Human Anatomy: Bones of Hands and Feet

Bones of the Hands and Feet

• The bones of the fingers and toes are called phalanges.

• Each finger has three bones, except for the thumb, which has two.

The Pelvic Girdle

• The large hip bone is called the os coxae.

• The superior portion of the pelvic girdle is called the ilium.

• The top of the hip is called the iliac crest.

• The posterior portion of the hip bone where one sits is called the ischium.

• The anterior portion of the pelvic girdle is called the pubis.

• The socket of the hip joint is called the acetabulum.

• The largest foramen in the body is the obturator foramen.

The Thigh

• The large bone of the thigh is called the femur.

• The portion of the femur that fits into the acetabulum (socket of the hip) is called the head of the femur.

• The large, blunt processes on the proximal end of the femur are called trochanters.

• The condyles of the femur articulate with the tibia, forming the knee joint.

The Lower Leg and Foot

• The patella is the kneecap.

• The medial bone of the leg is called the tibia.

• The tibia articulates with the femur to form the knee joint.

• The prominence just below the knee is called the tibial tuberosity.

• The inner ankle is called the medial malleolus.

• The smaller, lateral bone of the leg is called the fibula.

• The short bones of the ankle are called tarsals.

• The heel bone is called the calcaneus.

• The Achilles tendon attaches to the heel bone.

• The long bones of the foot are called metatarsals (five in total).

• There are 28 phalanges in the feet.

• Each great toe has two phalanges.

• The other toes have three phalanges each.

The Axial Skeleton

• The axial skeleton has 80 bones.

• The skull comprises 28 bones.

• The ears have six auditory ossicles.

• There is only one hyoid bone.

• The chest contains 25 bones (including the sternum and ribs).

• Osteoporosis is the decreased bone mass often due to low estrogen levels after menopause.

Bone Fractures

• A fracture is a break in a bone.

• A complete fracture is a break that extends all the way across the bone.

• A partial fracture is a break that extends part way across the bone.

• A simple fracture is a break that only affects the bone itself.

• A compound fracture is a break where the broken bone protrudes through the skin.

• A displaced fracture means the broken ends are moved out of position.

• Reduction is the realignment of the broken ends of a bone.

• A greenstick fracture is a fracture where the bone bends on one side and breaks on the opposite side.

• A comminuted fracture is a fracture where the bone is broken into several pieces.

Joints

• Arthrology is the study of the joints of the body.

• A joint (also called an articulation or arthrosis) is the site where two or more bones meet.

• Synarthroses are immovable joints.

• The tissue between the surfaces of synarthrosis joints is cartilage.

• Synarthroses include cranial sutures and sternocostal joints.

• Amphiarthroses are slightly movable joints.

• Amphiarthroses include the pubic symphysis, sacroiliac articulation, and intervertebral joints.

• Diarthroses are freely movable (synovial) joints.

• The structures of diarthroses include:

  • Articular cartilage covers the surfaces of the joint.

  • The joint cavity is found between the articular surfaces.

  • A joint capsule surrounds the surfaces.

  • Synovial fluid lubricates the joint.

• Examples of diarthroses include the shoulder, elbow, and wrist.

Movements at Joints

• Gliding joints permit limited movement.

• Hinge joints permit flexion and extension.

• Pivot joints permit rotation.

• Ball-and-Socket joints permit movement in all directions.

Muscles

• Myology is the study of muscles.

• Muscle fibers are the contractile structures within muscle cells.

• Skeletal muscle is attached to bones and is responsible for movement.

• Cardiac muscle is found only in the heart and pumps blood.

• Smooth muscle is found in the walls of internal organs.

• The roles of muscles include:

  • Movement
  • Production of heat
  • Maintaining posture
  • Stabilizing joints

• Muscle fibers contract together in groups called fascicles.

• The belly of a muscle is the thickest part.

• Fascia is a sheet of connective tissue that surrounds muscle tissue.

