Anatomy 1.5 Muscle and Nervous Tissue

Anatomy Subject: Date: Muscle & Nervous Tissue Title: Lecturer: Roberto SJ. Tan, M.D., FPPS. Sem/ A.Y.: Transcribers: Cabello R., Cacapit J., Cachero B., Cacuyog J., Cafugauan E., Cai, C. Trans Subject Head: Jacinto, C. (09157536686 | [email protected])

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I. OUTLINE Muscle Tissue a. Muscle i. Terminologies ii. Classification of Muscle Tissue b. Types of Muscle Tissues i. Skeletal Muscle 1. Organization of Skeletal Muscle 2. Organization of Skeletal Muscle Fibers 3. Structural Organization of Myofibrils ii. Cardiac Muscle 1. Structure and Function 2. 3 Main Junctional Specializations iii. Smooth Muscle c. Organelles d. Motor End Plate e. Muscle Tissue Regeneration Nervous Tissue a. Nervous System and Its Development b. Cells in the Nervous System i. Neuron 1, Parts of a Neuron 2. Classification of Neurons 3. Synapse ii. Neuroglial cells 1. Astrocytes 2. Schwann Cells 3. Oligodendrocytes 4. Microglia 5. Ependymal Cells c. Nerve Regeneration i. Nerve Regeneration: CNS ii. Nerve Regeneration: Peripheral Nerve Fiber iii. Unsuccessful Nerve Regeneration II. OBJECTIVES Muscle Tissue a. Enumerate the characteristics and functions of each type of muscle tissue b. Classify muscle tissue based on morphology and function c. Differentiate the 3 types of muscle tissue under light microscopy d. Describe the structure of a sarcomere e. Explain the regenerative capabilities of muscle tissue Nervous Tissue a. Show the general organization of the nerve cell b. Identify the parts of a neuron under light microscopy c. Classify neurons based on the number of processes, shape, size, and function d. Describe the formation, structure and function of the myelin sheath e. Classify synapses based on their ultrastructure f. Classify the different nerve endings in the body g. Identify the neuroglia and differentiate each as to morphology, origin, distribution in the CNS, and function h. Describe the regenerative capabilities of nervous tissue

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June 25, 2014 1st/A.Y. 2014-2015

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MUSCLE & NERVOUS TISSUE A. MUSCLE TISSUE

a. Muscle  Responsible for the MOST TYPES OF BODY MOVEMENT  Made up of groups of elongated muscle cells with filaments  ORIGIN: MESODERMAL  Differentiation - gradual process of lengthening, with synthesis of myofibrillar proteins (maturation process) Terminologies  Sarcolemma – cell membrane  Sarcoplasm – cytoplasm of muscle cells  Sarcoplasmic reticulum – smooth endoplasmic reticulum (ER) of muscle cells  Sarcosome – specialized mitochondria  Sarcomere – found in striated muscle fibers; considered as the functional unit Classification of Muscle Tissue According to MORPHOLOGY  Smooth – has no striations; located in the walls of blood vessels, viscera (organs), and dermis of skin  Striated – display characteristic alternations of dark and light bands According to FUNCTION  Voluntary – has conscious control or action  Involuntary – has NO conscious control or action

Figure 1: Types of Muscles b. Types of Muscle Tissue Skeletal Muscle  Long muscle fibers (up to 30 cm); Dm: 10-100um  Cylindrical and multinucleated cells with oval nuclei found at periphery of cell, under the cell membrane  Striated and pink to red in color due to rich vascular supply and presence of myoglobin

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ANATOMY 1.5: Muscle & Nervous Tissue Organization of Skeletal Muscle

Structural Organization of Myofibrils

Figure 2: Organization of Skeletal Muscle Fibers arranged regularly:  Epimysium  dense irregular CT (fascia)  Perimysium  (invagination – Ms bundles)  Endomysium  delicate CT Figure 4: Schematic Diagram of Muscle Fiber Structure Organization of Skeletal Muscle Fibers 4 Muscle Proteins  Actin  thin filament;  2 strands of globular G-actin monomers in double helical formation;  contains binding site for myosin  Myosin  2 heavy and 2 light chains;  heavy chains contain ATP binding site  Troponin  Tropomyosin Figure 3: Myofibril schematic diagram 

