Muscular System

The Muscular System

B. Pimentel, M.D. University of Makati – College of Nursing

Functions Movement – skeletal muscle contractions move the body as a whole or in parts. Heat production – muscle cells are numerous and very active, this results in catabolism producing the majority of heat. Posture – maintaining body positions such as standing and sitting erect

MAJOR PROPERTIES OF MUSCLE

1.

Excitability – ability to be stimulated

2.

Contractility – ability to contract or shorten and produce body movement

3.

Extensibility – ability to extend or stretch muscles to their original length

4.

Elasticity – ability to recoil to its original length.

CHARACTERISTICS OF MUSCLE TISSUE TYPES

SKELETAL

CARDIAC

SMOOTH

PRINCIPAL LOCATION

Skeletal Wall of heart   Walls of muscle groupsINVOLUNTARY many hollow organs

PRINCIPAL FUNCTION

Movement ofPumping bone, heatblood production, posture

TYPE OF CONTROL

VOLUNTARY

ofMovement in walls of hollow organs

INVOLUNTARY INVOLUNTARY

STRUCTURE Epimysium (facia) – connective tissue sheath, which surrounds each skeletal muscle Perimysium – loose connective tissue, which surrounds muscle fiber bundles Endomysium – surrounds each muscle fiber Sarcoplasm – myofibril cytoplasm. Myofibril – protein fibers that extend from one end of the muscle fiber to another. Actin and Myosin myofilaments.

STRUCTURE

STRUCTURE

STRUCTURE Sarcolemma – plasma membrane of the myofibril Sarcoplasmic Reticulum – a network of tubules and sacs that is similar but not identical to E.R. T-tubules – extend transversely across the sarcoplasm at right angles to the long axis of the cell. Separate from the sarcoplasmic reticulum. Triad – a triplet of tubules with a T-tubule sandwiched between two sarcoplasmic reticulums. Allows electrical impulse to travel along a T-tubule to stimulate membranes of adjacent sacs of the sarcoplasmic reticulum.

STRUCTURE

Membrane Potentials Resting Membrane Potential The intracellular surface of the sarcoplasm is negatively charged compared with that of the extracellular surface of the sarcoplasm.  

Intracellular [K+] is higher vs. extracellular [K+] The cell membrane is more permeable to [K+]

Positively charged potassium ions readily diffuse across the membrane from intra to extracellular spaces, resulting in a –70 to –90 millivolts.

Membrane Potentials Resting Membrane Potential Equilibrium is achieved when the tendency of K+ to diffuse is opposed  

The increasing intracellular negative charge Shift of K+ concentration gradient

Action Potential Depolarization Occurs when the intracellular membrane becomes less negative than the extracellular membrane. Gated sodium channels open when the cell is stimulated. This allows positive sodium ions to diffuse into the cell. Making the intracellular space less negative. Once the intracellular membrane becomes positive the gated sodium ion channels close.

Action Potential Depolarization

Action Potential Depolarization

Action Potential Depolarization

Action Potential Repolarization Begins as soon as the sodium ion channels close. Thus the movement of sodium into the cell ceases and gated potassium channels open begins moving potassium out of the cell. The potassium gated channels close when the resting membrane potential is reached.

NEUROMUSCULAR JUNCTION Motor neurons – nerve cells along which action potentials travel to stimulate muscle fibers Neuromuscular junction (synapse) – motor neuron axons and its branches innervating the muscle fibers Presynaptic terminal – axon terminal that contains synaptic vesicles containing acetylcholine. Synaptic cleft – space between pre and post synapse. Postsynaptic terminal – sarcoplasm membrane opposite the presynaptic terminal or motor end plate.

NEUROMUSCULAR JUNCTION

NEUROMUSCULAR JUNCTION

Function of Neuromuscular Junction

1.

Action potential arrives at presynaptic terminal, increasing the permeability of calcium.

2.

Calcium enters the presynaptic terminal and initiates the release of acetylcholine (Ach).

3.

Diffusion of Ach across the synaptic cleft and binding to receptor sites on the motor end plate, causing an increase of sodium permeability of the sarcoplasm.

4.

Resulting in depolarization; once the threshold has been reached an action potential begins.

5.