• Epimysium surrounds the entire muscle.

• Perimysium surrounds fascicles.

• A tendon is a tissue that connects a muscle to a bone.

• An aponeurosis is a sheet of connective tissue that attaches a muscle to a bone.

• Sarcoplasmic reticulum is a modified smooth ER that stores calcium.

• Myofibrils are cylindrical organelles in muscle tissue.

• A motor unit is made up of a single motor neuron and several muscle fibers.

Muscle Contraction

• A motor neuron stimulates muscle fibers within a motor unit.

• A motor unit is one motor neuron and all of the skeletal muscle fibers that it stimulates.

• A twitch contraction is a jerky contraction in response to a single strong stimulus.

• The latent period is the delay between the reception of a nerve impulse and the beginning of the contraction.

• The contraction period is the part of the twitch contraction in which the muscle shortens.

• The relaxation period is the part of the twitch contraction in which the muscle returns to its resting length.

• Tonic contractions are responsible for posture and are a result of the alternating contraction of motor units in the muscles.

• The refractory period of contraction is the time during which a muscle cannot respond to another stimulus.

• Tetanic contractions occur when there is partial or no relaxation between stimuli.

• Isotonic contractions are contractions where the tension on the muscle remains constant as the muscle shortens.

• Isometric contractions are contractions where the muscle contracts but does not shorten.

Muscle Anatomy and Actions

• The muscles deltoid and trapezius are named after their shapes.

• The rectus abdominis is named for its location.

• Origin is the point where a muscle is attached to a stationary bone.

• Insertion is the point where a muscle is attached to a movable bone.

• Sternocleidomastoid is a muscle named for its attachments.

• External obliques are named for their directions.

• Maximus or magnus are terms for large muscles.

• Minimus is a term for small muscles.

• Biceps and triceps are terms for muscles with two or three heads, respectively.

• Internal obliques and external obliques are paired muscles.

• Flexor refers to a muscle that produces flexion.

• Flexion is the movement of a joint that decreases the angle between the bones.

• Extension is the movement of a joint that increases the angle between the bones.

• Abduction is the movement of a limb away from the midline of the body.

• Adduction is the movement of a limb towards the midline of the body.

• Supination is the movement of the palm of the hand so that it faces upwards.

• Pronation is the movement of the palm of the hand so that it faces downwards.

• Inversion is the movement of the sole of the foot so that it faces inwards.

• Constriction is the narrowing of a structure.

• Dilation is the widening of a structure.

• Elevation is the movement of a structure upwards.

• Depression is the movement of a structure downwards.

• Circumduction is the movement of a limb in a circular motion.

• Rotation is the movement of a structure around its axis.

• Extensor refers to a muscle that produces extension.

Cranial Bones

• There are eight cranial bones that protect the brain.
• Frontal bone:
  • Forms the forehead
  • Contains the superior border of the eye orbit
  • Possesses a ridge above the eye orbit called the supraorbital margin
  • Has a flat portion between the eyebrows termed the glabella
• Parietal bones: Form the top and upper sides of the cranium.
• Temporal bones:
  • Contain the ear canals
  • The flat portion is called the temporal squama
  • Another name for the ear canal is the external auditory meatus
  • The mastoid process is found behind the ear lobe
  • Contain the inner ear and ear bones (ossicles)
  • The petrous portion houses these structures.
• Sphenoid bone:
  • Forms part of the anterior cranial floor and lateral eye orbits
  • It resembles a bat shape.
  • The sella turcica of the sphenoid bone houses the pituitary gland.
• Ethmoid bone:
  • Forms the superior nasal septum.
  • The crista galli is a superior median ridge.
  • The cribriform plate allows passage for the olfactory nerves.
• Occipital bone:
  • Contains the foramen magnum which is an opening for the passage of the spinal cord
  • The external occipital protuberance is a tubercle on the posterior surface.
• The occipital bone articulates with the 1st cervical vertebra, also known as the atlas.

