Neurophysiology Flashcards
Which autonomic receptor is blocked by hexamethonium at the ganglia, but not at the neuromuscular junction?
(a) Adrenergic α receptors
(b) Adrenergic β1 receptors
(c) Adrenergic β2 receptors
(d) Cholinergic muscarinic receptors
(e) Cholinergic nicotinic receptors
The answer is E [I C 2 a].
Hexamethonium is a nicotinic blocker, but it acts only at ganglionic (not neuromuscular junction) nicotinic receptors. This pharmacologic distinction emphasizes that nicotinic receptors at these two locations, although similar, are not identical.
A 66-year-old man with chronic hyper-tension is treated with prazosin by his physician. The treatment successfully decreases his blood pressure to within the normal range. What is the mechanism of the drug’s action?
(a) Inhibition of β1 receptors in the sinoatrial (SA) node
(b) Inhibition of β2 receptors in the SA node
(c) Stimulation of muscarinic receptors in the SA node
(d) Stimulation of nicotinic receptors in the SA node
(e) Inhibition of β1 receptors in ventricular muscle
(f) Stimulation of β1 receptors in ventricular muscle (g) Inhibition of α1 receptors in ventricular muscle
(h) Stimulation of α1 receptors in the SA node
(i) Inhibition of α1 receptors in the SA node
(j) Inhibition of α1 receptors on vascular smooth muscle (K) Stimulation of α1 receptors on vascular smooth muscle (L) Stimulation of α2 receptors on vascular smooth muscle
The answer is J [I C 1 a; Table 2.2].
Prazosin is a specific antagonist of α1 receptors, which are present in vascular smooth muscle, but not in the heart. Inhibition of α1 receptors results in vasodilation of the cutaneous and splanchnic vascular beds, decreased total peripheral resistance, and decreased blood pressure.
Which of the following responses is mediated by parasympathetic muscarinic receptors?
(a) Dilation of bronchiolar smooth muscle
(b) Erection
(c) Ejaculation
(d) Constriction of gastrointestinal (GI) sphincters
(e) Increased cardiac contractility
The answer is B [I C 2 b; Table 2.6].
Erection is a parasympathetic muscarinic response. Dilation of the bronchioles, ejaculation, constriction of the gastrointestinal (GI) sphincters, and increased cardiac contractility are all sympathetic α or β responses.
Which of the following is a property of C fibers?
(a) Have the slowest conduction velocity of any nerve fiber type
(b) Have the largest diameter of any nerve fiber type
(c) Are afferent nerves from muscle spindles
(d) Are afferent nerves from Golgi tendon organs
(e) Are preganglionic autonomic fibers
The answer is A [II F 1 b; Table 2.5].
C fibers (slow pain) are the smallest nerve fibers and therefore have the slowest conduction velocity.
When compared with the cones of the retina, the rods
(a) are more sensitive to low-intensity light
(b) adapt to darkness before the cones
(c) are most highly concentrated on the fovea
(d) are primarily involved in color vision
The answer is A [II C 2 c (2); Table 2.7].
Of the two types of photoreceptors, the rods are more sensitive to low-intensity light and therefore are more important than the cones for night vision. They adapt to darkness after the cones. Rods are not present in the fovea. The cones are primarily involved in color vision.
Which of the following statements best describes the basilar membrane of the organ of Corti?
(a) The apex responds better to low frequencies than the base does
(b) The base is wider than the apex
(c) The base is more compliant than the apex
(d) High frequencies produce maximal displacement of the basilar membrane near the helicotrema
(e) The apex is relatively stiff compared to the base
The answer is A [II D 4].
Sound frequencies can be encoded by the organ of Corti because of differences in properties along the basilar membrane. The base of the basilar membrane is narrow and stiff, and hair cells on it are activated by high frequencies. The apex of the basilar membrane is wide and compliant, and hair cells on it are activated by low frequencies.
Which of the following is a feature of the sympathetic, but not the parasympathetic nervous system?
(a) Ganglia located in the effector organs
(b) Long preganglionic neurons
(c) Preganglionic neurons release norepinephrine
(d) Preganglionic neurons release acetylcholine (ACh)
(e) Preganglionic neurons originate in the thoracolumbar spinal cord
(f) Postganglionic neurons synapse on effector organs
(g) Postganglionic neurons release epinephrine
(h) Postganglionic neurons release ACh
The answer is E [I A, B; Table 2.1; Figure 2.1].
