Anatomy and Physiology of Gorilla Muscles

1. Introduction to Anatomy and Physiology of Gorilla Muscles

Gorillas (genus Gorilla) are the largest of the extant primates and are classified as belonging to the family Hominidae together with the other great apes and humans. They are closely related to humans, sharing around 98% of the same DNA and genetic blueprint. Western gorillas (Gorilla gorilla，G. gorilla) were first described by Thomas Stamford Raffles in 1774.

They were first scientifically described by Johann Friedrich Gmelin in 1788. Eastern gorillas (Gorilla beringei, G. beringei) were first described by the naturalist Paul Du Chaillu in 1861. The muscle anatomy of gorillas was less known compared to chimps and humans. The first thorough description of the muscles and joints of the gorilla’s forelimb was published by B. B. S. with subsequent descriptions of more forelimb muscles with extensions to overall shoulder girdle myology 1 ; 2.

A detailed description of the hindlimb musculature was published only recently. Considering these previous contributions, the aim of the present study was to provide thorough descriptions of the remaining musculature of the head, neck, thorax, and abdominal wall of the gorilla.

2. Comparative Anatomy of Gorilla Muscles

Gorillas display 423 muscles in the body, 192 in the head and 169 in the trunk and limbs. These muscles are divided into several groups according to position, shape and functions. Anatomy and Physiology of Gorilla Muscles have different types of muscles: Striated muscles (Skeletal muscles), smooth muscles and cardica muscles.

The striated muscles are also called voluntary muscles. The Anatomy and Physiology of Gorilla Muscles has two areas of striated muscles, Lingual muscles and Trunco-lingual (Tongue moving) muscles. The striated muscles present in the head are: sphenoid muscle, Masseter muscle, Mylo-hyoid muscle, Sterno-hyoid muscle, Sterno-thyroid muscle,

Thyro-hyoid muscle, Scalenes, Serratus Dorsalis dorsalis, Longiscapitis, Longus colli, External abdominal oblique, Internal abdominal oblique, Rectus abdominis, Pectoralis major, Pectoralis minor based on the position, shape and functions 1. In the arm, Trapezius, Serratus Dorsalis ventralis, Rhomboideus major, Rhomboideus minor, Latissimus dorsi, Supraspinatus, Infraspinatus, Teres major, Teres minor, Subscapularis, Biceps brachii, Bracchialis,

Triceps bracchii, Anconeus are the striated muscles present. In the forearm region, Pronator teres, Supinator, Extensor carpi radialis longus, Extensor carpi radialis brevis, Extensor carpi ulnaris, Extensor digitorum, Extensor polices longus, Extensor polices brevis, Extensor indicis, Flexor carpi radialis, Flexor carpi ulnaris,

Flexor digitorum profundus, Flexor digitorum superficialis, and Flexor polices longus are the muscles present 2. They are arranged in layers such as superficial, intermediate and deep layers. In the chest region, Serratus ventralis is the striated muscle present. In the thigh region, Gluteus maximus, Gluteus medius, and tensor fascia lata are the striated muscles present. In the hind limb, the “pelvic girdle” is supported by the bones, which are ilium, ischium and pubis.

The striated muscles present in the hind limb are grouped according to position, such as gluteal muscles, crural muscles and foot muscles of foot. They are Gluteus maximus, Gluteus medius, Gluteus superficialis, and piriformis muscles based on the position. But in Gibbons, no gluteus minimus and 3 gluteal muscles are present while in lower apes, 4 gluteal and 1 piriformis muscles are present.

2.1. Muscle Types and Functions

There are three types of Anatomy and Physiology of Gorilla Muscles: the skeletal muscles, also known as striated muscles, the smooth muscles, and the cardiac muscles. The skeletal muscles of gorillas and humans are similar in appearance that are composed of long, cylindrical, striated cells that are multi-nucleate.

The muscular system of gorillas is composed of more than 600 muscles with unique functions and capabilities. Muscles info regarding the temporal bones, hyoids, jaws, and necks therefore were specifically considered 3.

