CH17: The Special Senses Flashcards
What are the cell types that make up the olfactory epithelium?
The olfactory epithelium consists of three kinds of cells: olfactory sensory neurons, supporting epithelial cells, and basal epithelial cells
Olfactory sensory neurons are the first-order neurons of the olfactory pathway. Each olfactory sensory neuron is a bipolar neuron with an exposed, knob-shaped dendrite and an axon projecting through the cribriform plate that ends in the olfactory bulb
Extending from the dendrite of an olfactory sensory neuron are several nonmotile olfactory cilia, which are the sites of olfactory transduction. (Recall that transduction is the conversion of stimulus energy into a graded potential in a sensory receptor
The plasma membrane of olfactory cilia contain olfactory receptor proteins that detect inhaled chemicals. Chemicals that bind to and stimulate the olfactory sensory neurons in the olfactory cilia are called ordrants
Supporting epithelial cells are epithelial cells of the mucous membrane, lining the nose. They provide physical support, nourishment, and electrical insulation for the olfactory sensory neurons and help detoxify chemicals that come into contact with the olfactory epithelium
Basal epithelial cells are stem cells located between the bases of supporting epithelial cells. They continually undergo cell division to produce new olfactory sensory neurons, which live for only about two months before being replaced. This process is remarkable considering that olfactory sensory neurons are neurons and, as you have already learned, mature neurons are generally not replaced.
Describe how an odorant causes the sensation of smell
Binding of an odorant to an olfactory sensory neuron protein stimulates a membrane protein called a G protein, which activates the enzyme adenyl cyclase, which produces cAMP. This molecule opens a cation channel that allows sodium and calcium ions in the cytosol, causing a depolarizing receptor potential to form in the membrane of the olfactory sensory neuron. A nerve impulse is generated when the receptor potential reaches threshold
Describe the olfactory pathway
The olfactory pathway is the route taken by olfactory information from its origin in olfactory sensory neurons to the part of the brain where conscious awareness of smell takes place
On each side of the nose, some 40 or so bundles of axons olfactory sensory neurons form the right and left olfactory (I) nerves. The olfactory nerves pass through the cribriform foramina of the cribriform plate and extend to parts of the brain known as olfactory bulbs, which contain ball-like arrangements called glomeruli (singular is glomerulus).
These converge onto second order neurons of the olfactory pathway, forming the olfactory tract
Some of the axons of the olfactory tract project to the olfactory cortex in the temporal lobe of the cerebrum, where conscious awareness of smell occurs
Other axons of the olfactory tract project to the limbic system; these neural connections account for our emotional responses to odors
List and describe the components of a taste bud
Each taste bud is an oval consisting of three kinds of epithelial cells: supporting epithelial cells, gustatory epithelial cells and basal epithelial cells
The supporting epithelial cells surround about 50 gustatory epithelial cells. Gustatory microvilli project from each gustatory epithelial cell to the external surface through the taste pore, an opening in the taste bud
Basal epithelial cells are stem cells found at the periphery of the taste bud which produce. produce supporting epithelial cells, which then develop into gustatory epithelial cells. Each gustatory epithelial cell has a life span of about 10 days. This is why it does not take taste receptors on the tongue too long to recover from being burned by that too hot cup of coffee or cocoa
Describe the various locations of taste bauds
Taste buds are not actually the buds we see. Taste buds are found in elevations on the tongue called lingual papillae, which increase the surface area and provide a rough texture to the upper surface of the tongue. Three types of lingual papillae contain taste buds:
About 12 very large, circular vallate papillae form an inverted V-shaped row at the back of the tongue. Each of these papillae houses 100-300 taste buds
Fungiform papillae are mushroom shaped elevations scattered over the entire surface of the tongue that contain about 5 taste buds each
Foliate papillae are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood
Describe how gustation is sensed?
Chemicals that stimulate gustatory epithelial cells are known as tastants. Once a tastant is dissolved in saliva, it can make contact with the plasma membrane of the gustatory microvilli, which are the sites of taste transduction
The result is a depolarizing receptor potential that stimulates exocytosis of synaptic vesicles from the gustatory epithelial cell. In turn, the liberated neurotransmitter molecules trigger graded potentials that produce nerve impulses in the first-order sensory neurons that synapse with gustatory receptor cells.
The sodium ions (Na+) in a salty food enter gustatory epithelial cells via Na+ channels in the plasma membrane. The accumulation of Na+ inside the cell causes depolarization, which leads to release of neurotransmitter.
The hydrogen ions (H+) in sour tastants flow into gustatory epithelial cells via H+ channels. Again, the result is depolarization and the liberation of neurotransmitter.
What are the parts of the outer ear
The external (outer) ear consists of the auricle, external acoustic meatus and eardrum
The auricle or pinna is a flap of elastic cartilage shaped like the fared end of a trumpet and covered by skin. The rim of the auricle is the helix and the inferior portion is the lobule, which capture sound
The external acoustic meatus, also called the ear canal is a 2.5 cm long curved tube that lies in the temporal bone and leads to the eardrum
The tympanic membrane, also called the eardrum is a thin, semitransparent partition between the external acoustic meatus and middle ear. It vibrates when sound reaches it and hits bones in the inner ear
Describe the structures of the medial ear
The middle ear is a small, air-filled cavity (tympanic cavity) in the petrous portion of the temporal bone that is lined by epithelium. It is separated from the external ear by the tympanic membrane and from the internal ear by a thin, bony partition that contains two small openings, the vestibular window and the cochlear window
Extending across the middle ear and attached to it by ligaments are the three smallest bones in the body, the auditory ossicles. They are named for their shapes, and are the malleus, incus and stapes, commonly called the hammer, anvil and stirrup
The “handle” of the malleus attaches to the internal surface of the tympanic membrane. The head of the malleus articulates with the body of the incus
The incus the middle bone in the series, articulates with the head of the stapes.
The base or footplate of the stapes fits into the vestibular (oval) window, which is enclosed by a membrane called the secondary tympanic membrane
Besides the ligaments, two tiny skeletal muscles also attach to the ossicles. The tensor tympani is supplied by the mandibular branch of the trigeminal (V) nerve, and it limits movement and increases tension on eardrum to prevent damage to inner ear from loud noises
The stapedius is the smallest skeletal muscle in the body, and is supplied by the facial (VII) nerve. By dampening large vibrations of the stapes due to loud noises, it protects the vestibular window, but it also decreases the sensitivity of hearing.
The anterior wall of the tympanic cavity contains an opening that leads directly to the auditory tube, or pharyngotympanic tube, commonly known as the eustachian tube.
The auditory tube, which consists of both bone and elastic cartilage, connects the tympanic cavity with the nasopharynx (superior portion of throat). It is normally closed at its medial (pharyngeal) end.
How do we hear
How is sound transduction formed
Explain how the vestibular system works?
