Anatomy and physiology musculoskeletal
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Transcript of Anatomy and physiology musculoskeletal
![Page 1: Anatomy and physiology musculoskeletal](https://reader033.fdocuments.net/reader033/viewer/2022042607/55aa58561a28abbe508b4605/html5/thumbnails/1.jpg)
Anatomy and Physiology of Musculoskeletal
daninurriyadi
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Periferal nervous system
Afferent
Efferent
somatomotoric autonomic
Parasympathic Sympathic
Central Nervous System
RECEPTOR
Somatic Visceral
EFFECTOR
Skeletalmuscle
Smooth muscleCardiac muscleGland
ascendense descendense
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The Skeleton
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The Skull
• The skull, the body’s most complex bony structure, is formed by the cranium and facial bones
• Cranium – protects the brain and is the site of attachment for head and neck muscles
• Facial bones– Supply the framework of the face, the sense organs, and
the teeth– Provide openings for the passage of air and food– Anchor the facial muscles of expression
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Skull: Anterior View
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Parietal Bones and Major Associated Sutures
• Form most of the superior and lateral aspects of the skull
Figure 7.3a
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Occipital Bone and Its Major Markings
• Forms most of skull’s posterior wall and base
• Major markings include the posterior cranial fossa, foramen magnum, occipital condyles, and the hypoglossal canal
Figure 7.2b
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Vertebral Column
• Formed from 26 irregular bones (vertebrae) connected in such a way that a flexible curved structure results– Cervical vertebrae – 7 bones of the neck– Thoracic vertebrae – 12 bones of the torso– Lumbar vertebrae – 5 bones of the lower back
– Sacrum – bone inferior to the lumbar vertebrae that articulates with the hip bones
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Vertebral Column
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Vertebral Column: Ligaments
• Anterior and posterior longitudinal ligaments – continuous bands down the front and back of the spine from the neck to the sacrum
• Short ligaments connect adjoining vertebrae together
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Vertebral Column: Ligaments
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Vertebral Column: Intervertebral Discs
• Cushionlike pad composed of two parts– Nucleus pulposus – inner gelatinous nucleus that
gives the disc its elasticity and compressibility– Annulus fibrosus – surrounds the nucleus pulposus
with a collar composed of collagen and fibrocartilage
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Vertebral Column: Intervertebral Discs
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Sacrum
• Sacrum– Consists of five fused vertebrae (S1-S5), which
shape the posterior wall of the pelvis
– It articulates with L5 superiorly, and with the auricular surfaces of the hip bones
– Major markings include the sacral promontory, transverse lines, alae, dorsal sacral foramina, sacral canal, and sacral hiatus
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Coccyx
• Coccyx (Tailbone)– The coccyx is made up of four (in some cases
three to five) fused vertebrae that articulate superiorly with the sacrum
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Sacrum and Coccyx: Anterior View
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Sacrum and Coccyx: Posterior View
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Bony Thorax (Thoracic Cage)
• The thoracic cage is composed of the thoracic vertebrae dorsally, the ribs laterally, and the sternum and costal cartilages anteriorly
• Functions– Forms a protective cage around the heart, lungs, and great
blood vessels
– Supports the shoulder girdles and upper limbs
– Provides attachment for many neck, back, chest, and shoulder muscles
– Uses intercostal muscles to lift and depress the thorax during breathing
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Bony Thorax (Thoracic Cage)
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Pectoral Girdles (Shoulder Girdles)
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The Upper Limb
• The upper limb consists of the arm (brachium), forearm (antebrachium), and hand (manus)
• Thirty-seven bones form the skeletal framework of each upper limb
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Arm
• The humerus is the sole bone of the arm
• It articulates with the scapula at the shoulder, and the radius and ulna at the elbow
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Arm• Major markings
– Proximal humerus includes the head, anatomical and surgical necks, greater and lesser tubercles, and the intertubercular groove
– Distal humerus includes the capitulum, trochlea, medial and lateral epicondyles, and the coronoid and olecranon fossae
– Medial portion includes the radial groove and the deltoid process
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Humerus of the Arm
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Forearm
• The bones of the forearm are the radius and ulna • They articulate proximally with the humerus and distally
with the wrist bones
