Chapter 16 Sense Organs - Flashcards (Question and Answer)

A comprehensive set of Q&A flashcards covering receptors, senses, and the neural pathways for taste, smell, hearing, balance, and vision from Chapter 16.

What is a receptor?

A structure that detects a stimulus, such as bare nerve endings or sense organs.

What is a sense organ?

A structure combining nerve tissue with other tissues to improve stimulus response.

What is transduction in sensory physiology?

Converting stimulus energy into nerve signals; includes sensation (detecting) and perception (interpreting).

What four kinds of information do sensory receptors transmit?

Modality, location, intensity, and duration.

What determines the modality of a sensory signal?

The specific brain region wired to receive that information.

What is a receptive field?

The area a sensory neuron detects stimuli within; smaller fields (e.g., fingertips) mean higher precision.

How is stimulus intensity encoded by receptors?

By which fibers respond, how many fibers respond, and how often they fire.

How is stimulus duration encoded, and what is sensory adaptation?

by how long and how fast fibers fire; adaptation is a diminished response to prolonged stimulus. Phasic receptors respond initially then fade; tonic receptors maintain activity.

Name the five classifications of receptors by stimulus modality.

Thermoreceptors, photoreceptors, nociceptors, chemoreceptors, mechanoreceptors.

Name the receptor classifications by origin of stimuli.

Exteroceptors (external), interoceptors (internal), and proprioceptors (body position).

What is meant by general versus special senses in receptor distribution?

widespread (touch, temperature, pain);

or senses only in the head (vision, hearing, taste, smell, balance).

What are unencapsulated nerve endings?

Dendrites without connective tissue, like free nerve endings (temp/pain), tactile discs, and hair receptors.

What are encapsulated nerve endings?

Nerve fibers wrapped in glial cells or connective tissue, e.g., Meissner’s, Krause, Ruffini, and Pacinian corpuscles.

Describe the somatosensory three-neuron pathway.

1. Receptor to brainstem/spinal cord. 2. Crosses over, ends in thalamus (except proprioception to cerebellum). 3. Thalamus to primary somesthetic cortex.

What are nociceptors?

Receptors that detect tissue injury and cause pain.

Name the three origins of nociceptive pain.

Visceral pain, deep somatic pain, and superficial somatic pain.

What are A-delta and C fibers in pain transmission?

A-delta fibers carry fast, sharp pain (myelinated); C fibers carry dull, aching pain (unmyelinated).

Which pathways carry pain signals to the brain?

Spinothalamic tract (conscious pain), spinoreticular tract (to reticular formation/limbic system), and gracile fasciculus (visceral pain).

What is referred pain?

Pain felt in a different location than its source, due to converging neural pathways.

What are endogenous opioids and where are they produced?

Pain-blocking peptides (enkephalins, endorphins, dynorphins) produced by the CNS and other organs.

How does spinal gating of pain work?

Opioids activate neurons in the spinal cord that block pain signals; descending nerves and mechanoreceptor input also help gate pain.

What are gustation and taste buds?

Gustation is the sense of taste; taste buds are clusters of 50-100 taste cells, mostly on the tongue.

Name the four lingual papillae that have taste buds and one that does not.

Filiform (no taste buds); Foliate (degenerate with age); Fungiform (tip/sides); Vallate (rear).

What are taste cells and basal cells in a taste bud?

Taste cells detect taste and synapse with neurons; basal cells are stem cells that replace taste cells.

What are the five primary tastes (and two proposed additions)?

Salty, Sweet, Umami, Sour, Bitter; plus proposed oleogustus (fats) and Water.

Which nerves carry taste information and where do they project?

Facial (VII), Glossopharyngeal (IX), and Vagus (X). They project to the solitary nucleus, then to the hypothalamus/amygdala, thalamus, and gustatory cortex.

What is olfaction and where are odorants detected?

Olfaction is the sense of smell; odorants are detected in the olfactory mucosa within the nasal cavity.

How many olfactory receptors are there and how many odors can humans distinguish?

About 400 receptor types; humans can distinguish roughly 2,000–10,000 odors.

Describe olfactory transduction.

An odorant binds a G protein-coupled receptor, activating a cAMP system that opens ion channels, causing depolarization and action potentials.

What is the olfactory projection pathway?

Olfactory cells send axons to olfactory bulbs, synapse in glomeruli, then the olfactory tract projects to the primary olfactory cortex and other areas for memory/emotion.

What are the main properties of pitch and loudness?

Pitch depends on vibration frequency (Hz); loudness depends on amplitude (dB). Humans hear 20-20,000 Hz; typical conversation \approx 60 dB; pain at 120-140 dB.

