The Muscular System Notes.doc

The Muscular System DISCUSS THESE CHARACTERISTICS OF MUSCLES: EXCITABILITY, EXTENSIBILITY, ELASTICITY, AND CONTRACTILITY.  EXCITABILITY – can receive and respond to a stimulus  EXTENSIBILITY – the fibres can extend beyond original shape  ELATICITY – the ability of a muscle fibre to recoil...

The Muscular System DISCUSS THESE CHARACTERISTICS OF MUSCLES: EXCITABILITY, EXTENSIBILITY, ELASTICITY, AND CONTRACTILITY.  EXCITABILITY – can receive and respond to a stimulus  EXTENSIBILITY – the fibres can extend beyond original shape  ELATICITY – the ability of a muscle fibre to recoil and resume its resting length after being stretched  CONTRACTILITY – the fibres shortened when stimulated DISTINGUISH BETWEEN VOLUNTARY AND INVOLUNTARY MUSCLE AND RELATE TO THE THREE TYPES OF MUSCLE TISSUE.  SKELETAL - muscles that are usually attached to bones / voluntary  SMOOTH – walls of hollow internal organs / involuntary  CARDIAC – heart ♥ / involuntary DESCRIBE THE BASIC APPEARANCE OF THE VARIOUS TYPES OF MUSCLE. SKELETAL  cells are long / threadlike  striated  multinucleated  stimulated by a nerve fibre / contracts producing movements SMOOTH MUSCLE  no striations  individual smooth muscle cells are spindle shaped  only one centrally located nucleus CARDIAC  striated  uninucleated  branching cells that fit tightly together at unique junctions called intercalated disks DISCUSS THE MAJOR FUNCTIONS OF MUSCLES. MOVEMENT  all movements within the body require muscle contraction  skeletal muscles are responsible for all locomotion and manipulation  blood flowing through our vessels is the work of the heart’s contraction and the smooth walls of the vessels to maintain BP POSTURE MAINTENANCE  skeletal muscles must continually contract and relax to maintain posture – muscle tone JOINT STABILITY  as muscles pull on our bones and cause movements  they stabilize the joints of the skeleton  skeletal muscles stabilize joints that require extra stability (shoulder) HEAT GENERATION The Muscular System  as muscles contract they generate heat which is vital to maintain normal body temperature  skeletal muscle accounts for 40% of body mass GUARDS ENTRANCES / EXTIS  urinary / digestive system openings are guarded by two sets of muscles  the most external is composed of skeletal muscle and provides voluntary control over processes (swallowing / urination / defecation ) IDENTIFY THE MAIN ORGAN AND ACCESSORY STRUCTURES OF THE MUSCLE SYSTEM.  “machines of our body”  each skeletal muscle is an organ of the muscular system  tendons assist in the function of the muscular system EXPLAIN WHY MUSCLE IS AN ORGAN.  Definition: a structure consisting of a group of tissues with a specialized function.  recall the four types of tissues  muscles are composed of skeletal / nervous / connective tissue  provides the function of: movement / maintaining posture / stabilizing joints / generates heat / guarding entrances and exits IDENTIFY THE STRUCTURE AND FUNCTION OF TENDONS.  each muscle is separated from its adjacent one and is held in place by connective tissue called fascia  if the fibres extend beyond the muscle covering it becomes a tendon  the tendon can become continuous with the fibres of the bone’s periosteum and functions to attach muscle to bone DESCRIBE THE ORGANIZATION OF A SKELETAL MUSCLE.  locate the fascia – the external covering of a muscle / made of connective tissue / separates one muscle from another  as previously discussed when the fascia extends beyond the muscle it becomes the tendon and serves as an attachment to the periosteum of the related bone  locate the epimysium – another layer of connective tissue surrounding the entire muscle / under the fascia / composed primarily of collagen  located the perimysium – another layer of connective tissue that separated the entire muscle in compartments  each of these compartments are called a fascicle  the perimysium also contains a nerve and blood vessels supplying innervation and blood flow to each fascicle  locate the endomysium – a more delicate connective tissue which surrounds each individual muscle fibre (cell)  locate the myofibrils which are bundled within the muscle cell The Muscular System  they are made up of two filaments / actin (thin) myosin (thick) / collectively they comprise the contractile units of the muscle cell EXPLAIN THE RELATIONSHIP BETWEEN THE MUSCLE AND NERVOUS SYSTEMS.  