• They also articulate with each other proximally and distally at small radioulnar joints
• Interosseous membrane connects the two bones along their entire length
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Bones of the Forearm
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Hand
• Skeleton of the hand contains wrist bones (carpals), bones of the palm (metacarpals), and bones of the fingers (phalanges)
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Pelvic Girdle (Hip)
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The Lower Limb
• The three segments of the lower limb are the thigh, leg, and foot
• They carry the weight of the erect body, and are subjected to exceptional forces when one jumps or runs
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Femur
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Tibia and Fibula
Figure 7.29
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Foot
• The skeleton of the foot includes the tarsus, metatarsus, and the phalanges (toes)
• The foot supports body weight and acts as a lever to propel the body forward in walking and running
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Tarsus
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Arches of the Foot• The foot has three arches maintained by
interlocking foot bones and strong ligaments
• Arches allow the foot to hold up weight
• The arches are:– Lateral longitudinal – cuboid is keystone of this arch– Medial longitudinal – talus is keystone of this arch– Transverse – runs obliquely from one side of the foot
to the other
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Arches of the Foot
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Joints
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Fibrous Structural Joints: Sutures
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Fibrous Structural Joints: Syndesmoses
• Bones are connected by a fibrous tissue ligament
• Movement varies from immovable to slightly variable
• Examples include the connection between the tibia and fibula, and the radius and ulna
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Fibrous Structural Joints: Syndesmoses
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Fibrous Structural Joints: Gomphoses
• The peg-in-socket fibrous joint between a tooth and its alveolar socket
• The fibrous connection is the periodontal ligament
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Cartilaginous Joints
• Articulating bones are united by cartilage
• Lack a joint cavity
• Two types – synchondroses and symphyses
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Cartilaginous Joints: Synchondroses
• A bar or plate of hyaline cartilage unites the bones
• All synchondroses are synarthrotic• Examples include:
– Epiphyseal plates of children
– Joint between the costal cartilage of the first rib and the sternum
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Cartilaginous Joints: Synchondroses
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Cartilaginous Joints: Symphyses
• Hyaline cartilage covers the articulating surface of the bone and is fused to an intervening pad of fibrocartilage
• Amphiarthrotic joints designed for strength and flexibility
• Examples include intervertebral joints and the pubic symphysis of the pelvis
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Cartilaginous Joints: Symphyses
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Synovial Joints
• Those joints in which the articulating bones are separated by a fluid-containing joint cavity
• All are freely movable diarthroses
• Examples – all limb joints, and most joints of the body
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Synovial Joints: General Structure
• Synovial joints all have the following– Articular cartilage– Joint (synovial) cavity– Articular capsule– Synovial fluid– Reinforcing ligaments
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Synovial Joints: General Structure
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Synovial Joints: Friction-Reducing Structures
• Bursae – flattened, fibrous sacs lined with synovial membranes and containing synovial fluid
• Common where ligaments, muscles, skin, tendons, or bones rub together
• Tendon sheath – elongated bursa that wraps completely around a tendon
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Synovial Joints: Friction-Reducing Structures
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Types of Synovial Joints
• Plane joints– Articular
surfaces are essentially flat
– Allow only slipping or gliding movements
– Only examples of nonaxial joints
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Types of Synovial Joints
• Hinge joints– Cylindrical projections of one bone fits into a trough-
shaped surface on another– Motion is along a single plane– Uniaxial joints permit flexion and extension only– Examples: elbow and interphalangeal joints
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Types of Synovial Joints
Figure 8.7b
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Pivot Joints
• Rounded end of one bone protrudes into a “sleeve,” or ring, composed of bone (and possibly ligaments) of another
• Only uniaxial movement allowed
• Examples: joint between the axis and the dens, and the proximal radioulnar joint
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Pivot Joints
