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Ch 18 General and Special Senses Intro A sensory receptor is a specialized cell or cell process monitoring conditions in the body or environment. Stimulation alters the production of action potentials in the sensory neuron Keep the nervous system updated on changes to the body’s internal and externa...

Ch 18 General and Special Senses Intro A sensory receptor is a specialized cell or cell process monitoring conditions in the body or environment. Stimulation alters the production of action potentials in the sensory neuron Keep the nervous system updated on changes to the body’s internal and external environment The sensory information arriving at the CNS is called sensation A perception is conscious awareness of a sensation general Senses: Touch, temperature, pain, pressure, vibration, and proprioception Receptors are distributed all over the body special Senses: Smell, taste, equilibrium, hearing, and vision Receptors localized within sense organs Regardless of the type all sensory information is processed in the central nervous system Receptors The simplest receptor of the body are free nerve endings Often respond to multiple stimuli Pressure, temp, pain, etc Special sensory sensors often only respond to a single type of stimuli Know as receptor specifity The area monitored by the receptors is called the receptive field Ability to localize stimuli depends on the size of the receptive field The larger the field the harder to localize Sensory Interpretation Each sensory pathway carries information for a specific sensation from a specific region Know as sensory coding Sensory information is transmitted to the brain according to : The location of the stimulus The type of stimulus Two receptor types based on activity level: Tonic Always on (proprioceptors and photoceptors) Phasic Must receive stimulation to activate (touch receptors) Sensory Adaptation Adaptation is the reduction of stimulation in response to a constant stimulus Can be either peripheral or central (PNS vs CNS) peripheral Adaptation is when a receptor alters its level of activity Gradually declines due to synaptic fatigue Central Adaptation is when the CNS removes conscious awareness of a continued stimulus Level of stimulation is subconsciously restricted to ignore source of stimulus The General Senses Divided into 3 classes: 1. Exteroceptors- external senses 2. Interoceptors- internal senses 3. Proprioceptors- body position A more detailed division based on type of sensation gives 4 classes: 1. 2. 3. 4. Nociceptors- pain Thermoreceptors- temperature Mechanoreceptors- physical distortion of epithelial surface Chemoreceptors- chemicals inside or around the body Nociceptors There are 3 types: 1. Sensitive to extreme temperature 2. Sensitive to physical damage 3. Sensitive to dissolved chemicals Felt as: fast Pain- sudden onset ends as soon as cause of damage removed Slow Pain- later onset less generalized and sharp than fast pain Reffered Pain- from visceral organs felt in generalized areas no the organ itself Generally areas that share a spinal nerve Thermoreceptors Two types: warm Cold- 3-4 times more common Both are phasic receptors Very receptive to temp changes but acclimate quickly Mechanoreceptors There are 3 classes of mechanoreceptors: Tactile- touch, pressure, vibration Both Fine touch and Crude Touch Receptors Vary in size of receptive field Baroreceptor- stretch receptors in blood vessels and urinary tracts A type of stretch receptor Proprioreceptors- detect position of joints and skeletal muscles Golgi tendon organs monitor the tension on the muscles Chemoreception Chemoreceptors are specialized to detect changes in the concentration of specific chemicals Many of the body's internal process rely on chemoreceptors to function Two of the special senses are based on chemoreception 1. 2. Olfaction- smell Gustation- taste Olfaction The olfactory organs consist of the following: Specialized olfactory epithelium Bipolar olfactory sensory neurons Supporting cells Basal epithelial cells A layer of connective tissue, the laminar propria contains Olfactory glands- produce thick pigmented mucus Blood vessels Nerves Olfactory stimulation recaches the cerebral cortex directly Certain smells trigger emotional and behavioral responses This is due to olfactory receptors in the limbic system Gustation Taste provides information about food and liquid we eat and drink Gustatory epithelial cells, taste receptors, are found in the taste buds Distributes over tongue pharynx and larynx The tongue has numerous epithelial projections called lingual papillae Gustatory information is carries by the Facial, Glossopharyngeal, and Vagus nerves There are thought to be 4 primary taste sensations: Sweet, Sour, Bitter, Salty However, 2 additional tastes have been identified 1. Umami- associated with the A.A. glutamate 2. Water- receptors present especially in the pharynx Equilibrium and Hearing The ear is divided into 3 anatomical regions: The External Ear The Middle Ear The Inner Ear The external ear is the visible portion and includes The Auricle External Acoustic meatus Tympanic Membrane The middle ear contains air-filled space called the tympanic cavity Contains the auditory ossicles These are the malleus, incus, and stapes Communicates with the nasopharynx The auditory tube, or eustachian Tube, helps equilibrate pressure between the middle and outer ear. Vibration of the tympanic membrane converts arriving sound into mechanical movements of the auditory ossicles The inner ear contains the sensory receptors for both equilibrium and hearing Receptors found within the fluid-filled membranous labyrinth A bony labyrinth within the temporal bone surrounds and protects the ML The ML is subdivided into the vestibule, semicircular canals, and cochlea Equilibrium The vestibular complex provides information about rotation, gravity and acceleration Consists of the 3 semi-circular canals, the utricle and saccule The semi-circular canals are divided into anterior, posterior, and horizontal Each canal surrounds a semi-circular duct Ducts contain an ampulla that contains sensory receptors Rotation in the anterior-posterior plane stimulates the anterior canal Rotation in the horizontal plane activates the horizontal duct Rotation in the coronal place activates the posterior duct Hearing The cochlea coils around a central hub, or modiolus Encloses the spiral ganglion, containing the sensory cells of the cochlear duct The spiral organ contains the hair cells of the cochlear duct Sensory receptors found in the basilar membrane Hearing is the detection of sounds waves They enter the external meatus and are transmitted to the tympanic membrane The tympanic membrane vibrates in response to sound waves between 2020,000 Hz Intensity of sound is determined by the amount of distortion in the basilar membrane Vision The visual structures are contained within the eye Enable us to detect light & create detailed visual images The accessory structures of the protect, lubricate and support the eye Eyelids, palpebrae , are continuations of the skin Separated by the palpebrae fissure Connected by the medial and lateral angles Eyelashes are associated with large sebaceous glands These tarsal glands secrete a lipid substance that prevents lashes from sticking together At the medial angle is the lacrimal caruncle produces the waxy buildup found around the eye in the mornings- “Sleep” in the eyes The conjunctiva is a layer of epithelium Covers the inner surface of the eyelids and outer surface of the eye The epithelial covering of the conjunctiva changes to squamous epithelial covering at the cornea The lacrimal apparatus produces, distributes and removes tears A constant flow of tears keeps the conjunctival surfaces moist and clean Tears reduce friction, remove debris, prevent bacterial infection The lacrimal apparatus consists of: Lacrimal gland Superior & Inferior Lacrimal canaliculi Lacrimal sac Nasolacrimal duct The Eye The eyeball lies within the orbit of the skull along with the Extra-ocular muscles The lacrimal gland The cranial nerves and blood vessels that supply the eye and parts of face The wall of the eye is made up of 3 distinct layers: 1. Outer fibrous layer: Contains the sclera or “white of the eye” 2. Intermediate vascular layer or choroid: Contains the Iris 3. Inner layer or retina The eye itself is hollow and has 2 separate cavities 1. The Anterior Cavity-Subdivided into the Anterior and Posterior chamber 2. The Posterior Cavity-Contains the vitreous body Retinal Organization The retina contains several layers of cells. The outermost layer contains the visual There are 2 types of photoreceptors: 1. Rods- very light sensitive, do not detect color 2. Cones- detect color, give clearer images, require more light Rods/Cones not evenly distributed: The more toward the center of the retina the fewer rods and more cones Almost all the cones are within the macula The area where the visual image arrives after passing through the cornea and lens The center of the macula contains a region called the fovea This is the “focus” point in the visual field Visual Pathways Each rod and cone monitors a specific receptive field An image results from processing information from the entire receptor population The optic nerves reach the diencephalon after a partial decussation at the optic chiasm Each eye also receives slightly different images because: The fovea are 2-3 inches apart Nose and eye socket block the view