100 billion neurons, 10x more glial cells neurons are anatomically independent - come close, but never touch - differ from "regular" cells neurons have "specialized extensions" - dentrites and axons specialized structures - terminal buttons - produce neurotransmitters communicate through electrochemical process communicate across synapses do not heal sponteneously (brain, spinal cord) The nerve impulse usually travels from the dendrites and soma to the branching ends of the axon Different types: Purkinje - spread out, 1000s of dentritic spines, mostly in cortex sensory "interneurons" - connect one neuron to another (reflex) pyramidal - motor neurons - wide branching dentrites, carry information to distant targets bipolar - visual (eye) limited area, short axon Axons covered in myelin sheath - inscrease speed, insulates, white matter myelin formed by glial cells, called oligodentrocytes (CNS) and by Schwann cells (PNS) develops at birth, susceptible to breakdown (MS) buldles of myelinated neurons make up tracts, pathways, or fibers in the CNS and PNS cell bodies are grey - nuclei (CNS) and ganglia (PNS) Glial cells: from Greek gliok: nerve glue offer structural support to neurons physical and chemical buffers between neurons supply nutrients oligodentrocytes (myelin), microglia (scavengers), astrocytes (fill up empty spaces) spinal cord injury induces increased expression of the death receptor CD95/Fas by neurons, lymphocytes, microglia Blood-brain Barrier - semi-permeable membrane Protects the brain from "foreign substances" in the blood that may injure the brain. Protects the brain from hormones and neurotransmitters in the rest of the body. Maintains a constant environment for the brain. (see here) Synapses Action Potential Ion Channels Neuromuscular Junction Ion Channels More on Action Potential Inhibition/Excitation Ion Movement Inhibition/Excitation Synapse Overview Reuptake of Neurotransmitter Blocking the Receptor Drugs as Agonists Block Reuptake Summary Dopamine Example: Levodopa Bromocryptine Ritilin