Ach is broken down by acetylcholinesterase

MUSCLE CONTRACTION Occurs as actin and myosin myofilaments slide past one another Sarcomeres shorten 

Extends from one Z line to another.  Z line – filamentous network of protein forming a disk like structure for the

attachment of actin myofilaments anchoring them in place.  I band – from one side of the Z disk to the other. Consists of only actin fibers.  A band – extends the length of the myosin filaments within a sarcomere the

actin and myosin filaments overlap at both ends of the A band.  H zone – center of each A band, smaller. Only myosin filaments present.  M line – is in the middle of the H zone, consists of delicate fibers that attach to

the center of myosin filaments, anchoring them

The Sarcomere

MUSCLE CONTRACTION (The Sliding Filament Model) Muscle contraction that results in the shortening of the sarcomere without changing the length of the actin and myosin filaments. Muscle contracts when myosin crossbridges attach to actin and the molecule bends

MUSCLE CONTRACTION (The Sliding Filament Model)

What happens when muscle contracts? The Z lines move closer together The I band becomes shorter The A band stays at the same length

Action Potential, Neuromuscular Junction and the Sarcomere Excitation and Contraction Nerve impulse → the motor end plate → release of the neurotransmitter (acetylcholine) → binds to receptors on the motor end plate of the muscle → initiates an impulse that travels along the sarcolemma, through the T tubule, to sacs of the sarcoplasmic reticulum → calcium is released into the sarcoplasm → it binds to troponin molecules on the actin filaments → tropomyosin moves to expose myosin attachment sites on the actin myofilaments → a cross bridge is formed between when the head of the myosin bind with the actin myofilaments

Action Potential, Neuromuscular Junction and the Sarcomere Excitation and Contraction

Action Potential, Neuromuscular Junction and the Sarcomere Excitation and Contraction During contraction ATP is broken down to ADP to produce energy to pull the thin filaments toward the center of each sarcomere This cycle repeats several times per second, as long as ATP is present

Action Potential, Neuromuscular Junction and the Sarcomere Excitation and Contraction

Muscle Relaxation After the impulse is over, the sarcoplasmic reticulum begins actively pumping calcium back into sacs. As calcium is stripped from troponin molecules in the actin (thin) filaments, tropomyosin returns to its position, blocking the active sites of the actin filaments. Myosin cross bridges are prevented from binding to actin and thus can no longer sustain contraction. Since the thick and thin myofilaments are no longer connected, the muscle fiber returns to its resting length

Muscle Twitch, Summation, Tetanus and Recruitment

Muscle Twitch Contraction of a muscle in response to a stimulus that causes an action potential in one or more muscle fibers 

Lag or Latent Phase – the time period between the stimulus of the motor neuron and the beginning of contraction.  Stimulus  Action potential along the axon of the motor neuron  Release of acetylcholine from the presynaptic terminal  Opening of Na channels  Release of Ca from the sarcoplasmic reticulum  Ca binds to troponin  Tropomyosin exposes myosin binding sites  Cross bridge formation

Muscle Twitch, Summation, Tetanus and Recruitment 

Contraction Phase – contraction of the muscle  Cross bridge movement and cycling  Increase the tension produced by the muscle fibers



Relaxation Phase – relaxation of the muscle  Ca diffuses away from the troponin molecules  Ca is actively transported back into the sarcoplasmic reticulum  Tropomyosin blocks the myosin binding sites  Inhibition of cross bridge formation  Tension decreases

Muscle Twitch, Summation, Tetanus and Recruitment Summation Increasing the force of contraction of the muscle fibers within the muscle Rapid stimulation 

As the frequency of action potentials increases the frequency of contraction increases.

Muscle Twitch, Summation, Tetanus and Recruitment 



Incomplete Tetanus – muscle fibers partially relax between contractions. Tetanus – action potentials are produced so quickly that there is no relaxation.

Build up of Ca in the myofibrils Ca is released at a higher rate from the sarcoplasmic reticulum that its uptake

Muscle Twitch, Summation, Tetanus and Recruitment Recruitment Increases the number of muscle fibers contacting 

As the number of motor units stimulated increases, the more muscle fibers are stimulated to contract

ENERGY REQUIREMENTS ATP is the immediate energy source of muscle. It must be synthesized continuously to sustain muscle contraction. Creatine Phosphate – resting conditions, energy from aerobic respiration is used to synthesize creatine phosphate. 

This accumulates in the cell and functions to store energy to synthesize ATP.



Creatine phosphate stores are quickly depleted during intense muscular contractions. Sustains maximum contraction for 8 to 10 seconds.

ENERGY REQUIREMENTS Aerobic vs. Anaerobic Anaerobic Respiration – absence of oxygen breakdown of glucose to produce 2 ATP molecules and lactic acid 





Occurs in the cytoplasm of cells Less efficient than aerobic respiration but quicker synthesis of ATP. Used for short periods of intense exercise, such as sprinting provides up to 3 minutes of energy.

