Digital Neuroanatomy

DIGITAL NEUROANATOMY

EM NEUROHISTOLOGY George R. Leichnetz, Ph.D. Professor, Department of Anatomy & Neurobiology Virginia Commonwealth University 2004 Acknowledgement: EM’s from Dr. John T. Povlishock

Press the Å and Æ keys on your keyboard to navigate through this lecture Electron-Microscopic Neurohistology At the ultrastructural level, neuron cell bodies (soma) contain abundant rough endoplasmic reticulum (RER; Nissl substance), mitochondria, lysosomes, and lipofuscin (pigment of age).

Lipofuscin Mitochondria

Cytoplasm is rich with organelles

Nucleus Lysosomes Nucleus Nucleolus Nucleolus Perineuronal oligodendrocyte Rough endoplasmic reticulum The cell body (soma, (Nissl substance) perikaryon) of the neuron contains nucleus, nucleolus, RER, free ribosomes, Golgi apparatus, mitochondria, and Nucleus lysosomes.

Perineuronal oligodendrocyte

Multiple lysosomes

Rough endoplasmic Large reticulum (Nissl) dendrite

Dendrite Golgi Complex - In its perinuclear location, the Golgi is contiguous with the cisternae of the RER and concentrates newly RER synthesized proteins in vesicles.

Nucleus Golgi Complex Hippocampal Pyramidal Cell with adjacent Perineuronal Oligodendrocytes

Apical dendrite Perineuronal Myelinated oligodendrocyte axon

Lysosomes

Abundant unmyelinated Lipofuscin axons in cross section Lipofuscin (pigment of old age) probably Nucleus & derived from lysosomes, nucleolus Capillary have a signet-ring appearance (vacuole Perineuronal with dark cap). oligodendrocyte Large dendrites (near Myelinated axon Axodendritic synapse w the cell body) contain synaptic vesicles neurotubules, neurofilaments, and Axon terminal mitochondria.

Large dendrite Mitochondrion

Neurofilaments

Neurotubules A large dendrite gives off a dendritic spine (see challis shape with spiny apparatus, smooth ER) which has an axospinous synapse.

Dendritic spine

Dendrite

Spine Dendrite

Axospinous synapse

Dendrite

Axon

Astrocytic processes with glycogen The dendritic spine has a challis-like shape and contains the spine apparatus (smooth ER).

Spine apparatus

Dendrite Axospinous synapse At the ultrastructural level, axon terminals are seen to contain abundant synaptic vesicles and mitochondria. Here the terminal bouton ends on the dendrite of another neuron (axodendritic synapse). Translucent round vesicles typically contain excitatory neurotransmitters, like glutamate. Typically excitatory axons terminals end in asymmetric synapses. Clear, round synaptic vesicles In an asymmetric excitatory synapse, the post-synaptic density is thicker. Asymmetric There are pleomorphic axon terminals in the CNS that contain both flattened (inhibitory) and spheroidal (excitatory) synaptic vesicles. This co-localization of vesicles suggests that both may be released from the terminal. Myelinated axon w neurofilaments Multiple axodendritic synapses on a large

Myelin dendrite. The axon terminal boutons contain clear round synaptic vesicles and Dendrite mitochondria. The dendrite is seen to contain neurotubules, neurofilaments, and Axon terminal w mitochondria. large mitochondria

Myelinated axons This axon terminal (axodendritic synapse) appears to contain both round and flat clear synaptic vesicles. Flattened vesicles typically contain inhibitory neurotransmitters, like GABA.

Dendrite w neurotubules & neurofilaments

Flat translucent vesicle

Axon terminal bouton

Mitochondrion Axon terminal with dense core vesicles which typically contain catecholamines, like norepinephrine and dopamine.

Dense core vesicles

Protoplasmic astrocytic process w glycogen granules

Myelinated axon The major dense line results Myelinated Axon from the fusion of the inner leaflets of the Schwann cell membrane that wraps the axon. The intraperiod line (alternating between major dense lines) results from the fusion of the outer leaflets.

The myelin sheath of PNS Major dense line axons is made up of concentric wrappings of the Schwann cell membrane The thicker the myelin, the faster the around the axon. conduction velocity of the nerve. Unmyelinated axons Unmyelinated axons are not “uninsulated”. The Schwann cell membrane invests a group of axons but does not give rise to concentric wrappings of Schwann cell myelin around membrane individual axons.

Schwann cell nucleus Protoplasmic Astrocyte Protoplasmic astrocytes are found in gray matter in the CNS. Its cytoplasm Large astrocytic contains abundant process w glycogen organelles like granules mitochondria.

Protoplasmic astrocyte nucleus The Interfascicular Oligodendrocyte oligodendrocyte is responsible for myelinization of Myelinated axons CNS axons. It extends its membrane to surround multiple axons (>50). The cell is heterochromatic, is electron-dense, Oligodendrocyte nucleus and is seen here in the midst of a whole field of myelinated axons. Fibrous astrocytes, Capillary found in CNS white matter (containing

Dendrite myelinated axons), have glial filaments in their cytoplasm.

Dendrite

Myelinated axons Fibrous astrocyte Myelinated processes in white axon matter adjacent to a brain capillary.

Axodendritic synapse

Fibrous astrocyte processes w glial filaments

Dendrite w neurotubules and neurofilamaents Excitatory axon terminal containing clear, round synaptic Axodendritic synapse vesicles

Fibrous astrocytic processes w glial filaments

Mitochondria

Dendrite w Myelinated neurotubules and axon neurofilaments