Chapter 6: Skin & The Integumentary System
Skin & its Tissues
The Skin (Integument): composed of 2 regions:
- Epidermis: outermost layer composed of epithelial cells
- Dermis: underlying layer composed of fibrous connective tissue; vascularized (many blood vessels)
Subcutaneous layer (hypodermis): just deep to the dermis
- mostly adipose with some areolar connective tissue
- insulates, absorbs shocks, & anchors skin loosely to muscles
Epidermis: keratinized stratified squamous epithelium
- no blood vessels; cells in lower layers (close to dermis) have adequate blood supply; as cells divide, new cells are pushed toward surface away from blood & soon die
- keratinocytes: dominant skin cells; produce the fibrous protein keratin
· tightly connected by adhesion junctions
· outermost cells dead & keratinized; lifespan of 25-45 days
· thick skin has accelerated cell division & keratinization
· areas subject to regular pressure may develop even greater rate of cell division (calluses, corns)
- melanocytes: spider-shaped cells that produce the pigment melanin
· located in deepest layer of epidermis; melanosomes in melanocyte processes transfer melanin to keratinocytes
· melanin granules protect the cell nucleus from UV radiation
Layers of Epidermis:
- Thick skin has 5 layers (strata)
· Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum & stratum corneum
- Thin skin has only 4 layers... missing stratum lucidum; stratum corneum thinner
Skin Color: dictated by 3 pigments: melanin, hemoglobin & carotene
- melanin: produced from amino acid tyrosine in melanocytes
§ color ranges from yellow to reddish-brown to black
§ amount of melanin produced is mostly genetically determined; differences in skin color generally result from differences in melanin production
§ freckles & pigmented moles are due to local melanin accumulations
§ protects cell nucleus from UV light-induced mutations; UV repair mechanisms may stimulate synthesis
- hemoglobin: oxygenated hemoglobin in dermal capillaries gives fair skin a pinkish color
- carotene: yellow-orange pigment found in plants (carrots...)
§ accumulates in stratum corneum & hypodermis; most evident in thick skin
- biochemical imbalances (liver) may lead to accumulation of pigment bilirubin (breakdown product of red blood cells); produces jaundice
Dermis: strong, flexible connective tissue
- fibroblasts, macrophages, white blood cells with collagen & elastin fibers
- rich supply of nerve fibers, blood vessels & lymphatic vessels
- houses hair follicles, oil & sweat (sudoriferous) glands
- upper layer composed of areolar connective tissue
§ dermal papillae: projections that indent the epidermis; contain capillary loops & touch receptors (Meissner's corpuscles)
§ dermal ridges on palms of hand & soles of feet form epidermal ridges - genetically determined pattern of ridges; leaves fingerprint
- lower layer composed of dense irregular connective tissue
Accessory Structures of the Skin
Nails: scalelike epidermal modifications at posterior ends of fingers & toes
- nails consist of a nail plate over a surface of skin called the nail bed
- epithelial cells at base of nail plate produce new growth - cells become keratinized to form new nail plate as they grow out over nail bed
- cuticle (eponychium): fold of skin over nail root
- lunula: whitish half moon shaped base resulting from thicker skin in the area
- blood in dermal blood vessels beneath nail give pink color to nails
Hair & hair follicles:
- hair are flexible strands of mostly dead, keratinized cells
- hair has shaft (above skin) & root (below skin)
- melanin from melanocytes at base of follicle produce color
- hair follicle: extends from epidermal surface to dermis or hypodermis
§ hair cells at base of follicle/root divide to produce the hair; cells eventually die as they move further away from blood supply through root into shaft
§ arrector pili muscle: smooth muscle bundle that contracts to raise hair
- alopecia: hair loss brought on by aging & hormones
Sebaceous glands: oil glands usually associated with hair follicles
- holocrine glands that secrete sebum (mix of oil & cellular debris) through ducts into hair follicles
· sebum keeps hair & skin soft & waterproof
Sweat glands (sudoriferous glands): exocrine glands that produce watery secretion
- coiled tubular glands in the dermis/hypodermis with epithelial cells that secrete sweat through ducts that open through pores at skin surface
- eccrine glands: most numerous sweat glands; throughout skin, but most numerous in forehead, neck & back
· sweat helps to regulate body temperature in response to heat or exercise
· sweat is mostly water, plus small amounts of salt & wastes (urea, uric acid)
- apocrine glands: become active at puberty; most numerous in axillary regions & groin; activated by emotion, fear, pain
- ceruminous glands: modified sweat glands in external ear; secrete earwax
- mammary glands: modified sweat glands in breast; secrete milk
Regulation of Body Temperature
- hypothalamus of brain is main integrating center for thermoregulation; includes heat-loss center & heat-promoting center
- heat-promoting mechanisms:
o vasoconstriction of cutaneous blood vessels (blood rerouted to internal organs)
o increase in metabolic rate
o shivering (contraction of skeletal muscle)
o enhanced thyroxine release (increases metabolism & heat)
- heat-loss mechanisms:
o vasodilation of cutaneous blood vessels (heat lost through skin)
o enhanced sweating
Healing of Wounds:
- epidermal wound healing: abrasions & minor burns cause damage to epidermis
§ basal cells migrate to bridge gap in broken tissue
§ epidermal growth factor stimulates basal stem cells to divide & replace damaged cells & new strata
- Deep wound healing:
§ blood clot forms to loosely unite wound edges
§ inflammation occurs, accompanied by heat, redness, pain & swelling
§ clot becomes a scab, epithelial cells begin to migrate beneath scab to bridge wound , & granulation tissue forms (blood capillaries form & fibroblasts secrete collagen fibers to fill gap)
