CONTENT • INTRODUCTION • NERVOUS SYSTEM CLASSIFICATIONS • ELEMENTS OF NERVOUS SYSTEM • TERMINOLOGY • CENTRAL NERVOUS SYSTEM • MENINGES • SPINAL CHORD • CEREBELLUM • BRAIN • BRAIN STEM
LECTURE OBJECTIVES • Terminal Objective • Understand the histology of CNS and PNS • Enabling Objectives • Describe the general classification of a nervous system. • Explain some nervous system terminology. • Remember histological characteristics of nervous system elements. Neurons and Glia. • List the meninges and Describe the contents of each meninges. • Explain the blood brain barrier and forms Cerebrospinal Fluid. • Signify histological characteristics of brain.
LECTURE DISCUSSION • The discussion questions for the Neurohistology lecture are: • What anatomical features of the cells called neurons are unique to that type of cell? And what are a few features that neurons share with all cells? • In the 1900's a scientist named Golgi stated that all neurons were connected by fibers that merged, forming a meshwork of cells he called a syncitium. Information passed through this syncitium flowing along the continuous mass of fibers. At the same time, another scientist named Ramon y Cajal, stated that there was a gap between each neuron. Every cell was surrounded by a membrane that did not merge with other cells. • Who was right? Or in other words, how do neurons connect with each other? • How many neurons are in the human brain? How many neurons are born per minute of human gestation? • What are the four types of glial cells in the nervous system? Where are they found and, briefly, what do they do?
Divisions of the Nervous System • INTRODUCTION: • The nervous system provides for the control and coordination of all the body's activities. • It makes use of millions of nerve cells having especially the properties of excitability and conductivity. • Nervous system = communication system of body; receptor collects stimuli,transforms to electrical signal, passes signal to CNS (interpretation), finally passes toeffectors(response)
NERVOUS SYSTEM CLASSIFICATIONS • ANATOMICALLY, THE NERVOUS SYSTEM IS DIVIDED INTO • Central Nervous System • Peripheral Nervous System
NERVOUS SYSTEM CLASSIFICATIONS • FUNCTIONALLY, THE NERVOUS SYSTEM IS DIVIDED INTO • SOMATIC PART • AUTONOMIC PART
In the CNS, collections of neurons are called nuclei. In the PNS, collections of neurons are called ganglia. In the CNS, collections of axons are called tracts. In the PNS, collections of axons are called nerves. Differences between the PNS and the CNS
ELEMENTS OF NERVOUS SYSTEM • NERVE CELLS NEURON • Unipolar or Pseudounipolar = cell body + axon only (photoreceptors of eye, embryonically) or proximal regions of axon and dendrite fuse to form singlecommon segment leaving cell body (spinal ganglia) • Bipolar = single axon + single dendrite (retina of eye, ganglia of auditory nerve) • Multipolar = numerous dendrites + one axon (by far the most common)
ELEMENTS OF NERVOUS SYSTEM • GLİAL CELLS • CNS • Oligodendrocytes, • Astrocytes, • Ependymal cells, • Microglia, • Special glial cells • PNS • Schwann cells, • Satellite/Capsule cells, • Enteric (gut) glia • Blood vessels • Connective tissue enclosing sheaths
COVERING (MENINGES) OF THE BRAIN • The meninges are three layers of protective tissue • They are called the dura mater, arachnoid mater, and the pia mater. • The meninges of the brain and spinal cord are continuous. • They are linked through the magnum foramen. • First, there is your skin (scalp). • Pia; Arachnoid; Dura = PAD
Skin • Epidermis • Dermis • Subcutaneus Connective Tissue (Hypodermis) • Galea Aponeurotic • Loose Areolar Connective Tissue • Pericranium (Periosteum) • Skull • Epidural Space • Dura Mater • Periosteal Layer (osteobastic layer + dense irregular CT) • Meningeal Layer (Simple Squamous Epithelium + Loose CT + Adipose Tissue) • (Falx Cerebri) • Subdural Space • Arachnoid (Simple Squamous Epithelium) • Subarachnoid Space • Arachnoid Granulation (Villi) • Arachnoid Trabeculae • Pia Mater • Epipial Layer • Intima Pia
DURAL MATER • Separations of the two layers create the dural sinuses, the duralrefections, and the trigeminal cave ( of Meckel ). • The internal layer continues through the magnum foramen to encloses the spinal cord ending in the second segment of the sacrum. • Dura(pachymeninx) • Periosteal layer • Meningeal layer • Associated spaces (Dural Venous Sinuses) • Epidural (extradural) Space
DURA MATER HISTOLOGY • Dura mater: (pachymeninx): DenseFibrousConnective Tissue; • The dura materis divided into two portions. • Osteoblastic layer: • The external layer of the dura mater, derived from the internal layer of cranial periosteum, • It is adherent to the inner surface of the skull, and continuous with the ectocranialperiosteum through the foramina of the skull. • Contain Rich Vascular Plexus • Specialized layer: • The internal layer, is the true meningeal dura mater. • Internal surface covered by a layer of Squomous cell (Mesodermal Orginate).
