* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download L11Nervous tissue strusture 11
Mirror neuron wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Signal transduction wikipedia , lookup
Neural coding wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Subventricular zone wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Central pattern generator wikipedia , lookup
Apical dendrite wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Biological neuron model wikipedia , lookup
Electrophysiology wikipedia , lookup
Multielectrode array wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Neurotransmitter wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Optogenetics wikipedia , lookup
Chemical synapse wikipedia , lookup
Single-unit recording wikipedia , lookup
Circumventricular organs wikipedia , lookup
Development of the nervous system wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Synaptic gating wikipedia , lookup
Axon guidance wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Node of Ranvier wikipedia , lookup
Neuroregeneration wikipedia , lookup
Nervous system network models wikipedia , lookup
Synaptogenesis wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
•21/04/36 Lecture 1: Introduction &Nervous Tissue Organization Dr. Amjad El-Shanti MD,MPH, PhD Assistant professor of Public Health- Epidemiology 2014-2015 Definitions • Anatomy: Branch of medical science concerned with the structure and organization of human Body (Cells, Tissues, Organs, Systems). • Macro-anatomy: (Shape, Size, Weight, Dimensions, Color, Content, Surfaces, Location, Nerve supply, blood supply). • Micro-anatomy: Microscopic study of Tissues and cells structures. (Histology, Cytology). • Histology: The study of minute structure of tissues by microscope. • Cytology: The study of molecular structure of cells by microscope. • Embryology: The study of development of human systems and organ since fertilized egg till full term Baby (Intra-uterine development) •1 •21/04/36 Physiology • Physiology: Branch of medical science concerned with the function of human body at different levels (Cell, Tissue, Organ, System) to survive or to keep the state of homeostasis. • Homeostasis: refers to attempt of human body to still balance, equilibrium, and constant. Nervous Tissue Functions • Neurons are the cells in the nervous system which are responsible for sending messages. • They have three major purposes 1. to gather and send information from the senses such as touch, smell, sight etc. 2. to send appropriate signals to effector cells such as muscles, glands etc. 3. to process all information gathered and provide a memory and cognitive ability thus allowing us to take voluntary action on information received (Interpretation). •2 •21/04/36 Organization • The Human Nervous System consists of the Central Nervous System & the Peripheral Nervous System. • Central Nervous System: 1 - Brain 2 - Spinal cord • Peripheral Nervous System: 1 - Cranial nerves (12 pair) & their branches 2- Spinal nerves (31 pair) & their branches Divisions of Peripheral Nervous System 1 - Somatic - supplies & receives fibers (neurons) to & from the skin, skeletal muscles, joints, & tendons 2 - Visceral - supplies & receives fibers to & from smooth muscle, cardiac muscle, and glands. The visceral motor fibers (those supplying smooth muscle, cardiac muscle, & glands) make up the Autonomic Nervous System. The ANS has two divisions: – Parasympathetic division - important for control of 'normal' body functions, e.g., normal operation of digestive system – Sympathetic division - also called the 'fight or flight' division; important in helping us cope with stress •3 •21/04/36 Histology • Nervous Tissue consists of only two principal kinds of cells: 1. Neuroglia 2. Neuron • Neuroglia serve as a special supporting and protecting component of nervous system. Neurons make up the nervous tissue that forms the structural and functional portion of the system. • Neuroglia • general functions include: 1 - forming myelin sheaths 2 - protecting neurons (via phagocytosis) 3 - regulating the internal environment of neurons. Types of neuroglia or (Glia cells): • – 1. 2. 3. 4. _ 1. 2. •4 The following four neuroglia are found in the CNS: Astrocytes have numerous processes that give the cell a star-shaped appearance. Astrocytes maintain the ion balance around neurons and control the exchange of materials between blood vessels and neurons. Oligodendrocytes have fewer processes than astrocytes. They wrap these cytoplasmic processes around neurons to create an insulating barrier called a myelin sheath. Microglia are phagocytic macrophages that provide a protective function by engulfing microorganisms and cellular debris. Ependymal cells line the fluid-filled cavities of the brain and spinal cord. Many are ciliated. Two kinds of neuroglia are found in PNS: Schwann cells (neurolemmocytes) wrap around axons to produce an insulating myelin sheath. Schwann cells provide the same function in the PNS as oligodendrocytes provide in the CNS. Satellite cells are located in ganglia where they surround the cell bodies of neurons. •21/04/36 Neuron • • • Neurons in the human Nervous systemmvary widely in their size and shape. However, all neurons have some features in common. A neuron consists of: 1. a cell body, called the soma, (Perikaryon) 2. with arms that reach out to connect to the network of other neurons in the brain. One arm, the dendrite, receives signals, 3. while the other arm, the axon, sends signals. • All electrical signals are unidirectional; they flow from the receiving point on the dendrite or cell body out through the axon. Cell Body • • • • • The cell body of a neuron is called the soma. It contains the same organelles as other cells in the body, including the nucleus ,mitochondria ,endoplasmic reticulum ,ribosomes ,and Golgi apparatus. There are granules in cytoplasm: (Inclusions and Characteristic Structures) Inclusions: Lipofuscin (By-products of lysosomal activity, increased with age, Clumps of yellowish browm granules). Characteristic structures for neuron: 1. Nisssl bodies: (Chromatophilic substances that responsible for protein synthesis which flow to axon). 