Musculoskeletal muscles Chapter 4 SEHS Muscle Tissue Lecture

Musculoskeletal muscles

Chapter 4 SEHS Muscle Tissue Lecture Outline 2

INTRODUCTION • Motion results from alternating contraction (shortening) and relaxation of muscles; the skeletal system provides leverage and a supportive framework for this movement. • The scientific study of muscles is known as myology. Principles of Human Anatomy and Physiology, 11 e 3

Chapter 10 Muscle Tissue • Alternating contraction and relaxation of cells • Chemical energy changed into mechanical energy Principles of Human Anatomy and Physiology, 11 e 4

OVERVIEW OF MUSCLE TISSUE • Types of Muscle Tissue • Skeletal muscle tissue is primarily attached to bones. It is striated and voluntary. • Cardiac muscle tissue forms the wall of the heart. It is striated and involuntary. • Smooth (visceral) muscle tissue is located in viscera. It is nonstraited (smooth) and involuntary. • Table 4. 4 compares the different types of muscle. Principles of Human Anatomy and Physiology, 11 e 5

3 Types of Muscle Tissue • Skeletal muscle – attaches to bone, skin or fascia – striated with light & dark bands visible with scope – voluntary control of contraction & relaxation Principles of Human Anatomy and Physiology, 11 e 6

3 Types of Muscle Tissue • Cardiac muscle – striated in appearance – involuntary control – autorhythmic because of built in pacemaker Principles of Human Anatomy and Physiology, 11 e 7

3 Types of Muscle Tissue • Smooth muscle – attached to hair follicles in skin – in walls of hollow organs -- blood vessels & GI – nonstriated in appearance – involuntary Principles of Human Anatomy and Physiology, 11 e 8

Functions of Muscle Tissue • Producing body movements • Stabilizing body positions • Regulating organ volumes – bands of smooth muscle called sphincters • Movement of substances within the body – blood, lymph, urine, air, food and fluids, sperm • Producing heat – involuntary contractions of skeletal muscle (shivering) Principles of Human Anatomy and Physiology, 11 e 9

Properties of Muscle Tissue • Excitability – respond to chemicals released from nerve cells • Conductivity – ability to propagate electrical signals over membrane • Contractility – ability to shorten and generate force • Extensibility – ability to be stretched without damaging the tissue • Elasticity – ability to return to original shape after being stretched 10 Principles of Human Anatomy and Physiology, 11 e

SKELETAL MUSCLE TISSUE • Each skeletal muscle is a separate organ composed of cells called fibers. Principles of Human Anatomy and Physiology, 11 e 11

Skeletal Muscle -- Connective Tissue • Superficial fascia is loose connective tissue & fat underlying the skin • Deep fascia = dense irregular connective tissue around muscle • Connective tissue components of the muscle include – epimysium = surrounds the whole muscle – perimysium = surrounds bundles (fascicles) of 10 -100 muscle cells – endomysium = separates individual muscle cells • All these connective tissue layers extend beyond the muscle belly to form the tendon Principles of Human Anatomy and Physiology, 11 e 12

Connective Tissue Components Principles of Human Anatomy and Physiology, 11 e 13

Muscle Fiber or Myofibers • Muscle cells are long, cylindrical & multinucleated • Sarcolemma = muscle cell membrane • Sarcoplasm filled with tiny threads called myofibrils & myoglobin (red-colored, oxygen-binding protein) Principles of Human Anatomy and Physiology, 11 e 14

Myofibrils & Myofilaments • Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic reticulum) • The sarcoplasmic reticulum encircles each myofibril. It is similar to smooth endoplasmic reticulum in nonmuscle cells and in the relaxed muscle stores calcium ions. • Myofilaments (thick & thin filaments) are the contractile proteins of muscle Principles of Human Anatomy and Physiology, 11 e 15

Sarcoplasmic Reticulum (SR) • System of tubular sacs similar to smooth ER in nonmuscle cells • Stores Ca+2 in a relaxed muscle • Release of Ca+2 triggers muscle contraction Principles of Human Anatomy and Physiology, 11 e 16

Filaments and the Sarcomere • Thick and thin filaments overlap each other in a pattern that creates striations (light I bands and dark A bands) • The I band region contains only thin filaments. • They are arranged in compartments called sarcomeres, separated by Z discs. • In the overlap region, six thin filaments surround each thick filament Principles of Human Anatomy and Physiology, 11 e 17

