Are cranial nerves part of central or peripheral nervous system?
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
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?
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
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?
Muscle fibres arranged circularly around pupil -> Innervated by parasympathetic nerve fiber -> Contraction reduces pupil diameter in bright light (to reduce light entry)
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:
- 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?
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:
Contains fluid aqueous humor - derived from plasma Function: Supplies nutrients to avascular cornea & lens, maintains intraocular pressure & shape of anterior eye – continuously produced
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.
What are the 3 types of cones? Do they need light to function? How is the perception of colours achieved using cones?
- 3 types - detect red, green and blue.
- Need light to function.
- Stimulation in various combinations provides perception of colours.
Does macula have any rods?
Which site has the densest concentration of cones, and the sharpest vision?
Which site has a blind spot (no photoreceptors)
Does optic nerve (CN 2), attach to the eye.
Why does optic disc not have photoreceptors?
Blood vessels travel through optic disc -> choroid layer, we can’t also have photoreceptors in that surface.
Describe structure of optic nerve:
Extension of brain that has meningeal layers.
How does this information get sent to brain and how do we then interpret it as sight?
How does it get there?
Visual info sent from photoreceptors in retina via optic nerve, cranial nerve 2 to primary visual cortex in occipital lobe.
Photoreceptors in retina from each eye -> into the optic chiasm -> converge at optic chiasm -> nerve fibres of temporal sides continue on the path towards back of brain, but nerve fibres from nasal side cross over to opposite sides.
What does optic nerves become posterior to the optic chiasm?
- Optic tracts, that contain mix of crossed and uncrossed optic nerve fibers.
What structure takes visual information to the visual cortex?
Why do we nerve fibres cross over? Why do we have an optic chiasm?
Nerve fibres from nasal side cross coz right and left visual fields cross.
Thus, crossing over means visual fields don’t overlap and can be processed by each visual cortex. Info is shared b/w both sides, and interpreted as whole visual field of view.
Describe the process in which a whole visual field of view is seen.
Visual info processed by left visual cortex:
- Temporal nerve fibres go to left visual cortex. But info from nasal side of right eye are going to cross over and converge and be processed by left visual cortex.
Visual info processed by right visual cortex:
Right visual cortex processing info from temporal side of right eye and nasal side of left eye.
Visual info interpreted by right and left visual cortex:
When info is shared b/w two visual cortexes, brain constructs this as entire visual field.
Are the intrinsic and external skeletal muscles of ear mostly vestigial?
What is the function of auricle/pinna?
Funnels sound into external auditory meatus.
Describe structure of external ear.
Elastic cartilage covered in skin, connected to brain via ligaments and skeletal muscles.
No cartilage in lobes of ear.
What is the external ear called?
What are the epidermal features of external auditory meatus/acoustic canal?
Hair cells and ceruminous glands (make cerumen, “ear wax”) to trap foreign particles and prevent damage to delicate tympanic membrane.
So is lateral side of tympanic membrane external ear, of middle ear. And in medial side of tympanic membrane external or middle ear?
Lateral side = external ear.
Medial side = middle ear.
Describe the structure of tympanic membrane.
Tough connective tissues centre within a fibrocartilaginous ring attaching to temporal bone.
What is another name for middle ear?
Describe structure of tympanic cavity.
Air-filled and mucous membrane-lined space, connected to nasopharynx via pharyngotympanic/Eustachian tube.
Contains oval window.
Describe structure of Pharyngotympanic membrane:
Walls contain elastic cartilage.
Pharyngotympanic tube remain normally closed, when does it open?
Opens to equilibrate pressure in cavity with outside.
What are the three types malleus, incus and stapes?
Malleus, incus and stapes.
What does the malleus connect with?
What does stapes connect with?
What is the function of auditory vesicles?
Going to move and vibrate when we hear sounds. E.g. movement of skeletal muscles restricted when -> loud sounds.
Describe structure/components of internal ear.
Oval window connects to series of cavities within temporal bone -> contains membranous ducts.
Describe structure of bony labyrinth.
Three semicircular canals and cochlea.
Describe structure of membranous labyrinth.
Semicircular canals and cochlear duct which contains periosteum and clear fluid.
What are the component (s) in internal ear.
Cochlear and cochlear duct.
Describe structure of cochlea.
Bony structure that curls in on itself.
Contains lymphatic fluid .
Describe structure of cochlear duct.
Has stereocilia (sensory epithelium containing hair cells) Contains clear lymphatic fluid.
In the internal ear, what does the vestibulocochlear nerve branch into?
Branches into cochlear nerve and vestibular nerve.
What is the function of cochlear duct, and how is this info provided?
- By branching fibres (through cochlear swirl) of cochlear duct.
What is the function of semicircular ducts and how is this info provided?
- Sense of balance
- By vestibular nerve
How does our body translate sound?
1 & 2. Curvatures of the auricle direct sound into the external auditory meatus
3. Sound waves hitting the tympanic membrane causes it to vibrate, converting sound waves into mechanical movements
4 & 5. The organization of auditory ossicles means that the in-out movement of tympanic membrane produces rocking motion, acting as lever system on the oval window.
5 & 6. Vibration of the oval window generates a wave in the lymphatic fluid which travels through the swirl
7. Waves bend the stereocilia which are detected by receptors of the Cochlear Nerve fibres
8. The Cochlear Nerve is a branch of the Vestibulocochlear Nerve (CN 8; VIII) that sends the sensory information to the Primary Auditory Cortex (Temporal Lobe) to be interpreted as sound
What are the borders of the oral cavity?
Anteriorly: labia & teeth Laterally: cheeks Superiorly: hard palate (cranial bones) & soft palate Inferiorly: tongue Posteriorly: oropharynx
What is the entire oral cavity lined by (what is its outer surface made of).
Oral mucosa - epithelium with serous glands.
What is our enhanced by?
Assistance of saliva and sense of smell.
What are the functions of the tongue?
- Eating/drinking and swallowing.
- Detects taste.
Describe structure/components of tongue.
Intrinsic skeletal muscle fibres arranged longitudinal, vertical, and transversal to allow movement.
Has 4 types of papillae: Fungiform papillae. Filiform papillae Foliate papillae Vallate papillae.
3 of the 4 papillae contain taste buds. What are these taste buds called?
What is the role of taste?
Role in selection of food/drink.
How is taste different to flavour?
Flavour = thermoreception and mechanoreception.
What are the four types of papillae, their structure and location within tongue.
- V-shaped line, anterior to terminal groove. - Linear fold on lateral surface. Anterior to terminal groove. - Fungiform: found on outer surface of tongue. - Filiform: cone-shaped projections.
Say if the 4 papillae have numerous, some, very few or no gustatory receptors.
Vallate/circumvallate = numerous gustatory receptors
Foliate = very few gustatory receptors
Fungiform = some gustatory receptors
Filiform: No gustatory receptors.
Does each gustatory receptor detect different taste.
No. All gustatory receptors detect all taste.
In terms of taste, which nerve detects body of tongue (anterior 2/3 of tongue).
In terms of taste, which nerve detects root of tongue (posterior 1/3 of tongue).