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A Band  Anisotropic  Dark areas in the center of sarcomeres I Band  Isotropic  Light areas on either side of Z disk H Band  Pale area; center of A band Z line/disk  Center of adjacent sarcomere  Passes through center of each I band, to which thin filaments are attached Sarcomere: Smallest contractile unit (Z line – Z line)

The sliding filament mechanism of muscle contraction  2 Z disks are brought closer together as thin filaments are brought together as thin filaments slide past the thick filaments Morphological Changes in Sarcomere during Muscle Contraction  I band  narrower  H band  extinguished  Z disks move closer together  A band  unaltered Cardiac Muscle    

85-100μm (mature); 15μm in diameter Cross striated banding pattern(branching) 1 or 2 centrally located pale-staining nuclei Endomysial CT with rich capillary network

Structure and Function  Diads – 1 T-tubule  1 sarcoplasmic reticulum cisternae  Numerous mitochondria  occupies 40% or more of the cytoplasmic volume  Intercalated disk  represent junctional complexes between adjacent cardiac muscle cells 3 Main Junctional Specializations  Fasciae adherentes  most prominent found in transverse portions, serves as anchoring sites for actin filaments of terminal sarcomeres  Maculae adherentes (desmosomes)  found in transverse portions, bind cardiac cells together to prevent their pulling apart under constant contractile activity

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ANATOMY 1.5: Muscle & Nervous Tissue  Gap Junction  found in lateral portions, provide ionic continuity between adjacent cells Smooth Muscle  Elongated non-stiated spindle shaped cells – fusiform (largest at midpoint & taper towards ends)  Length: 20μm (small blood vessels) & 500μm (pregnant uterus)  Centrally-located, cigar-shaped nucleus Table 1: Summary of the morphology of the 3 types of muscle tissue Skeletal Muscle

Cardiac Muscle

Mutinucleated

UniMultinucleated

Striated Nucleus Periphery Oval Nucleus

Smooth Muscle or

Striated at

Centrally Nucleus

Skeletal Muscle

d. Motor End Plate

Uninucleated Unstriated

Located

Shaped

Voluntary

 Mitochondria  Membrane-enclosed organelles with enzyme arrays specialized for aerobic respiration and production of Adenosine triphosphate (ATP).  Considered as the powerhouse of the cell  Sarcoplasmic Reticulum  Branching network of SER – cisternae (end)  keeps the Calcium ions, sequestration and release of Ca+  Transverse tubules  Finger – like invaginations of sarcolemma, regulation of Calcium influx/efflux and propagation of depolarization signals (deepest region in the muscle tissue); penetrates deep so that Ca+ distribution is uniform

Involuntary Cardiac Muscle

Centrally Nucleus Cigar Nucleus

Located Shaped

Involuntary Smooth Muscle

Figure 7: Micrograph of muscular innervation (legend: MEP-Motor End Plate, S- Striated Muscle Fiber, NB – Nerve Bundle  Myoneural junction  Branching myelinated motor nerves – “dilated termination”  Neuromuscular Spindle

Figure 5: Muscle tissues under light microscopy. Table 2: Comparison of sarcoplasmic reticulum in muscle types

Figure 8: Micrograph showing the Neuromuscular Spindle c. Organelles

 Receptor for proprioception (sense of position)  1.5 mm long with CT – fluid-filled space with -20 myofibers; “intrafusal fibers” (encapsulated) e. Muscle Tissue Regeneration  Skeletal Muscle- can regenerate when tissues are damaged; satellite cells found at the basal lamina divides and the cells fuse with existing muscle fibers to regenerate and repair the damaged fibers  Smooth Muscle- greatest capacity to divide; smooth muscle cells can undergo mitotic division  Cardiac Muscles- cannot regenerate; absence of stem cells or satellite cells B.

