Sensory physiology 1 Flashcards
There are 4 classifications of sensory receptors:
- Mechanoreceptors for example cochlear hair cells.
- Chemoreceptors for example olfactory and taste.
- Photoreceptors for example rods and cones
- Thermoreceptors for example touch.
The internal and external environment is constantly monitored by…
… your sensory receptors.
Each receptor has a threshold that …
… must be reached for the signal to be passed to the CNS through sensory transduction.
Afferent/sensory nerve fibres pass …
… the signal through the pathway.
There are two types of sensory receptors when it comes to stimulus reaction
what are they?
- Rapidly adapting receptors which signal the onset and offset of a stimulus.
- Slowly adapting receptors which continuously signal the intensity of the stimulus.
Process of sensory transduction?
Stimulus -> receptor ->
what does each sensory receptor have?
a receptive field that it responds to.
Afferent/sensory fibres often …
… serve more than one receptor increasing the receptive field.
The degree of overlap between neighbouring fibres determines …
… the resolution of the system.
Sensory information is relayed via …
… ascending nerve tracts to the cerebral cortex that has lateral inhibition to prevent divergence of the sensory information allowing for an accurate internal representation of the world.
Vision can also be described as…
… “eyesight” or “sight”.
Define protanopia
inability to perceive colours on the red spectrum of visible light
Define Deuteranopia
inability to perceive colours on the green spectrum of visible light
Define Tritanopia
inability to perceive colours on the blue spectrum of visible light
Mesenchyme surrounds the …
… developing eyeball (optic globe) between the fifth and seventh weeks to form the choroid and sclera.
Vacuolization within this mesenchyme in the seventh week forms the …
… anterior chamber
Vacuolization within this mesenchyme in the seventh week forms the anterior chamber.
Shortly thereafter…
… vacuolization in the layer of mesenchyme immediately anterior to the lens forms the posterior chamber.
Function of the pupillary membrane?
initially separates the anterior and posterior chambers
The pupillary membrane, which initially separates the anterior and posterior chambers, breaks down in …
… early foetal life.
Eye lid function?
protection
What does the iris contain?
contains muscles
- circular muscles
- radial muscles.
Lens function?
light focusing, muscles
Intraocular pressure is linked to…
… the production and drainage of aqueous humour
In ophthalmology, normal intraocular pressure as that between …
… 10 mmHg and 20 mmHg
The average value of intraocular pressure is…
… 15.5 mmHg with fluctuations of about 2.75 mmHg.
Ocular hypertension is defined by…
… intraocular pressure being higher than normal, in the absence of optic nerve damage or visual field loss.
Ocular hypotension, hypotony, or ocular hypotony, is typically defined as…
… intraocular pressure equal to or less than 5 mmHg. Such low intraocular pressure could indicate fluid leakage and deflation of the eyeball.
what is the optic nerve more precisely known as…
the photosensitive ganglion cells
The optic nerve, or more precisely, the photosensitive ganglion cells through the retinohypothalamic tract, is responsible for …
… the afferent limb of the pupillary reflex.
-> Detection of incoming light.
The oculomotor nerve is responsible for …
… the efferent limb of the pupillary reflex
-> Response to initiate contraction of the iris muscles (=pupil “contraction”).
What do rods detect?
Rods = low light (intensity)
What do cones detect?
Cones = colours
CN II = ?
optic
CN III = ?
oculomotor
The macula is the part of the eye that …
… processes what is seen directly in front of the observer (central vision).
The fovea centralis, or fovea, is a …
… small depression within the neurosensory retina where visual acuity is the highest. The fovea itself is the central portion of the macula, which is responsible for central vision.
There are no photoreceptors (i.e., rods or cones) in the …
… optic disk, and, therefore, there is no image detection in this area. “blind spot”
What is the optic disc?
“the blind spot” no photoreceptors this is where the optic-nerve fibres leave the eye.
What is temporal to the optic disc?
macula
What is the Macular centre: fovea
pit where there is sharp central vision, but less sensitive to light because its lack of rods.
How many cones?
7 million cones
how many rods?
75 to 150 million rods
What are rods responsible for?
vision at low light levels (scotopic vision). They do not mediate colour vision and have a low spatial acuity.
What are cones responsbile for?
