Sunday, August 9, 2020

Locomotion and Movement - Notes | Class 11 | Part 3: Human Skeletal System

20. LOCOMOTION AND MOVEMENT 

HUMAN SKELETAL SYSTEM


It consists of a framework of bones (206) & few cartilages.

Human skeletal system has 2 parts: axial & appendicular.

1.  Axial skeletal system (80 bones)


Includes bones of head, vertebral column, sternum & ribs.

a. Bones of Head (29 bones)
It includes skull, Hyoid and Ear ossicles.

⇒ Skull (22): Include cranial bones and facial bones.
  • Cranial bones (8): Include Frontal (1), Parietals (2), Temporals (2), Occipital (1), Sphenoid (1) & Ethmoid (1).
  • Facial bones (14): Include Nasals (2), Maxillae (2), Zygomatics (2), Lacrimals (2), Palatines (2), Inferior nasals (2), Mandible (1) and Vomer (1).
Skull articulates with First vertebra (atlas) with the help of 2 occipital condyles (dicondylic skull).

⇒ Hyoid bone (1): U-shaped bone seen below buccal cavity.

⇒ Ear ossicles (3 x 2 = 6): Malleus (2), Incus (2) & stapes (2).

b. Vertebral column
Formed of 26 vertebrae. It includes 
  • Cervical vertebrae (7)
  • Thoracic vertebrae (12) 
  • Lumbar vertebrae (5)
  • Sacral vertebrae (1-fused) 
  • Coccygeal vertebrae (1-fused) 
Vertebra has a central hollow portion (neural canal) through which the spinal cord passes.

Number of cervical vertebrae are 7 in almost all mammals.

The vertebral column protects the spinal cord, supports the head and serves as the point of attachment for the ribs and musculature of the back.

c. Sternum or Breast bone (1) 

Flat bone on the ventral midline of thorax.

d. Ribs (12 pairs)
⇒ True ribs (first 7 pairs): 

They are attached to thoracic vertebrae and ventrally connected to sternum with the help of Hyaline cartilage.

⇒ Vertebrochondral (false) ribs (8th, 9th & 10th pairs): 

They do not articulate directly with the sternum but join the 7th rib with the help of Hyaline cartilage.

⇒ Floating ribs (11th & 12th pairs): 

They are not connected ventrally (no connection with sternum or other ribs).

Each rib has 2 articulation surfaces on its dorsal end and is hence called bicephalic.

2.  Appendicular skeletal system (126 bones)

a. Bones of fore-limbs (30 x 2 = 60) 
  • Humerus (1) 
  • Radius (1) 
  • Ulna (1)
  • Carpals (wrist bones-8)
  • Metacarpals (palm bones-5)
  • Phalanges (digits-14)
b. Bones of hind-limbs (30 x 2 = 60) 
  • Femur (thigh bone- 1)
  • Patella (knee cap- 1)
  • Tibia (1)
  • Fibula (1)
  • Tarsals (ankle bones-7)
  • Metatarsals (5)
  • Phalanges (digits-14)
c. Pectoral girdles (2x2=4) 

Include clavicle (2) & scapula (2).

Scapula (shoulder blade) is a large triangular flat bone situated in the dorsal part of the thorax between the second and 7th ribs. 

Scapula has a slightly elevated ridge (spine) which projects as a flat, expanded process (acromion). The clavicle (collarbone) articulates with this.

Below the acromion is glenoid cavity which articulates with the head of humerus to form the shoulder joint.

d. Pelvic girdles (2) 

Formed of 2 coxal bones. 

Each coxal bone is formed by the fusion of 3 bones- Ilium, Ischium & pubis.

At the point of fusion of Ilium, Ischium and Pubis is a cavity (Acetabulum) to which the thigh bone articulates.

The 2 halves of the pelvic girdle meet ventrally to form pubic symphisis containing fibrous cartilage.

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