Aerobic Respiration – requires oxygen and breaks down glucose to produce ATP, Carbon dioxide, and water.  Occurs in the mitochondria  Net gain of 38 ATP molecules per glucose molecule.  Can utilize fatty acids and amino acids to generate ATP

OXYGEN DEBT/EXCESS After intense exercise, the rate of aerobic metabolism remains elevated for a time. The oxygen taken in the body is above that needed for resting metabolism This reestablishes ATP and creatine phosphate levels in muscle fibers.

FATIGUE Psychological fatigue  Most common type of fatigue Muscle Fatigue  ATP is utilized faster than it is produced  Lactic acid build up  Force of contractions become weaker

TYPES OF MUSCLE CONTRACTIONS

1.

Isometric contraction – length of the muscle does not change, but the tension increases during contraction process. Postural muscles.

2.

Isotonic contraction – the amount of tension produced by the muscle remains constant but the length of the muscle changes. Voluntary movements.

3.

Concentric contractions – isotonic contractions in which muscle tension increases as the muscle shortens

4.

Eccentric contractions – isotonic contractions in which tension is maintained as the muscle lengthens

TYPES OF MUSCLE FIBERS Fast and Slow Twitch Fibers Fast Twitch – low oxidative muscle fibers, respond rapidly to stimuli and contain myosin molecules that break down ATP more rapidly than slow twitch.  Less developed blood supply  Few myoglobin  Fewer and smaller mitochondria  Large stores of glycogen and are well adapted to anaerobic respiration  Fatigue occurs quickly

TYPES OF MUSCLE FIBERS Fast and Slow Twitch Fibers Slow Twitch – high oxidative muscle fibers. Contract slower as compared with fast twitch.  Better developed blood supply  More mitochondria  More fatigue resistant  Aerobic respiration  Contain large amounts of myoglobin

SKELETAL MUSCLE ANATOMY Terminologies Tendon – connective tissue that attaches muscle to bone. Aponeurosis – a very broad, sheetlike tendon. Origin – the end of the muscle attached to a fixed or usually proximal segment. Insertion – end of the muscle where the attachment to the bone moves. Agonist – a muscle causing an action during contraction. Antagonist – a muscle working in opposite direction to an agonist. (i.e. triceps muscle working against the biceps). Synergists – muscles that work together to cause a movement. Prime Mover – one muscle of a synergist group that plays the major role. Fixator – muscles that stabilize the joints that the muscle

SKELETAL MUSCLE ANATOMY Nomenclature Muscles can be named according to their location, size, shape, orientation, origin and insertion, number of heads, and or function. Location – pectoralis (chest), gluteus (buttock), and brachial (arm) are a few examples of name by location. Size – maximus (large), minimus (small), longus (long) brevis (short). Shape – deltoid (triangle), quadratus (quadrangle) Orientation – fascicular orientation, rectus (straight), and oblique.

SKELETAL MUSCLE ANATOMY Nomenclature Origin and Insertion – sternocleidomastoid muscle is named for its origin and insertion. Number of Heads – biceps (2 heads), triceps (3 heads). Function – abductor muscle moves bone away from midline, adductor moves a bone towards the midline, flexor, extensor…

SKELETAL MUSCLE ANATOMY Muscles of the Head Facial Expressions Occipitofrontalis – raises the eyebrows Orbicularis oculi – closes the eyelids; “crows feet” Orbicularis oris – pucker the mouth Buccinator – whistling Zygomaticus – smiling Levator labii superioris – sneer Depressor anguli oris – frowns and pouting

SKELETAL MUSCLE ANATOMY Muscles of the Neck Neck Flexion Muscles Sternocleidomastoid Origin - manubrium and medial clavicle Insertion - mastoid process Action - flexion of head and neck, rotation, and lateral flexion Palpation - anterolateral side of neck Rectus capitis anterior, Rectus capitis lateralis, Longus capitis, Longus colli, 8 pair of hyoid muscles

SKELETAL MUSCLE ANATOMY Muscles of the Neck Neck Extension Muscles Trapezius – extends the head and neck Splenius capitis (O- vertebral processes, I - occipital bone), Semispinalis capitis, Splenius cervicis, Rectus capitis posterior major and minor, Obliquus capitis superior and inferior Neck Lateral Flexion Muscles Sternocleidomastoid, levator scapulae, scalenus anterior, cervical flexors, cervical extensors

SKELETAL MUSCLE ANATOMY Muscles of the Neck

SKELETAL MUSCLE ANATOMY

SKELETAL MUSCLE ANATOMY Muscles Moving the Vertebral Column Trunk Extension Muscles Erector spinae 1. Iliocostalis 2. Longissimus 3. Spinalis Deep back muscles – extension, lateral flexion and rotation of the vertebral column

