Topics to be Learn

  • 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
  • Group of Skeleton
  • Types of Joints
  • Disorders Related to Muscles
  • Disorders Related to Bones
Introduction 

Organisms exhibit a variety of movements:

  • Internal movements: E.g., streaming of protoplasm, peristalsis, respiration, beating of heart.
  • External movements: E.g., walking, running, swimming, Movement of ear.
Muscle Groups Responsible for Human Movement

1. Smooth / Non-striated / Visceral / Involuntary muscles:

  • Bring about involuntary movements like peristalsis in the alimentary canal.
  • Control constriction and dilation of blood vessels.
2. Cardiac muscles:
  • Perform rhythmic contractions.
  • Responsible for contraction and relaxation of the heart.
3. Skeletal / Striated / Voluntary muscles:
  • Control voluntary movements of limbs, head, trunk, eyes, etc.
  • Responsible for running and speaking.
Tendons
  • Skeletal muscles are attached to bones by tendons.
  • Tendons are inelastic, thick bands of collagen fibers.
  • They facilitate the movement of skeletal parts.
Locomotion
  • Defined as the change in locus of the whole body from one place to another.
  • Achieved through the combined action of bones, joints, and skeletal muscles.
Types of Locomotory Movements in Animals
 

Location of Skeletal Muscles
  • Skeletal muscles that move bones are not located on the same bone but on the bone above it. 
  • Example: Biceps and triceps (located in the upper arm) move the forearm.
Structure of Skeletal Muscles
  • At any joint: Two types of bones: Stationary and Movable.
  • Origin: End of the skeletal muscle attached to the stationary bone.
  • Insertion: End attached to the movable bone.
  • Belly: Middle thick part of the muscle where fibers are maximum.
  • Large muscles are typically fusiform in shape.
Types of Striated Muscles
  1. Agonists: Prime movers initiating movement. Example: Biceps.
  2. Antagonists: Perform actions opposite to prime movers. Example: Triceps.
  3. Synergists: Assist prime movers. Example: Brachialis assists biceps.
Working of Skeletal Muscles
 
Antagonistic Muscles
  • Definition: Muscles working in pairs to produce opposite actions. Example: Biceps (flexors) and triceps (extensors).
Key features:
  • Biceps cause flexion (folding), while triceps cause extension.
  • One muscle is usually stronger than its counterpart. 
  • Example: Biceps are stronger than triceps.
Important Antagonistic Muscle Pairs
 
Structure of Myosin and Actin Filaments
 
Myosin Filament
  • Made of polymerized proteins.
  • Function: Myosin accounts for 55% of muscle proteins.
Structure:
  • Heavy chains: Two coils forming a double helix.
  • Myosin head: Globular protein mass with ATPase activity (splits ATP for energy).
  • Light chains: Two light chains attached to each myosin head.
Actin Filament
  • Composed of three components:
1. F Actin:
  • Backbone of actin filaments.
  • Two helical strands made of G actin molecules.
  • Each G actin has one bound ADP molecule.
2. Tropomyosin:
  • Two strands loosely connected to F actin.
  • Covers myosin-binding sites on actin at rest.
3. Troponin:
  • Complex of three globular proteins.
  • Binds to actin, tropomyosin, and calcium ions.
  • Facilitates tropomyosin attachment to actin.
  • Affinity for calcium ions triggers the contraction process.

Sliding Filament Theory
  • Proposed by H.E. Huxley and A.F. Huxley.
  • Also known as the ‘Walk Along Theory’ or ‘Ratchet Theory’.
Key Concept: Interaction of actin and myosin filaments causes muscle contraction.
  • Myosin filaments interdigitate with actin filaments.
  • A cross-bridge connects the myosin head to the actin backbone (hinge joint).
  • ATP is required to move the myosin head for contraction.
  • ATPase activity in the myosin head releases energy from ATP for movement.
Process of Contraction:
  • Myosin head binds to the actin filament's active site and pulls it inward.
  • Actin filaments slide over myosin filaments, causing the muscle fibers to contract.
Sarcomere: Functional Unit of Myofibril
  • Organized into bands and zones

