Nervous tissue. Department of Histology and Embryology Medical college in Three Gorges University. Content. Neuron Synapses Neuroglia Nerve fiber Nerve ending. Outline. More pay attention to the microstructure of neuron and its classification
Nervous tissue Department of Histology and Embryology Medical college in Three Gorges University
Content • Neuron • Synapses • Neuroglia • Nerve fiber • Nerve ending
Outline • More pay attention to the microstructure of neuron and its classification • Master the microstructure of the synapses • Know the micrograph and function of glia • Familiar the microstructure of nerve fiber
Nervous tissue is composed of nerve cells and neuroglia. The specialized cells that constitute the functional units of the nervous system are called neurons. The function of neuron:generate nerve impulses in response to stimuli and transmit them along cellular processes.
Neuroglia or glia: neurons are supported by a special kind of connective tissue within the brain and spinal cord, that is called neuroglia,it also located in the PNS. Function: support, protect, connect
Nervous system Brain and spinal cord Central nervous system Peripheral nervous system The nervesand their associated ganglia.
Neuron Microstructure LM: EM: Function Classification
1.Microstructure of neuron Dendrites Cell body Axon
Cell membrane Cell body Cytoplasm Neurons Nucleus Dendrites Processes or neurites Axon
Cell body: Perikaryon The cell body,soma, is the part of neuron that contains nucleus and surrounding cytoplasm, also called perikaryon. It is the trophic center of the neuron. The protein and enzymes synthesis in this area. Where is cell body
Cell body: Perikaryon • Position: only in grey matter in CNS which also contains dendrites and axons starting from or ending on the cell bodies,ganglia in PNS • Shape:They can be pyramidal, spherical, ovoid or pear-shaped. • Size: Measuring 5-150 um in diameter. Microscopic examination
Cell body: Perikaryon (1)Cell membrane: the structure is as the same as the normal cell. It functions in getting the stimuli and integration and conducting the nerve impulse. (2) The nucleus is large and pale with H-E stain,prominent nucleoli are very clear.
Cell body: Perikaryon (3)Cytoplasm: the cytoplasm has some distinctive characteristics not seen in other cells. The cytoplasm is basophilic and full of neurofibrils.
Neurofibril Nissl body H-E stains Silver nitrate
Cell body: Perikaryon Nissl bodies: The cytoplasm shows the presence of a granular material that stains intensely with basic dyes; this material is the Nissl substance(also called Nissl bodies or granules).
Nissil body 细颗粒样的尼氏体
axon hilllock Neurofibrils
Cell body: Perikaryon • Neurofibrils are thin black fibers observed in LM with silver nitrate slides, which is composed of microtubule and filaments in EM. EM
synapse RER ribosome pigment mitochondria microtube
EM: rough surfaced endoplasmic reticulum. The presence of abundant granular endoplasmic reticulum is an indication of the high level of protein synthesis in neurons. Mitochondria, SER,lysosomes,Golgi complexes,ribosome etc. The proteins are needed for maintenance and repair, and for production of neurotransmitters and enzymes.
Neurites or processes The processes arising from the cell body of a neuron are called neurites.Most neurons give off a number of short branching processes called dendrites and one longer process called an axon.
Dendrites Cell body collaterals Axon
Nissl body Neurofibril Dendrites Axon H-E stains Silver nitrate 不同形态
Dendrites The dendrites are characterized by the fact that they terminate near the cell body. They are irregular in thickness, and Nissl granules extend into them. They bear numerous small spines which are of variable shape.
Axon • Every neuron has only one long thin process or axon which arises from a special region or axon hillock, which is devoid of Nissl bodies. It carries the impulse received by the neuron to distant region.
An axon may have not much branches than that of dendrites. If branches, that arise near the cell body and lie at right angles to the axon are called collaterals. At its termination the axon breaks up into a number of fine branches called telodendria which may end in small swellings (terminal boutons.
The axon is identified according to the axon hillock with LM.The part of the axon just beyond the axon hillock is called the initial segment.
Neurites or processes Dendrites Axons many one short long irregular in thickness uniform in diameter Nissl granules No Nissl substance spines axon hillock impulse towards the soma away from the cell body
Identification of dendrites from axon 1) morphology 2) Axon hillock in LM 3) Dendrites have microtubule associated protein (MAP-2 ) in immunocytochemically, not present in axons. distinguished from axons
2. Classification of neuron Dendrites Cell body Axon
1)According to the number of the processes unipolar,or pseudounipolar neuron bipolar neuron multipolar neuron
Unipolar neuron multipolar neuron bipolar neuron
Unipolar neuron Spinal ganglia
Unipolar neuron Satellite cells
Bipolar neuron Retina of eye
axon hilllock multipolar neuron
According to the size of cell body and the length of axon: According to Cajal (1889): Golgi type I neurons: long axon Golgi type II neurons: short axon
According to their function: Sense ( afferent )neurons: Interneurons Motor( efferent ) neurons
The classification of neurons: • According to the number of process The shape of the cell body is dependent on the number of processes arising from it. The most common type of neuron gives off several processes from the cell body is, therefore, multipolar. Some neurons have only one axon and one dendrite and are bipolar.
Another type of neuron has a single process (which is highly convoluted). After a very short course this process divides into two. One of the divisions represents the axon; the other is functionally a dendrite, but its structure is indistinguishable from that of an axon. This neuron is described as unipolar,
but from a functional point of view it is to be regarded as bipolar. (To avoid confusion on this account this kind of neuron has been referred to, in the past, as a pseudounipolar neuron. Depending on the shapes of their cell bodies some neurons are referred to as stellate (star shaped) or pyramidal.
According to the neurotransmitter they release • Cholinergic neurons: acetylcholine • Aminergic neurons: adrenaline, non • Peptidergic neurons: neuropeptids
The Synapse 突触: Concept: Synapses are highly specialized intercellular junctions which link the neurons of each nervous pathway. Similar intercellular junctions link neurons and their effector cells such as muscle fibers;where neurons synapse with skeletal muscle they are referred to as neuromuscular junction or motor end plate.
Cell body Processes synapse
Classification of synapses: According the constitution: axodendritic synapse axosomatic synapse axoaxonal synapse dendro-axonic dendro-dendritic somato-somatic synapse somato-dendritic synapse