Notes-Part-2-Class-11-Science-Biology-Chapter-16-Skeleton and Movement-Maharashtra Board

Topics to be Learn : Part-1 Movement and Locomotion Location and Structure of Skeletal Muscles Working of Skeletal Muscles Structure of Contractile Proteins Mechanism of Muscle Contraction Physiology of Muscle Contraction Relaxation of Muscle Fibres Properties of Muscles on Electrical Stimulation Skeletal System Topics to be Learn : Part-2 Group of Skeleton Types of Joints Disorders Related to Muscles Disorders Related to Bones

Group of skeleton :

(1) Axial Skeleton : Axial skeleton situated along the vertical axis.

Skull :

Skull is made up of 22 bones. It is located at the superior end of vertebral column.

The bones of skull are joined by fixed or immovable joints except for jaw. Skull consists of cranium or brain box and facial bones.

Cranium: It is made up of four median bones and two paired bones.

• Frontal bone: It is median bone (unpaired) forming forehead, roof of orbit (eye socket) and the most anterior part of cranium. It is connected to two parietals, sphenoid and ethmoid bone.
• Parietal bones: These paired bones form the roof of cranium and greater portion of sides of the cranium.

• Temporal bones: Theseipaired bones are situated laterally just above the ear on either side. Each temporal bone gives out zygomatic process that joins zygomatic bone to form zygomatic arch. Just at the base of zygomatic process is mandibular fossa, a depression for mandibles (lower jaw bone) that forms the only movable joint of the skull. This bone harbors the ear canal that directs sound waves into the ear. The processes of temporal bones provide points for attachment for various muscles of neck and tongue.
• Occipital bone: It is a single bone present at the back of the head. It forms the posterior part and most of the base of cranium. The inferior part of this bone shows foramen magnum, the opening through which medulla oblongata connects with spinal cord. On the either sides of foramen magnum are two prominent protuberances called occipital condyles. These fit into the corresponding depressions present in 1^st vertebra.
• Sphenoid bone: Median bone present at the base of the skull that articulates with all other cranial bones and holds them together. This butterfly shaped bone has a saddle shaped region called sella turcica. In this hypophyseal fossa, the pituitary gland is lodged.
• Ethmoid bone: This median bone is spongy in appearance. It is located anterior to sphenoid and posterior to nasal bones. It contributes to formation of nasal septum and is major supporting structure of nasal cavity.

Functions of skull:

• It protects the brain.
• It provides sockets for ear, nasal chamber and eyes.
• Mandible bone of the skull helps in opening and closing of the mouth

Hyoid bone :

• It is a ‘U’ shaped bone that does not articulate with any other bone.
• It is suspended from temporal bone by lingaments and muscles.

• It is located between mandible and larynx.
• It has horizontal body and paired projections called horns.
• It provides site for attachment of some tongue muscles and muscles of neck and pharynx.

Know This : Details of Human Skeleton Axial skeleton : Skull : Cranium 8, Face 14, Hyoid 1, Ear ossicles 6, Vertebral column 26 Thorax Sternum 1, Ribs 24 Subtotal : 80 Appendicular skeleton : Pectoral Girdle : Clavicle 2, Scapula 2 Upper Limbs : Humerus 2, Radius 2, Ulna 2, Carpals 16, Metacarpals 10, Phalanges 28, Pelvic Girdle, Hip bone 2, Lower Limbs : Femur 2, Patella 2, Tibia 2, Fibula 2, Tarsals 14, Metatarsals 10, Phalanges 28 Subtotal : 126 Total : 206

Sutures in skull and their location :

Skull has many sutures (type of immovable joints) present, out of which four prominent ones are

• Coronal suture: Joins frontal bone with parietals.
• Sagittal suture: Joins two parietal bones.
• Lambdiodal suture: Joins two parietal bones with occipital bone.
• Lateral/squamous sutures: Joins parietal and temporal bones on lateral side

Ear ossicles : Three tiny bones namely malleus, incus and stapes, together called ‘ear ossicles’ are present in each middle ear.

Vertebral Column :

• Human vertebral column or backbone is a part of axial skeleton.
• Human backbone or vertebral column is made up of a chain of irregular bones called vertebrae.
• It consists of 33 vertebrae during childhood. In adults, five sacral vertebrae fuse to form one sacrum and four coccygeal vertebrae fuse to form single coccyx, thus total number of bones are 26.
• There are five types of vertebrae, cervical (neck), Thoracic (chest), lumbar (abdominal), sacral (hip region, fused in adults forming  sacrum) and coccygeal (fused to form vestigial tail bone called coccyx).

