Introduction to Nervous System PDF

Introduction to Nervous System Jean-Pierre Louboutin 4/9/2024 Jean-Pierre Louboutin - Neurologist - MD: dissertation on correlations between clinical, neurophysiological and neuroradiological data in Multiple Sclerosis - PhD: dissertation on morphological and physiological pr...

Introduction to Nervous System Jean-Pierre Louboutin 4/9/2024 Jean-Pierre Louboutin - Neurologist - MD: dissertation on correlations between clinical, neurophysiological and neuroradiological data in Multiple Sclerosis - PhD: dissertation on morphological and physiological properties during skeletal muscle regeneration - Research in USA (Philadelphia) focused on gene/cell therapy/immunology (University of Pennsylvania, UPENN, 6 years) and also on physiopathology and molecular therapy of HIV-1- associated dementia (Thomas Jefferson University, 7 years) A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives Introduction to Nervous System  Definitions Four basic types of animal tissues:. Nervous tissue. Epithelia. Connective tissue. Muscle tissue - Nervous system and endocrine system control the functions of the body - Nervous system is composed of specialized cells whose function is to receive sensory stimuli and to transmit them to effector organs, whether muscular or glandular - The nervous system of higher species has the ability to store sensory information received during past experiences - The nervous system is divided into two main parts: + Central Nervous System (CNS) consists of brain and spinal cord + Peripheral Nervous System (PNS) consists of cranial nerves and spinal nerves which are located outside the CNS and associated ganglia - The autonomic nervous system is concerned with the innervation of involontary structures (heart, smooth muscles, glands). It is distributed throughout central and peripheral nervous systems. Divided into 2 parts, both having afferent and efferent fibers: + Sympathetic part: prepares the body for an emergency + Parasympathetic part: conserving and restoring energy A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives  Organization of the Central Nervous System - Central Nervous System (CNS) consists of brain and spinal cord - Cells of the nervous tissue are neurons: excitable nerve cells with typically several dendrites and only one axon - Neurons are the core components of the nervous system - Surrounding the CNS neurons are supportive cells called neuroglia (or glia). These cells form the nonneural component of the CNS - Brain and spinal cord are covered with a system of membranes called meninges and are suspended in the cerebrospinal fluid - Brain and spinal cord contain gray and white matters  Meninges and Cerebrospinal fluid - CNS surrounded by bones and cerebrospinal fluid (CSF) - Dura mater is the toughest outermost connective tissue layer around the CNS - Arachnoid mater and dura mater cover the CNS on external surfaces - Pia mater adheres to surfaces of brain and spinal cord - Between pia mater and arachnoid mater is subarachnoid space - CSF circulates in subarachnoidoid space and protects brain and spinal cord  White and gray matter - Brain and spinal cord contain gray and white matters + Gray matter: - Gray matter of the CNS consists of neurons, their dendrites and the supportive cells, called glia (or neuroglia) - Represents the sites of connections or synapses between numerous neurons and dendrites - Gray matter covers the surface of the brain (cerebrum) and the cerebellum + White matter: - White matter in the CNS is devoid of neuronal bodies and consists primarily of myelinated axons and supportive myelinating cells called oligodendrocytes - The myelin sheaths around the axons gives a white color to this region of the CNS Major divisions of the CNS Spinal cord Runs through the vertebral canal Surrounded by 3 meninges Protected by CSF in subarachnoid space Extends from foramen magnum (continuous with medulla oblongata) to second lumbar vertebra Regions - Cervical - Thoracic - Lumbar - Sacral - Coccygeal Gives rise to 31 pairs of spinal nerves – All are mixed nerves Not uniform in diameter - Cervical enlargement: supplies upper limbs - Lumbar enlargement: supplies lower limbs. Conus medullaris- tapered inferior end - Ends between L1 