W4: Chemical Senses

Question 1

What is chemosensation?

Answer 1

The body’s ability to detect and transducer a series of chemical stimuli into electrical impulse that are interpreted by the brain, giving rise to a response.

Question 2

What are the two types of systems in humans that transducer chemical signals into electrical impulses?

Answer 2

Olfactory and gustatory systems: smell and taste
Separate chemosensory systems in the mouth, nose and airways = chemosensation (less specialised and wide ranging, evoked by many chemical agents)

Question 3

What are the neuronal substrates for chemosensation?

Answer 3

Trigeminal nerve CNV - it’s nerve endings innervate the skin covering the face, mucous membranes of the nasal and oral cavities, and cornea and conjunctiva of the eye.
Glossopharyngeal nerve CNIX - supplies the lining of the oropharynx
Vagus nerve CNX - supplies the linings of the respiratory tract

Question 4

What are the cellular mechanisms of smell and taste?

Answer 4

Activation of heterotrimeric G-protein coupled receptors

Question 5

What are the cellular mechanisms of chemosensation?

Answer 5

Activation of chemosensory receptors by chemicals involves direct fasting of ion channels. Depolarisation of sensory nerve terminals causes APs and afferent signalling to the brain that initiates sensations and reflexes.

Question 6

Chemosensory CNS-mediated reflexes

Answer 6

Sneezing, coughing, mucus secretions, salivation, lacrimation, bronchospasm, respiratory depressions

Question 7

What is the function of chemosensory CNS-mediated reflexes?

Answer 7

Protective responses aimed at diluting and/or expelling foreign materials.

Question 8

Where is the olfactory mucosa located?

Answer 8

Within the middle of the anterior cranial fossa (the base). The roof of the nasal cavity.

Question 9

Classify the epithelium of the olfactory region

Answer 9

Thick pseudo-stratified columnar epithelium without goblet cells

Question 10

Classify the epithelium of the non-olfactory regions/upper respiratory epithelium.

Answer 10

Pseudostratified ciliated columnar epithelium

Question 11

What is the main secretion of non-olfactory region/upper respiratory epithelium?

Answer 11

Mucous from goblet cells

Question 12

What is the mucous of the upper respiratory epithelium like and why?

Answer 12

Thick, highly sticky and adherent to trap and remove dust and bacteria in air as it passes through the respiratory passages.

Question 13

How is mucous transporter in the upper respiratory epithelium?

Answer 13

Muco-ciliary escalator mechanism of the cilia lining the respiratory epithelium.

Question 14

What is the nerve supply of the non-olfactory regions/upper respiratory epithelium?

Answer 14

Sensory supply from CNV1 and CNV2

Parasympathetic supply is derived from the greater branch of CNVII acting via the pterygopalatine ganglion.

Question 15

What 5 cell types make up the olfactory epithelium?

Answer 15

Olfactory cells, supporting cells, basal cells, brush cells, olfactory/bowman’s glands

Question 16

Describe olfactory cells of the olfactory epithelium.

Answer 16

Bipolar olfactory receptor neurones which congregate to form the olfactory nerve.
One dendrite extends to the surface forming a swelling from which non-motile cilia extend parallel within the surface.

Question 17

Describe supporting cells of the olfactory epithelium.

Answer 17

Analogous to neural glial cells
The supporting sustentacular cells of the olfactory epithelium function as metabolic and physical support for the olfactory cells.

Question 18

Describe the basal cells of the olfactory epithelium.

Answer 18

Rest of the basal lamina of the olfactory epithelium. Stem cells capable of division and differentiation into either supporting or olfactory cells.

Question 19

Describe brush cells of the olfactory epithelium.

Answer 19

Microvilli bearing columnar cells with basal surface in contact with afferent nerve endings. Specialised for transduction of general sensation. Nerve fibres are terminal branches of the trigeminal nerve rather than the olfactory nerve.

Question 20

Describe olfactory/bowman’s glands of the olfactory epithelium.

