Nerve

I.	Development

	A.	Germ Layer - Ectoderm
		1.	Skin
		2.	Nervous System
			A.	Nerve Cells - Neurons
			B.	Glial Cells - glue (Neuroglia)
				1.	Astrocytes - blood brain barrier
				2.	Ependymal cells - production of Cerebral Spinal Fluid (CSF)
				3.	Microglia - WBCs of CNS
				4.	Oligodendrocytes - Myelin formation (CNS)
				5.	Schwann cells - Myelin formation (PNS)
				6.	Satellite cells (amphicytes) - surround neuron cell bodies in peripheral ganglia - exchange nutrients and wastes.
		
	B.	Embryonic cells - Nerve Growth Factor (NGF)

II.	Neurons

	A.	Cell with central nucleus surrounded by perikaryon
		1.	Nissl bodies
		2.	Neurofilaments
		3.	Mitochondria
		4.	Golgi apparatus
		
 B.	Processes
 		1.	Dendrites
 			A.	None to 50,000 per cell
 			B.	Bring information/impulse into cell
 			C.	Covered with spines, dynamic structures
 			D.	90% of gray matter in cerebral cortex is dendrites.
 			E.	Intelligence is proportional to number of contacts - constantly establishing new and better contacts.

 		2.	Axon
 			A.	One and only one for each cell
 			B.	Information leaves via the axon
 			C.	Starts at axon hillock - clear, does not stain
 			D.	May have collaterals (many recurrent)
 			E.	Branched end (teleodendria)
 			F.	Terminal boutons - swelling of synapse
 			G.	Variable length, up to 1 meter
 			H.	Surrounded by Schwann cell
 				1.	Unmyelinated - surround many processes
 				2.	Myelinated - Embryonic origin, wrapped	

	 		I.	Factors of Axon Classification
		  		1.	  Diameter
		  			a.	 Larger Faster
		  			b.	Less Cytoplasmic Ionic Resistance

		  		2.	 Myelination
		  			a.	Faster
		  			b.	 Larger Jumps

		  		3.	Propagation speed
		  			a.	Faster - Urgent Information
               					Position
               					Balance
              				            Delicate touch
               					Pressure
               					Skeletal Muscle

		  			b.	 Slower - Less Urgent
               					Temperature
              					 Pain
               					General touch and pressure
               					Smooth muscle
               					Cardiac Muscle
               					Glands
               					Peripheral effectors

		  		4.	Type A -  Largest 4 - 20 microns
         					Speeds to 140 meters per second  (300mph)

		  		5.	Type B -  Diameter 2 - 4 microns
          					Speeds around 18 meters per second  (40 mph)

		  		6.	Type C -  Unmyelinated, < 2 microns
         					 Speeds of 1 meter per second

	C.	Synapse - Functional junction between axon and 
 		1.	Connections
 			A.	Dendrite
 			B.	Nerve cell body
 			C.	Axon Hillock
 			D.	Muscle cell
 			E.	Effector cell (gland)
 
 		2.	Structure
 			A.	Presynaptic terminal - versicles filled with neurohumeral transmitters
 			B.	Synaptic gap or cleft - several hundred angstrom spacing
 			C.	Postsynaptic terminal
		 		1.	Neurohumeral transmitter receptors
		 		2.	Cause postsynaptic thickening
		 		3.	Learning and memory, education changes postsynaptic thickening
		 	D.	Neurohumerases locally break down neurohumeral transmitters
		
		3.	Classification by transmitter
	D.	Structural Classification
	   	1.	Number of processes
	      		A.	Unipolar (sensory)
	      		B.	Bipolar (I/O)
		      	C.	Multipolar (Processing)
	   	2.	Length of process
	   	3.	Size of cell - 4 - 120 microns
	   	4.	Shape of cell
		      	A.	Star
		      	B.	Flask
			C.	Pyramidal
			D.	Spindle

	E.	Types of cell
		1.	Sensory
		2.	Association -Number increases with evolution
		3.	Motor

	F.	Processing
		1.	Divergence - one to many
		2.	Convergence - many to one
		3.	Serial - one to one
		4.	Parallel processing - multitasking
		5.	Reverberation - feedback (recurrent collaterals)

	G.	Organization
		1.	Central Nervous System - CNS (Brain and Spinal Cord) (Command and control)
		2.	Peripheral Nervous System - PNS
		3.	Somatic Nervous System - SNS (muscles)
		4.	Autonomic Nervous System - ANS
	 		A.	Sympathetic Nervous System - SNS
	 		B.	Parasympathetic Nervous System - PNS

		5.	Afferent division - information in
		6.	Efferent division - commands out


	H.	Wallerian regeneration
		1.	Cell lives or dies
		2.	Degeneration distal to the Node of Ranvier proximal to the site of injury
		3.	Growth bud to site of innervation
		4.	Surrounded by Schwann cells