Neurophysiology - PNS Afferent AQs Answers.docx

**[Neurophysiology -- PNS Afferent AQ Answers]:** **Question 1** - **1a:** What are the anatomical components of the peripheral nervous system (PNS)? - **Answer:** The components of the PNS are the cranial and spinal nerves. - **1b:** What is the functional organization of...

**[Neurophysiology -- PNS Afferent AQ Answers]:** **Question 1** - **1a:** What are the anatomical components of the peripheral nervous system (PNS)? - **Answer:** The components of the PNS are the cranial and spinal nerves. - **1b:** What is the functional organization of the PNS? In other words, can you schematically explain the organization of the efferent division and the afferent division of the PNS? - **Answer:** There are two divisions of the PNS. The afferent division consists of sensory innervation which include somatosensory, special sensory, and visceral innervation. The efferent division consists of somatic and autonomic innervation. Autonomic innervation includes cardiac, smooth muscle, glandular, and adipose innervation. The autonomic system also breaks down into the sympathetic, parasympathetic, and enteric nervous systems. **Question 2** - **2a:** Sensory information enters the afferent division of the PNS. What are exteroceptors? - **Answer:** Exteroceptors are sensory receptors that receive external stimuli for both special and somatic senses, and send the sensory information to the CNS. - **2b:** What are proprioceptors and what type of information do they send to the CNS? - **Answer:** Proprioceptors are sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position of the limb in space.  - **2c:** What are interoceptors and what type of information do they send to the CNS? - **Answer:** Interoceptors are receptors that receive stimuli of internal organs (i.e., visceral senses). **Question 3** - How many pairs of cranial nerves are there and are these nerves mixed? In other words, do all cranial nerves contain both sensory and motor nerve fibers? - **Answer:** There are 12 pairs of cranial nerves. Some, but not all, are mixed. **Question 4** - **4a:** How many pairs of spinal nerves are there? - **Answer:** There are 31 pairs of spinal nerves. - **4b:** What are the different types of intervertebral disc abnormalities that can occur and how can these issues relate to spinal stenosis? - **Answer:** Intervertebral disc deterioration and herniation are intervertebral disc abnormalities that can occur. These can lead to spinal stenosis, causing a narrowing of the open spaces within your spine. This can put pressure on your spinal cord and spinal nerves. **Question 5** - **5a:** What is a ventral root composed of? - **Answer:** A ventral root is composed of motor neurons. - **5b:** What is a dorsal root composed of? - **Answer:** A dorsal root is composed of sensory neurons. - **5c:** What is a dorsal root ganglion composed of? - **Answer:** A dorsal root ganglion contains the cell bodies of unipolar neurons. - **5d:** What is a ventral ramus? - **Answer:** A ventral ramus is the anterior division of a spinal nerve. - **5e:** What is a dorsal ramus? - **Answer:** A dorsal ramus is the posterior division of a spinal nerve. - **5f:** What are the sympathetic chain ganglia? - **Answer:** Sympathetic chain ganglia are paired bundles of nerve fibers, and aggregations of nerve cell bodies, that run from the base of the skull to the coccyx. They are part of the autonomic nervous system. - **5g:** What two components of the PNS combine to form a spinal nerve? - **Answer:** Ventral and dorsal roots combine to form a spinal nerve. **Question 6** - **6a:** Can you draw a spinal reflex arc? - **Answer:** - **6b:** What are the three neurons involved and how do they communicate with one another? - **Answer:** The three neurons involved include: afferent neurons, interneurons and motor neurons. These neurons communicate through the neurotransmitters that are released in the synaptic clefts between them. **Question 7** - If you touched a hot stove with your hand, you would reflexively remove your hand from the stove. Does the brain regulate this muscle activity required to remove your hand? Do you sense the pain before or after your hand is withdrawn? - **Answer:** No, the brain does not regulate this muscle activity required to remove your hand. The pain is perceived in the brain after the hand