The dynamic human model includes a flexible outer skin securable over the skeleton model and the muscles, whereby a portion of the flexible outer skin may be removed for exposing the skeleton model and the muscles.

The outer layer is divided into separate regions that are not normally visible to the human eye. The boundaries of the regions, or the entire region, may be illuminated to show a color change when contacted, such as by using pressure or a probe. The illumination of color change in the outer layer shows interaction patterns of the body, including which nerves are associated with a particular region of the body. 

The dynamic human model also includes optical elements disposed in the flexible outer skin, whereby the optical elements are adapted to be selectively activated for displaying nerve patterns in the human body. The nerve patterns include a dermatome map and cutaneous innervation patterns.  

Integumentary system

The integumentary system is the organ system that protects the body from various kinds of damage, such as loss of water or abrasion from outside. The system comprises the skin and its appendages. The integumentary system has a variety of functions; it may serve to waterproof, cushion, and protect deeper tissues, excrete wastes, and regulate temperature, and is the attachment site for sensory receptors to detect pain, sensation, pressure, and temperature. 

skin

The skin is the largest organ in the body. In humans, it accounts for about 12 to 15 percent of total body weight. It distinguishes, separates, and protects the organism from its surroundings. 

The human skin (integument) is composed of a minimum of two major layers of tissues: the epidermis and dermis. The epidermis forms the outermost layer, providing the initial barrier to the external environment. Beneath this, the dermis comprises two sections, the papillary and reticular layers, and contains connective tissues, vessels, glands, follicles, hair roots, sensory nerve endings, and muscular tissue. The deepest layer is the hyperdermis, which is primarily made up of adipose tissue. Substantial collagen bundles anchor the dermis to the hypodermic in a way that permits most areas of the skin to move freely over the deeper tissue layers. 

DERMATOME

A dermatome is an area of skin that is mainly supplied by a single spinal nerve. There are 8 cervical nerves (C1 being an exception with no dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the brain. 

Along the thorax and abdomen the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different in which the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints. 

cutaneous innervation

Cutaneous innervation refers to the area of the skin which is supplied by a specific cutaneous nerve. 

peripheral nervous system

The peripheral nervous system (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 one 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, 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.

central nervous system

The central nervous system (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 skin are categorized depending on whether the skin is hairy, nonhairy, or an exposed mucous membrane.

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 ganglion 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 fasciculus. 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 posterior column-medial lemniscus pathway 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 ascent to the somatosensory areas in the postcentral gyrus of the cerebral cortex.