SPECIAL SENSES

Question 1

Which cranial nerves carry a special sense and which one do they carry?

Answer 1

Smell - Olfactory (CN I)
Taste (gustation) - Facial (CN VII), Glossopharyngeal (CN IX), and Vagus (CN X)
Vision - Optic (CN II)
Hearing - Vestibulocochlear (CN VIII)
Balance - Vestibulocochlear (CN VIII)

Question 2

Differentiate among the olfactory nerve, bulb and tract. Which one is outside the skull? Which one(s) is inside the skull?

Answer 2

bulb - structure that sits on top of the cribriform plate within the anterior cranial fossa; receives input from the olfactory nerve and processes smell information;
Location: Inside the skull

nerve - fibers pass through the cribriform plate of the ethmoid bone to reach the olfactory bulb;
location: outside the skull (in the nasal cavity)

tract - bundle of axons that extends from the olfactory bulb and carries processed olfactory information to the brain (e.g., the limbic system and cerebral cortex).
Location: Inside the skull (extends from the olfactory bulb toward deeper brain structures).

Question 3

Olfactory pathway

Answer 3

1. Olfactory nerves start in olfactory epithelium
2. Nerves synapse in the olfactory bulb
3. Olfactory bulb neurons send axons to cortex via the olfactory tract (bypasses thalamus)
4. Olfactory tract axons project to the primary olfactory area then to the limbic system (amygdala) and hypothalamus (emotional areas!)

Question 4

What is unique about olfaction compared to other senses?

Answer 4

The only sense that is not modulated by the thalamus before going to the cortex. It goes to the limbic system in the cortex.

Question 5

Do olfactory neurons regenerate?

Answer 5

Only basal cells (divide and give rise to new olfactory receptors); only neurons in the CNS that can regenerate

Question 6

What kind of epithelial cells are in taste buds?

Answer 6

Sensory cells: constantly renewed (live ~100 days), long
microvilli at the apical surface that extend into the taste
pore
Basal cells: divide, mature, and replace old sensory cells
Support cells: equivalent to glia; nourish

Question 7

What types of papillae contain taste buds? What type doesn’t?

Answer 7

Containing taste buds: Vallate papillae (form a V-shape at back of tongue), Fungiform papillae (mushroom-shaped elevations scattered over the entire surface), and Foliate papillae (small trenches on the
lateral margins of the tongue)

Non containing taste buds: Filiform papillae (contain tactile receptors but no taste buds; increase friction between the tongue and food) cat !

Question 8

Which 3 cranial nerves carry taste? With regard to the tongue, which nerve serves the anterior 2/3 and which the posterior 2/3?

Answer 8

1. Facial (CN VII) - serves the anterior two-thirds of the tongue
2. Glossopharyngeal (CN IX) - serves the posterior one-third of the tongue
3. Vagus (CN X) - serves the throat and epiglottis (minor
   contribution)

Question 9

Which nerve carries general sensation?

Answer 9

Cranial nerve V on the anterior 2/3 (presulcal)
Cranial nerve IX on the posterior 1/3 (post-sulcal)

Question 10

What are the 3 layers (tunics) of the eye?

Answer 10

1. An outer fibrous layer (off white layer)
2. An intermediate vascular layer (dark blue layer)
3. An inner neural layer (red layer)

Question 11

What is the fibrous layer?

Answer 11

• The sclera and cornea consist of dense collagenous connective tissue
• The cornea is avascular with regularly spaced collagen fibers that are smaller than the wavelength of light

Question 12

What is the sclera?

Answer 12

Tough opaque outer covering, forms the white part of the eye, provides protection, maintains the
shape of the eyeball, serves as the site of muscle attachment for the extrinsic eye muscles

Question 13

What is the cornea?

Answer 13

Transparent anterior surface of the outer tunic, main refractive index of the eye

Question 14

What do the sclera and the cornea have in common? what is different?

Answer 14

The sclera and cornea consist of dense collagenous connective tissue

The cornea is avascular with regularly spaced collagen fibers that are smaller than the wavelength of light

sclera is opaque, cornea is transparent

Question 15

What are the components of the vascular tunic?

Answer 15

middle layer of the eyeball, three parts: choroid, ciliary body, and iris

Question 16

What is the choroid?

Answer 16

highly vascularized, provides nutrients to the
posterior (deep) surface of the retina, lines most of the
sclera

Question 17

What are the components of the ciliary body?