is withdrawn. **Question 8** - **8a:** What are mechanoreceptors and what are some general examples? - **Answer:** Mechanoreceptors respond to mechanical stimuli. Some examples of mechanoreceptors include tactile receptors, baroreceptors and proprioceptors. - **8b:** What are the three examples of tactile receptors in the skin and what do they detect? - **Answer:** Pacinian corpuscles sense deep touch, while Meissner\'s corpuscles and Merkel cells sense light touch. - **8c:** What do ipsilateral and contralateral mean? - **Answer:** Senses that are processed ipsilaterally converge at the level of the brain stem. Senses that are processed contralaterally converge at the level of the spinal cord. **Question 9** - **9a:** Which receptors would inform you of an ice cube that was just placed on your arm? - **Answer:** Thermoreceptors. - **9b:** Which receptors would inform you of the taste of a cup of coffee? - **Answer:** Chemoreceptors. - **9c:** Which receptors would inform you of the pain of stepping on a nail? - **Answer:** Nociceptors and mechanoreceptors. **Question 10** - **10a:** Are nociceptors tonic or phasic receptors? - **Answer:** Nociceptors are tonic (slowly adapting). - **10b:** When you put on your shirt/top/blouse in the morning, you can feel it on your skin; however, several hours later the feeling is "gone." Based on this fact, are tactile receptors tonic or phasic? - **Answer:** Tactile receptors are phasic (quickly adapting). - **10c:** Are odorant receptors phasic or tonic? - **Answer:** Odorant receptors are phasic. **Question 11** - **11a:** The receptor portion of tactile receptors (e.g., Meissner's and Pacinian corpuscles) is literally a modification of what portion of the neuron? - **Answer:** The receptor portion of one of these sensory neurons is a modification of a dendrite. - **11b:** What happens to the membrane of the receptor as a result of receiving a stimulus? - **Answer:** As a result of receiving a stimulus, ion channels open, allowing sodium to enter, leading to the generation of the first action potential at the initial segment of the neuron. **Question 12** - **12a:** If you had a lesion on your arm, what medications could you take to reduce the activity of prostaglandins, histamine and substance P? - **Answer:** To reduce the activity of prostaglandins, you would take an NSAID (e.g., ibuprofen, aspirin); to reduce the activity of histamine, you would take an antihistamine (e.g., Benadryl); to reduce the activity of substance P, you would take capsaicin. - **12b:** What do opiates mimic? - **Answer:** Heroin and prescription opioids chemically resemble the brain's natural opioids (i.e., endorphins). - **12c:** Does nociceptive information travel to the brain contralaterally or ipsilaterally? - **Answer:** Nociceptive information travels to the brain contralaterally. **Question 13** - **13a:** The phenomenon of referred pain is thought to exist as the result of \"cross-talk" between neurons. Where is it believed that this cross-talk occurs? - **Answer:** Cross-talk occurs in the spinal cord gray matter or dorsal root ganglia. - **13b:** Can you use this information to explain how an individual can experience pain in the arm when they are having chest pain due to a heart attack? - **Answer:** When a person is having a heart attack, the pain fibers in the heart and hand go to the spinal cord and they converge (cross-talk). The pain fibers from the heart can induce action potentials in the pain fiber coming from the arm. **Question 14** - **14a:** What are the five different types of special senses? - **Answer:** Taste (gustation), smell (olfaction), sight (vision), hearing (audition) and balance/equilibrium (equilibrioception). - **14b:** Based on your list, would you expect these senses to enter the nervous system at the level of the spinal cord or brain? - **Answer:** These senses enter the nervous system at the level of the brain. **Question 15** - **15a:** How many cells are involved in the peripheral processing of olfactory information? - **Answer:** There is one cell involved in the peripheral processing of olfactory information -- bipolar olfactory neuron. - **15b:** In what cell are action potentials generated? - **Answer:** An action potential is generated in the primary bipolar sensory neuron and the secondary sensory neuron. **Question 16** - Thinking anatomically, can