SKELETAL MUSCLE ANATOMY Muscles Moving the Vertebral Column Trunk Flexion Muscles 1. Rectus Abdominis (parallel to midline) Origin - crest of pubis Insertion - cartilage 5,6,7 ribs and xiphoiud process 2. Internal Obliques (high medial to low lateral) Origin - external surface of lower 8 ribs Insertion - linea alba 3. External Obliques (high lateral to low medial) Origin - linea alba and lower 4 ribs Insertion - iliac crest, lumbordorsal fascia

SKELETAL MUSCLE ANATOMY Thoracic Muscles Thoracic Muscles External intercostals – elevate the ribs Internal intercostals – depresses the ribs; contract during forced expiration Diaphragm – major muscle in normal respiration

SKELETAL MUSCLE ANATOMY Thoracic Muscles

SKELETAL MUSCLE ANATOMY Abdominal Wall Muscles Linea alba – located midline the abdomen; it is composed of connective tissue Rectus abdominis – laterally on each side of the linea alba Tendinous intersection – traverses the width of the rectus abdominis Group of abdominal muscle responsible for flexion, rotation or compression of abdominal contents 1. External oblique 2. Internal oblique 3. Transversus abdominis

SKELETAL MUSCLE ANATOMY Abdominal Wall Muscles

SKELETAL MUSCLE ANATOMY Upper Limb Muscles Arm Movements Pectoralis major – adducts the arm and flexes the shoulder Origin - clavicle, ribs, sternum Insertion - lateral humerus Latissimus dorsi – medially rotates and adducts the arm; extends the shoulders Origin - illium, sacrum, T6-L5 Insertion - anterior humerus Deltoid – major abductor of the upper limb Origin - clavicle, scapula, lateral acromian Insertion - deltoid tuberosity

SKELETAL MUSCLE ANATOMY Upper Limb Muscles

SKELETAL MUSCLE ANATOMY Upper Limb Muscles

Rotator cuff muscles 1. Infraspinatus 2. Subscapularis 3. Supraspinatus 4. Teres minor

SKELETAL MUSCLE ANATOMY Upper Limb Muscles Rotator cuff muscles Muscle

Origin

Insertion

Action

Palpate

Supraspinatus

supraspinous fossa

greater tubercle abduction

deep to deltoid

Infraspinatus

infraspinous fossa

greater tubercle abduction horizontal

deep to deltoid

Teres Minor

posteriorly lateral scapula

greater tubercle horizontal deep to deltoid abduction, external rotation

Subscapularis

subscapular fossalesser tubercle

internal rotation, deep to deltoid adduction

SKELETAL MUSCLE ANATOMY Upper Limb Muscles

SKELETAL MUSCLE ANATOMY Upper Limb Muscles Forearm Movements Triceps brachii – primary extensor of the elbow Biceps brachii and Brachialis – primary flexors of the elbow

SKELETAL MUSCLE ANATOMY Upper Limb Muscles Wrist and Finger Movements Retinaculum – fibrous connective tissue that covers the flexors and extensors Flexor carpi – flexes the wrist Extensor carpi – extends the wrist Flexor digitorum – flexes the fingers Extensor digitorum – extends the fingers

SKELETAL MUSCLE ANATOMY

Wrist and Finger Movements

SKELETAL MUSCLE ANATOMY Lower Limb Muscles Thigh Movements Iliopsoas – flexes the hip Tensor Facia Latae – a tense, thick band of facia on the lateral side of the thigh Gluteus maximus – extends the hip, abducts and laterally rotates the thigh Gluteus medius – abducts and medially rotates the thigh

Leg Movements Quadriceps femoris – primary extensors of the knee Sartorius – flexes the hip and knee; rotates the thigh laterally Hamstrings – knee flexors

SKELETAL MUSCLE ANATOMY Lower Limb Muscles

SKELETAL MUSCLE ANATOMY Lower Limb Muscles

SKELETAL MUSCLE ANATOMY Lower Limb Muscles Ankle Movement Gastrocnemius and Soleus – joins to form the Achilles tendon or Calcaneal; plantar flexion of the foot

SKELETAL MUSCLE ANATOMY Lower Limb Muscles

Resources Textbook Essential of Anatomy & Physiology 

Seeley, Stephens and Tate

Regional Atlas of Human Anatomy 

Clemente

Essentials of Human Anatomy 

Burkel

Textbook of Medical Physiology 

Guyton

Basic Histology 

Junqueira, Carneiro and Kelley

On-line Resources Wayne State University – Academic Resources Library University of Minnesota – Hematology Center Medline PLUS McGraw-Hill (On-line Resource) Getbodysmart.com Redcross.org

Thank You!