each skeletal muscle is connected to a nerve cell called a motor neuron  this provides communication to the CNS (brain and spinal cord) and the CNS provides the information to contract  a muscle fibre contracts only when it stimulated by a motor neuron EXPLAIN THE RELATIONSHIP BETWEEN THE NEUROMUSCULAR JUNCTION, SYNAPSE, MOTOR NEURON, VESICLES, NEUROTRANSMITTERS, MUSCLE FIBRES, MOTOR END PLATE, AND RECEPTORS.  the neuromuscular junction includes the end of a motor neuron and the motor end plate of a muscle fibre  collectively where these two structures meet is called a neuromuscular junction  the synapse (synaptic cleft) is the narrow space between the end of the motor neuron and the muscle fibre / the impulse must “jump” across this space into the muscle to produce contraction  the motor neuron is a nerve fibre that transmits impulses from the CNS to an effector (muscle fibre)  locate the synaptic vesicles within the terminal end of the motor neuron (axon) / stored in these vesicles are neurotransmitters  when the impulse gets to the end of the motor neuron it cannot get across the synapse with the aid of a neurotransmitter  neurotransmitters are chemical that is secreted by the terminal end of the axon (motor neuron) / this “bridges” the gap or the synaptic cleft allowing the impulse to continue on to the muscle (effector)  a muscle fibre is a single muscle cell and is capable of contracting when stimulated by a motor neuron  locate the motor end plate – this is the specialized junction / region of a muscle / contains the membrane’s receptors  receptors are the sites that can receive the neurotransmitter and allow the impulse to be transferred to the muscle fibre IN REVIEW: MUSCLE FIBRE ↓ connected to The Muscular System ↓ MOTOR NEURON (nerve cell) ↓ meet at the neuromuscular junction ↓ NEUROTRANSMITTER is released ↓ this “bridges” the gap (synaptic cleft) between the ↓ NEURON and the MUSCLE ↓ the IMPULSE crosses the SYNAPTIC CLEFT ↓ stimulating the MUSCLE FIBRE to contract EXPLAIN THE ROLE OF NEUROTRANSMITTERS IN MUSCLE CONTRACTION.  Answered in previous objective NAME THE BODY’S MAIN NEUROTRANSMITTER.  Acetylcholine OUTLINE THE PROCESS OF MUSCLE CONTRACTION AND RELAXATION.  Recall myofibrils / the thread like components within the muscle cell  myofibrils are composed of two protein filaments: actin (thin) / myosin (thick)  they are bundled together and give the muscle cell a striated appearance  the final result of a muscle contraction is a sliding movement within the myofibrils in which the filaments of actin and myosin merge  the myosin molecule is made up of a protein strand with globular parts that project outward called cross bridges  in the presence of Ca ions the cross bridges react with the opposing actin filaments forming links  the reaction between actin and myosin generates the required force needed for a muscle contraction  a skeletal muscle fibre does not contract until it is stimulated by a neurostransmitter  acetylcholine is synthesized in the cytoplasm of the motor neuron and is stored in the synaptic vesicles  recall that when a nerve impulse jumps across the synaptic cleft acetylcholine is released  this stimulates a muscle impulse which passes in all directions over the surface of the muscle fibre membrane  Ca ions are released from storage areas which promotes the reaction between the actin / myosin filaments producing a muscle contraction (ATP required) The Muscular System  Ca pump (active transport) removes the Ca ions and the linkages are broken allowing the actin / myosin filaments to slide apart causing relaxation of the muscle fibre  Acetylcholine decomposes by an enzyme “cholinesterase” which prevents continued stimulation to the muscle fibre IDENTIFY THE ROLE OF CALCIUM IN MUSCLE CONTRACTION.  