Nervous Tissue Flashcards
Embryonic origin of nervous tissue
Generate from Ectoderm
1. Neural plate: which thickens to form neural tube (neural fold, grove, coalescence of lateral ends of neural plate)
2. Neural crest: which leaves CNS to differentiate into components of PNS
Three zones of neural tube
- Ventricular zone: germinal or ventricular cells produces ependymoblast, glioblast and immature neurons. Ependymoblast converts into ependymal cells and choroid plexus
- Intermediate zone: Immature neurons leave from ventrical zone to intermediate zone to travel to cortical plate. Gliogenesis occurs to form glial cells. excess neuronal cells undergo apoptosis
- Cortical plate: contains mature neurons and oligodendrocytes and astrocytes - from glioblasts.
Function of different neuronal cells
Microglia - forms from monocyte for phagocytic purpose
Ependymal cells - lining of ventricular cavities of the brain and central canal in spine
Astrocyte - generates vascular end foot around the blood vessels to form BBB
Oligodendrocyte - myelination of neurons in CNS
Schwann cells - myelination of neurons in PNS
Choroid plexus: main source of CSF
Components of neuron
- soma or cell body: contains nucleus and perikaryon (cytoplasm), leucocytes, neurofilaments and neurotubules, nissl bodies (rER), Golgi, stem of dendrites and axon originates from the soma
- dendrites: receiver of synaptic information from surrounding neurons
- Axon: starts from the axon hillock (site for action potential generation) and terminates into telodendron
Information is received and integrated by surface of soma and dendrites and transmitted by axon
Types of neurons
- multi polar: contains one axon process and multiple dendrites eg: Pyramidal cell in cerebral cortex and perkinje cells of cerebellar cortex
- Bipolar: contains 2 processes coming out of the soma eg: neurons in auditory, visual and vestibular system
- Pesudounipolar: have one process coming out of the soma but then it divides into two branches. eg sensory ganglia of cranial and spinal nerves
Different types of synapses
- chemical and 2. electrical
also based on location of post synaptic neuron - axospinous : axon terminal facing spine of a dendrite
- axoaxonic: axon terminal ending on axon
- axosomatic: axon terminal on soma of the neuron
- axodendritic: axon terminal facing shaft of a dendrite
Axon transport
- anterograde: moving toward plus end of a microtubule and toward the axon terminal facilitated by kinesin protein
- retrograde: moving towards the cell nucleus of a neuron, towards negative end of a microtubule facilitated by dyenin protein
Glial cells
- astrocyte:
a. fibrous: found in white matter
b. protoplasmic: found in grey matter
- participate in normal and abnormal activities of CNS
- assist with BBB formation
- assist in mechanical and metabolic activities of a neuron - Oligodendrocyte:
- forms myelin sheath on multiple axons
Difference in myelination of CNS vs PNS
CNS
- cell : olidendrocyte
- covers multiple axons with myelin sheath
- myelin sheath does not contain basal lamina
- axon does not contain connective tissue
- at node cytoplasm is not retained
- nodes are covered by vascular end legs of astrocytes
PNS
- cell: Schwann cell
- only covers one axon with one Schwann cell
- connective tissue present
- retains cytoplasm at node
- contains basal lamina
- nodes are covered by Schwann cells
Saltatory conduction
is the process in which action potential jumps from one node to the next.
A segment of myelin sheath covered by an individual oligodendrocyte is called internode and space between two internode is called node of Ranvier contains high concentration of voltage gated Na channels that is essential for saltatory conduction
Microglia
generated from erythromyeloid precursor in yolk sac
- phagocytic reaction
-inflammatory reaction
- immunosurveillance
- generate cytokines mediators
- trophic factors to support neurons
