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
o joined with short connective tissue fibers... in middle age, connective tissue ossifies forming synostoses
- syndesmoses: bones connected by ligament; immovable or slightly movable
o examples include connections between bones of lower arm (radius & ulna) & lower leg (tibia & fibula)
- gomphoses: peg in socket joint; only example is tooth in bony alveolar socket
o connected by short periodontal ligament
Cartilagenous Joints: bones joined by cartilage; no joint cavity
- synchondroses: bones joined by hyaline cartilage; almost always synarthrotic
o examples are epiphyseal plates in long bones of children, joint between costal cartilage of first rib & manubrium of sternum
- symphyses: articular surfaces of bone covered with hyaline cartilage fused to plate of fibrocartilage
o fibrocartilage compressible - shock absorber, but limited movement; joints are amphiarthrotic
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
- articular capsule: external fibrous capsule (dense irregular CT) & internal synovial membrane (loose CT)
o synovial membrane lines all internal joint surfaces except hyaline cartilage
- synovial fluid: occupies free spaces in joint cavity; reduces friction
o mostly blood filtrate; viscous fluid containing hyaluronic acid
o weeping lubrication: fluid forced from cartilage during compression & soaked back up when pressure is relieved
- 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
- bunion: swollen bursa at base of big toe
- Tendon Sheath: elongated bursa wrapped around a tendon
Factors Influencing Stability of Synovial Joints:
- articular surfaces: better fit = more stable
- ligaments: generally, more ligaments = more stable... but ligaments may break if stressed; if only ligaments joining bones, poor stability
- 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
Types of Synovial Joints:
Plane Joints: flat articular surfaces, allow only short slipping or gliding movements
- example: joints between vertebral articular processes
Hinge Joints: cylindrical projection of one bone fits into trough-shaped 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
Condyloid (Ellipsoidal) Joints: oval articular surfaces of one bone fit into depression of another
- example: radiocarpal joints
Saddle Joints: 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
Movements of Synovial Joints:
- Nonaxial: slipping movement only; no axis
- Uniaxial: movement in one plane
- Biaxial: movement in two planes
- Multiaxial: movement in multiple planes
Gliding movements: flat or nearly flat bone glides over similar surface
- intercarpal or intertarsal joints & flat articular processes of vertebrae
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
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
- Protraction: nonangular anterior movement (moving jaw forward)
- Retraction: nonangular posterior movement (moving jaw backward)
- Elevation: lifting a body part superiorly
- Depression: lowering a body part inferiorly
- Opposition: touching thumb to tip of other digits
o Opposition is a distinguishing primate characteristic
Common Joint Injuries:
Sprains: ligaments of joint are stretched or torn
- partially torn ligaments can heal; fully torn ligaments require surgical repair
Cartilage Injuries: tearing of knee menisci or damage to articular cartilages of other joints
- generally will not heal; cartilage fragments interfere with joint function
- arthroscopic surgery can remove cartilage fragments
Dislocations: bones are forced out of alignment
- often accompanied by a sprain, inflammation & joint immobilization
- subluxation is partial dislocation
- repeat dislocations of same joint common
Inflammatory & Degenerative Conditions:
Bursitis: inflammation of bursa; often occurs in prepatellar bursa of knee joint (housemaid's knee) & olecranon process associated bursa of elbow (student's elbow)
- treated with anti-inflammatory agents or aspiration
Tendonitis: inflammation of tendon sheaths; similar symptoms & treatments
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
- Rheumatoid 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
Chapter 9: Muscles & Muscle Tissue
Muscle Types:
Skeletal muscle tissue: attach to & cover bony skeleton
- longest of muscle types; striated; under voluntary control
Cardiac muscle tissue: occurs only in walls of heart
- striated; involuntary
- pacemaker cells set rate of contraction
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
Muscle Functions:
- producing movement
- maintaining posture
- stabilizing joints
- generating heat
Functional characteristics of muscles:
- excitability (irritability): receive & respond to stimuli
- contractility: shorten forcibly when stimulated
- extensibility: can be stretched or extended
- elasticity: recoil & resume resting length following stretch
Skeletal Muscle Anatomy:
Connective Tissue wrappings:
- 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)
Nerve & Blood Supply: each muscle generally served by 1 nerve, an artery & 1 or more veins
- nerve ending controls muscle cell activity
- arteries lead to winding capillaries that deliver nearly continuous oxygen; veins carry away large amounts of metabolic waste
Attachments: most muscles attached to bones in at least 2 places
- origin: point of attachment to less movable (immovable) bone
- insertion: point of attachment to more movable bone
- direct (fleshy) attachments: epimysium of muscle fused to periosteum or perichondrium
- indirect attachments: extension of muscle's CT in the form of tendon or aponeurosis anchors muscle to CT covering of bone or to fascia of another muscle
Microscopic Anatomy of Skeletal Muscle:
- 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 ACh esterase 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 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
Isotonic contractions: muscle changes in length & moves load
Isometric contractions: muscle neither shortens nor lengthens
- example: muscle attempts to move a load requiring force greater than available
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
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))
o intermediate filaments with dense bodies... anchor thin filaments & form intracellular cytoskeleton
Contraction of Smooth Muscle:
- uses sliding filament mechanism
- no troponin or TnC... calcium binds calmodulin & myosin light chain kinase to activate myosin
o calcium ions bind & activate calmodulin
o activated calmodulin activates myosin light chain kinase
o the activated kinase transfers phosphate from ATP to myosin cross bridges (heads)
o phosphorylated myosin heads interact with actin of thin filaments - produces shortening of the muscle
o intracellular calcium levels drop - relaxation
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
Chapter 10: The Muscular System
Muscle Attachment Sites:
- origin: site of muscle's attachment to more stationary bone
- insertion: site of muscle's attachment to more movable bone
- belly: fleshy part of muscle between tendons of origin & insertion
- tendonitis (tenosynovitis): painful inflammation of tendons, tendon sheaths & synovial membranes of a joint
o most commonly affected tendons are those of: elbow (tennis elbow), wrists, shoulders, finger joints (trigger finger), ankles & feet
o accompanied by swelling (fluid accumulation), tenderness & pain
o can be caused by trauma, strain or excessive exercise
- 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)
- 1st class levers: fulcrum is between effort & load (e.g.: scissors & seesaws; atlanto-occipital joint))
- 2nd class levers: load is between fulcrum & effort (e.g.: wheelbarrow; probably no examples in body)
- 3rd class levers: effort is between fulcrum & load (e.g.: forceps; elbow joint)
o most common levers in body
Fascicle arrangement: affect a muscles range of motion & power
- 5 patterns: parallel, fusiform (spindle-shaped), circular, triangular or pennate (feather-shaped)
- longer fibers = greater range of motion; more fibers is usually associated with more power
- 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
- static stretching: holding a muscle in lengthened position (to point of slight discomfort; 15-30 sec.) to increase range of motion
o benefits may include improved performance, decreased risk of injury, reduced soreness & improved posture
Muscle Names: see table 11.2 page 314
Muscles of the Head & Neck:
- orbicularis oris
o origin: muscle fibers surrounding mouth opening
o insertion: skin at corner of mouth
o action: closes & protrudes lips (assists in speech)
- 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
- 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
- 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
- orbicularis oculi
o origin: medial wall of orbit
o insertion: circular path around orbit
o action: closes eye
- 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
- 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 (frontal belly); draws scalp posteriorly (occipital belly)
- 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
- 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
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
- 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
Chapter 12: The Nervous System & Nervous Tissue
