Cell Types

1. Compared to other cell types, what makes neurons different

2. Describe the histology

Neurons Difference:

• high rate of protein synthesis and metabolism

• large amounts of Golgi apparatus + organized stacks of RER (Nissl substance)

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Histology

• nucleic acids associated with the dense collection of ribosomal RNA can be stained with dyes that bind nucleic acids.

• typical appearance of neurons histologically is a prominent, basophilic cell body with a clear nucleus and single nucleolus.

Describe the four types of neuron structure

Types:

• Multipolar:

  • multiple dendrites attached to the cell body and usually a single axon.

    • EX: Motor Neurons in SC

• Bipolar:

  • single process from each end of the soma in opposite directions

    • EX: olfactory epithelial cells.

• Unipolar:

  • Only in Dev

  • single process emerging from the cell body with no dendrites

• Pseudounipolar:

  • single process that emerges from the soma that then divides into two processes

    • EX: Sensory Ganglion

Describe axonal transport

• Fast vs Slow:

  • Both?

  • Consists of?

  • Rate?

• Retrograde:

  • Importance?

• Clinical Application:

Fast vs Slow:

• Both:

  • Definition: process of components moving Soma → Axon terminals (anterograde transport)

  • Requires Energy:

• Slow:

  • Consists of:

    • soluble substances

    • cytoskeletal proteins

    • EX: neurofilaments and components of microtubules

  • Rate: few millimeters a day.

• Fast:

  • Consists of:

    • synaptic vesicles

    • neurotransmitter components

    • mitochondria

  • Rate: up to 400 mm/day

• Clinical:

  • Transport tends to slow with age and in neurodegenerative diseases.

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Retrograde Transport:

• less well understood

• different rates for different substances

• Importance:

  • for feedback from axon terminals that can modify neuronal metabolism and responsiveness

List the functional categories of neurons and what type they are

Draw out the functional zones of neurons

STATs: difference between dendrites and cell body

The dendrites typically receive most synapses (8,000 on a spinal motor neuron) while the cell body receives fewer (2,000).

Describe Axons:

• STATs: Length/ Diameter

• Relationship to Speed of AP?

STATs:

• Length: can be more than a meter in length

• Diameter: less than 1 micron to more than 20 microns.

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AP Speed (conduction velocity):

• depends upon the thickness of the axons.

1. Which Neurons are myelinated

2. Describe the characteristics of neurons that are likely to be myelinated

1. Myelination of Neurons

   • White matter in the CNS

   • most peripheral nerves in the PNS

2. Characteristics?

   • Larger axons are more likely to be myelinated

   • thickness of the "wrap" varies.

   • NOTE: even axons that don't have myelin are usually surrounded by either a Schwann cell or oligodendrocyte

Describe the Gray/White matter Difference in Cortext vs other places

• Cerebral cortex (and brain nuclei): rich in neuronal cell bodies → gray matter

• Areas under the cortex: rich in myelinated axons → White matter

Define laminae

Laminae - (layer, stratum) a flat slender sheet-like layer of functionally and sometimes anatomically similar neurons.

Describe Astrocytes

• Two Types and Differences

Astrocytes:

• protoplasmic

  • located in gray matter

  • puffy, protoplasmic appearance

• fibrous astrocytes

  • in white matter

  • more fibrous appearance

  • greater abundance of intermediate filaments

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NOTE:

These differences in morphology probably reflect the functional specialization related to the support of the cellular environment in synapse-rich regions and axons.

Describe the histological differences between Neurons and Neuroglials

Neuroglias:

• less Nissl substance (nucleic acids)

  • smaller and generally do not have a prominent nucleolus.

• nuclei have a speckled appearance

List out the function of the astrocytes

Function:

• physical isolation and regulation of the neural environment of the CNS

• scavenge K in extracellular environment

• regulate extracellular ion concentrations

• participate in neurotransmission (particularly glutamate and GABA)

• participate in neurovascular coupling

• supply nutrients to neurons and synapses from the circulation

• Contribute to BBB (astrocyte end feet)

  • NOTE: most restriction is @ level of capillary endothelials

• Repair/Response to injury/stress

• important in the migration of neurons to their appropriate location in the CNS

1. Describe the location of astrocytes in relation to other neural structures

2. B/c of the above answer, what was believed?

Location: surround everything of CNS:

• form a continuous layer on

  • surface of the CNS → glial-pial membrane

  • all blood vessesl of CNS

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believed that astrocytes were primarily a scaffold element of the CNS much the same as fibroblasts are in the structure of organs peripherally.

Describe how astrocytes respond to injury

astrocytes respond to an area of tissue damage by walling off the injured area with astrocytic process, and re- establishing the isolated CNS environment.

Describe Myelination:

• % lipid?

• Function?

• Large vs small axons?

• Describe the Formation

myelination,

• (80% lipid) neuroglial membranes.

• Function:

  • insulates axons from one another

  • controls ionic environment of axon,

  • increases conduction velocity of axons.

• Large vs small:

  • Large axons have thicker myelin sheaths and faster conduction velocities

• Formation:

  • Glial cells respond will usually provide one segment to an axon (internodal segment), but may myelinate up to 40 axons

    • NOTE: segments vary between 200 and 1000 microns in length

Describe the other functions of oligodendrocytes

• also observed in the vicinity of the cell bodies of neurons (perineuronal oligodendrocytes; satellite cells).

• role of these perineuronal cells in both locations is not clear, but they appear to regulate the environment around the neuronal cell body.

Describe Microglia

• Function?

• Existence?

• Establishes?

Describe when other immune cells will help the microglial cells

Microglial cells

• Function

  • immune cells of the CNS

  • primary mediators of inflammation

  • major phagocytic cells (dead/injured) in the CNS

• Existence?

  • 1% of cells in the CNS

  • not derived from neuroectoderm (like astrocytes/oligodendrocytes)

  • exist in a quiescent state

• establish interconnected territories, but are not coupled by gap junctions

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Outside Help:

• In areas of direct CNS injury,

  • peripheral macrophages "gitter cells" may enter to help

• NOTE: Peripheral macrophages and immune cells (e.g. lymphocytes, neutrophils) do not normally enter the CNS in large numbers, but may do so with injury or infection

[REVIEW] Ependymal Cells