The Ribs

• True ribs:
  • Also called vertebrosternal ribs.
  • Connect directly to the sternum.
• False ribs:
  • Vertebrochondral ribs connect to the sternum indirectly through cartilage.
  • There are 2 pairs (4) of floating ribs.

Bone Composition

• Bones are made of both organic and inorganic materials.
  • The organic part is called osteoid and provides flexibility.
  • Hydroxyapatites (calcium salts) are the inorganic component, primarily made of calcium phosphate, which provides hardness.

Bone Cells

• Osteoblasts are bone-depositing cells found in the periosteum and endosteum.
• Osteoclasts are responsible for bone reabsorption, which is vital for repair and remodeling.
• Osteocytes are mature bone cells embedded in bone tissue.

Bone Formation

• Ossification, also known as osteogenesis, is the term for bone formation.
• Intramembranous ossification: Takes place when mesenchyme in membranes transforms into bone, like in cranial bones.
• Endochondral ossification: This process involves the conversion of hyaline cartilage into bone, forming most of the bones in the skeleton. It's how most bones develop.
• Fontanels: The soft spots in a baby's skull where ossification is incomplete. They are typically filled with fibrous membranes.
• There are six fontanels in a baby's skull.
• These fontanels close by around 18 months of age and are replaced by sutures.

Bone Growth

• Longitudinal growth: Occurs due to the division of chondrocytes within the epiphyseal plates. It ceases around age 18 for females and 21 for males.
• Appositional growth: Involves the addition of new bone layers on the surface, continuing throughout life.
• Estrogen and testosterone play a significant role in bone growth spurts due to the elongation of long bones.

Muscle Types

• There are three primary types of muscle tissue:
  • Skeletal muscle: Attached to bones, responsible for voluntary movement.
  • Cardiac muscle: Found in the heart.
  • Smooth muscle: Lines internal organs and blood vessels, and is responsible for involuntary movements.

Muscle Function

• Muscles are vital for various bodily functions, including:
  • Movement: Contracting muscles allow for locomotion.
  • Heat production: Muscle contractions generate heat, particularly during shivering, a reflex for warmth.
  • Maintaining posture: Muscles maintain body posture and stability.
  • Stabilizing joints: Muscles help reinforce and stabilize joints.

Muscle Anatomy

• Fascicles: Bundles of muscle fibers.
• Belly: The fleshy portion of a muscle.
• Fascia: Connective tissue that surrounds and compartmentalizes muscles.
• Epimysium: Connective tissue covering the entire muscle.
• Perimysium: Connective tissue surrounding fascicles.
• Tendon: Connective tissue that attaches muscle to bone.
• Aponeurosis: A broad, flat tendon.

Contraction Process

• Sarcoplasmic reticulum: Plays a key role in muscle contraction by releasing and storing calcium ions.
• Myofibrils: Contain the contractile proteins, actin and myosin.
• Motor units: Consist of a single motor neuron and multiple muscle fibers that it innervates.
• A motor unit is the smallest functional unit of contraction.
• A single muscle fiber can only receive signals from a single motor neuron.
• Muscle twitch: A single, brief contraction caused by a single nerve impulse.
• Tetanic contractions: Repeated nerve impulses produce sustained contractions.
• Isotonic contractions: Generate muscle tension while the muscle length changes.
• Isometric contractions: Muscle tension increases without a change in muscle length.