Nervous System Function:
- Sensory Input: sensory receptors detect internal stimuli, & send information to central nervous system
- Integration: nervous system processes information & makes decisions for appropriate responses
- Motor Output: motor neurons carry information about decision to effectors (muscle cells, glands) to generate response
Organization of the Nervous System
Central Nervous System (CNS): brain & spinal cord
Peripheral Nervous System (PNS): nerves that extend from the CNS (outside the CNS)
- Sensory (afferent) division: nerves that convey impulses to the CNS from sensory receptors
o sensory neurons link body parts to CNS
o somatic afferent fibers: convey impulses from skin, skeletal muscles & joints
o visceral afferent fibers: convey impulses from visceral organs (organs of ventral body cavity)
- Motor (efferent) division: transmits impulses from the CNS to effector organs (muscles & glands)
o motor neurons activate muscle contraction & glandular secretion
o somatic nervous system (voluntary nervous system): somatic motor neurons that conduct impulses from the CNS to skeletal muscles
o autonomic nervous system (ANS... also involuntary nervous system): visceral motor neurons that regulate activity of smooth muscle, cardiac muscle & glands
§ sympathetic division: mobilizes body systems (accelerates circulatory & respiratory systems, slows digestion) during emergency
§ parasympathetic division: generally opposite of sympathetic responses... conserves energy, promotes nonemergency functions (digestion)
Histology of Nervous Tissue:
Neurons:
- extreme longevity
- most neurons are amitotic (some olfactory & hippocampal neurons can divide)
- high metabolic rate
- 3 functional components:
o receptive or input region
o conducting component
o secretory or output component
- cell body (perikaryon or soma): contains nucleus & most organelles (no centrioles)
o Nissl bodies (chromatophilic substance): rough ER of neuron
o neurofibrils: bundles of intermediate filaments (neurofilaments) - maintain shape
o pigments: melanin (black), red iron-containing pigment & lipofuscin
§ lipofuscin called aging pigment (accumulates in elderly)
o cell body is part of receptive surface of neuron - receives information from other neurons
o ganglia: clusters of neuronal cell bodies in PNS
o nuclei: clusters of neuronal cell bodies in CNS
- processes: dendrites & axons; extend from cell body
o CNS consists of neuronal cell bodies & processes; PNS consists mostly of processes
o tracts: bundles of neuronal processes in CNS
o nerves: bundles of neuronal processes in PNS
o dendrites: main receptive or input regions - convey signals (short distance graded potentials) toward cell body
§ dendritic spines: ends of dendrites; convey incoming messages toward the cell body
o axon: arises from axon hillock; may be very short or very long
§ may have branches called axon collaterals
§ ends in terminal branches with endings called axon terminals (synaptic knobs or boutons)
§ conducting component of neuron - generate & transmit nerve impulses
§ axon terminals are secretory component of neuron - secrete chemicals called neurotransmitters stored in vesicles into the extracellular space
§ axolemma: plasma membrane of axon
§ transport of materials along axons involves microtubules & motor proteins (e.g.: kinesin)
- myelin sheath & neurolemma: myelin sheath (whitish protein-lipoid segmented sheath) formed by oligodendrocytes in CNS & Schwann cells in PNS - cells wrap themselves around axon of neuron
o myelinated fibers conduct impulses rapidly; unmyelinated fibers conduct impulses slowly
o neurolemma: bulge of plasma membrane with nucleus & most of cytoplasm of Schwann cell just external to myelin sheath
o nodes of Ranvier: gaps in myelin sheath between adjacent Schwann cells
o white matter: myelinated fiber tracts in CNS
o gray matter: mostly nerve cell bodies & unmyelinated fibers in CNS
Classification of Neurons:
Structural:
- multipolar neurons: 3 or more processes; most common type
- bipolar neurons: 2 processes, usually an axon & a dendrite with cell body in between
- unipolar neurons (pseudounipolar neurons): 1 process emerging from cell body forming proximal & distal branches
Functional:
- sensory or afferent neurons: transmit impulses from sensory receptors in skin or internal organs toward CNS
o almost all are unipolar neurons
o cell bodies are located in ganglia outside CNS (spinal cord)
- motor or efferent neurons: carry impulses away from CNS to effector organs (muscles & glands)
o multipolar neurons
o cell bodies generally located in CNS
- interneurons (association neurons): between sensory & motor neurons in neural pathways; integrate signals within CNS