SubduralDural Reflections: • The internal layer forms the fivedural reflections, namely, • The tentorium cerebelli, • Thefalxcerebri, • The falxcerebelli, • The diaphragm sellae and • Thetentorium bulbusolfactorium.
DURAL VENOUS SINUSES Superior Sagittal Sinus (SSS) Sagittal Inferior Sinus (SIS) Straight (rectus) Sinus (SS) Occipital Sinus Confluence of Sinuses Sphenoparietal Sinus (SpS) Transverse Sinus (TS) Cavernous Sinus (CS) Intercavernous Sinus (ICS) Superior Petrosal Sinus (SPS) Inferior Petrosal Sinus (IPS) Sigmoid Sinus (SigS) Basilar Venous Plexus (sinus)
DURAL VENOUS SINUSES • Dural venous sinuses are frequently located where the meningeal and periosteal layers of the dura. • superior sagittal sinus • inferior sagittal sinus • straight (rectus) sinus • transverse sinus • occipital sinus • confluence of sinuses • sigmoid sinus • cavernous sinus • intercavernous sinus • sphenoparietal sinus • superior petrosal sinus • inferior petrosal sinus • basilar venous plexus (sinus)
DURAL VENOUS SINUSES • The dural venous sinuses carry both venous blood and CSF. • Venous drainage into the dural sinuses comes from cerebral veins, diploic veins and emissary veins. • CSF enters the venous sinuses via the arachnoid villi. • The dural venous sinuses eventually deliver most of their contents to the sigmoid sinuses • Sigmoid siuses continuous with the internal jugular veins.
Leptomeninges: Arachnoid + PiaARACHNOID • The arachnoid or arachnoid mater is the middle layer of the meninges. • The term arachnoid refers to the spider web like appearance of the blood vessels within the space. • In some areas, it projects into the sinuses formed by the dura mater.
HISTOLOGY OF ARACHNOID • The arachnoid is avascular and made of two components: • A layer of elastic and collagenous loose connective tissue. • Trabeculae extend from the arachnoid into the pia forming the subarachnoid space. • In some areas, the arachnoid extends superficially to penetrate the dural sinuses. • Arachnoid allows drainage of CSF. • This channels called arachnoidgranulations or arachnoid villi. • Arachnoid villi have valves to prevent the backflow from the sinuses. • The membrane and its trabeculae are composed of thin collogeneous and elastic fibers, • All surface are covered by a simple squamous epithelium.
ARACHNOID • The subarchanoid space lies between the arachnoid and pia mater. • It is filled with cerebrospinal fluid. • They transfer cerebrospinal fluid, the fluid found in the ventricles, back into the bloodstream. • This space includes blood vessels of the brain and cranial nerves.
SUBARACHNOID SPACE • Progressively thicker. • Located between the arachnoid membrane and the pia • Bridged by numerous trabeculae • Filled with CSF • CSF accumulates in expansions of the subarachnoid spaces known as subarachnoid cisterns.
SUBARACHNOID CISTERNS • Some of these subarachnoid cisterns provide potential sites for sampling the CSF. • Cisterna magna (cerebellomedullary cistern ) • Suprasellar cisterns • Interpeduncular cistern • Chiasmatic cistern • Quadrigeminal cistern (AKA superior cistern or cistern of the great cerebral vein)
ARACHNOID VILLI (GRANULATION) • Specializations of the arachnoid are located lateral to the longitudinal cerebral fissure. • In this location, the villi protrude into the superior sagittal sinus. • They provide the route for CSF. • CSF flow from the subarachnoid space into the dural venous sinuses.
PIA MATER • Piais a thin layer of connective tissue that is closely adherent to the brain tissue and cannot be separated from it. • The pia follows the contours of the brain, traveling down into the sulci • HISTOLOGY: • The Pia is composed to two layers: • Epipial layer contains the blood vessels. • Intima pia is most closely associated with the neural tissue. • Pia materconsist of thin cellular, vascular and collagenous tissue. • Arachnoid and pia comprise the leptomeninges.
SUBDURAL HAEMOTOMAS • Subdural space is located from the arachnoid membrane to the dura. • A space only arises by a aggressive cleaving between the fibroblasts of the inner dura, • This space is occured in sub-duralhaematomas.
CHOROID PLEXUS • All of the ventricles contain choroid plexuses • Choroid plexus produce cerebrospinal fluid. • The choroid plexuses are formed by the fusion of the pia mater, the most internal layer of the meninges and the ependyma, the lining of the ventricles. • The epithelium ofchoroid plexus is classified as simple cuboidal. • The cells will exhibit cilia and microvilli at their free surface. • This epithelial lining continues into the spinal cord and forms the ependyma. • Choroid plexus is composed to numerous attenuated and fenestrated capilaries. • Pink-staining calcified concretions may be seen in the histologic slides and they are called "brain sand" or corpora arenacea.
CEREBROSPINAL FLUID • The central nervous system is cushioned from shock by cerebrospinal fluid (CSF) which fills the ventricles of the brain, the subarachnoid space and the central canal of the spinal cord. • CSF is formed by the choroid plexuses which are vascular structures that project into the brain ventricles. • Filtrate from the capillaries in the plexuses pass through the cuboidal epithelial lining to enter the ventricles.
