Nervous Tissue

Nervous Tissue

1. Neurons

   • connect all regions of the body to the braina nd spinal cord
   • Can reach grat lengths and make very complicated connections with other cells
   • NS provides things such as taste, touch, sensing, thinking, remembering, controlling muscle activity, regulating glandular secretion
   • undergoes mitotic division
   • Possess ELECTRICAL EXCITABILITY (the ability to convert stimulus into an action potential
   • A STIMULUS: is any change in environment that can initiate a action potential
   • ACTION POTENTIAL: is an electrical signal that travels along the surface of the neuron membrane. I MOVES DUE TO THE IONS IN THE IS FLUID AND THE IONS INSIDE THE NEURON.
   • Travel rapidly and at a constant strength 0.5-130m per second
   • Components of a Neuron
     • CELL BODY (SOMA or PERIKARYON): has a nucleus surrounded by cytoplasm that has typical organelles (lysosome, mit and Golgi). ALSO HAVE FREE RIBOSOMES and clusters of Rough ER called NISSL BODIES
       • Proteins produce by the nissl bodies go to repair the damaged axons in PNS, replace cellular components, material for growth of neurons
       • Neurofibrils: made of bundles of Intermediate Filaments that provide cell shape and support
       • Microtubules: assess movement of materials between cell body and the axons
       • Ageing neurons have LIPOFUSCIN: a pigment that occurs in yellow/ brown grandules in cytoplasm, made from lyosomes
     • DENDRITES
       • Are the receivers of chemical messengers as its membrane contain many receptor sites
       • The cytoplasm contains nissl bodies, mit, and other organelles
     • AXONS:
       • Moves nerve impulses towards other neurons (muscle fibre or gland cells)
       • Is long and cylindrical that joins to the cell body by a axon hillock
         • Part closet to the axon hillock is called the INITIAL SEGMENT. The initial segment and axon hillock is called the trigger zone
       • AXON CONTAINS: Mit, microtubules, and neurofibrils. NO ROUGH ER PRESENT MEANS NO PROTEIN SYNTHESIS
       • Cytoplasm is called the AXOPLASM and the plasma membrane is called the AXOMELLA
       • Side branches off the axon are called AXON COLLATERALS. They usually branch off on right angles
       • AXONS END BY DIVIDING INTO FINE PROCESSES CALLED AXON TERMINALS
   • COMMUNICATION BETWEEN 2 NEURONS
     • BETWEEN THE NEURON AND THE EFFECTOR IS CALLED THE SYNAPSE
     • At the end of axon terminals they all have tiny membrane sacs called SYNAPSE VESICLES that store a chemical called neurotransmitter
       • A neurotransmitter is a molecule that excites the or inhibits another neuron. THE SIGNAL THAT IS PASSED BETWEEN THE SPACE
       • A neuron can contain several neurotransmitters, each having DIFFERENT EFFECT ON THE POSTSYNAPTIC CELL
   • CLASSIFICATION
     • UNI POLAR: Have dendrites and ONE AXON THAT IS FUSED TOGETHER to make one continuous string. USUALLY FUNCTION AS SENSORY RECEPTORS- trigger zone is between the dendrites and the axon
     • MULTIPOLAR: Usually have several dendrites and ONE AXON
     • BIPOLAR: Have ONE MAIN DENDRITE and ONE AXON (found in retina of the eye, inner ear)
     • Can also be classified as PURKINJE CELLS: this is a neuron in which ONLY effectors can come from the dendrites and PYRAMIDAL CELLS: is where effectors and neurotransmitters can come and leave in the same dendrites
   • FUNCTIONAL CLASSIFICATION: classified by direction in which nerve pulses are transported with respect to the CNS
     • Afferent neurons (otherwise known as sensory, receptor neurons, and afferent axons), carry nerve impulses from receptors or sense organs toward the CNS
     • MOTOR/EFFERENT NEURONS: carry action potentials away form the CNS to the effectors in the PNS
     • INTERNEURONS OR ASSOCIATION NEURONS: are neurons that forms a connection between 2 or more neurons in order to get the effect to the PNS

2. Neuroglia-make up half the volume of the CNS BUT DO NOT GENERATE OR PROPAGATE ACTION POTENTIALS

   • Are smaller cells than neurons but greatly out number them by 25x
   • FUNCTION: support, nourish and protect neurons, and maintains the interstitial fluid with baths them
   • Can continue to divide in the mature NS
   • ASTROCYTES, OLIGODENDROCYTES, MICROGLIA, EPENDYMAL CELLS ARE FOUND IN THE CNS
     • ASTROCYTES: are star shaped and are the largest and most numerous
       • PROTOPLASMIC ASTROCYTES: have many short branching processes found in grey matter
       • FIBROUS ASTROCYTESS: have many long unbranching processes and is located in white matter
     • OLIGODENDROCYTES: forms and maintains the myelin sheath
     • MICROGILA: are phagocytes
     • EPENDYMAL CELLS: are cuboidal and columnar with cilia and microvilli. WHICH LINE THE VENTRICLES OF THE BRAIN, CENTRAL CANAL AND THE SPINAL CORD, THEY assist the circulation of CF and form a blood-CF barrier
   • SCHWANN CELLS AND SATELITE CELLS ARE FOUND IN THE PNS- completely surround axons and cell bodies
     • SCHWANN CELLS: encircles the axons of the PNS and form myelinated sheath around the axons, but THEY CAN ONLY MYELINATE ONE AXON AT A TIME, BUT THEY CAN ENCLOSE MORE THAN 20 UNMYELINATED AXONS
     • SATELITE CELLS: are flat cells that surround the cell bodies of the PNS and refulate the exchange of matrial between the cellbodies and the IF

3. Both neurons and neuroglia are structured differently depending on whether they're in the CNS or PNS

4. MYELINATION: is when axons are covered in multilayers of lipid and protein covering called myelin sheath. THE SHEATH ELECTRICALLY STIMULATES THE AXON OF THE NEURON WHICH INCREASES THE SPEED OF THE NERVE IMPULSE CONDUCTION

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