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)

Where is the blind spot located in the eye?

Optic disk where optic nerve exits the eye.

What are the difference between Wet and Dry Age-related Macular degeneration?

1. Wet = abnormal bloos vessel growth under the retina causing detatchment

   •  less common

2. Dry = material accumulates on th retina causing gradual vision loss. 

   • more common

   • dry progresses to wet typically (not the other way around)

What are the 3 main components of the ear? 

1. Outer ear = pinna (entire ear structure outside the skull) and canal

2. Middle ear = air space containing 3 small bones

3. Inner ear = contains the sensory receptors for hearing and equilibrium 

What structure of the outer ear has a thin lining and contains ceruminous glands (producing ear wax)?

External auditory canal/Meatus

3 ossicles of the middle ear. 

Malleus → incus → stapes (in contact with inner ear) 

fx: amplifies sound waves and transmits to the inner ear

What are the 3 divisions of the inner ear. Describe each.

1. Vestibule - 2 bony structures involved in maintaining equilibrium 

2. Semicircular canal - 3 bony tubes in 3 planes involved in equilibrium

3. Cochlea - snail-shell shaped struture used for hearing 

What is the name of the spiral organ, composed of hair cells that lies within the cochlea ?

Organ of Corti - located inside cochlear duct

The sensory receptors within the vestibule and semicircular canals are _____. What are the 2 types?

Ciliated

1. Maculae → in the vestibule; senses position of the head relative to gravity and acceleration

2. Cristae → in the semicircular canals; detects rotational acceleration

*supplied by the vestibular nerve (CN8)

What is the difference between sensorineural hearing loss and Conductive hearing loss?

Sensorineural = damage to auditory nerves or cochlea

• ex. age related hearing loss

Conductive hearing loss = problems with the structures that conduct sound waves to the inner ear 

• ex. wax accumulation, otosclerosis, damage to tympanic membrane/ossicles 

What are the 2 cranial nerves involved with taste receptors?

Facial (CN7) and Glosspharyngeal (CN9)

• most taste receptors are located on the vallate papillae

Which lobe of the brain receives impulses from olfactory receptors?

Temporal lobe

Which receptors detect light touch? 

Mesinners corpuscle (tactile corpuscles) 

• fingertips, toes, lips, tip of the tongue 

Which receptors detect pressure ?

Pacinian corpuscle - located in subcuntaneous tissue in skin and near the joints

Sense of positioning is detected by which receptors?

Proprioceptors - located in muscles, tendons, joints 

What do Nociceptors detect?

Pain - widely distributed

2 pathways of pain to the CNS.

• sharp acute pain pathway

• slow chronic pain pathway

What are 5 methods of pain relief?

1. Analgesics → non-narcotic drugs, narcotics → acts on CNS

2. Anaesthetics → prevent pain, relieve chronic pain

3. Endorphins → released naturally by the body

4. Applications of heat or cold

5. Relaxation or distraction techniques