and L2. Cauda equina - origin of spinal nerves extending inferiorly from conus medullaris. Filum terminale- anchors spinal cord to coccyx Meninges of the spinal cord Connective tissue membranes - Dura mater: outermost layer; continuous with epineurium of the spinal nerves - Arachnoid mater - Pia mater: bound tightly to surface - Forms the filum terminale- anchors spinal cord to coccyx - Forms the denticulate ligaments that attach the spinal cord to the dura Spaces - Epidural: external to the dura - Anesthestics injected here - Fat-fill - Subdural space: between dura and arachnoid - Serous fluid - Subarachnoid: between pia and arachnoid - Filled with CSF (lumbar puncture between L3-L4 or better between L4-L5) Structure of the spinal cord. Anterior median fissure and posterior median sulcus - deep clefts partially separating left and right halves. Gray matter: neuron cell bodies, dendrites, axons - Divided into horns. Posterior (dorsal) horn. Anterior (ventral) horn. Lateral horn. White matter - Myelinated axons - Divided into three columns (funiculi). Ventral. Dorsal. Lateral - Each of these divided into sensory or motor tracts. Commissures: connections between left and right halves - Gray with central canal in the center - White (only anterior). Roots - Spinal nerves arise as rootlets then combine to form dorsal and ventral roots - Dorsal and ventral roots merge laterally and form the spinal nerve  Brain - Lies in the cranial cavity - Continuous with spinal cord through the foramen magnum - Surrounded by 3 meninges - Can be divided in 3 divisions: + hind brain + midbrain + forebrain - Hind brain can be divided into medulla oblongata, pons and cerebellum - Forebrain can be divided into: diencephalon and cerebrum - Medulla oblongata, pons and midbrain form the brainstem Anatomical planes of the brain  Cerebrum Lateral Cerebellum Brainstem Cerebrum Sagittal Diencephalon Midbrain Brainstem Cerebellum Pons Medulla oblongata Spinal cord  Brainstem + Medulla oblongata: connects the pons superiorly to the spinal cord inferiorly - Contains numerous collections of neurons called nuclei - Serves as conduits for ascending and descending nerve pathways + Pons: anterior surface of cerebellum, inf. to midbrain, superior to medulla oblongata - Pons, or bridge: large number of transverse fibers connecting the two cerebellar hemispheres. Many nuclei and ascending and descending nerve fibers + Midbrain: Connects the forebrain to the hindbrain- Dorsal region: tectum - Contains many nuclei (substantia nigra and red nucleus) and ascending and descending nerve fibers Coronal section 3: Midbrain 4: Pons 5: Medulla oblongata 6: Spinal cord  Cerebellum - Posterior to pons and medulla oblongata - Two laterally placed hemispheres connected by a median portion, vermis - Connected: + to the midbrain by superior cerebellar peduncles + To the pons by middle cerebellar peduncles + To the medulla oblongata by inferior cerebellar peduncles - Surface layer of each cerebellar hemisphere called cortex and composed of gray matter - Numerous convoluted folds called cerebellar folia separated by sulci. Covered by pia mater - Consists of an outer gray matter or cortex and an inner white matter  Diencephalon - Almost completely hidden from the surface of the brain. Contains: + Thalamus: consists of several nuclei receiving data from sensory systems and projecting to sensory areas of cerebral cortex + Ventral hypothalamus: important endocrine role + Epithalamus: pineal gland + Subthalamic nucleus Coronal section Diencephalon 2: Thalamus  Cerebrum - Largest part of the brain - Two cerebral hemispheres connected by bundles of white matter called corpus callosum - Each hemisphere extends from frontal to occipital bones in the skull - Surface layer of each hemisphere, the cortex, is composed of gray matter - Several folds or gyri, separated by fissures, or sulci (increasing the surface area of cortex) - Surface of each hemisphere is divided into lobes - Within the hemisphere is a central core of grey matter, basal nuclei or basal ganglia - Fan-shaped collection of nerve fibers, named the corona radiata, converges from the cerebral cortex to the basal nuclei then passes between them as the internal capsule - Nucleus situated on medial side of internal