by Microbiology Doctor-dr
The Human SkeletonOver 200 bones of various forms, sizes, and functions make up a fully grown human skeleton. A baby is born with more bones than an adult. In adults, several of the bones that are distinct as children become fused or linked. Bones range in size from the teeny-tiny bones of the middle ear, which you heard about in Chapter 3, to the thighbones, which are the body's largest and strongest bones. Some bones, like the long bone in Figure 11-1, are long and cylindrical. Some are short, flat, or knobby, while others are short, flat, or knobby..
Examining the human skeleton in two parts: the axial skeleton and the appendicular skeleton, is a great technique to analyse it. Figure 11-3 depicts these two skeletal components. Refer to Plate One for a more thorough representation of the human skeleton.
Figure 11-3 The axial skeleton is shown in dark brown; the appen dicular skeleton is shown in light brown.
The Axial Skeleton
The axial skeleton is made up of the head, chest, and spine bones. The important organs of the body, such as the brain, spinal cord, heart, and lungs, are protected by the bones of the axial skeleton.
Skull There are 28 bones in the skull. The head's frame is made up of twenty-two of them. Sound waves are carried from the eardrums to the brain by the remaining six bones, three in each ear. The brain is protected by the cranium, which is a component of the skull. The skull is made up of eight bones that are held together by inflexible joints. The joints' zig-zagged form makes them stronger than if they were straight lines. You will be unable to feel these joints if you attempt to do so.
The bones of the cranium are not connected at birth. As seen in Figure 11-4, there are gaps between them. These openings allow the bones to glide under one another during birth, allowing the baby's head to pass through the birth canal. The cranium does not fully fuse until the child is roughly two years old, despite the fact that some of the bones connect three months after birth. Always safeguard a baby's head until the skull closes since there are sensitive places between the unfused bones.
Put your hand on your face. Can you tell how many bones there are in your face just by touching it? To form a section of the face, six facial bones are fused together with immovable joints. Two make up the nasal bridge, two make up the cheeks, and two make up the upper jaw. The jawbone, the seventh bone in the skull, is the only one that can move. The jawbone, the largest bone in the head, may move up, down, and sideways. You can talk and chew food with this range of motion.
Sinuses are air passageways in the skull that are hollow. They're linked to the nose and the throat. The sinuses help the skull to be lighter. They also serve as echo chambers, enhancing the voice's tone. Mucous membranes border the sinuses, which help to warm and moisten breathed air. Much of the moisture in exhaled air is also reabsorbed by the sinuses.
Figure 11-4 The bones in the skull are separate at birth. They form strong joints during early childhood.
Backbone The backbone, also known as the spinal column, is made up of 33 tiny bones known as vertebrae [VUR tuh bree]. The spinal cord is shielded by the spinal column. Stroke your vertebrae with your hand. Each bump represents a different vertebra. Cartilage discs operate as shock absorbers between the vertebrae.
The spinal column is divided into regions, as shown in Figure 11-5. The cervical vertebrae [SUR vih kuhl] are seven bones in the neck that support the head. The cervical vertebrae provide significant flexibility to the neck and allow the head to move in a variety of directions. Turn your head from side to side or stretch it upward. Take note of how much you're moving. The twelve thoracic vertebrae [thuh RAS ik] support the frame of the chest below the neck. The five lumbar vertebrae [LUM bur] are located in the lower back, which bears the majority of the body's weight. The vertebrae in the lower back are the largest and strongest in the spinal column.
In the hip area, the sacrum's five vertebrae [SAY krum] are joined. On both sides, they are connected to the hip bones. The pelvis is a set of bones that includes the sacrum and hip bones. The sacrum is the joint that joins the spine to the pelvis. The coccyx [KAHK siks], often known as the tailbone, is located below the sacrum. Three to five fused vertebrae make up the coccyx.
Chest The heart and lungs are protected by the chest bones, which form a cage. As you breathe, this frame expands and contracts. Take a deep breath and pay attention to how your chest expands. As you inhale and exhale, try measuring your chest using a tape measure. The sternum, often known as the breastbone, is a flat bone that runs across the centre and front of the chest. It acts as a support for the ribs and the muscles that aid in breathing. The heart is also protected by the sternum.
The ribs are divided into twelve pairs, but they are not all the same. Take a look at Figure 11-3 to see how the ribs are viewed. The ribs connect to the thoracic vertebrae in the back, but their attachments in the front differ. At the ends of the top seven ribs is cartilage that links directly to the sternum. The three pairs of ribs are not directly attached to the sternum because they are low. These three pairs are joined by cartilage that reaches all the way to the sternum. The sternum is not attached to the lowest two pairs of ribs. They are simply connected in the rear.
Figure 11-5 The Backbone
The Appendicular Skeleton
The appendicular skeleton is made up of the appendages, or limbs, that connect to the axial skeleton [ap un DIK yuh lur]. The bones of the hips, legs, and feet, as well as the bones of the shoulders, arms, and hands, make up the 126 bones of the appendicular skeleton. The appendicular skeleton allows the body to move freely.
Pectoral Girdle A collarbone extends from the top of the sternum to the shoulder blade on either side of the body. The pectoral girdle [PEK tur ul] is made up of the collarbones and shoulder blades. The shoulder blade is a big flat bone located in the upper back below the shoulder. Your collarbones and shoulder blades are plainly felt. The pectoral girdle is a structure that connects the arms to the axial skeleton.
