Ch15 Autonomic nervous system

What are the general functions of sensory receptors?

They provide information about external and internal environments, respond to specific stimuli, convert stimulus energy into electrical signals, and send action potentials to the CNS for interpretation.

How do sensory receptors act as transducers?

They convert stimulus energy (light, chemicals, sound, pressure) into electrical energy by opening modality-gated channels and generating receptor potentials that lead to action potentials.

What is a receptive field and how does its size affect stimulus localization?

A receptive field is the distribution area of a sensory neuron’s endings. Smaller fields allow precise localization; larger fields reduce precision.

What is sensory adaptation and how do tonic and phasic receptors differ?

Adaptation is decreased sensitivity to continuous stimulus. Tonic receptors adapt slowly and respond continuously (pain, head position). Phasic receptors adapt rapidly and respond only to new stimuli (pressure).

How are sensory receptors classified by stimulus origin?

Exteroceptors (external environment), Interoceptors (internal organs), Proprioceptors (body and limb position).

What is the difference between somatic and visceral sensory receptors?

Somatic receptors detect tactile, proprioceptive, and pain stimuli from skin, muscles, joints. Visceral receptors detect stretch, chemicals, temperature, and pain from internal organs.

What are the major types of sensory receptors based on modality?

Chemoreceptors, Thermoreceptors, Photoreceptors, Mechanoreceptors, Nociceptors.

What is referred pain and what is its clinical significance?

Pain from internal organs perceived on the body surface due to shared pathways; helps diagnose organ issues.

What is olfaction and where are olfactory organs located?

Olfaction is the sense of smell; organs are located in the superior nasal cavity within the olfactory epithelium.

What are the three types of cells found in the olfactory epithelium?

Olfactory receptor cells, Supporting cells, Basal cells.

What is the function of olfactory receptor cells?

They detect odorants using chemoreceptors on olfactory hairs and generate action potentials.

Describe the olfactory pathway from receptor to brain.

Odorant binds → receptor depolarizes → axons form CN I → pass through cribriform plate → synapse in olfactory bulb → mitral/tufted cells form olfactory tracts → project to primary olfactory cortex, hypothalamus, amygdala.

What role does the olfactory bulb play in smell perception?

It is the first processing center; glomeruli organize signals and enhance weak odor detection.

How does olfactory discrimination occur?

Different odorants stimulate different receptor combinations; the brain interprets unique glomerular activation patterns.

What is gustation and where are taste buds located?

Gustation is taste; taste buds are located in papillae on the tongue (fungiform, foliate, vallate) and in the pharynx/epiglottis.

What are the five basic taste sensations?

Sweet, Salt, Sour, Bitter, Umami.

What are the three types of cells found in taste buds?

Gustatory cells, Supporting cells, Basal cells.

Describe the gustatory pathway from taste receptor to brain.

Tastants dissolve → depolarize gustatory cells → CN VII or CN IX → nucleus solitarius (medulla) → thalamus → primary gustatory cortex (insula).

What cranial nerves are involved in taste sensation?

CN VII (anterior tongue), CN IX (posterior tongue), CN X (epiglottis/pharynx).

How does the brain interpret different taste modalities?

By integrating gustatory signals with smell, texture, and temperature; different tastants activate distinct receptor pathways.

What are the three tunics of the eye and their functions?

Fibrous (protection, shape), Vascular (blood supply, pigment, controls pupil), Retina (photoreception).

What are the components of the fibrous tunic?

Cornea and Sclera.

What are the components of the vascular tunic?

Choroid, Ciliary body, Iris.

What is the function of the pupil and how is it regulated?

Controls light entry; sphincter pupillae constricts, dilator pupillae dilates.

What are the two layers of the retina and their roles?

Pigmented layer (absorbs light), Neural layer (photoreceptors → bipolar cells → ganglion cells).

What are rods and cones and how do they differ in function?

Rods: dim light, black/white, peripheral, blurry image. Cones: bright light, color, sharp image, concentrated in fovea.

What is the fovea centralis and why is it important?

Region of highest visual acuity; contains only cones.

What is the optic disc and why is it called the blind spot?

Where ganglion axons exit as optic nerve; no photoreceptors present.

What are the two main cavities of the eye and what do they contain?

Anterior cavity (aqueous humor), Posterior cavity (vitreous humor).

What is the function of the lens and how does it change shape?

Focuses light; flattens for distant vision, becomes spherical for near vision (accommodation).

Describe the visual pathway from photoreceptors to the brain.

Photoreceptors → bipolar cells → ganglion cells → optic nerve → optic chiasm → optic tract → thalamus → visual cortex.

What is the role of the optic chiasm in vision?

Medial fibers cross; allows binocular vision and depth perception.

What are the three regions of the ear and their functions?

External (collects sound), Middle (transmits vibrations), Inner (hearing and equilibrium).

What is the function of the auricle and external acoustic meatus?

Auricle funnels sound; meatus directs sound to tympanic membrane.

What is the role of the tympanic membrane?

Vibrates in response to sound waves.

Name the auditory ossicles and their order from outer to inner ear.

Malleus → Incus → Stapes.

What is the function of the auditory (Eustachian) tube?

Equalizes pressure between middle ear and nasopharynx.

What structures are found in the cochlea?

Cochlear duct, scala vestibuli, scala tympani, basilar membrane, organ of Corti.

Describe the pathway of sound from the external ear to the cochlea.

Sound → auricle → meatus → tympanic membrane → ossicles → oval window → cochlear fluid → basilar membrane.

What is the function of the organ of Corti?

Contains hair cells that transduce sound vibrations into electrical signals.

Describe the auditory pathway from cochlear nerve to auditory cortex.

CN VIII → cochlear nucleus → superior olive or inferior colliculus → thalamus (MGN) → auditory cortex.

What structures are responsible for detecting equilibrium?

Utricle, Saccule, Semicircular ducts.

What is the function of the vestibule and semicircular canals?

Vestibule: static equilibrium & linear acceleration. Semicircular canals: angular acceleration.

What is the role of the maculae in static equilibrium?

Hair cells with otolithic membrane detect head tilt and linear acceleration.

How do the crista ampullaris and cupula function in dynamic equilibrium?

Rotation moves endolymph → bends cupula → hair cells depolarize/hyperpolarize.

Describe the equilibrium pathway from vestibular receptors to the brain.

CN VIII → vestibular nuclei/cerebellum → thalamus → cortex.

How do the special senses integrate with the central nervous system?

They send labeled-line signals to specific brain regions; integration occurs with memory, emotion, and motor systems.

What are common disorders associated with each special sense?

Smell: anosmia. Taste: ageusia. Vision: myopia, hyperopia, astigmatism, presbyopia, color blindness. Hearing: deafness, tinnitus. Equilibrium: vertigo.

How does damage to cranial nerves affect sensory perception?

CN I → loss of smell CN II → vision loss CN VII/IX/X → taste loss CN VIII → hearing/equilibrium deficits

What diagnostic tools are used to assess sensory system function?

Vision tests, audiometry, tuning forks, balance tests, smell identification tests.

How do aging and disease affect the special senses?

Reduced receptor sensitivity, decreased olfaction, presbyopia, hearing loss, slower neural processing.