Action Systems, Sensation, and Perception (Umwelt)

Comprehensive practice flashcards covering motor systems, elementary action units, sensory Umwelten, olfaction, gustation, audition, and visual processing based on lecture transcripts and accompanying figures.

Reflex

An elementary unit of action characterized as a fixed response to a stimulus; it operates at a moderately fast speed ($50\,\text{msec}$ to $250\,\text{msec}$) and is simple to program, but has rigid stimulus-response links vulnerable to disruption.

Oscillator

An elementary unit of programmed movement generated centrally by pacemaker neurons or circuits of normal neurons firing cyclic bursts, producing rhythmic actions such as walking, running, or swallowing.

Servomechanism

A goal-directed behavioral unit operating in three steps: receiving sensory input, comparing it to an internally set goal value, and correcting discrepancies via negative feedback until the goal is matched.

Moth Phototaxis

A servomechanism behavior where the eye-wing stroke circuit strives to equate light stimulation across both eyes, maximize stimulation, and turn the dorsal body surface toward light, causing the moth to become trapped in circles around a light source.

Reflex Chain

A combination of within-category reflexes where the response of one reflex becomes the sensory stimulus for the next, exemplified by the four-step courtship sequence in Dutch Cabbage Butterflies.

Fixed Action Pattern (FAP)

A programmed oscillator combination triggered by an innate releaser that, once initiated, proceeds through its entire motor sequence without requiring continued sensory guidance.

Hierarchical Organization of Action

A neural organization principle where semi-autonomous lower motor units carry out specific programs while higher brain units govern them through potentiation and descending inhibition.

Praying Mantis Copulation Disinhibition

A hierarchical action mechanism in Mantis religiosa where the head continuously inhibits an autonomous copulatory FAP housed in the thorax; decapitation by the female removes descending inhibition and releases copulation.

Lordosis Reflex Hierarchy

A sexually receptive posture reflex autonomously located in the spinal cord that is hierarchically inhibited by descending pathways; estrogen acts on the hypothalamus to release descending inhibition when tactile stimulation occurs.

Neuromuscular Junction

The synapse between an alpha motor neuron axon terminal and a muscle fiber where acetylcholine binds to ionotropic receptors, causing $\text{Na}^+$ influx, depolarization, intracellular $\text{Ca}^{2+}$ release, and contraction, ended by acetylcholinesterase.

Alpha Motor Neurons

Neurons projecting from the spinal ventral horn directly to muscle fibers to initiate and execute muscle contractions.

Gamma Motor Neurons

Motor neurons that project to muscle spindles to regulate and maintain tension within the muscle spindle.

Pyramidal Motor System

The direct motor pathway originating in the primary motor cortex (MI) that projects via the internal capsule, cerebral peduncles, and medullary pyramids, decussating to innervate spinal motor neurons controlling fine hand and finger movements.

Secondary Motor Cortex (MII)

Cortical area (also known as the supplementary motor cortex) active prior to movement initiation; responsible for planning, rehearsing, and timing actions, and whose electrical stimulation produces an urge to move.

Premotor Cortex

Frontal cortical region containing mirror neurons that fire both when performing a motor action and when observing another perform it; damage disrupts sensory-triggered movements.

Posterior Parietal Cortex

Parietal area providing spatial representation for action; stimulation elicits an urge to move or the illusion of having moved, while right unilateral lesions produce hemi-spatial neglect.

Hemi-Spatial Neglect

A cognitive impairment typically caused by right parietal stroke where the patient neglects the left side of space, body care, and internal mental imagery of scenes.

Red Nucleus

An extrapyramidal midbrain structure that provides auxiliary voluntary control over hand movements, acting synergistically with the pyramidal tract such that voluntary grasping is lost only when both systems are lesioned.

Reticular Formation

An extrapyramidal brainstem network functioning as an oscillator pattern generator for innate actions (smiling, crying, swallowing), a postural vestibulomotor servomechanism, and an intermediary for voluntary gestures.

Locked-In Syndrome

A condition resulting from ventral brainstem damage (such as ventral pons and medullary pyramids) that abolishes all descending voluntary movement except vertical eye movements or blinks, leaving cognition intact.

Striatal $D_1$ Dopamine Receptor

A dopamine receptor coupled to an excitatory $G_s$ protein that increases $\text{cAMP}$, forming the direct 'Go' pathway projecting straight back to the substantia nigra.

Striatal $D_2$ Dopamine Receptor

A dopamine receptor coupled to an inhibitory $G_i$ protein that decreases $\text{cAMP}$, forming the indirect 'Stop' pathway projecting via the globus pallidus before returning to the midbrain and cortex.