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Condyloid, or Ellipsoidal, Joints
• Oval articular surface of one bone fits into a complementary depression in another
• Both articular surfaces are oval• Biaxial joints permit all angular motions• Examples: radiocarpal (wrist) joints, and
metacarpophalangeal (knuckle) joints
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Condyloid, or Ellipsoidal, Joints
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Saddle Joints
• Similar to condyloid joints but allow greater movement
• Each articular surface has both a concave and a convex surface
• Example: carpometacarpal joint of the thumb
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Saddle Joints
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Ball-and-Socket Joints
• A spherical or hemispherical head of one bone articulates with a cuplike socket of another
• Multiaxial joints permit the most freely moving synovial joints
• Examples: shoulder and hip joints
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Ball-and-Socket Joints
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Synovial Joints: Knee
• Largest and most complex joint of the body• Allows flexion, extension, and some rotation• Three joints in one surrounded by a single joint
cavity– Femoropatellar– Lateral and medial tibiofemoral joints
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• Tendon of the quadriceps femoris muscle
• Lateral and medial patellar retinacula
• Fibular and tibial collateral ligaments
• Patellar ligament
Synovial Joints: Knee Ligaments and Tendons – Anterior View
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• Anterior cruciate ligament• Posterior cruciate ligament• Medial meniscus (semilunar cartilage)• Lateral meniscus
Synovial Joints: Knee – Other Supporting Structures
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Synovial Joints: Knee – Other Supporting Structures
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• Adductor magnus tendon
• Articular capsule• Oblique popliteal
ligament• Arcuate popliteal
ligament• Semimembranosus
tendon
Synovial Joints: Knee – Posterior Superficial View
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Synovial Joints: Shoulder (Glenohumeral)
• Ball-and-socket joint in which stability is sacrificed to obtain greater freedom of movement
• Head of humerus articulates with the glenoid fossa of the scapula
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Synovial Joints: Shoulder Stability
• Weak stability is maintained by:– Thin, loose joint capsule– Four ligaments – coracohumeral, and three
glenohumeral– Tendon of the long head of biceps, which travels
through the intertubercular groove and secures the humerus to the glenoid cavity
– Rotator cuff (four tendons) that encircles the shoulder joint and blends with the articular capsule
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Synovial Joints: Shoulder Stability
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Synovial Joints: Shoulder Stability
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Synovial Joints: Hip (Coxal) Joint
• Ball-and-socket joint
• Head of the femur articulates with the acetabulum
• Good range of motion, but limited by the deep socket and strong ligaments
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• Acetabular labrum• Iliofemoral
ligament• Pubofemoral
ligament
• Ischiofemoral ligament
• Ligamentum teres
Synovial Joints: Hip Stability
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Synovial Joints: Hip Stability
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Synovial Joints: Elbow
• Hinge joint that allows flexion and extension only
• Radius and ulna articulate with the humerus
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• Annular ligament• Ulnar collateral ligament• Radial collateral ligament
Synovial Joints: Elbow Stability
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Synovial Joints: Elbow Stability
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Sprains
• The ligaments reinforcing a joint are stretched or torn
• Partially torn ligaments slowly repair themselves
• Completely torn ligaments require prompt surgical repair
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Cartilage Injuries
• The snap and pop of overstressed cartilage
• Common aerobics injury
• Repaired with arthroscopic surgery
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Dislocations
• Occur when bones are forced out of alignment• Usually accompanied by sprains, inflammation, and joint
immobilization• Caused by serious falls and are common sports injuries• Subluxation – partial dislocation of a joint
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Muscles and Muscle Tissue
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Functional Characteristics of Muscle Tissue
• Excitability, or irritability – the ability to receive and respond to stimuli
• Contractility – the ability to shorten forcibly
• Extensibility – the ability to be stretched or extended
• Elasticity – the ability to recoil and resume the original resting length
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Muscle Function
• Skeletal muscles are responsible for all locomotion
• Cardiac muscle is responsible for coursing the blood through the body
• Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs
• Muscles also maintain posture, stabilize joints, and generate heat
