Costanzo | Physiology | Chapter 3 | Neurophysiology | Study Guide
I. Organization of the Nervous System
Divisions: The nervous system consists of the central nervous system (CNS) (brain and spinal cord) and the peripheral nervous system (PNS) (sensory receptors and nerves outside the CNS).
CNS Components:
Spinal Cord: Most caudal part, containing 31 pairs of spinal nerves.
Brain Stem: Includes the medulla (autonomic centers), pons (balance and posture), and midbrain (eye movements).
Cerebellum: Coordinates movement, planning, and execution.
Diencephalon: Contains the thalamus (relay center) and hypothalamus (body temperature, hunger, thirst, and endocrine control).
Cerebral Hemispheres: Includes the cerebral cortex (higher functions), basal ganglia (movement control), and hippocampus/amygdala (memory and emotion).
II. General Features of Sensory and Motor Systems
Synaptic Relays: Relay nuclei integrate converging information, particularly in the thalamus.
Decussations: Most pathways are bilaterally symmetric and cross the midline (contralateral).
Nerve Fiber Classification:
Erlanger and Gasser system: Uses letters A (alpha, beta, gamma, delta), B, and C [201, 204t].
Lloyd and Hunt system: Applies to sensory fibers using Roman numerals I (a, b), II, III, and IV [201, 205t].
Velocity: Conduction velocity increases with fiber diameter and myelination.
III. Sensory Systems and Receptors
Sensory Transduction: Process of converting environmental stimuli into electrical energy (receptor potential).
Types of Receptors:
Mechanoreceptors: Pressure/changes in pressure (e.g., Pacinian corpuscles, hair cells) [209, 212t].
Photoreceptors: Light (rods and cones) [209, 212t].
Chemoreceptors: Chemicals (olfaction, taste, O2, CO2) [209, 212t].
Thermoreceptors: Temperature [209, 213t].
Nociceptors: Pain or noxious stimuli [209, 213t].
Adaptation: Phasic receptors adapt rapidly (e.g., vibration); tonic receptors adapt slowly (e.g., steady pressure).
IV. Somatosensory System and Pain
Dorsal Column System: Carries fine touch, pressure, vibration, and proprioception; crosses the midline in the brain stem.
Anterolateral System: Carries pain, temperature, and light touch; crosses the midline in the spinal cord.
Pain: Fast pain (precisely localized) is carried by A delta fibers; slow pain (aching/burning) is carried by C fibers.
V. Vision
Photoreceptors: Rods have low thresholds and are sensitive to low light (night vision); cones have high thresholds and provide color/acuity (day vision) [238, 241t].
Transduction Steps: Light → photoisomerization of rhodopsin → activation of transducin → stimulation of phosphodiesterase → decreased cyclic GMP → closure of Na+ channels → hyperpolarization of the receptor.
Optic Lesions: Cutting an optic nerve causes ipsilateral blindness; cutting the optic chiasm causes bitemporal hemianopia [258, 259, 263f].
VI. Audition and Vestibular Systems
Audition: Sound waves bend hair cells in the Organ of Corti. High frequencies are detected at the stiff base of the basilar membrane; low frequencies at the compliant apex.
Vestibular Organ: Consists of semicircular canals (angular acceleration) and otolith organs (utricle and saccule for linear acceleration).
VII. Olfaction and Taste
Olfaction: Odorants bind to receptors coupled to Golf and adenylyl cyclase, increasing cAMP to open cation channels.
Taste: Five qualities—salty, sweet, sour, bitter, and umami.
VIII. Motor Systems and Reflexes
Muscle Spindle: Stretch receptors correcting changes in muscle length.
Reflexes:
Stretch Reflex: Monosynaptic (e.g., knee jerk); contraction of the same muscle [295, 296f].
Golgi Tendon Reflex: Disynaptic; relaxation of the same muscle.
Flexor-Withdrawal Reflex: Polysynaptic; flexion on the ipsilateral side and extension on the contralateral side.
Movement Control: Basal ganglia influence the motor cortex via direct (excitatory) and indirect (inhibitory) pathways.
IX. Higher Functions and CSF
EEG: Records alternating synaptic potentials; alpha waves (eyes closed), beta waves (eyes open).
Sleep: REM (paradoxical) sleep shows an EEG similar to being awake.
CSF: Formed by the choroid plexus at 500 mL/day.
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Chapter 3 Study Guide
I. Glossary of Key Terms
Across-fiber pattern code: A coding system where each fiber responds to many stimuli but has a preferred one.
Ageusia: Absence of taste.
Alpha rhythm: EEG waves (8–13 Hz) seen in an awake adult with eyes closed.
Cochlear microphonic: Oscillating receptor potential of auditory hair cells.
Hemianopia: Loss of vision in half the visual field of one or both eyes.
