Chapter 5: The Integumentary System
The Skin (Integument): composed of 2 regions:
- Epidermis: outermost layer composed of epithelial cells
- Dermis: underlying layer composed of fibrous connective tissue; vascularized
Epidermis: keratinized stratified squamous epithelium
-
Layers of Epidermis:
o Stratum Basale: basal layer; deepest epidermal layer firmly attached to dermis
• single layer of cells; cell division produces new keratinocytes for all layers
• dead cells hardened by keratin (keratinized)
• protects skin with keratin & thick plasma membranes; glycolipids prevent water loss
-
Cell types in epidermis:
o keratinocytes: produce the fibrous protein keratin
• tightly connected by desmosomes
• outermost cells dead & keratinized; lifespan of 25-45 days
• thick skin has accelerated cell division & keratinization
o Langerhans' cells (epidermal dendritic cells): macrophages; part of immune system - kill microbes
• produced in bone marrow; migrate to epidermis & form network around keratinocytes
o melanocytes: spider-shaped cells that produce the pigment melanin
• located in deepest layer of epidermis; transfer melanin to keratinocytes
• melanin granules protect the cell nucleus from UV radiation
Skin Color: dictated by 3 pigments: melanin, carotene, & hemoglobin
- melanin: passed from melanocytes to basal keratinocytes
o melanin color ranges from yellow to reddish-brown to black
o freckles & pigmented moles are due to local melanin accumulations
- carotene: yellow-orange pigment found in plants (carrots...)
o accumulates in stratum corneum & dermis; gives skin yellowish color
- hemoglobin: oxygenated hemoglobin in dermal capillaries gives fair skin a pinkish color
Dermis: contains both loose & fibrous connective tissue
- collagen fibers: flexible but resist stretching (prevent skin from being torn)
- elastic fibers: stretch to allow movement of underlying muscles & joints
- dermal papillae: projections that indent into & anchor epidermis
- dermal ridges on palms of hand & soles of feet form epidermal ridges
o increase friction for better grip
o genetically determined pattern of ridges; leaves fingerprint
- rich supply of blood vessels nourishing skin
o increased blood flow: blushing; reduced blood flow: cyanosis
o restricted blood flow (in bedridden) can lead to decubitus ulcers (bedsores)
- accessory structures: hair follicles, nails, oil & sweat (sudoriferous) glands
- sensory nerve fibers: take nerve impulses to & from accessory structures
Subcutaneous Layer (Hypodermis): layer just deep to the dermis
- mostly adipose (fat) tissue with some other loose connective tissue
- adipose tissue serves as reserve energy store
- insulates, absorbs shocks, & anchors skin loosely to muscles
Accessory Structures of Skin:
Hair & hair follicles:
- hair is flexible strands of mostly dead, keratinized cells
- hair is found on all body parts except the palms, soles, lips, nipples & portions of external reproductive organs
o puberty stimulates new hair growth (axillary & pelvic regions in both sexes, & in several other body regions in males)
- hair follicle: extends from epidermal surface to dermis
o cells at base of follicle continually divide, pushing older cells toward surface & away from blood vessels (nourishment) - cells become keratinized & eventually die toward top of follicle
- hair has root within follicle & shaft extending beyond skin
- melanin from melanocytes at base of follicle produce color
- alopecia: hair loss brought on by aging & hormones
- each follicle has one or more sebaceous (oil) glands that empty into follicle
- arrector pili muscle: smooth muscle bundle that contracts to raise hair
Nails: scalelike epidermal modifications at dorsal surface of distal region of fingers & toes
- nail root cells produce new growth - cells become keratinized as they grow out over nail bed
- nail body: visible portion of nail
- cuticle: fold of skin over nail root
- blood in dermal blood vessels beneath nail give pink color to nails
- lunula: whitish half moon shaped base resulting from thicker skin in the area
Sweat (sudoriferous) glands: eccrine & apocrine
- eccrine sweat glands: far more numerous - most abundant on palms of hands, soles of feet & forehead
o ducts
opens into pore at skin surface
o secrete sweat: 99% water with salts, vitamin C, antibodies, metabolic wastes (form of excretion)
o sweat prevents overheating; regulated by sympathetic division of autonomic nervous system
- apocrine sweat glands: mostly confined to axillary & anogenital regions
o ducts
empty into hair follicles
