General Anatomy of Skeletal Muscles PDF

General anatomy of skeletal muscles Dr. Alyaa Mousa MED, PhD ID#7114 Classifications of skeletal muscles Describe the basis of classification into different types. Describe the functional groups of skeletal muscles. Describe the sensory and mot...

General anatomy of skeletal muscles Dr. Alyaa Mousa MED, PhD ID#7114 Classifications of skeletal muscles Describe the basis of classification into different types. Describe the functional groups of skeletal muscles. Describe the sensory and motor nerve supply to a skeletal muscle Skeletal Muscle Skeletal muscles are muscles which are attached to the skeleton. 40% of human body mass Skeletal muscles are mainly responsible for locomotion, and voluntary contraction and relaxation. Structure of Skeletal muscles Skeletal muscles are composed of clusters of muscle cells. Muscle fibers Myofibers Myocytes A muscle consists of packages of muscle cells called fascicles A muscle cell is long and spindle shaped Fascicle Arrangement Classification of Skeletal Muscles By the way fascicles are organized By relationships of fascicles to tendons Fascicle Arrangement Organization of Skeletal Muscle Fibers Four patterns of fascicle organization Parallel Convergent Pennate Circular Classification of Skeletal Muscles Parallel (most common) - fascicles are parallel to the long axis of the muscle -Strap-like with broad attachments (aponeuroses) ex. Sartorius and Sternohyoid - Strap-like with tendinous intersections ex. Rectus abdominis - Fusiform, is a spindle-shaped muscle with an expanded belly ex. biceps brachii - when contracted muscle shortens, get larger in diameter - Not very powerful Classification of Skeletal Muscles Convergent - fascicles converge toward a single insertion tendon - triangular or fan-shaped ex,. pectoralis major Classification of Skeletal Muscles Pennate - fascicles attach obliquely to a central tendon - Pennate muscles with the highest concentration of fibers, shorten little, but are very powerful - unipennate, fascicles insert into only one side tendon ex. extensor digitorum longus - bipennate, fascicles insert into both sides of tendon ex. rectus femoris - multipennate, tendon branches ex. Deltoid & subscapularis Classification of Skeletal Muscles Deltoid 3 Extensor digitorum muscle 1 Rectus femoris 2 Classification of Skeletal Muscles Circular - arranged in concentric rings around opening or recess - typically found surrounding external body openings - as muscle contracts, diameter of opening decreases - This type of muscles are called sphincters which literally means squeezers ex. orbicularis oris muscles (muscle of the mouth)  Functional Muscle Groups Muscles can be classified into four functional groups Prime movers (agonists) Antagonists Synergists Fixators  Prime Movers A muscle that Origin of Coracoid provides the major Biceps Brachii Process force for producing a specific movement is called a prime mover or agonist The biceps brachii is the prime mover of elbow flexion  Antagonist Muscles that oppose or reverses a prime mover are called antagonist When a prime mover is active, the antagonist muscles are often stretched and may be in a relaxed state Antagonists also regulate the action of prime mover  Synergist Synergist- muscle that aids prime mover in a movement and helps prevent rotation In two joint muscles synergists stabilize a joint as the muscle acts on the other brachialis Assist the biceps to create the movement and stabilize the elbow joint.  Fixator When a synergist immobilize a muscle’s origin they are called fixators Their action serves to stabilize the bone upon which a prime mover acts Serratus anterior holds the scapula against the thorax while a prime mover acts upon the arm Naming Skeletal Muscles Direction of Muscle Fibers Action Location Skeletal Origin Muscle & Size Insertion Number Shape Of Origins  Naming skeletal muscles (examples) Direction of fascicles and fibers: rectus (straight); transversus (right angle) and oblique (oblique) to midline Location: brachialis is in arm (brachium = arm) Size: minimus (smallest), longus (long), brevis (short) Number of origins: biceps (“two heads”), triceps (“three heads”), quadriceps (“four heads”) Shape: deltoid is triangular (delta = triangle) Action: “flexor,” “extensor,” “adductor” or “abductor” appear in the name Naming Skeletal Muscles Relative Position Externus (superficialis) Visible at body surface Internus (profundus) Deep muscles Extrinsic Muscles outside an organ Intrinsic Muscles inside an organ  Direction of Muscle Fibers Relative to the Midline RECTUS = parallel to the midline