Hypermetropia: Farsightedness.
Nystagmus: Rhythmic eye movements caused by vestibular stimulation.
Receptor potential: A graded potential in a sensory receptor caused by transduction.
Synergy: Coordination of the rate, range, force, and direction of movement.
Tonotopic map: Spatial mapping of sound frequencies along the basilar membrane.
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II. 50 Question-and-Answer Quiz
What does the CNS include? Brain and spinal cord.
How many pairs of spinal nerves exist? 31 pairs.
What is the function of the medulla? Autonomic regulation of breathing and blood pressure.
Which part of the brain coordinates posture? Pons and cerebellum.
Where is the relay center for sensory information? Thalamus.
What is the "between brain"? Diencephalon.
What does the amygdala control? Emotions and ANS communication.
What is a decussation? A site where pathways cross to the contralateral side.
Which fibers are the largest and fastest? A alpha (Aα) [204t].
What is sensory transduction? Converting a stimulus into electrical energy.
Which receptor type detects light? Photoreceptors.
Which receptor detects vibration? Pacinian corpuscle [226, 227t].
What define an area of the body that changes a neuron's firing rate? Receptive field.
What is lateral inhibition? Pattern of inhibitory fields aiding stimulus localization [222, 223f].
What is a phasic receptor? A rapidly adapting receptor [224, 225f].
Which pathway carries fine touch? Dorsal column system.
Where does the anterolateral system cross? Spinal cord.
Which fibers carry fast pain? A delta fibers.
What wavelength range is visible light? 400 to 750 nanometers.
Where is visual acuity highest? Fovea.
What is the blind spot? Optic disc.
Which photoreceptors are for color vision? Cones.
What is the photosensitive pigment in vision? Rhodopsin.
What G protein is involved in vision? Transducin.
What happens to Na+ channels in light? They close.
What is the effect of light on photoreceptors? Hyperpolarization.
What is bitemporal hemianopia? Loss of both temporal visual fields.
What unit measures sound pressure? Decibels.
Which fluid has high K+ in the ear? Endolymph.
Where are auditory hair cells located? Organ of Corti.
Which membrane separates the scala media from scala tympani? Basilar membrane.
Where are high frequencies detected? Base of basilar membrane.
What does the saccule detect? Linear acceleration in all directions.
What are the otolith organs? Utricle and saccule.
What provides neurogenesis in the olfactory system? Basal cells.
What G protein is used in olfaction? Golf.
What are the five taste qualities? Salty, sweet, sour, bitter, umami.
Which papillae are largest but fewest? Circumvallate.
What are extrafusal muscle fibers? Fibers that make up the bulk of muscle.
Which reflex is monosynaptic? Stretch reflex.
What senses muscle contraction/shortening? Golgi tendon organ.
What is the clasp-knife reflex? Abnormal exaggerated Golgi tendon reflex.
What is the result of a flexor-withdrawal reflex? Ipsilateral flexion, contralateral extension.
What is synergy? Coordination of movement parameters.
What are Purkinje cells? Output cells of the cerebellar cortex.
What is the overall output of the direct basal ganglia pathway? Excitatory.
What does an EEG record? Alternating synaptic potentials.
When are delta waves seen? Stage 3 and 4 sleep.
Where is CSF formed? Choroid plexus.
What is the rate of CSF formation? 500 mL/day.
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III. Short Answer Questions
Describe the difference between first-, second-, and third-order sensory neurons.
Answer: First-order neurons are primary afferents closest to the receptor; second-order neurons are in relay nuclei (usually crossing the midline); third-order neurons are typically in the thalamus.
How does the basilar membrane act as a frequency analyzer?
Answer: Its physical properties change from the base (stiff/narrow) to the apex (compliant/wide), allowing different regions to vibrate at specific frequencies.
Explain "diffusion trapping" in the olfactory system.
Answer: This term is not explicitly defined for olfaction in the source; however, in a renal context, it refers to NH3 combining with H+ to become NH4+. For olfaction, the text focuses on odor maps generated across receptors.
What are the three components of the "triple response" in skin?
Answer: Red line, red flare, and a wheal (local edema).
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IV. Essay Questions
Compare and contrast the dorsal column and anterolateral somatosensory systems.
Focus: Discuss types of sensations carried, fiber types (A beta vs. A delta/C), and specifically where each system decussates (medulla vs. spinal cord).
Describe the step-wise sequence of events in visual transduction.
Focus: Start with light striking the retina, photoisomerization of retinal, the role of transducin, the decrease in cyclic GMP, the closure of Na+ channels, and the resulting hyperpolarization.
Explain the direct and indirect pathways of the basal ganglia.
Focus: Outline the structures involved (striatum, globus pallidus segments, thalamus) and how the net effect of the direct pathway is excitation while the indirect is inhibitory [306-307, 307f].
