Tissues are groups of cells that are similar in structure and function.* Epithelium * Muscle Coverings Movement Linings of surfaces* Connective * Nervous Support Control Bone, ligaments, fat Brain, nerves, spinal cord
•Muscle – a Latin word for “littlemouse”•Muscle is the primary tissue in the •Heart (cardiac MT) •Walls of hollow organs (Smooth MT)•Skeletal muscle •Makes up nearly half the body’s mass
Functions of muscle tissueContractility Long cells shorten and generate pulling forceExcitability Electrical nerve impulse stimulates the muscle cell to contractExtensibility Can be stretched back to its original length by contraction of an opposing muscleElasticity Can recoil after being stretched
Location Function Appearance Control striated, multi-Skeletal movement, nucleated skeleton voluntary heat, posture (eccentric), fibers parallelCardiac heart pump blood striated, one involuntary continuously central nucleus Peristalsis,Visceral G.I. tract, blood uterus, eye, no striations, one(smooth pressure, involuntary blood central nucleus pupil size,muscle) vessels erects hairs
•Nervous tissue comprises the nervous system.•Nervous tissue includes: •Nerve cells: •Neurons. •Supportive cells: •Schwann cells in peripheral nervous system (P.N.S) •Glial cells in central nervous system (C.N.S) •Nerve fibers. •Nerve endings: •Receptors or sensory nerve endings. •Effectors or motor nerve endings.
The neuron is the structural and functional unit of thenervous system.•The neuron has 2 highly developed physiologicproperties: •Irritability, is the capacity to generate nerve impulses in response to various stimuli. •Conductivity, is the ability to transmit the impulses along the processes of the neuron.
Fine structure of neuron•The cell body of the neuron contains:•Central euchromatic vesicular nucleus (open-face nucleus).•Perinuclear very well developed Golgi Complex.•Mitochondria (are found throughout the neuron i.e. in cell body and itsprocesses).•Rough Endoplasmic reticulum (rER) is present only in cell body and dendritesand not present in the axon or axon hillock. RER appears as clumps ofbasophilic material called Nissl granules.•Neurofibrils (are distributed throughout the neuron and appear by lightmicroscope).•Microtubules are found all over the neuron.•Inclusions found in nerve cells include: •a) fat droplets •b) pigments as lipofuscin, melanin •c) glycogen present only in embryonic neurons, but in adult neurons it is absent because it depends on oxidative metabolism. Therefore nervous system is vulnerable (sensitive) to anoxia.•N.B.:•Centrioles are not found in mature neurons, so they are incapable of celldivision.
Processes of theneuron: They arethe axon and thedendrites.
•The axon (axis cylinder): •It is the efferent process of the neuron which carries the impulse away from the cell body. •It originate from the cell body by a conical portion called “axon hillock”. •It is a single, thin, long process with uniform size. •It gives some collateral branches and many terminal branches. •It is surrounded with a membrane called axolemma and its cytoplasm is called axoplasm. •It contains mitochondria, microtubules and neurofibrils. •It does not contain Nissl granules. •As the axon is devoid of rER, it depends on the proteins synthesized in the cell body which is conveyed by the aid of the movements of microtubules throughout the axon by a process called axoplasmic transport.•The Dendrites: •They are the afferent processes of the neuron which carry the impulse to the neuron. •They are multiple, short, thick processes and their thickness decreases towards its end. •They have many branches with spines. •They contain mitochondria, microtubules and neurofibrils. •They contain Nissl granules.
Types of the neurons: are classified according tonumber of processes into:•Pseudo-unipolar neurons: which have single process, thendivides into axon and dendrite. They are present in dorsalroot ganglion (also called spinal ganglion or sensory ganglion).•Bipolar neurons: they are spindle-shaped with 2 processes;one axon and one dendrite. They are present in areas ofspecial sensations as: retina, olfactory mucosa and inner ear.•Multipolar neurons: they have several processes, the nervecell body takes several shapes as follows: •Pyramidal cells: as in cerebral cortex. •Purkinje (flask-shaped) cells; as in cerebellar cortex. •Stellate cells: as in •Gray matter of spinal cord (anterior horn cells). •Autonomic ganglia.
Types of nerve fibers:•In CNS, all the fibers have no neurilemmasheath and may be: •Non-myelinated (naked): as in grey matter. •Myelinated: as in white matter.•In PNS, all the fibers (except the nerve endings)have neurilemma sheath and may be: •Non-myelinated: as post-ganglionic sympathetic fibers. •Myelinated: as all the peripheral nerves.
Schwan cells (neurolemmal cells)•These cells surround the axons of peripheral nerves. They looklike tubes which envelop the axon. They have peripheral ovalnucleus and basophilic cytoplasm.• Whether the nerve fiber is myelinated or not, it is related toSchwann cells. •If the axon is myelinated, one Schwann cell is related to each axon. •In non-myelinated axons, one Schwann cell is related to several axons.•Functions of Schwann cells: •They have a protective and a metabolic role for the axons. •They act as an insulator for the nerve impulse. •They are essential for regeneration of injured peripheral neurons. •They form myelin sheath which is important because: •It insulates the nerve impulse. •It increases the conduction velocity of the axon.
Satellite Cells: form a layer around ganglion cellsand separate them from blood capillaries. It helps metabolic exchange between ganglion cells and blood.
Spinal (sensory) ganglion Autonomic GanglionSurrounded by thick connective tissue Surrounded by thin connective tissuecapsule. capsule.Cells are round or oval (pseudo- Cells are stellate (multipolar)unipolar)Cells are arranged in groups Cells are scatteredCells are not of same size Of equal small sizeFew number of cells Large number of cellsCells with central nuclei Cells with peripheral nucleiMyelinated nerve fibres separate the Unmyelinated nerve fibres separate thegroups of cells cellsCells are surrounded by many satellite Few satellite cellscellsNo synapse between neurons Has synapses between neurons
Neuroglia•Neuroglial cells are the supporting cells within the CNS. They have a function similar to Schwann cells in PNS. They have many types:•Astrocytes: these cells support the neurons. They are either fibrous or protoplasmic. •Fibrous astrocytes: With long processes which branch infrequently. They are found in white matter. They have euchromatic nuclei and a vascular pedicle, i.e. one process ends on a small blood vessel. Their cytoplasm contains neuroglial fibers. •Protoplasmic astrocytes: With short processes. They are found in gray matter. Their cytoplasm is rich in cytoplasmic granules called gliosomes which are considered as lysosomes.
Oligodendrocytes: Microglial cells:With few processes, (dark) – Small in size with fewnuclei, and contain many processes and elongated microtubules. It is dark nucleus. Function: responsible for myelin phagocytosis. formation in CNS by sending processes to several axons.