Understanding the Hand Anatomy

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Table of Contents

Introduction
Types of Muscles
Sensory Stimulus Pathways
Adduction Movement
Stroke
Conclusion
References

Introduction

The human body comprises different parts that perform distinct and coordinated functions. In conjunction with the brain, the body parts respond accordingly to both internal and external environments. The excellent functionality of the different parts of the body, including the hand, thigh, neck, girdle, pectoral, and legs, are critical for the normal functioning of a human being. The brain is considered the command center of the body. According to Ramadan and Vasilakos (2017), it is equal to the computer’s central processing unit (CPU) because it controls everybody’s duty and action. This paper aims to understand how the human hand and the specific muscles work in partnership with the brain.

Types of Muscles

Interossei Muscles

The interossei have both the palmar and dorsal small muscles. The muscles commence between the bones of the hand, towards the fingers. The muscles allow the bending of the metacarpophalangeal joint, where the finger bones intersect the hand ones. Burin et al. (2017) opine that the dorsal interossei enable people to spread their fingers away from each other while the palmar interossei pull their fingers together. It is regarded as the first muscle to shrink among patients with cubital tunnel syndrome (Urits et al., 2019). The dorsal interosseous pulls the thumb close to the index finger, providing stability when pinching. Therefore, the interossei muscles are part of the muscles which form the human hand.

Hypothenar

The hypothenar muscles are the other muscles which form part of the hand. The flexor digiti minimi, opponens digiti minimi, and equally the abductor digit minimi from the hypothenar muscles (May, 2020). These muscles form a bulk on the small finger. Specifically, the abductor allows the little finger to pull sideways from the ring finger (May, 2020). The opponents enable a person to cup hands, bringing the small and thumb fingers together.

Elbow Muscles

The elbow contains four muscles, including the biceps, brachialis, triceps brachii, and lacertus. According to Gaspar et al. (2018), the biceps help an individual rotate the palm down and up. They equally help the brachioradialis and the brachialis to bend the elbow. The brachialis is another muscle that is deep and large in the arm’s front, lying beneath the biceps muscle, attaching to the ulna’s coronoid process (Van Den Bekerom et al., 2016). The triceps are three-headed in the arm’s back, delivering the critical role of elbow strengthening (Alves et al., 2018). Therefore, a person can throw items and push up a chair due to the strength of the triceps.

Sensory Stimulus Pathways

There are several unconscious processes that an individual goes through to sense an external stimulus. Whether in the presence or absence of light, the human hand skin must feel different external stimuli, including the crawling of bugs on the hand. First, skin on the human hand has multiple anodes that help one develop a feeling that something has touched them. Anodes are at the epidermis and dermis, which are the topmost layers of the skin. Villard et al. (2017) allude that receptors are small in size, collecting accurate information regarding touch. Conduits often sense pain, pressure, friction, temperature, and even stretch.

The idea of feeling a bug crawling on the skin allows an individual to flick it off before biting the skin. According to Yu and Smith (2017), the hairs that project from the follicles in the hand skin sense different environmental changes. It is the root plexus that surrounds the follicle base that senses any interference and disturbance on the skin (Yu & Smith, 2017). As a bug crawls on the skin, it touches the hairs on the hand and sends a signal to the follicles, simultaneously transferring the same signals to the plexus and back to the skin that something is crawling. The hair root plexus sends the received information to the central nervous system (CNS), which incorporates the brain and the backbone. Subsequently, the CNS responds by activating the eyes’ skeletal muscles and removing the bug.

The skin acts as a critical sense organ due to the dermis, epidermis, and hypodermis, containing the nerves’ specialized sensory structures, sensing and detecting touch. These receptors are concentrated on the fingertips, especially the Pacinian corpuscle, which responds to skin vibrations (Yu & Smith, 2017). The Merkel cells in the stratum basale are equally regarded as the touch receptors. Sensory nerves are connected to each hair follicle throughout the hand skin. The motor nerves innervate the glands and arrector pili muscles, which helps humans sense the bug. The initiation point of the tracts starts at the epidermis and its termination is at the peripheral nerves where neurons are located. Chemical synapses occur in the epidermis, releasing neurotransmitters which bind receptors on the postsynaptic cell, making the hand quick to respond to external stimuli.

