What Cell Make Up the Brain and Spinal Cord

Transcription

1 What Cell Make Up the Brain and Spinal Cord Jennifer LaVail, Ph.D. (

2 What kinds of cells are these?" Neuron?" Epithelial cell?" Glial cell?"

3 What makes a neuron special? The neuron has the same biochemistry and complement of organelles as other cells of the body.

4 Cell types But, neurons are remarkable for their polarity. Structurally the two most distinctive features of the neuron are its polarized shape and localized secretory function.

5 Parts of the neuron Among all the cells in" our body, only neurons" have axons." The axon requires unusual modifications of the cytoskeleton and specialized" intracellular transport mechanisms." Action potential"

6 Microtubule polarity Microtubule polarity Fibroblasts have continuous µts. Fibroblasts have unipolar µts. Neurons have multiple µts." Axons have unipolar µts." Dendritic µts have mixed polarity.

7 Soma The neuron cell body is the primary location of protein synthesis." Most of the proteins for axon maintenance and synaptic function" have to be transported to the axon." Where is the cell body?"

8 The soma What is special" about this neuron" cell body?" Electron micrograph of a neuronal cell body Cytoplasm = pink; nucleus = yellow

9 Electron micrograph of Nissl bodies (stacks of RER) protein synthesis machines

10 DRG axon hillock Neuron cell body also has polarity axon hillock - region with no ribosomes beginning of the axon."

11 Neuronal polarity

12 Dendrites pyramidal-purkinje Dendrites" Input region of neuron" Form of energy varies, e.g.," chemical, stretch, thermal, " neurochemical." Integrates excitatory and inhibitory" synaptic inputs.

13 processes Principal structures of a neuron Cell Body" Dendrites" Axon hillock" Initial Segment" Axon" Synaptic terminals Pyramidal neuron, rat cerebral cortex Blowfly neuron

14 Motoneuron axons grow long distances to muscle endplateso"

15 Motor end plate 2 The structure of chemical synapses Neuromuscular junction in Lateral rectus muscle

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17 Chemical Synapse" Voltage-sensitive" calcium channels" Synaptic cleft" nm"

18 Axon terminal

19 synapse CNS synapses" Synaptic components:" Synaptic vesicles" Presynaptic membrane" Synaptic cleft" Postsynaptic membrane

20 Synapse em-2 Two large synaptic terminals containing mitochondria contacting a dendrite A synaptic terminal containing dense cored vesicle indicating the presence of catecholamine transmitters

21 Synapse em3 A large dendrite and spine contacted by many synaptic boutons

22 Distinguishing characteristics of axons and dendrites! Characteristic!!Axon!!!Dendrite! Ontogeny" " "develops early " "develops later Length " " "several µm to >1 m " "limited" Size/Shape " "0.1 to 20 µm " "0.1 5 µm" " " "uniform diameter " "tapered" Axon hillock " "present " " "absent" " " "" RER " " "absent " " "present" Cytoplasm vol. " "100 x greater " "relatively little" Number per neuron" "1 " " "> 1" " " "" Excitability " "conducts AP " "passive spread" Myelin " " "present on axons " "rare but glial wrap " " " " >than 1 um" Major Point: Mature axon has no RER, ribosomes, Golgi, so no way to make proteins. Proteins have to be transported into and along axon.!

23 giraffe Neuron cell body" ~100 µm"

24 Embryonic neurons move, axons grow." Motile embryonic neuron Differentiating neuronal cells (actin, microtubules and DNA)" Torsten Wittman"

25 Axonal transport The components of axonal transport cargo" motor" microtubules Cargo comprised of protein, peptides, proteoglycans and amino acids." Most are transported within organelles. (No synaptic vesicle transport)." Rates are about mm/day or much slower, 1-2 mm/day." Bidirectional movement depends on balance of cytoplasmic motors."

26 Axonal transport of virus" HSV transport

27 Cell with myelin The myelin sheath along a myelinated CNS axon is composed of sections of myelin made from a number of individual cells Remember, however, not all axons are myelinated. Small diameter axons generally have no myelin covering.

28 Myelin

29 Axon PNS In the PNS axons less than 1 µm in diameter are unmyelinated.

30 sizes RELATIVE SIZES Structure " " "(mm) " " µm " "nm" Visual Cortex (thickness) "5 " " " "" Cortical column (thickness) "0.25 " "250 " "" Neuron cell body " " " " "" Red blood cell " " " " " 7 " "" Neuromuscular junction" " " " 2-4 " " "" Sympathetic axon " " " " 0.2 " "200" CNS synaptic bouton " " " " " Dense core synaptic vesicle " " " " "100" Synaptic vesicle" " " " " " " 50" Smooth endoplasmic reticulum " " " " " 5

31 Immunostaining Techniques:" Axonal transport" using virus or small" molecules as tracers." More details tomorrow" Red = biocytin. Retrograde label from thalamic injection Green = calbindin

32 glia Glia Astrocytes structural support insulation nutrition ion sink scar formation Oligodendrocytes myelin in the CNS Schwann cells myelin in the PNS Microglia inflammatory cells

33 Astrocyte diagram The astrocyte, unsung hero of the nervous system

34 Astrocytes Astrocytes (green) in the cerebral cortex

35 Spot the astrocytes! They are blue!

36 GFAP astrocytes Slide 18 astrocyte process White matter of spinal cord stained with astrocyte marker -GFAP (green). " Schwann cell myelin in rootlets of dorsal root ganglion cells stained with " myelin-p0 marker, orange.

37 Glia astrocyt The Structure of CNS glial cells Astrocyte Functions: Support" Sink for neurotransmitters and ions in ECS" Deliver nutriments" Phagocyte necrotic cells" Sink for material in perivascular space" endothelial cell" Pericyte (dendritic cell) astrocyte astrocyte end feet

38 BBB The blood brain barrier: tight junctions between endothelial cells

39 The blood brain barrier