Physiology of Muscle Contraction
  1. Relaxation Phase: Tropomyosin and troponin complex block the actin's active sites, preventing myosin interaction.
  2. Impulse Transmission: Action potential spreads through the sarcolemma and enters the muscle via the motor end plate.
  3. Calcium Ion Release: Sarcoplasmic reticulum releases Ca²⁺ ions into the sarcoplasm via transverse tubules (T-tubules). Ca²⁺ binds to troponin, altering the troponin-tropomyosin complex.
  4. Active Site Exposure: Tropomyosin detaches, revealing the active sites on actin filaments (F actin).
  5. Energy Utilization: Myosin head cleaves ATP, attaching to actin’s active site to form an acto-myosin complex.
  6. Contraction: Myosin heads tilt backward, pulling actin filaments inward, leading to muscle contraction.
T Tubules (Transverse Tubules):
  • Invaginations of the sarcolemma penetrate into the myocyte interior.
  • Highly branched and interconnected with the sarcoplasmic reticulum.
  • Essential for calcium transients during excitation-contraction coupling, ensuring synchronized contraction.
  • Unique to striated muscle cells.

Muscle Relaxation
  • Both contraction and relaxation are active processes requiring ATP hydrolysis.
Steps in Muscle Relaxation:
  1. Stimulation ceases, breaking the actomyosin complex. Myosin head detaches from actin filaments (ATP-dependent).
  2. Ca²⁺ ions are pumped back into the sarcoplasmic reticulum (energy-dependent).
  3. Troponin-tropomyosin complex re-establishes, covering actin's active sites due to the absence of Ca²⁺ ions.
  4. Actin filaments return to their original position, stopping interaction with myosin.
  5. Muscle relaxes.

Role of Calcium Ions: Calcium ions are critical in muscle contraction (released into sarcoplasm) and relaxation (stored in the sarcoplasmic reticulum).

Types of Levers in the Human Body

Muscles and bones act as levers to facilitate movement. Levers are classified based on the position of fulcrum, effort, and load:

  1. First-class Lever: Fulcrum between load and effort (e.g., nodding the head).
  2. Second-class Lever: Load between fulcrum and effort (e.g., standing on toes).
  3. Third-class Lever: Effort between fulcrum and load (e.g., bicep curls).
Properties of Muscles on Electrical Stimulation

1. Single Muscle Twitch:

  • Caused by a single, brief stimulation.
  • Occurs in 3 stages: a) Latent period: No contraction. b) Contraction period: Muscle shortens. c) Relaxation period: Muscle returns to rest.

2. Summation: Repeated stimuli before the end of a twitch result in greater tension (staircase phenomenon).

3. Tetanus: Rapid, frequent stimuli cause continuous contraction without relaxation.

4. Refractory Period: Muscle fibers cannot respond to a new stimulus for 0.02 seconds after a stimulus.

5. Threshold Stimulus: Minimum stimulus strength required for contraction.

6. All or None Principle: Muscle fibers contract fully or not at all:

  • Sub-threshold stimulus: No contraction.
  • Threshold stimulus: Full contraction.

7. Oxygen Debt: During strenuous exercise, insufficient oxygen causes anaerobic glycolysis, leading to:

  • Accumulation of lactic acid, causing fatigue, pain, and cramps.
  • Recovery requires extra oxygen to oxidize lactic acid and restore ATP/creatine phosphate levels.
Know This

Rigor Mortis:

  • Post-death muscle stiffening caused by the absence of fresh ATP.
  • Lack of ATP prevents detachment of myosin from actin, resulting in permanent contraction.

Oxygen Debt Recovery:

  • Oxygen is used to oxidize lactic acid and restore creatine phosphate and ATP stores during recovery.

Components of the Skeletal System: Bones, tendons, ligaments, and joints are the main components of the skeletal system.

