The musculoskeletal system
Introduction
This chapter looks at the parts of our bodies that are responsible for our limbs and organ movements and contractions. It will discuss different parts of our skeleton and groups of muscles that form our musculoskeletal system.
Functions of the musculoskeletal system
Most muscles that cause movement 'work together' with the bone. Normally all our movements involve several different muscles. Muscles, like the diaphragm, do not need bones to work with, and function just by being attached to large masses of tissue. The diaphragm causes our lungs to expand and contract when we breathe.
The human skeleton
The skeleton is the supporting system of the body which is divided into the axial skeleton and appendicular skeleton. See image 1.
The axial skeleton
The axial skeleton forms the central axis (line) of our body. It consists of the skull, the vertebral column, the ribs and the sternum (breastbone).
The skull
The skull consists of many different bones. The bones of the skull can be divided into the cranium which encloses and protects the brain, and the facial bones.
The cranium
The cranium consists of eight flat bones which are rigidly attached to each other. These bones protect our brain. The frontal bone forms the forehead and portions of the eye sockets (or orbits). The occipital bone, at the base of the skull contains a large opening through which the spinal cord passes. The organs of hearing are in the temporal bone, one on each side.
The facial bones
The facial skeleton consists of 14 irregular bones, which are all (with the exception of the lower jawbone) firmly attached to the cranium by means of sutures. Sutures are fibrous skull joints. Facial bones include the nasal bones, the two jawbones and the cheek bones. The upper and lower jaws have pockets into which teeth fit. Human teeth mostly consist of material called dentine.
The vertebral column
The vertebral column forms the central part of the skeleton. It supports the skull and protects the spinal cord (the column of nerve tissue that carries messages between the brain and the rest of the body). The vertebral column consists of separate bones called vertebrae. The vertebral column is flexible because vertebrae are attached to each other by fibrous cartilaginous discs.
The ribs
The ribs are flat, narrow, curved bones. The first seven ribs on each side are joined to the breastbone. These ribs are referred to as true ribs. The cartilages (rubbery, fibrous, dense connective tissue) of the eighth, ninth and tenth ribs are joined to the rib immediately above. The last two pairs of ribs have free ends and are called the floating ribs. Our ribs, with their attached muscles, play an important role in the process of breathing.
The sternum (breastbone)
The sternum is a long, flat, dagger-shaped bone. It is in the centre of the chest region. The broad upper end supports the collar bones. The twelve pairs of our ribs and the sternum form our thorax (the part of the human torso between the neck and the diaphragm).
The appendicular skeleton consists of the bones of the limbs, the pelvic girdle and the shoulder girdle.
The pectoral (shoulder) girdle
A girdle is an encircling or ring-like structure. The pectoral girdle consists of two shoulder blades and two collar bones. These bones are connected to one another, allowing some degree of movement.
The skeleton of the upper limbs, or arms, may be divided into five main regions: an upper arm bone, the forearm, the wrist, the palm of the hand and the fingers.
The pelvic (hip) girdle
The pelvic girdle consists of two hip bones. The strong muscles of our back, legs and the buttocks are attached to it. The pelvic girdle protects some of the internal organs. In females it forms a strong, basin-like structure for supporting and protecting the developing foetus during child-bearing.
The lower limbs (legs)
The skeleton of the lower limbs may be divided into five main regions: the upper leg (thigh), the lower leg, the ankle, the arch of the foot and the toes.
See animation 1.
Human muscles
Muscles are made of fibres. Muscle fibres are long, multinucleated cells, also known as myocytes. Fibres contract and relax, creating movements. Muscles are connected to the bones by fibrous cords called tendons. See image 2.
Types of muscles
There are three main types of muscles: skeletal, smooth and cardiac.
- Skeletal muscles move our bones. We can see or feel this group of muscles. Skeletal muscles are a voluntary type of muscle which means that we can control them. All skeletal muscles come in pairs - one for each direction. See image 3.
- Smooth muscles are muscles of the internal organs. Unlike skeletal muscles, this type of muscles can stretch and maintain tension for long periods of time. The movements of smooth muscles are involuntary.
- Cardiac muscle is our heart's muscle. The cardiac muscle is also an involuntary muscle. It is responsible for the heart 'pumping'.