o almost all are multipolar neurons
o > 99% of neurons in body
Supporting cells (neuroglia): neurons associate with nonnervous supporting cells called neuroglia or glial cells
Neuroglia of CNS:
- astrocytes: star-shaped; most abundant & versatile glial cells
o anchor neurons to capillaries & aid in exchange & permeability
o control chemical environment surrounding neurons - clean up potassium ions & neurotransmitters
- microglia: small ovoid cells with long "thorny" processes that contact neurons
o can transform into phagocytic cells & engulf/break down bacteria & cell debris
- ependymal cells: shape varies from squamous to columnar; many are ciliated
o line central cavities of brain & spinal cord, between tissue fluid of interneuronal space & cerebrospinal fluid (CSF) within cavities
o cilia circulate CSF (CSF is secreted by capillaries of choroid plexuses
- oligodendrocytes: wrap processes around thicker neurons of CNS - produce myelin sheath of CNS neurons
Neuroglia of PNS:
- satellite cells: surround neuron cell bodies in ganglia; function unknown
- Schwann cells (neurolemmocytes): wrap around larger nerve fibers of PNS - produce myelin sheath of PNS neurons
- important in regeneration of PNS neurons
Neurophysiology:
- neurons highly irritable (respond to stimuli) - can be excited or inhibited; sufficient stimulation results in conduction of an electrical impulse (action potential) along the length of the axon
- voltage (potential): potential energy generated by separated charge
- current: flow of electrical charge from one point to another - used to do work
- resistance: block to charge flow by intervening substances
- voltage (V) = current (I) x resistance (R)
- ion channels in plasma membrane include passive (leakage) channels & active (gated) channels
o gated channels: have a molecular gate - 1 or more protein molecules that change shape to open or close the channel
o chemically-gated (transmitter-gated) channels: open when neurotransmitter binds
o voltage-gated channels: open & close in response to changes in membrane potential
o electrochemical gradients: ions flow from region of higher concentration to region of lower concentration (diffuse) & toward opposite electrical charge
§ basis of action potentials
Membrane potentials:
- resting membrane is polarized - the inside of the neuron is negative with respect to the outside (fewer positively charged ions)
- sodium ion concentration is higher outside cell than inside; potassium ion concentration is higher inside cell than outside
- positive sodium ions outside neuron balanced with (-) chloride ions; positive potassium ions inside neuron balanced with negatively charged (anionic) proteins
- potassium ions diffuse more easily & rapidly than sodium ions - leaves inside of cell with excess negative charge
- the voltage in a resting neuron is between -40 mV & -90 mV
- an ATP-dependent sodium-potassium pump can move sodium back out of cell & potassium back into cell
- graded potentials: short distance signal; local changes in membrane potential that decrease in strength with distance (fade quickly)
o generator potential: excitation of sensory neuron by energy
o postsynaptic potential: stimulation by neurotransmitter released by another neuron
- action potentials: long-distance signals that do not decrease in strength; in neurons, nerve impulses
o only axons can generate action potentials (total change in voltage inside neuron of ~ 100mV (from -70mV to +30mV))
- depolarization: inside of cell becomes less negative (e.g.: -70mV ® -50mV)
- hyperpolarization: inside of cell becomes more negative (e.g.: -70mV ® -90mV)
Action Potential:
- resting state: voltage-gated channels closed; diffusion of sodium & potassium ions through leakage channels
- depolarizing phase: increase in sodium permeability & reversal of membrane potential
o local influx of sodium leads to slight depolarizations
o fast sodium channel activation gates open quickly & sodium rushes into cell
o more sodium channels open - positive feedback cycle
o if threshold voltage (generally between -50mV & -55mV) is reached by sodium influx, all sodium channels open & action potential is generated
o voltage inside cell becomes positive (about +30mV)
- repolarizing phase: decrease in sodium permeability & increase in potassium permeability
o action potential is rapid; lasts ~ 1 sec.... buildup of positive charge in cell resists further sodium entry & slow sodium inactivation gates close
o as sodium entry declines, slow potassium gates open & potassium rushes out of the cell
o cell returns to negative resting potential, but...