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Skeletal Muscle• Each muscle is a discrete organ composed of
muscle tissue, blood vessels, nerve fibers, and connective tissue
• The three connective tissue sheaths are:– Endomysium – fine sheath of connective tissue
composed of reticular fibers surrounding each muscle fiber
– Perimysium – fibrous connective tissue that surrounds groups of muscle fibers called fascicles
– Epimysium – an overcoat of dense regular connective tissue that surrounds the entire muscle
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Major Skeletal Muscles: Anterior View
• The 40 superficial muscles here are divided into 10 regional areas of the body
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Plantar Muscles: Fourth Layer
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Skeletal Muscle
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Skeletal Muscle: Nerve and Blood Supply
• Each muscle is served by one nerve, an artery, and one or more veins
• Each skeletal muscle fiber is supplied with a nerve ending that controls contraction
• Contracting fibers require continuous delivery of oxygen and nutrients via arteries
• Wastes must be removed via veins
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Skeletal Muscle: Attachments• Most skeletal muscles span joints and are
attached to bone in at least two places• When muscles contract the movable bone, the
muscle’s insertion moves toward the immovable bone, the muscle’s origin
• Muscles attach:– Directly – epimysium of the muscle is fused to the
periosteum of a bone– Indirectly – connective tissue wrappings extend
beyond the muscle as a tendon or aponeurosis
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Microscopic Anatomy of a Skeletal Muscle Fiber
• Each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma
• Fibers are 10 to 100 µm in diameter, and up to hundreds of centimeters long
• Each cell is a syncytium produced by fusion of embryonic cells
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Microscopic Anatomy of a Skeletal Muscle Fiber
• Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin
• Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules
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Myofibrils
• Myofibrils are densely packed, rodlike contractile elements
• They make up most of the muscle volume • The arrangement of myofibrils within a fiber is such that
a perfectly aligned repeating series of dark A bands and light I bands is evident
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Myofibrils
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Sarcomeres
• The smallest contractile unit of a muscle• The region of a myofibril between two successive
Z discs• Composed of myofilaments made up of
contractile proteins– Myofilaments are of two types – thick and thin
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Sarcomeres
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Myofilaments: Banding Pattern
• Thick filaments – extend the entire length of an A band
• Thin filaments – extend across the I band and partway into the A band
• Z-disc – coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another
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Myofilaments: Banding Pattern
• Thin filaments do not overlap thick filaments in the lighter H zone
• M lines appear darker due to the presence of the protein desmin
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Myofilaments: Banding Pattern
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Ultrastructure of Myofilaments: Thick Filaments
• Thick filaments are composed of the protein myosin
• Each myosin molecule has a rodlike tail and two globular heads– Tails – two interwoven, heavy polypeptide chains
– Heads – two smaller, light polypeptide chains called cross bridges
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Ultrastructure of Myofilaments: Thick Filaments
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Ultrastructure of Myofilaments: Thin Filaments
• Thin filaments are chiefly composed of the protein actin• Each actin molecule is a helical polymer of globular
subunits called G actin• The subunits contain the active sites to which myosin
heads attach during contraction
• Tropomyosin and troponin are regulatory subunits bound to actin
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Ultrastructure of Myofilaments: Thin Filaments
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Arrangement of the Filaments in a Sarcomere
• Longitudinal section within one sarcomere
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Sarcoplasmic Reticulum (SR)
• SR is an elaborate, smooth endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril
• Paired terminal cisternae form perpendicular cross channels
• Functions in the regulation of intracellular calcium levels
• Elongated tubes called T tubules penetrate into the cell’s interior at each A band–I band junction
• T tubules associate with the paired terminal cisternae to form triads
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Sarcoplasmic Reticulum (SR)
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T Tubules
• T tubules are continuous with the sarcolemma
• They conduct impulses to the deepest regions of the muscle
• These impulses signal for the release of Ca2+ from adjacent terminal cisternae