§ extensive growth of epithelial cells beneath scab, as well as growth of fibers & blood vessels
· fibrosis: scar tissue formation
§ scab sloughs off once epidermis is restored
Homeostatic imbalances of skin:
Skin cancer
- basal cell carcinoma
- squamous cell carcinoma
- melanoma
Burns:
- first-degree: only part of epidermis is destroyed
- second-degree: portion of epidermis & part of dermis destroyed
- third-degree: epidermis & full thickness of dermis & associated structures destroyed
Chapter 7: The Skeletal System
Functions of bones:
- Support
- Protection
- Movement
- Mineral storage: calcium & phosphate
- Blood cell formation (hematopoiesis): in some red bone marrow
Bone structure:
Gross anatomy of long bones:
- compact bone: dense outer layer of bone
- spongy bone (cancellous bone): trabeculae - needle-like or flat pieces internal to compact bone; spaces between trabeculae filled with red or yellow bone marrow
- epiphyses: ends of bone (distal & proximal epiphyses); often more expanded than diaphysis; outer compact & internal spongy bone
o joint surfaces covered by articular cartilage
- diaphysis (shaft): forms long axis of bone; thick collar of compact bone surrounding medullary (marrow) cavity
o in adults, marrow cavity contains fat - yellow bone marrow cavity
- periosteum covers entire surface of bone except joint surfaces
o osteoblasts: bone-forming cells
o osteoclasts: bone-destroying cells
o nutrient foramen: site of nutrient entry from vessels in periosteum at shaft of bone
o endosteum: covers trabeculae of spongy bone & canals of compact bone; contains osteoblasts & osteoclasts
Microscopic structure of bone:
Compact bone (lamellar bone): units called osteons
- osteons: cylinder oriented parallel to long axis of bone; within each cylinder is tubes (concentric circles) of bone matrix (lamellae)
- collagen fibers in lamella run in same direction.. in adjacent lamellae run in opposite direction (resists stress)
- central (Haversian) canal: runs through center of osteon; carries blood vessels & nerve fibers
- perforating (Volkmann's) canal: at right angles to long axis; connect blood vessels & nerves of periosteum to those of central canals & medullary cavity
- osteocytes: bone cells in small cavities called lacunae
- canaliculi: connect lacunae to each other & central canal
Spongy bone: trabeculae... a few cell layers of irregularly arranged lamellae & osteocytes connected by canaliculi
- no osteons; nutrients delivered by capillaries in endosteum
Bone development:
- osteogenesis (ossification)... in infants & adolescents for skeleton formation & growth; in adults for bone remodeling
- Intramembranous ossification: membrane bone forms from fibrous membrane
o Ossification center appears in fibrous connective tissue membrane
o Bone matrix (osteoid) is secreted within membrane
o Woven bone (trabeculae) & periosteum form
o Bone collar of compact bone forms & red marrow develops
- Endochondral ossification: bone forms by replacing hyaline cartilage (at primary ossification center)
o Bone collar forms around diaphysis of cartilage
o Central cartilage calcifies & cavitates
o Periosteal bud enters internal cavity & spongy bone forms
o Diaphysis elongates & medullary cavity forms
o Ossification of epiphyses at secondary ossification centers
- Following secondary ossification, hyaline cartilage remains only:
o On epiphyseal surfaces (joints)
o At junction of diaphysis & epiphysis (forms epiphyseal (growth) plates)
Bone Functions
Support & Protection
- bones give shape to body structures & support weight
- bones protect vital body regions (skull protects brain; ribs protect heart & lungs)
Body Movement
- bones act as levers & joints act as fulcrums in producing movement
- lever: rigid structure that can move around a fixed point or fulcrum
- 2 forces act on lever: effort & load (resistance)
- when load is close to fulcrum, & effort is applied far away, the lever acts at a mechanical advantage (& vice-versa)
Blood cell formation (hematopoiesis) in bones:
- Hematopoiesis occurs in red marrow (in cavities of spongy bone of long bones & diploe of flat bones)
- In infants, medullary cavity & all spongy bone have red bone marrow
- In adults, red bone marrow in the head of the femur & humerus, & diploe of flat bones & some irregular bones (hip bone)
- During anemia (blood cell deficiency), yellow marrow can revert to red marrow
Mineral storage in bone:
- mineral salts - mostly calcium phosphates, stored in bone
- calcium salt crystals pack around collagen fibers in matrix
- hormonal regulation of calcium:
o parathyroid hormone (PTH, from parathyroid gland): stimulates osteoclasts to resorb bone to raise blood calcium levels
o calcitonin (from parafollicular (C) cells of thyroid): inhibits osteoclasts & stimulates calcification of bone matrix to lower blood calcium levels
Skeletal Organization
Human Skeleton: 206 named bones
- Axial skeleton: 80 bones... bones of skull, vertebral column & thoracic (rib) cage. hyoid bone (supports tongue) & auditory ossicles (middle ear bones)
- Appendicular skeleton: 126 bones... bones of upper limbs & lower limbs, pectoral girdle (shoulder bones) & pelvic girdle (hip bones)
- Cranial Bones: 8 bones which enclose & protect the brain
o frontal bone: forms the forehead, roofs of the orbits & anterior part of cranial floor
· frontal sinuses: cavities in frontal bone medial above each eye
· supraorbital foramen (notch): complete (foramen) or incomplete (notch) opening above orbits
o parietal bones (2): form the greater portions of the sides & roof of the cranial cavity
§ coronal suture: joins frontal bone with both parietal bones
§ sagittal suture: joins 2 parietal bones
o occipital bone: forms the posterior part & most of the base of the cranium
· foramen magnum: large opening at base of skull where the medulla oblongata of brain connects with the spinal cord
