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|Cellular functions||Generalized into one cell.||Divided according to the cell’s specialization. The effectivity level is then generally higher.|
|Relationship with environment||Dependence of cell on outside environment, and vulnerability upon changes.||A separate inner environment can be maintained through homeostasis.|
Nervous System Functions
Input/its anticipation > Regulation > Integration > Regulation > Output/its anticipation.
- Homeostasis maintenance.
- Coordination of physiological processes.
- Response generation to stimuli from the outside environment.
|Mediator||Chemical compounds i.e. hormones.||Neurotransmitters.|
|Conduction method||Non-specific i.e. blood.||Target cells are always specific.|
|Binding site at target||Receptor.||Post-synaptic knob (Ion channels).|
|Speed of action||High.||Low.|
Overlaps of humoral and nervous regulation e.g. the hypothalamus involve neurosecretory cells which release their hormonal product into the bloodstream.
Compartmentalization: Through tissues, organs, and systems with specialized functions in common. They are separated to enable the possibility of having different internal environments.
Of the CNS: Barriers separating neural components from the intravascular compartment:-
- Blood-brain barrier = hematoencephalic barrier.
- Barrier between blood and cerebrospinal fluid = hematoliquor barrier.
- Most superficial barrier = meningeal barrier.
Said barriers create a certain extent of pressure between the skull and brain: Intracranial pressure. (IP) The driving force of blood into the skull (pressure gradient): Cerebral perfusion pressure. (CPP)
CPP = MAP – IP MAP = Mean arterial pressure
- Astrocytes’ perivascular feet
- Lamina basalis of the capillary endothelium
- capillary’s endothelial cells themselves (occluding junctions).
Ependymal cells (occluding junctions).
|Circulation Space/Liquor Space||Lined-by ependyma in ventricles.
With a 150-250 ml capacity.
|Production||Choroid plexus (70% of it) + Cellular metabolism + Capillary filtration.
Mg2+ and Na2+: High concentration.
K+ and Ca2+: Low concentration.
|Functions||Protective: Shock absorption following head traumas.
Maintenance of nervous cells’ microenvironment: Metabolic, immunological, and transport functions.
VRS = Virchow Robin Space: Between pia mater and artery/vein.
Circumventricular Organs: Secretory and receptive regions with a modified, almost-compromised blood-brain-barrier. They are richly vascularized.
- Pineal gland and subcommissural organ.
- Area postrema.
- Eminentia mediana of the pituitary gland.
- VOLT (The vascular organ of lamina terminalis).
- The subfornical organ.
Neuron: Glia ratio is variable, being ranging from 1 : 1-50.
|Oligodendrocytes||Myelin sheath production for all CNS neurons.|
|Microglia||Act as macrophages in grey matter.|
|Satellite cells||Lining cell bodies of peripheral neurons, and separating them from the surrounding connective tissue.|
|Shwann cells||Formation of a Schwann sheath around all PNS neurons, or a myelin sheath around some.|
*Non-myelinated fibres: Generally evolutionarily old.
- Classification by the number of processes.
- Classification by the length of the axon.
- Classification by the dendritic pattern.
Notes by: Lina El Rifaie