Figure 6: Organelles in Muscle Fiber

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NERVOUS TISSUE

a. Nervous System  composed of a network of billions of nerve cells (neurons) assisted by glial cells CABELLO, CACAPIT, CACHERO, CACUYOG, CAFUGAUAN, C AI

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ANATOMY 1.5: Muscle & Nervous Tissue Development of Nervous Tissues

Ectoderm

Neuroepithelium

Neural Plate

Neural Groove

Neural Tube Figure 9: Embryonic development of neural tube (which gives rise to the neurons, neuroglia, ependyma and choroid plexus). b. Cells in the Nervous System Neurons  functional structural unit of a nervous tissue  Functions: receptive, integrative, and motor function  5 to 150 μm in diameter Parts of a Neuron

 Polygonal with concave surfaces between many cell processes in CNS while in the dorsal root ganglia (in PNS), they have a round cell body from which only 1 process exits.  Nucleus  Large, spherical to ovoid, centrally located  Nucleolus prominent  Contains finely dispersed chromatin (may appear “vesicular”)  Cytoplasm  with abundant RER  contains Nissl bodies stacked with RER cisternae and polyribosomes seen as clumps of basophilic material  represent sites for protein synthesis  Smooth Endoplasmic Reticulum (SER)  abundant, extends into the axons and dendrites  Golgi Complex  located ONLY in the soma  consists of multiple parallel arrays of smooth cisternae arranged around the periphery of the nucleus  responsible for packaging of neurotransmitter substances  Mitochondria  found in soma, dendrites & axon  most abundant in axon terminals  more slender  constantly moving along microtubules in the cytoplasm  Centriole  characteristic of preneuronal multiplying cells during embryonic development  only occasionally encountered in adult neurons  believed to be vestigial structures (because neurons do not undergo mitosis) Inclusions  Melanin  coarse, dark-brown/black granules found in some regions of the CNS and sympathetic ganglia (PNS)  Lipofuscin  golden-brown granules  irregularly shaped  remnants of lysosomal enzymatic activity which increase with age  Lipid droplet  result of faulty metabolism  Secretory granules  contains signalling molecules and are found in neurosecretory cells Cytoskeletal components  Microtubules  Neurofilaments  Microfilaments  Neurofibrils

 Dendrites  Cell body projections    

Figure 10: Schematic Diagram of a Neuron  Cell Body/Perikaryon/Soma  Central portion which contains the nucleus and perinuclear cytoplasm

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With abundant mitochondria RECEIVES stimuli from sensory cells, axons and other neurons impulse received are transmitted towards soma Dendrite branching pattern—permits a neuron to receive & integrate multiple impulses  Some have spines (permits dendrites to form synapses with other neurons)  Sometimes contain vesicles & transmit impulses to other dendrites

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ANATOMY 1.5: Muscle & Nervous Tissue Table 3: Summary of Perikaryon parts Cell Body/ Perikaryon/ Soma Description and function/s  Large, spherical to ovoid, centrally located  (CNS) Polygonal with concave surfaces bet. many cell processes Nucleus  (DRG in PNS) Round with only 1 process exit  Nucleolus prominent  With finely dispersed chromatin  With abundant RER, Nissl Cytoplasm bodies and polyribosomes; site for protein synthesis  Abundant and extends into SER axon and dendrites  ONLY in the soma  With multiple parallel arrays of smooth cisternae at the Golgi complex nucleus’ periphery  Site for neurotransmitter substance packaging  Most abundant in axon terminal but found in the Mitochondria soma, dendrites and axon  Slender and constantly moving across cytoplasm  Unique in preneuronal Centriole multiplying cells (embryonic dev’t)  Microtubules – essential for transport of vesicles and organelles (soma and axon)  Neurofilaments – abundant in soma and cell processes Cytoskeletal  Microfilaments – composed components of 2 strands of polymeryzed G-actin (helical)  Neurofibrils – possibly represent clumped bundles of neurofilaments