Facial Muscles

• Occipitofrontalis: Raises the eyebrows.
• Masseter: Elevates the mandible (jaw).
• Temporalis: Elevates and retracts the mandible.
• Procerus: Depresses the medial portion of the eyebrows.
• Nasalis: Compresses the nasal cartilages.
• Orbicularis Oculi: Closes the eyelids.
• Corrugator Supercilli: Draws the eyebrows medially.
• Levator Palpebrae Superioris: Elevates the upper eyelid
• Orbicularis Oris: Closes and protrudes the lips.
• Levator Labii Superioris: Elevates the upper lip.
• Zygomaticus Major: Elevates and retracts the upper lip, creating a smiling expression.
• Zygomaticus Minor: Elevates the upper lip, potentially contributing to a sad expression.
• Buccinator: Compresses cheeks.
• Risorius: Draws the angles of the mouth laterally, similar to a smile or grin.
• Depressor Anguli Oris: Draws the angles of the mouth downward, often associated with a frown or other negative expressions.
• Depressor Labii Inferioris: Draws the lower lip downward.
• Mentalis: Protrudes the lower lip.
• Sternocleidomastoid: Extends up each side of the neck, a cylindrical muscle on each side.
• Digastricus: Attaches to the hyoid bone.
• Platysma: Extends from the clavicle, mandible, and lower lip. It contributes to an expression of horror or fright.

Chest and Back Muscles

• Pectoralis Major: The large muscle on the anterior chest.
• External Intercostals: Used for inhalation.
• Internal Intercostals: Used for exhalation.
• Latissimus Dorsi: Large muscle in the lower back, extends and adducts the arm.
• Trapezius: Large muscle of the upper back, involved in shrugging the shoulders.

Abdominal Muscles

• External Oblique: The outermost layer of the abdominal muscles, running diagonally.
• Internal Oblique: The middle layer, also running diagonally, but in the opposite direction of the External Oblique.
• Transversus Abdominis: The innermost layer, running horizontally.
• Rectus Abdominis: The muscle between the pubis and xiphoid process.
• Linea Alba: A fibrous band that runs down the midline of the abdomen, connecting the abdominal muscles.

Lower Back and Pelvic Muscles

• Psoas Major: A powerful muscle that flexes and laterally rotates the thigh.
• Diaphragm: The primary muscle of respiration, assisting in inhalation.

Shoulder and Arm Muscles

• Deltoid: A triangular muscle that abducts the arm.
• Teres Major: A muscle that helps internally rotate and adduct the arm.
• Biceps Brachii: Located on the anterior arm, primarily responsible for flexing the forearm.
• Coracobrachialis: Assists in flexing and adducting the arm.
• Brachialis: Found in the anterior arm, assists in flexing the forearm.
• Triceps Brachii: Located on the posterior arm, primarily responsible for extending the forearm.

Hand and Forearm Muscles

• Flexor carpi ulnaris: Flexes and adducts the hand at the wrist.
• Palmaris longus: Flexes the hand at the wrist.
• Flexor digitorum superficialis: Flexes the middle phalanges of the fingers 2-5.
• Brachioradialis: Flexes the forearm at the elbow.
• Flexor carpi radialis: Flexes and abducts the hand at the wrist.
• Pronator Teres: Pronates the forearm.
• Supinator: Supinates the forearm.
• Extensors: Muscles that extend the hand and wrist.
• Extensor carpi ulnaris: Extends and adducts the hand at the wrist.

Leg Muscles

• Sartorius: The longest muscle in the body, flexes and laterally rotates the thigh.
• Quadriceps Femoris: Includes four muscles that extend the leg at the knee.
• Adductor Longus: Adducts the thigh.
• Adductor Magnus: Adducts and extends the thigh.
• Gluteus Maximus: The largest muscle in the body, responsible for extending and externally rotating the thigh.
• Hamstring muscles:
  • Consist of three muscles:
    • Biceps femoris: Flexes the leg at the knee and extends the thigh.
    • Semitendinous: Extends the thigh and flexes the leg.
    • Semimembranous: Extends the thigh and flexes the leg.
• Tibialis Anterior: Dorsiflexes and inverts the foot.
• Gastrocnemius: A major calf muscle, plantarflexes the foot at the ankle and flexes the leg at the knee.
• Soleus: Located deep to the gastrocnemius, a calf muscle responsible for plantarflexing the foot.