Flashcards in Medical Physiology Block 2 Week 3 Deck (85):
Describe the property of sensory “univariance”. Give an example.
the sensory receptor and its subsequent neural circuits do not know what stimulated them—they give the same type of response regardless (sour and salt taste bud receptors have same outcome following during stimuli)
Identify the 5 major classes of taste qualities. Which qualities are sensed through a primary ionotropic receptor mechanism? Which are sensed through a primary metabotropic receptor mechanism?
Salt & Sour (ionotropic); Sweet, umami, bitter (metabotropic)
Golf activation leads to a nonspecific cation conductance carried by Na+, K+ and Ca2+. Yet, K+ conductance is hyperpolarizing. How does this signaling path lead to the firing of an action potential?
Dependent on the reversal potential of channels (further from reversal potential means more relative conductance)
Accommodation is a process by which the eye changes its focal power. If ciliary muscles contract, how does this contribute to accommodation? Does ciliary muscle contraction act to increase or decrease focal power?
To accommodate, the ciliary muscle fibers contract and release some of the tension in the zonal fibers. Relieved of the radial pull of its fibers, the lens becomes rounder (relaxed); Increase curvature = increased ability to bend light (increased power)
Miosis and mydriasis are constriction and dilation of the pupil, due to parasympathetic and sympathetic input, respectively. With this knowledge, identify the transmitters responsible for miosis and mydriasis.
Miosis- Parasympathetic: acetylcholine; mydriasis- sympathetic: norepinephrine
Photoreceptors exhibit a tonic current in the dark. Identify the conductance(s) and locus (loci) responsible for the dark current. What effect does light have on the dark current?
In the absence of light, Na + (some calcium) enters the outer segment of the rod through cGMP-gated channels (non-selective cation) and depolarizes the cell. The electrical circuit for this dark current is completed by K + leaving the inner segment. The dark current, which depolarizes the cell, leads to constant transmitter release; Phosphodiesterase (effector enzyme) inhibits cGMP (second messenger) production (Turns off the Na/Ca channel)
Dark current has a very high signal to noise ratio. What specialization in the molecular mechanism for the dark current makes this possible?
The absorption of one photon suppresses a surprisingly large current and thus represents an enormous amplification of energy; the high density of rhodopsin molecules maximizes photon capture rate
11-cis-retinal is the photon-absorbing molecule common to all photoreceptors, yet S, M and L cones and rods all detect different wavelength light at different efficiencies. What molecular signaling step allows this specificity between receptor sub-types?
difference in amino acid sequence of opsin molecule; affect charge distributions and interaction with retinal
Calcium influx through a final TRPM5-dependent signaling step is common to several taste qualities. How is specific perception of these taste qualities achieved?
"It appears that sweet-sensing taste cells do not express receptors for either bitter or umami" (may have receptors for salt or sour)
What cell types do autonomic nervous system neurons innervate? is this interaction excitatory, inhibitory, or modulatory?
smooth muscle, cardiac muscle, secretory epithelia, and glands; modulatory
What is a feature of the relay of information in the ANS? How does this compare to somatic motor and sensory systems?
Two neurons; two synapses (cell bodies in the CNS (preganglionic neuron) and periphery (postganglionic neuron)); somatic motor = one neuron, one synapse, cell bodies in the CNS; sensory = one neuron, one synapse, cell bodies in the PNS
Where is the cell body of a postganglionic sympathetic neuron located?
paraverterbral ganglia (enter through white ramus; adjacent to vertebral column, adjacent ganglia are fused (i.e. C1-C4); axons exit the ganglia into the mixed spinal nerve through the gray ramus); prevertebral ganglia (lies in front of the aorta and along its major arterial branches; must travel through paravertebral ganglia)
Where is the cell body of a preganglionic sympathetic neuron located?
The cell bodies of preganglionic sympathetic motor neurons are located in the thoracic and upper lumbar spinal cord between levels T1 and L3. At these spinal levels, autonomic neurons lie in the intermediolateral cell column , or lateral horn, between the dorsal and ventral horns
Are gray ramus commincans present at every level of the spinal cord? white ramus commincans?