 Nerve fiber – axon + certain sheaths of ectodermal origin  Synapse – region where impulses can be transmitted between cells Myelin Sheath  Fatlike substance covering axons  concentric layers of mixed lipids alternating with thin layers of the protein neurokeratin  associated only with axons  Unmyelinated Axons  Myelinated Axons  Produced by Oligodendrocytes (CNS), Schwann cells (PNS) Structure of Myelin Sheath  Nodes of Ranvier  sites of discontinuity between successive Schwann cells along the axon  Internodal segments  consists of a singular Schwann cell & its concentric lamellae of myelin around the axon  delineated by successive nodes of Ranvier  Incisure of Schmidt-Lantermann  aligned sites of local separation of the myelin lamellae by residues of cytoplasm trapped in the spiral structure Functions of the Myelin Sheath  Increases the speed of conduction from 1 m/s in slender unmyelinated axons to 120 m/s in heavily myelinated axons of large calibre  Serves as a high-resistance low-capacitance insulator  Role in nutrition of the axon  Protective role assuring continuing conductivity Mechanism of Myelination  Schwann cells or oligodendrocytes concentrically wrap its membrane around the axons to form the myelin sheath  Wrapping may continue for more than 50 turns  Cytoplasm is squeezed back into the body of the cell bringing the cytoplasmic surfaces of the membranes in contact with each other forming the major dense line that spirals through the myelin sheath  Peripheral Nerve Sheaths

 Axon  Axis cylinder with varying diameter  Usually very long processes (may be up to 100cm in length) with only 1 axon per neuron.  Conducts impulses AWAY from the soma to other neurons, muscles or glands (Impulse conduction) Axonal transport  Crucial to trophic relationships  Interruptions lead to atrophy of target cells  Anterograde: soma to axon terminal; via kinesin  Retrograde: axon terminal to soma; via dynein  Pathway followed by toxins and neurotropic viruses to penetrate and invade the CNS Parts of the axon  Axolemma – cell membrane  Axoplasm – axon cytoplasm  Axon hillock – where axon arises; absent RER  Collateral branches  Axon terminal

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Figure 11: Micrograph of Peripheral Nerve Sheaths  Epineurium  envelops the nerve & sends extensions into it to surround the separate nerve fascicles w/in it  outermost sheath  thick & strong investment composed of dense irregular connective tissue  associated with adipose tissue in larger nerve

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ANATOMY 1.5: Muscle & Nervous Tissue  Perineurium  covers each bundle of nerve fiber (fascicle)  consists of dense CT, of a few to several layers of flattened epithelium-like cells bounded both internally & externally by a basal lamina  barrier to passage of particulate tracers, dye molecules/toxins into the endoneurium, thus protecting the perineural compartment  Endoneurium  surround individual nerve fibers (axons)  delicate, loose connective tissue consisting of small fibrils of collagen, fibroblasts, fixed macrophages, capillaries, perivascular mast cells, & EC fluid  thin layer of reticular fibers produced by Schwann cells Classification of Neurons

 Originates in the CNS and transmits impulses to effector organs throughout the body such as muscle fibers, exocrine and endocrine glands  Interneurons  Located completely in the Central Nervous System or function as interconnectors or integrators that established According to SIZE  Golgi Type I  Very long axons that originate from neurons in the motor nuclei of the CNS  Example: Purkinje cells of cerebellum  Golgi Type II  Very short axons  Interneurons of the CNS  Example: granule cells of cerebellum

According to MORPHOLOGY (No. of processes)

Figure 12: Schematic Diagram of Neuron Morphological Types  Bipolar  Possess 2 processes emanating from the soma, a single dendrite and a single axon  Found in the vestibular, cochlear, ganglia, olfactory epithelium of the nasal cavity, inner nuclear layer of retina; where they serve the senses of sight, smell and balance  Pseudounipolar  Present in the dorsal root ganglia and the ganglia of some cranial nerves  single process (axon) leaves body then bifurcates  Peripheral branch  proceeds to its destination in the body  Central  enters the CNS  Multipolar  Various arrangements of multiple dendrites emanating from soma and a single axon  Most common and possess various arrangement of multiple dendrites emanating from the soma and a single axon  Mostly motor neurons, in ventral horn of spinal cord  Some are named according morphology (e.g. Pyramidal cells )  Unipolar  Possess only one process that bifurcates close to the perikaryon, with the long branch extending to a peripheral ending and other toward the CNS  exists in early embryonic life