Answer 20

Secretes mucous of the olfactory epithelium. The mucous serves a critical role in being the medium in which odoriferous molecules are dissolved to kick-start the chemical signalling that results in the sense of smell.

Question 21

What is the purpose of the non-motile cilia of the olfactory epithelium?

Answer 21

Increase SA

Question 22

What does the lamina propria blend with?

Answer 22

Lamina propria blend with the submucosa. Contains the mucous glands and the venous sinuses.

Question 23

Describe how air flows through the nasal cavity.

Answer 23

• air rushes into the nose via the anterior nasal aperture, making a large volume in the vestibule of the cavity.
• the change in cross-sectional resistance to the movement of air drops the velocity of air in the nasal cavity, so air stops moving,
• the turbinate bones bring about turbulent flow of air, so airflow circulates and remains here.
• airborne molecules are detected by the olfactory mucosa and a signal picked up.
• once the air has been humidity to within 1°C of body temperature, it is conducted out through restricted posterior aperture and the velocity of movement increases again

Question 24

What is the purpose of air moving through the nasal cavity?

Answer 24

The design of the nasal cavity acts to reduce speed of airflow and disturb the laminar airflow by making it turbulent.
Dust particles in the air are filtered out; mucous trapd dust and bacteria; muco-ciliary escalator transports mucous to oropharynx for swallowing.

Question 25

Functions of the olfactory cilia

Answer 25

Detection of odours
Generation of electrical excitation
Signal amplification
Adaptation
Desensitisation
Masking
Largely the cilia are responsible for the transductory mechanisms. Occurs by G-protein coupled receptors that will eventually give rise to a change of signal from chemical to electrical impulses that will be picked up by the olfactory nerve.

Question 26

What is taste?

Answer 26

The sensation produced when a substance in the mouth reacts chemically with taste buds in the oral cavity.

Question 27

What is gustation?

Answer 27

The sense of taste

Question 28

What are substances that stimulate taste?

Answer 28

Tastants

Question 29

What are taste buds?

Answer 29

Anatomically sensory structures that detect taste stimuli.

Question 30

What is the tongue divided into?

Answer 30

Dorsal surface is divided by the sulcus terminalis into anterior 2/3 (oral) and posterior 1/3 (pharyngeal)
Divided by a grooved into left and right halves by the median sulcus.

Question 31

What are lingual papillae?

Answer 31

Irregularities and elevations in the mucosa of the tongue. Present only anteriorly to the sulcus terminalis on the dorsum of the tongue.

Question 32

What is the specialised mucosa of the oral cavity?

Answer 32

Papillae and associated taste buds

Question 33

What are the different papillae?

Answer 33

Filiform papillae: no tastebuds
Fungiform papillae: rounded with tastebuds
Circumvallate papillae: large papillae with tastebuds
Foliage papillae

Question 34

What is the nerve supply of the posterior 1/3 of the tongue?

Answer 34

Glossopharyngeal nerve supplies the posterior 1/3 of the tongue, both for general sensation and special taste sensation.

Question 35

What is the nerve supply of the anterior 2/3 of the tongue?

Answer 35

General sensation is supplied by the lingual nerve, a branch of CNV3. Special taste sensation is supplied by the chorda tympani branch of CNVII.

Question 36

What are the intrinsic muscles of the tongue?

Answer 36

Superior longitudinal muscle
Inferior longitudinal muscle
Vertical muscle
Transverse muscle

Question 37

What do the intrinsic muscles of the tongue do?

Answer 37

Alter the shape of the tongue, by lengthening and shortening it, curling and uncurling its apex and edges as in tongue rolling, and flattening and rounding its surface. Provides shape and helps facilitate speech, swallowing and eating.

Question 38

What are the extrinsic muscles of the tongue?

Answer 38

Geniogloss
Hyoglossus
Styloglossus
Palatoglossus

Question 39

Origin and insertion of intrinsic tongue muscles

Answer 39

Originate and insert within the tongue

Question 40

Origin and insertion of extrinsic tongue muscles

Answer 40

Originate from bone and extend to the tongue