Sympathetic preganglionic neurons originate in spinal cord segments T1–L3. Thus, the designation is thoracolumbar. The sympathetic nervous system is further characterized by short preganglionic neurons that synapse in ganglia located in the paravertebral chain (not in the effector organs) and postganglionic neurons that release norepinephrine (not epinephrine). Common features of the sympathetic and parasympathetic nervous systems are preganglionic neurons that release acetylcholine (ACh) and postganglionic neurons that synapse in effector organs.
Which autonomic receptor mediates an increase in heart rate?
(a) Adrenergic α receptors
(b) Adrenergic β1 receptors
(c) Adrenergic β2 receptors
(d) Cholinergic muscarinic receptors
(e) Cholinergic nicotinic receptors
The answer is B [I C 1 c].
Heart rate is increased by the stimulatory effect of norepinephrine on β1 receptors in the sinoatrial (SA) node. There are also sympathetic β1 receptors in the heart that regulate contractility.
Cutting which structure on the left side causes total blindness in the left eye?
(a) Optic nerve
(b) Optic chiasm
(c) Optic tract
(d) Geniculocalcarine tract
The answer is A [II C 3 a].
Cutting the optic nerve from the left eye causes blindness in the left eye because the fibers have not yet crossed at the optic chiasm.
Which reflex is responsible for monosynaptic excitation of ipsilateral homonymous muscle?
(a) Stretch reflex (myotatic)
(b) Golgi tendon reflex (inverse myotatic)
(c) Flexor withdrawal reflex
(d) Subliminal occlusion reflex
The answer is A [III C 1].
The stretch reflex is the monosynaptic response to stretching of a muscle. The reflex produces contraction and then shortening of the muscle that was originally stretched (homonymous muscle).
Which type of cell in the visual cortex responds best to a moving bar of light?
(a) Simple
(b) Complex
(c) Hypercomplex
(d) Bipolar
(e) Ganglion
The answer is B [II C 5 b (2)].
Complex cells respond to moving bars or edges with the correct orientation. Simple cells respond to stationary bars, and hypercomplex cells respond to lines, curves, and angles. Bipolar and ganglion cells are found in the retina, not in the visual cortex.
Administration of which of the following drugs is contraindicated in a 10-year-old child with a history of asthma?
(a) Albuterol
(b) Epinephrine
(c) Isoproterenol
(d) Norepinephrine
(e) Propranolol
The answer is E [I C 1 d; Table 2.2].
Asthma, a disease involving increased resistance of the upper airways, is treated by administering drugs that produce bronchiolar dilation (i.e., β2 agonists). β2 Agonists include isoproterenol, albuterol, epinephrine, and, to a lesser extent, norepinephrine. β2 Antagonists, such as propranolol, are strictly contraindicated because they cause constriction of the bronchioles.
Which adrenergic receptor produces its stimulatory effects by the formation of inositol 1,4,5-triphosphate (IP3) and an increase in intracellular [Ca2+]?
(a) α1 Receptors
(b) α2 Receptors
(c) β1 Receptors
(d) β2 Receptors
(e) Muscarinic receptors
(f) Nicotinic receptors
The answer is A [I C 1 a].
Adrenergic α1 receptors produce physiologic actions by stimulating the formation of inositol 1,4,5-triphosphate (IP3) and causing a subsequent increase in intracellular [Ca2+]. Both β1 and β2 receptors act by stimulating adenylate cyclase and increasing the production of cyclic adenosine monophosphate (cAMP). α2 Receptors inhibit adenylate cyclase and decrease cAMP levels. Muscarinic and nicotinic receptors are cholinergic.
The excessive muscle tone produced in decerebrate rigidity can be reversed by
(a) stimulation of group la afferents
(b) cutting the dorsal roots
(c) transection of cerebellar connections to the lateral vestibular nucleus
(d) stimulation of α-motoneurons
(e) stimulation of γ-motoneurons
The answer is B [III E 3 a, b].
Decerebrate rigidity is caused by increased reflex muscle spindle activity. Stimulation of group Ia afferents would enhance, not diminish, this reflex activity. Cutting the dorsal roots would block the reflexes. Stimulation of α- and γ-motoneurons would stimulate muscles directly.
Which of the following parts of the body has cortical motoneurons with the largest representation on the primary motor cortex (area 4)?
(a) Shoulder
(b) Ankle
(c) Fingers
(d) Elbow
(e) Knee
The answer is C [II B 4].
Representation on the motor homunculus is greatest for those structures that are involved in the most complicated movements—the fingers, hands, and face.
