Anatomy of special sense organs Flashcards
1
Q
Development of the eye
A
- First; optic vesicle is formed from an outgrowth of the neural tubule
- optic vesicle contacts the ectoderm, causing formation of the lens placode
- optic vesicle flattens and folds inward to form optic cup ( becomes the retina)
- lens placode folds inward to become lens vesicle
- lens vesicle induces ectoderm to become the cornea
- optic stalk becomes the optic nerve
- hyaloid vessels eventually regress
2
Q
3 main layers of the eye
A
- called tunicae
- Outer layer; fibrous tunic. Dense collagen tissue, protects eye and hold its shape
- Middle layer; vascular tunic. Contains blood vessels & structures that hold the lens, regulate pupil size,
and produce fluid that fills the eyeball - Inner layer; the retina
3
Q
Fibrous tunic
A
- sclera
- cornea
4
Q
Vascular tunic
A
- choroid; highly vascular nourishes the outer layers of the retina. Supplied by ophthalmic artery
May have tapetum lucidum, reflective for better low light vision - ciliary body
- iris
5
Q
Nervous tunic
A
- retina
- neural layer
- pigmented layer
6
Q
Chambers of the eyeball
A
- Anterior chamber (in-front of lens)
- Posterior chamber (in-front of lens)
- Vitreous chamber
7
Q
Bony orbit
A
- eye sits within the bony orbit of the skull
- complete in humans, incomplete in most companion species
8
Q
Extra-ocular muscles
A
- move the eye in orbit
- 4x rectus muscles; move left right up and down
- 2x oblique muscles; rotate around visual axis
- 1x retractor bulbi; retracts eyeball into head
9
Q
Third eyelid
A
- only present in some species
- contains t-shaped cartilage
- has extra tear gland; accessory lacrimal gland
- kept retracted by smooth muscle under sympathetic control
10
Q
Tear Glands
A
- washes eye of debris
- lipid top layer; prevent evaporation
- watery middle layer; moistens cornea
- mucus bottom layer; sticks tear film to eye
11
Q
Species differences (eye)
A
- Birds have fewer retinal blood vessels; don’t block the retina as much better vision; pecten instead
- Many species have bony rings called sclerotic rings to hold shape and attach to muscles
- Snakes have no eyelids
12
Q
Development of the ear
A
- Inner ear forms first
- ectoderm thickens to form otic placodes
- roll inward to form otic pit
- pinch of to form otic vesicle
- otic vesicle forms membranous labyrinth
- middle ear forms from an outgrowth of the 1st pharyngeal pouch ( endoderm)
- external ear forms from 1st pharyngeal groove (ectoderm)
- eardrum forms where the pouch and groove meet
- bones form endochondrally from neural crest cells
13
Q
Outer ear
A
- pinna; skin and cartilage
- auricular muscles
- ear canal (external auditory meatus)
- eardrum (tympanic membrane)
14
Q
Pinna & auricular muscles
A
- funnel-shaped to collect sound waves
- pinna can be moved by auricular muscles to locate sound
- used for communication
- innervated by CN VII (facial nerve)
15
Q
External auditory meatus
A
- contains sebaceous and modified apocrine (ceruminous) glands
- cerumen catches objects that may damage eardrum
- ## in carnivores and pigs there is a bend
16
Q
Tympanic membrane
A
- separates the outer and middle ear
- stretched over tympanic ring
- first ossicle (malleus) attaches to it
- sound waves cause the membrane to vibrate
17
Q
Middle ear
A
- Inside the temporal bone of the skull
- lined with mucous membrane
- communicates with pharynx via auditory tube; pressure equalisation and drainage
18
Q
Guttural pouches in horses
A
- outpouchings of the auditory tube
- may function in brain cooling
- 2x compartments divided by stylohyoid bone; lateral and medial
- blood vessels & CN IX, X, XI, XII nearby
19
Q
Ossicles
A
- Malleus; hammer shaped
- Incus; anvil shaped
- Stapes; stirrup shape
- transmit vibrations and amplify them
20
Q
Inner ear
A
Consists of;
- membranous labyrinth
- osseous labyrinth
- perilymph fills space between labyrinths
Functions;
- hearing via the cochlear
- balance via vestibular system
21
Q
3 parts of the cochlea
A
- the cochlear duct
- the scala vestibuli
- the scala tympani
- the two scala communicate at the cochlea’s spiral
22
Q
The cochlea and hearing
A
- stapes vibrate compressing perilymph in the scala vestibuli.
- transmitted to endolymph in cochlear duct via Reissner’s membrane
- movement of endolymph causes pressure on the tectorial membrane
- tectorial membrane puts pressure on the hair cells which send impulse along cochlear nerve to the brain
23
Q
Vestibular system and balance
A
- 3x semicircular canals & enlargements of membranous labyrinth called saccule and utricle
- semicircular canal senses head rotation
- saccule and utricle sense accelerations
- Information is carried by the vestibular part of the
vestibulocochlear nerve to the brain
24
Q
Semicircular canals
A
- Three canals roughly perpendicular to each other
- Can sense movement in 3x directions
- Pitch, roll and yaw
- Rotations cause an endolymph current moving hair cells in the ampulla
25
Q
Saccule and Utricle
A
- contain hair cells in thickened patches (maculae)
- covered in gel-like layer containing otolith crystals
- endolymph movement bends hairs transmits impulse down vestibulocochlear nerve
26
Q
Species differences (ear)
A
- only mammals have an external pinna
- reptiles and birds have only one ossicle called columella
27
Q
Olfactory organ
A
Olfactory mucosa in dorsocaudal nasal cavity
- covers the lateral wall and ethmoidal conchae
- distinguished histologically by presence of olfactory neuronal cells
28
Q
Olfactory cells
A
- olfactory neuronal dendrites reach the epithelium; present cilia into the cavity
- axons combine to form the fascicles of the olfactory nerve; pass through cribriform plate to connect directly to olfactory bulb on the brain
- Bowman’s glands below epithelium; wash away odour particles, humidify epithelium & bind odourants
29
Q
Vomeronasal Organ
A
- The ‘sexual’ nose; detects pheromones
- Flehmen reaction; detection of oestrus by males
- 2 narrow parallel ducts embedded in hard palate
- part-lined by olfactory mucosa
