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By the end of this section, you will be able to:
  • Describe four important mechanoreceptors in human skin
  • Describe the topographical distribution of somatosensory receptors between glabrous and hairy skin
  • Explain why the perception of pain is subjective

Somatosensation is a mixed sensory category and includes all sensation received from the skin and mucous membranes, as well from as the limbs and joints. Somatosensation is also known as tactile sense, or more familiarly, as the sense of touch. Somatosensation occurs all over the exterior of the body and at some interior locations as well. A variety of receptor types—embedded in the skin, mucous membranes, muscles, joints, internal organs, and cardiovascular system—play a role.

Recall that the epidermis is the outermost layer of skin in mammals. It is relatively thin, is composed of keratin-filled cells, and has no blood supply. The epidermis serves as a barrier to water and to invasion by pathogens. Below this, the much thicker dermis contains blood vessels, sweat glands, hair follicles, lymph vessels, and lipid-secreting sebaceous glands ( [link] ). Below the epidermis and dermis is the subcutaneous tissue, or hypodermis, the fatty layer that contains blood vessels, connective tissue, and the axons of sensory neurons. The hypodermis, which holds about 50 percent of the body’s fat, attaches the dermis to the bone and muscle, and supplies nerves and blood vessels to the dermis.

Illustration shows a cross section of mammalian skin. The outer epidermis is a thin layer, smooth on the outside, bumpy on the inside. The middle dermis is much thicker than the dermis. Blood, nerve and lymph vessels run along the bottom of it, and smaller capillaries and nerve endings extend to the upper part. One nerve ends in a receptor. Sweat glands extend from the dermis into the epidermis. Hair follicles extend from the base of the dermis to the upper part where they are joined by oil glands. Hairs extend from the follicles, through the epidermis and out of the skin. The hypodermis is a fatty layer beneath the dermis.
Mammalian skin has three layers: an epidermis, a dermis, and a hypodermis. (credit: modification of work by Don Bliss, National Cancer Institute)

Somatosensory receptors

Sensory receptors are classified into five categories: mechanoreceptors, thermoreceptors, proprioceptors, pain receptors, and chemoreceptors. These categories are based on the nature of stimuli each receptor class transduces. What is commonly referred to as “touch” involves more than one kind of stimulus and more than one kind of receptor. Mechanoreceptors in the skin are described as encapsulated (that is, surrounded by a capsule) or unencapsulated (a group that includes free nerve endings). A free nerve ending    , as its name implies, is an unencapsulated dendrite of a sensory neuron. Free nerve endings are the most common nerve endings in skin, and they extend into the middle of the epidermis. Free nerve endings are sensitive to painful stimuli, to hot and cold, and to light touch. They are slow to adjust to a stimulus and so are less sensitive to abrupt changes in stimulation.

There are three classes of mechanoreceptors: tactile, proprioceptors, and baroreceptors. Mechanoreceptors sense stimuli due to physical deformation of their plasma membranes. They contain mechanically gated ion channels whose gates open or close in response to pressure, touch, stretching, and sound.” There are four primary tactile mechanoreceptors in human skin: Merkel’s disks, Meissner’s corpuscles, Ruffini endings, and Pacinian corpuscle; two are located toward the surface of the skin and two are located deeper. A fifth type of mechanoreceptor, Krause end bulbs, are found only in specialized regions. Merkel’s disks (shown in [link] ) are found in the upper layers of skin near the base of the epidermis, both in skin that has hair and on glabrous    skin, that is, the hairless skin found on the palms and fingers, the soles of the feet, and the lips of humans and other primates. Merkel’s disks are densely distributed in the fingertips and lips. They are slow-adapting, unencapsulated nerve endings, and they respond to light touch. Light touch, also known as discriminative touch, is a light pressure that allows the location of a stimulus to be pinpointed. The receptive fields of Merkel’s disks are small with well-defined borders. That makes them finely sensitive to edges and they come into use in tasks such as typing on a keyboard.

Questions & Answers

Which of the following statements regarding membrane transport is false? 1. Glucose is transported only by facilitated diffusion 2.Each protein carrier will only bind and b transport one type of solute.
#2. Each protein carrier will only bind and b transport one type of soluble
Only
#2 is false for the regarding membrane transport.
Only
Tanks a lot
Thanks a lot
what is gene
Okello Reply
what is somatic cell
garaadmaxamed Reply
what is Biology?
garaadmaxamed
is the study of living things
garaadmaxamed
what is biology
Isiaka Reply
is the study of all living things
Motinga
and their interactions with each other and the environment
Angela
it is the study of all living organisms and their characteristics
ketchem
the study of living things and their surroundings
Ade
what's is biology
Mohamed Reply
what's is dna
Mohamed
deoxybonucliec acid
Gibril
explain the osomor regulations in amoeba and paramecium
Adannaya Reply
explain the osimoregulation in man
Adannaya
who can explain the osmoregulation in amoeba and in man
Adannaya
Hello how are you every body
Sitali Reply
join the conversation
Sitali
l am fine every body
Memiru
I'm very fine_hopefully everyone is fine
Rorisang
what is meant by submicroscopic?
anji Reply
what is anabolic and catabolic
Jonathan
hi
Alpha
hi berther
Memiru
hallo
Memiru
what is the meaning of biology
Dorathy Reply
biology is scientific study of living things
GUYO
what is chromosomes?
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it is a cell structure that contains DNA histones protein and other structural proteins
Ekechi
what is DNA
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Hassan Reply
liver is an organ in the body that meterbolise nutrients and produce bile.
Ekechi
what is the function of granum?
Gulfam
what is the faction of liver cancer
Kashah
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Eric Reply
Biology is you
muayad
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and. evolution
Suzette
biology is the study of living things and none living things
Ekechi
study of living organisms
anji
The mamalian endoskeleton has 206 bones
kaazim Reply
hii
Hannah
hi
Suzette
how you
Hannah
good thanks
Suzette
have you done the actual course?
Suzette
How many bones do human body have?
moses Reply
I don't know please help me
Kisito
206
Waneh
206
Moses
206
anji
what are these geneti materials
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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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