Touch
Pain and Touch
Pain is a complex sensory and emotional experience that is typically triggered by harmful or potentially harmful
stimuli, and it serves as a protective mechanism to alert the body of potential injury or damage.
It is processed in a way that involves the activation of different sensory receptors in the body.
Understanding pain requires us to look at different types of receptors and the neural pathways that
convey these sensations to the brain.
The sense of touch is in a sense not really a single sense but instead several distinct related senses
1. Light touch / texture: This involves sensing the light contact or texture on the skin, usually detected by
mechanoreceptors like Merkel cells or Meissner’s corpuscles. These receptors respond to the fine details of
touch, such as textures and shapes.
Deep touch / pressure: This refers to the sensation of deeper pressure or contact with the skin, often detected
by mechanoreceptors like the Pacinian corpuscles (which are sensitive to vibration and pressure) and Ruffini
endings (which detect skin stretch and sustained pressure).
Stretch: Stretch receptors in the skin and muscles detect the stretching or deformation of tissues. These are
important in proprioception (the sense of body position) and are detected by muscle spindle fibers and other
mechanoreceptors
The above are mechanical.force
Heat: Heat is detected by warmth thermoreceptors in the skin, which respond to temperature increases.
Extreme heat can also activate nociceptors, leading to a painful sensation. This is part of the body’s way of
protecting itself from potentially harmful stimuli.
Cold: Cold stimuli are detected by cold thermoreceptors in the skin. These receptors are activated when the
temperature drops and cause sensations of coldness. Extreme cold can activate nociceptors, leading to a pain
response.
Pain – different kinds of pain
These different types of touch detect different kind of forces
around the world but all of them rely on a single sensory organ
– the skin – there are processed in similar ways
The main sensory organ of the sense touch is the skin which is
the largest organ and most complex and the most nerve fiber
running through the brain
But the retina has more photoreceptors than the receptors that the skin has
,The touch organ – the human skin
The human skin is a complex and multifunctional organ that serves as the body's first line of defense and
plays a vital role in sensory perception. The skin is composed of three main layers, each with specific
functions:
1. Epidermis (Outer Protective Layer)
• The epidermis is the outermost layer of the skin, serving as a barrier to protect the body from external
threats like pathogens, chemicals, and physical damage.
• Structure: It is made up primarily of keratinocytes, which are cells that produce keratin, a protein
that provides strength and waterproofing.
• Function: The epidermis also plays a key role in the body's UV protection, as it contains melanocytes
that produce melanin, the pigment that gives skin its color and helps protect against UV radiation.
• The epidermis is avascular, meaning it doesn't contain blood vessels. Nutrients and oxygen are
supplied by diffusion from the underlying dermis.
• The outermost part of the epidermis is made up of dead skin cells, which constantly shed and are
replaced by new cells coming from deeper layers.
2. Dermis (Middle Layer)
• The dermis lies directly beneath the epidermis and is much thicker. It holds most of the skin's sensory
receptors and glands.
• Structure: It contains two layers:
o The papillary dermis: The upper layer, which is thinner and has a loose, fibrous structure.
o The reticular dermis: The deeper layer, which is thicker and made of dense connective tissue,
providing strength and elasticity to the skin.
, • Function: The dermis houses important structures such as:
o Sensory receptors: These include mechanoreceptors (for touch, pressure, and vibration),
thermoreceptors (for heat and cold), and nociceptors (for pain). These receptors allow the skin
to detect various types of sensory input from the environment.
o Hair follicles: The dermis is where hair grows, with each follicle having an associated
sebaceous (oil) gland.
o Sweat glands: These help with thermoregulation by secreting sweat to cool the body.
o Blood vessels: These supply nutrients and oxygen to the dermis and help regulate body
temperature through vasodilation (widening of blood vessels to release heat) and
vasoconstriction (narrowing of blood vessels to retain heat).
3. Hypodermis (Subcutis)
• The hypodermis, also known as the subcutis, is the deepest layer of the skin. Technically, it's not part
of the skin, but it plays an important role in supporting the skin and its functions.
• Structure: This layer is made up of loose connective tissue and adipose tissue (fat). It acts as a
cushion that absorbs shocks and insulates the body, helping to maintain body temperature.
• Function: The hypodermis has two key functions:
o Anchoring: It connects the skin to underlying structures like muscles, joints, and bones.
o Energy storage: The fat stored in the hypodermis provides a reserve of energy that the body
can use when needed.
Summary of Functions:
• Protection: The skin protects the body from mechanical damage, pathogens, UV radiation, and
dehydration.
• Sensory Perception: The skin is involved in touch, pain, temperature, and pressure sensation, largely
due to the mechanoreceptors, thermoreceptors, and nociceptors in the dermis.
• Temperature Regulation: Through the activity of sweat glands and blood vessels, the skin helps
regulate body temperature.
• Excretion: Sweat glands also help excrete waste products like salts and urea.
• Synthesis of Vitamin D: Exposure to UV light triggers the skin to synthesize Vitamin D, which is
important for calcium absorption and bone health.
Sensing Touch & Pressure: The Skin’s Mechanoreceptors
The skin can sense touch and pressure thanks to specialized sensory nerve endings called mechanoreceptors.
These receptors respond to mechanical stimuli—things like stretching, vibration, indentation, and pressure
applied to the skin. They convert these mechanical forces into electrical signals (nerve impulses) that are sent
to the brain, where they are interpreted as sensations of touch.
