Functional Human Anatomy: Bone Tissue and Joints

Functional Anatomy Overview

Functional anatomy differs from descriptive anatomy in that it focuses on the functionality and relationships between morphological tissues rather than providing a detailed description. Functional anatomy aims to answer questions such as how the body creates specific movements. This is due to functional differences between tissues that work together towards the same goal.

Bone Tissue Composition

Bone tissue is a complex tissue with a rich composition of extracellular matrices generated by multiple components and cell phenotypes during tissue generation. The inorganic components, such as Potassium, Calcium, and Sodium, are the most prevalent in the bone. Bone is an optimal surface for tissue generation also due to its organic components, including collagen, bone sialoproteins, and matrix metalloproteinase. In fact, the bone cell population can repopulate a surface and matrix. However, it is important to note that bone tissue also contains organic parts.

So, the bone cell population is capable of inducing remineralization of inorganic components and producing or mineralizing extracellular matrices to maintain a specific structure.

Types of Bone Tissue

The human body has two types of bone: compact and spongy. Compact bone is also known as cortical bone. This bone tissue is a dense material composed of organic substances and inorganic salts, with only small spaces (lacunae) that contain bone cells (osteocytes).

The second type of bone tissue is relatively softer and has a spongy appearance with numerous large spaces. This type of bone tissue is found in the marrow space (medullary cavity) of a bone and is also known as trabecular bone.

Trabecular Bone Function

Trabecular bone, also known as sponge bone, serves the primary function of facilitating movement in the body. While muscles are responsible for movement, the presence of lighter tissue in certain areas can enhance mobility and conserve energy. Compact bone is typically found in areas that require high compression resistance or protection of vital organs, such as rib cages.

We can summarize these functions as stability and defensive needs.

Mechanical Properties of Bones

The mechanical properties of bones are determined by the arrangement of trabecular bone in response to mechanical pressure and action on the body.

Areas experiencing higher compression must be reinforced or made sturdier to act as shields. The ability of bones to grow or remodel in response to demands is summarized in Wolff's law. This law also states that bone tissue should not be imagined as static. It needs to interactcontinually with other tissues and cell populations, making it a dynamic tissue. It is also capable of developing high resistance and counteractive abilities against vibrational force, particularly in certain areas.

Bone Adaptation to Mechanical Disturbances

As previously mentioned, the mechanical properties of bones are determined by the arrangement of trabecular bone. Additionally, this trabecular bone is arranged in a non-fixed manner, allowing the body to move and adapt to mechanical disturbances. This is significant because external mechanical forces can stimulate the synthesis of new bone tissue. These forces are distributed differently throughout the body, and gravity also exerts pressure on different parts of the body, generating friction. This friction causes the bone tissue to generate or reconstruct more structures that can withstand these pressures.

Bone Tissue Generation

Osteoblasts and osteoclasts have opposing functions: respectively, the former constructs new bone while the latter destroys old bone.

Bone Histology Review

Mature compact bone has a layered structure known as lamellar. It contains an intricate network of vascular canals called haversian systems, which provide blood supply to the osteocytes. The bone is arranged in concentric layers around these canals, forming structural units called osteons. In contrast, immature compact bone lacks osteons and has a woven structure. The bone matrix is formed around a framework of collagen fibers and is eventually replaced by mature bone in a remodeling process of bone resorption and new bone formation that creates the osteons.

Hormonal Regulation of Bone Growth

Hormones can regulate bone growth, as demonstrated in this summary. Both hormones and nutrition are essential for maintaining active and functional bone growth.

• Growth hormone (pituitary gland) stimulates epiphyseal plate activity
• Thyroid hormone modulates activity of growth hormones . ensures that the skeleton has proper proportions as it grows
• Excesses or deficits can cause abnormal skeletal growth such as gigantism or dwarfism
• Testosterone and estrogens (at puberty) . Promote adolescent growth spurts
• End growth by inducing epiphyseal plate closure-> ending longitudinal bone growth

Thyroid hormones regulate the ability of growth hormones to ensure that the skeleton grows with correct proportions. Osteoclasts stimulate the molecules obtained from calcium activity and its impact on our body.

Additionally, bone tissue serves as a reserve for other components, such as calcium. Therefore, if we need more calcium, it can be obtained by breaking down old bone tissue, which is also rich in calcium. This can then be used for other needs.

Bone Morphology and Functionality

The extracellular matrix (ECM) plays a crucial role in guiding cell differentiation by adapting to a particular shape. While it helps cells repopulate the surface, it is not sufficient for cell colonization. Adequate mechanical properties of the bone tissue are required for this purpose. Additionally, the morphology of the bone provides insights into the functionality of the bone tissue.

