ENT Physiology

Question 1

What is sound?

Answer 1

A pressure wave caused by oscillating molecules, set in motion by vibrations

Question 2

What frequency range can humans perceive?

Answer 2

20-20,000Hz

Question 3

What is the threshold for normal hearing?

Answer 3

Above 20 dB HL is normal hearing, below this is classed as hearing loss

Question 4

Why does the vibrations of sound waves need to be amplified in the middle ear?

Answer 4

At the external ear the sound wave vibrations move air, whereas in the inner ear they have to move liquid, which requires more energy – therefore has to be amplified

Question 5

What is the resting state of the cartilaginous Eustachian tube (in terms of open/closed)?

Answer 5

Closed, but opened bu tensor veil palatine and elevator palatine m.

Question 6

What is the function of the Eustachian tube?

Answer 6

Equalise ears and act as ventilation pathway for middle ear mucosa

Question 7

Where does the Organ of Corti sit?

Answer 7

On the basilar membrane of the cochlea

Question 8

What are the respective functions of the inner and outer hair cells?

Answer 8

• Inner hair cells are involved in sound perception and send to the brain
• Outer hair cells have more a of a regulatory role, modulating the sound being sent to the brain

Question 9

How do the hair cells produce the electrical signals?

Answer 9

Transduction: they convert mechanical ‘bending force’ into electrical impulses. The sterocilia at the ends of the hair cells are arranged in height order and move in the liquid. Bending causes them to open an ion channel and depolarise

Question 10

What is meant by the tonotopic organisation of the basilar membrane?

Answer 10

• At the base records high frequency hearing, at the apex high frequency hearing is recorded
• The membrane is thicker at the base then becomes thinner, which is what allows it to detect different frequencies

Question 11

Where does the process of hearing culminate in the brain?

Answer 11

In the Superior Temporal gyrus in the primary auditory cortex

Question 12

What are the five key vestibular end organs involved in balance and how do they work?

Answer 12

• Maculae of the utricle & saccule ‘otolith organs’
• Capula in the ampullae of lateral, posterior & superior semicircular canal

There are stereocilia in these areas projecting into the gelatinous matrix. On movement these stereocilia move and fire APs. They are arranges in all orientations so that all directions of movement are detected

Question 13

What is nystagmus and how does it occur?

Answer 13

• Eyes flick back and forwards
• Occurs with damaged vestibulo-ocular reflex, where the brain is pushing the oculomotor muscles to cause the eye to drift, then they correct themselves and flick back

Question 14

Where do the vestibular nuclei have outputs to?

Answer 14

• Vestibulospinal tract – motor output to the neck, back and leg muscles (telling them to keep you upright)
• Medial longitudinal fasciculus and ocular muscles – motor output to eyes
• Medial lemniscus and thalamus to cerebrum

Question 15

What are the sense organs of taste, and what do they contain?

Answer 15

Taste buds, consist of sensory chemoreceptor cells which synapse with afferent nerve fibres, and support cells

Question 16

What is the life span of taste buds?

Answer 16

10 days

Question 17

Where are taste buds present?

Answer 17

Mainly in the tongue, palate, epiglottis, and pharynx

Question 18

In the tongue, where are the majority if the tasge buds?

Answer 18

In the papillae (finger-like structures)

Question 19

What are the 4 types of papillae, and which ones dont contain taste buds?

Answer 19

• Filliform: most numerous – do not contain taste buds
• Fungiform
• Vallate
• Foliate

Question 20

How do taste buds send sigals about taste?

Answer 20

• Binding of taste provoking chemical (tastant) to receptor cells alters cell ionic channels and produces depolarising receptor potential
• Receptor potential initiates action potentials in the afferent nerve fibres, which synapse with receptor cells
• Signals conveyed by cranial nerves via brainstem and thalamus to cortical gustatory areas

Question 21

Which cranial nerves are involved in the afferent signals to the brain from the tongue?

Answer 21

• VIIth cranial nerve (chorda tympani branch of facial nerve) - anterior 2/3rds of the tongue
• IXth cranial (glossopharyngeal) nerve - posterior third of the tongue
• Xth cranial (vagus) nerve - areas other than tongue, including e.g. epiglottis and pharynx

Question 22

What are the 5 primary tastes and what stimulates them?

Answer 22

• Salty: stimulated by chemical salts especially sodium chloride (NaCl)
• Sour: stimulated by acids which contain free hydrogen ions (H+)
• Sweet: stimulated by configuration of glucose
• Bitter: stimulated by diverse group of tastants, including e.g. alkaloids, poisonous substances and toxic plant derivatives
• Umami (meaty or savory): triggered by amino acids especially glutamate

Question 23

What is Aquesia and what can cause it?

Answer 23

• Loss of taste function
• Can be caused by e.g. nerve damage; local inflammation (including e.g. glossitis, radiation, tobacco); some endocrine disorders

Question 24

What is Hypoguesia and what can cause it?

Answer 24

• Reduced taste function
• Can be caused by e.g. chemotherapy; medications

Question 25

What is dysguesia and what can cause it?

Answer 25

• Distortion of taste function
• Many causes including e.g. glossitis; gum infections; tooth decay; reflux; upper respiratory infections; medications; neoplasms; chemotherapy; zinc deficiency

Question 26

What 3 cell types does olfactory mucosa contain?

Answer 26

• Olfactory receptor cells
• Supporting cells
• Basal cells (secrete mucus)

Question 27

What is the structure of olfactory rods like?

Answer 27

• Olfactory receptors are specialised endings of renewable afferent neurons
• Each neuron has a thick short dendrite and an expanded end called an olfactory rod
• From the olfactory rods, cilia project to the surface of the olfactory mucosa, where odorants bind

Question 28

What is the life span of olfactory receptors, and where are new receptors made?

Answer 28

2 months, and basal cells act as precursors

Question 29

What froms the olfactory nerve?

Answer 29

Axons from the olfactory receptors

Question 30

How do odorants reach olfactory receptors during quiet breathing, and how can this be enhanced?

Answer 30

• During quiet breathing odorants only reach smell receptors by diffusion - olfactory mucosa is above the normal path of airflow
• The act of sniffing enhances smelling by drawing air currents upwards within the nasal cavity

Question 31

What qualities must a substance have to be smelled?

Answer 31

1) sufficiently volatile i.e. some of its molecules can enter the nose with inspired air
(2) sufficiently water soluble i.e. can dissolve in the mucus coating of olfactory mucosa

Question 32

What is anosmia and what can cause it?

Answer 32

• Inability to smell.
• Causes include: viral infections; allergy; nasal polyps; head injury

Question 33

What is hyposmia and what can cause it?

Answer 33

• Reduced ability to smel
• Causes similar to those for anosmia
• May be an early sign of Parkinson’s disease

Question 34

What is dysosmia?

Answer 34

• Altered sense of smell
• Examples include: differently interpreting some odours; and hallucinations of smell