· occipital condyles: oval processes on either side of the foramen magnum that articulate with the atlas (1st cervical vertebra)\
· lambdoid(al) suture: joins 2 parietal bones with occipital bone
o temporal bones (2): form the inferior lateral aspects of the cranium & part of the cranial floor
· zygomatic process: articulates with the temporal process of the zygomatic bone to form zygomatic arch
· external acoustic meatus: ear canal
· mastoid process: rounded projection posterior to external auditory meatus; point of attachment for several neck muscles (sternocleidomastoid)
· styloid process: sharp, toothlike projection that serves as the point of attachment for muscles & ligaments of the tongue & neck
· squamous(al) suture: joins parietal bone with temporal bone on both lateral aspects of skull
o sphenoid bone: forms middle part of the base of the skull
· articulates with all the other cranial bones, holding them together
· sphenoidal sinuses: cavities at medial aspect that drain into nasal cavity
· sella turcica: saddle-shaped structure on superior surface of medial aspect that houses the pituitary gland of brain
o ethmoid bone: spongelike bone located on the midline in anterior part of cranial floor, intermediate to orbits
· ethmoidal sinuses: air cavities between nasal cavity & orbits
· perpendicular plate: forms superior portion of nasal septum
· cribriform plate: in anterior floor of cranial cavity; forms roof of nasal septum
· crista galli: ridge above cribriform plate; point of attachment for membranes covering brain
· superior & middle nasal conchae: lateral projections in nasal cavity; help to filter & warm inspired air
§ superior nasal conchae are usually not visible within nasal cavity
§ inferior nasal conchae are separate bones (not part of ethmoid bone)
- Facial Bones: 14 bones
o maxillae (2): form the upper jawbone
· articulate with every other bone of face except mandible (jawbone)
· maxillary sinus: cavity in each maxilla that empties into nasal cavity
· palatine process: forms anterior 3/4 of hard palate (roof of mouth)
· cleft palate & cleft lip may be due to incomplete fusion of the palatine processes or palatine bones
o palatine bones (2): form posterior 1/4 of hard palate & part of the floor & lateral wall of nasal cavity, & a small portion of orbits
o zygomatic bones (2): cheek bones; form prominences of cheeks & part of lateral wall & floor of orbits
· temporal process: projection toward temporal bone that, with zygomatic process of temporal bone, forms zygomatic arch
o lacrimal bones (2): form anterior part of medial wall of orbits
o nasal bones (2): form part of bridge of nose (rest of nose is cartilage)
o vomer bone: forms superior aspect of nasal septum
o inferior nasal conchae (2): lateral projections in walls of nasal cavity; inferior to middle nasal conchae of ethmoid bone
o mandible: jawbone
· only movable facial bone (other than auditory ossicles)
· mandibular condyles (condylar processes): articulate with temporal bone to form temporomandibular joint (TMJ)
· coronoid processes: anterior to mandibular condyles; point of attachment for temporalis muscle
Infantile Skull: at birth, skull is incompletely developed; fibrous membranes called fontanels connect cranial bones
- fontanels (soft spots): fibrous membrane-filled spaces in fetal & newborn skull between cranial bones that allow for growth of skull & flexibility during childbirth
o replaced later by bone to become sutures
Hyoid Bone: U-shaped bone suspended from the styloid processes of the temporal bones by ligaments & muscles
- doesn't articulate with any other bone
- located in anterior neck between mandible & larynx; supports tongue & attaches to muscles of tongue, neck & pharynx
Vertebral Column (spine or backbone): forms skeleton of trunk of the body with sternum & ribs
- encloses & protects spinal cord, supports head & is point of attachment for ribs, pelvic girdle & back muscles
- composed of 24 vertebrae, sacrum & coccyx
o 7 cervical vertebrae in neck region
o 12 thoracic vertebrae posterior to thoracic cavity
o 5 lumbar vertebrae in lower back region
o sacrum: 5 fused sacral vertebrae
o coccyx: 4 fused coccygeal vertebrae
- cervical, thoracic & lumbar vertebrae are movable; sacrum & coccyx are not
- intervertebral discs: fibrocartilage & elastic tissue discs between bodies of adjacent vertebrae
- form intervertebral joints; highly resistant to shock
- vertebra parts:
o body: broad flat region that accommodates intervertebral disc
o pedicles: connect body to processes
o lamina: flat smooth surface on either side of spinous process
o vertebral foramen: opening between body & processes for spinal cord
o transverse processes: lateral processes on either side of spinous process
o spinous process: posterior process
o superior articular processes
o inferior articular processes
- cervical vertebrae (7)
o have transverse foramen in transverse processes for vertebral artery, vein & nerve to pass (thoracic & lumbar vertebrae do not have transverse foramen)
o spinous process of C2 - C6 is bifid (split into 2 parts)
o atlas (C1): 1st cervical vertebra; articulates with occipital condyles at base of skull
· lacks body & spinous process
· joints provide up & down head movement (yes)
o axis (C2): 2nd cervical vertebra
· dens (odontoid process): peglike projection that makes a pivot the atlas & head rotate around (no)
- thoracic vertebrae (12): giraffe/elephant
o larger than cervical vertebrae; spinous process projects inferiorly
o articulate with ribs
- lumbar vertebrae (5): moose
o larger that thoracic vertebrae; spinous process projects posteriorly
- sacrum (5 fused vertebrae)
o vertebrae begin to fuse between 16-18 years of age; ends around age 30
o sacral tuberosity on anterior medial sides joins with ilium to form sacroiliac joint
- coccyx (usually 4 fused vertebrae)
o vertebrae fuse between 20-30 years of age
Ribs (24; 12 pairs): give structural support to sides of thoracic cavity & protection to organs of thoracic cavity