Answer 17

anterior portion of the vascular tunic, consists of ciliary processes and ciliary muscle. The ciliary processes contain capillaries and secrete aqueous humor (fluid that fills the anterior and posterior cavities)

Extending from the ciliary process are zonular fibers (suspensory ligaments) that attach to the lens

Question 18

What is the function of the ciliary muscle?

Answer 18

Ciliary muscles are arranged longitudinal, oblique, and circularly.

Contraction or relaxation of the ciliary muscle changes the tension on the zonular fibers, which alters the shape of the lens, adapting it for near or far vision.

Note- lens is avascular

Question 19

What type of tissue is the iris and what is its function?

Answer 19

Iris: colored part of the eye, sphincter and dilator muscles control the diameter of the pupil

Tissues (smooth muscle):
1. Constrictor pupillae (circular); innervated by parasympathetic fibers
2. Dilator pupillae (radial): innervated by sympathetic fibers

Response varies with different levels of light and emotional state

Question 20

How many layers of neurons are in the retina?

Answer 20

Photoreceptor layer: detects light

Bipolar neuron layer: relay to ganglion neurons

Ganglion neuron layer: output to thalamus

Question 21

What is the difference between rods and cones?

Answer 21

Two types of photoreceptors: rods and cones. Rods allow us to see in dim light. Bright light stimulates the
cones, which produce color vision

Question 22

What are the macula lutea and the fovea centralis, what is their relationship to one another?

Answer 22

Macula lutea (yellow spot, fewer blood vessels) is in
the exact center of the posterior portion of the
retina, at the visual axis of the eye

Fovea centralis (fc), a small depression in the center of the macula lutea, contains only cones and is the area of highest visual acuity or resolution (sharpness of vision)

Question 23

What is the blind spot?

Answer 23

The optic disc - no rods or cones (exit of optic nerve)

Question 24

Be able to trace the route of light and visual information: from cornea to retina

Answer 24

1. Cornea
2. Aqueous humor
3. Pupil
4. Lens
5. Vitreous humor
6. Retina
7. Ganglion cell layer, Rods and Cones (RETINA)

Question 25

Be able to trace the route of light and visual information: from retina to visual cortex

Answer 25

1. Rods and Cones, ganglion cell layer (RETINA) 2. Optic nerve 3. Optic chiasm 4. Optic tract 5. Lateral geniculate body 6. Visual cortex, area 17

Question 26

What thalamic nucleus is the relay for vision?

Answer 26

Lateral geniculate nucleus (LGN)

Question 27

What are the 3 divisions of the ear? and what are their functions?

Answer 27

1. The external ear, which collects sound waves and channels them inward 2. The middle ear, which conveys sound vibrations to the oval window 3. The internal ear, which houses the receptors for hearing and equilibrium

Question 28

External ear

Answer 28

The external ear consists of the auricle (pinna) The structure of the auricle is made of elastic cartilage Opening of the external acoustic meatus The external acoustic meatus ends at the tympanic membrane Cerumen = ear wax

Question 29

Middle ear

Answer 29

The middle ear is a small, air-filled cavity in the temporal bone that is lined by epithelium The auditory ossicles are connected to one another by synovial joints and attached by ligaments

Question 30

What are the 3 ossicles and what is their order external to internal?

Answer 30

Three ossicles: malleus, incus, and stapes (a.k.a., hammer, anvil and stirrup) The malleus is in contact with the tympanic membrane The head of the malleus articulates with the incus The incus, articulates with the stapes The footplate of the stapes fits into the oval window of the cochlea

Question 31

Are there any muscles in the middle ear? if so, what is their function and what are their innervations?

Answer 31

1. Tensor tympani: limits movement and increases tension on the eardrum (CN V) 2. Stapedius: dampens large vibrations of the stapes due to loud noises, to protect the oval window (CN VII) 3. Auditory tube (pharyngotympanic tube, a.k.a. the Eustachian tube): connects the middle ear with the nasopharynx, equilibrates pressure

Question 32

What are the 3 main areas of the inner ear and what are their functions?

