Chapter 57. Touch, Movement, and Pain

axon

part of a neuron specialized to send impulses to other neurons

inner ear

innermost part of the ear, containing the cochlea and semicircular canals

kinesthesia

one of the senses; receptors in muscles, tendons, and joints detect position and movement of the parts of the body

mechanoreceptors

receptor cells that generate neural impulses when stimulated by pressure, vibration, or stretching

myelin

fatty, insulating coating on some axons; speeds up the movement of the neural impulse

neural impulse

an electrical signal that carries a message along an axon

nociceptors

receptors that signal potential tissue damage; brain uses these signals to perceive pain

pain

unpleasant perceptual experience that arises when body tissues are damaged

parietal lobe

upper back part of each hemisphere; processes sensory input for touch and body position

perception

organizing and interpreting information from the senses to understand its meaning

semicircular canals

three small tubes in the inner ear that detect head position and rotation

sensory receptors

specialized cells in the sensory systems that can capture energy or information from a stimulus and convert that information into neural impulses

somatosensory cortex

area within the parietal lobes that receives and processes information from the body senses

thalamus

main relay center in the brain for sensory information on the way to processing areas in the cerebral cortex

thermoreceptors

receptors that signal warmth or cold

touch

one of the senses; receptors in the skin and other organs detect pressure, vibration, movement, temperature, and pain

vestibular sense

one of the senses; receptors in the inner ear detect movements of the head

Touch, Movement, and Pain

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Learning Objectives:

Identify the receptor cells for the sensations generated within the skin and internal organs.

Identify the brain area that processes and perceives the information from body senses within the skin and internal organs.

Explain how touch signals can sometimes diminish the experience of pain.

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The figure is a woman with various touch senses labeled. These include the following: movement of head; position of limbs; touch, including pressure and vibration; pain, including skin damage; pain, including internal organs; and temperature of warmth and cold.

1. How many senses do humans have? If you say “five,” you are lumping several distinctively different senses under the label touch. It would be better to call the sense of touch something like “body-sense,” to include a group of systems that detect the following: a) external objects pressing or vibrating against our skin, b) temperature, c) pain signals indicating damage to our skin or internal organs, and d) changes to our body position.

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The figure is a cross-section of the layers of the skin. The outer layer is labeled the epidermis and is responsible for sensing skin stretching, vibrations, light pressure, heavy pressure, warmth, cold, and pain. The inner layer is labeled the dermis and includes the sensory receptor cells responsible for various touch sensations. Ruffini endings are associated with skin stretching. Pacinian corpuscles are responsible for sensing vibrations. Merkel disks are responsible for sensing light pressure. Meissner corpuscles are responsible for sensing heavy pressure. Free nerve endings are responsible for sensing warmth, cold, and pain.

2. The body sensations we call touch originate in specialized sensory receptor cells buried in the skin. Most of these cells are mechanoreceptors, because they generate neural impulses when the skin around them is squeezed or moved. Some receptors respond primarily to light touch or vibration, while others are specialized for heavy, continuous pressure. Other cells called thermoreceptors detect warmth or cold.

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The figure is a cross-section of the layers of the skin. The outer layer is labeled the epidermis and is responsible for sensing skin stretching, vibrations, light pressure, heavy pressure, warmth, cold, and pain. The inner layer is labeled the dermis and includes the sensory receptor cells responsible for various touch sensations. Ruffini endings are associated with skin stretching. Pacinian corpuscles are responsible for sensing vibrations. Merkel disks are responsible for sensing light pressure. Meissner corpuscles are responsible for sensing heavy pressure. Free nerve endings are responsible for sensing warmth, cold, and pain.

3. Scattered throughout the body, in both the skin and internal organs, are special “harm detectors” called nociceptors. These sensory receptors generate neural impulses when they detect potentially damaging events, such as extreme heat or a cut on the skin. The brain uses these signals to create the perception of pain, which helps us avoid further damage.

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The figure has two images. The first image displays the anatomy of an arm. Tendon stretch receptors are located in the tendons connecting the bicep to the bone. Muscle tension receptors are located in the bicep muscle. Joint movement receptors are located in the elbow joint. The second image displays the anatomy of the inner ear. The semicircular canals are large circular canals filled with fluid. These are attached to the cochlea, which is snail shaped.

4. In addition to detecting external objects, our “body-sense” detects the position and movement of the body. Mechanoreceptors in the muscles, tendons, and joints generate neural impulses when the arms or legs are moved—a sense called kinesthesia. Highly specialized cells in the semicircular canals of the inner ear are responsible for our vestibular sense, detecting rotation of the head or forward-backward movement of the head (and the whole body).

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The figure is a cross-section of the layers of the skin. The outer layer is labeled the epidermis and is responsible for sensing skin stretching, vibrations, light pressure, heavy pressure, warmth, cold, and pain. The inner layer is labeled the dermis and includes the sensory receptor cells responsible for various touch sensations. Ruffini endings are associated with skin stretching. Pacinian corpuscles are responsible for sensing vibrations. Merkel disks are responsible for sensing light pressure. Meissner corpuscles are responsible for sensing heavy pressure. Free nerve endings are responsible for sensing warmth, cold, and pain.

5. All the neural impulses from these various “body-sense” receptors travel to the brain’s parietal lobe, where they are processed in the somatosensory cortex, creating perceptions of events happening outside or inside the body.

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Practice 1: Exploring the Body Senses

Roll over each label to view that component of somatosensory perception.

Somatosensory component:

Special mechanoreceptors in the semicircular canals within the inner ear detect rotation of the head and straight-line movement of the head.

Nociceptors in the skin and internal organs detect injury or potential damage to body tissues.

Thermoreceptors in the skin and internal organs detect warmth and cold.

Mechanoreceptors embedded in the skin detect light touch, heavy pressure, vibration, and stretching of the skin.

Mechanoreceptors in muscles, tendons, and joints detect position and movement of arms and legs.

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Practice 2: Interaction of Pain and Touch

This person has an injured elbow. Select the "Pain pathway" button to view the signals that will be perceived as pain. Then select the "Block pain" button to view one way of reducing the experience of pain.

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Sebastian Kaulitzki/ShutterStock

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Quiz 1

Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

Select the NEXT button and move to Quiz 2.

Perhaps you should go back to review sensory receptors and brain areas involved in touch, movement, and pain.

somatosensory cortex

mechanoreceptor

vestibular sense

kinesthesia

nociceptor

thermoreceptor

generates neural impulses when stimulated by pressure, vibration, or stretching

generates neural impulses that signal potential tissue damage; brain uses these signals to perceive pain

receives and processes information from the skin and internal organs

has receptors in the inner ear that detect movements of the head

has receptors in muscles, tendons, and joints that detect position and movement of the parts of the body

generates neural impulses that signal warmth or cold

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Select the NEXT button and move to the Conclusion.

Try to respond to the statements again.

Quiz 2

Indicate whether each of the statements below is True or False. Then, select the CHECK ANSWER button.

True	False
		The sensory receptors that the body uses to detect touch and vibration are different from the receptors that detect tissue damage.
		Signals travel from nociceptors to the spinal cord on thick, myelinated axons.
		The experience of pain can be influenced by other simultaneous events detected by the somatosensory system.

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Congratulations!

You have completed the activity Touch, Movement, and Pain.