Yes; no (only T1-L3)
Where do the cell bodies of preganglionic parasympathetic neurons found? postganglionic?
The cell bodies of preganglionic parasympathetic neurons are located in the medulla, pons, and midbrain and in the S2 through S4 level of the spinal cord (four cranial nerves: the oculomotor nerve (CN III), the facial nerve (CN VII), the glossopharyngeal nerve (CN IX), and the vagus nerve (CN X); sphlanic nerves innervate GI tract); near target organs
Describe the parasympathetic superior salivatory nucleus axis.
is in the rostral medulla and contains parasympathetic neruons that project through facial nerve (CN VII) to the pterygopalatine ganglion; postganglionic fibers supply the lacrimal glands (tears), submandibular ganglion (mandibular and sublingual glands)
Describe the parasympathetic axis supplying the parotid gland (salivary gland)
the inferior salivatory nucleus and the rostral part of the nucleus ambiguus (rostral medulla) contain parasympathetic neurons that project though the glossopharyngeal nerve (CN IX) to the otic ganglion (supplies parotid gland)
Which is the most important cranial nerve in the parasympathetic system? why?
vagus (cranial nerve X); originates in nucleus ambiguus and dorsal motor nucleus of the vagus; this nerve supplies parasympathetic innervation to all the viscera of the thorax and abdomen, including the gastrointestinal tract between the pharynx and distal end of the colon. electrical stimulation of the nucleus ambiguus results in activation of striated muscle in the pharynx, larynx, and esophagus and slows the heart. Stimulation of the dorsal motor nucleus of the vagus initiates secretion of gastric acid, insulin, and glucagon.
Which region of the CNS receives visceral afferents (not considered a part of the ANS)?
nucleus of the solitary tract (medulla); "lower brainstem command center for visceral control"
Describe the enteric nervous system. Know the major plexuses of the ENS.
The enteric division is a self-contained nervous system that surrounds the gastrointestinal tract and receives sympathetic and parasympathetic input; In the intestinal wall, the myenteric plexus is involved primarily in the control of motility, whereas the submucosal plexus is involved in the control of ion and fluid transport. Both the myenteric and the submucosal plexuses receive pre ganglionic parasympathetic innervation from the vagus nerve (or sacral nerves in the case of the distal portion of colon and rectum) (post-ganglionic sympathetic innervation as well)
What are varicosities?
points of contact between postganglionic cells and their targets (bulbous expansions along axon)
In what regions of the body are sympathetic and parasympathetic innervation antagonist? different outcomes? only by one system?
cardiac muscle (heart rate), gut (peristalsis); salivary glands; sweat glands, piloerector muscle, and most peripheral blood vessels only receive sympathetic input
How does the CNS control the ANS?
hypothalamus (coordinates ANS with endocrine system; cerebral control center for ANS?), NTS, and forebrain regulate system through feedback loops and reflexes; response to fear
All preganglionic neurons release which neurotransmitter onto postganglionic neurons? What receptor is part of the synaptic transmission?
Acetycholine; nicotinic (N2; ionotropic)
All postganglionc parasympathetic neurons release which neurotransmitter onto visceral targets? receptor involved?
acetycholine; muscarinic (metabotropic)
Which neurons in the ANS are myelinated?
Which neurotransmitter is released by postganglionic sympathetic neurons onto visceral targets? receptor involved? what is an exception to this paradigm?
norepinephrine; alpha & beta adrenergic receptors; chromaffin cells in the adrenal medulla secrete epinephrine into the bloodstream to act on sweat glands
What are the downstream targets of muscarinic Ach receptors?
1. stimulate the hydrolysis of phosphoinositide and thus increase [Ca 2+ ] i and activate protein kinase C. 2 inhibit adenylyl cyclase and thus decrease cyclic adenosine monophosphate (cAMP) levels. 3. directly modulate K + channels through the G protein βγ complex; M 1 , M 3 , and M 5 (subtypes) preferentially couple to Gα q; M 2 and M 4 preferentially couple to Gα i or Gα o to inhibit adenylyl cyclase and thus decrease [cAMP] i
What is the distribution of alpha and beta adrenergic metabotropic receptors in the human body?