- most (rib pairs 1 though 10) attach directly or indirectly to sternum
- all ribs attach posteriorly to thoracic vertebrae
- 7 true pairs of ribs: attached directly to sternum through costal cartilage
- 5 false pairs of ribs: attached indirectly (through cartilage-costal cartilage connection) ,or not at all, to sternum
o 2 pairs of floating ribs (rib pairs 11 & 12): not attached to sternum
- rib fractures are most common chest injuries
o may puncture heart or great vessels, lungs, trachea, bronchi, esophagus, spleen, liver or kidneys
Sternum (breastbone): located in center of anterior thoracic wall
- composed of 3 parts:
o manubrium: superior rounded part
· suprasternal (jugular) notch: depression on superior surface
· articulates with costal cartilage of 1st & 2nd ribs
o body: long middle part
· articulates directly or indirectly with costal cartilage of 2nd through 10th ribs
o xiphoid process: inferior, smallest part
- clavicle (2): (collarbone); S-shaped bone in anterior & superior thoracic cavity, above 1st rib
o rounded medial end articulates with manubrium of sternum
o flat lateral end articulates with acromion of scapula
o one of the most frequently broken bones (falling on arm)
- scapula (2): (shoulder blade); large triangular flat bone in posterior thoracic between 2nd & 7th ribs
o spine: sharp ridge running diagonally across posterior surface
o acromion: lateral end of spine; articulates with clavicle
o glenoid cavity (fossa): lateral shallow depression; articulates with head of humerus
o coracoid process: lateral projection at anterior surface; point of tendon attachment
- humerus (2): longest & largest bone of arm; articulates proximally with scapula & distally with ulna & radius
o head: rounded superior portion; articulates laterally with glenoid cavity of scapula to form glenohumeral joint
o greater tubercle: lateral projection distal to head & neck
o lesser tubercle: projects anteriorly
o deltoid tuberosity: lateral roughened area at middle of shaft; point of attachment for tendons of deltoid muscle
o capitulum: lateral rounded knob that articulates with head of radius
o trochlea: medial spool-shaped projection that articulates with ulna
o coronoid fossa: anterior depression that receives coronoid process of ulna
o olecranon fossa: posterior depression that receives olecranon of ulna
o medial & lateral epicondyles: projections on either side of distal end; points of tendon attachment
- radius: at lateral (thumb) aspect of forearm
o head: articulates with capitulum of humerus
o radial tuberosity: rough process for attachment of tendons from biceps brachii
o styloid process: lateral process
- ulna: at medial (pinky) aspect of forearm; looks like wrench
o olecranon process: superior process that fits with olecranon fossa of humerus
o coronoid process: inferior to olecranon; fits with coronoid fossa of humerus
o trochlear notch: receives trochlea of humerus
o styloid process: medial process
- carpals (8): wrist bones
o arranged in 2 transverse rows
o proximal row; from lateral to medial
· scaphoid, lunate, triquetrum, pisiform
o distal row; from lateral to medial
· trapezium, trapezoid, capitate, hamate
o Sally Left The Party To Take Cathy Home
- metacarpals (5 on each hand)
o numbered I - V, starting at thumb
- phalanges (14 on each hand)
o each finger has proximal, middle & distal phalanges, except thumb has only proximal & distal phalanges
Pelvic Girdle: Coxal Bone - connects lower limbs with sacrum & vertebral column
- Coxal Bone (Hip Bone): 3 fused bones: ilium, ischium & pubis
o ilium: broad flat bone; forms superior part of pelvic girdle
· iliac crest: rounded /curved region at top of ilium
· anterior superior & anterior inferior iliac spines
· acetabulum: lateral socket for head of femur
o ischium: posterior & inferior part of pelvic girdle
· ischial tuberosity: rough region at posterior & inferior aspect
· greater & lesser sciatic notches
· ischial spine: between greater & lesser sciatic notches
o pubis: anterior & inferior part of pelvic girdle
· pubic symphysis: fibrocartilage joint between 2 pubic bones
· obturator foramen: large opening running blood vessels & nerves between ischium & pubis
o Female pelvis is wider & shallow that male's, which accommodates childbirth
Bones of Lower Limb (Leg):
- femur (2): upper leg (thigh) bone
o articulates with tibia - tibiofemoral joint
o head: articulates with acetabulum of coxal bone; points medially
· fovea capitis femoris: small shallow depression at center of head
o neck: slender region inferior to head
o greater & lesser trochanters: lateral & medial projections (greater trochanter is lateral & superior)
o medial & lateral condyles: articulate with medial & lateral condyles of tibia
- patella (kneecap): triangular bone anterior on leg at junction of femur & tibia
- tibia (shin bone): wider bone of lower leg; articulates with femur & fibula at proximal end & talus & fibula at distal end
o anterior crest: sharp ridge on anterior surface (close to skin surface of shin)
o intercondylar eminence (tubercles): 2 small superior projections in articulation with femur
o medial malleolus: projection at inferior (distal) aspect
- fibula: thin, smaller bone of lower leg; articulates with tibia proximally & talus distally
o anterior crest: sharp ridge on anterior surface
o lateral malleolus: projection at inferior (distal) aspect
- tarsals (7 on each leg): ankle bones
o calcaneus: heel bone
o talus: anterior & superior to calcaneus; has wheel-like projection articulates with tibia & fibula
o cuboid
o navicular
o lateral, intermediate & medial cuneiforms
- metatarsals (5 on each foot)
o numbered I - V, starting at big toe
- phalanges (14 on each foot)
o each toe has proximal, middle & distal phalanges, except big toe has only proximal & distal phalanges
Joints
Classification of Joints:
- Structural Classification: Fibrous, Cartilagenous & Synovial Joints
- Functional Classification:
o synarthroses: immovable joints (sutures...)