2. Neurofibrill: for supporting and transporting. • •5 The basic functions that: keep the cell alive, such as replication, respiration, and protein production, are carried out in the cell body. •21/04/36 Intracellular systems for transporting Axoplasmic Flow Axonal Transport Slower Faster Convey axoplasm in one direction from cell body to axon terminal Convey materials in both directions (away cell body , and toward cell body) 1-Supplies new axoplasm for 1- Transport organelles and developing and regenerating materials that form axons axolemma, Synaptic end bulbs, synaptic vesicles. 2- Returning materials to cell 2- Renew axoplasm in bodies growing and mature axon. Dendrite • There are many types of dendrites ,but, in general, a dendrite looks like a tree whose trunk ends in the soma. • Its branches, called dendritic spines, are stretched out to receive signals from the axons of other neurons. • Dendrites contain many receptors which can bind to signaling molecules called neurotransmitters . • These receptors are sometimes also found on the soma. • When these receptors bind enough neurotransmitter molecules, the neuron undergoes a change, becoming more or less likely to send a signal to the next neuron. • The type of change depends on the type of neurotransmitter that is bound. Some neurotransmitters excite the cell while others depress it. Still others have cause various biochemical reactions within the postsynaptic neuron . •6 •21/04/36 Axon • • • • • • • • • The axon is a long, thin structure which sends out signals from the cell. The end of the axon is called the terminal bouton . Axon terminal)Each signal travels along the neuron's axon to the terminal bouton, where it is then transmitted to the next neuron. The axon is covered in myelin, a thick phospholipid substance that insulates the nerve to help transmit the electrical signal along the length of the axon. Periodic gaps in the myelin sheath ,called nodes of Ranvier ,allow the signal to refresh itself as it propagates along the axon. The small area, like a neck, that lies between the soma and the axon is called the axon hillock. Electrical charge builds up at the axon hillock until it is sufficient to generate an action potential. When there is enough charge to make an action potential capable of propelling itself all the way down the axon, the action potential initiates at the axon hillock and travels down the axon to the terminal bouton . Axoplasm: cytoplasm of axon Axolemma: sheath of axon Difference between Dendrites and Axon Axons 1.Take information away from the cell body 2.Smooth Surface 3.Generally only 1 axon per cell 4.No ribosomes (No Nissl bodies)= (No protein synthesis) 5. Can have myelin 6.Branch further from the cell body 7. Thin, Long •7 Dendrites 1.Bring information to the cell body 2.Rough Surface (dendritic spines) 3.Usually many dendrites per cell 4.Have ribosomes (Nissl bodies)= (Prptein syntheisi) 5.No myelin insulation 6.Branch near the cell body 7. Thick, short •21/04/36 Neuron structure Nerve fibers and Myelination • • Nerve Fiber: Axon with sheaths. Myelin sheath : 1. 2. 3. • Schwan cell (Neurolemmocyte): 1. 2. 3. 4. 5. 6. 7. •8 increases speed of nerve impulse conduction Increases insulate and maintain the axon. White color (white matter in brain ans spinal cord). Along axon Encircles axon It has nucleus, cytoplasm pushed outside layer Neurolemma= membrane of neuolemmocyte (20-30layers every cell). Outer neurolemma responsible for regeneration injured axons. Schwann cells are located at regular intervals along the process (axons) & so a section of a myelinated axon would look like this. Between areas of myelin are non-myelinated areas called the nodes of Ranvier. •21/04/36 Myelination Myelin Sheath and Schwan cells •9 •21/04/36 Classifications of neurons • Anatomical (Structural) Classification: by number of processes 1. Multipolar neurons are so-named because they have many (multi-) processes that extend from the cell body: lots of dendrites plus a single axon. Functionally, these neurons are either motor (conducting impulses that will cause activity such as the contraction of muscles) or association (conducting impulses and permitting 'communication' between neurons within the central nervous system). 2. Unipolar neurons have but one process from the cell body. However, that single, very short, process splits into longer processes (a dendrite plus an axon). Unipolar neurons are sensory neurons - conducting impulses into the central nervous system (posterior root ganglia of spinal cord). 3. Bipolar neurons have two processes - one axon & one dendrite. These neurons are also sensory. For example, biopolar neurons can be found in the retina of the eye, internal ear. and olfactory areas. : • Physiological Clssification:Neurons can also be classified by the direction that they send information. 1. Sensory (or afferent) neurons: send information from sensory receptors (e.g., in skin, eyes, nose, tongue, ears) TOWARD the central nervous system. 2. Motor (or efferent) neurons: send information AWAY from the central nervous system to muscles or glands. 3. Interneurons: send information between sensory neurons and motor neurons. Most interneurons are located in the central nervous system Neuron Types 1. Bipolar 2. Unipolar 3. Multipolar •10