Nose-Ear_20Slides.pdf

Sense of Smell

Structures and Cells

  • Olfactory organ: A yellow/brown mass located on each superior nasal concha.

  • Olfactory bulb: Located inside the cranium.

  • Ethmoid bone: Contains the cribriform plate, essential for olfactory function.

Structure of Olfactory Receptor Cells

  • Three types of special cells associated with smell:

    1. Olfactory receptor cells (blue)

    2. Columnar epithelial cells (tan)

    3. Nerve fibers of the olfactory bulb (red)

  • Olfactory receptor cells (blue cells):

    • Bipolar neurons with a distal end having cilia.

    • The proximal end goes through the crib plate and synapses with neurons of the olfactory bulb.

    • Cilia: Secret water fluid and contain plasma membrane receptors that respond to odorants.

Signal Transmission

  1. Odorants bind to receptors:

    • Odorant molecules in the air activate olfactory receptor cells.

  2. Activation of receptor cells:

    • Sends electric signals to the olfactory bulb.

  3. Relayed in glomeruli:

    • Signals are organized in the glomeruli for further processing before going to the brain.

  4. Higher brain regions:

    • Signals are transmitted to interpret and identify smells.

Olfactory Cortex

  • Olfactory sensory input is relayed to two places:

    • Temporal Lobe: Interpretation (distinguishing between scenarios such as fish or rose).

    • Base of Frontal Lobe: Memory and recognition (e.g., connection of smells to past experiences).

  • Olfactory code: Combinations of activated neurons are interpreted as specific smells.

Sensory Adaptation

  • Rapid adaptation; intensity of a smell can be reduced by 50% in seconds with constant exposure.

  • Age-related decline: Approximately 1% of receptors are damaged or lost per year as a person ages.

Emotions, Memory & Smell, the Limbic Connection

  • Smell is closely tied to the limbic system, affecting emotional responses and memory recall.

Sense of Taste

Structures Involved in Taste

  • Papillae: Contains taste buds responsible for the sense of taste.

  • Taste cells and taste pores: Key structures that mediate taste perception.

  • Supporting sensory cells with nerve fibers and taste hairs facilitate the detection of taste.

Steps to Tasting

  1. Food molecules dissolve in saliva.

  2. Receptor sites respond to matching chemoreceptors.

  3. Taste hair membrane depolarizes.

  4. Impulse is transmitted to nerve fibers.

Information is sent to cranial nerves.

Nerve Pathway for Taste

  • Three nerves involved: Facial, Glossopharyngeal, and Vagus nerves.

  • Path follows: Medulla -> Thalamus -> Gustatory Cortex in the Parietal Lobe.

Primary Taste Sensations

  • Four primary tastes learned in early education:

    1. Sweet

    2. Sour

    3. Bitter

    4. Salty

  • Loss of smell/taste affects food choices and safety awareness.

External Ear

  • Outer auricle or pinna: Visible part of the ear.

  • External auditory meatus: Canal (2.5 cm) leading to the tympanic membrane (eardrum) which directs sound waves.

  • Ceruminous glands: Secret earwax to protect the ear.

Middle Ear

  • Components of the Middle Ear:

    • Tympanic membrane

    • Tympanic cavity (air-filled), auditory tube

    • Auditory ossicles (three tiny bones: malleus, incus, stapes).

  • Auditory Tube: Connects middle ear to throat, helping to equalize air pressure.

Inner Ear

  • Structure: Three sections of the labyrinth:

    1. Semicircular canals: (Three loops for equilibrium)

    2. Vestibule: Mid-equilibrium

    3. Cochlea: Chambers for hearing (snail-shaped).

Cochlea Structure

  • Three inner ducts:

    1. Scala vestibuli: Receives vibrations from the oval window (perilymph).

    2. Cochlear duct: Center containing the organ of Corti (endolymph).

    3. Scala tympani: Lower chamber (perilymph), with a round window.

  • Membranes conduct vibrations (perilymph for outer ducts, endolymph for inner duct).

Frequency of Vibrations

  • Different sections of the basilar membrane respond to varying frequencies.

  • Higher frequencies affect areas closer to the oval window while lower frequencies affect remote areas.

Conductive Hearing Loss

  • Characteristics: Vibrations fail to pass through the middle ear, with 95% of cases being conductive.

  • Causes of conductive hearing loss:

    1. Blockage in auditory meatus.

    2. Otosclerosis.

    3. Damage to tympanic membrane.

Sensory Hearing Loss (Nerve Deafness)

  • Possible causes include:

    1. Loud noises (temporary and permanent effects).

    2. Tumors of the temporal lobe.

    3. Brain damage (e.g., TBI or stroke).

Corrections for Hearing Loss

  • Hearing aids: Effective for conductive and some nerve losses.

  • Cochlear implants: Bypass damaged structures and connect directly to the cochlear nerve, using an external speech processor.

Hearing Tests

  • Rinnes Test: Assesses conductive deafness by comparing hearing with a tuning fork in the ear versus on the mastoid process.

  • Weber Test: Differentiates between nerve and conduction damage using vibrations through the skull.

Equilibrium

  • Definition: Balance state between gravity and muscle tone.

  • Two types of equilibrium:

    1. Static

    2. Dynamic

  • Associated with the vestibular branch of the vestibulocochlear nerve, connecting to the occipital lobe.

Structures for Equilibrium

  • Static Equilibrium: Organs located in the vestibule (Utricle and Saccule).

  • Dynamic Equilibrium: Three semicircular canals containing endolymph.

Impulse Processing for Balance

  • Head movements cause fluid in canals to bend the cupula, triggering hair cells to send balance-related impulses to the cerebellum.

  • Cerebellum processes this data along with visual input to coordinate movement and maintain equilibrium.

Equilibrium Lab Tests

  • One Foot Test: Evaluates balance with and without visual assistance.

  • Romberg Test: Assesses integration of sensory information for equilibrium.

  • Barany Test: Observes nystagmus reflex after spinning to understand vestibular function.