Neurohistology - BIOL 2051/2052 Lecture Notes PDF

Neurohistology BIOL 2051/2052 Dr. Melissa Andrews ([email protected]) October 15, 2024  Lecture Objectives Identify and describe the different cell types in the central and peripheral nervous systems (neurons, glia, other supporting cells) Describe the charact...

Neurohistology BIOL 2051/2052 Dr. Melissa Andrews ([email protected]) October 15, 2024  Lecture Objectives Identify and describe the different cell types in the central and peripheral nervous systems (neurons, glia, other supporting cells) Describe the characteristic Histology and Anatomy of the: – Cytoarchitecture of cerebral cortex, cerebellar cortex, ganglia – Supporting cell types (astrocytes, microglia) Distinguish myelination differences (oligodendrocytes and Schwann cells) in the central and peripheral Recommended reading: Chapter 1 (Studying the nervous systems Nervous System in Humans and Other Animals) in Neuroscience, 3rd ed by Purves et al (check later editions for chapter number) rvous Tissue and Neurons Ectodermally derived One of the four basic tissue types Consisting of two principal cell types neurons supporting cells (neuroglia) Neurons Neurons are excitable cells with long cytoplasmic extensions specialised for reception of stimuli and conduction of a nerve impulse (action potentials). Neurons do not undergo cell division and replication Example of a multipolar Neuronal structure Dendrites receive information from adjacent axons. Axons send information Myeli from one end of the n neuron to other (faster if begin s myelinated). after the AIS Signals from the cell soma are summated at the axon hillock. The hillock is considered the ‘trigger zone’ which must reach threshold potential to achieve an action potential. Both the hillock and Axon hillock and axon initial segment MAP2 - neuron-specific cytoskeletal proteins found in dendrites (microtubule associated protein) bIV spectrin – cytoskeletal Neuronal Arrows indicate direction of signal transmission subtypes 3 types of neurons: -Motor neurons relay commands from brain and spinal cord to muscles and glands. -Sensory neurons -Interneurons Cell soma diameter: ranges ltipolar neurons – Golgi stain Golgi stain: Nervous tissue treated with potassium dichromate and silver nitrate results in silver precipitation (from silver chromate) inside the neurons tor Neurons in the spinal cord Cell bodies of multipolar motor neurons are large and are found in the ventral horn of the spinal cord. olar neurons – Nissl stain and protein synthesi nucleolus Nissl substance xon endrite Nissl substance stains rough endoplasmic reticulum and polyribosomes, important in protein synthesis. Nissl substance is largely absent in the axon.  Arrows indicate direction of signal Neuronal transmission subtypes 3 types of neurons: -Motor neurons -Sensory neurons are excited by specific stimuli. -Interneurons Cell soma diameter: ranges pinal Ganglia Ganglia are Dorsal root ganglia are aggregations of nerve surrounded by a connective cells (ganglion cells) tissue capsule, which is outside the CNS. continuous with the peripheral nerve Individual ganglion cells are surrounded by a layer of flattened satellite (fibroblast) cells. pinal Ganglia Satellite Cells Ganglion Cell Ganglion Cell Satellite Cells  Arrows indicate direction of signal Neuronal transmission subtypes 3 types of neurons: -Motor neurons -Sensory neurons -Interneurons integrate information from sensory to motor neurons. Cell soma diameter: ranges from rebral Cortex (Neocortex) The cerebral cortex is divided into six layers each housing neurons whose morphology is characteristic of that layer. ytoarchitecture of the cerebral cortex rebral Cortex (Neocortex) Deep to the grey matter is white matter composed of myelinated fibres. I Superficially, the II meningeal layers can be observed. III IV V VI amidal neurons (Golgi stain) Note: ‘Pyramidal’ and ‘granule’ neurons are not unique to the cortex erebellar Cortex Cytoarchitecture of the cerebellar cortex: three layers within the gray matter with a variety of cell types, with 3 layers:fibres in the white myelinated outer matter (deep Molecular to gray matter) layer a single layer of Purkinje cells a Granular layer Molecular layer: basket cells, stellate cells Purkinje Layer: Purkinje cells Granule layer: Granule cells (most abundant neuron in brain), erebellar Cortex 3 layers: outer Molecular layer a single layer of Purkinje cells a Granular layer kinje neurons (cerebellum) Purkinje neurons are the largest cell in the cerebellum They have pear-shaped cell bodies and a distinctive dendritic tree (in the molecular layer), they receive afferent pporting cells - neuroglia Glia Neuron Neuroglial cells function in the metabolism and support of neurons In the CNS there are astrocytes, oligodendroglia, ependymal cells and microglia In the PNS there are Schwann cells and satellite cells Astrocytes Example of a protoplasmic astrocyte Provide structural and metabolic support for neurons Types: fibrous (in white matter) protoplasmic (in gray matter) Müller glia (in retina) radial glia (specialised cells in developing CNS) Examples of fibrous astrocytes ood-Brain Barrier Form glial-limiting membrane around blood vessels and along CNS surface (as part of the blood brain barrier) A barrier composed of endothelial cells joined by tight junctions Prevents diffusion of solutes and fluid into brain and spinal cord O2, CO2, lipid soluble molecules (hormones) >500daltons MW not permissible Microglia Serve an immune function within the CNS able to phagocytose cell debris in response to injury Normally exist as ‘resident microglia’ but become ‘activated’ upon CNS damage and actively move towards sites of injury Release cytokines which can both help and hinder recovery  ligodendrocytes Form myelin sheath around CNS axons, with one oligodendrocyte able to myelinate several axons Diseases that affect oligodendrocytes include multiple sclerosis and leukodystrophies One of the last cell types to form Schwann cells during development Form myelin sheath around PNS axons, with one Schwann cell able to myelinate one axon Plays key role in organisation of connective tissue sheaths around peripheral nerves during development and Myelination Myelin consists of ~80% lipid and provides insulation as well as enhanced conduction velocity for action potentials Myelination 1 cell: many axons Scanni Myelin - oligodendrocytes ng EM Myelin – Schwann cells Cell bod y Cell body Layers of myelin 1 cell: 1 axon Transmiss ion EM nation required? – Not all axons are myelinated Electron micrograph of unmyelinate d axons in the PNS. hwann cells ‘envelope’ unmyelinated axons contacting 1 or more ax nmyelinated axons are not associated with glial cells. inated axons have ‘continuous conduction’ of action potentials due t flow (low conduction). es of unmyelinated axons are sensory fibres carrying pain, temperat