Nervous Tissue PDF

NERVOUS TISSUE Prepared by: Catherine Denise M. Palabyab, RMT, MD Medical Laboratory Science Department NERVOUS SYSTEM ORGANIZATION Develops from the ectoderm, beginning in the third week of development NEURON Neuron: Functional unit of bothe the PNS and CNS 3 MAIN...

NERVOUS TISSUE Prepared by: Catherine Denise M. Palabyab, RMT, MD Medical Laboratory Science Department NERVOUS SYSTEM ORGANIZATION Develops from the ectoderm, beginning in the third week of development NEURON Neuron: Functional unit of bothe the PNS and CNS 3 MAIN PARTS OF A NEURON 1. CELL BODY/ PERIKARYON/ SOMA- Contains the nucleus and most of the cells organelles 2. DENDRITES ○ numerous elongated processes extending from the perikaryon ○ Receive stimuli from other neurons through synapses 3. AXON ○ single long process ○ Transmits impulses away from the cell body towards other neurons NEURON NEURON CELL BODY/ PERIKARYON Contains the nucleus and the cytoplasm In contact with nerve endings Abundant intermediate filaments called: NEUROFILAMENT CELL BODY/ PERIKARYON PARTS OF THE CELL BODY Nucleus ○ Large, euchromatic nucleus with a prominent nucleolus, indicating intense synthetic activity. Cytoplasm ○ Numerous polyribosomes and RER d/t active production of proteins ○ RER rich regions are called basophilic Nissl bodies ○ Nissl bodies -large masses of free polysomes and RER indicating the cell’s high rate of protein synthesis. DENDRITES short, small processes emerging and branching off the soma most synapses on dendrites occur on dendritic spines→ membrane protrusions along the small dendritic branches, Changes in dendritic spines are of key importance in the constant changes of the neural plasticity which underlies adaptation, learning, and memory postnatally. AXONS AXOLEMMA ○ The plasma membrane of the axon ○ its contents are known as axoplasm (cytoplasm) AXON HILLOCK ○ Where axons originate from a pyramid-shaped region of the perikaryon ○ Has concentrated ion channels which generate action potential NEURON CLASSIFICATION OF NEURONS A. ACCORDING TO ITS NUMBER OF PROCESSES FROM THE CELL BODY UNIPOLAR ○ Present in the dorsal root ganglia of of the spinal cord BIPOLAR ○ Purely sensory ○ Sensory neurons of the retina. ○ Olfactory epithelium MULTIPOLAR ○ One axon, 2 or more dendrites ○ Most common ANAXONENIC ○ Many dendrites but with no true axon ○ Does not produce action potentials CLASSIFICATION OF NEURONS B. ACCORDING TO FUNCTION SENSORY (AFFERENT) ○ Receives stimuli from receptors MOTOR (EFFERENT) ○ Sends impulses to the effector organs (muscle, glands) Somatic Voluntary control Innervates skeletal muscle Autonomic Involuntary control Innervates glands , cardiac muscle, smooth muscle ASSOCIATION/INTERNEURONS ○ Establish connections with other neurons through circuits in the CNS ○ Either multipolar or anaxomic ○ 99% of all adult neurons MATTERS OF THE MIND IN GRAY AND WHITE WHITE MATTER VS GRAY MATTER The brain and spinal cord contain gray and white matter GRAY MATTER - abundant in cell bodies ○ Where neuronal cell bodies and their supportive cells called neuroglia are concentrated ○ Site of synapses between neurons ○ Covers the cerebrum and cerebellum WHITE MATTER - abundant in axons ○ Devoid of neuronal cell bodies ○ Composed of myelinated and some unmyelinated nerve axons and their supportive cells called oligodendrocytes ○ White in color due to presence of myelin sheaths MYELIN SHEATH AND THE MYELINATION OF AXONS MYELIN SHEATH lipid-rich, insulating layer that wraps around axons in the nervous system. Increase the speed of nerve impulse conduction along the axon. provide protection and support for axons. In the PNS→ Myelin sheath is formed by Schwann cells In the CNS→ Myelin sheath is formed by Oligodendrocytes NODES OF RANVIER spaces in the myelin sheath between individual cells that myelinate the axons allow for saltatory conduction, where the nerve impulse jumps rapidly between nodes, speeding up transmission. MYELIN SHEATH AND THE MYELINATION OF AXONS MYELIN SHEATH lipid-rich, insulating layer that wraps around axons in the nervous system. Increase the speed of nerve impulse conduction along the axon. provide protection and support for axons. In the PNS→ Myelin sheath is formed by Schwann cells In the CNS→ Myelin sheath is formed by Oligodendrocytes NODES OF RANVIER spaces in the myelin sheath between individual cells that myelinate the axons allow for saltatory conduction, where the nerve impulse jumps rapidly between nodes, speeding up transmission. MYELIN SHEATH AND