you explain why smell is the only special sense that does not enter the brain by relaying through the thalamus? - **Answer:** The primary neurons enter the brain through tiny holes in the floor of the cranium and synapse with the secondary neurons in the olfactory bulbs at the base of the brain. **Question 17** - **17a:** What are the five different tastes we can perceive and what is/are the tastant(s) for each of these different tastes? - **Answer:** For bitter, the tastants are coffee, beer, unsweetened cocoa, earwax, etc.; for sweet, the tastants are monosaccharides; for umami, the tastant is glutamate; for sour, the tastant is proton; for salty, the tastant is sodium. - **17b:** Is "spicy" one of the basic tastes? Why or why not? - **Answer:** **Our bodies detect spice using a completely different system than the one for taste**. The nerve that sends touch, pain, and temperature feelings from your face to your brain, interprets it. - **17c:** Many individuals who have experienced COVID-19 symptoms have been said to have "lost their sense of taste". Is this a true statement? - **Answer:** Technically, no. Many patients notice a loss of their sense of smell. However, because smell is necessary to taste flavor, these individuals are no longer able to discern flavors. **Question 18** - **18a:** How many cells are involved in the peripheral processing of gustatory information? - **Answer:** 2 cells are involved in the peripheral processing of gustatory information. These are the taste receptor cell and the bipolar sensory neuron. - **18b:** In what cell are action potentials generated? - **Answer:** Action potentials are generated in the bipolar sensory neuron. **Question 19** - What are the three layers of the eyeball, and what composes each layer? - **Answer:** The sclera is composed of thick connective tissue and forms the "white" of the eye, as well as the cornea of the eye. The choroid is composed of vascular tissue and forms the ciliary body and iris. The retina is composed of photoreceptors, also known as rods and cones, bipolar cells, and ganglion cells. **Question 20** - What is the relationship between the lens, the ciliary body, and suspensory ligaments? - **Answer:** The lens is attached to the ciliary body via the suspensory ligaments. **Question 21** - **21a:** Where is aqueous humor located? - **Answer:** The aqueous humor is located in the anterior chamber of the eye. - **21b:** Where is the vitreous humor located? - **Answer:** The vitreous humor is located in the posterior chamber of the eye.  - **21c:** What are the functions of the aqueous and vitreous humors? - **Answer:** The aqueous humor plays an essential role in nourishing the cornea and the lens by supplying nutrition such as amino acids and glucose. It also maintains intraocular pressure. The vitreous humor (or body) allows the light to pass through the lens to the retina and helps to keep the eye in its round shape.  - **21d:** What is glaucoma? - **Answer:** Glaucoma is the term applied to a group of eye diseases that gradually result in loss of vision by permanently damaging the optic nerve. This disease can occur due to high pressure in the eye due to an overaccumulation of fluid (aqueous humor). **Question 22** - **22a:** If you were to stand straight and look straight ahead, where would most light entering your pupil light fall on your retina? - **Answer:** If you were to stand straight and look straight ahead, where would most light entering your pupil light fall on the fovea centralis. - **22b:** What is the visual axis (i.e., principal optical axis)? - **Answer:** The visual axis is an imaginary straight line that passes through the center of the pupil and lands on the center of the fovea centralis. - **22c:** What is the optic disc, why is it also known as the blind spot? - **Answer:** The optic disc optic is the point of exit for ganglion cell axons leaving the eye. There are no photoreceptors in this area. Therefore, it is known as the blind spot. **Question 23** - **23a:** What is refraction? - **Answer:** Refraction is the bending of light rays as they pass through different refractive media. - **23b:** What is a refractive index? - **Answer:** A refractive index is the number that reflects the degree to which a particular medium bends light rays. Larger numbers bend light more than smaller numbers. - **23c:** What is the