Cutaneous innervation
Encyclopedia
Cutaneous innervation refers to the area of the skin
which is supplied by a specific cutaneous nerve
.
Dermatomes are similar; however, a dermatome only specifies the area served by a spinal nerve
. In some cases, the dermatome is less specific (when a spinal nerve is the source for more than one cutaneous nerve), and in other cases it is more specific (when a cutaneous nerve is derived from multiple spinal nerves.)
Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details. The borders designated by the diagrams in the 1918 edition of Gray's Anatomy
, provided below, are similar but not identical to those generally accepted today. The concept of autonomous territory and the concept of maximal territory of cutaneous distribution for every cutaneous branch are immensely useful to clinicians assessing patients with neurological disorders..
(PNS) is divided into the somatic nervous system
, the autonomic nervous system
, and the enteric nervous system
. However, it is the somatic nervous system, responsible for body movement and the reception of external stimuli, which allows to understand how cutaneous innervation is made possible by the action of specific sensory fibers located on the skin
, as well as the distinct pathways they take to the central nervous system. The skin, which is part of the integumentary system
, it plays an important role in the somatic nervous system because it contains a range of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury.
(CNS) works with the peripheral nervous system in cutaneous innervation. The CNS is responsible for processing the information it receives from the cutaneous nerves that detect a given stimulus, and then identifying the kind of sensory inputs which project to a specific region of the primary somatosensory cortex.
are categorized depending on whether the skin is hairy, nonhairy, or an exposed mucous membrane.
The first one, Meissner’s corpuscles are encapsulated nerve endings attached to the epidermis in the dermal papilli that detect changes in texture and vibrations.
Merkel's discs are arborizations of nonmyelinated axons that that end in terminals on specialized tactile cells and which detect sustained touch and pressure.
Lastly, there are also “free” nerve endings which are similar in structure to those in hairy skin, though they are more numerous.
of those areas.
The cornea
, one of the other exposed mucous membranes, contains “free” nerve endings served by nonmyelinated axons.
The conjunctiva
contains a less dense distribution of “free” nerve endings that are served by both myelinated and unmyelinated axons.
Epicritic neurons detect gentle touch such as caresses; light vibrations; the ability to recognize the shape of an object being held; and two-point discrimination, or the spacing of two points being touched simultaneously.
Protopathic neurons are responsible for detecting pain, itch, tickle, and temperature.
The different types of stimuli that are detected by a given receptor allow for a relative specificity between stimuli and receptor.
neurons will take within the central nervous system. The sensory neurons coming from the body synapse in the dorsal horn of the spinal cord
, bringing in information about touch sensations (epicritic), or modalities of pain (protopathic). While both types of sensory neurons must first synapse in the dorsal horn of the spinal cord, the area of the dorsal horn where they synapse is different. Their pathway to the thalamus is also different.
Neurons that carry information about touch, vibration, and proprioception sensations from the lower body enter the spinal cord below spinal level T6, where they synapse in the dorsal horn to form reflex circuits, but also send axon branches through the gracile fascicle to the brainstem. Similarly, information from the upper body enters the spinal cord at level T6 and above, and ascend toward the brainstem in the cuneate
fascicle. Together the gracile and cuneate form the dorsal column in the spine.
Neurons that carry information about pain and temperature synapse in the dorsal horn at the anterolateral fascicles.
While the neurons for touch sensations ascend ipsilaterally through the dorsal column-medial lemniscal system to the thalamus; neurons for pain and temperature ascend contralaterally to the thalamus through the anterolateral system
.
When both sensory pathways reach the integrating center that is the thalamus, they make their final assent to the somatosensory areas in the postcentral gyrus
of the cerebral cortex
.
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
which is supplied by a specific cutaneous nerve
Cutaneous nerve
A cutaneous nerve is a nerve that innervates the skin.-Human anatomy:In human anatomy, cutaneous nerves are responsible for providing sensory innervation to the skin. They are generally thought of as sensory-only nerves, but they may provide motor innervation to structures in the skin, e.g...
.
Dermatomes are similar; however, a dermatome only specifies the area served by a spinal nerve
Spinal nerve
The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body...
. In some cases, the dermatome is less specific (when a spinal nerve is the source for more than one cutaneous nerve), and in other cases it is more specific (when a cutaneous nerve is derived from multiple spinal nerves.)
Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details. The borders designated by the diagrams in the 1918 edition of Gray's Anatomy
Gray's Anatomy
Gray's Anatomy is an English-language human anatomy textbook originally written by Henry Gray. The book is widely regarded as an extremely influential work on the subject, and has continued to be revised and republished from its initial publication in 1858 to the present day...
, provided below, are similar but not identical to those generally accepted today. The concept of autonomous territory and the concept of maximal territory of cutaneous distribution for every cutaneous branch are immensely useful to clinicians assessing patients with neurological disorders..
Importance of the peripheral nervous system
The peripheral nervous systemPeripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
(PNS) is divided into the somatic nervous system
Somatic nervous system
The somatic nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles...
, the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
, and the enteric nervous system
Enteric nervous system
The enteric nervous system is a subdivision of the autonomic nervous system that directly controls the gastrointestinal system in vertebrates.It is derived from neural crest.-Function:...
. However, it is the somatic nervous system, responsible for body movement and the reception of external stimuli, which allows to understand how cutaneous innervation is made possible by the action of specific sensory fibers located on the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, as well as the distinct pathways they take to the central nervous system. The skin, which is part of the integumentary system
Integumentary system
The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages...