capsule is the caudate nucleus - On the lateral side of the internal capsule is the lentiform nucleus, formed of putamen and globus pallidus - Cavity present within each hemisphere is the lateral ventricle - Lateral ventricles communicate with the 3rd ventricle through the interventricular foramina  Parietal lobe Frontal lobe Occipital lobe External view Lateral sulcus Temporal lobe Sagittal section Corpus callosum Lateral sulcus Central sulcus  Lateral ventricle Frontal lobe Corpus callosum Caudate nucleus Corona Internal radiata capsule Putamen Globus Pallidus Lateral sulcus Gray matter Temporal White lobe matter Coronal section A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives  Major divisions of the PNS PNS consists of cranial and spinal (peripheral) nerves and their associated ganglia - There are: + 12 pairs of cranial nerve which leave the brain and pass through foramina in the skull + 31 pairs of spinal nerves which leave the spinal cord and pass through intervertebral foramina in the vertebral column - Spinal nerves are named according to the regions of the vertebral column with which they are associated: + 8 cervical + 12 thoracic + 5 lumbar + 5 sacral + 1 coccygeal - Note that there are 8 cervical nerves for only 7 cervical vertebrae and 1 coccygeal nerve for 4 coccygeal vertebrae - There are: + 12 pairs of cranial nerve + 31 pairs of spinal nerves leaving the spinal cord and pass through intervertebral foramina in the vertebral column - Spinal: + 8 cervical + 12 thoracic + 5 lumbar + 5 sacral + 1 coccygeal - Note: 8 cervical nerves for only 7 cervical vertebrae and 1 coccygeal nerve for 4 coccygeal vertebrae - Spinal nerve connected to the spinal nerve by two roots: + anterior root consisting of bundles of fibers called carrying nerve impulses away from the nervous system: efferent fibers. Efferent fibers that go to skeletal muscles and cause them to contract are motor fibers + posterior root consisting of bundles of fibers called afferent fibers that carry nervous impulses to the CNS. Because these fibers are concerned with conveying information about sensations of pain, touch, temperature and vibration, they are called sensory fibers. Cell bodies of these nerve fibers are located in posterior root ganglion - The spinal nerve roots pass from the spinal cord to the level of their respective intervertebral foramina, where they unite to form a spinal nerve. Here, motor and sensory fibers become mixed together  Ganglia of PNS - Divided into: + sensory ganglia of spinal nerves (posterior root ganglia) and cranial nerves - Situated on the posterior root of each spinal nerve + autonomic ganglia - Located along the course of efferent nerve fibers of the autonomic nervous system - Found in paravertebral sympathetic chains around the roots of visceral arteries in abdomen and close to the walls of various organs A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives  Brain development - Three main layers are differentiated before the formation of the Nervous System: + Innermost layer: Entoderm gives rise to gastrointestinal tract, lungs, liver + Mesoderm gives rise to muscle, connective tissues, vascular system + Outermost layer: Ectoderm gives rise to the skin and the nervous system - During 3rd week of development, ectoderm on dorsal surface of the embryo becomes thickened to form the neural plate - The plate develops a neural groove which then deepens and is bounded on either side by neural folds - Later on, the neural folds fuse converting the neural groove into a neural tube - During the invagination of the neural plate to form the neural groove, cells forming the lateral margin of the plate do not become incorporated in the neural tube but instead form a strip of ectodermal cells that lie between the neural tube and the covering ectoderm. This strip of cells is called neural crest - Cells of the neural crest will differentiate into cells of posterior root ganglia, sensory ganglia of cranial nerves, autonomic ganglia, melanocytes, cells of suprarenal medulla  Formation of neural plate Formation of neural tube Neural groove deepens and is bounded on either side by Neural groove deepening to neural fold form neural tube Formation of neural crest - In earliest stages, neural tube