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Triad Relationships
• T tubules and SR provide tightly linked signals for muscle contraction
• A double zipper of integral membrane proteins protrudes into the intermembrane space
• T tubule proteins act as voltage sensors• SR foot proteins are receptors that regulate Ca2+ release
from the SR cisternae
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Sliding Filament Model of Contraction
• Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree
• In the relaxed state, thin and thick filaments overlap only slightly
• Upon stimulation, myosin heads bind to actin and sliding begins
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Sliding Filament Model of Contraction
• Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere
• As this event occurs throughout the sarcomeres, the muscle shortens
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Skeletal Muscle Contraction• In order to contract, a skeletal muscle must:
– Be stimulated by a nerve ending– Propagate an electrical current, or action potential,
along its sarcolemma– Have a rise in intracellular Ca2+ levels, the final trigger
for contraction
• Linking the electrical signal to the contraction is excitation-contraction coupling
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Nerve Stimulus of Skeletal Muscle
• Skeletal muscles are stimulated by motor neurons of the somatic nervous system
• Axons of these neurons travel in nerves to muscle cells
• Axons of motor neurons branch profusely as they enter muscles
• Each axonal branch forms a neuromuscular junction with a single muscle fiber
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Neuromuscular Junction• The neuromuscular junction is formed from:
– Axonal endings, which have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh)
– The motor end plate of a muscle, which is a specific part of the sarcolemma that contains ACh receptors and helps form the neuromuscular junction
• Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft
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Neuromuscular Junction
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Neuromuscular Junction
• When a nerve impulse reaches the end of an axon at the neuromuscular junction:– Voltage-regulated calcium channels open and
allow Ca2+ to enter the axon– Ca2+ inside the axon terminal causes axonal
vesicles to fuse with the axonal membrane
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Neuromuscular Junction
– This fusion releases ACh into the synaptic cleft via exocytosis
– ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma
– Binding of ACh to its receptors initiates an action potential in the muscle
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Destruction of Acetylcholine
• ACh bound to ACh receptors is quickly destroyed by the enzyme acetylcholinesterase
• This destruction prevents continued muscle fiber contraction in the absence of additional stimuli
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Action Potential
• A transient depolarization event that includes polarity reversal of a sarcolemma (or nerve cell membrane) and the propagation of an action potential along the membrane
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Role of Acetylcholine (Ach)
• ACh binds its receptors at the motor end plate
• Binding opens chemically (ligand) gated channels
• Na+ and K+ diffuse out and the interior of the sarcolemma becomes less negative
• This event is called depolarization
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Depolarization
• Initially, this is a local electrical event called end plate potential
• Later, it ignites an action potential that spreads in all directions across the sarcolemma
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• The outside (extracellular) face is positive, while the inside face is negative
• This difference in charge is the resting membrane potential
Action Potential: Electrical Conditions of a Polarized Sarcolemma
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• The predominant extracellular ion is Na+
• The predominant intracellular ion is K+
• The sarcolemma is relatively impermeable to both ions
Action Potential: Electrical Conditions of a Polarized
Sarcolemma
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• An axonal terminal of a motor neuron releases ACh and causes a patch of the sarcolemma to become permeable to Na+ (sodium channels open)
Action Potential: Depolarization and Generation of the Action Potential
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• Na+ enters the cell, and the resting potential is decreased (depolarization occurs)
• If the stimulus is strong enough, an action potential is initiated
Action Potential: Depolarization and Generation of the Action Potential
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• Polarity reversal of the initial patch of sarcolemma changes the permeability of the adjacent patch
• Voltage-regulated Na+ channels now open in the adjacent patch causing it to depolarize
Action Potential: Propagation of the Action Potential
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• Thus, the action potential travels rapidly along the sarcolemma
• Once initiated, the action potential is unstoppable, and ultimately results in the contraction of a muscle
