Special Senses (Start Exam 4)

Question 1

Smell - Olfaction

Answer 1

A. Receptors - located in the nasal mucosa of the most superior aspect of the nasal cavity.
B. Nasal mucosa = nasal epithelium - composed of 2 cell types:
1. Supporting cells - columnar epithelial cells (pseudostratified) with cilia - very similar to typical respiratory epithelium - also mucous producing glands in lamina propria.
2. Olfactory cells - bipolar neurons intermixed with supporting cells. Distal end has 6-8 free ending dendrites called “olfactory hairs”. Proximal end has axon which passes through the cribiform plate of the ethmoid bone to synapse on cells in the olfactory bulb within the cranial cavity (directly inferior to frontal lobe) - these fibers = true olfactory nerve.
C. Axons of cells in the olfactory bulb transmit impulses posteriorly to various regions within the brain via the olfactory tract (actually in learning the cranial nerves - it is a misnomer to call the olfactory tract cranial nerve I - but it is often done.)

Question 2

Taste - Gustatory Sense

Answer 2

A. Receptors - located in many parts of the oral cavity, but most concentrated on the surface of the tongue.

1. Taste buds - a capsule of specialized epithelial cells surrounding 4-20 specialized taste receptors called:
a. gustatory cells - these have a dendrite like process called:
b. gustatory hair - at their apical portion which projects through an opening in the epithelium called the:
c. gustatory pore - Dendrites of neurons of the cranial nerves involved in taste are stimulated by gustatory cells.

B. Papillae - taste buds on the tongue are usually associated with 3 types of C.T. elevations on tongue.

1. Filiform papillae - pointed projections over anterior 2/3's of tongue.  Some have buds.
2. Fungiform papillae - mushroom-shaped structures mostly found at tip and lateral edges of the tongue.  Most have taste buds.
3. Circumvallate Papillae - shaped like small guard towers in inverted "V" shape on posterior portion of the tongue - largest type - all have taste buds.

C. Mechanism

1. Substances must be dissolved in saliva and enter the gustatory pores and come in contact with gustatory hairs.
2. Depending on what substance is dissolved in the saliva - it will be interpreted by our brain as tasteless, bitter, sour, sweet, or salty due to impulses from our taste receptors - all other "tastes" which we identify are actually odors being interpreted by olfactory stimulation.
3. Impulses for taste are transported mostly via cranial nerve VII (Facial) which supplies the anterior 2/3's of the tongue.
4. Impulses also transported along with cranial nerve IX (Glossopharyngeal) for posterior 1/3 of tongue and with cranial nerve X (Vagus) which supplies the throat region.

Question 3

Structures directly related to vision:

Answer 3

1. Eyeball
2. Optic Nerve
3. Brain

Question 4

Accessory Structures which aid efficiency of visual system

Answer 4

1. Eyebrows - similar to hair follicles on the scalp - but don’t increase in length. Hairs themselves are also much more coarse. Function may be debated - but most likely a barrier to help prevent perspiration from getting into one’s eyes.
2. Palpebrae = eyelids = epidermis and dermis overlying skeletal muscle and connective tissue.
   a. upper eye lid is movable - contains levator palpebrae superioris (a skeletal muscle)
   b. skeletal muscle fibers in both eyelids are from the orbicularis oculi.
   c. each eyelid contains a tarsal plate which is a thick fold of C.T.
   - small smooth muscle attached to tarsal plate controlled by sympathetic input
   d. the innermost portion of each eyelid is a mucous membrane = palpebral conjunctiva.
   e. function: protection from excess light and foreign objects - also for continuous spread of lubricating fluid over the eyes.
3. Eyelashes - short thick hairs which line the border of each eyelid.
   a. base of hair follicles have glands - glands of Zeis - sebaceous glands.
   (note: infection of these glands is called - sty
   b. function: also aid in protection of eyes.
4. Lacrimal Apparatus - structures which manufacture and drain away tears.
   a. lacrimal glands - in superior lateral portion of each orbit. Peanut - almond size and shape. Compound tubuloacinar gland. Manufactures and excretes tears.
   b. lacrimal ducts - distribute lacrimal fluid (tears) onto the inner surface of the eyelid, which in turn spreads it across surface of the eye.
   c. lacrimal canals - exit from tiny papilla at the inferior medial aspect of the eye and drain into a space within the lacrimal bones called the lacrimal sac.
   d. nasolacrimal duct - exits lacrimal sac and drains into inferior meatus of nasal cavity.
   e. lacrimal secretion - water mostly - some salts - some mucous - some lysozyme. Cleans, lubricates, and moistens. Normally produce about 1 ml/day. However, irritation of eye’s surface will increase this greatly. May also notice excess tearing if nasolacrimal duct is blocked (e.g. Hayfever).