o in addition to components of sweat, secretion contains lipid & proteins
- ceruminous glands: modified apocrine glands in the external ear canal
o secrete cerumen (earwax); deters insects & blocks foreign material
Sebaceous (oil) glands: located all over body except palms of hand & soles of feet
- secrete sebum (rich in oils) into hair follicle (or pore)... bacteriocidal; lubricates hair & skin
- inflammation/infection can lead to acne; overactivity leads to seborrhea
Mammary glands: modified sweat glands in breasts
- lobules within breast lobes contain numerous alveoli
- after childbirth, alveoli secrete milk, which enters a duct leading to nipple
Functions of Skin:
Protection: the skin forms a protective covering over body, guarding it from physical trauma
Synthesis of Vitamin D: UV light (sunlight) assists skin cells in producing vitamin D
Sensory Reception & Communication: specialized nerve endings in dermis are sensory receptors for touch, pressure. Pain, hot & cold
Body Temperature Regulation: some energy from breaking down ATP in chemical reactions is released as heat
- hypothalamus in brain has homeostatic mechanism for regulation of body temperature (36.2-37.7°C)
- skin regulates body temperature:
o blood vessels in dermis can constrict to receive less blood or dilate to receive more blood
o sweat glands can secrete sweat to cool body
- hyperthermia: body temperature above normal (regulatory mechanisms overcome)
o heat exhaustion: individual becomes tired; may be accompanied by headaches, vomiting
o heat stroke: elevated temperature (up to 43°C or 110°F); dizziness, confusion & delusions may occur
• important to cool body immediately: person is immersed in cool water, & fluids given to restore water & salt balance
o fever: elevated body temperature brought on by illness
• bacteria release pyrogens that reset the thermostat at higher temperature (accompanied by chills)
• thermostat reset when infection is cleared & fever breaks
-
hypothermia: body
temperature below normal (regulatory mechanisms overcome)
o body
temperature 90-95°C: uncontrollable shivering, incoherent speech &
lack of coordination
o body
temperature 80-90°C: pulse rate slows, hallucinations occur, person loses
consciousness
Disorders of skin:
- athlete's foot: caused by fungal infection, usually in skin of toes, sole of foot
- eczema & psoriasis: rapid cell division in skin cells, resulting in scaling, itching
o eczema: caused by sensitivity to chemicals (detergents), fabrics, heat
o psoriasis: chronic autoimmune disorder, may be hereditary (inherited); results in reddish (scaly) patches
o melanoma: malignant skin cancer; starts in melanocytes
• characterized by unusual moles that are linked to sun exposure
• may metastasize or spread to nearby organs or tissues
o basal cell carcinoma: most common skin cancer; UV exposure causes basal cells of epidermis to overgrow, forming tumor
o squamous cell carcinoma: tumors form in cells of lower layers of epidermis
• more likely to metastasize than basal cell carcinoma
-
Burns
o first-degree: only epidermis is destroyed
o second-degree: entire epidermis & part of dermis is destroyed
o third-degree: full thickness (epidermis & dermis) is destroyed
o fourth degree: tissue down to bone is destroyed
Wound Healing:
-
if blood vessel is torn,
blood clots at vessel tear &
forms scab
-
basal layer of epidermis
produces new cells at rapid rate to replace damaged cells
-
if wound is deep, scar
tissue may form (many collagen
fibers add strength, but few cells present)
Effects of Aging: epidermis maintains thickness, but there is
decreased turnover of skin cells; epidermis becomes less firmly attached to
dermis; adipose tissue declines
-
decline in numbers of:
blood vessels, sweat glands, hair follicles, sebaceous glands & melanocytes
-
UV radiation can cause
rough skin, unusual pigmentation, wrinkles
Chapter 6: The Skeletal System
Classification of bone:
Human Skeleton: 206 named bones
- Axial skeleton: 80 bones... bones of skull, vertebral column & rib cage
- Appendicular skeleton: 126 bones... bones of upper & lower limbs, pectoral & pelvic girdles
Functions of bones:
- supports body & its organs against pull of gravity
- protects soft body parts
- blood cell formation (hematopoiesis): in some red bone marrow
- mineral storage: calcium salts (calcium phosphate)
- bones (particularly those of arms & legs) provide sites for muscle attachment & permit flexible movement
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
- 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
