Motor End Plate: Structure and Function
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Questions and Answers

What neurotransmitter is contained within the synaptic vesicles at the motor end plate?

  • Serotonin
  • Dopamine
  • Norepinephrine
  • Acetylcholine (correct)

    • What happens to muscle fibers if the nerve supply to skeletal muscle is cut?

  • The muscle fibers will duplicate.
  • The muscle fibers will hypertrophy.
  • The muscle fibers will remain unchanged.
  • The muscle fibers will atrophy. (correct)

    • What unique structure is found in the cardiac muscle fibers joining them together?

  • Axon terminals
  • Intercalated discs (correct)
  • Synaptic vesicles
  • Sarcolemma folds

    • What structural feature increases surface area in the motor end plate?

    <p>Junctional folds</p> Signup and view all the answers

    Why can't cardiac muscle regenerate?

    <p>Because it lacks stellate cells</p> Signup and view all the answers

    What is a key characteristic of cardiac muscle?

    <p>Joined by intercalated discs</p> Signup and view all the answers

    Which type of muscle is controlled by the autonomic nervous system?

    <p>Smooth muscle</p> Signup and view all the answers

    Why can't cardiac muscle regenerate?

    <p>It lacks stellate cells</p> Signup and view all the answers

    Where is smooth muscle typically found?

    <p>In the walls of viscera</p> Signup and view all the answers

    What structural feature is common in smooth muscle cells?

    <p>Caveolae in the sarcolemma</p> Signup and view all the answers

    What are the two main components of the protoplasm?

    <p>Cytoplasm and nucleus</p> Signup and view all the answers

    Which of the following is classified as a non-membranous organelle?

    <p>Ribosomes</p> Signup and view all the answers

    What is the role of cytoplasmic organelles?

    <p>Involved in metabolism</p> Signup and view all the answers

    Which of the following is a component of the cytoplasm?

    <p>Cytosol</p> Signup and view all the answers

    Which organelle is involved in the structural framework of the cell?

    <p>Cytoskeleton</p> Signup and view all the answers

    Cytoplasmic inclusions are described as being:

    <p>Temporarily seen in the cytoplasm</p> Signup and view all the answers

    Which type of muscle tissue is voluntary and connected to bones for movement?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which of the following is NOT a connective tissue layer of skeletal muscle?

    <p>Myofibril</p> Signup and view all the answers

    What is the function of the sarcoplasmic reticulum in a skeletal muscle cell?

    <p>Storage and release of calcium ions</p> Signup and view all the answers

    Skeletal muscle fibers are characterized by which of the following features?

    <p>Striations and multiple peripheral nuclei</p> Signup and view all the answers

    What are the main components of a myofibril within skeletal muscle fiber?

    <p>Actin and Myosin</p> Signup and view all the answers

    What type of tissue surrounds each individual muscle fiber in skeletal muscle?

    <p>Endomysium</p> Signup and view all the answers

    Where are macro vesicles usually found?

    <p>At the trans face of the Golgi complex</p> Signup and view all the answers

    What is one function of the macro vesicles?

    <p>Processing secretory products</p> Signup and view all the answers

    What can happen to macro vesicles after they contain formed substances?

    <p>They fuse with the cell membrane to discharge contents</p> Signup and view all the answers

    Which type of molecule is formed by adding carbohydrate fractions to proteins?

    <p>Glycoproteins</p> Signup and view all the answers

    What are produced by the macro vesicles besides glycoproteins?

    <p>Complex carbohydrates, mucoproteins, lipoproteins, and relatively pure proteins</p> Signup and view all the answers

    What are the main functions of mitochondria?

    <p>Cell respiration, Protein synthesis by transamination, and Heat production.</p> Signup and view all the answers

    What does the mitochondrial matrix contain?

    <p>Mitogenome, Ribosomes, and Enzymes of the Krebs cycle</p> Signup and view all the answers

    What is the significance of the mitochondrial inner membrane?

