Special senses Flashcards
Are cranial nerves part of central or peripheral nervous system?
PNS
How are cranial nerves different to spinal nerves?
- Spinal nerves branch off of the spinal cord, then exit through intervertebral foramina.
- Cranial nerves travel through cranial bones and off to eyes, ears mouth, for example.
- Some cranial nerves are sensory only. No peripheral nerves like this
Some cranial nerves are motor only. No peripheral nerves like this.
What is the general process of sensory receptors?
Receive sensory information from the body part -> Sent to brain -> Interpreted as smell, sound (or whatever).
List all the special senses, and the its cranial nerve, and nerve type (sensory/motor/mixed).
Pneumonic for whole table:
Special Senses: Cranial Nerve: Sally Omlette Saw Of Harold Vagina Tasting From Grocery
Smell Olfactory
Sight Optic
Hearing Vestibulocochlear
Tasting Facial and Glossopharyngeal.
Which respiratory tract is the nasal cavity part of?
Upper respiratory tract.
What is the nasal cavity lined with?
Specialised ‘respiratory - type epithelium’ - containing seromucous glands.
What are the functions of nasal cavity?
- Mucus secretions protect epithelium
- Warms & humidifies inhaled air
- Provides immunological & mechanical (ciliary clearing) defense against infective & inert particles
Describe the structure of conchae (composition of its components).
Lateral wall of conchae = comprised of hyaline cartilage and cranial bones.
Lateral walls of nasal cavity contain:
Three paired projections and crevices to increase surface area in contact with air:
- Superior, middle and inferior conchae (projections)
- Superior, middle and inferior meatus (crevices in b/w projections.
Where is the olfactory region in relation to the superior conchae and nasal cavity root?
Superior to nasal cavity roof and superior conchae.
How do olfactory nerve fibres become olfactory/respiratory epithelium?
They pass b/w cells, and become olfactory/respiratory epithelium.
What are olfactory bulbs?
Olfactory nerve fibres that travel from nasal cavity -> to holes in cranial bones -> back into cranial bones.
What is a cranial nerve 1?
olfactory bulbs that become olfactory nerve tracts.
Olfactory nerve tracts = extension of brain that have meningeal coverings.
Where is the olfactory information sent from the olfactory nerve tracts?
Olfactory cortex.
What is the structure of orbit contents and muscles in the eye?
- Orbit: Comprised of 7 cranial bones, bony cavities for eyes (R & L), contain muscle, lacrimal system & fat
- Orbicularis oculi: Circular skeletal muscles that close eyelids Extra-ocular muscles: Skeletal muscles within the orbital cavity - move eye right, left, up, down, rotate and opens eyelid (covered in Head & Neck week)
- Lacrimal apparatus: Production, movement & drainage of fluid from eye surface (tears)
What is the function of cornea?
Function of cornea: Bend light into pupil, into the eye.
What is the structure of cornea?
- Anterior surface = thin layer of epithelium (edges continuous with edges of conjunctiva)
- Middle = collagen fibers (protein, not cells)
- Posterior surface = epithelium
- Avascular
What is the function of conjunctiva?
Provides mechanical protection and lubrication of eyes.
What is the structure of conjunctiva?
- Epithelium with secretory cells, fibrous tissue & conjunctival blood vessels
- Covers posterior surface of eyelids and reflects to cover anterior surface of eyeball
- *Anatomically independent of the cornea, but histologically the anterior epithelium is continuous
- Conjunctiva extends over the anterior sclera but not as far as extraocular muscle attachment
What is the function of iris?
Regulates the amount of light that enters eyes
Describe the structure (also components) of the iris:
- Thin diaphragm of tissue resting on lens
- Melanocytes contain pigment that gives colour − few melanocytes = blue colour − many melanocytes = brown colour
- Vascularised to supply pupillae muscles
- Opening in iris is the pupil (“little person”)
What are the two muscles of the iris?
Dilator pupillae and Sphincter pupillae.
How does the sphincter and dilator pupillae work to increase and reduce light entry?
Sphincter:
Muscle fibres arranged circularly around pupil -> Innervated by parasympathetic nerve fiber -> Contraction reduces pupil diameter in bright light (to reduce light entry)
Dilator:
Muscle fibres arranged radially around pupil -> Innervated by sympathetic nerve fiber -> Contraction increases pupil diameter in dim light/fright or slight mode (to increase light entry)
What is the function of lens?
Function: Refracts (bends) light onto retina to focus on images/objects (AKA accommodation)
Describe structure of lens:
- Avascular
- Biconvex disc: connective tissue capsule, epithelial layer, layered crystalline lens fibers (not cells)
What are some components that interact with lens that alter curvature of lens:
- Suspensory ligaments (aka zonular fibers).
- Ciliary muscles.
Is action of ciliary muscles controlled by sympathetic or parasympathetic stimulation?
Parasympathetic stimulation.
What adjusts curvature of lens and how is it adjusted?
Contraction/relaxation of ciliary muscles adjusts the curvature of lens.
To focus, ciliary muscles can contract/relax, pulling on suspensory ligaments altering the curvature of the lens
− Flatter lens to focus on distant images/objects
− Rounder lens to focus on closer images/objects
What does the curvature of lens adjusts and alters?
- Adjusts focus
Alters e refraction of light for near or far vision
Describe the structure (also includes components) and function anterior and posterior eye cavities:
Anterior cavity:
Contains fluid aqueous humor - derived from plasma Function: Supplies nutrients to avascular cornea & lens, maintains intraocular pressure & shape of anterior eye – continuously produced
Posterior cavity:
Contains gelatinous mass called vitreous humor – formed during development & is not replaced • Comprised of collagen fibers & proteoglycans Function: Stabilizes the shape of eye which could otherwise be distorted by extraocular muscles pulling on it
Describe the structure, location and function of fibrous tunic:
- Outermost layer but deep to conjunctiva anteriorly
- Continuous with cornea
- Tough fibrous connective tissue
- Protection, support, provide extraocular muscle attachment
What is the structure of vascular tunic - choroid? What is its function?
- Numerous blood vessels, lymphatics, *heavily pigmented & includes the smooth muscles of ciliary & iris
- Blood vessels enter at same point as optic nerve (optic disc)
- Blood supply to retina, pupil/lens size/shape, regulates aqueous humor
What is the structure of the neural tunic and what are its components?
- Innermost tunic, avascular
- Contains photoreceptors (macula and fovea), which are not evenly distributed.
Are rods sensitive or insensitive to light? Do they enable to see in dim or bright light? Can they distinguish between colours?
- Highly sensitive to light
- Enable us to see in dim light (twilight, moonlight)
- Do not distinguish colours.