Endoskeleton vs. Exoskeleton

 
Exoskeleton

Components:

  • Chitinous structures, nails, hooves, scales, plates, hair, fur, muscular foot, tube feet, and more.
Functions:
  • Provides support.
  • Aids in movement and locomotion (e.g., nails, tube feet).
  • Offers protection from predators.
Examples in Animals:
  • Reptiles: Scales and plates (e.g., snakes) provide grip on rough surfaces.
  • Fishes: Possess dermal scales (bony).
  • Echinoderms: Use tube feet for locomotion.
  • Molluscs: Have muscular foot for movement.
Bones
  • Types of Bones: Long bones, short bones, flat bones, irregular bones, and sesamoid bones.
Functions of Bones:
  • Provide shape to the body and form its framework.
  • Protect vital organs to ensure smooth body function.
  • Enable movement and locomotion via joints.
  • Act as a surface for muscle attachment.
  • Serve as calcium reservoirs.
  • Are sites for hemopoiesis (blood cell formation).
Lever System in the Human Body
  • Joints act as fulcrums, and bones function as levers.
  • Muscles generate the force needed for movement.

Axial Skeleton
  • Situated along the vertical axis.
  • Includes the skull, vertebral column, and rib cage.
Skull
  • Composed of 22 bones.
  • Located at the superior end of the vertebral column.
  • Bones joined by fixed joints, except for the jaw (movable joint).
  • Divided into: Cranium (Brain Box) & Facial Bones
Cranium
  • Protects the brain.
  • Contains 4 median bones and 2 paired bones:

1. Frontal Bone (Unpaired):

  • Forms the forehead, roof of orbit (eye socket), and the anterior part of cranium.
  • Articulates with parietals, sphenoid, and ethmoid bones.

2. Parietal Bones (Paired): Form the roof and sides of the cranium.

3. Temporal Bones (Paired): Located above the ears on both sides.

  • Zygomatic process: Joins zygomatic bone to form the zygomatic arch.
  • Mandibular fossa: Depression for the mandible (lower jaw).
  • Ear canal: Directs sound waves to the ear.
  • Provides attachment for neck and tongue muscles.

4. Occipital Bone (Unpaired): Forms the posterior and base of the cranium.

  • Foramen magnum: Connects medulla oblongata with the spinal cord.
  • Occipital condyles: Fit into the 1st vertebra (Atlas).

5. Sphenoid Bone (Unpaired): Butterfly-shaped bone at the base of the skull.

  • Features: Sella turcica: Houses the pituitary gland.

6. Ethmoid Bone (Unpaired):

  • Spongy bone located anterior to sphenoid and posterior to nasal bones.
  • Supports the nasal cavity and contributes to the nasal septum.
Facial Bones
  • Total: 14 bones that shape the face.
  • Growth stops at age 16.

Components:

  1. Nasals (Paired): Form the bridge of the nose.

  2. Maxillae (Paired): Upper jaw bones, join all facial bones except the mandible. Contain the upper row of teeth.

  3. Palatines (Paired): Form the roof of the buccal cavity and the floor of the nasal cavity.

  4. Zygomatic Bones (Paired): Commonly known as cheekbones.

  5. Lacrimal Bones (Paired): Smallest facial bones. Form the medial wall of the orbit. Contain lacrimal fossa for tear collection.

  6. Inferior Nasal Conchae (Paired): Contribute to the lateral wall of the nasal cavity. Help swirl and filter air before entering the lungs.

  7. Vomer (Unpaired): Triangular bone that forms the inferior portion of the nasal septum.

  8. Mandible (Unpaired): Forms the lower jaw. Largest and strongest facial bone. Only movable bone in the skull.

  • Curved horizontal body.
  • Rami: Perpendicular branches for muscle attachment.
  • Contains the lower row of teeth.

Functions of Skull
  • Protects the brain.
  • Provides sockets for: Ears, Nasal chamber & Eyes
  • Mandible bone: Aids in opening and closing the mouth.
Hyoid Bone
  • 'U'-shaped bone that does not articulate with any other bone.
  • Suspended from the temporal bone via ligaments and muscles.
  • Location: Between the mandible and larynx.
  • Structure: Horizontal body. Paired projections called horns.
  • Functions: Provides attachment sites for: Tongue muscles & Neck and pharynx muscles.
Know This: Details of Human Skeleton
 
Axial Skeleton

Subtotal: 80 bones

Appendicular Skeleton
 

Subtotal: 126 bones

Total Bones in Human Skeleton: 206 bones

Sutures in Skull (Immovable joints in the skull)
  • Coronal Suture: Joins frontal bone with parietal bones.
  • Sagittal Suture: Joins two parietal bones.
  • Lambdoidal Suture: Joins two parietal bones with the occipital bone.
  • Lateral/Squamous Sutures: Joins parietal and temporal bones laterally.
Ear Ossicles
  • Three tiny bones in each middle ear: Malleus, Incus & Stapes
  • Together, these are called ear ossicles.