The mechanoreceptors change shape as pressure or touch is detected and this change leads to some
change on the membrane potential
There are four primary types of mechanoreceptors in the skin, each with distinct functions based on:
Pain and Touch
Pain is a complex sensory and emotional experience that is typically triggered by harmful or potentially harmful
stimuli, and it serves as a protective mechanism to alert the body of potential injury or damage.
It is processed in a way that involves the activation of different sensory receptors in the body.
Understanding pain requires us to look at different types of receptors and the neural pathways that
convey these sensations to the brain.
The sense of touch is in a sense not really a single sense but instead several distinct related senses
1. Light touch / texture: This involves sensing the light contact or texture on the skin, usually detected by
mechanoreceptors like Merkel cells or Meissner’s corpuscles. These receptors respond to the fine details of
touch, such as textures and shapes.
Deep touch / pressure: This refers to the sensation of deeper pressure or contact with the skin, often detected
by mechanoreceptors like the Pacinian corpuscles (which are sensitive to vibration and pressure) and Ruffini
endings (which detect skin stretch and sustained pressure).
Stretch: Stretch receptors in the skin and muscles detect the stretching or deformation of tissues. These are
important in proprioception (the sense of body position) and are detected by muscle spindle fibers and other
mechanoreceptors
The above are mechanical.force
Heat: Heat is detected by warmth thermoreceptors in the skin, which respond to temperature increases.
Extreme heat can also activate nociceptors, leading to a painful sensation. This is part of the body’s way of
protecting itself from potentially harmful stimuli.
Cold: Cold stimuli are detected by cold thermoreceptors in the skin. These receptors are activated when the
temperature drops and cause sensations of coldness. Extreme cold can activate nociceptors, leading to a pain
response.
Pain – different kinds of pain
These different types of touch detect different kind of forces
around the world but all of them rely on a single sensory organ
– the skin – there are processed in similar ways
The main sensory organ of the sense touch is the skin which is
the largest organ and most complex and the most nerve fiber
running through the brain
But the retina has more photoreceptors than the receptors that the skin has
,The touch organ – the human skin
The human skin is a complex and multifunctional organ that serves as the body's first line of defense and
plays a vital role in sensory perception. The skin is composed of three main layers, each with specific
functions:
1. Epidermis (Outer Protective Layer)
• The epidermis is the outermost layer of the skin, serving as a barrier to protect the body from external
threats like pathogens, chemicals, and physical damage.
• Structure: It is made up primarily of keratinocytes, which are cells that produce keratin, a protein
that provides strength and waterproofing.
• Function: The epidermis also plays a key role in the body's UV protection, as it contains melanocytes
that produce melanin, the pigment that gives skin its color and helps protect against UV radiation.
• The epidermis is avascular, meaning it doesn't contain blood vessels. Nutrients and oxygen are
supplied by diffusion from the underlying dermis.
• The outermost part of the epidermis is made up of dead skin cells, which constantly shed and are
replaced by new cells coming from deeper layers.
2. Dermis (Middle Layer)
• The dermis lies directly beneath the epidermis and is much thicker. It holds most of the skin's sensory
receptors and glands.
• Structure: It contains two layers:
o The papillary dermis: The upper layer, which is thinner and has a loose, fibrous structure.
o The reticular dermis: The deeper layer, which is thicker and made of dense connective tissue,
providing strength and elasticity to the skin.
, • Function: The dermis houses important structures such as:
o Sensory receptors: These include mechanoreceptors (for touch, pressure, and vibration),
thermoreceptors (for heat and cold), and nociceptors (for pain). These receptors allow the skin
to detect various types of sensory input from the environment.
o Hair follicles: The dermis is where hair grows, with each follicle having an associated
sebaceous (oil) gland.
o Sweat glands: These help with thermoregulation by secreting sweat to cool the body.
o Blood vessels: These supply nutrients and oxygen to the dermis and help regulate body
temperature through vasodilation (widening of blood vessels to release heat) and
vasoconstriction (narrowing of blood vessels to retain heat).
3. Hypodermis (Subcutis)
• The hypodermis, also known as the subcutis, is the deepest layer of the skin. Technically, it's not part
of the skin, but it plays an important role in supporting the skin and its functions.
• Structure: This layer is made up of loose connective tissue and adipose tissue (fat). It acts as a
cushion that absorbs shocks and insulates the body, helping to maintain body temperature.
• Function: The hypodermis has two key functions:
o Anchoring: It connects the skin to underlying structures like muscles, joints, and bones.
o Energy storage: The fat stored in the hypodermis provides a reserve of energy that the body
can use when needed.
Summary of Functions:
• Protection: The skin protects the body from mechanical damage, pathogens, UV radiation, and
dehydration.
• Sensory Perception: The skin is involved in touch, pain, temperature, and pressure sensation, largely
due to the mechanoreceptors, thermoreceptors, and nociceptors in the dermis.
• Temperature Regulation: Through the activity of sweat glands and blood vessels, the skin helps
regulate body temperature.
• Excretion: Sweat glands also help excrete waste products like salts and urea.
• Synthesis of Vitamin D: Exposure to UV light triggers the skin to synthesize Vitamin D, which is
important for calcium absorption and bone health.
Sensing Touch & Pressure: The Skin’s Mechanoreceptors
The skin can sense touch and pressure thanks to specialized sensory nerve endings called mechanoreceptors.
These receptors respond to mechanical stimuli—things like stretching, vibration, indentation, and pressure
applied to the skin. They convert these mechanical forces into electrical signals (nerve impulses) that are sent
to the brain, where they are interpreted as sensations of touch.
The mechanoreceptors change shape as pressure or touch is detected and this change leads to some
change on the membrane potential
There are four primary types of mechanoreceptors in the skin, each with distinct functions based on:
