Muscular System Lesson PDF

10/12/2023 MUSCULAR SYSTEM CHAPTER 6 1 The Muscular System  Muscles are responsible for all types of body movement  Three basic muscle types are found in the body  Skeletal muscle  Cardiac muscle  Smooth muscle 2 1 10/12/2023 3 Smooth Muscle Characteristics  Spindle-shaped cells  Invo...

10/12/2023 MUSCULAR SYSTEM CHAPTER 6 1 The Muscular System  Muscles are responsible for all types of body movement  Three basic muscle types are found in the body  Skeletal muscle  Cardiac muscle  Smooth muscle 2 1 10/12/2023 3 Smooth Muscle Characteristics  Spindle-shaped cells  Involuntary – no conscious control  Found mainly in the walls of hollow organs  Arranged in layers (often one circular and one longitudinal) 4 2 10/12/2023 5 6 3 10/12/2023 Cardiac Muscle Characteristics  Joined to another muscle cell at an  Involuntary  Found only in the heart  Arranged in spiral bundles 7 8 4 10/12/2023 SKELETAL MUSCLE CHARACTERISTICS  Large, cigar shaped cells  Largest of all muscle fibers  Respond to voluntary AND involuntary control 9 Function of Muscles  Produce movement  Maintain posture  Stabilize joints  Generate heat 10 5 10/12/2023 11  Each muscle fiber (cell) is wrapped in endomysium.  Clusters of muscle fibers called fasiculi are wrapped in perimysium  Bundles of fasiculi called whole muscle are wrapped in epimysium  A Tendon is the continuation of epimysium beyond the muscle, where it joins with a bone ANATOMY OF SKELETAL MUSCLE 12 6 10/12/2023 13 MUSCLE CELL ANATOMY  Plasma membrane =  Nucleus =  Endoplasmic Reticulum =  Organelles = 14 7 10/12/2023 15 SARCOPLASMIC RETICULUM: A specialized organelle that surrounds each myofibril. Stores and releases Calcium SARCOLEMMA: The plasma membrane of muscle cells 16 8 10/12/2023  Each muscle fiber is made up of myofibrils  Each myofibril is divided into sarcomeres  Sarcomeres contain myofilaments which are necessary for muscle contraction  Myofilaments are proteins actin & myosin MICROSCOPIC ANATOMY OF SKELETAL MUSCLE 17 Muscle fiber or cell Myofibril 18 9 10/12/2023 Sarcomere Myofilaments within the sarcomere 19 Properties of Skeletal Muscle Activity  Irritability – the ability to receive stimulation and respond to stimulus  Contractility – the ability to shorten when an adequate stimulus is received 20 10 10/12/2023  Skeletal muscles must be stimulated by a nerve to contract  Motor unit:  One neuron +  Muscle cells stimulated by that neuron 21 NERVE-MUSCLE COMMUNICATION ANATOMY  NEURON: one nerve cell Cell body (at the spinal cord end) Axon Axon Terminals 22 11 10/12/2023 23 NERVE-MUSCLE COMMUNICATION ANATOMY  NEUROMUSCULAR JUNCTION  Area of communication between the nerve and the muscle fiber  SYNAPTIC CLEFT  Fluid filled space between the end of the nerve and the muscle 24 12 10/12/2023 25 Nerve Stimulus to Muscles  Neuromuscular junctions – meeting place of nerve and muscle  Neurotransmitter – chemical released by nerve upon arrival of nerve impulse  The neurotransmitter for skeletal muscle is acetylcholine (Ach) 26 13 10/12/2023 Nerve Stimulus to Muscles 27 Transmission of Nerve Impulse to Muscle  Arrival of message causes the sarcolemma to temporarily let in Sodium  Sodium rushes into the cell generating an action potential  Once started, muscle contraction cannot be stopped (all-or-nothing) 28 14 10/12/2023 29 30 15 10/12/2023 SO HOW DOES THE MUSCLE CONTRACT? 31 SLIDING FILAMENT THEORY  Na+ causes Ca++ to be released from the intracellular storage sites.  Ca++ causes proteins on ACTIN (thin filament) to change shape & position  Myosin heads attach to the vacated binding sites  Myosin heads pop forward toward the center of the sarcomere dragging the ACTIN with it  ATP is required to re-set the heads 32 16 10/12/2023 The Sliding Filament Theory 33 Contraction of a Skeletal Muscle  Muscle fiber contraction is “all or none”  Within a skeletal muscle, not all fibers need to be stimulated during the same interval  Different combinations of muscle fiber contractions may give differing responses  Graded responses = different degrees of skeletal muscle shortening 34 17 10/12/2023 Types of Graded Responses  Twitch - Single, brief contraction  Tetanus (summing of contractions)  One contraction is immediately followed by another  Unfused (incomplete) tetanus  Some relaxation occurs between contractions  Fused (complete) tetanus  No evidence of relaxation before the following contractions  The result is a sustained muscle contraction 35 36 18 10/12/2023 Muscle Response to Strong Stimuli  Muscle force depends upon the number of fibers stimulated  More fibers contracting results in greater muscle tension  Muscles can continue to contract until they run out of energy 37 ENERGY  The body’s usable form is ATP  Adenosine Tri-Phosphate  ATP = ADP + P + usable energy 38 19 10/12/2023 Energy for Muscle Contraction  Initially, muscles use stored ATP for energy  Bonds of ATP are broken to release energy  Only 4-6 seconds worth of ATP is stored by muscles  After this initial time, other pathways must be utilized to produce ATP 39 40 20 10/12/2023 MAKING ENERGY FOR MUSCLE CONTRACTION  ATP= ADP + P + energy + heat loss  Creatine Phosphate + ADP = ATP, then  Aerobic respiration = lots of ATP  Made from complete breakdown of glucose  takes a while to make  Anaerobic respiration = small amount of ATP  Made from incomplete breakdown of glucose  makes it quickly  Causes a build up lactic acid 41 42 21 10/12/2023 MUSCLE CONTRACTION  Muscle fatigue –  occurs after prolonged physical activity  Muscle cells are depleted of oxygen  ATP is running low  Lactic acid is building up 43 Types of Muscle Contractions  Isotonic contractions  Myofilaments are able to slide past each other during contractions  The muscle shortens  Isometric contractions  Tension in the muscles increases  The muscle is unable to shorten 44 22 10/12/2023 Muscle Tone  Some fibers are contracted even in a relaxed muscle  Different fibers contract at different times to provide muscle tone  The process of stimulating various fibers is under involuntary control 45 Muscles and Body Movements Muscles are attached to at least two points Origin – attachment to an immovable bone Insertion – attachment to a moveable bone 46 23 10/12/2023 47 5 GOLDEN RULES 1) Muscles cross a joint (few exceptions) 2) Bulk lies proximal to joint 3) All have at least 2 attachments 4) Can ONLY pull 5) When contracting, insertion moves toward origin 48 24 10/12/2023 Types of Body Movements  Flexion & Extension  Rotation & circumduction  Abduction & adduction  Pronation & supination  Inversion & eversion  Dorsiflexion & plantar flexion  Hyperextension 49 Types of Muscles  Prime Mover – muscle with the major responsibility for a certain movement  Antagonist – muscle that opposes or reverses a prime mover  Synergist – muscle that aids a prime mover in a movement and helps prevent rotation  Fixator – stabilizes the origin of a prime mover 50 25 10/12/2023 Naming of Skeletal Muscles  Direction of muscle fibers  Example: rectus (straight)  Relative size of the muscle  Example: maximus (largest)  Location of the muscle  Example: many muscles are named for bones (e.g., temporalis)  Number of origins  Example: triceps (three heads) 51 52 26 10/12/2023 SPECIFIC MUSCLES  Frontalis  deltoid  orbicularis oris  Triceps brachii  orbicularis oculi  external oblique  buccinator  internal oblique  masseter  transverse abdominus  temporalis  rectus abdominus  trapezius  intercostal muscles  pectoralis major  diaphragm  latissimus dorsi  gluteal group  sternocleidomastoid  quadriceps  biceps brachii  hamstrings 53  gastrocnemus 27