remains in communication with amniotic cavity through anterior and posterior neuropores Anterior neuropore Neural plate Fusion of neural folds Posterior neuropore - Later, the anterior neuropore closes first, then the posterior neuropore. Neural tube closure is complete within 28 days. Neural tube located beneath the surface ectoderm - Proliferation of cells at the cephalic end of the neural tubes causes it to dilate and form three primary brain vesicles about 3 weeks after the closure of the caudal neuropore: + Forebrain vesicle or prosencephalon + Midbrain vesicle or mesencephalon + Hindbrain vesicle or rhombencephalon - The rest of the tube elongates and will form the spinal form - During the 5th week, secondary swellings develop in prosencephalon and rhombencephalon and the number of vesicles becomes five: + telencephalon + diencephalon + mesencephalon + metencephalon + myelencephalon - The telencephalon becomes cerebral hemispheres containing corpus striatum, cerebral cortex, white matter, olfactory system - The diencephalon gives thalamus, hypothalamus, subthalamus, epithalamus - The mesencephalon becomes midbrain (tectum and cerebral peduncles) - The metencephalon gives pons and cerebellum - The myelencephalon becomes the medulla oblongata Formation of the brain vesicles - The telencephalon becomes cerebral hemispheres containing corpus striatum, cerebral cortex, white matter, olfactory system - The diencephalon gives thalamus, hypothalamus, subthalamus, epithalamus - The mesencephalon becomes tectum and cerebral peduncles - The metencephalon gives pons and cerebellum - The myelencephalon becomes the medulla oblongata A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives Neurobiology of neurons and neuroglia  Definitions - Cells of the nervous tissue are neurons - Neurons are the core components of the nervous system - Each neuron consists of: + a cell body, or soma, containing:. a nucleus. a nucleolus (function: transcribe ribosomal RNA). the surrounding cytoplasm (called perikaryon in neurons). numerous different organelles + numerous dendrites that form a dendritic tree + a single axon - Surrounding the CNS neurons are supportive cells called neuroglia (or glia). These cells form the nonneural component of the CNS - A number of specialized types of neurons exist: + Sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs. Sensory neurons then send signals to the spinal cord and brain + Motor neurons receive signals from the brain and spinal cord. Cause muscle contractions and affect glands + Interneurons connect neurons to other neurons within the same region of the brain or spinal cord - Axons arise from region called axon hillock - A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling - Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form neural networks - Dendrites are covered with dendritic spines making synapses with other neurons - Dendrites receive and integrate information from dendrites, neurons and axons - Neurons synthesize neurotransmitters in cell body - Axons transport neurotransmitters in microtubules to synapses - Stimuli cause conduction of nerve impulse (action potential) along the axons - Initial segment of axon is site where nerve impulse is generated - Rate of impulse depends on axon size and myelination (importance of myelin sheath)  Myelin sheaths and myelination of axons - Specialized cells wrap around axons to form lipid-rich, insulating myelin sheath - Myelin composed of lipids (80%) and proteins (15%) - Myelin sheath extends along length of axons to its terminal branches - The main purpose of a myelin layer (or sheath) is to increase the speed at which impulses propagate along the myelinated fiber - Gaps between myelin sheath are called nodes of Ranvier. Accelerate the conduction of nerve impulses along axons. In large myelinated axons, nerve impulse jumps from one node to the other, resulting in faster conduction of impulse: saltatory conduction - In CNS, oligodendrocytes myelinate numerous axons. In PNS, Schwann cells myelinate only one axon. Unmyelinated axons do not show nodes of Ranvier Axon Schwann cell Myelin sheath Myelination of peripheral axon EM Neuron of the Peripheral Nervous System Types of neurons 1. Unipolar neurons: Only one process leaving