THE MYELINATION OF AXONS OLIGODENDROCYTES SCHWANN CELLS creating myelin sheaths around axons in creating myelin sheaths around axons in the the CNS. PNS. myelinates a single axon by wrapping myelinate multiple axons. around it multiple times. Have a basal lamina external to the plasma Do not directly envelop axons but membrane. instead send out extensions to wrap around them. Involved in the regeneration of damaged peripheral nerves. Disorders of oligodendrocytes→ multiple sclerosis CAN MYELINATE MULTIPLE AXONS No basal lamina MEDICAL APPLICATION MULTIPLE SCLEROSIS myelin sheaths surrounding axons are damaged by an autoimmune mechanism that interferes with the activity of the affected neurons and produces various neurologic problems. destructive actions of these cells exceed the capacity of oligodendrocytes to produce myelin and repair the myelin sheaths. SYNAPSE Where nerve impulses are transmitted Transmission is unidirectional Convert electrical signal from presynaptic cell into a chemical signal in the postsynaptic cells Act by releasing neurotransmitters SYNAPSE COMPONENTS 1. PRESYNAPTIC AXON TERMINAL 2. POST SYNAPTIC CELL MEMBRANE 3. SYNAPTIC CLEFT TYPES OF SYNAPSE TYPES OF SYNAPSE THE NEUROGLIA: THE SUPPORTING CELLS OF THE CNS “NERVE GLUE” Highly branched, supportive, non neuronal cells in the CNS and PNS Surrounds neurons, dendrites and axons No stimulation or conduction of impulses Smaller in size Dark staining nucleus More numerous than neurons: outnumber the neurons by 9:1 4 TYPES OF NEUROGLIA IN THE CNS 2 TYPES OF NEUROGLIA IN THE PNS 1. ASTROCYTES 1. SATELLITE CELLS 2. OLIGODENDROCYTES 2. SCHWANN CELLS 3. MICROGLIA 4. EPENDYMAL CELLS CNS SUPPORTING CELLS ASTROCYTES Star-shaped Astrocytes are the most abundant glial cells in the CNS. They provide structural support to neurons and help maintain the blood-brain barrier. Astrocytes regulate the extracellular environment by controlling ion concentrations and neurotransmitter levels. They contribute to the repair and scarring processes following CNS injury. Glial fibrillary acid protein (GFAP)- Proximal regions of the astrocytic processes are reinforced with bundles of intermediate filaments MARKER FOR ASTROCYTES CNS SUPPORTING CELLS OLIGODENDROCYTES responsible for producing myelin sheaths around axons in the CNS. can myelinate multiple axons, unlike Schwann cells in the PNS, which myelinate a single axon. Oligodendrocytes play a crucial role in increasing the speed and efficiency of nerve impulse conduction. Oligodendrocytes are the predominant glial cells in white matter, which is white because of the lipid concentrated in the wrapped membrane sheaths. CNS SUPPORTING CELLS MICROGLIA Microglia are the resident immune cells of the CNS. They are involved in immune surveillance, detecting and responding to pathogens, injury, and inflammation. Microglia can phagocytose cellular debris, dead neurons, and foreign invaders, helping to maintain CNS homeostasis. Can migrate unlike other glial cells Originate from monocytes CNS SUPPORTING CELLS EPENDYMAL CELLS Columnar or cuboidal cells line the ventricles of the brain and the central canal of the spinal cord. Involved in the production and circulation of cerebrospinal fluid (CSF). Ependymal cells also contribute to the formation of the blood-CSF barrier. Unlike a true epithelium there is no basal lamina. PNS SUPPORTING CELLS SCHWANN CELLS Schwann cells are the primary neuroglial cells in the PNS responsible for myelinating axons. They wrap around individual axons, creating the myelin sheath, which helps in insulating and speeding up the conduction of nerve impulses. Schwann cells also play a role in the regeneration of damaged peripheral nerves by forming bands of Büngner, which guide the regenerating axons. Additionally, Schwann cells can envelop and support unmyelinated axons, forming Remak bundles. PNS SUPPORTING CELLS SATELLITE CELLS smaller neuroglial cells found in clusters around neuronal cell bodies within ganglia in the PNS. Provide structural support and regulate the microenvironment around the neuron cell bodies. Nutrient and waste exchange for cell bodies in the ganglia trophic or supportive effect on these neurons, insulating, nourishing, and regulating their microenvironments. SUPPORTING CELLS CENTRAL NERVOUS SYSTEM BRAIN AND SPINAL CORD CENTRAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM REGIONS GRAY MATTER WHITE MATTER neuronal cell myelinated axons , bodies, dendrites, grouped together astrocytes, and as tracts, microglial cells