    <p>It forms cristae and contains the electron transport chain and ATP synthase.</p> Signup and view all the answers

    Which of the following stains is used for mitochondria?

    <p>Iron-hematoxylin</p> Signup and view all the answers

    Which feature is unique to mitochondrial DNA compared to nuclear DNA?

    <p>Called the mitogenome</p> Signup and view all the answers

    What is the size range of mitochondria?

    <p>0.2 - 5 µm</p> Signup and view all the answers

    Where is the Golgi complex typically positioned in glandular cells?

    <p>At one side of the nucleus (basal or apical)</p> Signup and view all the answers

    How many cisternae typically make up the Golgi complex?

    <p>3-12</p> Signup and view all the answers

    From where do the micro vesicles or transfer vesicles of the Golgi complex arise?

    <p>RER (Rough Endoplasmic Reticulum)</p> Signup and view all the answers

    What is the function of the micro vesicles when they fuse with the immature face of the Golgi complex?

    <p>Discharge contents and expand saccules</p> Signup and view all the answers

    What is the concave face of the Golgi complex known as?

    <p>Trans face</p> Signup and view all the answers

    What variations can be found in the Golgi complex depending upon cell activity?

    <p>Position, size, and shape</p> Signup and view all the answers

    What is the average length of a sarcomere?

    <p>2.5µm</p> Signup and view all the answers

    Which of the following is located in the center of the A band?

    <p>H zone</p> Signup and view all the answers

    What comprises the thin myofilaments?

    <p>Actin filaments, troponin, and tropomyosin</p> Signup and view all the answers

    What is the function of intermediate filaments in muscle fibers?

    <p>To regulate the spacing, attachment, and alignment of myofilaments</p> Signup and view all the answers

    Which part of the sarcomere is formed only of actin filaments?

    <p>I band</p> Signup and view all the answers

    Where is the M line located within a sarcomere?

    <p>Bisecting the H zone</p> Signup and view all the answers

    In which type of cells are smooth endoplasmic reticulum (SER) particularly abundant?

    <p>Leydig cells of testis</p> Signup and view all the answers

    Which of the following is NOT a function of the smooth endoplasmic reticulum?

    <p>Protein synthesis</p> Signup and view all the answers

    What role does the smooth endoplasmic reticulum play in muscle tissue?

    <p>Sequestration of calcium</p> Signup and view all the answers

    Which of the following compounds is synthesized by the smooth endoplasmic reticulum?

    <p>Cholesterol</p> Signup and view all the answers

    In which of the following processes is the smooth endoplasmic reticulum involved in liver cells?

    <p>Detoxification of drugs</p> Signup and view all the answers

    What is a primary function of the ribosomes on the rough endoplasmic reticulum?

    <p>Protein synthesis</p> Signup and view all the answers

    Which of the following is NOT a function of the rough endoplasmic reticulum?

    <p>Carbohydrate metabolism</p> Signup and view all the answers

    What gives the rough endoplasmic reticulum its rough appearance?

    <p>Presence of ribosomes</p> Signup and view all the answers

    How does the rough endoplasmic reticulum protect the cytoplasm?

    <p>By segregating proteolytic enzymes inside the cisternae</p> Signup and view all the answers

    Which of the following is true about some membranes of the rough endoplasmic reticulum?

    <p>They are continuous with the outer nuclear membrane</p> Signup and view all the answers

    Study Notes

    Tissue Types and Functions

    • Motor End Plate:
      • Specialized region of contact between motor nerve fiber and muscle fiber
      • Axon terminal contains numerous mitochondria and synaptic vesicles with acetylcholine (neurotransmitter)
      • Synaptic cleft is the space between the axon terminal and muscle fiber
      • Junctional folds are deep invaginations in the sarcolemma under the synaptic cleft to increase the surface area
      • Muscle fibers depend on the nervous system for their integrity and function
      • Denervation atrophy occurs if the nerve supply to skeletal muscle is cut
    • Cardiac Muscle:
      • Striated muscle of the heart
      • Cardiac muscle fibers are joined to each other by intercalated discs forming branched muscle fibers
      • Cardiac muscle has one or two nuclei centrally located and numerous mitochondria
      • No stellate cells, so unable to regenerate
    • Smooth Muscle:
      • Non-striated and involuntary controlled by autonomic nervous system
      • Found in wall of viscera, each muscle fiber is enclosed by thin basal lamina and fine network of reticular fibers
      • Sarcolemma has numerous caveola, possibly having a role similar to that of striated muscle

