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GENERAL ANATOMY-1 Reviewer Muscular System For Dentistry Types of Muscle Tissue
1. Skeletal Muscle - Attaches to and moves skeleton - 40% of body weight - Fibers are multinucleated (formed by fusion of embryonic cells) - Cells show obvious striations - Contractions are voluntary 2. Cardiac Muscle - Found only in the heart wall - Cells are striated - Contractions are involuntary 3. Smooth Muscle - Found in walls of hollow organs - Lacks striations - Contractions are involuntary - Key structures: o Sarcolemma: cell membrane o Sarcoplasm: cytoplasm o Sarcoplasmic reticulum: stores Ca++ Muscle Coverings - Epimysium: surrounds entire muscle - Perimysium: surrounds muscle fascicles - Endomysium: surrounds individual muscle fibers Morphology Comparison Feature Skeletal Muscle Cardiac Muscle Smooth Muscle Shape Cylindrical Branched Cylindrical Fusiform (spindle- shaped) Nucleus Multinucleated (peripheral) Mono/Binucleated (central) Mononucleated (central) Striations Present (+) Present (+) Absent (-)
Feature Skeletal Muscle Cardiac Muscle Smooth Muscle Control Voluntary Involuntary Involuntary Functional Unit Sarcomere Sarcomere Smooth muscle cell Specialized Junctions
- Skeletal Muscle Triad :
- Transverse tubule (T-tubule)
- Two terminal cisternae of sarcoplasmic reticulum
- Cardiac Muscle Diad :
- Transverse tubule (T-tubule)
- One terminal cisterna of sarcoplasmic reticulum
- Smooth Muscle : o No T-tubules o Has sarcoplasmic reticulum Myofilaments
- Actin (thin filaments): F-actin (with binding site), tropomyosin, troponin (I, C, T)
- Myosin (thick filaments): with cross-bridges Neuromuscular Junction (NMJ)
- Motor neurons innervate muscle fibers
- Motor end plate: site of contact
- Neurotransmitter: Acetylcholine
- Acetylcholine binds cholinergic receptors on the motor end plate
- Broken down by acetylcholinesterase
- Motor unit: a motor neuron plus all muscle fibers it controls Sliding Filament Theory of Muscle Contraction
- Stimulus reaches NMJ
- Enters muscle fiber via T-tubule
- Sarcoplasmic reticulum releases Ca++
- Calcium binds troponin on actin
- Tropomyosin moves, exposing binding sites
- Myosin heads attach to actin, causing contraction Cardiac Muscle
Selected Muscle Groups Muscles of Mastication: Masseter, Temporalis, Lateral and Medial Pterygoid Muscles of Facial Expression: (Not listed, but includes orbicularis oris, zygomaticus, etc.) Muscles of Tongue Extraocular Muscles Muscles of Middle Ear: Stapedius, Tensor Tympani Muscles of Pharynx: Superior, Middle, Inferior constrictors, Palatopharyngeus, Salpingopharyngeus, Stylopharyngeus Muscles of Neck: Platysma, Sternocleidomastoid, Scalenes (Anterior, Medius, Posterior), Suprahyoid and Infrahyoid groups Muscles of Thoracic Wall: External and Internal Intercostals, Transversus Thoracis Muscles of Abdominal Wall: External Oblique, Internal Oblique, Transversus Abdominis Muscles of Back: Superficial (trapezius, latissimus dorsi, rhomboids), Intermediate (serratus posterior), Deep (erector spinae, transversospinalis) Muscles of Pelvis: Piriformis, Obturator Internus Appendicular Muscles: Scapulohumeral group (rotator cuff muscles like supraspinatus, infraspinatus etc.), arm, forearm (anterior/posterior), intrinsic hand muscles (thenar, hypothenar) Gluteal Muscles: Gluteus maximus, medius, minimus, lateral rotators Thigh Muscles: Anterior (quadriceps), Medial (adductors), Posterior (hamstrings) Leg Muscles: Anterior, lateral, posterior (superficial and deep) Muscles of Sole: 4 layers including abductor hallucis, lumbricals, interossei Flashcards Q: What are the three types of muscle tissue? A: Skeletal, cardiac, smooth. Q: Which muscle type is voluntary and striated? A: Skeletal muscle. Q: Where is cardiac muscle found? A: Only in the heart wall. Q: What is a motor unit? A: A motor neuron and all the muscle fibers it innervates. Q: What neurotransmitter is released at the neuromuscular junction? A: Acetylcholine. Q: What is the functional unit of skeletal muscle? A: Sarcomere.
Q: What distinguishes smooth muscle from skeletal muscle? A: Smooth muscle lacks striations, has spindle-shaped cells, and contracts involuntarily. Q: What is the sliding filament theory? A: Muscle contraction occurs when myosin cross-bridges attach to actin after calcium exposes binding sites. Q: Name the three layers of connective tissue covering muscles. A: Epimysium, perimysium, endomysium. Q: What are the major muscles of mastication? A: Masseter, temporalis, lateral and medial pterygoid. Q: How do the nuclei differ between skeletal, cardiac, and smooth muscle? A: Skeletal muscle cells are multinucleated with peripheral nuclei; cardiac muscle has 1- 2 centrally located nuclei; smooth muscle has a single central nucleus. Q: Describe the difference between triadic and diadic junctions. A: Triadic junctions (skeletal) have one T-tubule and two terminal cisternae; diadic junctions (cardiac) have one T-tubule and one terminal cisterna. Q: What role does calcium play in muscle contraction? A: Calcium binds to troponin, causing tropomyosin to move and expose myosin binding sites on actin. Q: Explain the difference between isotonic and isometric contractions. A: Isotonic contractions shorten muscle length with constant tension; isometric contractions increase tension without changing muscle length. Q: What is muscle tone and why is it important? A: Muscle tone is the continuous partial contraction of muscles, maintaining posture and readiness for action. Q: Why is the finer control of movement associated with fewer muscle fibers per motor unit? A: Because fewer fibers allow more precise, delicate movements. Q: How do smooth muscle contractions differ from skeletal muscle contractions? A: Smooth muscle contractions are slower, sustained, resistant to fatigue, and can be initiated without nervous input. Q: What are the primary functions of the muscles of the back's deep layer? A: To maintain posture and control the movement of the vertebral column.