Sarcomere • Figure 10. 5 shows the relationships of the zones, bands, and lines as seen in a transmission electron micrograph. • Exercise can result in torn sarcolemma, damaged myofibrils, and disrupted Z discs (Clinical Application). Principles of Human Anatomy and Physiology, 11 e 18

Thick & Thin Myofilaments • Supporting proteins (M line, titin and Z disc help anchor the thick and thin filaments in place) Principles of Human Anatomy and Physiology, 11 e 19

Thick & Thin Myofilaments Overlap Dark(A) & light(I) bands (electron microscope) 20 Principles of Human Anatomy and Physiology, 11 e

The Proteins of Muscle • Myofibrils are built of 3 kinds of protein – contractile proteins • myosin and actin – regulatory proteins which turn contraction on & off • troponin and tropomyosin – structural proteins which provide proper alignment, elasticity and extensibility • titin, myomesin, nebulin and dystrophin Principles of Human Anatomy and Physiology, 11 e 21

The Proteins of Muscle -- Myosin • Thick filaments are composed of myosin – each molecule resembles two golf clubs twisted together – myosin heads (cross bridges) extend toward the thin filaments • Held in place by the M line proteins. Principles of Human Anatomy and Physiology, 11 e 22

The Proteins of Muscle -- Actin • Thin filaments are made of actin, troponin, & tropomyosin • The myosin-binding site on each actin molecule is covered by tropomyosin in relaxed muscle • The thin filaments are held in place by Z lines. From one Z line to the next is a sarcomere. Principles of Human Anatomy and Physiology, 11 e 23

• http: //www. youtube. com/watch? v=0 k. Fmbr. RJ q 4 w Principles of Human Anatomy and Physiology, 11 e 24

• http: //www. blackwellpublishing. com/matthe ws/myosin. html Principles of Human Anatomy and Physiology, 11 e 25

Human back muscles • http: //www. scivee. tv/node/2413 Principles of Human Anatomy and Physiology, 11 e 26

Structural Proteins • Structural proteins keep the thick and thin filaments in the proper alignment, give the myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix. – Titin helps a sarcomere return to its resting length after a muscle has contracted or been stretched. – Myomesin forms the M line. – Nebulin helps maintain alignment of the thin filaments in the sarcomere. – Dystrophin reinforces the sarcolemma and helps transmit the tension generated by the sarcomeres to the tendons. • Table 10. 1 reviews the type of proteins in skeletal muscle. Principles of Human Anatomy and Physiology, 11 e 27

The Proteins of Muscle -- Titin • Titan anchors thick filament to the M line and the Z disc. • The portion of the molecule between the Z disc and the end of the thick filament can stretch to 4 times its resting length and spring back unharmed. • Role in recovery of the muscle from being stretched. Principles of Human Anatomy and Physiology, 11 e 28

Structural Proteins • The M line (myomesin) connects to titin and adjacent thick filaments. • Nebulin, an inelastic protein helps align the thin filaments. • Dystrophin links thin filaments to sarcolemma and transmits the tension generated to the tendon. Principles of Human Anatomy and Physiology, 11 e 29

Sliding Filament Mechanism Of Contraction • Myosin cross bridges pull on thin filaments • Thin filaments slide inward • Z Discs come toward each other • Sarcomeres shorten. The muscle fiber shortens. The muscle shortens • Notice : Thick & thin filaments do not change in length Principles of Human Anatomy and Physiology, 11 e 30

Overview: From Start to Finish Basic Structures • Nerve ending • Neurotransmitter • Muscle membrane • Stored Ca+2 • ATP • Muscle proteins Principles of Human Anatomy and Physiology, 11 e 31

How Does Contraction Begin? 1. Nerve impulse reaches an axon terminal & synaptic vesicles release acetylcholine (ACh) 2. ACh diffuses to receptors on the sarcolemma & Na+ channels open and Na+ rushes into the cell 3. A muscle action potential spreads over sarcolemma and down into the transverse tubules 4. SR releases Ca+2 into the sarcoplasm 5. Ca+2 binds to troponin & causes troponintropomyosin complex to move & reveal myosin binding sites on actin--the contraction cycle begins Principles of Human Anatomy and Physiology, 11 e 32

Contraction Cycle • Repeating sequence of events that cause thick & thin filaments to move past each other. • 4 steps to contraction cycle – ATP hydrolysis – attachment of myosin to actin to form crossbridges – power stroke – detachment of myosin from actin • Cycle keeps repeating as long as there is ATP available & there is a high Ca+2 level near the filaments. Principles of Human Anatomy and Physiology, 11 e 33