Know This : Slipped disc : The bones of vertebral column are supported by the intervertebral discs. These intervertebral discs act as shock absorbers due to which they are constantly compressed. The disc consists of two parts - soft gelatinous inner part and tough outer ring. An injury can cause the inner portion to project through the outer ring. This is known as slipped disc

Atlas vertebrae:

• Atlas is the ring-like, 1^st cervical vertebrae. It has anterior, posterior arches and large lateral massesa
• It lacks centrum and spinous process. The superior surfaces of the lateral masses are concave and are known as superior articular facets.
• These facets articulate with the occipital condyles of the occipital bone thereby forming atlanto-occipital joints.
• This articulation permits ‘YES movement’ or nodding movement.
• The inferior surfaces of the lateral masses known as inferior articular facets articulate with axis vertebrae.

Axis vertebra :

• It is the 2nd cervical vertebrae.
• Centrum of this vertebra gives out tooth-like ‘Odontoid Process. Odontoid Process projects superiorly through the anterior portion of the vertebral foramen of the atlas.
• The odontoid process forms a pivot on which the atlas and head rotate. This arrangement allows No movement’ or side to side movement of the head.
• The articulation formed between the anterior arch of atlas, the odontoid process of the axis and between their articular facets is called as atlanto-axial joint.

Importance :

• Vertebral foramen : It houses spinal cord and its meninges
• Odontoid process : This process fits into the anterior portion of vertebral foramen of Atlas vertebra forming pivot joint.
• Inferior articular facet : It articulates with superior articular facet of axis and permits rotatory movement of head.

Typical cervical vertebrae :

• Vertebrae number 3 to 6 are called as typical cervical vertebrae.
• They show short centrum and bifid spinous process.
• The transverse processes of these vertebrae are reduced; each having large vertebrarterial canal at its base for the passage of vertebral artery.

7^th cervical vertebra (Vertebra prominens): It is the largest cervical vertebra where the neural spine is straight.

Thoracic vertebra :

• These are twelve in number and found in chest region.
• Centrum of thoracic vertebrae is heart shaped and all processes are well developed. Except for vertebrae number 11^th and 12^th  transeverse process of other thoracic vertebrae show facets for attachment with ribs.
• Thoracic vertebrae can be identified on the basis of centrum as the centrum of the thoracic vertebrae is heart shaped.

Lumbar vertebra :

• There are five lumbar vertebrae.
• These are well developed vertebrae that exhibit all characters of a typical vertebra.
• The centrum of the lumbar vertebrae is kidney shaped.

Sacrum:

• It is a triangular bone formed by the fusion of five sacral vertebrae.
• It is located in pelvic cavity between two hip bones.
• The anterior end of sacrum is broad and posterior end is narrow.
• It consists of vertebral foramina formed by the fusion of vertebrae.
• The reduced neural spines can be observed projecting from dorsal aspect of sacrum.
• Function: It gives strength to pelvic girdle.

Coccyx:

• It is a triangular bone which is formed by fusion of four coccygeal vertebrae.
• It is reduced and does not show vertebral foramina and spinous processes.
• The transverse processes of coccygeal vertebrae are reduced.

Know This : Approximately 8 % of humans have an extra pair of ribs attached to the lumbar vertebra. Such a rib is found in some types of gorillas. Hence 13th pair of ribs is called gorilla rib.

(2) Appendicular skeleton :

Appendicular skeleton consists of bones of limbs and girdles.

Pectoral girdle :

• The pectoral girdle, also known as the shoulder girdle, connects the forelimb skeleton to the axial skeleton.
• Each pectoral girdle is made up of a shoulder blade or scapula and a collar bone or clavicle.

Clavicle :

• It is ‘s’ shaped slender bone.
• One end of the clavicle is connected to the acromion process of the scapula.
• The other rounded end, known as the sternal end, connects to the manubrium of the sternum.
• This connects the upper arm and axial skeletons.

Scapula:

• It is a large, flat, triangular bone that occupies the posterior chest wall from the second to the seventh ribs and is attached to the axial skeleton by muscles and tendons.
• At its lateral angle, the scapula bears a concave socket called the glenoid cavity, into which the head of the humerus (the upper arm bone) fits. It is located in shoulder and hips.
• A beak-like coracoid process projects from the scapula, and an acromion process arises from the scapula. They can be felt as a high point of the shoulder. Both processes are intended for muscle attachment.

Pelvic girdle  : Pelvic girdle also known as hip girdle connects hind limb skeleton with axial skeleton.

• It is composed of two hip bones known as coxal bones. These coxal bones join the sacrum posteriorly.
• The coxal bone is a large irregularly shaped bone composed of three parts: the ilium, the ischium, and the pubis.
• At the point of fusion of the ilium, ischium, and pubis, there is a cavity called the acetabulum, which forms a ball and socket joint with the thigh bone.
• The pubic symphysis is a cartilaginous joint that connects the two pubis bones medially. The pubis and ischium together form a bone ring that encloses the obturator foramen.