Question 5

Eyeball

Answer 5

• composed of: a) fibrous tunic, b) vascular tunic, c) retina. About 1 inch in diameter, only 1/6 shows, the remainder is within orbit.
  a. Fibrous tunic - composed of cornea anteriorly and sclera posteriorly.
• sclera - white of the eye - white fibrous coat over the entire eye except anterior portion.
• Cornea - a transparent part of the eye covering the iris and pupil anteriorly - nonvascular but highly innervated.
• most external layer - bulbar conjunctiva

Question 6

Vascular tunic - middle layer of eyeball

Answer 6

• Choroid - thin dark brown membrane immediately within sclera. Contains large amount of pigment and many blood vessels. Absorbs light (stops reflection).
• Ciliary body - anterior continuation of choroid - it contains the ciliary muscle - smooth muscle which changes the shape of the lens for near and far vision (and changes the size of the pupil somewhat).
• Iris - most anterior portion of vascular tunic - continuous with ciliary body. Consists of circular and radially arranged smooth muscle fibers. Opening in the center is the pupil. Between the cornea and the lens. Regulates the amount of light allowed to enter the eyeball.
• bright light - circular smooth muscle contract to decrease pupil size (sort of like sphincter)
• dim light - radial smooth muscle contracts to increase pupil diameter.

Question 7

Retina

Answer 7

• innermost coat - found in the posterior portion of the eye only.
  function - sensitive to light striking it, thus responsible for image formation
  Composed of 2 layers:
  (1) Pigmented layer - covers inside of choroid.
• Extends completely around the posterior chamber of the eye. (except is not on lens)
• Does not function directly in vision, but because of its pigmentation tends to absorb light and limit stimulation of visual receptors to direct light not light reflected within the eye.
  (2) Nervous layer - inside of (anterior to) the pigmented area.
• Extends only as far anteriorly as the most posterior aspect of the ciliary body.
• Note: Detachment of retina - usually happens due to trauma to the head - retina tears between nervous and pigmented layers - causes corresponding blindness in damaged area - can usually be surgically repairs.

Question 8

receptors at the terminal ends of photoreceptor cells are specialized receptors sensitive to light: what are they and details?

Answer 8

1. Rods - specialized for vision in dim light - black and white vision.
2. Cones - specialized for color vision - more important in finer discrimination - only stimulated by bright light. We have 10-20 times more rods than cones.
3. Macula Lutea - (yellow spot) - region in the exact center of the retina - does not contain rods, or contains very few rods - high concentration of cones.
4. Fovea - small depression in the center of the macula. Area of the most acute vision. No rods present. Highest concentration of cones in entire retina.
5. Impulses generated in the dendrites (receptors) of photoreceptor neurons are relayed anteriorly to bipolar neurons within the retina which in turn relay impulses anteriorly to ganglion neurons whose axons move toward the optic disc = blind spot where they exit as the optic nerve.

Question 9

Lens

Answer 9

• transparent - proteins arranged in circular “onion-like” pattern - supported by ligaments from the ciliary body (ciliary muscle) called the suspensory ligament - lens is enclosed in clear connective tissue capsule.

1. Cataract - loss of transparency of the lens - occurs in old age and some metabolic disorders (also x-rays and some drugs)
   - nuclear cataract - formed in core of lens.
   - cortical cataract - formed in outer layers.

