The tissues which provide structure to the body and enable movement are part of the musculoskeletal system. The tissues in the this system include the bones, cartilage, joint, tendons, ligaments and muscles. In this section we will examine each of these types of tissues, so that in the next section on locomotion, we can understand how these structures work together to bring about movement.
Bones provide the framework and internal core structure for the attachment of muscles. Bone is a living rigid tissue which forms the support structures for the rest of the body. The process of bone formation is called ossification. The matrix of bone contains a dense arrangement of collagen fibres together with mineral salts of calcium, magnesium and phosphates. The calcium salts give bone its hardness and rigidity while collagen fibres give bones its flexibility and strength.
Microscopic structure of a long bone
Bones are made up of numerous hollow tunnels called Haversian canals. Haversian canals occur within the matrix of bone tissue and run parallel to the length of the bone. Each Haversian canal consists of a nerve to carry impulses, blood vessels to transport gases, food and wastes and a lymph duct to drain tissue fluid. Under the microscope they appear as black circles against a lighter background.
Figure 6.25: A diagram of a section of compact bone showing Haversian canals.
Each Haversian canal is surrounded by concentric rings of compact bone called lamellae. Each of these layers contains a ring of fluid-filled cavities called lacunae. Each of these lacuna will contain a number of bone cells called osteocytes. The lacunae are linked to each other and to the Haversian canal by a system of very tiny interconnecting canals called canaliculi. Strands of cytoplasm extend through these canals which supply the osteocytes with oxygen and nutrients and remove waste products. The Haversian canals, lacunae, osteocytes and canaliculi together form a unit called an Haversian System and a number of these systems make up compact bones.
Apart from osteocytes which are embedded in the lacunae of bone there are two other types of bone cells.
Osteoblasts: Bone forming cells. These cells allow the bone to change and remodel its shape as the organism grows and responds to stresses. If a bone is broken or if strengthening is needed, bone cells lay down new tissue and repair damaged tissue
Osteoclasts: Special bone cells for destroying and reabsorbing bone tissue.
Functions of bone
Cartilage is a tough semi-transparent flexible tissue that consists of a tough matrix or jelly-like substance. The matrix is made up of collagen (a protein) and proteins with special carbohydrate chains called proteoglycans. Cartilage is enclosed by a fibrous capsule called the perichondrium. It consists of living cells called chondrocytes which secrete a rubbery protein matrix called chondrin. Chondrocytes occur in small fluid-filled spaces called lacunae which are scattered throughout the matrix. There are no blood vessels or nerves in the matrix.
Cartilage and bone
Infant and young children do not have bones like those of adults. Their bones are made mostly of cartilage - a firm, elastic, fibrous material. As the individual grows and matures, the cartilage is gradually replaced by bone cells which deposit crystals of calcium carbonate and calcium phosphate. This process called ossification greatly increases the strength of the bone.
Cartilage | Appearance | Location | Function |
Hyaline cartilage | glass-like, bluish-white, few fibres | at ends of bones, forms c-shaped structures in Trachea, joins ribs to sternum, larynx and tip of nose, temporary cartilage in bones | reduces friction at joints, allows movement of ribs during breathing, forms permanent structures, allows bones to increase in length |
Fibrocartilage | many white collagen fibres | discs between the vertebrae, in the rim of ball and socket joints, between pubic bones | acts as shock absorbers, makes the socket deeper while still allowing movement |
Elastic | many yellow fibres in matrix | in the pinna of the ear, in the epiglottis | maintains the shape of the ear, strengthens the epiglottis |
A joint is a point at which two bones make contact. It allows movement in many planes.
Another way of categorising joints is movable and immovable joints. Most joints in the skeleton are movable joints. Movable joints are also known as synovial joints. Synovial joints are characterised by the existence of capsules, which contain synovial fluid. The synovial fluid helps to prevent friction during movement.
Figure 6.26: Example of a synovial joint.
There are a number of different types of synovial joints. The four main types of synovial joints include:
Joints occur where two bones meet. Different types of joints allow for different types of movements. In this activity you will need to identify the different joint types, identify where they are located in the body and describe their motion.
For each of the following joints, you need to:
Activity: Movement at joints
Answers
Tendon and ligaments are dense bands of dense connective tissue. Ligaments join bone to bone, and tendons join muscles to bone. An example of a ligament is the anterior cruciate ligament (ACL) of the knee, and an example of a tendon is the Achilles tendon, which attaches your calf muscle to your heel. Tendons and ligaments are similar structures, but they have some important differences, which are summarised in Table 6.1.