α 1 Receptors predominate on blood vessels, α 2 on presynaptic terminals, β 1 in the heart, β 2 in high concentration in the bronchial muscle of the lungs, and β 3 in fat cells.
How do metabotropic beta adrenergic receptors mediate increased heart rate?
β 1 receptors in the heart activate the G s heterotrimeric G protein and stimulate adenylyl cyclase, which antagonizes the effects of muscarinic receptors (modulate potassium channel)
How do metabotropic receptors on the dendrites of postganglionic neurons modulate their output?
A well-characterized effect of muscarinic neurotransmission in autonomic ganglia is inhibition of a specific K + current called the M current (potassium channel; slow kinetics; may result in repetitive firing)
Describe the pathway of sympathetic innervation on endothelial smooth muscle
Three phases of contraction; 1. ATP binds to a P 2X purinoceptor on the smooth muscle cell, leading to depolarization, activation of voltage-gated Ca 2+ channels, increased [Ca 2+] i, and the rapid phase of contraction. 2. norepinephrine binds to an α 1-adrenergic receptor, which—through a G q/PLC/IP 3 cascade, leads to Ca 2+ release from internal stores and the second phase of contraction. 3. neuropeptide Y binds to a Y 1 receptor and somehow causes an increase in [Ca 2+] i and thus produces the slowest phase of contraction.
Describe the pathway of parasympathetic innervation on endothelial smooth muscle
The neuron releases NO, which diffuses to the smooth muscle cell. In addition, ACh binds to M 3 muscarinic receptors on endothelial cells, leading to production of NO, which also diffuses to the smooth muscle cell. Both sources of NO activate guanylyl cyclase and raise [cGMP] i in the smooth muscle cell and contribute to the first phase of relaxation. In the second phase, which tends to occur more with prolonged or intense stimulation, the neuropeptide VIP binds to receptors on the smooth muscle cell and causes a delayed relaxation through an increase in [cAMP] i or a decrease in [Ca 2+] i.
Be able to describe the cascade of events that occur during the fight-or-flight response
increases in heart rate, cardiac contractility, blood pressure, and ventilation of the lungs; bronchial dilatation; sweating; piloerection; liberation of glucose into the blood; inhibition of insulin secretion; reduction in blood clotting time; mobilization of blood cells by contraction of the spleen; and decreased gastrointestinal activity
Most sensory transduction cells (e.g., oxygen and taste sensors, but not olfactory receptors) lack their own axon to communicate with the CNS. How do these cells transmit information?
the communication system of choice is a relatively standard, Ca 2+ -dependent system of synaptic transmission onto a primary sensory neuron.
Are signals amplified in signal transduction? If yes, give an example.
Yes; the capture of one photon results in a 3% decrease in sodium conductance
How can information be coded in transduction?
Useful information may be encoded in many features of the firing, including its rate, its temporal patterns, its periodicity, its consistency, and its patterns compared with other sensory neurons of the same or even different modalities.
How do chemicals reach the human body? What is important about the transport of these chemicals?
Chemicals reach the human body by oral or nasal ingestion, contact with the skin, or inhalation, and once there, they diffuse or are carried to the surface membranes of receptor cells through the various aqueous fluids of the body (e.g., mucus, saliva, tears, cerebrospinal fluid, blood plasma); barriers that prevent infection
Which sensory transduction pathways result in the sensation of taste?
gustation and smell
Of the major sensory transduction pathways, which sensory receptor is actually a neuron?
olfactory nerve (synapses on olfactory bulb in brain)
Which sensory receptors are known to regenerate?
Taste buds (only if gustatory nerve is intact; trophic factors), olfactory nerves (rarity for neurons, this is exception), hair cells (questionable), retinal photoreceptors, and most other sensory receptors (according to literature)
Where are taste buds located?
dorsal surface of the tongue (concentrated in papillae; surrounded by basal cells, and sensory afferent neurons); The chemically sensitive part of a taste receptor cell is a small apical membrane region near the surface of the tongue. The apical ends have thin extensions called microvilli that project into the taste pore, a small opening on the surface of the tongue where the taste cells are exposed to the contents of the mouth.