Steps in the Contraction Cycle • Notice how the myosin head attaches and pulls on the thin filament with the energy released from ATP Principles of Human Anatomy and Physiology, 11 e 34

ATP and Myosin • • • Myosin heads are activated by ATP Activated heads attach to actin & pull (power stroke) ADP is released. (ATP released P & ADP & energy) Thin filaments slide past the thick filaments ATP binds to myosin head & detaches it from actin All of these steps repeat over and over – if ATP is available & – Ca+ level near the troponin-tropomyosin complex is high Principles of Human Anatomy and Physiology, 11 e 35

Excitation - Contraction Coupling • All the steps that occur from the muscle action potential reaching the T tubule to contraction of the muscle fiber. Principles of Human Anatomy and Physiology, 11 e 36

Relaxation • Acetylcholinesterase (ACh. E) breaks down ACh within the synaptic cleft • Muscle action potential ceases • Ca+2 release channels close • Active transport pumps Ca+2 back into storage in the sarcoplasmic reticulum • Calcium-binding protein (calsequestrin) helps hold Ca+2 in SR (Ca+2 concentration 10, 000 times higher than in cytosol) • Tropomyosin-troponin complex recovers binding site on the actin Principles of Human Anatomy and Physiology, 11 e 37

Overview: From Start to Finish • • • Principles of Human Anatomy and Physiology, 11 e Nerve ending Neurotransmittor Muscle membrane Stored Ca+2 ATP Muscle proteins 38

• CARDIAC MUSCLE TISSUE Overview Cardiac muscle tissue is found only in the heart walland top of Aorta (see Chapter 20). – Its fibers are arranged similarly to skeletal muscle fibers. – Cardiac muscle fibers connect to adjacent fibers by intercalated discs which contain desmosomes and gap junctions (Figure 4. 1 e). – Cardiac muscle contractions last longer than the skeletal muscle twitch due to the prolonged delivery of calcium ions from the sarcoplasmic reticulum and the extracellular fluid. – Cardiac muscle fibers contract when stimulated by their own autorhythmic fibers. • This continuous, rhythmic activity is a major physiological difference between cardiac and skeletal muscle tissue. Principles of Human Anatomy and Physiology, 11 e 39

Cardiac versus Skeletal Muscle • More sarcoplasm and mitochondria • Larger transverse tubules located at Z discs, rather than at A-l band junctions • Less well-developed SR • Limited intracellular Ca+2 reserves – more Ca+2 enters cell from extracellular fluid during contraction • Prolonged delivery of Ca+2 to sarcoplasm, produces a contraction that last 10 -15 times longer than in skeletal muscle Principles of Human Anatomy and Physiology, 11 e 40

SMOOTH MUSCLE • Smooth muscle tissue is nonstriated and involuntary and is classified into two types: visceral (single unit) smooth muscle (Figure 10. 18 a) and multiunit smooth muscle (Figure 10. 18 b). – Visceral (single unit) smooth muscle is found in the walls of hollow viscera and small blood vessels; the fibers are arranged in a network and function as a “single unit. ” – Multiunit smooth muscle is found in large blood vessels, large airways, arrector pili muscles, and the iris of the eye. The fibers operate singly rather than as a unit. Principles of Human Anatomy and Physiology, 11 e 41

Two Types of Smooth Muscle • Visceral (single-unit) – in the walls of hollow viscera & small BV – autorhythmic – gap junctions cause fibers to contract in unison • Multiunit – individual fibers with own motor neuron ending – found in large arteries, large airways, arrector pili muscles, iris & ciliary body Principles of Human Anatomy and Physiology, 11 e 42

INTRODUCTION • The voluntarily controlled muscles of the body make up the muscular system. • The muscular system and muscle tissue contribute to homeostasis by producing movement, stabilizing body position, regulating organ volume, moving substances within the body, and producing heat. • This chapter discusses how skeletal muscles produce movement and describes the principal skeletal muscles. Principles of Human Anatomy and Physiology, 11 e 43

Chapter 11 The Muscular System • Skeletal muscle major groupings • How movements occur at specific joints • Learn the origin, insertion, function and innervation of all major muscles • Important to allied health care and physical rehabilitation students Principles of Human Anatomy and Physiology, 11 e 44