Figure 13: Micrograph of Golgi type I and II cells (legend: P = Purkinje cells (Golgi Type I), Gr = Granule cells (Golgi Type II) According to SHAPE  Stellate – star-shaped  Pyramidal

Figure 14: Stellate Neuron Micrograph (DS = dendritic spines)

According to FUNCTION  Sensory or Afferent Neurons  Receives and transmits impulses to CNS for processing  Motor or Efferent Neurons

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ANATOMY 1.5: Muscle & Nervous Tissue Types of a Chemical Synapse  Axodendritic- axon synapses with a dendrite  Axosomatic- axon synapses with a cell body  Axoaxonic - axon synapses with another axon  dendrodentritic  somatodendritic  somatosomatic  somatoaxonic  dendroaxonic  axoaxodendritic

Figure 15: Pyramidal Neuron in the Cerebrum (Micrograph) Synapse  Site of transmission of nerve impulses  Point of contact of a neuron & another cell  Allows neurons to communicate with each other or with effector cells (muscle & gland) Types of Synapses  Electrical  Uncommon  Few places in the brain, retina and cerebral cortex  Rapid transmission  Transmit impulse via gap junctions that cross pre- and postsynaptic membranes  Thereby conducting neuronal signal directly  Ions pass freely through these gap junctions  Prominent in cardiac & smooth muscles  Chemical  release of neurotransmitters at axon terminal Components of a Synapse  Presynaptic membrane  production of neurotransmitters  Area where electrical signal (impulse) is converted into a chemical signal  Synaptic cleft  Gap between pre- and postsynaptic membranes  Small gap between that separates the pre- & postsynaptic membranes (12-20 nm)  May contain polysaccharides & some fine intersynaptic filaments  Postsynaptic membrane  Presynaptic neuron  neuron that transmits the impulse  Postsynaptic cell  cell that receives the impulse (neuron, muscle or gl.)  Bouton  expanded portion of the process that is involved in the formation of a synapse  Presynaptic axon terminal (Terminal Bouton) from which neurotransmitter is released  Synaptic vesicles  contain chemical neurotransmitters, fill the bouton

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Classification of Nerve Endings  Sensory receptors  Free (non-encapsulated)  no connective tissue  high amount in the body  For touch, heat and cold sensation  Encapsulated  e.g. Vater Pacinian corpuscle (in hypodermis)  pressure, concentric layer of lamellae. Vibration  e.g. Meissner’s corpuscle  touch, located in dermal papillae  e.g. neuromuscular spindle and golgi tendon organ for proprioception  located at deeper dermis (hypodermis)  Chemoreceptors  Baroreceptors  detect pressure changes  Receptor for special senses  rods and cones: for vision  organ of Corti: for hearing  Efferent Nerve Endings  Somatic: motor end plate  Visceral: in smooth muscle, cardiac muscle, glands b. Neuroglial Cells Astrocytes  Largest and most numerous  Star shaped with numerous branching processes  Bundles of intermediate filaments made of glial fibrillary acid that reinforces structure  Binds neurons to capillaries and pia mater 2 Types of Astrocytes

Figure 17: Schematic Diagram of Astrocyte Types  Protoplasmic  Many and short branching processes  Found in gray matter  Large ,spherical and pale staining nucleus  Abundant cytoplasm  Fibrous  Few, long and unbranched processes  Found in white matter

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ANATOMY 1.5: Muscle & Nervous Tissue  Ovoid nucleus  Euchromatic cytoplasm containing only few organelles, free ribosomes and glycogen Schwann cells  Flattened cells  Few mitochondria  Form myelinated and unmyelinated cover over axons of the PNS Oligodendrocytes  Scanty cytoplasm with smaller ovoid/ spherical nucleus  Fewer and short processes  Located in white matter Microglia  Dense, elongated nuclei  Small cell with short processes  Phagocytic in nature  Involved in inflammation and repair in the adult CNS  Produce and release neutral proteases and oxidative radicals Ependymal cells  Low columnar to cuboidal epithelial cells that line cavities of CNS  Abundant mitochondria and bundles of intermediate filaments  Possess short cytoplasmic processes and microvilli  Some are ciliated for the facilitation of movement of the cerebrospinal fluid (CSF) Table 4: Summary of Neuroglial cells Cells Origin Location    Astrocytes