Action Potential: Propagation of the Action Potential
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Action Potential: Repolarization• Immediately after the depolarization wave passes, the sarcolemma permeability changes
• Na+ channels close and K+ channels open
• K+ diffuses from the cell, restoring the electrical polarity of the sarcolemma
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Action Potential: Repolarization• Repolarization occurs
in the same direction as depolarization, and must occur before the muscle can be stimulated again (refractory period)
• The ionic concentration of the resting state is restored by the Na+-K+ pump
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Excitation-Contraction Coupling
• Once generated, the action potential:– Is propagated along the sarcolemma– Travels down the T tubules
– Triggers Ca2+ release from terminal cisternae
• Ca2+ binds to troponin and causes: – The blocking action of tropomyosin to cease
– Actin active binding sites to be exposed
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Excitation-Contraction Coupling
• Myosin cross bridges alternately attach and detach• Thin filaments move toward the center of the sarcomere
• Hydrolysis of ATP powers this cycling process• Ca2+ is removed into the SR, tropomyosin blockage is
restored, and the muscle fiber relaxes
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Excitation-Contraction Coupling
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• At low intracellular Ca2+ concentration:– Tropomyosin blocks the
binding sites on actin– Myosin cross bridges
cannot attach to binding sites on actin
– The relaxed state of the muscle is enforced
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
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• At higher intracellular Ca2+ concentrations:– Additional calcium binds
to troponin (inactive troponin binds two Ca2+)
– Calcium-activated troponin binds an additional two Ca2+ at a separate regulatory site
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
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• Calcium-activated troponin undergoes a conformational change
• This change moves tropomyosin away from actin’s binding sites
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
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• Myosin head can now bind and cycle
• This permits contraction (sliding of the thin filaments by the myosin cross bridges) to begin
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
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Sequential Events of Contraction• Cross bridge formation – myosin cross bridge attaches to
actin filament
• Working (power) stroke – myosin head pivots and pulls actin filament toward M line
• Cross bridge detachment – ATP attaches to myosin head and the cross bridge detaches
• “Cocking” of the myosin head – energy from hydrolysis of ATP cocks the myosin head into the high-energy state
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Myosin cross bridge attaches to the actin myofilament
1
2
3
4 Working stroke—the myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line
As new ATP attaches to the myosin head, the cross bridge detaches
As ATP is split into ADP and Pi, cocking of the myosin head occurs
Myosin head (high-energy
configuration)
Thick filament
Myosin head (low-energy configuration)
ADP and Pi (inorganic phosphate) released
Sequential Events of Contraction
Thin filament
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Contraction of Skeletal Muscle Fibers
• Contraction – refers to the activation of myosin’s cross bridges (force-generating sites)
• Shortening occurs when the tension generated by the cross bridge exceeds forces opposing shortening
• Contraction ends when cross bridges become inactive, the tension generated declines, and relaxation is induced
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Contraction of Skeletal Muscle (Organ Level)
• Contraction of muscle fibers (cells) and muscles (organs) is similar
• The two types of muscle contractions are:– Isometric contraction – increasing muscle
tension (muscle does not shorten during contraction)
– Isotonic contraction – decreasing muscle length (muscle shortens during contraction)
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Motor Unit: The Nerve-Muscle Functional Unit
• A motor unit is a motor neuron and all the muscle fibers it supplies
• The number of muscle fibers per motor unit can vary from four to several hundred
• Muscles that control fine movements (fingers, eyes) have small motor units
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Motor Unit: The Nerve-Muscle Functional Unit
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Motor Unit: The Nerve-Muscle Functional Unit
• Large weight-bearing muscles (thighs, hips) have large motor units
• Muscle fibers from a motor unit are spread throughout the muscle; therefore, contraction of a single motor unit causes weak contraction of the entire muscle
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Muscle Twitch• A muscle twitch is the response of a muscle to a
single, brief threshold stimulus
• The three phases of a muscle twitch are:– Latent period –
first few milli-seconds after stimulation when excitation-contraction coupling is taking place