Other soft tissue info on the temporalis and masseter muscles, more detailed muscle info on the surveys of colossal gorillas, and also similar new muscle data on seven adult all-male gorillas were added to the monkey dataset involved. Anatomy and Physiology of Gorilla Muscles of Adult gorilla muscles were found to be continuous with those of adult rhesus monkeys but are often enlarged and even more similar to those of baboons,

Japanese macaques, and tonkean macaques. Results support the view that gorillas may be more powerful with widening distinctions from other less muscular Old World monkeys like macaques and baboons.

2.2. Muscle Distribution and Size

The superficial muscles of the entire gorilla body were studied in situ, classified, and applied with special reference to their comparative anatomy and possible functions. The body was divided into five regions: region of the head, neck region, region of the thorax, region of the abdomen, region of the upper limb, region of the forearm and hand, region of the lower limb, region of the thigh, and muscle teres, deep portion of the trapezius, and anterior scapulo-humeralis.

The muscles of the head and neck region and effects of the other muscles were studied. The comparative anatomy between the gorilla’s muscles, particularly the muscles of the thorax, abdomen, upper and lower limb, thighs, forearm, and hand, were discussed.

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Expansion of cellulo-fibrous development of the part of the bile ducts and its mode of action. Musculi occipito-atlanto-rhombici iliaco-lumbalis. Muscles of the back and crest. Muscles of the lower leg and foot and an account of the history of the holm oak, whin, juniper, and forest trees in the British Isles 4.

3. Biomechanics of Gorilla Movement

The biomechanics of gorilla movement is not only fascinating but also provides insight into how muscles contract to generate force, thus providing the basic understanding needed to examine gorilla movements in more depth.

Force and moment generation by muscle contraction has been examined for many animals. Here, the basics of how muscle contractions generate force and moment are examined to provide the basic understanding needed to examine the movements of the gorilla in more detail.

Muscles are capable of acting as either motors (e.g., producing joint movement), brakes (e.g., resisting joint movement, storing energy), or both at different times. Contraction of a muscle can be isometric, concentric, or eccentric depending on the conditions of muscle loading 4. A muscle is said to be activated when its fibers are stimulated to contract, and the activation of one or more muscles is called a movement.

There is a vast literature on the Anatomy and Physiology of Gorilla Muscles and joints, muscle fiber types and muscle morphology, muscular mechanics and energetics, and muscular control. Selected aspects of each of these topics are briefly summarized here to give an adequate overview of muscular systems and their basic parameters and characteristics. The musculoskeletal anatomy of the western lowland gorilla has been described in detail.

3.1. Muscle Contraction and Force Generation

Skeletal muscle contraction is the primary mechanism by which anatomical structures move in a vertebrate 2. Skeletal muscle generates force through the biochemical interaction of myosin with actin filaments. Upon excitation of the muscle by an action potential, calcium ions bind to troponin proteins on the actin filaments which causes tropomyosin proteins, also bound to actin, to slide away.

By doing so, the active sites on the actin are unmasked and become accessible to myosin heads. The myosin heads hydrolyze ATP and bond to actin active sites to form the cross-bridge. The resulting conformational change drags the actin filaments towards the center of the sarcomere, producing the power stroke.

The myosin heads detach from the actin via hydrolysis of another molecule of ATP and re-hydrolyze or straighten to a resting conformation. The contraction cycle is repeated as long as the muscle is excited 3.

Muscle fibres contract isotopically when activated with a stimulus. The velocity of shortening or the overload of a muscle is determined by the difference between the lengthening slowest twitch times of the activated fibres versus the imposed length change.

The muscle-tendon component of the musculoskeletal system has a major role transmitting the forces generated in active muscle, where moment arms are defined by the geometry of input and output vectors in multi-dimensional coordinatesystems. In monophasic muscles, moment arms are fixed ratios of between-bracket input and output. Moment arms are thus independent of absolute or relative position but are dependent on the angle of input and output vectors.

3.2. Lever Systems in Gorilla Limbs

Anatomy and Physiology of Gorilla Muscles are large-bodied, relatively slow-moving, ground‐living primates. Of the anthropoid primates, along with orangutans, they have the most felid-like locomotion. However, Anatomy and Physiology of Gorilla Muscles are larger and heavier than most Felidae species. Consequently, due to physical size effects, gorilla locomotion would seem to be a viable test case for examining the limits of terrestrial agility in a species of substantial size and mass.

