1. Touch

2. The Sense of Touch
The overall sense of touch is one that has a high degree of variability
This is because it has a large group of neurons that have the ability to perceive many different sensations
Also the neurons can be located on many different structures around the body

3. The Sense of Touch
The sense of touch is regulated by sensory receptors that monitor the internal state of the body and the external environment
These are a group of mixed neurons that are responsible for sending information about the state of the body
The 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 task
It is two completely different systems that are functioning at the same time
Sensation is the ability to detect arriving information
Perception 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 perceptions
Most of the sensation of the body is picked up by neurons that are distributed throughout the body
Then 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 stimuli
They are highly sensitive to one singular form of stimuli and mostly blind to other types of stimuli
This sensitivity and simultaneous blindness is called receptor specificity

7. Types of Receptors
There are six major ways that sensory receptors can tell the world about the body
Temperature is the perception of heat energy inside and outside the body
Pain is the determination and discrimination of things that cause injury
Touch is the feel of the texture of an object

8. Types of Receptors
Pressure is the discrimination of the physical force that is pushing against the body
Vibration is the discrimination of the determination of the oscillation of receptors
Proprioception is the ability to sense how and the range that the joints of the body move

9. Types of Receptors
While we might think that there are more feelings, they are all just a combination of these senses
For 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 characteristics
Most neural receptors have a large number of dendrites called free nerve endings
These 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 field
This is a small patch of an organ that neurons are responsible for sending signals from
When neural fields are close together, they have high sensitivity
When 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 work
Since they can only send one signal per neuron, two stimuli on one neuron will only be sent as one signal
To test this we will test how close together two receptive fields are within the body

13. Demo
To do this in the body we will use pins to put an extremely light pressure on the skin
To start you will have the person being experimented on close their eyes
Then place heads of both pins touching the same point on their shoulder
Slowly pickup and then place down the pin very lightly several times to gradually increase the distance between the pin heads
Stop when the person with their eyes closed feels two completely different points of pressure
Measure the difference between the two points

14. Demo
Now that we have the hang of the experiment, repeat the experiment on other body parts
Use the cheek, a finger tip, the calf, the small of the back and the forearm
Measure and record all of the distance between the receptive fields in each area
Determine 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 body
General 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 environment
Proprioceptors report the positions of skeletal muscle and joints
Interoceptors provide information about the internal environment

17. General Sensory Receptors
Another classification for touch receptors is based on their excitatory stimulus
Nociceptors are stimulated by pain signals
Thermoreceptors are stimulated by changes in temperature
Mechanoreceptors are stimulated by physical changes
Chemoreceptors are stimulated by a chemical concentration

18. Nociceptors
Pain receptors (aka nociceptors) are very common in the outer portions of the skin, joint capsules, bones and around the walls of blood vessels
Noxa is Latin for harm
These detectors sense pain from areas of the body that can often become damaged or need to know when they are damaged
Nociceptors are sparse in internal organs and deep tissues

19. Nociceptors
Nociceptors are commonly nerves with large receptive fields
When nociceptors are tightly packed, it can be easy to pinpoint where a stimulus is coming from
This 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 sources
This means that nociceptors are receptive to changes in temperature, mechanical damage and dissolved chemicals
In very damaging situations, these different stimuli can be confused
A deep cut can be confused with a burning sensation

21. Video
=6s
What a pain!

22. What a Pain in the Nociceptor!
Pain is a very hard feeling to describe
That is because our brain does not categorize or remember pain
We 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 signals
Myelinated type A fibers will carry fast pain
Also known as prickling pain
This is pain that is quickly felt by the CNS and can cause a somatic reaction
They 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 pain
These are known as burning pain fibers or aching pain fibers
These sensations cause pain to be routed to the thalamus
From 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 mind
If 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 pain
Keep the thalamus occupied and you will not notice the slow pain
Every 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 TO
Anyone with a medical condition should probably sit this one out
Before we move on, please be sure that you are ready for this!

27. Demo
I 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 arm
The initial slap will cause the body react with fast pain
However, the slight red mark and swelling will cause the body to feel slow pain that feels like a tingling
DO NOT HURT YOUR PARTNER!!!!

28. Video https://www.youtube.com/watc h?v=YL_6OMPywnQ
Common problem with nociceptors

29. Thermoreceptors
Temperature receptors inside the skin, skeletal muscles, liver and the hypothalamus are called thermoreceptors
Thermoreceptors come in two indistinguishable varieties, cold receptors and warm receptors
Cold 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 conditions
That means you will feel the first few minutes you enter a room with air conditioning, but the feeling will quickly fade
This does not apply if the conditions are too extreme

31. Mechanoreceptors
Some general sensory receptors are used to pick up physical signals
Mechanoreceptors will pick and transmit sensory signals when their plasma membranes are distorted
They do this through mechanically gated ion channels in their plasma membranes

32. Mechanoreceptors
There are many different types of mechanical receptors
They are divided into three main categories
Tactile receptors provide the sensations of touch, pressure and vibration
Baroreceptors detect pressure changes
Proprioceptors 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 field
These are called fine receptors
Other receptors will tell general information about a large area because of their large receptive field
These are called crude receptors

34. Tactile Receptors
Two types of tactile receptors involve nerve endings are free nerve endings and the nerves at the root hair plexus
Free nerve endings are receptors that have their nerve endings between epithelial cells
Nerve endings that are associated with base of the root hair plexus provide information when the hair is distorted

35. Tactile Receptors
Tactile discs (Merkel discs) are fine touch and pressure receptors
These nerves associate with specific and large epithelial cells
Since they are only associated with one cell, they have small receptive fields

36. Tactile Receptors
Tactile corpuscles (Meissner's corpuscles) provide fine touch, pressure and vibration information
These are located mainly in the eyelids, lips, fingertips, nipples and genitals
The nerve endings are covered by modified Schwann cells
Easy way to identify them!

37. Tactile Receptors
Lamellated corpuscles are receptors that are sensitive to deep pressure and high frequency vibration
These are located skin, the fasciae and in the joint capsules
They cover their dendrites to be able to shield themselves from other types of stimulation other than deep pressure

38. Tactile Receptors
Ruffini Corpuscles are located deep within their organs and detect pressure
These receptors do not adapt as easily as other receptors to stimulation
That means when they are activated, you will feel the signals that they are sending