Answer 32

Semicircular Canal - Balance Vestibule - Balance Cochlea - Audition

Question 33

Be able to trace the route of an external vibration to the perception of sound: ear drum to ossicles to oval window to basilar membrane to round window

Answer 33

External Vibration → Ear Drum (Tympanic Membrane) → Ossicles (Malleus, Incus, Stapes) → Oval Window → Basilar Membrane → Round Window → Hair Cells → Auditory Nerve → Auditory Cortex

Question 34

Be able to trace the route of an external vibration to the perception of sound: hair cells to spiral ganglion to cochlear nuclei to thalamus (which nucleus?) to what area of the cortex?

Answer 34

Hair Cells (in cochlea) → 2. Spiral Ganglion → 3. Cochlear Nuclei (in brainstem) → 4. Medial Geniculate Nucleus (in thalamus) → 5. Primary Auditory Cortex (in temporal lobe) info from cochlear nuclei cross midline medial geniculate nucelus in thalamus primary auditory cortex (area 41)

Question 35

How do the basilar membrane and tectorial membrane work together to transduce vibration into sound?

Answer 35

The basilar membrane (bm) supports inner and outer hair cells. The vibration of the endolymph is transferred to the basilar membrane. The vibration comes to an end at the round window. As the basilar membrane vibrates, the microvilli (apical part of the cell) of the hair cells contact the tectorial membrane (which doesn't vibrate), this causes the hair cells to bend. Inner and outer hair cells populate the basilar membrane.

Question 36

Auditory pathway

Answer 36

1. Inner hair cells 2. Spiral ganglion neurons 3. Cochlear nuclei, brain stem 4. Coordinating centers within the brain stem determine directionality 5. Medial geniculate nucleus of the thalamus 6. Primary auditory cortex 7. Superior temporal gyrus 8. Brodmann's areas 41,42

Question 37

What thalamic nucleus is a relay for auditory information?

Answer 37

Medial Geniculate Nucleus

Question 38

What is the difference between static and dynamic equilibrium?

Answer 38

The receptor organs for equilibrium of the vestibular apparatus includes the saccule, utricle, and semicircular canals. Two types of equilibrium: 1. Static equilibrium maintenance of the position of the body relative to the force of gravity 2. Dynamic equilibrium is the maintenance of body position in response to sudden movements, acceleration

Question 39

What are the sensory structures in the semicircular canals? what is a cupula?

Answer 39

Each semicircular canal contains a crista ampullaris located within an enlarged area called the ampulla. These structures detect rotational (angular) acceleration of the head. The cupula is a gelatinous structure that sits on top of the crista ampullaris. It acts like a flexible barrier inside the ampulla. When the head moves, endolymph fluid within the semicircular canals lags behind due to inertia, pushing against the cupula and bending it. This bending stimulates hair cells within the crista ampullaris, sending signals to the brain about head rotation.

Question 40

What are the sensory structures in the utricle and saccule? what are the macula?

Answer 40

The utricle and saccule are two structures in the vestibular system of the inner ear, which are responsible for detecting linear acceleration. The sensory structures in both the utricle and saccule are known as maculae. The macula is a specialized sensory organ that contains hair cells, which are the receptors responsible for detecting changes in head position or linear acceleration. These hair cells are embedded in a gelatinous membrane that contains otoliths. Utricle: The macula of the utricle is oriented horizontally. It detects horizontal linear acceleration. Saccule: The macula of the saccule is oriented vertically. It detects vertical linear acceleration.

Question 41

Be able to trace the vestibular pathway: Utricle/Saccule and Semicircular canals to vestibular ganglion to brain stem (which nuclei?) to the thalamus (which nucleus) to what area of the cortex?

Answer 41

1. Hair cell of maculae or cristae 2. Vestibular ganglion 3. Vestibular nuclei brain stem (pons and medulla) 4. Ventral posterior nucleus of thalamus 5. Vestibular projections parallel spinothalamic (ALS) and medial lemniscus fibers and relay in the ventral posterior nucleus 6. Vestibular cortex is adjacent to the general sensory area for the head

Question 42

What modality is relayed through the medial geniculate nucleus? the lateral geniculate nucleus?

Answer 42

Medial Geniculate Nucleus (MGN) - Auditory information Pathway: The MGN receives auditory signals from the inferior colliculus (a part of the brainstem involved in processing sound). It then sends these signals to the primary auditory cortex in the temporal lobe, where sound is perceived and processed. Lateral Geniculate Nucleus (LGN) - Visual information Pathway: The LGN receives visual information from the retina via the optic tract and transmits it to the primary visual cortex in the occipital lobe.