Rectus Abdominis TRANSVERSE = perpendicular to midline (right angle) Transverse Abdominis OBLIQUE = diagonal to midline External Oblique Location Frontalis : near frontal bone Occipitalis: near occipital bone Brachialis: are (branchia) Gluteus: buttock (gluteal) Oris: mouth (oral) Oculi: eye (ocular) Mandibular: mandible Scapulae: scapula (shoulder) Buccinator: buckle (cheek) Femoris: femur (thigh)  Size Relative Size of Muscle MAXIMUS = largest Gluteus Maximus MEDIUS = middle Gluteus Medius MINIMUS = smallest Gluteus Minimus LONGUS = longest Fibularis Longus BREVIS = short Fibularis Brevis TERTIUS = shortest Fibularis Tertius  Number of Origins Number of tendons of origin BICEPS = Two Biceps Brachii Biceps Femoris TRICEPS = Three Triceps Brachii QUADRICEPS = Four Quadriceps Femoris  Shape Relative Shape of the Muscle Deltoid = triangular shape Δ Trapezius = trapezoid shape  Serratus = saw-toothed Rhomboideus = rhomboid shape Teres = round ○ Muscle Attachments 1) Origin – point of muscle attachment that doesn’t move during contraction 2) Insertion - muscle attachment that moves the most Action – at contraction, the insertion moves toward the origin 25 Action NAME ACTION EXAMPLE FLEXOR Decrease angle at a joint Flexor Carpi Radialis EXTENSOR Increase angle at a joint Extensor Carpi Ulnaris Move bone away from ABDUCTOR midline Abductor Pollicis Longus ADDUCTOR Move bone toward midline Adductor Longus LEVATOR Produce upward movement Levator Scapulae Produce downward DEPRESSOR movement Depressor Labii Inferioris SUPINATOR Turn palm upward/anterior Supinator Turn palm PRONATOR downward/posterior Pronator Teres  Innervation of Skeletal Muscle Motor fibers: These fibers make up to 60% of a nerve to skeletal muscle. They comprise of: Large myelinated alpha efferents which supply extrafusal muscle fibers. Smaller myelinated gamma efferents which supply intrafusal fibers of the muscle spindles which refine and control muscle contraction. The fine non-myelinated autonomic efferents which supply smooth muscle fibers of the blood vessels.  Innervation of Skeletal Muscle Motor axons innervate skeletal muscle fibers at junctions called neuromuscular junctions, or motor end plates A single neuromuscular is associated with each muscle fiber These junctions are similar to the synapses between neurons The neural part of the junction is a cluster of typical axon terminals separated from the plasma membrane (sarcolemma) of the underlying muscle cell by a synaptic cleft Although neuromuscular junctions resemble synapses they have several unique features Each axon terminal lies in a trough-like depression of the sarcolemma, which in turn shows groove-like invaginations The invaginations and the synaptic cleft contain a basal lamina that does not appear in synapses between neurons Innervation of Skeletal Muscle As in typical synapses, the axon terminals contain synaptic vesicles that release a neurotransmitter when a nerve impulse reaches the terminals The neurotransmitter (acetylcholine) diffuses across the synaptic cleft and binds to receptor molecules on the sarcolemma, where it induces an impulse that signals the muscle cell to contract Innervation of Skeletal Muscle This basal lamina contains the enzyme acetylcholinesterase which breaks down acetylcholine immediately after the neurotransmitter signals a single contraction This assures that each nerve impulse in the motor axon produces just one twitch of the muscle cell, preventing any undesirable additional twitches that would occur acetylcholine lingered in the synaptic cleft  Innervation of Skeletal Muscle Sensory fibers: They form up to 40% of a nerve to the muscle and comprise of: Myelinated fibers distributed to muscle spindles for proprioception, also to tendons Muscle Spindles: Muscle spindles are spindle-shaped sensory end organs of the skeletal muscle. Each spindle contains 6 to 13 intrafusal muscle fibers which are of two types, the larger nuclear bag fibers, and the smaller nuclear chain fibers. Innervation of Skeletal Muscle The spindle is innervated by both the sensory and motor nerves. The sensory endings are of two types: 1. The primary sensory endings (anulospiral endings) around the central nuclear region of the intrafusal fibers 2. The secondary sensory endings {flower spray endings) beyond the nuclear region on either side of these fibers. The motor nerve supply of the spindle is derived from gamma motor neurons of the spinal cord. Muscles spindles act as stretch receptors. They record and help regulate the degree and rate of contraction of the extrafusal fibers by influencing the alpha neurons.