refractive index of air, water, the cornea, and the lens? - **Answer:** Refractive index of air is 1.00, water is 1.33, cornea is 1.38, and lens is 1.41. - **23d:** If light passes from a medium with a refractive index of 2.0 into a medium with a refractive index of 1.0, what will happen to the light rays? - **Answer:** They will diverge. If light comes from a medium with a lower refractive index and enters a medium with a higher refractive index, then the light rays will converge. **Question 24** - **24a:** The human lens is concave or convex? - **Answer:** The human lens is convex. - **24b:** Does the human lens converge or diverge light rays? - **Answer:** The lens converges light rays. - **24c:** What does converging and diverging mean in reference to the visual axis? - **Answer:** To converge means to bend light towards the visual axis and to diverge means to bend light away from the visual axis. - **24d:** What is the focal length? - **Answer:** The focal length is the distance between the center of the lens and the focal point. - **24e:** What is the focal point? - **Answer:** The focal point is where the light rays converge after passing through the lens. - **24f:** A diopter is a unit of converging or diverging power? - **Answer:** A diopter is a unit of converging power. - **24g:** Which structure of the eye plays the most important role in focusing light on the retina? - **Answer:** The cornea plays the most important role in focusing light on the retina because it has the highest converging power. **Question 25** - **25a:** The refractive index of the cornea is 1.38 while that of water is 1.33. If the two indices are so similar, why don\'t humans have clear vision underwater? - **Answer:** The problem is that the reflective indices are too similar, so light rays don't converge much. This causes the focal point to form behind the retina, similar to hyperopia. - **25b:** How do swimming goggles help improve your underwater vision? - **Answer:** Swimming goggles help to improve your vision underwater because they restore the air-corneal interface. **Question 26** - What are the ways in which the image formed on your retina is different from the object itself? - **Answer:** Inverted, backwards, and a fraction of the actual size of the object. **Question 27** - **27a:** When is the near reflex triad employed? - **Answer:** The near reflex triad is employed in response to focusing on a near object, meaning that the object is closer than 20 ft from the eye. - **27b:** What is lens accommodation? - **Answer:** Lens accommodation is the process by which the eye increases its converging power by making the lens more convex. - **27c:** What is the state of the ciliary body, suspensory ligaments, and lens when an object is more than 20 feet away? - **Answer:** Ciliary muscles are relaxed, suspensory ligaments are taut, and the lens is flattened out. - **27d:** What is the state of the ciliary body, suspensory ligaments, and lens when an object is less than 20 feet away? - **Answer:** Ciliary muscles are contracted, suspensory ligaments are loose, and the lens is bulged (or very convex). **Question 28** - **28a:** If the ciliary muscles of the eye are relaxed, which receptor must be activated? - **Answer:** The **β**~2~ receptors must be activated if the ciliary muscles of the eye are relaxed. - **28b:** What neurotransmitter binds to the **β**~2~ receptor? - **Answer:** Norepinephrine. **Question 29** - **29a:** If the suspensory ligaments are loose, which receptor must be activated in the ciliary muscle? - **Answer:** Ciliary muscle contraction causes loosened suspensory ligaments. The M~3~ receptors must be activated in the ciliary muscles of the eye if contracted. - **29b:** Which neurotransmitter binds to the M~3~ receptor? - **Answer:** Acetylcholine. **Question 30** - **30a:** What is miosis? - **Answer:** Miosis is pupillary constriction. - **30b:** What is mydriasis? - **Answer:** Mydriasis is pupillary dilation. - **30c:** What are the muscles of the iris that control the diameter of the pupil? - **Answer:** Pupillary constrictor (sphincter) muscles and pupillary dilator (radial) muscles control the diameter of the pupil. - **30d:** The pupil is not an anatomical structure. How can it be likened to a black hole of the universe? - **Answer:** All light enters the pupil, but none exits it. That is why it appears