- undershoot: potassium permeability continues & gates are slow to close - neuron becomes hyperpolarized (more negative than resting potential), which local influx of sodium restores to normal
o sodium-potassium pump restores normal distributions of sodium & potassium ions inside & outside cell
- action potential is self-propagating: charge is carried along length of axon by attraction to adjacent areas of opposite charge
- action potential is all-or-none phenomenon: either happens completely or not at all
- absolute refractory period: period from opening of sodium channels to closing of activation gates
- relative refractory period: period following absolute refractory period when sodium gates are closed & potassium gates are open
- during refractory periods, neurons generally insensitive to additional action potentials
- Conduction velocities of axons:
o In general, the larger the axon's diameter, the faster it conducts impulses
o Speed of conduction influenced also by drugs (especially those that alter sodium permeability), cold & pressure
o Saltatory conduction: the presence of the myelin sheath insulates against leakage of charge & only allows generation of action potential at nodes of Ranvier between adjacent Schwann cells (or oligodendrocytes)
§ much faster than in unmyelinated axons... the electrical signal jumps from node to node along the axon
- Multiple sclerosis (MS): autoimmune disease - immune system attacks myelin proteins & destroys myelin sheath (& severs nerve fibers) - forms hardened lesions called scleroses
o results in short-circuiting of current in neurons, although axons are generally not damaged - symptoms may cycle
o treated with anti-inflammatory steroids & beta interferon to reduce severity of immune system attack
- Group A nerve fibers: somatic sensory & motor fibers; myelinated, large diameter
o Fast conduction: up to 150 m/s
- Group B nerve fibers: lightly myelinated, intermediate diameter
o Transmit impulses on average at 15 m/s
- Group C nerve fibers: unmyelinated, small diameter
o Slow conduction: 1 m/s or less
Synapse: junction that mediates transfer of information from neuron to neuron or effector (muscle, gland)
- axodendritic & axosomatic most common... also axoaxonic, dendrodendritic & dendrosomatic
- presynaptic neuron: conducts impulses toward synapse
- postsynaptic neuron: transmits signal away from the synapse
- Electrical synapses: less common; much like gap junctions
o Channel proteins connect neurons & allow ions to flow directly from one neuron to the next
- Chemical synapses: chemical neurotransmitters act to open or close ion channels
o Calcium gates open in the presynaptic axon terminal - calcium floods into axon terminal from extracellular space
o Neurotransmitter released from synaptic vesicles by exocytosis in response to calcium signal
o Neurotransmitter binds to postsynaptic receptors
o Ion channels open in postsynaptic membrane in response to neurotransmitter binding
o Neurotransmitter is removed from receptor by enzyme degradation, reuptake by astrocytes or the presynaptic terminal, or diffusion away from the synapse
o excitatory synapses: neurotransmitter binding causes depolarization of the postsynaptic membrane & excitatory postsynaptic potentials (EPSPs)
o inhibitory synapses: neurotransmitter binding causes hyperpolarization of the postsynaptic membrane & inhibitory postsynaptic potentials (IPSPs)
Integration of Synaptic Events:
- temporal summation: postsynaptic neuron stimulated by the same terminal in rapid succession
- spatial summation: postsynaptic neuron stimulated by multiple terminals at the same time
- synaptic potentiation: continuous use of synapse enhances presynaptic neuron's ability to excite postsynaptic neuron
- presynaptic inhibition: release of excitatory neurotransmitter is inhibited by activity of another neuron via axoaxonic synapse
Neurotransmitters:
- acetylcholine (ACh) - released at neuromuscular junctions throughout nervous system (excitatory for skeletal muscle; inhibitory for cardiac muscle; also used in ANS & CNS)
o Alzheimer disease is due to loss of neurons that use ACh as neurotransmitter
- biogenic amines: catecholamines (dopamine, epinephrine & norepinephrine) & indolamines (histamine & serotonin)...