Question 10

Lens separates two cavities in the eyeball:

Answer 10

1. Anterior Cavity
   a. anterior to the lens and posterior to the cornea
   b. contains aqueous humor - since lens and cornea do not have blood vessels, aqueous humor accomplishes a role in both nutrition and waste romoval for these tissues
   c. made up of 2 smaller chambers:
   - anterior chamber and the posterior chamber - separated by the iris
2. Posterior Cavity
   a. posterior to the lens and suspensory ligament
   b. contains a thicker and more viscous fluid called the vitreous humor which helps the eye to maintain its shape.
3. Intraocular pressure is due to pressures of both the aqueous humor and the vitreous humor, but is primarily effected by pressure of the aqueous humor.
   a. aqueous humor like CSF is continuously being formed by a choroid plexus located within the ciliary body in the posterior chamber of the anterior cavity. From this point it diffuses forward into the anterior chamber through the pupil, where it is then drained away by the Canel of Schlemm (Scleral Venous Sinus).
   a. Canel of Schlemm, or Scleral Venous Sinus - located peripherally around anterior chamber of eye. Returns fluid back to the circulation.
   b. Glaucoma - excessive intraocular pressure.

Question 11

Eye Muscles

Answer 11

1. Intrinsic Muscles = ciliary muscle and smooth muscle of the iris. These are innervated by fibers from the autonomic nervous system.
2. Extrinsic Muscles = muscles which move the eyeball. These are innervated by cranial nerves (CN III, IV, VI)
   a. Superior Oblique - rotates eyeball down and out
   b. Inferior Oblique - rotates eyeball up and out.
   c. Superior Rectus - rotates eyeball up
   d. Inferior Rectus - rotates eyeball down
   e. Medial Rectus - rotates eyeball medially
   f. Lateral Rectus - rotates eyeball laterally
   * All extrinsic muscles have their origins from a tendinous ring that encircles the optic foramen at the posterior aspect of the orbit. The muscles all insert on to the sclera of the eyeball.

Question 12

External Ear or Outer Ear

Answer 12

A. Pinna = Auricle = outer visible portion. Made of elastic cartilage covered with a epidermis and almost no underlying connective tissue.
Note: this is why an infection (i.e. pimple) on the outer ear is so painful.
B. External Auditory Meatus (canal) - opening, a tube-shaped opening in the temporal bone. It extends from the outer pinna to the “eardrum” and is covered with a thick skin (like the pinna) with very little connective tissue. The tissue contains specialized sebaceous glands called ceruminous glands which secrete cerumen (earwax). The external portion also has very coarse hairs (especially in older men). It is believed that both the cerumen and the hairs prevent foreign objects and inhibit insects from entering the ear.
C. Tympanic Membrane = eardrum - very thin membrane that separates the middle ear and the external auditory meatus.
Note: rigid fibers within tympanic membrane are arranged radially like spokes of a wheel and circularly around attachment to the malleus.

Question 13

Middle Ear = Tympanic Cavity

Answer 13

A. Cavity within the mass of the temporal bone - between external auditory meatus and inner ear.
B. Continuous posteriorly with the mastoid cavity within the mastoid process.
C. Continuous anteriorly with the eustachian or auditory tube which opens into the superior part of the pharynx.
Function of eustachian tube is for drainage of mucous from middle ear cavity and for equalization of pressure on both sides of the tympanic membrane.
Note: this provides a route for the spread of infection from nasopharynx to middle ear and mastoid.
D. Membrane is lined with a mucous secreting epithelium.
E. Contains the auditory ossicles - tiny bones responsible for the conduction of sound from the tympanic membrane to the inner ear. Three different bones:
1. Malleus = “hammer” - attached to the internal surface of the tympanic membrane. Articulates with the incus.
2. Incus = “anvil” - between malleus and stapes.
3. Stapes = “stirrup” - a stirrup-shaped bones whose footplate fits perfectly into a tiny opening into the inner ear called the oval window or fenestri vestibuli.