Arm Figure 11-3 shows the bones of the arm and hand. In the upper arm, you can see that there is only one bone. This bone has one end that fits into the shoulder blade. At the elbow joint, the opposite end meets the two forearm bones. Place one elbow on the desk and face you with the palm of your hand. Then, using your other hand, feel your forearm bones at your wrist. These two bones are side by side while your palm is up. The bones criss-cross as you rotate your hand over, palm down. Take note of how effortless this action is. This movement enables the arm and hand to complete a variety of demanding and precise activities.
Hand The wrist's eight tiny bones are inclined and arranged in two rows. The wrist's flexibility is provided by this set of bones. The wrist bones link to the five bones of the hand that make up the palm's frame. There are three bones in each finger. The thumb, on the other hand, has only two bones. Knuckles refer to all of the joints in the fingers and thumb.
The human hand is one of a kind. A large range of mobility is possible at the joint where the thumb meets the hand. As a result, the tip of the thumb can touch the tip of each finger. Humans can pick up and grasp little objects like sewing needles and pencils because of this.
Pelvis The bones of the hip, also known as the pelvis, form a sturdy ring that distributes the body's weight evenly over the legs. Most abdominal organs, particularly the reproductive organs, are protected by the pelvis. Although the pelvis is made up of many bones, they are fused together so securely that they are sometimes mistaken for one. Soon after birth, the hip bones unite.
The pelvis anatomy differs between men and women. Figure 11-6 is an example. The female pelvis is shallow and wide. with a wide aperture through which a baby can pass during birth The male pelvis, on the other hand, is narrow and deep, with a limited aperture.
Figure 11-6 The broader female pelvis can support a developing fetus and allows enough room for childbirth.
Leg The largest, strongest, and heaviest bones in your body are your thighbones. Because they must support the weight of your upper body whether walking, jogging, or jumping, they are quite heavy. From the pelvis to the knee, each thighbone extends. Two smaller bones share the body's weight below the knee. The bigger one is on the inside of the leg, while the smaller one is on the outside. The bigger bone carries and distributes the majority of the weight from the thighbone to the foot. The smaller bone provides for a greater range of motion in the ankle.
Tendons from the muscles surrounding the kneecap keep it in place. It protects the knee joint and allows for easy bending. Rest your heel on the floor with your leg straight and all your leg muscles relaxed. Then, using your thumb and forefingers, gently move the kneecap back and forth. It should be able to move freely. with a minimum of friction
Foot The foot has a structure similar to that of the hand, although it is stronger and more rigid. Five bones make a frame for the top of the foot, just as they do for the hand. These bones join together with the toes' bones. Like the thumb, the big toe contains only two bones. The additional toes, like the fingers, have three bones each. Walking stress is absorbed by the big bones of the foot and the tiny bones of the toes.
Joints
The structure of the foot is comparable to that of the hand, although it is stronger and more rigid. The top of the foot, like the hand, has five bones that form a frame. These bones connect to the bones of the toes. The big toe, like the thumb, has only two bones. Each of the extra toes, like the fingers, has three bones. The large bones of the foot and the small bones of the toes absorb the impact of walking.
Freely movable joints, partially moveable joints, and immovable joints are the three types of joints. The majority of the joints in the body may move freely. The hinge joint, pivot joint, gliding joint, and ball-and-socket joint are the four types of freely movable joints. Figure 11-7 depicts examples of each of these types of moveable joints.
The shoulder, seen in Figure 11-8, is a freely mobile joint. A sac wraps around the ends of the bones. This sac contains flu id, which lubricates the joint like oil. A thin coating of cartilage also protects the ends of the bones, preventing them from rubbing against one another and wearing down. Ligaments encircle the sac.
Hinges joints, such as the elbow and knee joints, swing back and forth like doors on hinges. Hinge joints can be found in a variety of places.
At the elbow, two bones in the forearm come together to form a pivot joint. One bone spins around another in a pivot joint. These bones can criss-cross in this type of joint, allowing you to twist a screwdriver or turn a doorknob.
Bones can glide over one another thanks to gliding joints. Gliding joints connect the bones of the wrist, allowing for a lot of movement. This holds true for the bones in the ankle as well. When the ball-shaped end of one bone fits into the cup-shaped segment of the bone joining it, a ball-and-socket joint is produced. Ball-and-socket joints include the shoulder and hip joints, for example. Ball-and-socket joints allow for practically unlimited movement.
Figure 11-8 The synovial capsule and articular cartilage protect the bones in a freely movable joint from rubbing on each other.
It's more difficult to identify partially moveable and immovable joints. The joint that connects a rib to the backbone is somewhat moveable. This joint provides robust support while allowing for little movement to allow for chest expansion during breathing. At partially moveable joints, the vertebrae also contact. Examine Figure 11-7. What are some examples of immobile joints?
Review of the Lesson
The smallest bones in the ear are the smallest, whereas the largest bones in the legs are the largest. Joints are where bones meet. Bones and joints work together to create a physical foundation that is strong, resilient, and allows for a wide range of motion. Vital organs are also protected by the skeleton. Joints are divided into three types: freely movable, partially moveable, and immovable joints.