Answers in previous objective  Ca initiates muscle contractions EXPLAIN HOW THRESHOLD STIMULUS AND THE ALL-OR-NONE PRINCIPLE RELATE TO MUSCLE CONTRACTION.  the minimal strength needed to cause a muscle contraction is called the threshold stimulus  a muscle fibre will remain inactive until the stimulus is strong enough to cause a threshold stimulus  its response to a threshold stimulus is contraction to its fullest extent  no partial contractions – all or none  if we look at muscle contraction on the gross level it is notable that a skeletal muscle consists of a huge number of cells  these cells contract with varying degrees of force for different periods of time  a closer look at the nerve / muscular functional unit or motor unit will reveal that each muscle is served by at least one motor nerve  this nerve contains hundreds of neuron axons forming many neuromuscular junctions  a motor neuron and all the muscle fibres it supplies is called a motor unit  when the motor neuron fires all the muscle fibres it innervates respond by contracting  muscles with fine motor control (eyes / fingers) have many small motor units while large muscles that have less precise movements have larger motor units  the muscle fibres in a single motor unit are not clustered together but are spread throughout the muscle, so stimulation of a single motor unit will cause a weak contraction throughout the entire muscle DISCUSS THE ROLE OF EXERCISE ON MUSCLE TISSUE.  Atrophy – without development / a = without / trophy = nourishment, development / decrease in the size of an organ or tissue  Hypertrophy – increased development / hyper = above or excessive / trophy = nourishment, development / increase in the size of an organ or tissue LOCATE THE MAJOR MUSCLES:  Head and neck – masseter, temporalis, trapezius, sternocleidomastoid, The Muscular System  Trunk – abdominals, pectoralis major  Upper extremities – biceps, triceps, deltoid, latissimus dorsi  Lower extremities – iliopsoas, gluteus maximus, the adductors, the hamstrings, the quadriceps, calcaneal tendon IDENTIFY THE MUSCLES WHICH OPERATE THE JAW, NECK, SHOULDER, ELBOW, WRIST, HIP, KNEE AND ANKLE JOINTS.  Muscles are classified into four functional groups: prime movers / antagonists / synergists / fixators  Prime movers = a muscle that provides the major force during movement  Antagonists = muscles that oppose or reverse a movement / when the prime movers are active, the antagonists are relaxed  Sometimes this relaxation provides some resistance  Prime movers and antagonists are located on opposite sides of the joint on which they act  Most movements involve the action of one or more synergists and aid prime movers by: promoting the same movement and reducing undesirable or unnecessary movements that might occur as prime movers contracts  When synergists immobilize a bone or a muscle’s origin it is called a fixator  Muscles that help to maintain upright posture are called fixators  Prime movers tend to get all the credit for causing certain movements  The action of antagonists and synergists muscles are important in effecting smooth, co-ordinated and precise movements  Every muscle is attached to bone or other connective tissue at least two points  Origin = attached to the immovable bone  Insertion = attached to the movable bone  During contractions insertion moves toward the origin  Body movements occur when muscles contract across joints  The type of movement depends on the mobility of the joint and where the muscles are located in relationship to the joint  Most obvious are the freely movable joints of the limbs  Less movable joints are also tugged into motion by the muscles (side to side movement of the vertebrae) JAW  closure is the work of the masseter and temporalis muscles