Vertebral Column

  • Part of Axial Skeleton.
  • Composed of irregular bones called vertebrae.
33 vertebrae during childhood, reduced to 26 bones in adults:
  • 5 sacral vertebrae fuse to form the sacrum.
  • 4 coccygeal vertebrae fuse to form the coccyx.
Five Types of Vertebrae:
  • Cervical: Neck region
  • Thoracic: Chest region
  • Lumbar: Abdominal region
  • Sacral: Hip region (fused to form sacrum in adults)
  • Coccygeal: Forms the vestigial tailbone (coccyx)
Spine Curvatures
  • The spine (vertebral column) is curved.
  • Four Curvatures: Cervical curvature, Lumbar curvature, Thoracic curvature & Sacral curvature
  • Primary Curvatures (concave): Thoracic & Sacral
  • Secondary Curvatures (convex): Cervical & Lumbar
Importance of Curvature:
  • Helps in balancing in an upright position.
  • Absorbs shocks during walking.
  • Protects vertebrae from fractures.
Know This: Slipped Disc
  • Intervertebral discs support the bones of the vertebral column.
  • These discs act as shock absorbers and are constantly compressed.
  • Structure of Intervertebral Disc: Soft, gelatinous inner part & Tough outer ring
  • Slipped Disc: Injury causes the inner portion to protrude through the outer ring.
Typical Vertebra (vary in size, shape, and processes but have a similar basic plan)

1. Centrum:
  • Prominent central body of the vertebra.
  • Flat in anterio-posterior aspect (amphiplatyan).
2. Neural Arch:
  • Formed by two short processes from the sides of the centrum.
  • Forms the vertebral foramen, which surrounds the spinal cord.
3. Neural Canal:
  • Formed by the vertebral foramina of all vertebrae.
  • Allows spinal cord, blood vessels, and protective fatty covering to pass through.
4. Spinous Process (Neural Spine):
  • Formed where the two processes of the centrum meet.
5. Zygapophyses:
  • Articulating processes from the base of the neural arch.
  • Superior zygapophyses (anterior) and inferior zygapophyses (posterior).
  • Allow slight movement between vertebrae.
6. Intervertebral Foramen:
  • Small openings formed between zygapophyses.
  • Allow passage of spinal nerves.
7. Transverse Processes:
  • Lateral processes from the base of the neural arch.
  • Used for muscle attachment.