    Cytoplasm

    • Gel-like fluid present between the plasma membrane and nucleus of the cell
    • Three main components:
      • Cytoplasmic organelles: involved in metabolism (e.g., mitochondria and endoplasmic reticulum)
      • Cytoplasmic inclusions: small particles seen temporarily in the cytoplasm, may or may not be membrane-bound, metabolically inactive (e.g., lipid droplets, glycogen granules, pigment granules)
      • Cytoskeletons: provide the structural framework to the cell

    Organelles

    • Membranous organelles:
      • Rough endoplasmic reticulum
      • Smooth endoplasmic reticulum
      • Mitochondria
      • Golgi apparatus
      • Lysosome
      • Peroxisome
    • Non-membranous organelles:
      • Ribosomes
      • Cytoskeleton
      • Microtubules
      • Microfilaments
      • Intermediate filaments

    Muscle Types

    • Muscular tissue:
      • Specialized tissue for contractility to produce movement in the organ
      • Divided into three types: skeletal muscle, smooth muscle, and cardiac muscle
    • Skeletal muscle:
      • Attached to bone for movement, voluntary controlled by motor and sensory fibers
      • Formed of cylindrical muscle fibers with uniform thickness, doesn't branch
      • Striated with multiple peripheral nuclei
    • Connective tissue coat of the muscle:
      • Epimysium: thick CT layer surrounds the whole muscle
      • Perimysium: thin CT layer surrounds each individual muscle
      • Endomysium: delicate CT surrounds each individual muscle fiber, consists of basal lamina synthesized by muscle fiber and reticular fibers and fibroblast

    EM Structure of Skeletal Muscle

    • Muscle filled with long striated myofibrils
    • Myofibril is a bundle of myofilaments
    • Two types of myofilaments: actin and myosin
    • Muscle fibers are rich in mitochondria, SR (Sarcoplasmic reticulum), glycogen, myoglobin, Golgi complex

    Sarcomere

    • Structural and functional unit of a myofibril
    • Formed by overlapping actin and myosin filaments
    • Segment between two Z-lines, with an average length of 2.5µm
    • Composed of a dark A band, which is intermediate between two light I bands
    • A band is formed of myosin filaments with overlapping portions of actin filaments
    • I band consists of actin filaments that do not overlap with myosin
    • In the center of the A band, the H zone consists of only myosin
    • H zone is bisected by the M line, the site of connection between myosin filaments

    Mitochondria

    • Ovoid-shaped structures, about 0.2-5µm in size, bound by a phospholipid bilayer membrane
    • Outer membrane is smooth and encloses the entire organelle
    • Inner membrane is folded to form cristae
    • Matrix space is filled with mitochondrial matrix, containing matrix granules, rich in cations such as Ca and Mg
    • Functions: cell respiration, absorption and secretion processes, protein synthesis, lipid metabolism, heat production, and calcium storage

    Golgi Complex

    • Present in nearly all cells, variable in position and size
    • Consists of three components: flattened vesicles or cisternae, microvesicles or transfer vesicles, and macrovesicles or secretory vacuoles
    • Functions: processing, modifying, and packaging of secretory products, addition of carbohydrate fractions to proteins, production of complex carbohydrates, mucoproteins, lipoproteins, and relatively pure proteins

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    Description

    Learn about the motor end plate, a specialized region of contact between motor nerve fibers and muscle fibers, and its role in muscle contraction.

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