Comparison of ligaments and tendons
Ligaments | Tendons |
join bone to bone | attach muscles to bones |
consist of white collagen fibres and a network of yellow elastic fibres | consist of non elastic collagen fibres which give tendons a white shiny appearance |
strong collagen fibres prevent dislocation at joints, and yellow elastic fibres allow flexibility at the joint | parallel arrangement of strong collagen fibres in order to efficiently convert muscle contraction into movement of the skeleton |
Voluntary muscles are normally connected to at least two bones. The point of attachment to the movable bone is called the point of insertion and the point of attachment of a muscle to the immovable bone is called the origin. Most muscles work in pairs and when a muscle works it needs to have an agonist and an antagonist.
An agonist is a muscle that acts to move a limb out of a particular position (contraction). An antagonist is a muscle that acts in opposition to the specific movement generated by the agonist and is responsible for returning the limb back to its original position (relaxation). Antagonistic pairs of muscles are necessary because each muscle can only exert a pulling force. A muscle cannot push itself back to its starting position. Therefore another muscle is required to pull in the opposite direction in order to return the agonist muscle back to its starting position. An example of this can be found in the contraction and relaxation of the biceps and triceps muscles when moving your forearm.
Example: Biceps and triceps
In the case of the biceps the two bones involved are the scapula (origin) and the humerus (insertion). The biceps muscle gets its name from having two tendons attached to the scapula. The tendons join to form a single muscle body, and then splits again into two tendons, one of which inserts at the radius, and the other of which inserts at the ulna. When the biceps muscle contracts, the forearm is lifted or bent, decreasing the angle between the forearm and humerus and flexing your arm. This ability of the biceps to decrease the angle between the joints results in it being called a flexor muscle.
Figure 6.27: Illustration of the triceps (extensor) and biceps (flexor) muscles
The biceps brachii muscle gets its name from being a two-headed muscle, attaching to the scapula at two points. Although it is commonly referred to as a `bicep', biceps is the correct form even in the singular. Similarly, the triceps brachii muscle joins at three points, and should be referred to as the triceps, whether you are talking about one or both arms.
Straightening of the forearm
When the arm is bent the biceps cannot contract since it is already in a contracted state. Muscles can only cause movement by pulling as they contract, not by pushing when they relax. Therefore, the straightening of the arm is brought about by the contraction of the triceps muscle (an extensor muscle) as it increases the angle between forearm and humerus. The triceps has three points of origin, two on the humerus and one on the scapula, and a single point of insertion on the ulna.
The mechanics of the antagonism within the biceps and triceps.
The aim of this dissection is for you to revise the theory behind tissues and apply your knowledge to actual tissues.
You will be working in pairs. Instructions for this activity will be written in italics.
1. Skin
Before you begin, look at the external appearance of the chicken wing.
Weigh the entire wing and record its mass in the table on the last page.
2. Connective tissue
The skin is held to the underlying pink tissue by a type of connective tissue.
Name this particular type of connective tissue.
Give two adjectives that accurately describe it.
3. Fatty tissue
Look at the underside of the skin you have removed. You should see clumps of yellow material. This is fat, or adipose tissue. It is also a type of connective tissue.
Take a small amount of this fatty tissue and squash it gently in a small beaker with some ether.
This oily stain is known as a translucent stain.
What do you think the function of connective tissue is here?
What do you notice? There is an oily stain on the paper after the ether has evaporated.
4. Muscle
Muscle is the pinky-orange tissue you can see under the skin. The muscles were most likely severed when the chicken was dismembered in the butchery. Muscles are all arranged in 'antagonistic pairs'. In an antagonistic pair, the action of one muscle (e.g. contraction) causes the opposite action to occur in the paired muscle (flexion).
Hold the wing in your left hand.
Describe what happens and name the type of action it caused.
Let go and pull various other muscles.
Can you get one to cause the opposite movement?
Carefully dissect out a single muscle in FULL. Remove it from the wing completely.
What type of tissue lies between the muscles?
5. Blood vessels
The smallest vessels you will be able to see are small arteries (arterioles) and small veins (venules). Capillaries are the very smallest blood vessels — so narrow in fact that erythrocytes can only fit through in single file. It is ONLY between these vessels and the surrounding tissues where diffusion of substances occurs. Capillaries will not be visible to the naked eye.
As you work, look out for blood vessels.
Name two substances that will diffuse into the tissues and out of the tissues in this wing.