Cones are active at higher light levels (photopic vision), are capable of colour vision and are responsible for high spatial acuity. The central fovea is populated exclusively by cones.
There are 3 types of cone pigments. Each one is …
most sensitive to a certain wavelength of light in air:
What are the 3 types of cone pigments?
short or “S” about 420–440 nm,
medium or “M” about 534–545 nm and
long or “L” about 564–580 nm
what will occur in order to see in the dark?
visual adaptation will occur.
In order to see in the dark, visual adaptation will occur.
This is usually achieved within …
… ~5 minutes (see Figure). Maximal adaptation is reached after ~15 to 20 minutes.
Dark adaptation forms the basis of the Duplicity Theory, which states that …
… above a certain luminance level (~0.03 cd/m2), the cone mechanism is involved in mediating vision: photopic vision. Below this level, the rod mechanism comes into play, providing scotopic (night) vision. The range where two mechanisms are working together is called the mesopic range, as there is not an abrupt transition between the two mechanisms.
Go look at slide 39
Accommodation and convergence of the humans’ eyes are needed to
… receive a clear image of the target object and to achieve single binocular vision in the visual cortex.
Accommodation is the process by which …
… the vertebrate eye changes optical power to maintain a sharp image (focus) on an object as its distance changes (as depicted in Figure 2)
What is convergence?
simultaneous inward movement of both eyes towards each other, usually in an effort to maintain single binocular vision when viewing an object (as shown in Figure 3).
The human eye can distinguish object as small as …
… 0.3 arc-minute.
The eye is not a single frame snapshot camera. It is more like a …
… video stream
The eye is not a single frame snapshot camera. It is more like a video stream.
The eye moves rapidly in …
… small angular amounts and continually updates the image in one’s brain to “paint” the detail
We also have two eyes, and our brains…
…combine the signals to increase the resolution further.
We also typically …
… move our eyes around the scene to gather more information.
Because of these factors, the eye plus brain assembles a …
… higher resolution image than possible with the number of photoreceptors in the retina.
Define peripheral vision
Peripheral vision is a part of vision that occurs outside the very centre of gaze. There is a broad set of non-central points in the visual field that is included in the notion of peripheral vision.
What are the different types of vision?
monocular
binocular
bind
What is the neural pathway of vision?
Retina,
Optic Nerve(s),
Chiasma (1/2 info),
Optic Tract(s),
Lateral Geniculate nuclei
(part of the thalamus)
Optic Radiations,
Visual cortex (processing)
located in the Occipital lobe
What is macular degeneration
A common age-related condition that affects the middle part of the field of view.
Who does macular degeneration usually effect?
Usually affects people in their 50s-60s.
Macular degeneration does not cause
total blindness, but it can make everyday activities such as reading and recognising faces difficult.
What does treatment of macular degeneration include?
Treatment involves regular injections into the eye of Anti-VEGF (vascular epithelium growth factor) medicines – ranibizumab (Lucentis), aflibercept (Eylea) and brolucizumab (Beovu)
What happens to the eyes in macular degenration without treatment?
Without treatment, vision will worsen over time. This can happen gradually over several years, or quickly over a few weeks/months.
What causes macular degenration?
The exact cause is unknown.
What links have been found with macular degeneration?
Links have been suggested to smoking, high blood pressure, being overweight, and having a family history of the disease.
cataract symptoms?
Cloudy area of lens, blurred vision.
causes of cataract?
age, trauma, radiation (X-rays), smoking or alcohol, incorrect diet (Vitamin C), genetic mutations, or as a side effect of certain medication.
treatment of cataract?
Replaced with an artificial or donor lens. One of the most performed surgeries in ophthalmology.
describe the treatment process of cataracts?
1) Incision is made
2) Emulsification breaks up cloudy lens
3) Intraocular lens is implanted
4) The incision heals on its own
What is Diabetic retinopathy caused by?
Caused by high blood sugar induced diabetes. The high blood glucose levels progressively damage the blood vessels that supply blood to retinal cells. This is accompanied by a loss of capillary cells, which induces permeability of the capillaries
Diabetic retinopathy treatment?
There is no cure, only management therapy such as anti-VEGF injections (similar to those given for macular degeneration), steroid injections, laser photocoagulation, and vitrectomy (partial or total removal of the vitreous humor).
Around 1/3 of patients with diabetes present…
…a form of retinopathy.