- epiphyses: ends of bone; often more expanded than diaphysis; outer compact & internal spongy bone
o Joint surfaces covered by articular cartilage
o Epiphyseal line: between diaphysis & each epiphysis - remnant of epiphyseal plate (site of bone growth during childhood)
- Periosteum: membrane that covers entire surface of bone except joint surfaces
o continuous with tendons & ligaments that anchor bones
o contains blood vessels that enter bones & deliver nutrients to bone cells
- Endosteum: inner membrane covers trabeculae of spongy bone & canals of compact bone; contains osteoblasts & osteoclasts
Hematopoietic tissue 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
Microscopic structure of bone:
Compact bone (lamellar bone): units called osteons or Haversian systems
- within each cylnder (osteon) is tubes (concentric circles) of bone matrix (lamellae)
- central (Haversian) canal: runs through center of osteon; carries blood vessels & nerve fibers
- osteocytes: bone cells in small cavities called lacunae
- canaliculi: connect lacunae to each other & central canal
- lacunae separated by bone matrix containing collagen fibers & mineral deposits (calcium phosphate)
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
- most of skeleton is cartilage model (cartilage shaped like future bones) during prenatal development
- cartilage models converted to bone when calcium salts deposited in bone matrix, first by cartilage cells & later by osteoblasts (bone-forming cells)
- endochondral ossification: bone forms by replacing hyaline cartilage
- intramembranous ossification: membrane bone forms from fibrous membrane
-
endochondral ossification:
o primary ossification center in middle of bone
o bone collar forms around diaphysis of cartilage
o central cartilage calcifies & cavitates
o diaphysis elongates & medullary cavity forms
o ossification of epiphyses at secondary ossification centers
o epiphyseal (growth) plates form at junction of diaphysis & epiphysis
Bone Remodeling: for bone growth, or to replace injured bone
- osteoclasts (giant multinucleate cells from same stem cells that differentiate into macrophages) secrete lysosomal enzymes to digest organic matrix & acids to release calcium into solution
- osteoclast damage repaired by osteoblasts
- osteoblasts take calcium from blood for new bone matrix
- some osteoblasts within new matrix become osteocytes (bone cells)
- requires calcium & phosphate & enzyme alkaline phosphatase
Repair of fractures:
Fracture types:
- displaced (ends out of alignment) & nondisplaced fractures
- complete (bone broken through) & incomplete fractures
- linear (along axis) & transverse (perpendicular to axis) fractures
- open (compound, breaks skin) & closed (simple) fractures
Reduction: realignment of broken bone ends
- closed reduction: bones coaxed into position by physician (or someone)
- open reduction: bone ends are secured together by pins or wires
- hematoma (mass of clotted blood) forms in space between broken bone as blood escapes from injured blood vessels
- fibrocartilage callus forms to fill space between broken ends of bone (collagen fibers tie bone ends together)
- bony callus forms from fibrocartilage callus as osteoblasts produce spongy bone to join bone ends together
-
bone remodeling: osteoblasts build new compact bone at
periphery & form medullary cavity from spongy bone
- consists of bones arranged along (longitudinal) axis of body
- includes: skull bones, auditory ossicles (ear bones), hyoid bone, ribs, sternum (breastbone) & vertebral column (backbone)
- cranial bones: 8 bones which enclose & protect the brain
o frontal bone: forms forehead & part of nose & orbits
o parietal bones (2): posterior to frontal bone; form roof & sides of cranium
o temporal bones (2): inferior to parietal bones; help form base of cranium
• external auditory meatus: canal to middle ear
• mandibular fossa: articulates with mandible
• mastoid process: point of attachment for neck muscle (sternocleidomastoid)
• styloid process: point of attachment for muscles of tongue & larynx
• zygomatic process: helps form cheekbone
o occipital bone: forms dorsal part of skull & base of cranium
• foramen magnum: large opening where spinal cord joins brain
• occipital condyles: articulate with 1st cervical vertebra
o sphenoid
bone: forms sides & base of cranium
& part of orbits
• articulates
with all other cranial bones
• sella turcica: depression that houses pituitary gland of brain
o ethmoid bone: forms part or orbits & nasal cavity
• perpendicular plate: upper nasal septum
• cribriform plate: contains opening for olfactory (smell) nerve fibers
