ANP W13 The Sensory System

What are the 3 classifications of Sensory Receptors based on its structure?

1. Free dendrite (pain/temp)_

2. End-organ/modified or encapsulated’ dendrite (touch/pressure)

3. Specialized (rods and cons of retina)

What are the 4 classifications of Sensory receptors based on function (type of stimulus they respond to)

1. Chemoreceptors → taste and smell

2. Photoreceptors → light

3. Thermoreceptors → temperature

4. Mechanoreceptors → movement

Sensory receptors can be classified based on the distribution. What receptors are considered Special Sense?

Special sense = localized special sense organ

1. Vision

2. Hearing

3. Equilibrium

4. Taste

5. Smell

Sensory receptors can be classified based on the distribution. What receptors are considered General sense?

General sense = widely distributed receptors throughout body

1. Pressure

2. Heat/cold

3. Pain/Touch from skin and internal organs

4. Proprioception (sense of position from muscles, tendons and joins)

What is a palpebra? What muscle is it attached to?

eyelid → protecting front of the eye.

upper eyelid attached to levator palpebra

What is the conjunctiva?

Thin membrane lining the surface of the eyelid and covers the visible portion of the sclera (white part of eye)

How many extrinsic muscles does the eye have?

6 - originate on the bone of the orbit and insert on the surface of the sclera.

• named after their location and direction of the muscle fibres.

• responsible for “convergence” of the eyes = normal inward movement of both eyes to form 1 visual field.

Which nerve supplies the eye for transmit visual information to the brain?

Optic Nerve (CN 2) and Ophthalmic branch of the Trigeminal Nerve

Which cranial nerves innervate the eye muscles?

1. Trochlear CN 4

2. Abducens CN 6

3. Oculomotor CN 3 (largest)

What are the 3 layers of the eyeball?

1. Sclera (white part of the eye)

2. Choroid → vascular layer; delicate network of connective tissue; pigmented dark brown to help prevent light scatter

3. Retina → neural layer; contains rods and cones; covers posterior surface only

What are the 4 refractive parts of the eye?

1. Cornea

2. Aqueous Humor → watery fluid fills the eyeball anterior to the lens

3. Lens → biconvex shape

4. Vitreous body → soft jelly-like substance filling the space behind the lens and maintains eyeballs shape

What is Accommodation of the eye?

process of adjusting the lens thickness to allow for vision at near and far distances.

• Ciliary muscles contracts and removes the tension on suspensory ligaments.

What is the function of the Iris?

• Regulates amount of light entering the eye by contracting and relaxing circular muscle fibres and radial fibres of the iris to change the size of the pupil

Photoreceptor Rods

1. work best in dim light

2. does not detect colour

3. greater number than cones

4. Rhodopsin pigment → Vit A required to produce pigment

Photoreceptor Cones:

• Sensitive to light

• detects colour

• gives sharp images

• located in center of retina (fovea centralis)

• 3 types of cones. Red, green blue light (L,M,S)

What is Amblyopia?

loss of vision in a health eye because it cannot work properly with the other eye (from persistent strabismus)

• also called lazy eye

What is Inclusion conjunctivitis?

An acute eye infection caused by Chlamydia trachomatis.

• Trachoma = chronic infection from chlamydia that can cause blindness

What is the name of the type of conjunctivitis that is introduced at birth?

Ophthalmia neonatorum aka neonatal conjunctivitis

How does diabetes affect the retina?

Diabetic Retinopathy = high blood sugar damages the retina's blood vessels. This damage leads to leaking, swelling, abnormal blood vessel growth, and can result in blurred or distorted vision, floaters, and even blindness.

What is the disorder caused by retinal degeneration or lack of vitamin A that leads to inability to see in dim light ?

Nyctalopia (night blindness)