Muscle Attachment Sites: Origin and Insertion • Skeletal muscles shorten & pull on the bones they are attached to • Origin is the bone that does not move when muscle shortens (normally proximal) • Insertion is the movable bone (some 2 joint muscles) • Fleshy portion of the muscle in between attachment sites = belly Principles of Human Anatomy and Physiology, 11 e 45

Tenosynovitis • Inflammation of tendon and associated connective tissues at certain joints – wrist, elbows and shoulder commonly affected • Pain associated with movement • Causes – trauma, strain or excessive exercise Principles of Human Anatomy and Physiology, 11 e 46

Lever Systems and Leverage • A lever is a rigid structure that moves around a fixed point, the fulcrum (F) • The lever is acted on by two different forces: (Figure 11. 1 b). – resistance (load) (L), which opposes movement – effort (E) which causes movement Bones serve as levers and joints serve as fulcrums. • Leverage, the mechanical advantage gained by a lever, is largely responsible for a muscle’s strength and range of motion (ROM), i. e. , the maximum ability to move the bones of a joint through an arc. Principles of Human Anatomy and Physiology, 11 e 47

Levers Principles of Human Anatomy and Physiology, 11 e 48

Levers are categorized into three types – • First class levers (EFL) e. g. a seesaw – the head on the vertebral column (Figure 11. 2 a) • Second-class (FLE) eg. a wheelbarrow(Figure 11. 2 b) • Third-class (FEL) (Figure 11. 1 b) e. g. forceps the elbow joint (Figure 11. 2 c). Principles of Human Anatomy and Physiology, 11 e 49

Lever Systems and Leverage • Muscle acts on rigid rod (bone) that moves around a fixed point called a fulcrum • Resistance is weight of body part & perhaps an object • Effort or load is work done by muscle contraction • Mechanical advantage – the muscle whose attachment is farther from the joint will produce the most force – the muscle attaching closer to the joint has the greater range of motion and the faster the speed it can produce Principles of Human Anatomy and Physiology, 11 e 50

First - Class Lever • Can produce mechanical advantage or not depending on location of effort & resistance – if effort is further from fulcrum than resistance, then a strong resistance can be moved • Head resting on vertebral column – weight of face is the resistance – joint between skull & atlas is fulcrum – posterior neck muscles provide effort Principles of Human Anatomy and Physiology, 11 e 51

Second - Class Lever • Similar to a wheelbarrow • Always produce mechanical advantage – resistance is always closer to fulcrum than the effort • Sacrifice of speed force • Raising up on your toes – resistance is body weight – fulcrum is ball of foot – effort is contraction of calf muscles which pull heel up off of floor Principles of Human Anatomy and Physiology, 11 e 52

Third - Class Lever • Most common levers in the body • Always produce a mechanical disadvantage – effort is always closer to fulcrum than resistance • Favors speed and range of motion over force • Flexor muscles at the elbow – resistance is weight in hand – fulcrum is elbow joint – effort is contraction of biceps brachii muscle Principles of Human Anatomy and Physiology, 11 e 53

Fascicle Arrangements • A contracting muscle shortens to about 70% of its length • Fascicular arrangement represents a compromise between force of contraction (power) and range of motion – muscles with longer fibers have a greater range of motion – a short fiber can contract as forcefully as a long one. Principles of Human Anatomy and Physiology, 11 e 54

Coordination Within Muscle Groups • Most movement is the result of several muscle working at the same time • Most muscles are arranged in opposing pairs at joints – prime mover or agonist contracts to cause the desired action – antagonist stretches and yields to prime mover – synergists contract to stabilize nearby joints – fixators stabilize the origin of the prime mover • scapula held steady so deltoid can raise arm Principles of Human Anatomy and Physiology, 11 e 55

HOW SKELETAL MUSCLES ARE NAMED • The names of most of the nearly 700 skeletal muscles are based on several types of characteristics. • These characteristics may be reflected in the name of the muscle. • The most important characteristics include the direction in which the muscle fibers run, the size, shape, action, numbers of origins, and location of the muscle, and the sites of origin and insertion of the muscle • Examples from Table 11. 2 – triceps brachii -- 3 sites of origin – quadratus femoris -- square shape – serratus anterior -- saw-toothed edge Principles of Human Anatomy and Physiology, 11 e 56

