Introduction to Neuroscience


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Feature

Unicellular Organisms

Multicellular Organisms

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.
Stress level High. Low.
Life span Shorter. Longer.

Nervous System Functions

Input/its anticipation > Regulation > Integration > Regulation > Output/its anticipation.

  1. Homeostasis maintenance.
  2. Coordination of physiological processes.
  3. Response generation to stimuli from the outside environment.

Regulation

Feature Humoral Nervous
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).
Energetic demand Low. High.
Speed of action High. Low.
Effect duration Long. Short.

Overlaps of humoral and nervous regulation e.g. the hypothalamus involve neurosecretory cells which release their hormonal product into the bloodstream.

Cellular Basis

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

Meningeal Barrier

meninges_1

Blood-brain Barrier:cerebrospinal-fluid-choroid-plexus-ependymal-cell-capillary-ventricle-csf

  • Astrocytes’ perivascular feet
  • Lamina basalis of the capillary endothelium
  • capillary’s endothelial cells themselves (occluding junctions).

Hematoliquor Barrier:

Ependymal cells (occluding junctions).

Cerebrospinal Fluid:

Feature
Appearance Clear.
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.

450-750 ml/day.

Resorption Arachnoid granulations.
Composition Acellular.

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.

Circulation Compartments:

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.

Nervous Cells:

Neuron: Glia ratio is variable, being ranging from 1 : 1-50.

Glia Functions

Cell Function
Astrocytes
  • Blood-brain barrier formation.
  • Astrocytic scar formation upon brain tissue injury.
  • Metabolism of neurotransmitters.
  • Play a large role in the development of the brain.
Oligodendrocytes Myelin sheath production for all CNS neurons.
Microglia Act as macrophages in grey matter.
Ependyma
  • Ventricular lining (forming the liquoroencephalic barrier).
  • Choroid plexus covering.
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.

Neuron Types

  • Classification by the number of processes.
  • Classification by the length of the axon.
  • Classification by the dendritic pattern.

neurontype1neurontype2

Notes by: Lina El Rifaie

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