senses

• The sense organs can be classified as general or special and there are basic differences between the two groups.
• A stimulus is converted into a sensation.
• Meissner’s corpuscle: light, fluctuating touch.
• Pacinian corpuscle: vibrations and deep pressure.
• Hair receptor: hair movement and gentle touch.
• Markel’s disc: light, sustained touch.
• Skin surface: shaft of hair inside follicle.
• The anatomy of the nasal cavity and its sensory function in smell are discussed in detail.
• Senses are integrated.
• General senses often exist as individual cells or receptor units and are widely distributed throughout the body.
• Special senses are large and complex organs localized grouping of specialized receptors.
• Sensory receptor types can be classified by presence or absence of a covering capsule.
• Sensory receptors can also be classified by type of stimuli required to activate receptors.
• All sense organs have common functional characteristics and are able to detect a particular stimulus.
• A stimulus is converted into a nerve impulse and a nerve impulse is perceived as a sensation in the central nervous system (CNS).
• Sensory pathways involve the cell body, afferent neuron, and efferent neuron.
• Distribution of sensory receptors is widespread and single-cell receptors are common.
• Olfactory sensations are all perceived in the brain, not at individual receptors scattered throughout the body.
• Smell sensations are often powerful triggers of memory.
• Olfactory sensations are initiated by odor-causing chemicals, which send a nervous signal to the brain that is interpreted as a specific odor.
• Severe nasal congestion can interfere with the stimulation of olfactory receptors by food odors in the mouth, leading to dull flavor sensations.
• The olfactory system adapts quickly, and odorants are rapidly cleared.
• The integration of senses involves the brain, not individual receptors scattered throughout the body.
• Examples of general senses include free nerve endings, pain, temperature, crude touch, tactile (Meissner) corpuscles, fine touch, vibration, bulbous (Ruffini) corpuscles, touch, pressure.
• The binocular zone is the portion of the visual field associated with both eyes.
• The monocular zone is the portion of the visual field associated with only one eye.
• The occipital lobe is part of the visual cortex.
• Examples of special senses include lamellar (Pacini) corpuscles, pressure, vibration, bulboid corpuscles (Krause end bulbs), touch, golgi tendon receptors, important proprioceptors, muscle spindles, important proprioceptors.
• Phototransduction by retinal cells converts light stimuli into neural signals, and photoreceptors (rod and cone cells) consist of an outer segment, an inner segment, and a synaptic terminal.
• Rods provide indistinct gray vision at night, and cones provide sharp color vision during the day.
• The ciliary muscle regulates accommodation.
• The visual pathway involves the innermost layer of the retina which contains rods and cones.
• The amount of light entering the eye is controlled by the iris, a thin, pigmented, smooth muscle that forms a visible ringlike structure within the aqueous humor.
• Rods have high sensitivity, and cones have lower sensitivity.
• Color vision depends on the ratios of stimulation of the three cone types, and each cone type is most effectively activated by a particular wavelength of light in the range of color indicated by its name.
• The structure and function of the eye involves the aqueous humor in the anterior chamber in front of the lens and the vitreous humor in the posterior chamber behind the lens.
• The sensitivity of the eyes can vary markedly through dark and light adaptation.
• The eye refracts entering light to focus the image on the retina.
• Accommodation increases the strength of the lens for near vision, and the strength of the lens depends on its shape.
• An impulse travels from the rods and cones through the bipolar and ganglionic layers of the retina.