black. **Question 31** - **31a:** Can you list a few drugs that would cause miosis? - **Answer:** Opiates, such as heroin or morphine, and other central nervous system depressants, such as benzodiazepines and barbiturates, will cause miosis while under the influence of the drug. - **31b:** What receptors and neurotransmitters are responsible for miosis? - **Answer:** M~3~ receptors are responsible for miosis and acetylcholine is the neurotransmitter. - **31c:** Can you list a few drugs that would cause mydriasis? - **Answer:** Stimulant drugs like cocaine, amphetamines, methamphetamines, and ecstasy will cause mydriasis, along with cannabis and hallucinogenic drugs like LSD and ketamine. - **31d:** What receptors and neurotransmitters are responsible for mydriasis? - **Answer:** **α**~1~ receptors are responsible for mydriasis and norepinephrine is the neurotransmitter. **Question 32** - **32a:** If you were being chased by a bear in the woods, would your eyes undergo miosis or mydriasis? - **Answer:** Mydriasis. - **32b:** Which part of the ANS is elicited? - **Answer:** Mydriasis is elicited by the sympathetic system of the ANS. **Question 33** - **33a:** If an individual has an eyeball that is longer than normal, which refractive defect would they likely have? - **Answer:** If an individual has an eyeball that is longer than normal, they would have myopia. - **33b:** Where does the focal point form in this condition? - **Answer:** The focal point in this condition forms in front of the retina. - **33c:** Which type of lenses are used to correct for this refractive defect? - **Answer:** Concave, or diverging lenses, are used to correct for myopia. **Question 34** - **34a:** If an individual has an eyeball that is shorter than normal, which refractive defect would they likely have? - **Answer:** If an individual has an eyeball that is shorter than normal, they would have hyperopia. - **34b:** Where does the focal point form in this condition? - **Answer:** The focal point in this condition forms behind the retina. - **34c:** Which type of lenses are used to correct for this refractive defect? - **Answer:** Convex, or converging lenses, are used to correct for hyperopia. **Question 35** - What is presbyopia and how does the amplitude of accommodation of the lens change over time? - **Answer:** Presbyopia is a disease caused by loss of elasticity of the lens. The amplitude of accommodation decreases with age due to this, and as a result, the lens cannot bulge as much during lens accommodation. Thus, an individual with presbyopia is essentially farsighted. **Question 36** - **36a:** What is astigmatism? - **Answer:** Astigmatism is a defect in the eye or in a lens caused by a deviation from the spherical curvature. - **36b:** What is a cataract? - **Answer:** A cataract occurs when the lens of the eye accumulates pigments and becomes progressively opaque. - **36c:** What is LASIK? - **Answer:** LASIK is laser eye surgery or laser vision correction. Essentially, it is a procedure where the cornea is reshaped with a laser to change the way light rays bend. **Question 37** - **37a:** What is a Snellen chart? - **Answer:** A Snellen chart is an eye chart that can be used to measure visual acuity. - **37b:** What does 20/20 vision literally mean? - **Answer:** 20/20 vision is considered \"normal\" vision. From 20 feet away, the smallest you can read are the letters on the 20/20 line of the Snellen chart. Most humans should theoretically be able to read that line from 20 feet away. - **37c:** What does it mean to have 20/40 vision? - **Answer:** If your visual acuity is 20/40, you are myopic. From 20 feet away, the smallest you can read are the letters on the 20/40 line of the Snellen chart. However, someone with 20/20 vision can read that same line from 40 feet away. - **37d:** If the Snellen chart reveals that your visual acuity is 20/20, does this mean you have perfect vision? - **Answer:** No, it just means you perfect visual acuity. **Question 38** - **38a:** A person's eyeglass prescription is -2.5. What are the units of this prescription? - **Answer:** The units are in diopters. - **38b:** Can diopters be converted into Snellen chart numbers? - **Answer:** No, diopters cannot be converted into Snellen chart numbers. - **38c:** Is this person myopic or hyperopic? - **Answer:** Myopic. **Question 39** - **39a:** What