o amphiarthroses: slightly movable joints (symphyses...)
o diarthroses: freely movable joints (most joints)
Fibrous Joints: bones joined by fibrous tissue; no joint cavity
- most are immovable or slightly movable
- sutures: between bones of the skull; initial connective tissue ossifies in middle age
- syndesmoses: bones (e.g.: radius & ulna) connected by ligament; slightly movable
- gomphoses: tooth in bony socket; connected by short periodontal ligament
Cartilagenous Joints: bones joined by cartilage; no joint cavity
- synchondroses: bones joined by hyaline cartilage; almost always synarthrotic
o epiphyseal plates; joint between costal cartilage of first rib & sternum
- symphyses: articular surfaces of bone covered with hyaline cartilage fused to plate of fibrocartilage (absorbs shock; slightly moveable)
o examples are intervertebral joints (discs) & pubic symphysis
Synovial Joints: bones separated by fluid-containing joint cavity
- all are freely movable
- rich supply of blood vessels & nerve endings (sense stretch)
- articular cartilage: hyaline cartilage protects bone ends
- joint (synovial) cavity: potential space with synovial fluid (reduces friction)
- joint capsule: external fibrous capsule (dense irregular CT) & internal synovial membrane (loose CT)
o synovial membrane lines all internal joint surfaces except hyaline cartilage
- reinforcing ligaments: capsular, extracapsular or intracapsular ligaments
- fatty pads: cushioning in some synovial joints
- menisci (articular discs): fibrocartilage discs in some synovial joints
o separate articular surfaces & improve fit between bones
- bursae: flattened fibrous sacs lined with synovial membrane & containing film of synovial fluid
Types of Synovial Joints:
Ball & Socket Joints: ball-shaped head of one bone fits into cuplike socket of another
- example: shoulder & hip joints
Condyloid (Ellipsoidal) Joints: oval condyle of one bone fit into depression of another
- example: radiocarpal joints
Plane (Gliding) Joints: flat joint surfaces, allow only short slipping/gliding movements
- example: joints between vertebral articular processes
Hinge Joints: convex projection of one bone fits into concave surface on another
- example: interphylangeal joints
Pivot Joints: rounded end of one bone protrudes into a bony ring/sleeve on another
- example: atlas & axis articulation
Saddle Joints: resemble condyloid joints; each bone has both concave & convex articular surfaces (like saddle); greater freedom of movement
- example: carpometacarpal joints
Joint Angular movements: increase or decrease angle between 2 bones
- includes flexion, extension, abduction, adduction & circumduction
- flexion: decreases angle of joint & brings bones closer together
- extension: increases angle of joint & moves bones away from each other
o hyperextension: moving head backwards beyond straight
- dorsiflexion: lifting foot
- plantar flexion: depressing foot
- abduction: movement of limb away from midline
- adduction: movement of limb toward midline
- rotation: turning of bone around its long axis
o medial rotation: toward the midline; lateral rotation: away from midline
- circumduction: moving a limb so that it describes a cone in space
- pronation: rotating forearm medially so the palm faces posterior/inferiorly
- supination: rotating forearm laterally so the palm faces anterior/superiorly
- eversion: turning the sole of the foot laterally
- inversion: turning the sole of the foot medially
- retraction: nonangular posterior movement (moving jaw backward)
- protraction: nonangular anterior movement (moving jaw forward)
- elevation: lifting a body part superiorly
- depression: lowering a body part inferiorly
- opposition: touching thumb to tip of other digits
Chapter 8: The Muscular System
Skeletal muscle tissue: attach to & cover bony skeleton
- longest of muscle types; striated; under voluntary control
Skeletal Muscle Anatomy:
Connective Tissue wrappings:
- fascia: layers of connective tissue sepearating skeletal muscles
- aponeuroses: broad fibrous connective sheets attaching muscles to adjacent structures
- epimysium: dense irregular CT surrounding whole muscle
- perimysium: fibrous CT surrounding individual muscle fascicles (bundles of muscle fibers (cells))
- endomysium: reticular CT surrounding individual muscle fibers (cells)
Skeletal Muscle Fibers:
- skeletal muscle cells long (hundreds of cm) & wide; multinucleate
- sarcolemma: plasma membrane of muscle
- sarcoplasm: like cytoplasm of normal cell; contains many glycosomes (store glycogen) & myoglobin (carries & stores oxygen)
- myofibrils: contractile elements of skeletal muscle
o composed of thin filaments (actin, tropomyosin & troponin complex) & thick filaments (myosin)
o myosin composed of long central tails & laterally oriented heads (cross-bridges) that bind actin
o tropomyosin covers myosin binding sites on actin molecules in resting muscle
o troponin complex consists of: TnI (inhibits actin), TnT (binds tropomyosin & positions it on actin) & TnC (binds calcium to start contraction)
o striations result from alternating dark A bands (thick filaments with overlapping thin filaments) & I bands (thin filaments)
o A bands have lighter central H zone (no thin filaments) with central darker M line (desmin protein)
o I bands have darker central Z disc (connexin protein)
o Elastic filaments (composed of titin) hold thick & thin filaments in place & recoil to reform shape when muscle relaxes)
o A sarcomere is the region of a myofibril between adjacent Z discs
- sarcoplasmic reticulum: smooth ER of muscle cells; store calcium
o wraps around myofibrils; terminal cisternae are cross channels at A-I junctions