Adduction Movement

Adduction is one of the multiple hand muscle movements which take place in the fingers. As Assi et al. (2016) assert, adduction is a critical motion that brings all the hand fingers towards the middle finger. In other words, the movement involves the act of closing the finger together, for example, when one wants to slap another or when holding an object tight. Palmar interossei are the prime mover in adduction, helping humans to make a fist, whereas the antagonist for this kind of movement is the dorsal interossei. Extensors of the wrist form part of the synergist muscles that help and coordinate the movement of the fingers, whereby one of them is the extensor carpi radialis longus. For example, when one makes a fist flexed forwards towards their palm and equally makes another while the wrist is extended back, it becomes evident that the fist becomes strong when the wrist is extended back. Thus, it becomes clear that the wrist extensors aid the palmar interossei to close the hand fingers, hence considered to be palmar interossei synergists.

Stroke

In the primary somatosensory cortex and the primary motor cortex, the stroke will not affect the hand region’s anatomy. It will affect the functioning and ability of the hand. The hand becomes feeble in case of a stroke, because of the weakness of the biceps, triceps, and the other muscles. In the scenario of a stroke in the primary somatosensory cortex, the hand’s ability to sense different somatic sensations, including pain, vibration, touch, heat, and pressure, will be impaired. The hand becomes paralyzed, hence unable to sense different internal and external stimuli, for example, an internal cache, which enables a person to seek medical attention. Externally, the hand cannot sense pain or the crawling of a bug on the skin. An individual will realize that an insect is crawling on their hand when they only see it. A person cannot respond to external stimuli including excessive heat. Stroke is a devastating incident that can occur in the human body considering that it makes people susceptible to bodily danger because they cannot sense external stimuli apart from becoming weak to respond.

Conclusion

In conclusion, it is paramount to note that the removal of a crawling bug on the hand involves the sensory input and the motor output to respond. The nervous system has a tremendous impact on the muscular system. The hand has critical muscles including the elbow, hypothenar, and interossei muscles. Moreover, adduction is one of the movements that take place in the hand. It allows a person to bring fingers together to form a fist.

References

Alves, D., Matta, T., & Oliveira, L. (2018). Effect of shoulder position on triceps brachii heads activity in dumbbell elbow extension exercises. The Journal of Sports Medicine and Physical Fitness, 58(9), 1247−1252.

Assi, A., Bakouny, Z., Karam, M., Massaad, A., Skalli, W., & Ghanem, I. (2016). Three-dimensional kinematics of upper limb anatomical movements in asymptomatic adults: Dominant vs. non-dominant. Human Movement Science, 50(1), 10−18.

Burin, D., Garbarini, F., Bruno, V., Fossataro, C., Destefanis, C., Berti, A., & Pia, L. (2017). Movements and body ownership: Evidence from the rubber hand illusion after mechanical limb immobilization. Neuropsychologia, 107(4), 41−47.

Gaspar, M. P., Adams, J. E., Zohn, R. C., Jacoby, S. M., Culp, R. W., Osterman, A. L., & Kane, P. M. (2018). Late reconstruction of the interosseous membrane with bone-patellar tendon-bone graft for chronic essex-lopresti injuries: Outcomes with a mean follow-up of over 10 years. The Journal of Bone & Joint Surgery, 100(5), 416−427.

May, C. A. (2020). Long abductor digiti minimi muscle: Variation of the hypothenar muscles and clinical consequences. Clinical Anatomy, 33(5), 643−645.

Ramadan, R. A., & Vasilakos, A. V. (2017). Brain computer interface: Control signals review. Neurocomputing, 223(1), 26−44.

Urits, I., Gress, K., Charipova, K., Orhurhu, V., Kaye, A. D., & Viswanath, O. (2019). Recent advances in the understanding and management of carpal tunnel syndrome: A comprehensive review. Current Pain and Headache Reports, 23(10), 70.

Van Den Bekerom, M. P. J., Kodde, I. F., Aster, A., Bleys, R. L. A. W., & Eygendaal, D. (2016). Clinical relevance of distal biceps insertional and footprint anatomy. Knee Surgery, Sports Traumatology, Arthroscopy, 24(7), 2300−2307.

Villard, C., Eriksson, P., Kronqvist, M., Lengquist, M., Jorns, C., Hartman, J., Roy, J., & Hultgren, R. (2017). Differential expression of sex hormone receptors in abdominal aortic aneurysms. Maturitas, 96(1), 39−44.

Yu, C., & Smith, L. B. (2017). Multiple sensory-motor pathways lead to coordinated visual attention. Cognitive Science, 41(1), 5−31.

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