the cell body. Found in numerous sensory ganglia and peripheral nerves. Were initially bipolar during embryonic development 2. Bipolar neurons: Rare. Purely sensory neurons. Single dendritic tree and single axon. Found in retina, organs of hearing and equilibrium of the ear, olfactory epithelium of nose 3. Multipolar neurons: Most common type in the CNS. Include all motorneurons and interneurons of the brain,cerebellum and spinal cord. Numerous branched dendrites are projecting from the cell body. On the opposite side is a single axon 4. Pseudounipolar neurons: Sensory neuron in the PNS. One axon with 2 branches: one central (from cell body to spinal cord) and one peripheral (from cell body to periphery: skin, joint, muscle). No dendrites. Soma located in dorsal root ganglia A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives  Neurons in different parts of the brain 1. Cerebral cortex 2. Cerebellum 3. Spinal cord 1 2 3  Cerebral cortex + Layer I: Molecular layer. Covered by pia mater. Peripheral portion of layer I consists of glial cells and horizontal cells of Cajal + Layer II: External granular layer. Glial cells and small pyramidal cells. Apical dendrites directed toward the periphery of the cortex. Axons extend from the cell bases + Layer III: External pyramidal layer. Medium-sized pyramidal cells + Layer IV: Internal granular layer. Contains mainly small granules cells, glia and some pyramidal cells + Layer V: Internal pyramidal layer. Glial cells and largest pyramidal cells (especially in the motor area) + Layer VI: Multiform layer. Deepest layer. Adjacent to the white matter. Contains intermixed cells of varying sizes and shapes (granule cells, fusiform cells…). Bundles of axons leave the white matter 3 different types of silver staining A B C  Pyramidal cells stained by different types of silver impregnation Apical dendrite Apical dendrite Perikaryon Perikaryon Axon Nucleolus inside Pyramidal cells of Layer V the nucleus Pyramidal cells of Layer V Pyramidal cell of Layer V 3D- reconstruction Pyramidal cell of Layer V Different types of synapses between dendrites and axons  Cerebellum - Numerous convoluted folds called cerebellar folia separated by sulci. Covered by pia mater - Consists of an outer gray matter or cortex and an inner white matter - 3 different layers: + Outer molecular layer with fewer and smaller neurons but many fibers + Central Purkinje cell layer. Pyriform (pear-shaped), or pyramidal cells with ramified dendrites (tree) that extend into the molecular layer + Inner granular layer with numerous small neurons - White matter: core of each cerebellar folium. Consists of myelinated fibers or axons - Nerve axons are the afferent and efferent fibers of the cerebellar cortex  Purkinje cells - 3 different layers: + Outer molecular layer with fewer and smaller neurons but many fibers + Central Purkinje cell layer. Pyriform (pear-shaped), or pyramidal cells with ramified dendrites (tree) that extend into the molecular layer + Inner granular layer with numerous small neurons Hematoxylin Hematoxylin Silver staining Immunocytochemistry Spinal cord - Anterior gray horn: Multipolar motor neurons. Cytoplasm with prominent nucleus, a distinct nucleolus (stains dark), clumps of basophilic material called the Nissl Substance (granular endoplasmic reticulum), several radiating dendrites. Single axon - Nissl substance extends into the dendrites, not into the axon - Smaller glial cells - Silver staining: shows distribution of neurofibrils in both the gray matter and motor neurons. Fine neurofibrils throughout the cytoplasm and dendrites. Nuclei are yellow stained and nucleoli are dark stained. Many neurofibrils in the gray matter (belong to axons of anterior horn neurons or to glial cells) - Silver staining: shows distribution of neurofibrils in both the gray matter and motor neurons. Fine neurofibrils throughout the cytoplasm and dendrites. Nuclei are yellow stained and nucleoli are dark stained. Many neurofibrils in the gray matter (belong to axons of anterior horn neurons or to glial cells) A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives  Supporting cells in the CNS: Glia or neuroglia - Highly branched supportive nonneuronal cells in the CNS - Surround neurons, axons and dendrites - They do not become stimulated or conduct impulses - Different morphologically and functionally from the neurons - Can be distinguished by much smaller size - CNS contains tenfold more glial cells than neurons - Four types of glial cells are: + astrocytes + microglial cells + oligodendrocytes (role in myelin formation) + ependymal cells  Astrocytes - Small cell body, large oval nucleus, dark stained nucleolus - Long, thin and smooth radiating processes extending from the cell body (star-shaped like) - Two types: fibrous and protoplasmic Silver staining Immunocytochemistry Marker: glial fibrillary acidic protein (GFAP) - Astrocytes provide contact between neurons and capillaries. Support metabolic exchanges between neurons and capillaries - Perivascular feet of astrocytes cover the capillary basement membrane: form the blood-brain barrier which restricts the movement of molecules from the blood into the CNS - Astrocytes contain reserves of glycogen from which they release glucose contributing to energy metabolism of CNS - Astrocytes control chemical environment by reuptake of excessive potassium ions and some neurotransmitters like glutamate (then conversion of glutamate into glutamine). Role in detoxification - Role in brain inflammation and brain scar tissue (gliosis) EM  Microglial cells - Part of the mononuclear phagocyte system of the CNS originating from precursors in the bone marrow - Vary in shape, irregular contours; small deeply stained nucleus almost fills the entire cell - Cell processes are few, short and slender - Smallest glial cells; found in gray and white matter - Macrophages/phagocytes of the CNS: when tissue is damaged, microglia migrate to the area, proliferate, become phagocytic and remove dead or foreign tissue Silver staining - Marker: Iba-1  Oligodendrocytes - Small cells with few, thin, short processes without excessive branching - Found in both gray and white matter - In white matter, they form the myelin sheaths around several axons at one time by contrast to the Schwann cells in the PNS- Role in myelination Silver staining Silver staining EM Axon Myelin sheath  Ependymal cells - Line the ventricles in the brain and central canal of the spinal cord - Ciliated cells move the CSF through the central canal of the spinal cord A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives Peripheral nervous system  Definitions of peripheral nerve - Peripheral Nervous System (PNS) consists of neurons, glial cells (Schwann cells: myelinating cells) and axons outside the CNS - Cranial nerves arise from the brain and spinal nerves from the spinal cord - Ganglia are accumulation of neurons. They are covered by connective tissue - Nerves of PNS contains both sensory and motor neuron axons. These axons transmit informations between peripheral organs and the CNS Architecture of peripheral nerve - Peripheral nerve composed of numerous axons of different sizes surrounded by several layers of connective tissue. Partitioned into fascicles - Outermost connective tissue layer is epineurium - Connective tissue perineurium surrounds one or more nerve fascicles. Within each fascicle, are individual axons and their supporting cells, Schwann cells. Each Schwann cell myelinates a single axon - Loose vascular tissue layer endoneurium surrounds individual axons  Nerve Peripheral nerve Epineurium Perineurium fascicle Neurokeratin: protein network seen in myelin sheaths after myelin has been removed Osmic acid stains the myelin sheaths Osmium Nodes of Ranvier (accelerate the con- duction of nerve impulses along axons) Myelin sheath (dark band) Axon (lighter)  Dorsal root ganglia - Aggregation of neuron cell bodies located outside the CNS - Dorsal root ganglia located on dorsal nerve root - Numerous round unipolar neurons or sensory neurons - Numerous fascicles of nerve fibers pass between the unipolar neurons - Each dorsal ganglion enclosed by irregular connective tissue layer containing adipose cells, blood vessels and nerves - Nucleus with nucleolus - Small satellite cells: surround neurons of PNS ganglia; provide support, insulate and regulate metabolic exchange. They are enclosed by connective tissue capsule cells  Sympathetic and parasympathetic ganglia - Neurons are multipolar (par contrast with