Lecture 5 Flashcards
Where do pain fibers end?
In periaqueductal grey matter or periventricular nuclei
Periaqueductal grey matter or periventricular nuclei stimulate neurons that secrete __.
Enkephalins
Pain fibers synapse with:
Raphe magnus or paragigantocellularis nucleus
What are the causes of visceral pain?
1) Ischemia: Decrease or low blood flow to the tissue = tissue damage =
releases chemicals that excite the free nerve endings of pain receptors
2) Chemical irritation from perforated peptic ulcer, or acids from the biliary system
= irritates the viscera and peritoneum
3) Spasm of a hollow viscus = constriction or contraction of SI (intestinal
colic) = mechanical stimulation of the free nerve endings as they press on the
free nerve endings
4. Overdistension of a hollow viscus = increase the pressure on the walls of
the organs.
Cold receptors respond from -°C with a peak response at _°C.
7-44; 25
Warm receptors respond from -°C with a peak response at _°C, which can cause pain.
30-49; 44
What determines temperature sensation?
The relative degree of stimulation of the receptors
What are the 4 different receptors?
1) Warm
2) Cold
3) Burning hot
4) Freezing cold.
Can thermal receptors adapt to the stimulus?
Yes, but not completely
What does cold or warm temperature do?
Change the metabolic rate of the receptor = changes the rate of intracellular reaction (how?) By changing the permeability of
ions in the receptors, and the receptor potential = Change the action potential formed in the afferent neuron connected to these receptors.
If you increase the temperature from 15 to 20 °C:
The number of impulses
increases to around the level of 25°C (person feels too hot)
If a person stays under an increased temperature for a while, what happens?
There is a slight decrease in the number of impulses and the heat doesn’t feel as
intense or hot.
What is thermal adaptation?
It starts as fast adaptation then slow adaptation, but there is no complete adaptation to temperature
What are the 3 layers of the eye?
1) Sclera
2) Choroid
3) Retina
What surrounds 4/5 of
the eyeball? What about the last 1/5?
The sclera; The cornea (anteriorly)
What is the sclera made up of?
Very dense connective tissue
What determines whether one can undergo laser surgery or not?
The cornea
What is the choroid?
A vascular component of the eye which continues anteriorly with the ciliary body
Which muscle is part of the choroid? What does it continue as?
Ciliary muscle; continues anteriorly as the iris
What connects the ciliary body and the lens’ capsule? What is its function?
Suspensory ligaments, which (through the work of the ciliary muscle) change the shape of the lens.
What is the lens made up of?
Multiple layers of protein
What allows the lens to change shape? What are its shapes?
its flexibility; flatter (less convex) and fatter (more convex)
The __ divides the eyeball into 2 cavities:
Lens;
1) Anterior cavity: Between the lens and cornea
2) Posterior cavity: Extends behind to the retina
The 2 cavities of the eyeball are connected by the:
Pupil
The anterior cavity is divided into 2 chambers:
1) Anterior to the iris
2) Posterior to the iris (between the lens and the iris)
The anterior cavity contains a fluid called __, which the posterior cavity contains a fluid called __.
Aqueous humor; vitreous humor
What does the aqueous humor do?
Provides nutrition to the avascular cornea.
Where is the vitreous humor derived from?
The embryonic mesenchyme
What keeps the eyeball round and distended?
The intraocular fluid
Which fluid is dynamic and gets renewed?
Aqueous humor
What produces the aqueous humor?
The ciliary processes of
the ciliary body
What is the path of the aqueous humor?
Ciliary body => between the ligaments of the lens => through the pupil into the anterior chamber => goes between the cornea and the iris => through a meshwork of trabeculae => canal of schlemm => empties into aqueous veins => extraocular veins.
Aqueous humor lies __(behind/infront of) the lens, while the vitreous humor lies __(behind/infront of) the lens.
Infront of; behind
What is the normal intraocular pressure?
It is 15 mmHg with a range of 12-20 mmHg.
What is the level of intraocular pressure is determined by?
1) The resistance to outflow of aqueous humor through the canal of Schlemm
2) The amount of aqueous humor production
An increase in intraocular pressure can result in:
Damage to the optic nerve resulting in Glaucoma = blindness due to compression of the axons of the optic nerve.
Where does the retina develop from?
The ectoderm
What does the retina contain?
The visual receptors (Rods & cones)
What is the central part of the retina called?
Macula lutea
What’s the slight depression in the central part of the retina called?
Fovea
What is the fovea important for?
It has the highest concentration of cones receptors
What are cones receptors important for?
1) Sharp color vision
2) Highest acuity of vision
What is the optic disc?
Where optic nerve fibers pass through along with retinal artery & veins. It is a blind spot (no
rods and cones).
What are the most superficial vessels in our body?
Retinal vessels
What is the pressing force that keeps the retina and choroid adherent
together?
The vitreous humor
If the vitreous humor leaks, what happens?
Causes retinal detachment.
What does retinal detachment cause?
Causes the receptors on the retina to separate from the choroid = neural death = blindness.
Retinal detachment is a medical emergency, It has to be reattached within __ hours or else the patient will become permanently blind
48 hours
When light travels between two different media it __, due to:
refracts (bends); the change in speed
What is the refractive index?
The ratio of the speed of light in air to the speed of light in the substance.
(𝒔𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒂𝒊𝒓 (𝟑𝟎𝟎,𝟎𝟎𝟎𝑲𝒎/𝒔))/
(𝒔𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒕𝒉𝒆 𝒔𝒖𝒃𝒔𝒕𝒂𝒏𝒄e)
Since the speed is fastest in air, the refractive index would always be:
1 or more.
What is refraction?
Bending of light rays through an angulated interface between two media with different refractive indices.
The degree of refraction and the resulting degree of angulation of light increases as:
The difference in their R.I. increases.
The features of the eye (like cornea, lens, humor) have
different R.I. and thus they:
Cause light rays to bend = light rays become focused on the retina.
