ch.07. nervous-system.pptx

Nervous System Kristine Krafts, M.D. More Nervous System Lecture Objectives • Describe myelin and its production in the central and peripheral nervous systems. • Describe the histologic structure and distribution of the meninges. • Describe the blood-brain barrier. • Describe the histologic featur...

Nervous System Kristine Krafts, M.D. More Nervous System Lecture Objectives • Describe myelin and its production in the central and peripheral nervous systems. • Describe the histologic structure and distribution of the meninges. • Describe the blood-brain barrier. • Describe the histologic features of nerve fibers in the peripheral nervous system. Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Central nervous system • Peripheral nervous system Nervous System Lecture Outline • Organization of the nervous system Organization of Nervous System • Central nervous system (CNS) = brain + spinal cord • Peripheral nervous system (PNS) = peripheral nerves + nerve ganglia (groups of nerve cell bodies outside the CNS) • Peripheral nervous system has motor and sensory components. Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Neurons • Glial cells Two Main Cell Types in Nerve Tissue • Neurons (nerve cells) • Glial cells • Astrocytes • Oligodendrocytes • Ependymal cells • Microglia • Schwann cells Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Neurons Neurons Large pale nucleus Nucleolus Nissl substance Neuron cell body Gorgeous, sexy neuron and neuropil Gorgeous, sexy J. Crew shimmer net skirt Neuron • Cell membrane is covered with synapses from multiple dendrites • 1 axon per neuron • Abundant intermediate filaments called neurofilaments help support structure (and stain with silver Lipofuscin Liposfuscin pigment represents lysosomes with undigested debris. From the Latin fuscus (brown, muddy). As in obfuscate (to make something unclear). Dendrites • Dendrites are important signal reception and processing sites on neurons. • Dendrites branch to allow neurons to receive signals from numerous other neurons. • Dendritic spines are tiny protrusions from dendrites that receive information from a single axon. These guys facilitate learning, memory and neuronal plasticity. Neurons typically have numerous short dendrites which subdivide into thinner branches and receive Dendritic spines Purkinje cell pyramidal cell stellate cell cell of Martinotti horizontal cell of Cajal granule cell lower motor neuron The amount and type of dendritic branching can determine the type of neuron! Axons • Neurons typically have only one axon. The axon does not branch and has a constant diameter. • Axons arise from pyramid shaped axon hillock on neuron cell body. • Axons are usually very long processes. Axoplasm • Axoplasm = the cytoplasmic contents of an axon • Axoplasm contains neurofilaments, microtubules, mitochondria and some smooth ER. • Axoplasm does NOT contain rough ER or polyribosomes, so the axon depends on perikaryon for viability. • If severed, the peripheral part of the axon dies. Neuron Synapses Presynaptic axon terminal (terminal bouton) Contains synaptic vesicles and mitochondria. Synaptic cleft Space between pre and postsynaptic structures. Postsynaptic structure Dendrite, cell body, axon terminal, or effector cell. Membrane contains ion Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Neurons • Glial cells Glial Cells • 10x more abundant than neurons in brain • Support and protect neurons • Five types, each with different functions: • Astrocytes • Oligodendrocytes • Schwann cell • Ependymal cell • Microglial cells Location and Function of Glial Cells Glial cell type Locati Main functions on Astrocyte CNS Provides structural support, helps repair cells, participates in blood-brain barrier, provides nutrition Oligodendrocy te CNS Makes myelin, insulates axons Schwann cell PNS Makes myelin, insulates axons Ependymal cell CNS Lines cavities of CNS Microglial cell CNS Eats up debris and dead cells Neuropil is a dense network of glial fibers (especially those of astrocytes), axons, and dendrites in gray matter. Astrocytes and Neuropil Astrocytes • Most numerous of all the glial cells • Contain bundles of intermediate filaments called glial fibrillary acid protein (GFAP) • Bind neurons to capillaries and to pia mater • Bind to endothelial cells and neurons using little “end feet.” Involved in transfer of molecules from blood to neurons; also involved in blood-brain barrier. Astrocyte foot processes bind to capillaries and neurons Astrocytes • Contain receptors to respond to stimuli • Communicate with other glial cells • Support survival and activity of neurons by regulating composition of extracellular environment, absorbing excess neurotransmitters, and releasing neuroactive substances • Proliferate to form cellular “scar tissue” when Oligodendrocytes produce myelin in the CNS and are the predominant cell in CNS white matter. Ependymal cells Ependymal cells • Line central canal of spinal cord and ventricles of brain. • Cuboidal to low columnar, with cilia and microvilli. • In roof of ventricles, become connected with capillary loops, forming the choroid plexus. • Ependymal cells of the choroid plexus produce CSF by transporting and secreting materials Microglial cells Microglia • Small cells with short irregular processes. • Migrate throughout neuropil, secrete cytokines, and act as immune defender cells. • Originate from monocytes and have similar phagocytic functions. Main Glial Cell of the PNS Neurolemmocyte or Schwann cell Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Central nervous system • Spinal cord • Cerebrum • Cerebellum • Meninges Gross anatomy of brain Organization of Central Nervous System (CNS) • Organs • Cerebrum • Cerebellum • Brain stem • Spinal cord • Regions within organs • Gray matter • White matter • Meninges: connective tissue covering Gray Matter and White Matter • Gray matter contains neuron cell bodies, dendrites, unmyelinated axons, glial cells and synapses • White matter contains myelinated axons and oligodendrocytes • Brain: gray matter outside, white matter inside • Spinal cord: white matter outside, gray matter inside Spinal Cord Cross Section Gray matter inside White matter outside Central canal Spinal Cord Cross Section Gray matter inside White matter outside Spinal Cord White matter: myelinated axons and Gray matter: neurons Cerebral Cortex • Cerebral cortex has 6 poorlydefined layers. • Pyramidal neurons are the most abundant neurons in the cerebral cortex. Cerebral Cortex • This is a section from gray matter which is on the outside. • Note long dendrites of pyramidal neurons extending toward surface of cortex. • This is a silver stain which really highlights neural cells. Cerebellum Three layers of gray matter: 1. Molecular layer. Outermost layer. Contains granular cell axons, Purkinje dendrites, and glial cells. 2. Purkinje cell layer. Middle layer. Contains large, prominent “Purkinje” neurons. 3. Granular layer. Innermost layer. Contains very small neurons. Cerebellum: gray matter Meninges Three layers; surround brain and spinal cord. Dura mater (“tough mother”) Outermost layer. Dense connective tissue. Arachnoid (“spider-like”) Middle layer. Two parts: one is in contact with dura mater. Other contains trabeculae (like spider legs?) which connect arachnoid with pia. Pia mater (“tender mother”) Innermost layer. Loose connective tissue lining surface of brain. Blood-Brain Barrier • Prevents passage of some drugs and toxins from blood into CNS tissue • Exists because capillaries in brain are less permeable than capillaries elsewhere. • Brain capillaries have tight (occluding) junctions between endothelial cells. • Astrocyte foot processes surround capillaries and form part of barrier. BloodBrain Barrier 1. Astrocyte foot processes 2. Endothelial cell tight junctions Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Central nervous system • Peripheral nervous system Main Components of the Peripheral Nervous System • Nerves. Bundle of nerve fibers (axons) surrounded by glial cells (Schwann cells) and connective tissue. • Ganglia. Collections of neuron cell bodies. • Specialized nerve endings. Structures that perform special tasks, like responding to vibration. Schwann cells Schwann cell • Schwann cells surround and form myelin around PNS axons. • Small axons are have a Schwann cell but are not myelinated. Myeli n Schwann Cell Myelinating an Axon Axon Myeli n Nodes of Ranvier are breaks in myelin sheath. Action potentials jump between nodes. Nerve Fibers are Grouped into Nerve Bundles • Epineurium. Outer dense connective tissue fibrous coat surrounding nerve bundles and spaces between nerve fibers. • Perineurium. Surrounds each fiber bundle or fascicle. Cells of perineurium joined by tight junctions to prevent passage of most molecules. • Endoneurium. Surround each axon and its Schwann cell. Epineurium (E) and perineurium (P) surround nerve bundles (N) Epineurium, perineurium and endoneurium Nervous System Lecture Outline • Organization of the nervous system • Cells of the nervous system • Central nervous system • Peripheral nervous system