Biology 211 Anatomy & Physiology I Special Senses

Biology 211Anatomy & Physiology I

Special Senses

Special Senses

1. All confined to head

2. All special senses reach the central nervous system through cranial nerves

3. Consist of highly specialized cells which serve as receptors

4. These specialized receptor cells housed in sensory organs which are also specialized for a particular function.

Special Senses

Specialized Receptor Cells

Specialized Organ.....

TASTE:

SMELL:

VISION:

HEARING:

EQUILIBRIUM:

Gustatory Cells Taste Buds

Olfactory Cells Olfactory Epithelium

Rods & Cones Eye (Retina)

Hair Cells Cochlea

Hair Cells Vestibular Apparatus

Special Senses



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Hair Cells Cochlea



Most, but not all, taste buds are located on projections from the surface of the tongue called papillae

Some taste buds are also located on the cheeks, the palate, and the oropharynx

Each taste bud contains three types of cells:

Each taste bud also has a small hole, or taste pore, on its free surface (facing the inside of the mouth)

Each gustatory cell has long microvillus, called a gustatory hair, which extends out of the taste pore into the saliva of the mouth.

This gustatory hair contains receptors on its plasma membrane which can detect specific chemicals in the saliva.

At the other end, each gustatory cell is surrounded by dendrites of sensory neurons

Gustatory cells within taste buds can detect thousands of different types of molecules, but these are grouped into five general categories:

a) : sugars (glucose, fructose, lactose, sucrose, etc.) saccharin, aspartame, sucralose, xylitol, etc.

b) : sodium, potassium, lithium, many others

c) : citric acids, hydrochloric acid, carbonic acid, malic acid, tartaric acid, many others

d) : quinine, fatty acids, many others

e) : glutamate

Substances must be dissolved in saliva or other liquid before they can stimulate the gustatory cells.

Each gustatory cell can respond to only one substance (sodium, glucose, etc.) BUT each taste bud contains many different types of gustatory cells.

Taste buds with gustatory cells for different types of tastes are located in all regions of the tongue, but certain regions are more sensitive to specific tastes

Each gustatory cell has long microvillus, called a gustatory hair, which extends out of the taste pore into the saliva of the mouth.

This gustatory hair contains receptors on its plasma membrane which can detect specific chemicals in the saliva.

At the other end, each gustatory cell is surrounded by dendrites of sensory neurons

Each gustatory cell has a separate threshold: concentrations below this do not stimulate the receptors.

In general: Sweet & Salty substances have high thresholds Sour substances have moderate thresholds Bitter substances have low thresholds

These afferent neurons carry information for conscious perception of tastes.

They also form afferent limbs of reflexes whose efferent limbs stimulate saliva production, secretion of enzymes by stomach, liver, pancreas if necessary, gagging vomiting

Special Senses



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Hair Cells Cochlea


The olfactory epithelium (mucosa) is located high in the nasal cavity, just inferior to the cribriform plate of the ethmoid bone.

Each olfactory cell has long microvillus, called an olfactory hair, which extends into a layer of mucous on its free surface

This olfactory hair contains receptors on its plasma membrane which can detect specific chemicals in the mucous.

The axons of these olfactory cells (neurons) pass through the cribriform plate to synapse with neurons in the olfactory bulb. These axons are the olfactory nerve (C.N. I)

Substances must dissolve from the air into the mucous before they can stimulate the olfactory cells.

Each olfactory cell appears to be able to respond to many different substances.

Each olfactory cell has a separate threshold, but these are generally very low: just a few molecules of a substance may stimulate the olfactory cells.

Olfactory Pathways:

Axons of olfactory receptor cells pass through the cribriform plate of the ethmoid bone as the olfactory nerve, then synapse with afferent neurons in the olfactory bulb which lies just superior to it.

Axons of these afferent neurons pass through the olfactory tract to: - The thalamus and the olfactory cortex on the medial surface of the temporal lobe. This provides conscious perception and interpretation of smells- The hypothalamus and the brainstem. This provides reflexes (salivation, avoidance, etc.) and "associative responses" (activation of autonomic pathways, sexual responses, emotional responses, etc.)