CEREBROSPINAL FLUID • The production of CSF involves active secretion of certain ions followed by passive water movement. • The subarachnoid space, which dilates into chambers, cisterns, fills with CSF. • Theforamina of LushkaandMagendieis found between the fourth ventricleand subarachnoid space of spinal chord. • Some CSF may come out of the brain tissue via spaces between blood vessels and the pia. • CSF returns to the dural sinus blood through the thin walls of the arachnoid villi and granulations
Blood-brain barrier • The blood capillaries serving the brain tissue have a characteristic structure of unfenestrated endothelial cells. • Endothelial cells held together by tight/occluding junctions on a thick basal lamina, • Outer surface of capillaries is enclosed by glial cell processes (astrocytes' pedicles). • The endothelium has few transcytotic vesicles and is very selective transports. • In most regions of the brain the endothelium blocks the passage of most materials from the blood into the neural tissue. • This structure is called a blood-brain barrier (BBB).
CENTRAL NERVOUS SYSTEM • The central nervous system is divided into two parts: • The brain • The spinal cord. • BRAIN: • The average adult human brain weighs 1.3 to 1.4 kg (approximately 3 pounds). • The brain contains about 100 billion nerve cells (neurons) • And trillions of "support cells" called glia. • SPINAL CHORD • The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. • The vertebral column, the collection of bones (back bone) that houses the spinal cord, is about 70 cm long. • Therefore, the spinal cord is much shorter than the vertebral column.
PART OF CENTRAL NERVOUS SYSTEM DIENCEPHALON TELENCEPHALON MYELENCEPHALON MESENCEPHALON METENCEPHALON
NEOCORTEX = ISOCORTEX • >1010 neurones, each with 5,000 - 100,000 synapses; the most complex structure known. • Neocortex = isocortex: essentially same basic structure (machinery) everywhere, but modified by particular connections and by adaptation (learning). • Organised into columns ~ 300 μm diameter running from pia to white matter. • Most connections run ‘vertically’ (i.e. perpendicular to pia).
GROSS ANATOMY OF BRAIN • Brain composes to 4 main lobes. • Each of the main lobes: • Frontal, • Parietal, • Occipital, and • Temporal
GYRI AND SULCUS OF THE CEREBRAL CORTEX • The furrowed surface of the cortex can be viewed as hills (gyri) and valleys (sulci).
PRIMARY CORTICAL AREAS • Identify thefollowing primary cortical areas: • Auditory, • Visual, • Gustatory, • Olfactory, • Somatosensory, • Motor.
FUNCTIONAL DIVISION OF THE CEREBRAL CORTEX • Functional specializations is discovered by extirpation (ablation), clinical lesions, stimulation of certain regions, on gross and micro recording of the neurons' electrical activity, or PET-detected patterns of glucose use, in response to specific stimuli, e.g., visual.
BRAIN: HOMUNCULUS • The spatial representation of information is maintained in the cortex as maps. • Maps representing parts of the body are somatotopic. • A map of the body is called an homunculus. • Visual maps are "visuotopic" etc. • Motor maps are also somatotopic. • A given region of cortex can contain multiple maps.
BRAIN: CYTOARCHITECTURE • The cortex is divided into a number of functionally and cytoarchitectonically distinct regions. • Several large sulci divide up the main subdivisions.
HISTOLOGICAL DIVISION OF THE CEREBRAL CORTEX • Histological Classification is based on cell or cytoarchitecture, and fibro architecture. • Histologically defined areas often match with functional areas. • The histological parcellation of the cortex is commonly adopts by Brodmann.
CEREBRALCORTEXHISTOLOGY • In the cerebrum and cerebellum compose to cortex and white matter. • Thecell bodies and dendrites of neurons are on the surfaceand it is called cerebral cortex(shell) • Myelinated axons (white matter) is located in the internal part of the hemispheres. • The white matter of the cerebral hemispheres and spinal cord consists of myelin, oligodendroglia, astrocytes, microglia, and blood vessels. • White matter can not contains neurons. • The central portion of the cerebral hemispheres (basal ganglia - diencephalons) and the brainstem contain several masses of neurons (nuclei) • Nuclei are intimately mixed with white matter.
HISTOLOGY OF CEREBRAL CORTEX • The cortical surface is composed of six layers of fibers and cell bodies. • Between layers receive information from other neural areas and send information to other neural areas and the spinal cord. • The axonsof the cell bodiesform the white matter. • White matter is located the bottom of the layers.. • Layers 1, 3, and 5 are usually the easiest to identify.
NEO CORTEX HISTOLOGY • The neocortex represents the great majority of the cerebral cortex. • The six layers of this part of the cortex are numbered with Roman numerals from superficial to deep. • Layer I is the molecular layer, which contains very few neurons; • Layer II the external granular layer; • Layer III the external pyramidal layer; • Layer IV the internal granular layer; • Layer V the internal pyramidal (agranular) layer; and • Layer VI the multiform, or fusiform layer. • Each cortical layer contains different neuronal shapes, sizes and density as well as different organizations of nerve fibers.