Human Physiology: Reflex Arc, Sensory Systems, Optics, Hearing, and Balance Flashcards

Comprehensive vocabulary flashcards generated directly from the lab transcript, covering reflex arcs, cutaneous sensation, vision optics, auditory pathways, vestibular mechanics, and taste modalities.

Monosynaptic reflex

A simple reflex arc requiring only one synapse between the sensory and motor neurons, such as the knee-jerk or patellar reflex.

Alpha motoneuron

A motor neuron located within the central gray matter of the spinal cord that receives input from sensory neurons and directly innervates extrafusal muscle fibers.

Crossed-extensor reflex

A complex reflex that produces contraction of ipsilateral flexor muscles and contralateral extensor muscles while inhibiting antagonistic muscles.

Muscle spindles

Stretch receptors embedded within the connective tissue of skeletal muscle consisting of specialized thin intrafusal fibers innervated by sensory neurons.

Intrafusal fibers

Specialized thin muscle fibers inside muscle spindles arranged in parallel with extrafusal fibers that depolarize sensory neurons upon stretch.

Extrafusal fibers

Normal skeletal muscle cells innervated by alpha motoneurons that contract to shorten the muscle and reduce tension on intrafusal fibers.

Plantar reflex

A cutaneous reflex elicited by stimulating the sole of the foot, normally resulting in flexion of the toes through uninterrupted conduction along pyramidal motor tracts.

Babinski's sign

An abnormal cutaneous reflex response to foot sole stimulation where the great toe extends upward and other toes fan laterally, indicating damage to pyramidal motor tracts.

Punctate distribution

The discrete spatial clustering of sensory receptors at distinct points on the skin rather than a continuous or uniform distribution.

Two-point threshold

The minimum distance between two points of contact on the skin at which they are perceived as two separate touch sensations.

Sensory adaptation

The sensory phenomenon in which receptors respond intensely to acute environmental changes and then diminish or cease responding when stimuli remain constant.

Referred pain

Pain originating from visceral organ damage or trauma that is wrongly perceived as coming from a distant somatic location on the body surface.

Emmetropia

Normal visual acuity in which parallel rays of light coming from distant objects focus directly on the retina.

Myopia

A refractive error (nearsightedness) where image focus occurs in front of the retina due to an elongated eyeball, corrected using concave lenses.

Hyperopia

A refractive condition (farsightedness) where image focus falls behind the retina due to an eyeball that is too short, corrected using convex lenses.

Astigmatism

A visual refraction defect caused by irregular curvature of the cornea or lens, resulting in unequal refraction along different geometric planes.

Accommodation

The functional mechanism by which the eye alters lens convexity and refractive power via ciliary muscle contraction to keep objects at varying distances focused on the retina.

Presbyopia

Age-related decline in lens elasticity and convex accommodation ('old eyes'), leading to an increased distance for the near point of vision.

Near point of vision

The closest distance an object can be brought to the eye while still maintaining sharp visual acuity.

Nystagmus

Involuntary oscillatory movements of the eyes featuring a slow drift phase in one direction followed by a rapid corrective recovery phase.

Optic disc

The exact location on the retina where ganglion cell axons gather to form the optic nerve; also called the blind spot due to the absence of photoreceptors.

Macula lutea

A yellow-pigmented region of the retina surrounding the fovea centralis that houses a dense population of cone photoreceptors.

Fovea centralis

A tiny central depression in the macula lutea composed entirely of cones that provides maximum visual acuity.

Rhodopsin

The primary photochemical pigment in rod photoreceptors that dissociates into retinene and opsin upon absorption of light.

Conduction deafness

Hearing loss caused by mechanical damage or physical blockage in the outer or middle ear structures (such as ossicle damage or otitis media) impeding sound conduction.

Sensory deafness

Hearing loss resulting from inner ear cellular damage to the cochlea or lesions of the vestibulocochlear nerve (eighth cranial nerve).

Vestibular apparatus

The inner ear system composed of the semicircular canals, utricle, and saccule responsible for equilibrium and sensing body acceleration/position.

Cupula

A gelatinous sail-like structure inside the ampulla of semicircular canals containing hair cell processes that bends when endolymph moves.

Vertigo

An illusory sensation of rotational movement or spinning resulting from abnormal stimulation or disorders of the vestibular system.

Gustducin

A specialized family of G-proteins linked to taste cell membrane receptors that mediate second-messenger signaling for sweet, bitter, and umami sensations.