Sensation Sense Organs: Organs specifically designed to increase the ability to detect and transmit sensory signals to the CNS, which then sends the appropriate efferent response. Thousands of signals detected every second. Sensation: The conscious or unconscious awareness of stimuli. Perception: The conscious interpretation of sensations. Not all stimuli reach perception.
Sensory Receptors Sensory Receptor: Any structure specialized to detect a stimulus. Transducers: Receptors that translate stimulus energy into nerve energy via action potentials. Can be simple nerve endings or a complete sense organ. Adaptation: If a stimulus is prolonged, firing frequency & conscious sensations decline.
Sensory Receptors Sensory receptors transmit 4 types of information: Modality: Refers to the type of stimulus or sensation it produces. E.g. vision, hearing, taste. Location: Determined by which afferent (sensory) nerve fiber are firing & gives the brain the ability to identify the site or location of the stimulus. Intensity: Determined by the number & kind of nerve fibers which are firing & the time intervals between action potentials. Duration: Refers to the way nerve fibers change their firing frequencies over time.
Classification of Sensory Receptors General Somesthetic (General) Senses: Includes receptors in the skin, muscle, tendons, joint capsules, and viscera. Somatic Senses: Tactile senses, thermal sensations, pain sensations, proprioceptive sensations. Visceral Senses: Provides information about conditions within the internal organs. Special Senses: Limited to the head & innervated by the cranial nerves. Includes: Vision, hearing, equilibrium, taste & smell.
Classification of Sensory Receptors Overlapping Systems Chemoreceptors: Respond to chemicals, including odor & taste. Thermoreceptors: Respond to temperature (heat & cold). Nociceptors: Pain receptors. Mechanreceptors: Respond to the physical deformation of the plasma membrane. E.g. caused by touch, pressure, stretch, tension, or vibration. Photoreceptors: Respond to light. Osmoreceptors: Respond to osmotic pressure. Proprioreceptors: Sense the body position, muscle tension, & movement in space.
Classification of Sensory Receptors Microscopic Features Unencapsulated: Nerve endings of sensory dendrites are not wrapped in connective tissue. Example: Free nerve endings, Merkel discs, hair receptors. Encapsulated: Nerve endings are dendrites wrapped in glial cells or connective tissue & most are pressure, stretch, & touch receptors. Meissner Corpuscles: Tactile sensors located in the dermal papillae respond to light touch. Pacinian Corpuscles: Lamellated sensors located deep in the dermis respond to deep pressure, stretch, & vibration. Ruffini Corpuscles: Tonic receptors sense heavy touch & pressure. Krause End Bulbs: Similar to Meissner corpuscles but only found in mucous membranes. Separate Cells: A separate receptor cell synapses with the sensory neuron. Typically found with special sense synapses such as Photoreceptors in the eye Hair cells in the inner ear Taste buds on the tongue.
Special Sense 5 Special Sense: Touch Smell Taste Hearing Vision An addition: Equillibruim!
Touch Touch Receptors responsible for detecting stimuli against the skin were discussed in Chapter 5.
Pain Sensation Nocioceptors: Pain sensory neurons found in every bodily tissue except the brain. Analgesia: The relief of pain. Oligopeptides: Chemicals released by the CNS that have analgesic qualities. AKA edogenous opiods. E.g. Endorphins & dynorphins.
Types of Pain Slow Pain: Dull, achey pain signals carried along an unmeylinated neuron. Fast Pain: Sharp, stabbing, sudden pain signals carried along a myelinated neuron. Superficial Somatic Pain: Pain felt by receptors in the skin. Deep Somatic Pain: Pain felt in the muscles, joints, tendons, and fascia. Visceral Pain: Pain sensation from the receptors in the visceral organs. Referred Pain: Pain caused by an organ or specific area but felt in other areas served by the same spinal nerve.
Kinesthesia Kinesthesia: The perception of body movements. Proprioceptors: Sensory receptors that can sense the location of body parts, their movements, & muscle tension without visual input. Mostly done through the hair cells in the inner ear responsible for balance & equilibrium. Muscle Spindles: Involved in our stretch reflexes.