Parkinson's Disease

A movement disorder caused by the loss of substantia nigra dopamine neurons, producing resting tremor, shuffling gait, apraxia, an overactive indirect pathway, and an underactive direct pathway.

Huntington's Disease

A monogenic dominant disorder on chromosome 4 caused by $>30\text{--}38$ CAG repeats producing huntingtin protein with polyglutamine expansions, leading to striatal neuron degeneration and dance-like chorea movements.

Cerebellar Purkinje Cells

The outer cortical neurons of the cerebellum that send inhibitory projections to the deep cerebellar nuclei, which in turn send excitatory projections to the brain and spinal cord.

Umwelt

The species-specific perceptual world constructed differently by each organism according to its receptor screening, salience maps, and pattern impositions.

Noumena vs. Phenomena

Philosophical distinction introduced by Immanuel Kant where phenomena represents the world as perceived and constructed by an organism's senses, whereas noumena represents the actual world as it is.

Law of Specific Nerve Energies

The principle of labeled-line sensory coding stating that each sensory nerve line produces only one specific type of sensation regardless of how it is stimulated.

Cortical Homunculus

A distorted topographical map of the body in somatosensory (S1) and motor (M1) cortices, where cortical surface area is proportional to tactile sensitivity and motor precision rather than anatomical size.

Species' Cortical Maps

Topographic representations that selectively expand to reflect species-specific behavioral specializations, such as hands in humans, facial vibrissae barrels in rats, or star-like nasal rays in star-nosed moles.

Olfactory Transduction

The biochemical process where odorant binding to a G-protein-coupled receptor on an olfactory neuron opens $\text{Ca}^{2+}$ and $\text{Na}^+$ channels via second messengers, generating depolarizing EPSPs and action potentials.

Olfactory Glomerulus

A spherical synaptic structure in the olfactory bulb where axon terminals from olfactory sensory neurons expressing the same single receptor type converge onto dendrites of mitral, tufted, and periglomerular cells.

Vomeronasal Organ (VNO)

A specialized chemosensory organ found in the upper palate of many non-human mammals that projects to the accessory olfactory bulb to detect social pheromones.

Gustatory Receptor Cells

Cells bundled in taste buds on tongue papillae that detect five primary taste qualities: $\text{Na}^+$ for salt, $\text{H}^+$ for sour, and G-protein coupled receptors for sweet, bitter, and umami.

Supertaster

An individual possessing up to $400\%$ more fungiform papillae on their tongue who experiences intense bitterness when tasting 6-n-propylthiouracil (PROP).

Dysgeusia

A distortion of the sense of taste caused by medications, radiation, infections, or cancer treatment, often resulting in severe unintended weight loss.

Lateral Line Organ

An ancestral aquatic mechanoreceptor organ in fish consisting of hair cells that detect water pressure vibrations ($1\text{--}3\,\text{Hz}$), which served as the evolutionary precursor to vertebrate audition and vestibular systems.

Basilar Membrane

The tonotopically organized cochlear membrane that is narrow and stiff at the base to detect high frequencies (up to $20{,}000\,\text{Hz}$) and wide and floppy at the apex to detect low frequencies (down to $10\text{--}20\,\text{Hz}$).

Cochlear Prosthesis

An implanted auditory device that uses an external microphone and processor to deliver electrical place- and frequency-coded signals directly to auditory nerve fibers via an electrode array threaded into the cochlea.

Superior Olivary Nucleus

A medullary auditory nucleus receiving bilateral cochlear inputs that calculates sound localization using interaural relative amplitude differences for high frequencies and interaural time/phase disparities for low frequencies.

A1 Auditory Neuron (Noctuid Moth)

A low-threshold, sensitive auditory neuron in noctuid moths showing a graded response of action potentials to bat echolocation calls ($20\text{--}200\,\text{kHz}$), driving a left-right servomechanism for negative phonotaxis (flying away).

A2 Auditory Neuron (Noctuid Moth)

A high-threshold, all-or-none auditory neuron in noctuid moths that fires only when a bat is within $10\,\text{feet}$, triggering an emergency 'dive-and-flip' escape reflex while simultaneously inhibiting the A1 servomechanism.

Bullfrog Mate Call Recognition

A midbrain auditory feature extraction mechanism in Rana catesbeiana requiring sound energy simultaneously at $300\,\text{Hz}$ and $1500\,\text{Hz}$, with an absence of middle frequency energy that would otherwise activate inhibitory curves.