What kind of cells are taste buds?
Taste receptors are modified epithelial cells
Describe olfactory receptors.
in the thin olfactory epithelium , which is placed high in the nasal cavity; surrounding by basal cells (source of new receptors) and glia-like cells; Odorants must first dissolve in and diffuse through a thin mucous layer, which has both a viscous and a watery portion
Describe transduction of salt and sour taste
Salty taste is mediated by an epithelial Na + channel (ENaC). The taste channels are relatively insensitive to voltage and stay open at rest; Sour is mediated as extracellular H + activates TRPP3 (non-selective cation) channels (sensed by decrease in pH; H+)
Describe the transduction of sweet, bitter, and umami
G protein-coupled; stimulates phospholipase C, which in turn increases its production of the messenger inositol trisphosphate (IP 3). IP 3 triggers the release of Ca 2+ from internal stores, and the rise in [Ca 2+] i then activates the TRPM5 channel that is specific for taste cells. TRPM5 is a relatively nonselective cation channel that depolarizes the taste cell, triggering the release of neurotransmitter onto the primary gustatory axon
Can a taste receptor be sensitive to multiple tastes?
Yes; It is generally accepted that a receptor cell responds to only one out of the group of sweet, bitter, and umami
What are the gustducin subunits that respond to sweet? bitter? umami?
bitter = T2R homodimer; sweet = T1R2/T1R3; umami = T1R1/T1R3
Describe olfactory transduction.
Receptor activation stimulates a heterotrimeric G protein called Golf; cAMP binds to a cAMP-gated cation channel (Opening of this channel increases permeability to Na +, K +, and Ca 2; net inward current; Gs & AC); The increased [Ca 2+] i opens Ca 2+-activated Cl − channels. Opening of these channels produces more depolarization because of the relatively high [Cl −] i of olfactory receptor neuron; glutamatergic synapse on olfactory bulb
How is sensory transduction terminated in the various systems?
Termination of the olfactory response occurs when odorants diffuse away, scavenger enzymes in the mucous layer break them down, or cAMP in the receptor cell activates other signaling pathways that end the transduction process; The photoreceptor cell converts all- trans retinal to retinol (vitamin A), which then translocates to the pigment epithelium and becomes 11- cis retinal. This compound makes its way back to the outer segment, where it recombines with opsin
Can an olfactory neuron sense multiple smells?
How can the human eye be separated functionally?
A component that bends light and a component that turns light into neuronal signal
What are the layers of the eye (front to back)?
Tears, cornea, aqueous humor, iris and pupil, cornea and ciliary muscle, vitreous humor, retina (optic nerve, amacrine cells, bipolar cells, horizontal cells, photoreceptors, and epithelium)
What is a disease that results from buildup of pressure in the anterior chamber of the eye?
Glaucoma (aqueous humor cannot be drained by the canals of Schlemm)
What is the importance of the pupil and iris? Describe the papillary light reflex; why is this reflex important?
Pupil = aperture; iris = aperture stop; light entering the eye and exiting through the optic nerve first innervates the LGN before synapsing on the pretectal nucleus. The pretectal nucleus innervates both Edinger-Westphal nuclei (one on each side) and these preganglionic neurons innervate the ciliary ganglion (acetylcholine), which innervates sphincter muscles controlling the iris (acetylcholine; miosis); a smaller pupil diameter gives a greater depth of focus
Define refraction. Which part of the eye does most of the refractive work? Describe accommodation.
bending occurs when light moves from a faster media to a slower media (from air to another media); lower index of refraction means light travels faster in comparison to a different media; cornea; At rest, the lens is suspended around its edge by elastic zonal fibers that keep its capsule stretched and relatively flattened. To accommodate, the ciliary muscle fibers contract and release some of the tension in the zonal fibers. Relieved of the radial pull of its fibers, the lens becomes rounder (relaxed; increased curvature)
What is myopia?
nearsightedness (cornea curved too much or eye too long); treated with concave diverging lens
What are common features between olfaction and vision?
