1.1. neurology

1.1. neurology

GLIAL CELLS are found in both

• CNS

• PNS

Glial cells in PNS

• Schwann cells

• Satellite cells

Glial cells in CNS

• Astrocytes

• Oligodendrocytes

• Ependymal cells

• Microglia

Glial cells support inn

• Physical support of neurons (glia: glue in Greek)

• Metabolic support

• Modulation of neuronal communication

• Myelinization of axons

• Tissue repairing

• Defense

Astrocytes maintains

• Chemical environment for neuronal signaling

• Neuronal survival & tissue repairing

Neuronal survival & tissue repairing

• Astrocytes release substances (trophic factors, cytokines) for nervous tissue maintenance & repair.

Role of Astrocytes

• Nutrition role

• Synapse modulation role

• Protective role

Nutrition role

• Provide neurons with glucose, lactate & other metabolites

• Remove waste metabolites or cell debris from the area.

Synapse modulation

• Astrocytes participate in the communication between neurons

• Release of gliotransmitters (e.g. ATP)

• Re-uptake of neurotransmitters (glutamate)

• Regulation of extracellular levels of Ca2+ and K+ (critical for the synapses & the transmission of the electrical impulse)

Protective role

• Provide physical support to neurons

• Surrounds the capillaries & blood vessels, creating the blood-brain-barrier (BBB)

• Regulates the diffusion of certain molecules, drugs & nutrients from the blood to the extracellular space.

Astrocytes induce the formation of

• tight junctions

The tight junctions of astrocytes are found in

• Between endothelial (blood vessel) cells → preventing substances (toxins & microorganisms) to pass

BBB dysfunction lead to

• permeability compromised → disease

→

* Leakage of non-specific molecules from blood into brain

* Infections

* Inflammation

Main causes of BBB dysfunction

• Ischemia/reperfusion (Hypoxia / hypoglycemia)

• Osmotic shock

• Inflammatory processes

Diseases related to BBB dysfunctions

• Multiple sclerosis, epilepsy, stroke, Alzheimer’s disease

Parkinson disease

In Parkinson’s disease, dopaminergic neurons are lost → dopamine concentration in the striatum are too low →

Inability to initiate spontaneous movements

Treatment used for Parkinson disease

•  L-DOPA (because of dopamine itself cannot cross the BBB)

L-DOPA

• Dopamine precursor

• Crosses the BBB through an aminoacidic transporter

• Uptaken by neurons & converted to dopamine

• Compensating the dopamine deficiency

Oligodendrocytes

• Glial cells that create the myelin sheath around several neuronal axons in the CNS

Myelin sheath

Lipidic cover that supports & insulates the axon

Node of Ranvier

• Axon areas without myelin sheath.

• Accelerates impulse travelling through the axon

Impairment of oligodrendrocytes can lead to

 Multiple sclerosis

Multiple sclerosis occurs due to

Demyelination caused by autoimmune attack.

Loss of myelin sheath impairs

Impulse transmission

Symptoms of MS

• Fatigue, muscle spams, vision problems, numbness, balance problems, pain, depression

Microglia

• Resident immune cells in the CNS

• Response to pathogens (virus, bacteria) & damage

Functional states of Microglia

• Nurturer

• Sentinel

• Activated/warrior

Nurturer

• Clears debris, promotes tissue repair, supports survival of neurons & restores homeostasis.

Sentinel

• Scan the microenvironment.

• High motility.

Activated/warrior

• Responds to damage.

• Supports neurons (cytokines) & maintain the microenvironment (phagocytosis), causes inflammation.

Microglia

• Mediate neuroinflammatory processes

Neuroinflammatory processes release of

• Release of cytokines can produce local inflammation

Microglia participate in the

• remodelling & pruning of the dendritic tree (learning & memory process)

Microoglia are activated in the response to

Brain damage 

Ependymal cells

Specialized polar cells that form the ventricle walls (choroid plexus)

Ependymal cells participate in the

• Formation of the cerebrospinal fluid (CSF) & its circulation

Ependymal cells can act as

Precursors of brain cells

The choroid plexus consists of

• Modified ependymal cells surrounding a core of capillaries & loose connective tissue.

VENTRICLES

• Interconnected cavities inside the brain

• Connected with the spinal cord

• Filled with CSF

V1 & V2

• Lateral ventricles

V3 & V4

Descendant ventricles

CEREBROSPINAL FLUID

• Saline solution that fills the ventricle system.

CBF is secreted by the

• choroid plexus

CBF is absorbed to the blood by the

Arachnoid granulations

The role of CEREBROSPINAL FLUID

• Mechanical support 

• Nutrient distribution

• Elimination of waste from the CNS

Mechanical support CSF

• cushioning

• regulates pressure

Nutrient distribution CSF

• oxygen & glucose

• waste recollection

The flow rate of CSF through CNS is sufficient to

• Replenish the entire CSF volume approximately three times a day

CEREBROSPINAL FLUID composition

• Several salts (help control pressure & nerve function) & glucose (provides energy for brain cells)

• Low proteins (keeps the fluid thin & clear)

• No cells (no blood cells or other cells)

Alterations in CSF compositions can lead to

• symptom of pathologies development (CNS infections, demyelization or tumors)

 RADIAL GLIA

• special support cells in the developing brain

• scaffolding or guide rails for the brain

RADIAL GLIA & ependymal cells together could have

• behave as stem cells that can produce new neurons.

Adult neurogenesis

• described only in

• → subventricular zone (SVZ)

• → granular zone (GZ) of the dentate gyrus of the hippocampus

Adults hippocampal neurogenesis drops in patients with

• Alzheimers disease

Schwann cells

• lia cell that creates ONE myelin sheath (1mm) around a neuron axon

Charcot-Marie-Tooh disease

• Neurological disorders that affect the myelin sheath of the motor neurons

• Loss of muscle tissue & touch sensation in limbs

• Genetic origin, several mutations

Satellite cells

• Glial cells that wrap around nerve cell bodies located in ganglia, forming a capsule.

• Support role, probably regulating the microenvironment, but not fully understood

Neuroglia is found in

• CNS

• PNS

Glia in found PSN

• Satellite cells

• Schwann cells

Glia found in CNS

• Microglia

• Oligodendrocytes

• Astrocytes

• Ependymal cells

Satellite glia cells

• Surround neuron cell bodies in ganglia

• Regulate O₂, CO₂, nutrient, & neurotransmitter levels around neurons in ganglia

Schwann cells

• Surround axons in PNS

• Are responsible for myelination of peripheral axons

• Participate in repair process after injury

Oligodendrocytes

• Myelinate CNS axons

• Provide structural framework

Astrocytes

• Maintain blood-brain barrier

• Provide structural support

• Regulate ion, nutrient, and dissolved gas concentrations

• Absorb & recycle neurotransmitters

• Form scar tissue

Microglia

• Remove cell debris, wastes, & pathogens by phagocytosis

Ependymal cells

• Line ventricles (brain) and central canal (spinal cord)

• Assist in producing, circulating, & monitoring of cerebrospinal fluid