2 The Sense of TouchThe overall sense of touch is one that has a high degree of variabilityThis is because it has a large group of neurons that have the ability to perceive many different sensationsAlso the neurons can be located on many different structures around the body
3 The Sense of TouchThe sense of touch is regulated by sensory receptors that monitor the internal state of the body and the external environmentThese are a group of mixed neurons that are responsible for sending information about the state of the bodyThe sense of touch is considered a general sense due to its distribution throughout the body
4 Sensation and Perception Being able to determine stimuli and understand what the stimuli is is not an easy taskIt is two completely different systems that are functioning at the same timeSensation is the ability to detect arriving informationPerception is the ability to consciously determine the sensation
5 Sensation and Perception This means that the organization of the body needs different nerves to pick up the different sensations and perceptionsMost of the sensation of the body is picked up by neurons that are distributed throughout the bodyThen signals are sent to the CNS where they are processed and acted upon
6 Types of Receptors There are different types of receptors Each and every one of the types of receptors are designed to pick up distinct types of stimuliThey are highly sensitive to one singular form of stimuli and mostly blind to other types of stimuliThis sensitivity and simultaneous blindness is called receptor specificity
7 Types of ReceptorsThere are six major ways that sensory receptors can tell the world about the bodyTemperature is the perception of heat energy inside and outside the bodyPain is the determination and discrimination of things that cause injuryTouch is the feel of the texture of an object
8 Types of ReceptorsPressure is the discrimination of the physical force that is pushing against the bodyVibration is the discrimination of the determination of the oscillation of receptorsProprioception is the ability to sense how and the range that the joints of the body move
9 Types of ReceptorsWhile we might think that there are more feelings, they are all just a combination of these sensesFor example, there is no sensory neuron for “wet”The feeling of “wet” is just a combination of cold and pressure
10 The Detection of Stimuli Each type of receptor cell is different and distinct, however they all share a few common characteristicsMost neural receptors have a large number of dendrites called free nerve endingsThese free nerve endings are designed to pick up signals and send them down a neural pathway
11 The Detection of Stimuli Free nerve endings are spread out along a receptive fieldThis is a small patch of an organ that neurons are responsible for sending signals fromWhen neural fields are close together, they have high sensitivityWhen neural fields are far apart, they generally have a lower sensitivity
12 Demo Lets test the sensitivity of receptive fields In order to do this we first need to understand how they workSince they can only send one signal per neuron, two stimuli on one neuron will only be sent as one signalTo test this we will test how close together two receptive fields are within the body
13 DemoTo do this in the body we will use pins to put an extremely light pressure on the skinTo start you will have the person being experimented on close their eyesThen place heads of both pins touching the same point on their shoulderSlowly pickup and then place down the pin very lightly several times to gradually increase the distance between the pin headsStop when the person with their eyes closed feels two completely different points of pressureMeasure the difference between the two points
14 DemoNow that we have the hang of the experiment, repeat the experiment on other body partsUse the cheek, a finger tip, the calf, the small of the back and the forearmMeasure and record all of the distance between the receptive fields in each areaDetermine the size of the receptive field of each body part
15 General Sensory Receptors While receptors for touch may be scattered throughout the body, there is not only one category or type of receptor that is used within the bodyGeneral sensory receptors are defined by the location that they reside in and the type of sensation that they interpret
16 General Sensory Receptors Based on location, general sensory receptors can be classified as…Exteroceptors provide information about the external environmentProprioceptors report the positions of skeletal muscle and jointsInteroceptors provide information about the internal environment
17 General Sensory Receptors Another classification for touch receptors is based on their excitatory stimulusNociceptors are stimulated by pain signalsThermoreceptors are stimulated by changes in temperatureMechanoreceptors are stimulated by physical changesChemoreceptors are stimulated by a chemical concentration
18 NociceptorsPain receptors (aka nociceptors) are very common in the outer portions of the skin, joint capsules, bones and around the walls of blood vesselsNoxa is Latin for harmThese detectors sense pain from areas of the body that can often become damaged or need to know when they are damagedNociceptors are sparse in internal organs and deep tissues
19 NociceptorsNociceptors are commonly nerves with large receptive fieldsWhen nociceptors are tightly packed, it can be easy to pinpoint where a stimulus is coming fromThis means that in certain areas of the body it can be very hard to determine where pain is coming from
20 Nociceptors Pain can come in many forms Nociceptors have to be ready to sense pain from a variety of sourcesThis means that nociceptors are receptive to changes in temperature, mechanical damage and dissolved chemicalsIn very damaging situations, these different stimuli can be confusedA deep cut can be confused with a burning sensation
