells) Diffrentiate to replace sensory nuerons
- replace every 30-60 days
- Bundles of axons of olfacory receptor cells form olfacotry nerve (I)