• crista galli: ridge at base of cranial cavity for meninges attachment
• superior & middle nasal conchae: projections in mucous membranes of nasal cavity for filtering & warming air
-
Facial Bones: 14 bones
o nasal bones (2): form bridge of nose (most of outer nose is cartilage)
o maxillae (2): form upper jaw
• palatine process: forms anterior portion of hard palate (roof of mouth)
o zygomatic bones (2): form sides of orbits & cheekbones
• temporal process: joins zygomatic process of temporal bone
o lacrimal bones (2): at medial walls of orbits (eye sockets)
• lacrimal fossa: has opening for tears
o palatine bones (2): form posterior portion of hard palate
o inferior nasal conchae (2): projections in mucous membranes of nasal cavity for filtering & warming air (like nasal conchae of ethmoid bone)
o vomer: forms lower part of nasal septum (joins with perpendicular plate of ethmoid bone)
o mandible: lower jaw
• only
movable bone of skull
• mandibular condyles (condylar processes): articulate with temporal bone to form temporomandibular joint (TMJ)
- Skull Features:
o orbits: eye sockets; contains eyeball & associated structures
o sutures: immovable joints (in adults) between flat bones of skull
o fontanels (soft spots): fibrous membrane-filled spaces in fetal & newborn skull between cranial bones that allow for growth of skull & flexibility during childbirth
• replaced later by bone to become sutures
o paranasal sinuses: paired cavities in bones surrounding nasal cavity that produce mucus & resonate to aid in voice production
• present in frontal, sphenoid, ethmoid & maxillary bones
• sinusitis: inflammation of mucosa of paranasal sinuses due to infection or allergic reaction; blockage leads to pressure buildup & headaches
Hyoid Bone
-
doesn't articulate with any other bone
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
• atlas (C1): 1st cervical vertebra; articulates with occipital condyles at base of skull
⋅ joints provide up & down head movement (yes)
• axis (C2): 2nd cervical vertebra
⋅ dens (odontoid process): peglike projection that makes a pivot the atlas & head rotate around (no)
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
- 4 slight bends seen from the side called normal curves
o abnormal curves: kyphosis, lordosis & scoliosis; due to various disorders
- intervertebral discs: fibrocartilage & elastic tissue discs between bodies of adjacent vertebrae
o form intervertebral joints; highly resistant to shock
Sternum (breastbone): located in center of anterior thoracic wall
- composed of 3 parts:
o manubrium: superior rounded part
o body: long middle part
o xiphoid process: inferior, smallest part
Ribs (24; 12 pairs): give structural support to sides of thoracic cavity & protection to organs of thoracic cavity
- 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
- consists of the bones of the upper & lower limbs (extremities), & the bones forming the pectoral & pelvic girdles (shoulder & hip bones) that connect the limbs to the axial skeleton
- clavicle (2): (collarbone)
o one of the most frequently broken bones (falling on arm)
- scapula (2): (shoulder blade)
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
o head
o greater tubercle & lesser tubercle
o deltoid tuberosity: 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; articulates with ulna
o olecranon fossa: posterior depression; articulates with ulna
- ulna: at medial (pinky) aspect of forearm; looks like wrench
o olecranon: 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
- radius: at lateral (thumb) aspect of forearm
o head:articulates with capitulum of humerus
o styloid process: lateral process
- carpals (8): wrist bones
- 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
• 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 accommodate 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
o greater & lesser trochanters: lateral & medial projections; points of tendon attachment
o linea aspera: narrow ridge posterior on shaft of femur
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 (can be felt close to skin surface of shin)
o tibial tuberosity: where patellar (kneecap) ligaments attach
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
- 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:
Functional Classification:
- Synarthroses: immovable joints (sutures...)
o sutures: between bones of the skull
• joined with short connective tissue fibers... in middle age, connective tissue ossifies forming synostoses
- Amphiarthroses: slightly movable joints (symphyses...)
