Neurophysiology
What structural factor of an axon significantly increases the conduction velocity of an action potential?
Myelin sheath
Which sensory pathway is the only one that relays directly to its primary cortex without passing through the thalamus first?
The Olfactory pathway (smell)
Which branch of the autonomic nervous system is known as the "rest and digest" system, and which major cranial nerve carries the majority of its preganglionic parasympathetic fibers?
The Parasympathetic division; carried primarily by Cranial Nerve X (Vagus nerve).
In a resting skeletal muscle sarcomere, what two structural proteins act as regulatory proteins to prevent myosin heads from forming a strong crossbridge with actin?
Troponin and Tropomyosin
In the sensory lab's two-point discrimination test, why do the fingertips have a much smaller threshold distance than the back of the hand or palm?
Fingertips have a high density of mechanoreceptors (Meissner's/Merkel's) with very small receptive fields, whereas the back of the hand has low receptor density and large primary neuron convergence.
If extracellular potassium [K+]out increases above normal levels (hyperkalemia), what happens to the resting membrane potential of a neuron, and how does this affect its likelihood of firing an action potential?
It depolarizes the resting membrane potential (moves Vm closer to threshold), making the neuron more excitable and prone to firing.
High-frequency (high-pitch) sound waves displace the basilar membrane near which structural region of the cochlea?
Near the stiff, narrow base of the basilar membrane (near the oval window).
What neurotransmitter is released by all preganglionic autonomic neurons, and which specific receptor type does it bind to on the postganglionic cell body?
Acetylcholine (ACh); binds to Nicotinic neuronal (NN) receptors.
What is the exact role of Ca2+ binding to Troponin C during skeletal muscle excitation-contraction coupling?
Ca2+ binding to Troponin C causes a conformational shift in tropomyosin, pulling it away to expose the myosin-binding sites on actin.
In the Rinne test, if a patient hears bone conduction longer than air conduction in their right ear, what type of hearing loss is indicated, and in which ear?
Conductive hearing loss in the right ear (affected ear).
During an action potential, why is it physically impossible for a second action potential to be initiated during the absolute refractory period regardless of stimulus strength?
Because voltage-gated Na+ channels are inactivated (inactivation gates are closed) and cannot re-open until the membrane repolarizes.
How does the brain distinguish between a weak sensory stimulus and a strong sensory stimulus if all action potentials are all-or-none and uniform in amplitude?
By action potential frequency (a higher frequency of APs indicates a stronger stimulus)
EC: population coding (recruiting a larger number of receptors)
Why is the adrenal medulla considered a modified sympathetic ganglion, and what chemical messengers does it release into the bloodstream?
It originates from modified postganglionic sympathetic tissue (chromaffin cells); upon preganglionic stimulation, it secretes Epinephrine (~80%) and Norepinephrine (~20%) directly into the blood.
Compare Slow-Oxidative (Type I) and Fast-Glycolytic (Type IIb/IIx) muscle fibers in terms of myosin ATPase speed, myoglobin content, and fatigue resistance.
Slow-Oxidative (Type I): Slow myosin ATPase, high myoglobin (red), highly fatigue-resistant.
Fast-Glycolytic (Type IIb): Fast myosin ATPase, low myoglobin (white), rapid fatigue.
What three hallmark physiological responses make up the mammalian dive reflex during cold face immersion, and which cranial nerve senses the cold water on the face?
Bradycardia (slowed HR), apnea (breath holding), and peripheral vasoconstriction; afferent signals carried via the Trigeminal nerve (CN V).
Explain how spatial summation differs from temporal summation at the trigger zone of a postsynaptic neuron
Spatial summation occurs when multiple separate presynaptic neurons release neurotransmitters simultaneously at different locations on the postsynaptic cell to combine their graded potentials.
Temporal summation occurs when a single presynaptic neuron fires in rapid succession, causing graded potentials to overlap over time at the same location.