Oligodendrocytes where most synapses occur. In deeper, inner regions, Thick cortex or surface layer of both the cerebrum and the cerebellum  CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER Composed of 3 layers ○ Thick outer MOLECULAR LAYER ○ Thin middle PURKINJE LAYER ○ Thick inner GRANULAR LAYER CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER Composed of 3 layers ○ Thick outer MOLECULAR LAYER Basket cells Unmyelinated axons course through horizontally ○ Thin middle PURKINJE LAYER Flasked- shaped Purkinje cells Purkinje cells give off thick dendrites that branch out to the molecular layer in the cerebellar surface ○ Thick inner GRANULAR LAYER Granule cells- unmyelinated cells coursing through horizontally Golgi Type II cells- larger than granule cells; CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER Purkinje cells give off thick dendrites that branch out to the molecular layer in the cerebellar surface CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER CENTRAL NERVOUS SYSTEM CEREBELLAR LAYER CENTRAL NERVOUS SYSTEM CEREBRAL LAYER Layer I: MOLECULAR LAYER M GP GP M Most superficial Predominant cell: Neuroglial cell Process inputs from other cortical regions Layer II: EXTERNAL GRANULAR PC: small pyramidal and granule cells Layer III: EXTERNAL PYRAMIDAL Medium sized pyramidal cells that project outputs to cortical areas Involves in corticocortical communication Contributes to higher cognitive function CENTRAL NERVOUS SYSTEM CEREBRAL LAYER Layer IV: INTERNAL GRANULAR Mainly small granule cells M GP GP M Layer V: INTERNAL PYRAMIDAL Contains the largest pyramidal cells Involved in motor control Layer VI: MULTIFORM LAYER Intermixed neurons Deepest layer Adjacent to the white matter CENTRAL NERVOUS SYSTEM CEREBRAL LAYER M GP GP M CENTRAL NERVOUS SYSTEM CEREBRAL LAYER M GP GP M CENTRAL NERVOUS SYSTEM SPINAL CORD INNER/DEEPER GRAY MATTER (H-SHAPED) OUTER/ PERIPHERAL: WHITE MATTER CENTRAL NERVOUS SYSTEM SPINAL CORD GRAY MATTER (CENTRAL) Inner layer Predominantly composed of cell bodies and interneurons H-shaped with 2 sides connected in the midline by the gray commissure Center of the gray commissure→ central canal Legs of the “H” form ○ ANTERIOR/ VENTRAL HORN More prominent Cell bodies of large motor neurons Ventral roots ○ POSTERIOR/ DORSAL HORN Sensory areas Cell Receive sensory information from dorsal roots CENTRAL NERVOUS SYSTEM SPINAL CORD CENTRAL NERVOUS SYSTEM SPINAL CORD CENTRAL NERVOUS SYSTEM SPINAL CORD GRAY MATTER WHITE MATTER Inner Outer H-shaped with 2 sides connected in Ascending and descending the midline by the gray commissure myelinated fibers Cell bodies and interneurons CENTRAL NERVOUS SYSTEM MENINGES 3 LAYERS DURA MATER ARACHNOID MATER PIA MATER CENTRAL NERVOUS SYSTEM MENINGES DURA MATER outermost and toughest layer dense, fibrous connective tissue. 2 Layers ○ Periosteal layer- attached to the inner surface of the skull ○ Inner meningeal layer In between 2 layers: DURAL SINUSES- contain venous blood CENTRAL NERVOUS SYSTEM MENINGES ARACHNOID MATER Middle layer Thin delicate later composed of collagen and elastic fibers SUBARACHNOID SPACE: beneath subarachnoid mater , contains the CSF Does not follow the contour of the brain and spinal cord but instead forms a loose covering CENTRAL NERVOUS SYSTEM MENINGES PIA MATER Innermost; directly adjacent to the brain and spinal cord Thin transparent membrane Adheres closely to the contours of the brain and spinal cord→ follows their convulsions Support and stability to the neural tissue Supplies blood vessels that nourish the brain and SC CENTRAL NERVOUS SYSTEM MENINGES NERVE ORGANIZATION nerve fibers are grouped into bundles to form nerves whitish, glistening appearance because of their myelin and collagen content bundles of nerve fibers surrounded by connective tissue fibers: FASCICLES LAYERS OF CONNECTIVE TISSUE AROUND NERVE FIBERS ENDONEURIUM PERINEURIUM EPINEURIUM NERVE ORGANIZATION ENDONEURIUM Innermost layer, surrounds the axons within a fascile support and protection to individual nerve fibers, as well as a pathway for blood vessels supplying nutrients and oxygen to the axons. PERINEURIUM surrounds each fascicle of nerve fibers. With specialized epithelial cells (perineural cells) joined together by tight junctions selective barrier, regulating the exchange of substances between the blood vessels and the nerve fibers within the fascicle.→ Blood-nerve barrier EPINEURIUM Outermost layer; surrounds the entire nerve Encompasses multiple fascicles NERVE ORGANIZATION END OF LECTURE