Neural tube

CNS  

Schwann cells

Neural tube

PNS

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 Oligodendro -cytes

Neural tube

CNS

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Ependymal cell

Neural tube

CNS

Microglia

Mesoderm

CNS

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Principal Functions Structural support Repair processes Regulate constituents of the extracellular environment Metabolic exchanges Myelin production that provides electric insulation One Schwann cell can form myelin around a segment of one axon only Myelin production that provides electric insulation Can serve more than one neuron and its processes Lining cavities of central nervous system Macrophagic activity

c. Nerve Regeneration  Microglia  phagocytose injured cells  Glial scar  hinder repair (this is a permanent process)  Neural Plasticity  Neuronal circuits may reorganize (growth of neural processes) form new connections or synapses  Functional recovery after neuronal injuries.  Stem Cells  New neurons  New astrocytes  Found in ependymal cells  Provide avenue in regeneration of new synapses Nerve Regeneration: CNS  Connective tissue sheaths are absent in the CNS  Injured cells are phagocytosed by special macrophages (microglia)  Space liberated by phagocytosis is occupied by proliferation of glial cells → form cell mass called GLIAL SCAR  Glial cell mass hinder the process of repair thus damage to the CNS may be permanent *Neuroplasticity – after an injury, neuronal circuits may be reorganization by the growth of neuronal processes, forming new connections or synapses. New communications are established with some degree of functional recovery. Nerve Regeneration: Peripheral nerve fiber  Neuron attempts to repair the damage, regenerate process and restore function  Axon reactions are localized in 3 regions:  Site of damage (local changes)  involves repair and removal of debris by neuroglial cells  Distal to the site of damage (anterograde changes)  portion of the axon distal that degenerates due to an injury and is phagocytosed (Wallerian degeneration)  Proximal to the site of damage (retrograde changes)  proximal portion of the injured axon undergoes degeneration followed by sprouting of a new axon whose growth is directed by Schwann cells.  Schwann cells proliferate and produce neutrophins for regenerative purposes. *Some changes occur simultaneously, others weeks or months apart

*Chromatolysis: dissolution of nucleus and RER from the distal injured part of the axon by degradation of macrophages. The proximal of the axon will then continue to repair until it reaches the distal part of the degenerated axon thereby re-establishing the connection. Unsuccessful nerve regeneration  Misalignment of proximal and distal  Complete removal of structure  Leads to shrinking of the nerve fibers  Formation of Neuroma  lump of unsuccessfully regenerated nerve fibers  may produce pain  tumor growing from a nerve or made up largely of nerve cells and nerve fibers

Figure 19: Neuroglial cells

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NOTES: Injured Axons:  After 3 weeks, axon appears smaller, no innervation=ATROPHY  After 3 months, the axon is already healed  Axon: 0.5-3mm/day (peripheral nerve growth after injury)  What happens when the axon doesn’t penetrate the tube? NEUROMA which causes pain. CABELLO, CACAPIT, CACHERO, CACUYOG, CAFUGAUAN, C AI

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ANATOMY 1.5: Muscle & Nervous Tissue IV.

GUIDE QUESTIONS

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True or False? Calcium is the only ion needed for the contraction of muscle tissue. 2. The time interval wherein, immediately after the generation of an action potential, no amount of stimuli will elicit another response/impulse. A. Time lapse limitation B. Impulse-stimuli correspondence C. Absolute refractory period D. Relative refractory period 3. Which of the following is true about axons? A. Nissel bodies are abundant in axon hillock B. Unmyelinated axons in the PNS are enclosed in Schwann cell sheaths C. Axons are immediately surrounded by connective tissue called epineurium Answer Key: 1)False 2) C 3) C V. 

STUDY GUIDES

VERY HELPFUL VIDEO HERE for Peripheral Nerve Regeneration: VI. REFERENCES

Mescher, A.L. (2009). Junquiera’s basic histology: Text & atlas. (12th ed). New York, NY, Mc-Graw Hill Medical. Tan, R. (2014). Muscles and Nervous Tissue [PowerPoint slides].

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