Senses Dueweke Anatomy/Physiology

What are our senses? Remember, all sensory info is picked up by sensory receptors and transmitted along sensory neurons (Afferent PNS) The simplest receptors are the dendrites of sensory neurons, called free nerve endings Can be sensitive to pain, chemicals, pressure, light More complex receptors are specialized cells designed to send out signaling chemicals and cause action potentials in adjacent sensory neurons

Stimulus Intensity & Location The area monitored by a single receptor cell is its receptive field The larger the receptive field, the poorer is your ability to localize (locate) the stimulus 2 point test

Sensation vs. Adaptation All sensory info arrives at the CNS in the form of action potentials sent from a sensory (afferent) fiber The stronger the stimulus, the higher the frequency (number) of action potentials Arriving information is called a sensation Adaptation – a reduction in sensitivity in the presence of a constant stimulus Ex: being in a hot bath or cold lake, neither temperature seems extreme after a while Reduces the amount of information arriving at the cerebral cortex

The General Senses Scattered throughout the body Relatively simple in structure Receptors are classified by what type of stimuli excites them (i.e. makes them send action potentials) 1.Pain = nociceptors 2.Temp = thermoreceptors 3.Touch/pressure/body position = mechanoreceptors 4.Chemicals = chemoreptors

Pain = Nociceptors Made of free nerve endings Found at superficial portions of skin, joint capsules, bone coverings, blood vessel walls

Types of Pain Fast Pain – “pricking pain”, cuts, injections Slow Pain – burning, aching Referred Pain – perception of being in pain coming from parts of the body that are not actually stimulated Caused by some visceral organs sharing the same spinal nerves as some body surfaces

Temperature = Thermoreceptors Free nerve endings in dermis, skeletal muscles, the liver, and hypothalamus Can be cold or hot Often on the same nerve pathways as pain receptors

Touch = Mechanoreceptors Sensitive to stretching, compression, and twisting Distortion of cell membrane cause ion channels to open/close Three types: Tactile = Touch (Merkel Cells, Meissner’s Corpuscles) Baroreceptors = Pressure (Pacinian Corpuscles) Proprioceptors = Position

Chemicals = Chemoreceptors Found in nose and on tongue Responds ONLY to water-soluble, and lipid- soluble substances that are dissolved in the extracellular fluid surrounding the receptor (reminder: water-soluble & lipid soluble means that can be dissolved in water, and lipids, respectively) Except for taste and smell, there are no well- defined chemosensory pathways in the body They are also found in the cardiovascular system to detect the presence of pH changes, CO2, and O2 in blood

The Special Senses There are 5 Special Senses in the body 1.Smell 2.Taste 3.Vision 4.Equilibrium 5.Hearing They have many of the same receptors as those found in the general senses, but are more complex in their anatomy

Smell The sense of smell is known as Olfaction All olfaction starts within the nasal cavity, has its information relayed to the olfactory bulb, and sent through the olfactory nerves to be interpreted in the cerebrum

The Nasal Cavity The nasal cavity is lined with an olfactory epithelium, which contains: Olfactory receptor cells - receive odorants (chemicals to be smelled) Olfactory glands – secretes mucus needed for: 1.protecting the nasal cavity from dust and debris 2.protect the olfactory receptors cells from damage from chemicals in odorants 3.allow the odorants to diffuse and dissolve before they can be received by the receptor cells

Olfactory Epithelium

Olfactory Receptor Cells Highly modified neurons Are constantly replaced by dividing basal cells in the olfactory epithelium Have odorant binding proteins on its surface When certain odorants bind to certain proteins, action potentials are sent up to the olfactory bulbs and are sent to the brain for interpretation Humans have million olfactory receptor cells in a surface area of 5 cm 2 A German Shepard dog has a surface area 72 times greater

Taste Taste receptors, aka gustatory receptors are found on the surface of the tongue, as well as in the pharynx and larynx Taste buds – made of gustatory receptor cells and supporting epithelial cells Dissolved chemicals from food slide down pores in the tongue and interact with the cell membranes of the gustatory receptor cells found within, sending action potentials Action potentials for signaling taste are sent along the glossopharyngeal, facial, and vagus nerves

Taste Sensations We have four basic taste sensations: Sweet Salty Bitter Sour We used to think they were mapped in certain regions of the tongue, but in fact they are dispersed all over the surface of the tongue In addition to the four basic tastes, we also have: Umami ( 旨味 ) = Savory found all over the tongue, is sensitive to the amino acid glutamate, which is responsible for the savory flavors in beef and chicken broth and parmesan cheese Water In Pharynx Used for signaling water balance and thirst in the hypothalamus