Nervous system Overview ( The master communication system)
Neuron process Cell body nucleus Neuroglia Nerve Tissue
COMPOSITION OF NERVE TISSUE Two principal types of cells, neurons and supporting cells Neuron, or nerve cell, is the functional unit of the nervous system. Specialized to receive stimuli from other cells and to conduct electrical impulses to other parts of the system via their processes. Specialized contacts between neurons for transmission of information from one neuron to the next are called synapses.
Neurons Structure Cell body Nucleus with nucleolus Cytoplasm (perikaryon) Cytoplasmic processes Dendrites Axon Function Conduct electrical impulses
NEURON Human nervous system contains over 100(10) billion neurons. show variation in size and shape, they fall into three general categories, Sensory Interneurons Motor
Neuron Classification
NEURON Sensory neurons impulses from receptors to the CNS. Two types. Somatic afferent fibers convey sensations of pain, temperature, pressure, and touch from the body surface & Pain and proprioception (nonconscious sensation) from organs within the body (e.g., muscles, tendons, and joints). Visceral afferent fibers pain and other sensations from mucous membranes, glands, and blood vessels.. Sensory neurons
NEURON Motor neurons impulses from the CNS or ganglia to effector cells. Two types. Somatic efferent neurons send voluntary impulses to skeletal muscles. Visceral efferent neurons transmit involuntary impulses to smooth muscle, cardiac conducting cells (Purkinje fibers), and glands Motor neurons
Interneurons, (intercalated neurons) form a communicating and integrating network between sensory and motor neurons. More than 99.9% of all neurons belong to this group NEURON DOG Pain Reflex
Components of a typical Spinal nerve
Classification of Neurons (1) by the Number of Processes 1. unipolar neuron 2. pseudounipolar neuron 3. bipolar neuron 4. multipolar neuron 5. Anaxonic neuron (2) by the Length of Axon 1. Golgi type I neuron 2. Golgi type II neuron (3) by the Morphology of Dendrites (Topognostic Value --- description of a special part ) 1. isodendritic neuron ( of equal size and shape) 2. allodendritic neuron ( deviating from normal ) 3. idiodendritic neuron ( related to a particular neuron)
1. unipolar neuron 2. bipolar neuron 3. pseudounipolar neuron 4. multipolar neuron a. axon d. dendrite
Classified on the basis of the number of processes extending from the cell body Multipolar neurons have one axon and two or more dendrites Bipolar neurons have one axon and one dendrite Unipolar (actually pseudounipolar) neurons have one process, the axon, which divides close to the cell body into two long processes. Majority of unipolar neurons are located in the dorsal root ganglia and cranial nerve ganglia. NEURON
NEURON Motor neurons and interneurons are multipolar Direction of impulses is from dendrite to cell body to axon. Dendrites and cell body of multipolar neurons are the receptor portions Axon is the conducting portion of the cell
NEURON Sensory neurons are unipolar Cell body one axonal branch extends to the periphery, and one extends to the CNS Also called pseudounipolar Peripheral process and central process Neuron
Neuroglia Six types of Neuroglial or glial cells 4 in CNS and 2 in the PNS CNS Astrocytes Oligodendrocytes Microglia Ependymal cells PNS Schwann cells Satellite cells
Astrocytes Star cells 20-50% of brain volume! Two types Protoplasmic (grey matter) Fibrous (white matter)
Astrocytes Two types Protoplasmic Astrocytes, located mainly in grey matter of brain, have short, thick processes with many branches, lie around neurons, synaptic areas, and blood vessels. Fibrous Astrocytes, found mainly in white matter and have long, slender processes with few or no branches.
Ependymal Cell The lining epithelium of CNS cavities Cell usually cuboidal epiththal type with few cilia E.M, luminal aspect ependymal cells have numerous microvilli. Help to form choroid plexuses that secrete CSF (CP consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue.)
Ependymal Cells
Oligodendrocyte Occur mainly in two locations: in the grey matter closely associated with the neurons (perineuronal satellite cells), And among bundles of axons in white. matter (interfascicular oligodendrocytes).
Oligodendrocyte Responsible for myelin formation, leaf-like cytoplasmic processes from the bodies of the cells extending to wrap around nerve fibers in a spiral fashion thus serving as Schwann cells in the PNS. Forms myelin sheaths around several adjacent nerve fibers (unlike Schwann cells)
Microglia Small, somewhat elongated cells with short, spiny processes, that contact nearby neurons Few in number, believed to be derived from mesoderm whereas all other types neuroglia are ectodemal. Lie in both white and grey matter, usually near blood vessels. Main source of phagocytic cells in the CNS
Schwann Cell Envelop all nerve fibers of the PNS and extend from their attachment to (entry or exit from) the spinal cord and brain stem almost to their termination. Surround the processes of nerve cells and isolate them from adjacent cells and extracellular matrix.
Schwann Cell Lie end to end in chains along the length of a nerve fiber Show some cytoplasmic interdigitation where two adjacent cells are apposed.
Satellite (Capsular) Cell Neuronal cell bodies of ganglia are surrounded by a layer of small cuboidal or squamous cells called satellite cells.
Satellite (Capsular) Cell Form a complete layer around the cell body, only their nuclei are typically visible in routine H&E preparations In its functional role the satellite cell is analogous to the Schwann cell except that it does not make myelin.
Synapses are specialized junctions between neurons that facilitate transmission of impulses from one (presynaptic) neuron to another (postsynaptic) neuron. Synapses also occur between axons and effector (target) cells, such as muscle and gland cells. A typical chemical synapse contains A presynaptic knob, Synaptic cleft, and Postsynaptic membrane Synapses