What are the components of the outer ear?

Auricle (pinna) and external auditory canal, protected by hair and cerumen (earwax).

What structures make up the middle ear?

Tympanic membrane (eardrum) and auditory ossicles (malleus, incus, stapes); auditory reflex protects inner ear; auditory (eustachian) tube connects to nasopharynx.

What are the three middle ear reflexes that protect the inner ear?

Tensor tympani and stapedius muscles contract to stiffen the eardrum and reduce stapes vibration, protecting the inner ear from loud sounds.

What are perilymph and endolymph, and where are they located?

1. is fluid between the bony and membranous labyrinths; 2. is fluid inside the membranous labyrinth.

What are the three scalae of the cochlea and their fluids?

Scala vestibuli (perilymph), scala tympani (perilymph), and cochlear duct/scala media (endolymph). The Organ of Corti is in the cochlear duct.

What is the function of outer and inner hair cells in the cochlea?

1. adjust cochlear sensitivity for better hearing precision.

2. convert sound to neural signals

How do hair cells transduce mechanical vibration into neural signals?

Basilar membrane movement bends stereocilia; tip links open ion channels; potassium enters, depolarizing the cell in high-K+ endolymph, releasing neurotransmitters.

Outline the auditory projection pathway from the ear to the cortex.

Hair cells --> spiral ganglion --> cochlear nerve (CN VIII) --> cochlear nuclei --> superior olivary nucleus --> inferior colliculus --> thalamus --> primary auditory cortex. Bilateral projections aid binaural hearing.

What structures detect static and dynamic equilibrium?

detected by maculae in the saccule and utricle, and by semicircular ducts (ampullae, crista ampullaris, cupula).

What are otoliths and their role in static and dynamic equilibrium?

Calcium carbonate-protein granules in the otolithic membrane that add weight, helping detect gravity and motion by bending hair cells.

What is the macula’s role in balance?

Maculae are patches of hair cells in the saccule and utricle that detect linear acceleration and head tilt via the otolithic membrane.

What are the basic components of the eye’s tunics?

Fibrous layer (sclera, cornea), vascular layer (choroid, ciliary body, iris), and inner layer (retina).

What are the major parts of the eye’s optical components and their roles?

Cornea (refracts light); aqueous humor (fills chambers); lens (adjusts focus via ciliary body); vitreous humor (maintains shape).

What structures regulate pupil size and accommodation?

Pupillary constrictor (parasympathetic, shrinks pupil) and pupillary dilator (sympathetic, enlarges pupil); accommodation involves ciliary muscle contracting to thicken the lens.

What is emmetropia?

When a relaxed eye focuses on distant objects, parallel light rays form a clear image on the retina without effort.

What are the retina’s essential components for vision?

Photoreceptors (rods, cones), bipolar cells, and ganglion cells; macula lutea/fovea centralis for high resolution; optic disc is the blind spot.

Differentiate rods and cones in the retina.

Rods: night (scotopic) vision, grayscale, high convergence, motion detection. Cones: day (photopic) vision, color, low convergence, high acuity in fovea.

What visual pigments do rods and cones use?

Rods use rhodopsin; cones use photopsins (three types for S, M, L wavelengths).

What happens during bleaching and regeneration of rhodopsin?

In light, retinal changes shape and detaches from opsin; rhodopsin regenerates in the dark

How do light and dark adaptation differ?

Light adaptation is fast (bleaching, pupil constriction); dark adaptation is slow (rhodopsin regeneration, pupil dilation) to improve low-light sensitivity.

What is the dual visual system?

Separate receptor systems and neural pathways for high-sensitivity night vision (rods) and high-resolution daytime color vision (cones).

What are the three cone types and their peak wavelengths?

Short-wavelength (S) at \approx 420 nm, Medium-wavelength (M) at \approx 531 nm, Long-wavelength (L) at \approx 558 nm.

What is color blindness and which cones are commonly involved?

Difficulty seeing colors, usually involving L (red) or M (green) cones; most commonly red-green color blindness from missing L or M opsins.

What is stereoscopic (depth) vision and what is required for it?

Depth perception using two eyes with overlapping visual fields, where the brain uses different viewpoints to create depth cues.

Outline the visual projection pathway through the brain.

Retina -> optic nerve -> optic chiasm (fibers cross) -> optic tracts -> lateral geniculate nucleus (thalamus) -> optic radiations -> primary visual cortex in occipital lobe. Some fibers go to superior colliculi.

What are the dorsal and ventral visual streams?

1. processes spatial location and motion ('where/how').

2. processes object recognition and color ('what').