are the three layers of cells of the retina? - **Answer:** The innermost layer that is closest to the vitreous body is the ganglion cell layer. The middle layer is the bipolar cell layer. The rearmost layer is the photoreceptor layer, where the rod and cone cells are located. - **39b:** What is the macula of the retina? - **Answer:** The macula of the retina is an indentation in the retina off-center from the optic disc. - **39c:** What is the fovea centralis? - **Answer:** The fovea centralis is a region of the retina in the center of the macula that has the highest concentration of cone photoreceptor cells. The visual axis normally falls on this location. **Question 40** - **40a:** In phototransduction, electromagnetic radiation gets transduced into electrical impulses. Which retinal cells are responsible for firing action potentials? - **Answer:** Ganglion cells are responsible for firing action potentials. - **40b:** Which cells have axons that comprise the optic nerve? - **Answer:** Ganglion cells have axons that comprise the optic nerve. **Question 41** - **41a:** What pigment is found in membrane discs of rods? - **Answer:** Rhodopsin is the pigment found in membrane discs of rods. - **41b:** What pigment is found in the membrane discs of cones? - **Answer:** Iodopsins, also known as photopsins, are found in the membrane discs of cones. - **41c:** What are the two structural components of rhodopsin? - **Answer:** The proteins opsin and retinal. - **41d:** Based on what you know about proteins and membranes, what structural type of protein would rhodopsin be classified as? - **Answer:** Rhodopsin is classified as an integral membrane protein. **Question 42** - **42a:** Would you expect cones to be more sensitive in the light or dark? - **Answer:** While one might think that cones are most sensitive and function best in bright [light](https://en.wikipedia.org/wiki/Light), they are actually most sensitive in the dark. - **42b:** Would you expect rods to be more sensitive in the light or dark? - **Answer:** Rods are responsible for black and white vision (or shades of gray), so they are most sensitive in the dark. **Question 43** - **43a:** Can you explain the processes that take place in the membrane discs of your rods in dim light? How much neurotransmitter is being released? - **Answer:** In dim light, photons activate rhodopsin, causing cis-retinal to change conformation to trans-retinal. Rhodopsin then activates transducin (a G-protein), which in turn activates a cGMP phosphodiesterase (PDE) which degrades cGMP to GMP. As cGMP is not bound to the Na^+^ channels, they are closed. K^+^ still leaves the cell through leak channels, causing hyperpolarization and inactivation of the cell. Less neurotransmitters are released than in the dark which reduces inhibition of the bipolar neurons leading to increased signals from the ganglion cells to the visual cortex about dim light. - **43b:** Can you explain the processes that take place in the membrane discs of your rods in the bright light? - **Answer:** In bright light, photons activate rhodopsin, causing cis-retinal to change conformation to trans-retinal and dissociate from opsin. As a result, rhodopsin becomes bleached and therefore rods are unresponsive to photons. - **43c:** Which cells of the retina have receptors for the released neurotransmitters? - **Answer:** Bipolar cells have receptors for the released neurotransmitters. **Question 44** - **44a:** When light hits rhodopsin, what conformation is retinal converted into? - **Answer:** When light hits rhodopsin, retinal is converted into the trans conformation. - **44b:** What does it mean when your rods are "bleached"? - **Answer:** When exposed to bright light, there is a conformational change that causes opsin to dissociate from retinal in rhodopsin and therefore rods are unresponsive to photons. - **44c:** After light exposure, how is retinal converted back to its original conformation? - **Answer:** The process, the retinoid cycle, is mediated by the pigmented epithelial cells at the back of the retina. **Question 45** - **45a:** Can you explain the process of light adaptation. That is, what happens in your eyes as you walk out of a movie theater into the bright light on a sunny afternoon? - **Answer:** With light adaptation, the bright light outside the dark theater momentarily dazzles us as our rods and