neurons of dorsal root ganglia) - Eccentric nuclei (eccentric: located at the periphery) - Satellite cells surround the multipolar neurons - In older individuals, lipofuscin pigment accumulates in cytoplasm of numerous cells  Receptor endings - Five types of receptor endings: + Mechanoreceptors: respond to mechanical deformation + Thermoreceptors: respond to changes in temperature + Nocireceptors: respond to any stimuli that bring damage to the tissue + Chemoreceptors: respond to chemical changes associated with taste and smell + Electromagnetic receptors: rods and cones of the retina are sensitive to changes in light intensity and wavelength  Type of Location Stimulus Sensory receptor modality Nonencapsulated receptors Free nerve Epidermis, Polymodality- Pain, touch endings dermis, Act as mechano- (crude), heat and ligaments, joint receptors, cold capsules, bone, thermoreceptors, dental pulp nocireceptors Merkel discs Hairless skin Mechanoreceptor Touch Hair follicle Hairy skin Mechanoreceptor Touch receptors Encapsulated receptors Meissner’s Dermal papillae Mechanoreceptor Touch corpuscules of skinof palm and sole of foot Pacinian Dermis, Mechanoreceptor Vibration corpuscules ligaments, joint capsules, peritoneum Ruffini Dermis of hairy Mechanoreceptor Stretch corpuscles skin Neuromuscular Skeletal muscle Mechanoreceptor Stretch-muscle spindles length Neurotendinous Tendons Mechanoreceptor Compression- spindles muscle tension  Skeletal muscle spindle - Muscle spindles are specialized stretch receptors located parallel to muscle fibers - Main function: to detect changes in the length of the muscle fibers: stimulates the muscle spindle and sends impulses via the afferent (sensory) axons into the spinal cord - These impulses result in a stretch reflex that immediately causes contraction of the extrafusal muscle fibers thereby shortening the stretched muscle and producing movement (example: tapping the patellar tendon of the knee)  Skeletal muscle contraction and effector endings - Skeletal muscles are voluntary muscles because stimulation for their contraction and relaxation is under conscious control - Large motor nerves innervate skeletal muscles - Motor unit corresponds to the skeletal muscle fibers innervated by a single motor neuron - Each skeletal muscle exhibits a specialized site where axons terminate: neuromuscular junction or motor endplate. Site where the impulse from the axon is transmitted to the skeletal muscle fiber  Neuromuscular junctions - Terminal end of each axon contains small vesicles of Histochemistry acetylcholine (ACh) Muscle fiber - Arrival of a nerve impulse at the axon terminal causes the synaptic vesicles to fuse with the plasma membrane of the axon and to release the ACh into the synaptic cleft - ACh then diffuses across the synaptic cleft, combines with ACh receptors on the cell membrane of the muscle fiber and stimulate the muscle to contract Axon - An enzyme called acetylcholinesterase (AChE), located in Node of Ranvier the synaptic cleft, inactivates the released ACh, preventing AChE further muscle stimulation and contraction until next staining impulse arrives - Staining of AChE demonstrates the neuromuscular junction Nerve AChE Muscle fiber Immunocytochemistry A. Introduction to Nervous System - Definitions - Organization of the Central Nervous System (CNS) + Meninges and Cerebrospinal fluid + White and gray matters + Major divisions of the CNS - Organization of the Peripheral Nervous System (PNS) - Brain development B. Neurobiology of neurons and neuroglia - Definitions - Neurons in: + Cerebral cortex (i.e., Pyramidal cells) + Cerebellum (i.e., Purkinje cells) + Spinal cord - Glial cells C. Peripheral nervous system - Nerve fibers and peripheral nerves - Receptor endings - Effector endings D. Objectives  Objectives - To know the definitions - To know the organization of CNS and PNS - To know the development of CNS - To know the different types of neurons (unipolar…) - To know and recognize the neurons in cerebral cortex, cerebellum and spinal cord - To know and recognize the different glial cells in the CNS - To know the definition and architecture of a peripheral nerve - To know the neurons and glial cells in the ganglia of PNS - To know effector and receptor endings