Smell Olfaction: The sense of smell. Located in the nose around 20 million receptors! Olfactory Receptors: First-order neurons whose dendrites contain the olfactory hairs (cilia) that respond to chemicals. Only sensory receptor in contact with the outside world. Receptors are replaced every few months. Supported by Basal stem cells, Columnar supporting cells and.. Olfactory glands (aka Bowmans glands): Produce the mucus that moistens the epithelium. Olfactory Epithelium: Contains most of the olfactory receptors. Odorant: A chemical responded to by the olfactory hairs.
Smell Olfactory Epithelium: Contains most of the olfactory receptors. Hyposomia: The gradual loss of smell as we get older.
Process of Smelling Odorants (chemicals) bind to the Olfactory Receptors. Odorants must be water-soluble, volatile, & reach the minimum threshold to be detected. Olfactory receptors send a signal to the Olfactory Nerves (Cranial nerve 1). Signal continues to the Olfactory Bulbs (first- order neuron) & synapses with the Olfactory Tract (second-order neuron). Signal is then transmitted to the brain, through the cortex & on to the thalamus to be perceived.
Taste Gustation: The chemically-based sense of taste. 5 Primary Tastes: Sweet: Least sensitivity. Sour Bitter: Most sensitive. Salty Umami: Meaty or Savory flavor. Flavor: A combination of taste, smell, and texture. MOST of taste perception is driven by scent.
Taste Taste Buds: Small organs made up of several components that allow us to perceive taste. Over 10,000 total, mostly on the tongue. Can be located on the papillae.
Taste Components of a taste bud: Gustatory Receptor Cells: Around 50 total in each taste bud. Taste Pore: A small opening in the top of the taste bud. Gustatory Hair: Projects through the taste pore to help trap chemicals to analyze.
Taste Papillae (elevations on the tongue that give it a rough texture). 4 types: Vallate Papillae: Twelve large circular papillae forming an inverted V at the back of the tongue. Each contains a few hundred taste buds. Fungiform Papillae: Mushroom-shaped papillae. Each contains around give taste buds. Found all over the tongue.
Taste Foliate Papillae: Found in the trenches on the sides of the tongue. These taste buds degenerate rapidly. Filiform Papillae: Threadlike papillae found all over the tongue. Contain no taste buds. Contain tactile receptors to detect texture. Increase friction between the tongue and food & move food around in the oral cavity.
Taste Tastant: Any chemical that stimulates our taste. Each tastant stimulates the receptors in a different way. G-Proteins: A specific protein some tastants must be linked to in order to reach threshold. Facial Nerve (CN 7) and Glossopharyngeal Nerve (CN 11) serve the tongue. Vagus Nerve (CN 10) serves the throat and epiglottis.
Taste Pathway of Taste Perception: Taste bud to the appropriate cranial nerve Cranial nerve to the gustatory nucleus in the medulla oblongata Medulla oblongata to the thalamus Thalamus to the gustatory cortex
Hearing Ear: The main sensory organ responsible for translating the smallest of vibrations into electrical signals to be interpreted as sound & provide sensory information on equilibrium. Responds to sound almost 1,000 times faster than the eyes due to light. 3 Regions of the Ear: External Ear Middle Ear Inner Ear
Hearing External Ear: The portion of the ear we can see! Auricle (Pinna): The flap of cartilage that funnels vibrations toward the auditory canal. Helix: The external rim. Lobule: The inferior portion we pierce for earrings. External Auditory Canal: Tube located just inside the ear; curved & approximately 1 inch long. The ear canal. Ceruminous Glands: Glands producing ear wax that line the external auditory canal. Tympanic Membrane aka the Eardrum: Thin flap of connective tissue separating the outer & middle ear.
Hearing Middle Ear: The epithelium-lined, air-filled cavity located within the temporal bone. Oval Window: Opening that leads to the inner ear. Contains the. Auditory Ossicles: Smallest bones in the body! Malleus (Hammer) Incus (Anvil) Stapes (Stirrup) Round Window: Located beneath the oval window. Tensory Tympani