21 Videohttps://youtu.be/I7wfDenj6CQ?t =6sWhat a pain!
22 What a Pain in the Nociceptor! Pain is a very hard feeling to describeThat is because our brain does not categorize or remember painWe might link experiences with pain, however we cannot remember the actual pain that we felt with different situations
23 What a Pain in the Nociceptor! There are two types of fibers that carry pain signalsMyelinated type A fibers will carry fast painAlso known as prickling painThis is pain that is quickly felt by the CNS and can cause a somatic reactionThey are also then routed to the primary sensory cortex where they are brought to conscious control
24 What a Pain in the Nociceptor! Slower Type C fibers carry sensations of slow painThese are known as burning pain fibers or aching pain fibersThese sensations cause pain to be routed to the thalamusFrom there the thalamus can direct it to the subconscious or the conscious brain
25 What a Pain in the Nociceptor! Pain can actually be offset by the mindIf you are experiencing a slow pain, often times you can redirect your mind to not let the thalamus to be able to focus on the painKeep the thalamus occupied and you will not notice the slow painEvery time I get poison ivy, I buy a new puzzle!
26 Demo Ok… this demo is going to cause a light amount of pain YOU DO NOT NEED TO PARTICIPATE IF YOU DO NOT WANT TOAnyone with a medical condition should probably sit this one outBefore we move on, please be sure that you are ready for this!
27 DemoI want you to give your partner a good and hearty slap on the upper arm!This one slap should not be one that leaves a bruise or lasting mark!However, if done well it should activate the pain receptors in the armThe initial slap will cause the body react with fast painHowever, the slight red mark and swelling will cause the body to feel slow pain that feels like a tinglingDO NOT HURT YOUR PARTNER!!!!
28 Video https://www.youtube.com/watc h?v=YL_6OMPywnQ Common problem with nociceptors
29 ThermoreceptorsTemperature receptors inside the skin, skeletal muscles, liver and the hypothalamus are called thermoreceptorsThermoreceptors come in two indistinguishable varieties, cold receptors and warm receptorsCold receptors outnumber warm receptors 3 to 1
30 Thermoreceptors These thermoreceptors are considered phasic receptors Phasic receptors are receptors that are active during changes, however will become inactive during periods of normal maintained conditionsThat means you will feel the first few minutes you enter a room with air conditioning, but the feeling will quickly fadeThis does not apply if the conditions are too extreme
31 MechanoreceptorsSome general sensory receptors are used to pick up physical signalsMechanoreceptors will pick and transmit sensory signals when their plasma membranes are distortedThey do this through mechanically gated ion channels in their plasma membranes
32 MechanoreceptorsThere are many different types of mechanical receptorsThey are divided into three main categoriesTactile receptors provide the sensations of touch, pressure and vibrationBaroreceptors detect pressure changesProprioceptors detect position of joints
33 Tactile Receptors There are many different types of tactile receptors Some receptors can tell detailed information about the source of information with a small receptive fieldThese are called fine receptorsOther receptors will tell general information about a large area because of their large receptive fieldThese are called crude receptors
34 Tactile ReceptorsTwo types of tactile receptors involve nerve endings are free nerve endings and the nerves at the root hair plexusFree nerve endings are receptors that have their nerve endings between epithelial cellsNerve endings that are associated with base of the root hair plexus provide information when the hair is distorted
35 Tactile ReceptorsTactile discs (Merkel discs) are fine touch and pressure receptorsThese nerves associate with specific and large epithelial cellsSince they are only associated with one cell, they have small receptive fields
36 Tactile ReceptorsTactile corpuscles (Meissner's corpuscles) provide fine touch, pressure and vibration informationThese are located mainly in the eyelids, lips, fingertips, nipples and genitalsThe nerve endings are covered by modified Schwann cellsEasy way to identify them!
37 Tactile ReceptorsLamellated corpuscles are receptors that are sensitive to deep pressure and high frequency vibrationThese are located skin, the fasciae and in the joint capsulesThey cover their dendrites to be able to shield themselves from other types of stimulation other than deep pressure
38 Tactile ReceptorsRuffini Corpuscles are located deep within their organs and detect pressureThese receptors do not adapt as easily as other receptors to stimulationThat means when they are activated, you will feel the signals that they are sending