The structure of the olfactory cAMP-gated channel is closely related to the light-activated channel in photoreceptors of the retina, which is normally gated by an increase in intracellular cyclic guanosine monophosphate ([cGMP] i ); retina and olfactory nerve are part of the nervous system; complex processing of information prior to synapse
What is the distribution of the retina? How are images projected onto the retina? Why is the retina at the back of the eye?
fovea in the middle (most receptors; color vision; 1:1 great resolution poor sensitivity), outer rods and peripheral vision is a mixture of both color and B/W; upside down and on the opposite site of the stimulus; , photoreceptors are close to the pigment epithelium, which aids the renewal process, and to the blood vessels that supply the retina.
Describe dark current
Inward Na+ (some Ca2+) in outer segment through non-selective cGMP-gated channel. Outward K+ in inner segment which is not regulated; In the dark, a constitutively active guanylyl cyclase that synthesizes cGMP from GTP keeps cGMP levels high within the photoreceptor cytoplasm. This high [cGMP] i causes the cGMP-gated cation channels to spend much of their time open and accounts for the dark current
How does calcium modulate visual transduction?
Ca 2+ , which enters through the relatively nonselective cGMP-gated channel, synergistically inhibits the guanylyl cyclase and stimulates the phosphodiesterase. These Ca 2+ sensitivities set up a negative feedback system. In the dark, the incoming Ca 2+ prevents runaway increases in [cGMP] i .
Describe the sensitivity for light of cones. Rods.
Cones: fast, less sensitive (so they don't saturate; S: 420, M: 530, L: 560); rods: slow, very sensitive (500); dependent on entrance of calcium into the cell and inhibiting guanylyl cyclase
Kinocilium and stereocilium of hair cells have a fundamentally different structure. Outline the basic structural features of each type of cilium
kinocillium = large; stereocilium = actin-based (connected by tip links); bending towards the kinocilium caused depolarization
Fundamental to hair cell signaling are the endolymph and perilymph. Describe the composition of each, respectively. What is the charge of endolymph in cochlear hair cells?
endolymph: bathing the stereovilli is singular in composition. It has a very high [K + ] (150 mM) and a very low [Na + ] (1 mM), more like cytoplasm than extracellular fluid; perilymph: bathes the basolateral side of the hair cells. In composition (i.e., relatively low [K + ], high [Na + ]), perilymph is similar to cerebrospinal fluid; +80 mV
Is a hair cell a neuron?
What is the resting potential of vestibular hair cells and cochlear inner hair cells?
Describe the TRPA1 channel?
found on hair cells; at rest, allows some conductance of potassium; when deflected towards kinocilium, potassium conductance causes depolarization; leads to Ca-mediated glutamate release
Describe the vestibular structures.
Two otilith organs: utricle (horizontal acceleration) and saccule (vertical acceleration); semicircular canals (3; rotation)
Describe vestibular transduction in the otilith organs. in semicircular canals
Acceleration of the head causes movement of endolymph bathing the macula (epithelium connected to calcium carbonate crystals) and bending of hair cells (since the inertia of the otiliths hinders their movement). Synapses onto CNVIII (cell bodies in Scarpa's ganglion); The hair bundles project into a gelatinous, dome-shaped structure called the cupula, which spans the lumen of the ampulla. The relatively stagnant endolymph exerts a force on the movable cupula
Describe the layers of the ear
Pinna and tragus (transport air waves into ear; may reflect); tympanic membrane transfers vibrations to the ossicles (malleus, incus, and stapes); stapes displaces the oval window (conversion of sound waves to displacement of fluid)
How is are signals (in the form of sound waves) amplified in the middle ear? (in other words: The middle ear acts as an “impedance-matching device”. What does this mean and how is this function achieved?)
Ear drum is much bigger than the oval window and ossicles act as a lever
Describe the cochlea.
Reissner's membrane (divides scala vestibuli and scala media) and the basilar membrane (divides scala media and scala tympani; organ of Corti) divide the cochlea into three spiraling fluid-filled compartments: the scala vestibuli (begins at its large end near the oval window—where vibrations enter the inner ear), the scala media, and the scala tympani (terminates at its basal or large end at the round window).