o symphyses: articular surfaces of bone covered with hyaline cartilage fused to plate of fibrocartilage
• fibrocartilage compressible - shock absorber, but limited movement; joints are amphiarthrotic
• examples are intervertebral joints (discs) & pubic symphysis
- Diarthroses: freely movable joints (synovial joints; includes most joints)
Synovial Joints: bones separated by fluid-containing joint cavity
- all are freely movable
- ligaments: bind bone to bone
- tendons: bind muscle to bone
- articular cartilage: hyaline cartilage protects bone ends
- synovial membrane lines all internal joint surfaces except hyaline cartilage
- synovial fluid: occupies free spaces in joint cavity; reduces friction
- 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
o bursitis: inflammation of bursae (e.g.: tennis elbow)
Types of Synovial Joints:
Saddle Jonts: resemble condyloid joints; each bone has both concave & convex articular surfaces (like saddle); greater freedom of movement
- example: carpometacarpal joints
Ball & Socket Joints: spherical (ball-shaped) head of one bone fits into cuplike socket of another
- example: shoulder & hip joints
Pivot Joints: rounded end of one bone protrudes into a bony ring/sleeve on another
-
example: atlas & axis articulation
Hinge Joints: cylindrical projection of one bone fits into trough-shaped surface on another
-
example: interphylangeal joints
Gliding Joints: flat or slightly curved articular surfaces, allow sliding or twisting movements in several planes
- example: joints between bones of wrists & ankles
Condyloid (Ellipsoidal) Joints: oval articular surfaces of one bone fit into depression of another
- example: radiocarpal joints
Movements of Synovial Joints:
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
- Circumduction: moving a limb so that it describes a cone in space (ball & socket joints)
Rotation: turning of bone around its long axis
- medial rotation: rotation toward the midline
- lateral rotation: rotation away from midline
Special movements:
- Supination: rotating forearm laterally so the palm faces anterior/superiorly
- Pronation: rotating forearm medially so the palm faces posterior/inferiorly
- Inversion: turning the sole of the foot medially
- Eversion: turning the sole of the foot laterally
- Elevation: lifting a body part superiorly
- Depression: lowering a body part inferiorly
Common Joint Injuries:
Sprains: ligaments of joint are stretched or torn
- partially torn ligaments can heal; fully torn ligaments require surgical repair
Arthritis: inflammation within or around a joint
-
Osteoarthritis: chronic;
results from excessive breakdown of articular cartilage
o Generally progresses slowly & is irreversible
o Treatments include magnetic therapy & SAM-e (S-adenosylmethionine) to build up cartilage
-
Rhematoid Arthritis: chronic;
autoimmune disease
o begins with inflammation of synovial membranes, which thickens into a pannus that destroys articular cartilages
o scar tissue forms & ossifies, fusing bone ends (ankylosis)
o treatments include antibiotics, anti-inflammatories, & immunosuppressants
-
Gouty Arthritis: uric
acid crystals deposit in soft tissues of joints; inflammation results;
may have genetic basis; treatments include
anti-inflammatories & avoidance of alcohol
Muscle Types:
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
Cardiac muscle tissue: occurs only in walls of heart
- striated; involuntary
- pacemaker cells set rate of contraction
Skeletal muscle tissue: attach to & cover bony skeleton
- longest of muscle types; striated; under voluntary control
Muscle Functions:
- stabilizing joints: tendons (often extend across joint) & ligaments
- maintaining posture: muscle tone (slight muscle contractions that oppose gravity & refine position)
- producing movement: skeletal muscle contractions move bones; cardiac muscle contractions propel blood through blood vessels; smooth muscle contractions moves food through digestive tract & controls diameter of blood vessels
- generating heat: muscle contraction releases heat energy that warms body
Skeletal Muscle Anatomy:
- muscles are covered by several layers of connective tissue called fascia
- skeletal muscle cells long (hundreds of cm) & wide; multinucleate
- muscle fibers (cells) can contain hundreds of myofibrils
- myofibrils: contractile elements of skeletal muscle
o composed of thin filaments (actin) & thick filaments (myosin)
- sliding filament mechanism: during contraction, the thin filaments slide past the thick filaments so that actin & myosin overlap to a greater degree
Innervation of Muscle:
- motor unit: the axon of a motor neuron branches to several muscle fibers
- a motor neuron fiber forms a neuromuscular junction with a muscle fiber
- sarcolemma: plasma membrane of muscle
- sarcoplasmic reticulum: smooth ER of muscle cells; store calcium
o wraps around myofibrils
o form triad with T-tubules of sarcolemma; triads sense voltage & regulate calcium release
- when nerve impulse arrives at neuromuscular junction, it moves down T tubules, prompting release of calcium from sarcoplasmic reticulum
- if ATP is available, actin filaments slide past myosin & sarcomere (contractile unit consisting of actin & myosin filaments) contracts
Physiology of Muscle Contraction:
- all or none law: when muscle fiber is stimulated, it either contracts completely or not at all
o total amount of contraction depends on how many muscle fibers contract