, it plays an important role in the somatic nervous system because it contains a range of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury.
Importance of the central nervous system
The central nervous systemCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
(CNS) works with the peripheral nervous system in cutaneous innervation. The CNS is responsible for processing the information it receives from the cutaneous nerves that detect a given stimulus, and then identifying the kind of sensory inputs which project to a specific region of the primary somatosensory cortex.
The role of nerve endings on the surface of the skin
Groups of nerve terminals located in the different layers of the skinSkin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
are categorized depending on whether the skin is hairy, nonhairy, or an exposed mucous membrane.
Hairy skin
The hairy parts of the body such as the forearm or the leg have two groups of nerve endings: those that end along with the hair follicles, and also with the arborizations of unmyelinated axons which are referred to as “free” nerve endings because they are served by both myelinated and unmyelinated axons.Nonhairy skin
Nonhairy skin, such as the palms of hands and the soles of feet, has three types of nerve terminations.The first one, Meissner’s corpuscles are encapsulated nerve endings attached to the epidermis in the dermal papilli that detect changes in texture and vibrations.
Merkel's discs are arborizations of nonmyelinated axons that that end in terminals on specialized tactile cells and which detect sustained touch and pressure.
Lastly, there are also “free” nerve endings which are similar in structure to those in hairy skin, though they are more numerous.
exposed mucous membranes
The exposed mucous membranes of the lips, the anal mucous membrane, and the external genital organs form the most densely innervated parts of the body. Though there is no specific categorization, both “free” nerve endings and unencapsulated nerve endings of myelinated axons are found within the dermisDermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
of those areas.
The cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, one of the other exposed mucous membranes, contains “free” nerve endings served by nonmyelinated axons.
The conjunctiva
Conjunctiva
The conjunctiva covers the sclera and lines the inside of the eyelids. It is composed of rare stratified columnar epithelium.-Function:...
contains a less dense distribution of “free” nerve endings that are served by both myelinated and unmyelinated axons.
Distribution of sensory neurons
The distribution of the sensory neurons within the skin accounts for the large and overlapping receptive fields of the skin. The size of the receptive fields in turn explains why almost any given stimulus to the human skin can potentially activate a very large number of nerve terminals. Therefore it is more likely that a stimulus caused by the prick of a needle be detected by more than a hundred nerve endings all sharing the same receptive field, than for that same needle prick to be detected by only one nerve ending.Types of sensory neurons
The different kinds of sensory stimuli that are picked up by sensory neurons are grouped into two categories: epicritic and protopathic.Epicritic neurons detect gentle touch such as caresses; light vibrations; the ability to recognize the shape of an object being held; and two-point discrimination, or the spacing of two points being touched simultaneously.
Protopathic neurons are responsible for detecting pain, itch, tickle, and temperature.
The different types of stimuli that are detected by a given receptor allow for a relative specificity between stimuli and receptor.
Pathways to the CNS
The sensory modality that is detected by the afferent fibers is an important factor to consider because it determines the pathway that the dorsal root ganglionDorsal root ganglion
In anatomy and neuroscience, a dorsal root ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.-Unique unipolar structure:...
neurons will take within the central nervous system. The sensory neurons coming from the body synapse in the dorsal horn of the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
, bringing in information about touch sensations (epicritic), or modalities of pain (protopathic). While both types of sensory neurons must first synapse in the dorsal horn of the spinal cord, the area of the dorsal horn where they synapse is different. Their pathway to the thalamus is also different.
Neurons that carry information about touch, vibration, and proprioception sensations from the lower body enter the spinal cord below spinal level T6, where they synapse in the dorsal horn to form reflex circuits, but also send axon branches through the gracile fascicle to the brainstem. Similarly, information from the upper body enters the spinal cord at level T6 and above, and ascend toward the brainstem in the cuneate
Cuneate
Cuneate means "wedge-shaped," it can apply to:*cuneate leaf, a leaf shape*the cuneate nucleus, a part of the brainstem*the cuneate fasciculus, a tract from the spinal cord into the brainstem...
fascicle. Together the gracile and cuneate form the dorsal column in the spine.
Neurons that carry information about pain and temperature synapse in the dorsal horn at the anterolateral fascicles.
While the neurons for touch sensations ascend ipsilaterally through the dorsal column-medial lemniscal system to the thalamus; neurons for pain and temperature ascend contralaterally to the thalamus through the anterolateral system
Anterolateral system
In the nervous system, the anterolateral system is an ascending pathway that conveys pain, temperature , and crude touch from the periphery to the brain. It comprises three main pathways:-External links:*...
.
When both sensory pathways reach the integrating center that is the thalamus, they make their final assent to the somatosensory areas in the postcentral gyrus
Postcentral gyrus
The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch...
of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
.
See also
- Cutaneous innervation of the upper limbsCutaneous innervation of the upper limbsCutaneous innervation refers to the area of the skin which is supplied by a specific nerve.Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details...
- Cutaneous innervation of the lower limbsCutaneous innervation of the lower limbsCutaneous innervation refers to the area of the skin which is supplied by a specific nerve.Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details...
- Cutaneous innervation of the headCutaneous innervation of the headCutaneous innervation refers to the area of the skin which is supplied by a specific nerve.Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details...
- AesthesiographyAesthesiographyAesthesiography comes from the Greek word “aesthesis” meaning "sensibility," and “graphy” in order to visualize hyposensibility of the skin. This term has been proposed by the French surgeon Létiévant....