cones are maximally sensitive. Rods and cones are both stimulated by the bright light and adaptation occurs as rods are immediately bleached and cone sensitivity reduces. The entire process occurs in a matter of a few minutes. - **45b:** Can you explain the process of dark adaptation? - **Answer:** With dark adaptation, moving from a bright lit environment to a dark environment results in the perception of complete darkness as the photoreceptors responsible for black and white vision (rods) are bleached and nonresponsive. Over time, a period of up to 30 minutes, the retinoid cycle results in the regeneration of rhodopsin and the rods become active. Also, cone sensitivity increases to maximum as well. - **45c:** What is the most likely reason why pirates wore a patch over one eye? - **Answer:** Pirates likely wore an eyepatch in order to keep one eye always dark-adapted. Without a dark-adapted eye (the eye under the patch), going below the deck would be a challenge due to the darkness. Sliding the patch to the other eye reveals a dark-adapted eye, which allows the pirate to navigate quickly under the deck of the ship. **Question 46** - **46a:** What are the three different types of cone cells? - **Answer:** There are blue, green and red cone cells. - **46b:** What are their photoreceptor pigments collectively referred to as? - **Answer:** Their photoreceptor pigments are collectively referred to as photopsins, also known as iodopsins. **Question 47** - **47a:** What are the components of the external ear? - **Answer:** The auricle (i.e., the pinna), the auditory canal, and the outer layer of the eardrum (i.e., the tympanic membrane). - **47b:** What are the components of the middle ear? - **Answer:** The inner layer of the eardrum, the Eustachian tube (i.e., the internal auditory meatus), and the auditory ossicles (malleus, incus, and stapes). - **47c:** What are the components of the inner ear? - **Answer:** The cochlea, the vestibule, and the semicircular canals. - **47d:** What anatomical structure separates the external ear from the middle ear? - **Answer:** The tympanic membrane. - **47e:** What anatomical structure connects the middle ear to the pharynx? - **Answer:** The internal auditory meatus connects the middle ear to the pharynx. - **47f:** Why does this connection exist? - **Answer:** This exists to balance the pressures on either side of the tympanic membrane. **Question 48** - How is sound transduced through the ear? Sequentially discuss all structures of the external, middle and inner ear in your description. - **Answer:** First, sound waves strike the tympanic membrane, becoming vibrations. The vibrations then strike the malleus, incus, and stapes, vibrating them as well. The stapes, which is attached to the oval window, causes a vibration to be transduced through the oval window. Vibrations within the fluid will travel throughout each duct, and in the cochlear duct, hair cells will bend and release neurotransmitters. These neurotransmitters will send the signal to the brain. Eventually, the vibrations will reach the round window. Here, the vibrations will begin to dissipate. **Question 49** - **49a:** How does being in an airplane affect the ear? - **Answer:** The air pressure changes rapidly during ascent, and the internal auditory meatus can't react fast enough to accommodate this pressure change. - **49b:** What are some ways that these symptoms can be alleviated? - **Answer:** By yawning, chewing gum, or performing the Valsalva maneuver. Essentially, you would want to open the internal auditory meatus in order to allow the middle ear to get more air, equalizing the air pressure. **Question 50** - **50a:** The inner ear has a bony labyrinth and a membranous labyrinth. What are the three fluid-filled chambers of the cochlea? - **Answer:** The three fluid-filled chambers include the scala vestibuli (the vestibular duct), the scala media (the cochlear duct) and the scala tympani (the tympanic duct). - **50b:** What are the fluids that each chamber contains? - **Answer:** The vestibuli and tympani contain the fluid perilymph, while the media contains the fluid endolymph. - **50c:** What are the three membranes associated with these chambers? - **Answer:** The three membranes include the vestibular membrane, the tectorial membrane and the basilar membrane. - **50d:** What is the general function of