o terminal cisternae form triad with T-tubules of sarcolemma; triads sense voltage & regulate calcium release
Contraction of Skeletal Muscle Fiber: activation of myosin's cross bridges
- sliding filament mechanism: during contraction, the thin filaments slide past the thick filaments so that actin & myosin overlap to a greater degree
- nerve impulse leads to depolarization & calcium release from sarcoplasmic reticulum
- calcium binds to TnC, which changes shape & moves tropomyosin away from myosin binding sites on actin
- with myosin binding sites accessible on actin, activated myosin heads bind actin (cross bridge attachment)
- as myosin heads bind actin, they pivot as they change from high-energy shape to low-energy shape, pulling thin filament toward center of sarcomere
o ADP & P are released from myosin head
- a new ATP molecule binds the myosin head & myosin loses hold of actin (cross bridge detachment)
- hydrolysis of ATP to ADP + P by ATPase releases energy to return myosin to high-energy state... provides potential energy for myosin to again bind actin
Regulation of contraction:
- the axon of a motor neuron forms a neuromuscular junction with a muscle fiber
- the neurotransmitter acetylcholine (ACh) is released in synaptic vesicles from the axon terminal of the nerve cell into the synaptic cleft between the nerve cell & muscle cell
- the motor end plate of the muscle cell has ACh receptors that bind ACh; this binding opens sodium channels in the sarcolemma... sodium rushes in & triggers an action potential in the muscle cell:
o muscle cells are polarized with slight negative charge in resting state
o depolarization of the muscle cell results from the excess positive charge caused by the influx of sodium ions
o the local depolarization spreads to the rest of the muscle cell
o repolarization occurs as potassium ions flow out of the muscle cell to restore the resting potential
- ACh is degraded by acetylcholinesterase in synaptic cleft
- Excitation-contraction coupling: transmission of action potential past triads causes sarcoplasmic reticulum to release calcium ions into sarcoplasm
o Some calcium binds to troponin... (see above)
o Calcium signal is short-lived (30 ms); ATP-dependent calcium pump moves calcium back into sarcoplasmic reticulum
o As intracellular calcium levels drop, tropomyosin again blocks myosin binding sites on actin... relaxation occurs
Muscle metabolism: muscles need constant supply of ATP
ATP Sources:
- Direct phosphorylation: creatine phosphate converted to creatine by creatine kinase... phosphate released added to ADP to form ATP
- Anaerobic glycolysis & lactic acid formation: 2 ATP yield per glucose
o Lactic acid build up in muscles - causes fatigue
o Oxygen debt: need additional oxygen to oxidize & remove lactic acid from muscle cells
- Aerobic respiration: yields 36 or 38 ATP per glucose
Muscular Responses
Threshold stimulus: minimal stregth of stimuli to cause a contraction
Muscle twitch: response of muscle to a single brief stimulus... can be measured in lab using myogram; includes:
- latent period
- period of contraction
o tetanus: sustained muscle contraction - can be incomplete or complete
- period of relaxation
- muscle tone: most important stabilizing factor for most joints
o tendons kept taught by muscle tone - a low level of contractile activity in relaxed muscles
Smooth muscle tissue: occurs in walls of visceral organs (stomach, bladder), respiratory passageways & blood vessels
- forces fluids & other substances through body channels
- nonstriated; involuntary
- slow & sustained contractions
Smooth Muscle: spindle-shaped cells with centrally located nucleus
- has thin endomysium; no perimysium or epimysium
- lines walls of most blood vessels & hollow organs... 2 layers in most cases: longitudinal layer & circular layer
o 2 layers alternate contraction & relaxation: leads to peristalsis - moves contents along tube
- myofilaments: thick filaments (myosin) & thin filaments (actin & tropomyosin (no troponin))
Contraction of Smooth Muscle:
- uses sliding filament mechanism
- no troponin or TnC... calcium binds calmodulin & myosin light chain kinase to activate myosin
Regulation of Smooth Muscle Contraction:
- can use similar mechanism to skeletal muscle... neurotransmitter release at neuromuscular junction generates action potential, which leads to rise in intracellular calcium
- however, signal can be stimulatory or inhibitory for contraction
- can use a variety of neurotransmitters (ACh, norepinephrine...), whereas skeletal muscle cells use ACh
- smooth muscle cells can spontaneously depolarize in response to chemical stimuli
Cardiac muscle tissue: occurs only in walls of heart
- striated; involuntary
- pacemaker cells set rate of contraction
Major Skeletal Muscles
Muscle Attachment Sites:
- origin: site of muscle's attachment to more stationary bone
- insertion: site of muscle's attachment to more movable bone
- movements are often the result of several muscles acting as a group
- most muscles are arranged in opposing pairs:
o agonist (prime mover): contracts while antagonist stretches
o agonist & antagonist often located on opposite sides of bone (biceps brachii & triceps brachii)
- synergists: contract & stabilize intermediate joints (joint in between agonist & primary joint) to prevent unwanted movement
o wrist extensors contract to prevent wrist from flexing when fingers flex
- fixators: stabilize origin of prime mover so it acts more efficiently
o fixators hold scapula steady while arm moves
Muscles of the Head & Neck:
- epicranius (occipitofrontalis)
