Sensory Systems: Taste, Ear, Eye, and Neural Pathways

Gustation

The sense of taste.

Papillae Types

Vallate, foliate, fungiform, filiform (NO taste buds).

Taste Buds

Contain gustatory receptor cells.

Transduction (taste)

Chemical → neural signal.

Cranial Nerves for Taste

CN VII, IX, X.

Salty Taste

Na⁺ enters cell directly.

Sour Taste

H⁺ ions.

Sweet Taste

G- protein coupled receptors

Bitter Taste

G- protein coupled receptors

Umami Taste

G- protein coupled receptors

External Ear Structures

Auricle, ear canal, tympanic membrane.

Middle Ear Structures

Malleus, incus, stapes, Eustachian tube.

Inner Ear Structures

Cochlea (hearing), vestibule (balance).

Sound Pathway

Sound → tympanic membrane → ossicles → oval window → cochlea → hair cells → auditory nerve.

Scala Vestibuli

Upper chamber, perilymph.

Scala Tympani

Lower chamber, perilymph.

Scala Media (Cochlear duct)

Endolymph.

Organ of Corti

Contains hair cells (mechanoreceptors).

Tectorial Membrane

Gel layer above hair cells.

Transduction (hearing)

Fluid movement → basilar membrane moves → stereocilia bend → ion channels open → signal.

Frequency Encoding

Base = high frequency; Apex = low frequency.

Static Equilibrium

Utricle + saccule; detects gravity + linear acceleration.

Otoliths

Calcium crystals that shift and bend hair cells.

Dynamic Equilibrium

Semicircular canals; detects rotation.

Ampulla

Contains cupula.

Cupula Movement

Bends stereocilia.

Eye Tunics

Fibrous → sclera + cornea; Vascular → choroid, iris, ciliary body; Neural → retina.

Eye Chambers

Anterior → aqueous humor; Posterior → vitreous humor.

Light Path

Cornea → pupil → lens → vitreous humor → retina.

Fovea Centralis

Sharpest vision.

Optic Disc

Blind spot.

Photoreceptors

Rods → low light; Cones → color + detail.

Phototransduction

Light changes retinal shape; Rods = rhodopsin; Cones = RGB opsins.

Retinal Pathway

Pigmented epithelium → photoreceptor → bipolar cell → ganglion cell.

Visual Pathway

Retina → optic nerve → thalamus → occipital lobe.

General Rule (Sensory Pathways)

3 neurons + cross over + synapse in thalamus.

Dorsal Column Pathway

Touch, vibration.

Anterolateral Pathway

Pain, temperature.

1st order neuron

All sensory neurons from the 2nd or 3rd order will always synapse at the thalamus.

3rd order neuron

Sensory cortex.

Sensory pathways

Are ascending towards the brain.

Motor Pathways

Descending output.

Central Integration

Prefrontal cortex → premotor area → precentral gyrus primary motor cortex → posterior parietal cortex.

Motor cortex Mapping

Homunculus, a depiction of motor or sensory mapping on cerebellum.

Ascending Spinal Pathways

Only two ascending pathways: Dorsal column - medial lemniscal pathway and Anterolateral system.

Corticospinal tracts

Designing pyramidal tracts down and through spinal cord.

Corticobulbar tracts

Stay neck and above, involving cranial nerves of head and face.

Descending extrapyramidal tracts

Include vestibulospinal tract for postural control.

Autonomic nervous system

A motor nervous system that controls glands, cardiac muscle, and smooth muscle.

Primary target organs in ANS

Heart, blood vessels, lungs, eyes, viscera of thoracic and abdominal cavities.

Autonomic reflex Arc

Receptors detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli.

Divisions of ANS

Sympathetic division (fight or flight) and Parasympathetic division (calms body functions).

Sympathetic Nervous System

Thoracolumbar division with short preganglionic/long postganglionic fibers.

Parasympathetic Nervous System

Craniosacral division with long preganglionic/short postganglionic fibers.

Enteric Plexus

The nervous network of the digestive tract composed of 500 million neurons.

Neurotransmitters in ANS

Sympathetic and parasympathetic fibers secrete different neurotransmitters (norepinephrine and acetylcholine).

Hormone Structures

Peptide, steroid, amino acid derivative.

Anterior Pituitary Hormones

Stimulating/inhibiting hormones secreted by hypothalamus transferred via blood vessels to anterior pituitary gland.

Thyroid Gland

Located in the neck below the larynx and anterior to the trachea.

Parathyroid Glands

Two pairs of glands embedded in the posterior surfaces of the thyroid gland.

Adrenal Glands

Outer region producing steroid hormones and inner region containing chromaffin cells that release catecholamines.

Effects of Epinephrine/Norepinephrine

Increase blood glucose levels, elevate heart rate, elevate blood pressure.

The Pineal Gland

Regulates sleep-wake cycles through melatonin secretion.

Aging and the Endocrine System

Certain hormones and gland production decrease with age, including cortisol and aldosterone.

Overall impact of aging

These changes can affect hormone production, secretion and catabolism.