the cochlea? - **Answer:** The general function of the cochlea is to produce nerve impulses in response to sound vibrations. **Question 51** - **51a:** What is the sensory organ of audition? - **Answer:** The organ of Corti. - **51b:** What are all of the cells and membranes that make up the organ of Corti? - **Answer:** The cells and membranes that make up the organ of Corti are the tectorial membrane, outer hair cells, the basilar membrane, inner hair cells, and support cells. - **51c:** Where is the organ of Corti specifically located? - **Answer:** The organ of Corti is located within the cochlea. **Question 52** - **52a:** What is the function of the inner hair cells of the organ of Corti? - **Answer:** The inner hair cells fire nerve impulses to the brain in response to distortion of the basilar membrane. - **52b:** What is the function of the outer hair cells of the organ of Corti? - **Answer:** The outer hair cells push the tectorial membrane and they selectively amplify the vibration of the basilar membrane. - **52c:** These hair cells contain stereocilia. Are these motile structures? - **Answer:** No. Stereocilia are basically long microvilli. - **52d:** What are stereocilia supported by? - **Answer:** Stereocilia are supported by microfilaments. **Question 53** - What is the conformation of the basilar membrane at the base and at the apex of the cochlea? - **Answer:** The base is narrow, but thick, while the apex is broad, but thin. **Question 54** - **54a:** Elephants can hear sound frequencies of 15 Hz. Can humans hear these frequencies? - **Answer:** No. Humans can hear down to about 20 Hz. - **54b:** Where would sounds with a frequency of 19,000 Hz deform the basilar membrane? Where would a frequency of 20 Hz deform the membrane? - **Answer:** Sounds with a frequency of 19,000 Hz would deform the basilar membrane at the base, while sounds with a frequency of 20 Hz would deform the basilar membrane at the apex. **Question 55** - **55a:** What is a kinocilium? - **Answer:** The kinocilium is the tallest of the stereocilia of a hair cell. - **55b:** Are they motile structures? - **Answer:** No, they are not motile structures. - **55c:** What are kinocilia supported by? - **Answer:** The are supported by microtubules. - **55d:** How do they interact with stereocilia via the tip-link mechanism? - **Answer:** Stereocilia and the kinocilium are connected by small connective tissue fibers. When the stereocilia are pushed towards the kinocilium, the fibers pull open mechanically-gated potassium channels in the shorter stereocilia. - **55e:** How does all of this relate to the process of hearing? - **Answer:** Endolymph is potassium-rich. Potassium will enter the hair cell and cause a depolarization. As a result, neurotransmitters are released, which activates neurons of the cochlear nerve to send the signal to the brain to be processed. **Question 56** - **56a:** What are the two sensory organs of equilibrioception? - **Answer:** The sensory organs involved in equilibrioception are the crista ampularis and the macula. - **56b:** Where are each located and what are their general functions? - **Answer:** The crista ampularis is located at the base of each semicircular canal in the ampulla region and it is responsible for detecting the movement of the head, including turning right and left, tilting right and left and nodding. The macula is located in the utricle and saccule of the vestibule. They detect linear and horizontal acceleration and deceleration and tilting forwards and backwards. - **56c:** How does the function of the crista ampularis relate to that of the organ of Corti? - **Answer:** The cupula of the crista ampularis functions similarly to the tectorial membrane in the organ of Corti. - **56d:** How are the utricle and saccule involved in the detection of head movements? - **Answer:** The utricle and saccule are at a 90º angle to one another. The utricle is in the horizontal plane, so it detects horizontal acceleration and deceleration (i.e., driving a racecar), and additionally, head tilt. The saccule is in the vertical plane, so it detects vertical acceleration and deceleration (i.e., riding in an elevator). - **56e:** How does the function of the macula relate to that of the organ of Corti? - **Answer:** The otolith membrane of the macula functions like the tectorial membrane in the organ of Corti.