Question 14

Labyrinth - 2 major divisions

Answer 14

A. Bony labyrinth - series of tubular cavities within the petrous portion of the temporal bone. On the basis of its shape it can further be divided into the vestibule, the cochlea, and the semicircular canals.
B. Membranous labyrinth - membranes forming a series of sacs and tubes within the bony labyrinth.

Question 15

Endolymph

Answer 15

• fluid which circulates within the membranous labyrinth - very similar to CSF.

Question 16

Perilymph

Answer 16

• fluid outside endolymph.

Question 17

Vestibule

Answer 17

• oval-shaped central portion of the bony labyrinth. Contains the:
  1. utricle - and the:
  2. saccule of the membranous labyrinth.

Question 18

Semicircular canals

Answer 18

• 3 ring-shaped canals of hollow bone. Each in a plane 90° to the other two. (called superior, posterior, and lateral)
  1. The terminal portion of each canal communicates with the vestibule. They are slightly dilated and referred to as ampulla.
  2. The membranous labyrinth within the semicircular canals assumes the same shape as the bony labyrinth - called semicircular ducts or membranous semicircular canals.

Question 19

Cochlea

Answer 19

• shaped like a snail shell - actually a bony tube curled on itself 2 3/4 turns.
  1. Membranous labyrinth inside forms 3 tubes which run the entire length of the cochlea. In cross section these 3 tubes are separated by membranes forming the shape of a “Y”.

			scala vestibuli
			vestibular membrane
			cochlear duct
			organ of Corti
			scala tympani					
                        basilar membrane

2. Stem of the Y is a shelf of bone.
3. Tube running on one side - scala vestibuli.
4. Tube on the other side - scala tympani.
5. Tube between the “arms” of the “Y” - cochlear duct.
6. Between the cochlear duct and the scala vestibuli is the vestibular membrane (or Reissner’s membrane)
7. Between the cochlear duct and the scala tympani is the basilar membrane.
8. Note: endolymph fills the cochlear duct but perilymph is found in the scala vestibuli and the scala tympani.
9. Resting on the basilar membrane - organ of corti (spiral organ) - the real organ of hearing.
   a. Organ of corti - several epithelial cells and hair cells - receptors for sound. There is an inner row and several outer rows of hair cells.
   b. These cells have hair-like processes on their apical ends which touch an overlying membrane called the tectorial membrane.
10. Fenestra vestibuli - oval window - opening filled by foot plate of stapes between the scala vestibuli and the middle ear cavity.
11. Fenestra cochlea - round window - membrane covered opening between scala tympani and middle ear cavity. Scala tympani is continuous with the scala vestibuli at the terminal end of the cochlear duct.

Question 20

Equilibrium-Two types:

Answer 20

1. Static Equilibrium - orientation relative to gravity.

2. Dynamic Equilibrium - orientation during movement.

Question 21

Utricle and Saccule of the Vestibule in the inner ear contain sensory hair cells called:

Answer 21

1. otolith organs. Their apical ends are covered with a gelatinous material containing microscopic crystals of calcium carbonate called:
2. otoliths which add mass to the material.
3. Movement of this gelatinous material in response to gravity or inertia will cause a bending of the hairs which like in the organ of corti will result in stimulation of dendrites in contact with the hair cells.
   Note: both for static and dynamic equilibrium.
4. However, these dendrites are from vestibular portion of vestibulocochlear nerve (cranial nerve VIII).

Question 22

Semicircular canals

Answer 22

• are more specifically for maintenance of dynamic equilibrium.
  1. They are all 3 at right angles to each other. Movement in any plane then will result in movement of endolymph within one or more of the canals.
  2. At the base of each canal is the expanded region - ampulla which contains an elevated area of hair cells = crista covered by a gelatinous dome = cupola into which the hairs project.
  3. Movement of the endolymph in the canals will cause the cupola to move thus bending the hairs of the hair cells - stimulating dendrites of VIII.

Question 23

Problems with the ear

Answer 23

A. Tinnitus - ringing in the ears - can be a terrible affliction for some people - can only be corrected by physically overriding with other sound.

B. Otitis Media - middle ear infection
- has highest risk in infants and young children.