Nervous System
The nervous system is divided into the Central Nervous system (CNS) consisting of the Brain and Spinal cord, and the Peripheral Nervous system (PNS) that includes nerves, plexes, and ganglia outside the CNS.
Neurons are classified based on number and arrangement of processes; Unipolar, Bipolar and Multipolar, and length and destination of axons.
The Brain is divided into white and grey matter, the grey matter contains the nerve cell bodies, dendrites and proximal portions of axons; cluster of nerve cell bodies called nuclei
The White matter consists of axons surrounded by myelin; bundles of these axons are called tracts
Cerebellum
The Cerebellum is responsible for maintaining balance and equilibrium, muscle tone, and coordination of skeletal muscles. The Cerebellum is thrown into folds known as folia.
There are four layers of the cerebellum
Outer Molecular Layer
Purkinje Cell layer
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Inner Granular Layer
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White Matter : Medulla
Outer Molecular Layer : Contains stellate cells, basket cells, dendritic trees of purkinje cells
Dendritic trees
Purkinje Cell Layer : The soma of these massive cells occupy this layer, there are only neutrons in the cerebellum whose axon exit the region.
Inner Granular Layer : Contains granule cells.
White Matter: medulla
Cerebrum
The Cerebrum is responsible for learning, memory, information, analysis, initiation of motor response, and sensory integration.
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Grey Matter has 6 layers from outside in.
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Outer Molecular Layer
Outer granular Layer
Outer Pyramidal Layer
Inner Granular Layer
Inner Pyramidal Layer
Multiform Layer
The layers of the cerebrum are difficult to distinguish, it is easiest to looks for the pyramidal cells in the pyramidal layers first to orient yourself.
E
Capillary
The Choroid Plexus is part of the blood brain barrier and is responsible for producing much of the cerebrospinal fluid which fills the ventricles, central canal, and bathes outer surface of the CNS. This blood filtrate is rich in ions, glucose and is virtually protein free.
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This structure is invaginated folds of the Pia Mater and the innermost meaning of the brain and is found in the 3rd and 4th ventriacles of the brain. It consists of highly vascular loose CT covered by simple cuboidal epithelia (ependymal cells)(E) with tight junctions, dilated microvilli and lots of mitochondria. Here the capillaries are fenestrated.
Ventricle space (with CSF)
Choroid plexus tissue
Neuroglia
Support cells act as connective tissue for the CNS. Glial cells are smaller than neurons they outnumber them 10:1.
Astrocytes: Help establish the BBB, glycogen stores for neurons, mop up excess extracellular K+.
- Fibrous astrocytes with longer, less branching cytoplasmic projections are found in white and grey matter
-Protoplasmic astrocytes possessing shorter, more highly branched projections that wrap around blood vessels.
Oligodendrocytes : myelinate axons in the CNS, can insulate sacral axons. These cells are smaller than astrocytes, with a few short, stubby projections.
Found in grey and white matter. In this photo you can see the myelination of an axon by the thickening of it, the thin area is the node of Ranvier and is the non-myelinated part of the axon.
Central Canal of Spinal Cord
Ependymal Cells : Line ventricles and central canal
Microglia : Function as macrophages in the CNS, engulfing debris from dead cells. Once packed with material these cells are known as "glitter cells". Microglia are the smallest glial cells, with little cytoplasm and irregular short projections.
Spinal Cord
Nerves are bundled together and covered in sheaths of connective tissue, each single nerve is covered by the endoneurium, a group of nerves together is covered by the perineurium and the entire nerve bundle is covered by the epineurium.
