[image]EPITHELIAL CELLS.

The structure and function of neurons is thus similar to epithelial cells  (e.g., both cell types have distinctive poles)

EXTERNAL CELL MEMBRANE or PLASMALEMMA

Nerve cell membranes have the general asymmetric bilayer structure of all biological membranes and represent a hydrophobic barrier impermeable of most water-soluble subtances.

1. the CYTOSOL (including the cytoskeletal matrix
2. the MEMBRANOUS ORGANELLES

1. Many have general housekeeping functions and are common to all neurons
2. Others have specific roles in particular types of neurons
   • (e.g., enzymes involved in synthesis and degradation of the susbtance used as a neurotransmitter.)
     
3. Some are districuted unevenly in the cell because they interact to form aggregats, particles, or matrices.
4. Many cytosolic proteins involved in signaling are concentrated at the cell's periphery in trhe cytoskeletal matrix immediately adjacent to the plasmalemma

1. Mitochondria
2. peroxisomes
3. system of tubules, vesicles, and the vacuolar apparatus that consists of
   • endoplasmic reticulum(rough and smooth)
   • Golgi complex
   • secretory vesicles
   • endosomes
   • lysosomes
   • transport vesicles that interconnect these compartments

A specialized portion of the rough endoplasmic reticulum that forms a spherical cisterna called the NUCLEAR ENVELOPE, which surrounds the chromosomal DNA and its associated proteins and defines the nucleus.

The nuclear envelope is interrupted by the nuclear pores 

1. acts as a regulated calcium store throughout the neuronal cytoplasm
2. performs a variety of enzymatic reactions
3. involved in lipid metabolism

the major intrinsic determinant of the shape of a neuron and responsible for the asymmetric distribution of organelles within the cytoplasm

Containes 3 main filamentous structures

1. microtubules
2. neurofilaments
3. actin microfilaments.   These fiaments and their associated proteins account for about 25% of the total protein of the neuron 

MAPs.  Promote the oriented polymerization and assembly of the microtubules.

 MAPs in the axons differ from those in the dendrites.  (MAP2-present in dendrites but not axons; tau and MAP3--present in the axon)

10nm diameter.  the bones of the cytoskeleton.  They are the most abundant fibrillar components of the axon.  On average, there are 3-10 times more neurofilaments thant microtubules in an axon).

Unlike microtubules, neurofilaments are very stable & almost totally polymerized in the cell.

In Alzheimer's disease, they become modified and form a characteristic lesion called the neurofibrillary tangle. 

3-5nm in diameter--the thinnest of the three main types of fibers that make up the cytoskeleton

They are polar polymers of glubular actin monomers wound into a double-stranded helix.  

Unlike microtubules and neurofilaments, actin filaments form short polymers--concentrated at the cell's periphery just underneath the plasmalemma.  

Both are in a dynamic state, and undergo cycles of polymerization and depolymerization--this allows mature neuron to retract old processes and extend new ones

In addition to serving as cytoskeleton, they act as tracks along which other organelles and proteins are driven.  These filamentous polymers are polar, so each molecular motor drives its organelle cargo in one direction only.

insulate axons; speed transmission along axons (so it is critical for quick relfex movements)

composition:  70% lipid; 30% protein 

1.  dendrites (receives signals from other neurons

2.  cell body (contains DNA encoding neuronal proteins and the apparatus for synthesizing them

 3.    axon (projects over long distances to target cells)

4.    nerve terminals (for release of neurotransmitters at synapses with targets 

membrane bound vesicles that contain hydrolytic enzymes, arising from the Golgi apparatus

When particles (such as viruses or bacteria) are ingested by phagocytosis, lysosomes fuse with the particle-containing vesicle (called a phagosome) to deliver the hydrolytic enzymes

Lysosomes also fuse with organelles such as defective or worn out mitochodria, resulting in destruction and recycling of these structures 

These enzymes digest particles or cells taken into the cell by phagocytosis.  They also digest old organelles such as mitochondria. 

Hydrolytic enzymes that degrade proteins, nucleic acids, lipids, and carbohydrates are formed in the endoplasmic reticulum, then are transported to the Golgi apparatus by transport vesicles.

Lysosomes containing hydrolytic enzymes emerge from the Golgi Apparatus