PRINCIPLE SKELETAL MUSCLES • Exhibits 11. 1 through 11. 20 list the principle skeletal muscles in various regions of the body. • Figure 11. 3 shows general anterior and posterior views of the muscular system. • The exhibits contain objectives, an overview which provides a general orientation to the muscles, muscle names, origins, insertions, and actions, “relating muscles to movements, ” innervation, and Figures (11. 4 -11. 23) that show the muscles under consideration. Principles of Human Anatomy and Physiology, 11 e 57

Muscles of Abdominal Wall • Notice 4 layers of muscle in the abdominal wall Principles of Human Anatomy and Physiology, 11 e 58

Muscles of Abdominal Wall • 4 pairs of sheetlike muscles – rectus abdominis = vertically oriented – external & internal obliques and transverses abdominis • wrap around body to form anterior body wall • form rectus sheath and linea alba • Inguinal ligament from anterior superior iliac spine to upper surface of body of pubis • Inguinal canal = passageway from pelvis through body wall musculature opening seen as superficial inguinal ring • Inguinal hernia = rupture or separation of abdominal wall allowing protrusion of part of the small intestine (more common in males) Principles of Human Anatomy and Physiology, 11 e 59

Transverse Section of Body Wall • Rectus sheath formed from connective tissue aponeuroses of other abdominal muscles as they insert in the midline connective tissue called the linea alba Principles of Human Anatomy and Physiology, 11 e 60

Muscles Used in Breathing • Breathing requires a change in size of the thorax • During inspiration, thoracic cavity increases in size – external intercostal lift the ribs – diaphragm contracts & dome is flattened • During expiration, thoracic cavity decreases in size – internal intercostal mm used in forced expiration • Diaphragm is innervated by phrenic nerve (C 3 -C 5) but intercostals innervated by thoracic spinal nerves (T 2 -T 12) Quadratus lumborum fills in space between 12 th rib & iliac crest to create posterior body wall Principles of Human Anatomy and Physiology, 11 e 61

Muscles Used in Breathing • Breathing requires a change in size of the thorax • During inspiration, thoracic cavity increases in size – external intercostal lift the ribs – diaphragm contracts & dome is flattened • During expiration, thoracic cavity decreases in size – internal intercostal mm used in forced expiration • Diaphragm is innervated by phrenic nerve (C 3 -C 5) but intercostals innervated by thoracic spinal nerves (T 2 -T 12) Quadratus lumborum fills in space between 12 th rib & iliac crest to create posterior body wall Principles of Human Anatomy and Physiology, 11 e 62

Stabilizing the Pectoral Girdle • Anterior thoracic muscles – Subclavius extends from 1 st rib to clavicle – Pectoralis minor extends from ribs to coracoid process – Serratus anterior extends from ribs to inner surface of scapula • Posterior thoracic muscle – Trapezius extends from skull & vertebrae to clavicle & scapula – Levator scapulae extends from cervical vertebrae to scapula – Rhomboideus extends from thoracic vertebrae to vertebral border of scapula Principles of Human Anatomy and Physiology, 11 e 63

Axial Muscles that Move the Arm • Pectoralis major & Latissimus dorsi extend from body wall to humerus. Principles of Human Anatomy and Physiology, 11 e 64

Muscles that Move the Arm • Deltoid arises from acromion & spine of scapula & inserts on arm – abducts, flexes & extends arm • Rotator cuff muscles extend from scapula posterior to shoulder joint to attach to the humerus – supraspinatus & infraspinatus: above & below spine of scapula – subscapularis on inner surface of scapula Principles of Human Anatomy and Physiology, 11 e 65

Flexors of the Forearm (elbow) • Cross anterior surface of elbow joint & form flexor muscle compartment • Biceps brachii – scapula to radial tuberosity – flexes shoulder and elbow & supinates hand • Brachialis – humerus to ulna – flexion of elbow • Brachioradialis – humerus to radius Principles of Human Anatomy and – flexes elbow Physiology, 11 e 66

Extensors of the Forearm (elbow) • Cross posterior surface of elbow joint & forms extensor muscle compartment • Triceps brachii – long head arises scapula – medial & lateral heads from humerus – inserts on ulna – extends elbow & shoulder joints • Anconeus – assists triceps brachii in extending the elbow Principles of Human Anatomy and Physiology, 11 e 67

Cross-Section Through Forearm • If I am looking down onto this section is it from right or left arm? Principles of Human Anatomy and Physiology, 11 e 68

Muscle that Pronate & Flex • Pronator teres – medial epicondyle to radius so contraction turns palm of hand down towards floor • Flexor carpi muscles – radialis – ulnaris • Flexor digitorum muscles – superficialis – profundus • Flexor pollicis Principles of Human Anatomy and Physiology, 11 e 69

