Human Physiology: Reflexes, Cutaneous Sensations, Vision, Hearing, and Taste

50 vocabulary flashcards reviewing key concepts, anatomical structures, and diagnostic tests covered in human physiology sensory lab exercises.

Monosynaptic reflex

A simple reflex requiring only one synapse between the sensory neuron and the motor neuron in the central nervous system.

Alpha motoneuron

A motor neuron located within the central gray matter of the spinal cord that receives input from a sensory axon and leaves via the ventral root to innervate extrafusal muscle fibers.

Crossed-extensor reflex

A complex reflex in which sensory impulses cause ipsilateral flexor contraction and contralateral extensor contraction while inhibiting antagonistic muscles.

Muscle spindles

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

Intrafusal fibers

Specialized thin muscle fibers contained within muscle spindles that respond to stretch by depolarizing sensory neurons.

Extrafusal fibers

Normal muscle cells arranged in parallel with intrafusal fibers that contract when stimulated by alpha motoneurons.

Plantar reflex

A cutaneous reflex elicited by stimulation of the sole of the foot, normally causing downward flexion of the great toe and other toes.

Babinski's sign

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

Pyramidal motor tracts

Motor pathways that descend directly from the cerebral cortex to lower motor neurons in the spinal cord.

Punctate distribution

The spatial arrangement of cutaneous sensory receptors clustered at specific, discrete points on the skin surface.

Free nerve endings

Cutaneous receptors formed by unmyelinated dendrites around hair follicles and throughout the skin that mediate light touch, hot, cold, and pain.

Merkel's discs

Cutaneous receptors consisting of expanded dendritic endings associated with $50\text{--}70$ specialized cells at the base of the epidermis that detect sustained touch and indented depth.

Ruffini corpuscles

Cutaneous receptors deep in the dermis and hypodermis featuring enlarged dendritic endings within open, elongated capsules that sense skin stretch.

Meissner's corpuscles

Cutaneous receptors in the papillary layer of the upper dermis encapsulated in connective tissue that respond to texture changes and slow vibrations.

Pacinian corpuscles

Cutaneous receptors deep in the dermis encapsulated by concentric lamellae of connective tissue that detect deep pressure and fast vibrations.

Two-point touch threshold

The minimum distance at which two simultaneous points of contact on the skin can be felt as separate points.

Sensory adaptation

The phenomenon in which sense receptors respond strongly to acute environmental changes and then stop responding when stimuli remain constant.

Referred pain

Pain resulting from damage in a visceral organ or nerve trauma that is perceived at a different somatic location toward the body surface.

Phantom limb phenomenon

A condition in which amputees feel pain in a missing limb due to trauma of cut nerve fibers that originally conducted impulses from that region.

Iris

A colored muscular diaphragm in the anterior cavity of the eye that regulates light entry through the pupil.

Vitreous humor

A semi-gelatinous body occupying the posterior chamber that lends structural support to the eye.

Diopter

The unit expressing the refractive power of a lens, calculated as $\text{Strength (diopters)} = \frac{1}{\text{focal length (meters)}}$.

Emmetropia

Normal visual acuity where parallel light rays from an object $20\,\text{feet}$ or more away are focused directly on the retina.

Myopia

Nearsightedness, a refractive condition usually caused by an elongated eyeball where distant light rays focus in front of the retina.

Hyperopia

Farsightedness, a refractive condition usually caused by an eyeball that is too short, focusing images behind the retina.

Astigmatism

A visual defect produced by an abnormal curvature or irregularity of the cornea or lens, causing uneven refraction in different planes.

Cataracts

Cloudy patches in the visual field caused by damage from UV light, dehydration, or oxidation that changes the shape and causes aggregation of crystallin proteins in the lens.

LASIK

Laser-assisted in situ keratomileusis; a surgical procedure using a computer-guided laser to alter corneal curvature and correct refractive errors.

Accommodation

The ability of the eye to focus images of objects at varying distances onto the retina by changing lens convexity via ciliary muscle contraction.

Presbyopia

An age-related condition characterized by loss of lens elasticity and reduced capability to assume high convexity for near vision.

Near point of vision

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

Glaucoma

A disease involving loss of retinal ganglion cell axons in the optic nerve, frequently associated with elevated intraocular pressure from inadequate aqueous humor drainage.

Fovea centralis

A central pit within the macula lutea containing a high concentration of cone photoreceptors that provides maximum visual acuity.

Retinal disparity

The difference in image position between the two eyes that aids in three-dimensional vision and depth perception.

Nystagmus

Involuntary, oscillatory movement of the eyes consisting of a slow drift phase in one direction followed by a rapid movement back.

Optic disc

The region on the retina where ganglion cell axons gather to form the optic nerve, lacking photoreceptors and producing the blind spot.

Rhodopsin

The visual pigment in rod photoreceptors that dissociates into retinene and opsin when exposed to light.

Young-Helmholtz theory

The theory of color vision stating that three cone systems (blue, green, and red) mediate color perception through brain interpretation of their combined input.

S cones

Short-wavelength cone photoreceptors (blue cones) containing photopsin protein with maximal light absorption at shorter wavelengths.

M cones

Medium-wavelength cone photoreceptors (green cones) containing photopsin protein with maximal light absorption in the medium-wavelength range.

L cones

Long-wavelength cone photoreceptors (red cones) containing photopsin protein with maximal light absorption at longer wavelengths.

Gustducin

G-proteins coupled to membrane receptors in sweet, bitter, and umami taste cells that dissociate to activate second-messenger pathways during taste depolarization.

Basilar membrane

A flexible membrane in the cochlea that vibrates in response to fluid waves and carries the sensory hair cells of the organ of Corti.

Conduction deafness

Hearing loss caused by impaired transmission of sound waves through the outer or middle ear to the oval window.

Sensory deafness

Hearing loss resulting from damage to the sensory hair cells of the cochlea or the vestibulocochlear nerve.

Cupula

A gelatinous structure projecting into endolymph within semicircular canal ampullae that bends during fluid movement to stimulate hair cells.

Otitis media

An infection of the middle ear that can lead to conductive hearing loss.

Tinnitus

A sensation described as ringing in the ears, often serving as an early symptom of inner-ear disorders like Ménière's disease.

Vertigo

An illusion of movement or spinning caused by activation or dysfunction of the vestibular apparatus.

Umami

A category of taste perception producing a savory or meaty flavor triggered by the amino acid glutamate binding to G-protein-coupled receptors.