o origin: epicranial aponeurosis (frontal belly); occipital bone & mastoid process of temporal bone (occipital belly)
o insertion: skin over orbit (frontal belly); epicranial aponeurosis (occipital belly)
o action: draws scalp anteriorly (frontalis); draws scalp posteriorly (occipitalis)
- orbicularis oculi
o origin: medial wall of orbit
o insertion: circular path around orbit
o action: closes eye
- orbicularis oris
o origin: muscle fibers surrounding mouth opening
o insertion: skin at corner of mouth
o action: closes & protrudes lips (assists in speech)
- buccinator
o origin: alveolar processes of maxilla & mandible
o insertion: orbicularis oris
o action: presses cheeks against teeth & lips (whistling & blowing); draws corner of mouth laterally; assists in chewing
- zygomaticus major & minor
o origin: zygomatic bone
o insertion: skin at angle of mouth & orbicularis oris (z. major) & upper lip (z. minor)
o action: z. major draws mouth superiorly & laterally (smiling & laughing); z. minor raises upper lip
- platysma
o origin: fascia over deltoid & pectoralis major muscles
o insertion: mandible, muscles around mouth & skin of lower face
o action: draws outer lower lip inferiorly & posteriorly (pouting) & depresses mandible
- muscles that move eyeballs (6 muscles): superior, inferior, lateral & medial rectus muscles, & superior & inferior oblique muscles
- masseter
o origin: maxilla & zygomatic arch
o insertion: angle & ramus of mandible
o action: elevates mandible (closes mouth) & retracts mandible
- temporalis
o origin: temporal bone
o insertion: coronoid process & ramus of mandible
o action: elevates & retracts mandible
- suprahyoid muscles: elevate hyoid bone
- infrahyoid muscles: depress hyoid bone
- sternocleidomastoid
o origin: sternum & clavicle
o insertion: mastoid process of temporal bone
o action: flex cervical portion of vertebral column; extend head & elevate sternum during forced inhalation; laterally flex & rotate head side to side
Muscles that move the pectoral girdle (primarily scapula)
- pectoralis minor
o origin: 2nd or 3rd through 4th or 5th ribs
o insertion: coracoid process of scapula
o action: abducts & inferiorly rotates scapula; elevates 3rd through 5th ribs during forced inhalation (when scapula stabilized)
- serratus anterior
o origin: superior 8 or 9 ribs
o insertion: vertebral border & inferior angle of scapula
o action: abducts & superiorly rotates scapula; elevates ribs (when scapula stabilized)
- trapezius
o origin: occipital bone (superior nuchal line & ligamentum nuchae) & spines of 7th cervical & all thoracic vertebrae
o insertion: clavicle; acromion & spine of scapula
o action: elevates scapula & helps extend head; adducts & depresses scapula & rotates scapula upward; stabilizes scapula
- pectoralis major
o origin: clavicle, sternum & costal cartilage of 2nd to 6th ribs (sometimes 1st to 7th ribs)
o insertion: greater tubercle of humerus & intertubercular sulcus of humerus
o action: adducts & medial rotates arm at shoulder joint; flexes arm (clavicular head) & extends arm (sternocostal head)
- latissimus dorsi
o origin: spines of inferior 6 thoracic vertebrae & lumbar vertebrae; crests of sacrum & ilium & inferior 4 ribs
o insertion: intertubercular sulcus of humerus
o action: extends, adducts & medially rotates arm at shoulder joint; draws arm posteriorly & inferiorly
- deltoid
o origin: acromial extremity of clavicle; acromion & spine of scapula
o insertion: deltoid tuberosity of humerus
o action: abducts arm at shoulder joint (lateral fibers); flexes & medially rotates arm at shoulder joint (anterior fibers); extends & laterally rotates arm at shoulder joint (posterior fibers)
- infraspinatus
o origin: inferior to spine of scapula (infraspinous fossa)
o insertion: greater tubercle of humerus
o action: laterally rotates & adducts arm at shoulder joint
- teres major
o origin: inferior angle of scapula
o insertion: intertubercular sulcus of humerus
o action: extends arm & assists in adduction & medial rotation of arm at shoulder joint
- teres minor
o origin: inferior lateral border of scapula
o insertion: greater tubercle of humerus
o action: laterally rotates, extends & adducts arm at shoulder joint
- Flexors:
- biceps brachii
o origin: tubercle above glenoid cavity of scapula (long head); coracoid process of scapula (short head)
o insertion: radial tuberosity of radius (& bicipital aponeurosis)
o action: flexes forearm at elbow joint; supinates forearm at radioulnar joints & flexes arm at shoulder joint
- brachialis
o origin: distal anterior surface of humerus
o insertion: ulnar tuberosity & coronoid process of ulna
o action: flexes forearm at elbow joint
- brachioradialis
o origin: lateral border & distal end of humerus
o insertion: superior to styloid process of radius
o action: flexes forearm at elbow joint; supinates & pronates forearm at radioulnar joints
- Extensors:
- triceps brachii
o origin: inferior to glenoid cavity of scapula (long head); lateral & posterior surface of humerus (lateral head); posterior surface of humerus ( medial head)
o insertion: olecranon of ulna
o action: extends forearm at elbow joint & extends arm at shoulder joint
- Pronators:
- pronator teres
o origin: medial epicondyle of humerus & coronoid process of ulna
o insertion: midlateral surface of radius
o action: pronates forearm at radioulnar joints & weakly flexes forearm at elbow joint
- Flexors:
- flexor carpi radialis
o origin: medial epicondyle of humerus
o insertion: 2nd & 3rd metacarpals
o action: flexes & abducts hand at wrist joint
- palmaris longus
o origin: medial epicondyle of humerus
o insertion: flexor retinaculum & palmar aponeurosis
o action: weakly flexes hand at wrist joint