Where is the site of communication between the perilymph from the scal vestibuli and scala tympani?
Describe the stria vascularis. What has a similar function in vestibular system?
3 step pumping progress in two-layered epithelium: 1. active uptake of K from perilymph by spiral ligament fibrocytes (basal cells = gap junctions). 2. intermediate cells mediate facilitative diffusion of potassium into interstitial fluid. 3. marginal cells transport potassium into endolymph; vestibular dark cells
Describe auditory transduction.
Stapes moves outward causing the oval window to move outward (pressure in the scala vestibuli decreases) and the round window to move inward (pressure in scala tympani moves increase); Scala vestibuli pressure falls below scala tympani pressure resulting in the basilar membrane to bow upward; Upward movement of basilar membrane tilts hair bundles toward longer stereovilli, opening transduction channels (mechanical to electrical transduction). In outer hair cells, depolarization causes prestin to contract (leading to contraction of the outer hair cells are further upward movement of the basilar membrane; electrical to mechanical (amplify)); The upward movement of the basilar membrane—accentuated by the cochlear amplifier—forces endolymph to flow out of the inner sulcus, beneath the tectorial membrane, toward its tip (bend inner hair cells) In inner hair cells, depolarization causes enhanced transmitter release (glutamate; calcium dependent exocytosis; spiral ganglion)
What happens in the absence of prestin?
No amplification of the movement of the basilar membrane upwards and deafness
Describe the sensitivity to sound of the cochlea. Can it be modulated?
The basilar membrane resembles a harp. At one end—the base, near the oval and round windows—it has short, taut strings that vibrate at high frequencies. At the other end—the apex—it has longer, looser strings that vibrate at low frequencies; amplitude = rate-coding
What is the difference between glabrous and hairy skin?
Glabrous skin (or hairless) is found on the palms of our hands and fingertips and on the soles of our feet and pads of our toes; rest = hairy
Pacini’s corpuscles have a layered capsule surrounding their nerve ending. What is the function of the capsule in pressure sensation
Rapidly adapting sensor; If the stimulus pressure is maintained, the layers slip past one another and transfer the stimulus energy away so that the underlying axon terminal is no longer deformed and the receptor potential dissipates
What happens in damaged tissue?
Damaged skin (tissue damage) releases a variety of chemical substances from itself, blood cells, and nerve endings. These substances include bradykinin, prostaglandins, serotonin, substance P, K + , H + , and others; they trigger the set of local responses that we know as inflammation . As a result, blood vessels become more leaky and cause tissue swelling (or edema) and redness
Which somatosensory receptors have the smallest receptive field? slowest adaptation?
Meissner's corpuscle and Merkel's disk (glabrous skin); Ruffini's corpuscle
Secondary hyperalgesia is a sensitization of nociceptors to stimulation. Describe one mechanism underlying secondary hyperalgesia.
axon reflex (nociceptive) causes tissues surrounding a damaged area to become hypersensitive (inflammation may also)
What are the two sensory receptors in somatic muscle? Where are they located? What do they sense or how are they innervated?
Muscle spindle: located in modified muscle fibers called intrafusal muscle fibers (sensitive to muscle length and velocity; nuclear bag fibers and nuclear chain fibers). γ motor neurons (efferent) cause the intrafusal muscle fibers to contract in parallel with the extrafusal fibers (When the muscle is stretched, the muscle spindle stretches and the Ia afferent fires more strongly. When the muscle is released from the stretch and contracts, the muscle spindle becomes slack, causing the Ia afferent to fall silent. The muscle spindle is rendered insensitive to further stretches of muscle. To restore sensitivity, gamma motor neurons fire and cause the spindle to contract, thereby becoming taut and able to signal the muscle length again.); Golgi tendon organs (extrafusal fibers): respond to changes in tension
How are receptors for heat and for cold different?
Heat receptors have high sensitivity to increasing warm stimuli, however inactivate at larger skin temperatures (boundary between heat receptors and nociception (burning)); Cold receptors more dynamic, yet less sensitive