Atlas Vertebra (1st Cervical Vertebra)
  • Ring-like structure without centrum and spinous process.
  • Anterior and posterior arches with large lateral masses.
  • Superior articular facets (concave) articulate with occipital condyles of the occipital bone. Atlanto-occipital joints allow the YES movement or nodding movement.
  • Inferior articular facets articulate with the axis vertebrae.
Axis Vertebra (2nd Cervical Vertebra)
  • Odontoid Process (tooth-like) projects superiorly.
  • It fits through the anterior portion of the vertebral foramen of atlas.
  • Forms a pivot joint for NO movement or side-to-side rotation of the head.
  • Atlanto-axial joint formed between the odontoid process and atlas.
Key Importance
  • Vertebral Foramen: Houses the spinal cord and its meninges.
  • Odontoid Process: Forms pivot joint with atlas.
  • Inferior Articular Facet: Allows rotatory movement of the head.
Typical Cervical Vertebrae (3rd to 6th)
  • Short centrum and bifid spinous process.
  • Transverse processes reduced with vertebral artery canal for the passage of the vertebral artery.
7th Cervical Vertebra (Vertebra Prominens)
  • Largest cervical vertebra with a straight neural spine.
Thoracic Vertebrae
  • 12 thoracic vertebrae in the chest region.
  • Heart-shaped centrum and well-developed processes.
  • Transverse processes of 1st to 10th thoracic vertebrae have facets for rib attachment.
  • Centrum is heart-shaped, which helps identify thoracic vertebrae.
Lumbar Vertebrae
  • 5 lumbar vertebrae in the lower back.
  • Kidney-shaped centrum.
  • Typical vertebral structure with all standard features.
Sacrum
  • Triangular bone formed by fusion of 5 sacral vertebrae.
  • Located in the pelvic cavity between the two hip bones.
  • Anterior end is broad; posterior end is narrow.
  • Fusion creates vertebral foramina.
  • Reduced neural spines project from the dorsal aspect.
  • Function: Provides strength to the pelvic girdle.
Coccyx
  • Triangular bone formed by fusion of 4 coccygeal vertebrae.
  • Reduced, lacking vertebral foramina and spinous processes.
  • Transverse processes are reduced.
Thoracic Cage
  • Thoracic cage: Composed of 12 pairs of ribs and the sternum (breast bone).
Sternum
  • Shape and Size: Flat, narrow bone about 15 cm long.
  • Position: Located medially in the anterior thoracic wall (chest region).age. Attachment site for diaphragm and abdominal muscles. 
  • Ribs Attachment: Connected to the sternum by costal cartilages.
 Divided into 3 parts:
  • Manubrium: Top section, has two notches for clavicle attachment and two notches for the first two pairs of ribs.
  • Body: Flat bone with five notches for rib attachment.
  • Xiphoid process: Lowermost part, initially cartilaginous and ossifies with
Ribs
  • Shape: C-shaped bones, attached to corresponding thoracic vertebrae.
  • Number: 12 pairs of ribs, each attached to a thoracic vertebra.
  • Intercostal muscles: Attach in the intercostal space (space between ribs).

Posterior end: Has head and tubercle for attachment to vertebrae.

  • Head attaches to facet formed by demifacets of adjacent thoracic vertebrae.
  • Tubercle attaches to facets on the transverse processes of vertebrae.

Classification of ribs based on sternum attachment:

  • True ribs: First 7 pairs, attach directly to sternum via costal cartilages.
  • False ribs: Pairs 8, 9, 10; attach to rib 7’s cartilage, not directly to sternum.
  • Floating ribs: Pairs 11 and 12; no ventral attachment.
Know This
  • 13th rib: About 8% of humans have an extra pair of ribs attached to the lumbar vertebra. Known as the gorilla rib.
Appendicular Skeleton
  • Definition: Composed of bones of limbs and girdles.
Pectoral Girdle
  • Function: Connects the forelimb skeleton to the axial skeleton.
  • Components: Made up of the scapula (shoulder blade) and clavicle (collar bone).
Clavicle
  • Shape: S-shaped, slender bone.
  • Attachment: Acromion end: Connects to the acromion process of the scapula. Sternal end: Rounded end connects to the manubrium of the sternum.
  • Function: Connects upper arm and axial skeleton.
Scapula
  • Shape: Large, flat, triangular bone.
  • Position: Located on the posterior chest wall, between the second and seventh ribs.
  • Attachment: Attached to the axial skeleton by muscles and tendons.
Features:
  • Glenoid cavity: Concave socket where the head of the humerus fits.
  • Coracoid process: Beak-like projection for muscle attachment.
  • Acromion process: Projection forming a high point of the shoulder.
Bones of Forelimb
  • Total bones: 30 bones, including the humerus, radius, ulna, carpals (wrist bones), metacarpals (palm bones), and phalanges (digits).
Humerus
  • Location: Bone of the upper arm.
  • Proximal end: Hemispherical head with greater and lesser tubercles.
  • Bicipital groove: Groove between tubercles for biceps tendon attachment.
  • Deltoid tuberosity: Located on the shaft of the humerus.
  • Distal end: Trochlea (pulley-like structure) that articulates with the ulna.
Radius and Ulna

Radius:

  • Position: Located on the thumb side (laterally) of the forearm.
  • Proximal end: Disc-like head that articulates with the humerus.
  • Distal end: Styloid process.

