Sensory Physiology - Nov. 29th Flashcards
Mastery
Pain. What type of mechanism? look to the future? what is it influenced by?
Nociceptors
Cytokines
Hyper-Algesia
Three types
Mechanical nociceptors
Thermal nociceptors
Polymodal nociceptors
Primarily a protective mechanism
behavioural responses and emotional reactions
memory helps us avoid harmful events in future
Subjective perception influenced by other past experiences
Nociceptors
do not adapt to sustained stimulation
Cytokines will lower nociceptor’s threshold
greatly enhances receptor response to noxious stimuli
Hyper-algesia
Eg.
* Prostaglandins
* Bradykinin
* histamines
Three types
Mechanical nociceptors
* Respond to damage such as cutting, crushing, or pinching
Thermal nociceptors
* Respond to temperature
extremes
Polymodal nociceptors
* Respond equally to all kinds of damaging stimuli
Characteristics of Fast and Slow pain (table)
Pain
Substance P
Glutamate
Analgesic System
Pain
Two best-known pain neurotransmitters
Substance P
* Activates ascending pathways
Glutamate
* Major excitatory neurotransmitter
Brain has a built in analgesic system
Suppresses transmission in pain pathways
Depends on presence of opiate receptors
* Endogenous opiates – endorphins, enkephalins,
dynorphin
Visceral and Referred pain
Visceral and somatic afferent neurons often converge on the same neuron in the spinal cord leading to referred pain.
Referred pain is the sensation of pain at a site other than the injured or diseased tissue.
Three outer layers of the eye
Vitreous humour
Aqueous humour
Glaucoma
Schleroid
* White of the eye
* Continuous with cornea
Choroid
* Blood vessel layer
* Iris and ciliary body
Retina
* Back and sides only
* photoreceptors
Vitreous humour
- Gelatinous
- Maintains shape of eye
Aqueous humour
- Provides nutrients to the cornea
- 5 mL/day
Blocked drainage duct. *Canal of SCHLEM
- Aqueous humour fluid builds
- Build-up of pressure
- Can damage nerve
Iris and Pupil
Convex structures of eye
images on the retina
Pupil
- Eye opening for light
Iris
- Colour of the eye
- Controls amount of light entering eye
* Circular muscles constrict pupil
* Radial muscles dilate pupil
Convex structures of eye produce
convergence of diverging light rays that reach
eye
Images formed on the retina are upside down and
are only a small fraction of the object’s actual size
Light Refraction
what is refraction a result of
Accomodation
For far vision
For near vision
Refraction is a result of
Cornea
* Contributes most to refraction
* Refractive ability remains constant because curvature never changes. Constant
Lens
* Refractive ability can be adjusted by changing curvature as needed for near or far vision. focus on close or far objects
For far vision
- Light rays are parallel – need less bending
- Lens should be flatter
For near vision
- More bending needed
- Rounder lens
What does accommodation include and involve
far vision and near vision
- Ciliary muscles
- Suspensory ligaments
For far vision
- Ciliary muscles relax
- Suspensory ligament are pulled taut (tight)
- Lens is flatter / weaker
For near vision. ACCOMMODATION
- Ciliary muscles contract
- Suspensory ligaments go slack
- Tension in lens causes it to become rounder/stronger
Lenses
Convex lens
Concave
Eye Conditions
Emmetropia
Myopia
Hypermetropia or hyperopia
Presbyopia
Convex lens - convergent - Bends light rays in
Eg. the Lens of eye
Concave lens - divergent - Bends light rays out
Emmetropia
- Normal vision
Myopia
- Near-sightedness
- Lens is too strong or eye too long
- Focus is in front of retina
- Corrected with a concave lens
Hypermetropia or hyperopia
- Far-sighted-ness
- Lens too weak or eye to short
- The focus is behind retina
- Corrected with a convex lens
Presbyopia
- Loss of near vision with age
- Due to stiffening of lens
- Harder to become round
- Correct with reading glasses
Light transduction where does it occur
what makes up the eye
Retinal Layers, where does light go and what is the blind spot
Light transduction occurs on the retina
- Photoreceptors(Rods and cones)
- Bipolars
- Ganglions
- Optic nerve (blind spot, no rods or cones)
- Horizontal cells – lateral inhibition
- Amacrine cells – assist?
- The light must filter through cell layers before
hitting the rods and cones - Blind spot – where optic nerve leaves eye
Retina
Fovea
Macula lutea
Macular Degeneration
Fovea
- Pinhead-sized depression in centre of retina
- Most distinct vision
- Has only cones (no filtering)
Macula lutea
- Area immediately surrounding fovea
- High acuity
* cones only – but with overlaid bipolars and ganglions
Macular degeneration
- Loss of cones in macula
- Lose central vision
- Leading cause of blindness in western hemisphere “doughnut” vision
- Wet – more blood vessels – bleeding
- Dry – atrophy of pigment
Outer segment
Inner segment
Synaptic terminal
Outer segment
* Detects light stimulus
Inner segment
* Contains metabolic machinery of cell
Synaptic terminal
* Transmits signal generated in photoreceptor on light
stimulation to next cells in visual pathway