o biogenic amines are synthesized from amino acids (catecholamines from tyrosine; serotonin from tryptophan; histamine from histidine)
o norepinephrine (NE) plays a role in awakening from sleep, dreaming & mood
o epinephrine & norepinephrine regulate the fight-or-flight response of the sympathetic nervous system, and also act as hormones involved in blood pressure regulation
o dopamine is associated with behavior (emotional responses) & regulation of skeletal muscle tone/movement
o serotonin appears to be involved with mood, appetite, sensory perception, temperature regulation & sleep induction
o Parkinson Disease is due to a deficiency of dopamine
§ characterized by wide-eyed, unblinking expression, muscular rigidity & involuntary tremors
o catecholamines are inactivated by reuptake & recycled or degraded by enzymes (COMT or monoamine oxidase (MAO))
- amino acids: GABA, glycine, aspartate, & glutamate... (in CNS)
o aspartate & glutamate are excitatory neurotransmitters in the CNS
o GABA & glycine are inhibitory neurotransmitters in the CNS (open Cl- channels for hyperpolarization)
o in Huntington Disease there is a decrease in the neurotransmitter GABA
§ autosomal dominant disorder due to chromosomal changes (trinucleotide repeats)
§ leads to deterioration of nervous system; constant thrashing movements & eventually insanity & death
- peptides: substance P, endorphins & enkephalins...
o substance P mediates pain signals
o endorphins & enkephalins act as natural opiates, reducing perception of pain in stressful situations
- Other neurotransmitters:
o ATP & Other Purines: ATP is an excitatory neurotransmitter in the CNS & PNS; it¹s usually released with another neurotransmitter (norepinephrine, acetylcholine)
o nitric oxide: a gaseous neurotransmitter; short-lived & produced on demand from the amino acid arginine
§ diffuses out of neurons & activates production of the second messenger cyclic GMP in neighboring cells
§ nitric oxide is also a potent vasodilator (lowers blood pressure & increases blood flow)
- neurotransmitter effects:
o excitatory or inhibitory, depending on the receptor
o direct action (using channel receptors) or indirect action (using G protein-linked receptors & second messenger systems (cyclic AMP))
o agonists bind to neurotransmitter receptors & enhance neurotransmitter effects
§ isoproterenol (isuprel) enhances effects of epinephrine (used to dilate airways during asthma attack)
o antagonists bind to neurotransmitter receptors & block neurotransmitter effects
§ zyprexa used to block serotonin & dopamine in schizophrenia
Neural circuits: functional groups of neurons that integrate incoming information from other sources & forward processed information to other sources
- circuits: patterns of synaptic connections in neuronal pools
- reflexes occur over neural pathways called reflex arcs
- series circuit: one neuron stimulates the next in a sequence
- diverging circuit: one presynaptic neuron stimulates several postsynaptic neurons
- converging circuit: several presynaptic neuron stimulate one postsynaptic neuron
- reverberating circuit: branches from later neurons in ciircuit stimulate earlier neurons; prolongs output signal
- parralel after-discharge circuit: one presynaptic neuron stimulates several postsynaptic neurons which converge on one output neuron
Regeneration of Nerve Fibers:
- in general, mature neurons are amitotic (do not divide)
- if cell body remains intact, regeneration is possible
- following injury, the two ends of neuron surrounding site of injury seal off & swell from accumulation of materials
- Wallerian degeneration: the axon distal to the site of injury & its myelin sheath begins to disintegrate (debris cleaned up by macrophages & Schwann cells)
- Schwann cells proliferate in response to macrophage signals, & express cell adhesion molecules & release growth factors to stimulate axonal growth... then, they guide axon extensions across the gap (form regeneration tube to bridge gap) & remyelinate the axon
- The greater the distance between broken axon ends, the less the chance of regeneration