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Muscle Twitch– Period of contraction – cross bridges actively form
and the muscle shortens– Period of relaxation –
Ca2+ is reabsorbed into the SR, and muscle tension goes to zero
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Graded Muscle Responses
• Graded muscle responses are:– Variations in the degree of muscle contraction– Required for proper control of skeletal
movement
• Responses are graded by:– Changing the frequency of stimulation
– Changing the strength of the stimulus
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Muscle Response to Varying Stimuli
• More rapidly delivered stimuli result in incomplete tetanus
• If stimuli are given quickly enough, complete tetanus results
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Muscle Response: Stimulation Strength
• Threshold stimulus – the stimulus strength at which the first observable muscle contraction occurs
• Beyond threshold, muscle contracts more vigorously as stimulus strength is increased
• Force of contraction is precisely controlled by multiple motor unit summation
• This phenomenon, called recruitment, brings more and more muscle fibers into play
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Stimulus Intensity and Muscle Tension
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Treppe: The Staircase Effect
• Staircase – increased contraction in response to multiple stimuli of the same strength
• Contractions increase because:– There is increasing availability of Ca2+ in the
sarcoplasm– Muscle enzyme systems become more efficient
because heat is increased as muscle contracts
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Treppe: The Staircase Effect
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Muscle Tone
• Muscle tone:– Is the constant, slightly contracted state of all
muscles, which does not produce active movements
– Keeps the muscles firm, healthy, and ready to respond to stimulus
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Muscle Tone
• Spinal reflexes account for muscle tone by:– Activating one motor unit and then another– Responding to activation of stretch receptors in
muscles and tendons
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Isotonic Contractions
• In isotonic contractions, the muscle changes in length (decreasing the angle of the joint) and moves the load
• The two types of isotonic contractions are concentric and eccentric– Concentric contractions – the muscle shortens
and does work– Eccentric contractions – the muscle contracts as
it lengthens
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Isotonic Contractions
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Isometric Contractions
• Tension increases to the muscle’s capacity, but the muscle neither shortens nor lengthens
• Occurs if the load is greater than the tension the muscle is able to develop
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Isometric Contractions
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Muscle Metabolism: Energy for Contraction
• ATP is the only source used directly for contractile activity
• As soon as available stores of ATP are hydrolyzed (4-6 seconds), they are regenerated by:– The interaction of ADP with creatine phosphate (CP) – Anaerobic glycolysis – Aerobic respiration
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Muscle Metabolism: Energy for Contraction
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Muscle Metabolism: Anaerobic Glycolysis
• When muscle contractile activity reaches 70% of maximum:– Bulging muscles compress blood vessels– Oxygen delivery is impaired
– Pyruvic acid is converted into lactic acid
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Muscle Metabolism: Anaerobic Glycolysis
• The lactic acid:– Diffuses into the bloodstream– Is picked up and used as fuel by the liver,
kidneys, and heart– Is converted back into pyruvic acid by the liver
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Muscle Fatigue• Muscle fatigue – the muscle is in a state of
physiological inability to contract
• Muscle fatigue occurs when:– ATP production fails to keep pace with ATP use– There is a relative deficit of ATP, causing
contractures
– Lactic acid accumulates in the muscle– Ionic imbalances are present
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Muscle Fatigue
• Intense exercise produces rapid muscle fatigue (with rapid recovery)
• Na+-K+ pumps cannot restore ionic balances quickly enough
• Low-intensity exercise produces slow-developing fatigue
• SR is damaged and Ca2+ regulation is disrupted
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Oxygen Debt• Vigorous exercise causes dramatic changes in
muscle chemistry• For a muscle to return to a resting state:
– Oxygen reserves must be replenished– Lactic acid must be converted to pyruvic acid– Glycogen stores must be replaced– ATP and CP reserves must be resynthesized
• Oxygen debt – the extra amount of O2 needed for the above restorative processes
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Heat Production During Muscle Activity
• Only 40% of the energy released in muscle activity is useful as work
• The remaining 60% is given off as heat
• Dangerous heat levels are prevented by radiation of heat from the skin and sweating
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Force of Muscle Contraction
