Touch

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Video

• https://youtu.be/I7wfDenj6CQ?t=6s

• What a pain!

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

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

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

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!

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!

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!!!!

Video

• https://www.youtube.com/watch?v=YL_6OMPywnQ

• Common problem with nociceptors

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

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

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

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

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

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

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

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!

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

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