Medical Physiology Block 2 Week 3 Flashcards
(85 cards)
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)