CELLS IN THE NERVOUS SYSTEM

Transcription

1 NEURONS AND GLIA

2 CELLS IN THE NERVOUS SYSTEM Glia Insulates, supports, and nourishes neurons Neurons Process information Sense environmental changes Communicate changes to other neurons Command body response

3 THE NEURON DOCTRINE Cells are in the range of mm of diameter Need for techniques that allow to see such small structures Histology Microscopic study of tissue structure The Nissl Stain (late XIX century) Colors selectively only part of the cell (Nissl body) Facilitates the study of cytoarchitecture in the CNS Differentiation between neuron and glia The Golgi Stain (1873) Revealed the entire structure of the neuron

4 THE NEURON DOCTRINE

5 THE NEURON DOCTRINE Camillo Golgi s reticular theory Neurites of different cells are fused together to form a continuous reticulum, a network (like blood circulation) Santiago Ramon y Cajal s neuron doctrine Neuron are not continuous one another but communicate by contact Shared the 1906 Nobel Prize in Physiology or Medicine

6 THE NEURON Neuronal membrane separate the inside from the outside The Soma Cytosol: Watery fluid inside the cell Organelles: Membrane-enclosed structures within the soma Nucleus Rough Endoplasmatic Reticulum, Smooth Endoplasmatic Reticulum, Golgi Apparatus Mitochondria Cytoplasm: Contents within a cell membrane (e.g., organelles, excluding the nucleus)

7 THE NUCLEUS Contains chromosomes that have the genetic material (DNA) Genes: segment of DNA Gene expression: reading of DNA in order to synthesize proteins Protein synthesis happen in the cytoplasm RNA is the messenger that carry the information contained in the DNA to the cytoplasm

8 THE NUCLEUS The enzyme RNA polymerase binds to the promoter of the gene in order to initiate transcription Exons: coding regions Introns: non coding regions In the cytoplasm mrna transcript is used to assemble proteins from amino acids DNA transcription mrna translation Proteins

9 ROUGH ENDOPLASMATIC RETICULUM Major site for protein synthesis Contains ribosomes attached to the ER and free ribosomes Cytosol Membrane

10 SMOOTH ER and GOLGI APPARATUS Sites for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substances

11 THE MITOCHONDRION Site of cellular respiration (inhale and exhale) Pyruvic acid and O2, trough the Krebs cycle are transformed in ATP and CO2 1 Pyruvic acid = 17 ATP ATP- cell s energy source (by breakdown of ATP in ADP)

12 THE NEURONAL MEMBRANE Barrier that encloses cytoplasm ~5 nm thick Protein concentration in membrane varies Structure of discrete membrane regions influences neuronal function

13 THE CYTOSKELETON Not static Internal scaffolding of neuronal membrane Three bones Microtubules Microfilaments Neurofilaments Microtubules Big and run longitudinally along the neuron. Microfilaments Same size of the membrane. Role in changing cell shape Neurofilaments Mediam size. Structurally very strong

14 THE AXON The Axon is specialized for the transfer information over long distances Axon hillock (beginning) Axon proper (middle) Axon terminal (end) Differences between axon and soma ER does not extend into axon (This means no protein synthesis there) Protein composition: Unique Variable diameter and length

15 THE SYNAPSE The axon terminal is the site of contact with another neuron or cell (synapse) and transfer of information (synaptic transmission) In the Axon Terminal there are no microtubules Presence of synaptic vesicles (contain neurotransmitter) Abundance of membrane proteins post synapsis) Large number of mitochondria

16 THE AXOPLASMIC TRANSPORT Allows the transport of the proteins synthesized in the soma to the axon terminal Anterograde (soma to terminal): could be fast (1000mm per day) or slow (1-10 mm per day). Legs are Kinesin Retrograde (terminal to soma) transport: feedback information. Legs are dynein

17 THE DENDRITE Antennae of neurons All the dendrites of a neuron are called dendritic tree Dendritic spines Postsynaptic: receives signals from axon terminal by using protein molecules called receptors that detect neurotransmitters in the synaptic cleft

18 CLASSIFICATION OF NEURONS Classification Based on the Number of Neurites Single neurite Unipolar Two or more neurites Bipolar- two Multipolar- more than two Classification Based on Dendritic and Somatic Morphologies Stellate cells (star-shaped) and pyramidal cells (pyramidshaped) Spiny or aspinous

19 CLASSIFICATION OF NEURONS Further Classification By connections within the CNS Primary sensory neurons, motor neurons, interneurons Based on axonal length Golgi Type I - long axon, projection neurons Golgi Type II - short axon, local circuit neurons Based on neurotransmitter type e.g., Cholinergic = Acetycholine at synapses

20 GLIA Mainly supports neuronal functions Astrocytes Most numerous glia in the brain Fill spaces between neurons (Influence neurite growth) Regulate the chemical context of the external environment of the neurons Myelinating Glia Oligodendroglia (in CNS) and Schwann cells (in PNS) insulate axons Node of Ranvier: region where the axonal membrane is exposed