What occurs during visual accommodation when focusing on a near object versus a distant object in terms of ciliary muscle contraction, zonular fiber (suspensory ligament) tension, and lens shape?
For near vision, the ciliary muscle contracts (sphincter-like), which releases tension on the zonular fibers and allows the lens to become thick/spherical (increasing light refraction).
For distant vision, the ciliary muscle relaxes, pulling the zonular fibers taut and flattening the lens.
What sequence of chemical and electrical events occurs at the motor endplate when an action potential reaches the axon terminal of a somatic motor neuron?
ACh released into synaptic cleft, binds to Nicotinic muscle (NM) receptors on motor endplate, leading to opening of ionotropic channels which causes net Na+ influx, which generates a depolarizing End-Plate Potential (EPP) that triggers muscle membrane action potentials.
Compare smooth muscle and skeletal muscle on two key structural and regulatory features: presence of sarcomeres/striations, and source(s) of Ca2+ for contraction.
Sarcomeres/Striations: Skeletal muscle contains striations/sarcomeres; smooth muscle lacks sarcomeres and is non-striated.
Ca2+ Source: Skeletal muscle relies almost entirely on sarcoplasmic reticulum (SR) Ca2+ release; smooth muscle uses both extracellular Ca2+ influx across the sarcolemma and SR Ca2+ release
During Phase II (forced exhalation against resistance) of the Valsalva maneuver, why does heart rate initially rise?
High intrathoracic pressure impedes venous return to the heart, which leads to stroke volume and blood pressure fall, which leads to reduced baroreceptor stretch triggers parasympathetic withdrawal and increased sympathetic drive to increase heart rate.
An action potential travels down a myelinated axon via saltatory conduction. What happens at the nodes of Ranvier versus the internodes (i.e., area of axon in between the nodes) in terms of ion channel density and current flow?
Nodes of Ranvier: high concentration of voltage-gated Na+ channels generating full action potentials
Internodes: (under myelin), current flows rapidly and passively via electrotonic diffusion without ion flux across the membrane.
How do the otolith organs (utricle/saccule) and the semicircular canals differ in the type of acceleration they detect, and what structures inside them move to bend the hair cell stereocilia?
Otolith Organs: Sense linear acceleration and head tilt; heavy otoliths (calcium carbonate crystals) shift a gelatinous otolithic membrane over hair cells
Semicircular Canals: Sense rotational acceleration; endolymph fluid movement pushes against the flexible gel cupula inside the ampulla to bend hair cells.
Why can the same autonomic neurotransmitter (such as Norepinephrine) cause vasoconstriction in smooth muscle of digestive organs but vasodilation in smooth muscle of skeletal muscle arterioles?
Because the target tissues express different receptor isoforms/subtypes. Binding to alpha-1 adrenergic receptors on digestive blood vessels causes vasoconstriction, while binding to beta-2 adrenergic receptors on skeletal muscle arterioles causes vasodilation.
Compare the Muscle Spindle and the Golgi Tendon Organ (GTO) in terms of what stimulus each monitors (length vs. tension), and how each responds reflexively to protect or regulate the muscle.
Muscle Spindle: Monitors muscle length and rate of stretch. Reflexively causes contraction of the stretched muscle (via the monosynaptic stretch reflex) to maintain resting muscle length/tone and prevent overstretching.
Golgi Tendon Organ (GTO): Monitors muscle tension/force. Reflexively causes relaxation of the contracting muscle (via polysynaptic inhibition of alpha motor neurons) to protect the tendon and muscle from excessive tension damage.
In the patellar tendon reflex, describe the exact reflex arc pathway starting from the stimulus tap to the leg extension response, including whether interneurons are involved in the contraction of the agonist muscle.
Tap on patellar tendon stretches quadriceps
Muscle spindle detected stretch
Sensory (afferent) neuron fires to spinal cord
Monosynaptic direct connection to Alpha motor neuron in ventral horn
Efferent signal contracts Quadriceps (no interneurons involved in the excitatory pathway).