Muscles that Supinate & Extend • Supinator – lateral epicondyle of humerus to radius – supinates hand • Extensors of wrist and fingers – extensor carpi – extensor digitorum – extensor pollicis – extensor indicis Principles of Human Anatomy and Physiology, 11 e 70

Muscles that Move the Vertebrae • Quite complex due to overlap • Erector spinae fibers run longitudinally – 3 groupings • spinalis • iliocostalis • longissimus – extend vertebral column • Smaller, deeper muscles – transversospinalis group • semispinalis, multifidis & rotatores – run from transverse process to dorsal spine of vertebrae above & help rotate vertebrae Principles of Human Anatomy and Physiology, 11 e 71

Muscles Crossing the Hip Joint • Iliopsoas flexes hip joint – arises lumbar vertebrae & ilium – inserts on lesser trochanter • Quadriceps femoris has 4 heads – Rectus femoris crosses hip – 3 heads arise from femur – all act to extend the knee • Adductor muscles – bring legs together – cross hip joint medially – see next picture • Pulled groin muscle – result of quick sprint activity – stretching or tearing of iliopsoas or adductor muscle Principles of Human Anatomy and Physiology, 11 e 72

Adductor Muscles of the Thigh • Adductor group of muscle extends from pelvis to linea aspera on posterior surface of femur – pectineus – adductor longus – adductor brevis – gracilis – adductor magnus (hip extensor) Principles of Human Anatomy and Physiology, 11 e 73

Muscles of the Butt & Thigh • Gluteus muscles – maximus, medius & minimus – maximus extends hip – medius & minimus abduct • Deeper muscles laterally rotate femur • Hamstring muscles – semimembranosus (medial) – semitendinosus (medial) – biceps femoris (lateral) – extend hip & flex knee • Pulled hamstring – tear of origin of muscles from ischial tuberosity Principles of Human Anatomy and Physiology, 11 e 74

Cross-Section through Thigh • 3 compartments of muscle with unique innervation – anterior compartment is quadriceps femoris innervated by femoral nerve – medial compartment is adductors innervated by obturator nerve – posterior compartment is hamstrings innervated by sciatic nerve Principles of Human Anatomy and Physiology, 11 e 75

Muscles of the Calf (posterior leg) • 3 muscles insert onto calcaneus – gastrocnemius arises femur • flexes knee and ankle – plantaris & soleus arise from leg • flexes ankle • Deeper mm arise from tibia or fibula – cross ankle joint to insert into foot • tibialis posterior • flexor digitorum longus • flexor hallucis longus – flexing ankle joint & toes Principles of Human Anatomy and Physiology, 11 e 76

Muscles of the Leg and Foot • • • Anterior compartment of leg – extensors of ankle & toes • tibialis anterior • extensor digitorum longus • extensor hallucis longus – tendons pass under retinaculum Shinsplits syndrome – pain or soreness on anterior tibia – running on hard surfaces Lateral compartment of leg – peroneus mm plantarflex the foot – tendons pass posteriorly to axis of ankle joint and into plantar foot Principles of Human Anatomy and Physiology, 11 e 77

Muscles of the Plantar Foot • Intrinsic muscles – arise & insert in foot • 4 layers of muscles – get shorter as go into deeper layers • Flex, adduct & abduct toes • Digiti minimi muscles move little toe • Hallucis muscles move big toe • Plantar fasciitis (painful heel syndrome) chronic irritation of plantar aponeurosis at calcaneus – improper shoes & weight gain Principles of Human Anatomy and Physiology, 11 e 78

Compartment Syndrome • Skeletal muscles in the limbs are organized in units called compartments. • In compartment syndrome, some external or internal pressure constricts the structures within a compartment, resulting in damaged blood vessels and subsequent reduction of the blood supply to the structures within the compartment. • Without intervention, nerves suffer damage, and muscle develop scar tissue that results in permanent shortening of the muscles, a condition called contracture. Principles of Human Anatomy and Physiology, 11 e 79

IM injection • Intramuscular injection penetrates the skin, subcutaneous tissue and enters the muscle. • They are given when rapid absorption is necessary, for large doses, or when a drug is irritating to subcutaneous tissue. • Common sites of injection are the gluteus medius, vastul lateralis, and deltoid. • Intramuscular injections are faster than oral medications, but slower than IV. Principles of Human Anatomy and Physiology, 11 e 80