- flexor carpi ulnaris
o origin: medial epicondyle of humerus; coronoid process of ulna; ridge along anterior surface of radius
o insertion: pisiform, hamate & base of 5th metacarpal
o action: flexes & adducts hand at wrist joint
- Extensors:
- extensor carpi radialis
o origin: lateral supercondylar ridge of humerus
o insertion: 2nd metacarpal
o action: extends & abducts hand at wrist joint
- extensor digitorum
o origin: lateral epicondyle of humerus
o insertion: distal & middle phalanges of each finger
o action: extends distal & middle phalanges of each finger at interphalangeal joints; extends proximal phalanges of each finger at metacarpophalangeal joints; extends hand at wrist joint
- extensor carpi ulnaris
o origin: lateral epicondyle of humerus & posterior border of ulna
o insertion: 5th metacarpal
o action: extends & adducts hand at wrist joint
- abductor pollicis longus
o origin: posterior surface of middle of radius & ulna
o insertion: 1st metacarpal
o abducts & extends thumb at carpometacarpal joint & abducts hand at wrist joint
- rectus abdominis
o origin: pubic crest & pubic symphysis
o insertion: cartilage of ribs 5-7 & xiphoid process
o action: flexes vertebral column & compresses abdomen
- external oblique
o origin: lower 8 ribs
o insertion: iliac crest & linea alba
o action: compresses abdomen & flexes vertebral column
- internal oblique
o origin: iliac crest, inguinal ligament & thoracolumbar fascia
o insertion: cartilage of last 3 or 4 ribs; linea alba
o action: compresses abdomen & flexes vertebral column
- transverse abdominis
o origin: iliac crest, inguinal ligament, lumbar fascia & cartilage of lower 6 ribs
o insertion: xiphoid process, linea alba & pubis
o action: compresses abdomen
- diaphragm
o origin: xiphoid process of sternum, costal cartilage of lower 6 ribs & lumbar vertebrae
o insertion: central tendon
o action: increases height & volume of thoracic cavity, resulting in inhalation
- external intercostals
o origin: superior rib
o insertion: inferior rib
o action: elevates ribs & increases width & depth of thoracic cavity, resulting in inhalation
- internal intercostals
o origin: superior rib
o insertion: inferior rib
o action: further decreases width & depth of thoracic cavity during forced exhalation
- gluteus maximus
o origin: iliac crest, sacrum, coccyx & aponeurosis of sacrospinalis
o insertion: iliotibial tract & linea aspera under greater trochanter of femur
o action: extends thigh at hip joint & laterally rotates thigh
- gluteus medius
o origin: ilium
o insertion: greater trochanter of femur
o action: abducts thigh at hip joint & medially rotates thigh
- tensor fasciae latae
o origin: iliac crest
o insertion: iliotibial tract (& tibia)
o action: flexes & abducts thigh at hip joint
- adductor longus
o origin: pubic crest & pubic symphysis
o insertion: linea aspera of femur
o action: flexes & adducts thigh at hip joint & medially rotates thigh
- pectineus
o origin: superior ramus of pubis
o insertion: pectineal line of femur (between lesser trochanter & linea aspera)
o action: flexes & adducts thigh at hip joint
- Extensors:
- sartorius
o origin: anterior superior iliac spine
o insertion: medial surface & body of tibia
o action: flexes leg at knee joint; flexes, abducts & laterally rotates thigh at hip joint
- Quadriceps femoris muscle group:
- rectus femoris
o origin: anterior inferior iliac spine
o insertion: patella (via quadriceps tendon) & tibial tuberosity (via patellar ligament)
o action: extends leg at knee joint; flexes thigh at hip joint
- vastus lateralis
o origin: greater trochanter & linea aspera of femur
o insertion: patella (via quadriceps tendon) & tibial tuberosity (via patellar ligament)
o action: extends leg at knee joint
- vastus medialis
o origin: linea aspera of femur
o insertion: patella (via quadriceps tendon) & tibial tuberosity (via patellar ligament)
o action: extends leg at knee joint
- Flexors:
- Hamstring muscle group:
- biceps femoris
o origin: ischial tuberosity (long head); linea aspera of femur (short head)
o insertion: head of fibula & lateral condyle of tibia
o action: flexes leg at knee joint & extends thigh at hip joint
- semitendinosus
o origin: ischial tuberosity
o insertion: proximal medial surface of shaft of tibia
o action: flexes leg at knee joint & extends thigh at hip joint
- semimembranosus
o origin: ischial tuberosity
o insertion: medial condyle of tibia
o action: flexes leg at knee joint & extends thigh at hip joint
- tibialis anterior
o origin: lateral condyle & body of tibia (& interosseus membrane between tibia & fibula)
o insertion: 1st metatarsal & medial cuneiform
o action: dorsiflexes foot at ankle joint & inverts foot at intertarsal joints
- extensor digitorum longus
o origin: lateral condyle of tibia, anterior surface of fibula & (& interosseus membrane between tibia & fibula)
o insertion: middle & distal phalanges of toes 2-5
o action: dorsiflexes foot at ankle joint; extends distal & middle phalanges of each toe at interphalangeal joints; extends proximal phalanx of each toe at metatarsophalangeal joint
- fibularis (peroneus) longus
o origin: head & body of fibula & lateral condyle of tibia
o insertion: 1st metatarsal & medial cuneiform
o action: plantar flexes foot at ankle joint & everts foot at intertarsal joints
- gastrocnemius
o origin: lateral & medial condyles of femur & capsule of knee
o insertion: calcaneus (via calcaneal tendon)
o action: plantar flexes foot at ankle joint & flexes leg at knee joint
- soleus
o origin: head of fibula & medial border of tibia
o insertion: calcaneus (via calcaneal tendon)
o action: plantar flexes foot at ankle joint