NECK  Flexion / sternocleidomastoid  Extension / trapezius SHOULDER  Fixation / serratus anterior  Abduction / deltoid  Adduction / pectoralis major  Flexion / deltoid and pectoralis major The Muscular System  Extension / lattisimus dorsi ELBOW  Flexion / biceps brachii  Extension / triceps brachii WRIST  Flexion / anterior forearm muscles  Extension / posterior forearm muscles HIP  Fixator / gluteus medius and minimus  Abduction / gluteus medius and minimus  Adduction / adductor muscles  Flexion / iliopsoas  Extension / gluteus maximus KNEE  Flexion / hamstring  Extension / quadriceps ANKLE  Plantar flexion / posterior lower leg  Dorsiflexion / anterior lower leg LOCATE AND DESCRIBE THE ORGANIZATION OF THE GLUTEAL MUSCLES. GLUTEUS MAXIMUS  Longest and most superficial  Forms the bulk of the buttock  Thick coarse fibres  Important site for intramuscular injections GLUTEUS MEDIUS  Thick large muscles  Covered by the maximus  Sandwiched between the maximus and the minimus GLUTEUS MINMUS  Smallest and deepest  All three layered create the strength of the buttock  Maximus – thigh extension  Medius / minimus = thigh abduction LOCATE AND DESCRIBE THE STRUCTURE AND EXPLAIN THE MAJOR FUNCTIONS OF THE DIAPHRAGM.  Definition: a sheet like structure largely composed of skeletal muscle and connective tissue that separates thoracic and abdominal cavities. The Muscular System  Muscle fibres within the diaphragm are stimulated to contract by impulses automatically from the diaphragm – phrenic nerve  The diaphragm moves downward, increasing the size of the thoracic cavity  During relaxation the diaphragm springs upward forcing air out of the lungs / assisting in expiration DEFINE THE TERM HIATUS AND EXPLAIN ITS RELATIONSHIP TO THE DIAPHRAGM.  Hiatus = opening  Esophageal hiatus is the opening in the diaphragm for passage of the esophagus / vena cava / aorta DESCRIBE THE BASIC ORGANIZATION OF THE ABDOMINAL MUSCLES.  Broad flattened muscles in layers  Posteriorly connect to the ribs and vertebral column  Anteriorly to the linea alba (connective tissue) which extends from the xyphoid process to the symphysis pubis  Collectively the contraction of this muscle group, decreasing the size of the abdominal cavity and increasing pressure inside  This action assists in many physiological functions:  Expiration of air from the lungs  Defecation  Urination  Vomiting  Childbirth DESCRIBE THE LOCATION AND THE FUNCTION OF THE INGUINAL CANALS.  Bilateral areas in the groin  Inguinal canals form during development  Two months before birth the testes begin their descent through the inguinal canals / a slanting passage way through the oblique muscles of the inferior abdominal walls into the scrotum  Link the scrotal cavities to the peritoneal cavity / nerves and blood vessels pass through  In normal adult males the inguinal canals are closed  The spermatic cords present do create weak points in the abdominal wall musculature that remain throughout life  A common spot for hernias in men  In females these canals are very small and contain nerves and the round ligaments of the uterus  This structure maintains the strength of the abdominal wall and hernias are much less likely / rare The Muscular System LOCATE AND DESCRIBE THE MUSCLES OF THE PELVIC FLOOR, IDENTIFY THE STRUCTURES THAT PIERCE IT AND EXPLAIN THEIR IMPORTANCE.  Compare the male to the female  Various muscles support the pelvic viscera  Muscles involved: levator ani, superficial transverse perinea, bulbospongiosus, ischiocavernosus  Paired levator ani assist in forming the funnel shaped pelvic floor or pelvic diaphragm / weakens with age and childbirth  These muscles close the inferior outlet of the pelvis  Supports and elevates the pelvic floor and function as an antagonist to increase abdominal pressure  The pelvic diaphragm is pierced by the rectum and the urethra along with the vagina in the female  The ischiocavernosus and bulbospongiosus help to maintain erection of the penis and clitoris