Start with Vision:



VISION:

Other structures of eye regulate amount of light reaching retina and focus it on rod and cone cells.

The eyeball has three layers or "tunics:

Strong connective tissue Protects the eye Holds shape of eye Insertion of extraoccular muscles

Contains blood vessels Pigmented Contains smooth muscle cells

Contains rod and cone cells and Other neurons to transmit visual information to brain

Layers ("tunics") of the eyeball

Fibrous Layer Vascular Layer Sensory Layer

Focus:

Majority of light refraction (bending) occurs in cornea. Not adjustable

"Fine tuning" of light refraction occurs in lens: Thicker = more refraction Thinner = less refraction

Rods: Cones:

Special Senses



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Hair Cells Cochlea


Next: Hearing



HEARING

Located in inner ear. Outer ear and middle ear serve to transmit and regulate the volume of sound

Outer ear channels air vibrations(sound) to the tympanic membrane (eardrum)

The middle ear is an air-filled chamber containing three ossicles: the malleus, the incus, & the stapes

The inner ear contains a complex fluid-filled structure, the membranous labyrinth, which is embedded in the temporal bone.

Tympanic membrane

MalleusIncus

Stapes (attaches to oval window of inner ear)

The tympanic membrane is attached to the malleus, which is attached to the incus, which is attached to the stapes, which is attached to the oval window of the membranous labyrinth of the inner ear. The membranous labyrinth is fluid-filled.

Therefore: Vibrations of air (sound) vibrate the tympanic membrane Which makes the ossicles vibrate

Which makes the oval window vibrate

Which makes the fluid of the membranous labyrinth of the inner ear vibrate

This is how the vibrations get transmitted from the air of the outer ear to the receptor cells of the cochlea in the inner ear

The membranous labyrinth of the inner ear actually consists of two sets of tubes, one inside the other. The outer tube is filled with a fluid called , while the inner tube is filled with fluid called

At one end of inner ear, these two tubes (one inside the other) coil about 2 & 2/3 times to form the

Vibrations of the oval window actually make the perilymph vibrate. This must be transmitted to the endolymph within the cochlea before the hair cells can detect it.

Structure of cochlea if it could be uncoiled

Vibration of oval window causes vibration of perilymph of and which causes vibration of endolymph in

Vibration of the cochlear duct causes bending of hair cells within it.

When these hair cells bend, they send electrical signals through the vestibulocochlear nerve to the brain

Hearing involves two aspects of bending hair cells:

Which hair cells bend determines the pitch of the soundHow far hair cells bend determines volume of the sound

The membranous labyrinth of the inner ear also houses the specialized receptor cells for equilibrium - both position of the head ("static equilibrium") and movement of the head ("dynamic equilibrium").

Special Senses



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Hair Cells Cochlea

The parts of the membranous labyrinth responsible for equilibrium are the the and three which lie at right angles to each other.

The saccule and the utricle are responsible for detecting the position of the head ("static equilibrium").

Each of them contain a region of hair cells called a

The tips of these hair cells project into a gelatinous mass called the in which are embedded small crystals of calcium carbonate called

When the head changes position, gravity pulls on the otoliths, which causes the otolithic membrane to bend the hair cells (receptors)

When these hair cells bend, they send electrical signals to the brain through the vestibulocochlear nerve, telling it the new position of the head

A very similar situation tells your brain about movement of the head when hair cells of the semicircular canals bend.

Each semicircular canal has an enlargement, or at one end where the hair cells (receptors) are located

The tips of these hair cells in an ampulla of a semicircular canal project into a gelatinous mass called the in which are also embedded

When the head moves in any direction, movement of the endolymph in the semicircular pulls on the otoliths, which causes the cupula to bend the hair cells (receptors)

When these hair cells bend, they send electrical signals through the vestibulocochlear nerve to the brain, telling it which direction the head moved.

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Biology 211 Anatomy & Physiology I Special Senses