Characteristic Frequency (Best Frequency)

The specific acoustic frequency to which an individual auditory neuron responds most strongly at the lowest sound intensity threshold.

Rods

Photoreceptors specialized for dim light (scotopic vision) with a peak absorbance near $500\,\text{nm}$; numbering about $120\,\text{million}$ ($95\%$) per human eye and showing high convergence onto ganglion cells.

Cones

Photoreceptors clustered primarily in the fovea numbering about $6\,\text{million}$ ($5\%$) in humans, providing high-resolution photopic vision and color perception through a $1:1$ ratio connection with ganglion cells.

Photoreceptor Transduction

The retinal mechanism where photons cleave rhodopsin into retinal and opsin, closing $\text{Na}^+$ channels, hyperpolarizing the photoreceptor, and stopping glutamate release to disinhibit or excite downstream bipolar cells.

Human Cone Wavelength Peaks

The three spectral absorption peaks of human cone photopigments: Short (Blue) at $437\,\text{nm}$, Medium (Green) at $533\,\text{nm}$, and Long (Red) at $564\,\text{nm}$.

Honeybee Color Vision

A trichromatic visual system shifted toward shorter wavelengths ($300\text{--}650\,\text{nm}$) that detects ultraviolet patterns ($350\text{--}400\,\text{nm}$), fuses green and yellow, and is blind to red wavelengths above $590\,\text{nm}$.

Deuteranopia

Red-green color blindness resulting from the fusion or absence of differentiation between medium-wave (green) and long-wave (red) cone photopigments.

Opponent Process Theory

Hering's color coding theory stating that downstream visual neurons process color via antagonistic pairs (Blue vs. Yellow, Red vs. Green, White vs. Dark), producing color rebounds and afterimages via disinhibition.

Lateral Inhibition

Retinal processing where stimulated ganglion cells inhibit neighboring cells proportionally (e.g., $25\%$ of their own excitation) via horizontal and amacrine cells, sharpening edge contrasts and creating Mach band illusions.

On-Center Off-Surround Receptive Field

A circular receptive field organization where illumination in the center excites the neuron while illumination falling in the concentric surround inhibits firing.

Parvocellular Ganglion Cells (X Cells)

Small retinal ganglion cells concentrated in the fovea that receive cone inputs to process fine spatial detail, high acuity, and color vision.

Magnocellular Ganglion Cells (Y Cells)

Large retinal ganglion cells concentrated in the peripheral retina that pool signals from multiple rods, specialized for detecting motion, flicker, and dim light with low spatial resolution.

Lateral Geniculate Nucleus (LGN)

A six-layered thalamic nucleus where layers 1 and 2 are magnocellular and layers 3 through 6 are parvocellular, with layers 1, 4, and 6 receiving contralateral nasal retina inputs and layers 2, 3, and 5 receiving ipsilateral temporal inputs.

Dorsal Visual Stream

The 'Where' visual pathway projecting from V1 through V5/MST into the parietal cortex, dominated by magnocellular input and specialized for motion and spatial relationships.

Ventral Visual Stream

The 'What' visual pathway projecting from V1 through V4 into the inferior temporal cortex, dominated by parvocellular input and specialized for shape, color, and object identification.

V1 Simple Cells

Primary visual cortex neurons in Area 17 with bar-shaped receptive fields with distinct antagonistic on/off subregions, created by the aligned convergence of multiple center-surround LGN inputs.

V1 Complex Cells

Area 17 neurons with larger bar-shaped receptive fields lacking fixed inhibitory zones, requiring a properly oriented bar of light anywhere in the field and frequently sensitive to the direction of motion or illusory contours.

Hypercomplex Cells (End-Stopped Cells)

Visual neurons located in Area 18 (V2) that respond best to oriented bars or corners of a specific length, exhibiting strong inhibition when a bar extends beyond their receptive field boundary.

Prosopagnosia

A selective visual agnosia resulting from damage to the fusiform face area in the inferior temporal cortex, rendering an individual unable to recognize familiar faces while voice recognition remains intact.

Blindsight

The ability of individuals with complete destruction of primary visual cortex (Area 17/V1) to navigate obstacles or correctly guess visual locations above chance despite lacking conscious visual perception, mediated by subcortical pathways via the superior colliculus.

Critical Period in Visual Development

A developmental window (the first $3\,\text{months}$ in kittens, up to $5\,\text{years}$ in humans) during which abnormal visual experience like monocular deprivation or strabismus causes permanent, irreversible reorganization of cortical columns and synaptic connectivity via synaptic cell adhesion molecules (CAMs).