Types of joints :

Joint : A point where two or more bones get articulated is called joint or articulation or athrosis. The study of joints is called arthrology.

They are classified based on degree of flexibility or movement they permit into lastly synovial or freely movable or diaithroses type of joints.

Cartilaginous / slightly movable joints / amphiarthroses:

These joints are neither fixed nor freely movable. Articulating bones are held together by hyaline or fibrocartilages. They are further classified as

• Synchondroses: The two bones are held together by hyaline cartilage. They are meant for growth. On completion of growth, the joint gets ossified. e.g. Epiphyseal plate found between epiphysis and diaphysis of a long bone, Rib - Sternum junction.

• Symphysis: In this type of joint, broad flat disc of fibrocartilage connects two bones. It occurs in mid-line of the body. e.g. Intervertebral discs, manubrium and sternum, pubic symphysis.

Synovial joints / freely movable joints / diarthroses:

• It is characterized by presence of a space called synovial cavity between articulating bones that renders free movement at the joint.
• The articulating surfaces of bones at a synovial joint are covered by a layer of hyaline cartilage. It reduces friction during movement and helps to absorb shock.
• Synovial cavity is lined by synovial membrane that forms synovial capsule. Synovial membrane secretes synovial fluid.
• Synovial fluid is a clear, viscous, straw coloured fluid similar to lymph. It is viscous due to hyaluronic acid. The synovial fluid also contains nutrients, mucous ‘and phagocytic cells to remove microbes.
• Synovial fluid lubricates the joint, absorbs shocks, nourishes the hyaline cartilage and removes waste materials from hyaline cartilage cells (as cartilage is avascular). Phagocytic cells destroy microbes and cellular debris formed by wear and tear of the joint.
• If the joint is immobile for a while, the synovial fluid becomes viscous and as joint movement starts, it becomes less viscous.
• The joint is provided with capsular ligament and numerous accessory ligaments. The fibrous capsule is attached to periosteum of articulating bones. The ligament helps in avoiding dislocation of joint.

Know This : Tennis elbow : •     Tennis elbow is caused by inflammation of the tendon that connects the forearm muscles to the upper arm bone (humerus). •     It causes excruciating pain in the elbow. It is caused by extensive repetitive hand movement. This causes tendon damage and increases elbow joint tenderness. •     This disorder affects not only athletes, but also regular people whose jobs require extensive hand movement, such as carpenters, painters, plumbers, and so on.

Disorders related to muscles :

Muscular dystrophy:

• It is a genetic disorder that causes gradual wasting of various muscle groups. Typically, the voluntary skeletal muscles are weakened, whereas internal muscles such as the diaphragm are not affected in patients suffering from this disorder.
• Duchenne muscular dystrophy, which affects the lower limbs, is more common in boys.
• Limb girdle muscular dystrophy affects the muscles of the shoulders or hips and typically begins in adults between the ages of 20 and 30.
• This disease has no known cure.

 Myasthenia gravis:

• It is a weakness of skeletal muscles.
• It is caused by an abnormality at the neuromuscular junction that partially blocks muscle contraction.
• It is an autoimmune disorder caused by excessive production of certain antibodies in the blood stream. These antibodies bind to acetylcholine receptors of neuromuscular junction. Thus, the transmission of nerve impulses to the muscle fibres is blocked. This causes progressive and extensive muscle weakness.
• It may affect the eye and eyelid movements, facial expression and swallowing.
• The degree of muscle weakness varies fonn local to general.
• Symptoms : Ptosis (drooping or falling of upper eye lid), diplopia or double vision, difficulty in swallowing, chewing and speech.

Disorders related to bones :

Arthritis: It is an inflammation of joints. It is a painful disorder of bones, ligaments, tendons, etc. In this disorder, joints become swollen, stiff and painful. It can lead to disability.

Arthritis is of three types:

• Osteoarthritis: In this disorder, the joint cartilage is degenerated. It is caused by various factors like aging, obesity, muscle weakness, etc. This is the most common type of arthritis that affects hands, knees and spine.
• Gouty arthritis (Gout): In this disorder, joint pain occurs due to the deposition of uric acid in joints. If uric acid is produced in excess or is not excreted, it accumulates in joints as sodium urate which degenerates the cartilage, causing inflammation and pain. It generally affects the joints of feet.
• Rheumotoid arthritis: It is an autoimmune disorder where body’s immune system attacks its own tissues. In rheumotoid arthritis, synovial membrane swells up and starts secreting extra synovial fluid. This fluid exerts pressure on joint and makes it painful. Membrane may develop abnonnal granulation tissue called pannus. Pannus may erode cartilage. Fibrous tissue gets ossified and may lead to stiffness in joints.