Ulna:

  • Position: Located on the little finger side (medially) of the forearm.
  • Olecranon process: Forms the elbow joint with the humerus.
  • Radial notch: Located on the lateral side near the upper end for radius head attachment.

Articulation:

  • Radius and ulna articulate at the upper and lower extremities through superior and inferior radio-ulnar joints.
  • The interosseous membrane is present between their shafts.
Carpals
  • Location: Bones of the wrist.
  • Arrangement: Two rows of four bones each.
Metacarpals
  • Position: Five elongated bones forming the palm.
  • Connection: Proximal ends connect to carpals, and distal ends form knuckles.
Phalanges
  • Function: Form the bones of the fingers and thumb.
  • Total: 14 phalanges in each hand.
  • Four fingers: Each has three phalanges.
  • Thumb: Has two phalanges.
Pelvic Girdle
  • Function: Connects the hind limb skeleton with the axial skeleton.
  • Components: Composed of two coxal bones (hip bones) that join the sacrum posteriorly.
  • Coxal Bone Parts: Ilium, Ischium & Pubis
Key Features:
  • Acetabulum: Cavity formed by the fusion of ilium, ischium, and pubis. Forms a ball and socket joint with the thigh bone (femur).
  • Pubic symphysis: Cartilaginous joint connecting the two pubis bones medially.
  • Obturator foramen: Enclosed by the pubis and ischium.
Bones of Lower Limb
  • Total bones: Femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.
Femur
  • Location: Thigh bone; longest bone in the body.
Structure:
  • Head: Joins the shaft at an angle via a short neck.
  • Joint: Forms ball and socket joint with acetabulum of coxal bone.
  • Popliteal surface: Triangular flattened area on the distal third of the shaft.
  • Condyles: Distal end has two condyles that articulate with the tibia and fibula.
Patella
  • Function: Also known as the knee cap.
  • Type: Sesamoid bone (embedded in tendon).
  • Shape: Flat, rounded with a pointed lower end.
Tibia and Fibula

Tibia:

  • Position: Thicker and stronger than the fibula.
  • Upper end: Broad and expanded, articulates with femur.
  • Lower end: Articulates with talus (a tarsal bone).
Fibula:
  • Position: Long, slender bone located on the lateral side of the tibia.
  • Connection: The two bones are connected at the extremities, with an interosseous membrane between them.
Tarsals
  • Location: Bones of the ankle.
Arrangement: Seven tarsals arranged in three rows: a) Two proximal rows, b) One intermediate row & c) Four distal rows
Metatarsals
  • Function: Five metatarsal bones form the foot's support.
Attachment:
  • Proximal ends connect with the distal row of tarsals.
  • Distal ends articulate with phalanges.
Phalanges
  • Function: Bones of the toes.
Structure:
  • Big toe: Has two phalanges.
  • Other toes: Each has three phalanges.
Types of Joints

Joint

  • A point where two or more bones are connected.
  • Study of joints: Arthrology.
Synarthroses / Fibrous Joints / Immovable Joints
  • Articulating bones held by fibrous connective tissue.
  • Immovable or fixed joints.

1. Sutures:

  • Thin layer of dense fibrous connective tissue.
  • Allows growth in childhood, ossifies after growth.
  • Types: Butt, Scarf, Lap, Serrate joints.

2. Syndesmoses:

  • Greater distance between articulating bones.
  • Fibrous tissue arranged as sheets/bundles.
  • Examples: Distal tibiofibular joint, Interosseous membrane (tibia-fibula, radius-ulna).

3. Gomphoses:

  • Cone-shaped bone fits into a socket.
  • Example: Tooth and jaw bones.
Cartilaginous / Slightly Movable Joints / Amphiarthroses
  • Articulating bones held by hyaline or fibrocartilage.
  • Not fixed or freely movable.

1. Synchondroses:

  • Bones held by hyaline cartilage.
  • Ossify after growth.
  • Examples: Epiphyseal plate, Rib-sternum junction.

2. Symphysis:

  • Broad fibrocartilage connects bones.
  • Occurs in midline of the body.
  • Examples: Intervertebral discs, Pubic symphysis.
Synovial / Freely Movable Joints / Diarthroses
  • Characterized by synovial cavity between articulating bones.
  • Allows free movement.

1. Synovial Fluid:

  • Clear, viscous fluid with hyaluronic acid.
  • Lubricates joints, absorbs shocks, nourishes cartilage.
  • Contains phagocytic cells to remove microbes.

2. Synovial Membrane: Lines synovial cavity & Secretes synovial fluid.

3. Capsular Ligament: Helps avoid joint dislocation.

Types of Synovial Joints

1. Pivot Joint:

  • Rounded surface of one bone fits into a ring formed by another bone and ligament.
  • Allows rotation around its own axis.
  • Example: Atlas and axis vertebrae (head turning).

2. Ball and Socket Joint:

  • Ball-shaped surface of one bone fits into a cup-shaped depression of another.
  • Allows multi-axial movement.
  • Example: Shoulder, Hip joint.

3. Hinge Joint:

  • Convex surface of one bone fits into concave surface of another.
  • Allows mono-axial movement (flexion, extension).
  • Example: Elbow, Knee joint.

4. Condyloid Joint:

  • Convex oval-shaped projection fits into an oval-shaped depression.
  • Allows movement along two axes.
  • Example: Metacarpophalangeal joint.

5. Gliding Joint:

  • Articulating surfaces are flat or slightly curved.
  • Non-axial movement.
  • Example: Intercarpal joints.

6. Saddle Joint:

  • Articular surfaces shaped like a saddle.
  • Biaxial movement: flexion, extension, abduction, adduction, circumduction.
  • Example: Carpometacarpal joint (thumb).
Know This: Tennis Elbow
  • Caused by inflammation of the tendon connecting forearm muscles to the humerus (upper arm bone).
  • Results in pain in the elbow.
  • Caused by repetitive hand movement, leading to tendon damage.
  • Affects athletes and manual workers (e.g., carpenters, painters, plumbers).
Disorders Related to Muscles

Muscular Dystrophy

  • Genetic disorder causing gradual wasting of muscles.
  • Voluntary skeletal muscles are weakened; internal muscles (e.g., diaphragm) are unaffected.
Types:
  1. Duchenne Muscular Dystrophy: Affects lower limbs & More common in boys.
  2. Limb Girdle Muscular Dystrophy: Affects muscles of shoulders or hips & Starts between ages 20-30.
  • No known cure.
Myasthenia Gravis
  • Weakness of skeletal muscles.
  • Caused by an abnormality at the neuromuscular junction.
  • Autoimmune disorder: Antibodies block acetylcholine receptors, preventing nerve impulses from reaching muscle fibers.
  • Symptoms: Ptosis (drooping eyelids), Diplopia (double vision), Difficulty in swallowing, chewing, and speech.
  • Muscle weakness ranges from local to general.
Disorders Related to Bones

Arthritis

  • Inflammation of joints causing pain, swelling, and stiffness.
  • Leads to disability.
Types:
1. Osteoarthritis:
  • Degeneration of joint cartilage.
  • Caused by aging, obesity, muscle weakness.
  • Affects hands, knees, spine.
2. Gouty Arthritis (Gout):
  • Caused by excess uric acid deposited in joints.
  • Leads to inflammation and pain.
  • Affects joints, especially in feet.
3. Rheumatoid Arthritis:
  • Autoimmune disorder where the immune system attacks its own tissues.
  • Synovial membrane swells, secreting excess synovial fluid, causing pain.
  • Can cause joint stiffness and cartilage erosion.
Osteoporosis
  • Bones become porous and brittle.
  • Age-related; more common in women.
  • Bone resorption outpaces bone formation, leading to brittle bones.
  • Prevention: Adequate calcium intake and exercise at a young age.
Factors contributing to osteoporosis:
  • Decreased estrogen after menopause.
  • Vitamin D deficiency.
  • Low calcium intake.
  • Decreased secretion of sex hormones and thyrocalcitonin.