Anatomy and Physiology of Gorilla Muscles have no close living relatives that could provide a comparative zone of present-day control. Volume‐preserving CT data of a sub‐adult male western lowland gorilla was used as the basis for the first 3D musculoskeletal model of a gorilla. This model was used to examine the lever systems present in the limbs of gorillas 2 4.

The roughness and steepness of ground surface can be manipulated in gait simulation experiments with the model to investigate mid‐step and in‐stance leg adjustment with switching between preferred gait modes.

It is anticipated that the model would serve as a basis for fully understanding the biomechanical hinterlands present and the agility and strength afforded to a species by their anatomical system with regards to their locomotor behaviour. The anatomical analyses provide detailed descriptions of the 3D architecture of all limb/xial muscles of a gorilla, the moment arms of muscles controlling the key joints in the limbs, and the subsequent torque about these joints due to muscle forces.

4. Adaptations of Gorilla Muscles to Environment and Behavior

This section provides details on how the Anatomy and Physiology of Gorilla Muscles are adapted to their environmental and behavioral demands. Gorillas inhabit dense equatorial forests, using a variety of locomotor and postural behaviors to meet the challenges of this environment.

The overall architecture of the Anatomy and Physiology of Gorilla Muscles are described, as is its evidence for adaptability to a distinct set of postural and locomotor behaviors. Furthermore, the basic design of the muscular system of gorillas, including its size, mass distribution, and architectural characteristics, is proposed.

Anatomy and Physiology of Gorilla Muscles (Gorilla gorilla and G. beringei) are the largest extant group of apes, but what is remarkable is the difference in size between the two extant species in this genus 2. The muscular and skeletal systems of gorillas have adapted to their unique body size and weight.

As previously noted, the design of the limbs is especially adapted to facilitate a unique form of quadrupedal locomotion known as “knuckle-walking”. Moreover, a suite of adaptive features of both the skeleton and musculature have evolved in gorillas in response to potential biomechanical disadvantages associated with differences in body mass.

5. Implications for Conservation and Research

With origins in evolutionary biology, this basal data brings a new dimension to species conservation and biology. As with any anatomical research objectives, verifying the existence (presence or absence), estimating the muscle mass, demonstrating their use, and understanding the consequences of muscle designs and morphometrics are helpful.

Initial inferences from models should be resisted. Therefore, specifying the focal issue, preparing musculature samples that are as accurate and complete as possible, compiling quantitative muscle data, and a basis for artificial models is prudent.

This research permits engineers, roboticists, and other researchers to begin to design testable models of hindlimb physiology, kinematics, and biomechanics via forward dynamic modeling, to interpret the results of field or captive studies in new ways. This body of EFI studies is essential to understand phylogenetic inertia and species-specific specialization in muscle morphology, especially as it relates to function.

Our comparison of 23 other primates to two published muscle masses and attaching size datasets identified 13 gorilla hindlimb muscles with a greater cross-sectional area and six muscles with greater masses – suggesting functional differences. These findings may facilitate drawing insights from ligament morphometrics on the muscles in our cadaver.

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References:

1. M. Potau J, Arias-Martorell J, Bello-Hellegouarch G, Casado A et al. Inter- and Intraspecific Variations in the Pectoral Muscles of Common Chimpanzees (Pan troglodytes), Bonobos (Pan paniscus), and Humans (Homo sapiens). 2018. [PDF]

2. Goh C., L. Blanchard M, H. Crompton R, M. Gunther M et al. A 3D musculoskeletal model of the western lowland gorilla hind limb: moment arms and torque of the hip, knee and ankle. 2017. ncbi.nlm.nih.gov

3. B. Hanna J, Schmitt D. Comparative Triceps Surae Morphology in Primates: A Review. 2011. ncbi.nlm.nih.gov

4. Goh C, L Blanchard M, H Crompton R, M Gunther M et al. A 3D musculoskeletal model of the western lowland gorilla hind limb: moment arms and torque of the hip, knee and ankle. 2017. [PDF]