6. Nerves
Nerves are bundles of neurons enclosed in a membrane rather like a piece of electrical flex. They tend to be deep in the tissues for protection.
7. Tendons
Muscles are attached to bones by means of tendons. Tendons are made of a type of connective tissue that contains lots of white fibres made of collagen. It is this collagen that gives the connective tissue its properties.
Your task now is to remove all the muscles neatly from the bones.
Look carefully at how the tendon joins the muscle.
Collect ALL the muscles you remove.
How firmly are the muscles attached to bones?
Approximately how many muscles did you remove?
Describe how the tendon and muscle join.
Write down four adjectives to describe collagen from what you can observe.
8. Bone
You should now be left with some bones joined together with skin, muscles and 'proper' connective tissue removed.
Use the miniature hacksaw to cut a bone in half.
Describe what you see after sawing the bone in half.
Use the vernier calliper to measure the thickness of the bone wall.
The bones of most birds are hollow. Why are hollow bones an advantage for a bird?
9. Ligaments
Ligaments look similar to tendons and have a very similar histology with lots of collagen fibres. Ligaments join bone to bone, and also form protective capsular ligaments around synovial joints by for instance, keeping in the lubricating synovial fluid.
Can you see internal ligaments?
Write down three observable characteristics of the ligament you cut.
10. Cartilage
Look at the end of a bone and find the cartilage (it is pearly white in colour).
Try to remove it from the bone. Then try to scratch it first with your nail and, then with something very hard and sharp.
Describe what you observe.
What type of cartilage is this?
What do you think the function of cartilage is?
What common, man-made material is closest in its properties to cartilage?
Data (show all working)
Tissue | Mass, correct to 1 decimal place (g) |
Entire wing | |
Skin | |
Muscle | |
Subcutaneous Fat |
Tidy and clean the work station thoroughly after each session. Wash instruments in hot soapy water with a sponge/scourer, rinse in the cold sink (NOT under running water) and dry with a cloth. Replace apparatus in the correct containers. Scalpel blades are to be removed, cleaned, dabbed dry with roller-towel and returned to their envelopes.
Investigation: Dissection of animal tissue
The purpose of this dissection is to revise the theory behind tissues and apply it to actual tissues.
Information and Instructions:
Dissection and other instructions are given in italics.
Answers
1. Skin
2. Connective tissue
3. Fatty tissue
4. Muscle
NOTE TO TEACHERS: It is difficult to remove the entire muscle without damaging the tendons, where the muscle attaches to the bone. Very few learners will do this successfully. Most of them will cut through the muscle above the tendon.
5. Blood vessels
NOTE TO TEACHERS: It is not always possible to see the difference between arteries and veins. Learners should look for any narrow dark red / blackish tubes.
6. Nerves
NOTE TO TEACHERS: Learners sometimes find very narrow, whitish threads, which are the nerves. They are generally right against the bone and are often destroyed when learners remove the muscle.
7. Tendons
8. Bone
9. Ligaments
10. Cartilage
Questions
DATA (SHOW ALL WORKING)
Learners may not have tables of mass measurements if scales were not available.
Tissue | Mass, correct to 1 decimal place (g) |
Entire wing | |
Skin | |
Muscle | |
Subcutaneous Fat | (4+1+1) |
Mark Scheme: Chicken wing
Self-Assessment: Assess yourself after chatting through each point with your partner | Mostly no (0) | Mostly no | Yes | Very much so |
I followed the instructions carefully and read everything | ||||
We asked questions where we needed to | ||||
We did not ask irrelevant questions | ||||
I can now recognize all the tissues mentioned | ||||
I can confidently describe the tissues we saw | ||||
We worked well together | ||||
We stayed focused on the work | ||||
Our apparatus was clean and dry after our practical | ||||
I can confidently insert and remove scalpel blades | ||||
I used the apparatus well and successfully | ||||
Our wing was neatly dissected | ||||
Total (out of 33, convert to 15) | /33 /15 |
Locomotion refers to the ability to move. Specifically, it refers to the way in which organisms travel from one place to another. Examples of types of locomotion include running, swimming, jumping or flying. Human locomotion is achieved by the use of our limbs. Below we discuss the major organs and structures that bring about movement in humans.
Figure 6.28: A marathon event in progress: this locomotion is facilitated by the skeletal framework described in this section.
Watch this video and learn about the amazing ways that human bones, muscles and tendons have adapted for long-distance running.
The structures used during locomotion include: