anencephaly spina bifida occulta with meningocoele

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Anencephaly

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Anencephaly

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Spina bifida occulta with meningocoele

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Spina bifida with failure of neuropore closure

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Cortical dysplasia

Cortical dysplasia

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Support cells (neuroglia)- more abundant than neurons- more mitotic capability

Astrocytes1. Fill-in the space between neurons and blood vessels in brain.2. Most numerous glial cells in brain.3. Form the blood-brain barrier

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Astrocytes4. Envelope synapses, preventing spread of neurotransmitter.5. Take up and store neurotransmitter from the extracellular environment (ECF).6. Their membranes possess neurotransmitter receptors. Electrical and biochemical events can be triggered in these cell.

Astrocytes7. Can even release some of the stored neurotransmitters. May have an adjunct role.8. Can “sherpa” the growth of new neurons or processes.

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Potassium spatial buffering

Astrocytoma

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Oligodendrocytes

Demyelination (with plaques)

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Characteristic of MS

Oligodendroglioma

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Oligodendroglioma

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Ependymal cells

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Microglia

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Schwann cells

Schwann cells can regenerate damaged axons

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Neurofibromatosis

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caused by loss of tumor suppressor gene neurofibromin

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Neurofibromatosis

Gated Ion ChannelsA. Gated Na+ channels

1. localizationa. voltage-gated

a. voltage-gated- large concentration in hillock- found along the axon

Gated Ion ChannelsA. Gated Na+ channels

1. localizationb. ligand-gated at synapses

Gated Ion ChannelsA. Gated Na+ channels

1. localizationNa+ channels occupy only a small fraction of surface area

100-500 channels/m

Gated Ion Channels2. Often have two gates

a. activation (fast)b. inactivation (slow)

Gated Ion Channels3. factors contributing to specificity

a. anions at mouth of channelb. sizec. ability to dehydrate (shed water of hydration)

Electrical Properties of MembranesA. Conductance (g)

1. conferred by ion channels2. is inversely related to resistance

Electrical Properties of MembranesB. Current

- net flow of ions through the channel

Electrical Properties of MembranesC. Capacitance

1. conferred by membrane itselfbilayer is an insulating layer separating charges

2. capacitative current- ability of ions to interact across the membrane without crossing the bilayer

- charges collect on either side of the membrane- energy of the charges “stored” by the capacitor

Gated Na+ ChannelsA. Voltage-gated Na+ channels

1. current flowa. Na+ ions flow through channel at 6000/sec at emf of -100mVb. number of open channels depends on time and Vm

Gated Na+ ChannelsA. Voltage-gated Na+ channels

2. opening of channela. gating molecule responding to voltage change

The number and type of ion channels determines the electrical responses and characteristics of the cell.