- muscle twitch: response of muscle to a single brief stimulus (contraction, then relaxation)
o latent period
o period of contraction
• tetanus: maximal sustained muscle contraction - can be incomplete or complete
o period of relaxation
• if muscle is not allowed to rest, fatigue will set in
Chemistry of Muscle Contraction:
ATP Sources:
- Aerobic respiration: in mitochondria; yields 36 or 38 ATP per glucose
- Direct phosphorylation: creatine phosphate converted to creatine by creatine kinase... phophate 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
Aspects of Muscle Contraction:
- origin: site of muscle's attachment to more stationary bone
- insertion: site of muscle's attachment to more movable bone
- 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
- Isotonic contractions: muscle changes in length & moves load
- Isometric contractions: muscle neither shortens nor lengthens
o example: muscle attempts to move a load requiring force greater than available
- 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
- hypertrophy: increase in muscle size due to forceful muscle activity over prolonged period
o requires contraction to 75% of maximum tension, but usually only a few minutes of forceful activity several times a week
o results in increases in metabolic potential, number of myofibrils & possibly numbers of muscle fibers
- atrophy: decrease in muscle size due to lack of muscle activity or only weak contractions
Muscles of the Head &
Neck:
- orbicularis oris
o action: closes & protrudes lips (assists in speech)
- zygomaticus major & minor
o action: raises corner of mouth (smiling & laughing)
- buccinator
o action: presses cheeks against teeth & lips (whistling & blowing); assists in chewing
- orbicularis oculi
o action: closes eye
- masseter
o action: elevates mandible (closes mouth for chewing)
-
temporalis
o action:
elevates & retracts mandible (works with masseter for chewing)
- sternocleidomastoid
o action: extends head & elevates sternum during forced inhalation; rotates head side to side
- rectus abdominis
o action: flexes vertebral column & compresses abdomen
- external oblique
o action: compresses abdomen & flexes vertebral column
- internal oblique
o action: compresses abdomen & flexes vertebral column
- transverse abdominis
o action: compresses abdomen
- diaphragm
o action: increases height & volume of thoracic cavity, resulting in inhalation
- external intercostals
o action: elevates ribs & increases width & depth of thoracic cavity, resulting in inhalation
- external intercostals
o action: further decreases width & depth of thoracic cavity during forced exhalation
Muscles that move the pectoral girdle (primarily scapula)
- serratus anterior
o action: abducts & superiorly rotates scapula; elevates ribs (when scapula stabilized)
- trapezius
o action: elevates scapula & helps extend head; adducts & depresses scapula & rotates scapula upward; stabilizes scapula
- pectoralis major
o action: adducts & medial rotates arm at shoulder joint; flexes arm (clavicular head) & extends arm (sternocostal head)
- latissimus dorsi
o action: extends, adducts & medially rotates arm at shoulder joint
- deltoid
o action: abducts arm at shoulder joint
- infraspinatus
o action: laterally rotates & adducts arm at shoulder joint
- teres major
o action: extends arm & assists in adduction & medial rotation of arm at shoulder joint
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Flexors:
- biceps brachii
o action: flexes forearm at elbow joint; supinates forearm at radioulnar joints & flexes arm at shoulder joint
- brachialis
o action: flexes forearm at elbow joint
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Extensor:
- triceps brachii
o action: extends forearm at elbow joint & extends arm at shoulder joint
- flexor carpi muscles
o action: flex & abduct hand at wrist joint
- extensor carpi muscles
o action: extend & abduct hand at wrist joint
- extensor digitorum
o action: extends phalanges; extends hand at wrist joint
- palmaris longus
o weakly flexes hand at wrist joint
- gluteus maximus
o action: extends thigh at hip joint & laterally rotates thigh
- gluteus medius
o action: abducts thigh at hip joint & medially rotates thigh
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tensor fasciae latae
o origin: iliac crest
o insertion: iliotibial tract (& tibia)
o action: flexes & abducts thigh at hip joint
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adductor group
o includes adductor longus, adductor magnus, pectineus, & gracilis
o
action: adduct thigh at hip joint
- sartorius
o action: flexes leg at knee joint; flexes, abducts & laterally rotates thigh at hip joint
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Quadriceps femoris muscle group:
o includes rectus femoris, vastus lateralis, vastus medialis
o action:
extend leg at knee joint
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Hamstring muscle group:
- includes biceps femoris, semitendinosus, semimembranosus
o action: flex leg at knee joint
- tibialis anterior
o action: dorsiflexes foot at ankle joint & inverts foot
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extensor digitorum longus
o action:
dorsiflexes foot at ankle joint; extends phalanges
- fibularis (peroneus) longus
o action: plantar flexes foot at ankle joint & everts foot
- gastrocnemius
o action: plantar flexes foot at ankle joint & flexes leg at knee joint
- soleus
o action: plantar flexes foot at ankle joint