• Flat bones provide protection against mechanical forces and damage, such as the skull structure and brain cavity.
• Long bones maintain position and elongate muscles to aid in movement and sustain the lever system.
• Pneumatized bones contain inner holes in the bone structure and connect to the nasal cavity or other parts, similar to the empty cavity used near our lungs to modulate voice.
• Irregular bones include vertebrae. The body and arch of long bones allow for movement, flexibility, and counteract pressure on the spinal body to protect the spinal nerve.
• Short bones provide stability to the wrist and ankle joints and facilitate some movements.

This information relates to the mechanical, biochemical, and functional abilities of bones that support movement. However, it is important to note that the source of the body's ability to move is still unknown.

Sutural Bones Pneumatized Bones Flat Bones Parietal bone External table Sutura bon Internal Diploë table (spongy bone) Ethmoid Air cells Irregular Bones Long Bones Vertebra Humer us Short Bones Sesamoid Bones Patella Carpal bones Sutures

Muscular Tissue Overview

The human body contains numerous muscles, all of which share the ability to contract. Despite this commonality, muscles exhibit a wide range of forms and behaviours.

The three primary types of muscles are skeletal, smooth, and cardiac.

Skeletal muscle moves bones and other structures, while cardiac muscle contracts the heart to pump blood. Smooth muscle tissue, which forms organs such as the stomach and bladder, changes shape to facilitate bodily functions.

The three types of muscle tissue differ in their histological structure, with skeletal muscle being voluntary and cardiac and smooth muscle being involuntary. Additionally, the level of contraction differs between these types of muscle, with skeletal muscle contracting quickly, cardiac muscle contracting at an intermediate speed, and smooth muscle contracting slowly.

The muscular body operates at both a macroscopic and microscopic level.

Gross and Microscopic Features of Muscle

Gross features Microscopic features Property Skeletal Muscle Cardiac Muscle Smooth Muscle Features Skeletal Muscle Cardiac Muscle Smooth Muscle Location Attached to skeleton Heart Walls of blood vessels and hollow viscera Function Locomotion and movement of parts of body Pump blood into arteries Constriction of BVs, bronchi and peristalsis Shape of muscle fiber Cylindrical Cylindrical and branched Fusiform Speed of Fast Intermediate Slow Striations Yes Yes No Contraction Nerve supply Somatic NS Autonomic NS Autonomic NS Nuclei Many, located peripherally Single, located centrally Single, located centrally Control Voluntary Involuntary Involuntary Intercalated Discs Gap Junctions

Levels of Muscle Organization

In a microscopic view, there are different levels of organization.

• These include the epimysium, which serves as a bridge between the muscle and bone while protecting the muscle.
• The perimysium, on the other hand, protects the fascicle that shapes our muscle and contains the muscle fibers. Each fiber is isolated by a connective part called the endomysium.
• Lastly, the endomysium protects the singular muscle fiber, which is the minimal component of our muscles.

Epimysium Perimysium Tendon Endomysium Muscle fiber in middle of a fascicle (b) Blood vessel Perimysium wrapping a fascicle -Endomysium (between individual muscle fibers) Muscle fiber Fascicle (a) Perimysium 0 2013 Pearson Education, Ine Epimysium Bone Cells Connected by

Muscle Contraction and Movement

Every movement in the body is initiated by an origin. The sarcomere, which is a part of the muscle tissue, is responsible for creating and allowing contraction in the body. Actin and myosin are the components that enable movement and functionality in the body.

However, there are structures and body parts in the muscle that differ from each other. Additionally, the arrangement of individual muscle fibers affects how movement is performed. If the fibers of a muscle are all oriented in the same direction, it will create a contractive force that can only cause contraction in one direction. However, if there are multiple directions of contraction, we are able to move in different directions and perform various movements.

For instance, the following are examples of muscles and their directions of contraction: unipennate muscles, where the fibers are oriented in the same way, and bipennate muscles, where the fibers are oriented in a specular manner. Multipennate muscles have fibers oriented in three different directions. However, there are also more complex movements that involve fibers oriented in a circular way.

The mouth is an example of this, where circular fibers allow for opening and closing, as well as other movements achieved by relaxing and contracting these fibers.

Pennate Muscles Circular Muscles e Unipennate muscle (Extensor digitorum muscle) Bipennate muscle (Rectus femoris muscle) g Multipennate muscle (Deltoid muscle) h Circular muscle (Orbicularis oris muscle) Contracted Tendons Extended - tendon Relaxed

Types of Muscle Contraction

Another consideration must be made regarding contraction. When we think of muscular contraction, we often imagine the body in motion. However, this is not entirely accurate, as we are also capable of performing a different type of contraction by changing the volume or tension of our fibers. There are, in fact, two types of contraction: isotonic and isometric.

Isometric contraction is not associated with movement, but it is useful for increasing tension, which can then lead to movement. It is important to note that many isotonic contractions begin with an initial isometric contraction, where volume and tension work together to create movement.

So, isotonic and isometric contractions serve different purposes.

Isotonic contractions allow for movement in two ways: concentric and eccentric. Concentric contractions occur when tension accumulates in the muscle and it shortens, while eccentric contractions occur when the muscle lengthens.