• The force of contraction is affected by:– The number of muscle fibers contracting – the
more motor fibers in a muscle, the stronger the contraction
– The relative size of the muscle – the bulkier the muscle, the greater its strength
– Degree of muscle stretch – muscles contract strongest when muscle fibers are 80-120% of their normal resting length
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Force of Muscle Contraction
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Control of Body Movement
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Periferal nervous system
Afferent
Efferent
somatomotoric autonomic
Parasympathic Sympathic
Central Nervous System
RECEPTOR
Somatic Visceral
EFFECTOR
Skeletalmuscle
Smooth muscleCardiac muscleGland
ascendense descendense
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• Neural Reflexes: types & pathways• Autonomic Reflexes pathways and functions• Skeletal Muscle reflexes, myotactic units and
movement• Combining reflexive and voluntary behavior into
locomotion• Movement in visceral muscles
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• Stimulus• Sensory receptor• Sensory (afferent) neuron• CNS integration• Efferent (motor) neuron• Effector (target tissue)• Response (movement)• Feedback to CNS
Neural Reflexes: Overview
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Neural Reflexes: Overview
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• Effector Division– Somatic– Autonomic
• Integration site– Spinal– Brain
• Neurons in pathway– Monosynaptic– Polysynaptic
Neural Reflexes: Classification of Pathways
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Neural Reflexes: Classification of Pathways
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• Regulate internal organs• Integrate in spinal cord or lower brain• Coordinate with hormones & pacemakers
Autonomic Reflexes: “visceral reflexes”
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Autonomic Reflexes: “visceral reflexes”
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• Muscle spindle– In muscles– Sense stretch
• Golgi tendon organ– Near tendon– Sense force
• Joint receptors– Sense pressure– Position
Skeletal Muscle Reflex Sensory Receptors: Proprioceptors
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Skeletal Muscle Reflex Sensory Receptors: Proprioceptors
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• Muscle tone • Stretch reflex
Muscle Spindles: Mechanism
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• Alpha neurons• Gamma neurons
Muscle Spindle Innervation: Alpha-gamma Coactivation
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• Myotactic unit: all pathways controlling a joint
• Example: elbow joint – all nerves, receptors, muscles
A Myotactic Unit and Stretch Reflex Illustrated
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• Force pulls collagen fibers which squeeze sensors
• Overload causes inhibition of contraction
Golgi Tendon Reflex: Response to Excessive Force
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• Tendon strike stretches quads-reflexive contraction
• Reciprocal (hamstring) muscle is inhibited
Knee Jerk Reflex: Stretch & Reciprocal Inhibition
Reflexes
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Knee Jerk Reflex:
Stretch & Reciprocal Inhibition Reflexes
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• Pain stimulus• Nociceptors• Spinal integration• Flex appendage away• Signal to brain (feel pain)
Flexion Reflex: Pull away from Painful Stimuli
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Flexion Reflex: Pull away from Painful Stimuli
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• Opposite leg• Extensors
stimulated• Flexors inhibited• Body supported
Cross Extensor Reflex: To Keep Balance
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• Reflexive Movement– Spinal integration– Input to brain
• Postural reflexes – Cerebellum
integration– Maintains balance– Input to cortex
Movement: Coordination of Several Muscle Groups
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• Cortex at top of several CNS integration sites• Can be initiated with no external stimuli• Parts can become involuntary: muscle memory
Voluntary Movement: “Conscious”
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Voluntary Movement: “Conscious”
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• Cortex initiation• Central pattern
generators– In spine– Maintain motion
• Combines movements– Reflexive – Voluntary
Rhythmic Movements
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• Anticipates body movement– Reflexive adjustment to balance change– Prepares body for threat: blink, duck, "tuck & roll"
• Combines with feedback
Feed Forward: Postural Reflex
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• Reflex pathways: spinal, cranial – Sensor, afferent, integration, efferent, effector– Classified by effector, integration site or synapses
Summary
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• Proprioceptor types, functions, role in reflexes & balance
• Motor reflex pathways: stretch, Golgi tendon, flexion, reciprocal inhibition & crossed extensor
• Myotatic unit structure and coordination• Movement coordination: reflexive, voluntary,
rhythmic• Feed forward and feedback coordination • Visceral movement of body organs
Summary
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