Nervous System Cells Ch 12 *By the end of this, you should be able to answer all of Obj. 12 questions.

Somatic nervous system –Conscious control of skeletal muscles Autonomic nervous system (ANS) –Regulate smooth muscle, cardiac muscle, and glands –Divisions – sympathetic and parasympathetic---Ch 14 Objective What are the parts of the motor division?

Cells of The Nervous System Glia –Support the neurons Neurons –Excitable cells that initiate and conduct impulses that make all nervous system functions possible.

Glia FIVE MAJOR TYPES TO CONTINUE ON NEXT SLIDES 

Astrocytes Largest and most numerous type of glia Transfer nutrients from blood to neurons Cells extension connect to neurons and capillaries Forms the Blood Brain Barrier

Microglia Small, usually stationary cells In inflamed brain tissue, they enlarge, move about and carry on phagocytes

Ependymal cells Form thin sheets that line fluid- filled cavities in the CNS Some produce fluid and others aid in circulation of the fluid

Oligodendrocytes Hold nerve fibers together and produce myelin sheath

Schwann cells Found only in PNS Support nerve fibers and form myelin sheaths Gaps in the myelin sheath are called nodes of Ranvier

Cell body: functional portion Dendrites: short extensions that receive signals Axon: long extension that transmits impulses away

Myelinated Neurons Many vertebrate peripheral neurons have an insulating sheath around the axon called myelin which is formed by Schwann cells. Myelin sheathing allows these neurons to conduct nerve impulses faster than in non-myelinated neurons.

Saltatory Conduction in Myelinated Axons Myelin sheathing has bare patches of axon called nodes of Ranvier Action potentials jump from node to node Fig

Nerve Impulse - The Action Potential At rest, the inside of the neuron is slightly negative due to a higher concentration of positively charged sodium ions outside

When stimulated past threshold, sodium channels open and sodium rushes into the axon, causing a region of positive charge within the axon.

The region of positive charge causes nearby sodium channels to open. Just after the sodium channels close, the potassium channels open wide, and potassium exits the axon.

This process continues as a chain-reaction along the axon. The influx of sodium depolarizes the axon, and the ourflow of potassium repolarizes the axon.

The sodium/potassium pump restores the resting concentrations of sodium and potassium ions

Repolarization, Hyperpolorization, and Refractory Period in the Action Potential… Answering Obj. #9…we are going to explore this in the virtual action potential lab!! (But before then, check out the page number given on your objective sheet).

Types of Synapses Electrical synapses- Occur where cells joined by gap junctions allow an action potential to simply continue along a post synaptic membrane Chemical synapses- occurs where presynatptic cells release chemical transmitters [neurotransmitters] across a tiny gap to the postsynaptic cell possibly inducing an action potential there. ws/nmj.html

Neurotransmitters Means by which neurons communicate with one another. FOUR CLASSES OF NEUROTRANSMITTERS: –Acetylcholine –Amines –Amino Acids –Other small transmitters

Acetylcholine Unique chemical structure; acetate with choline Deactivated by acetycholinesterase, with the choline molecules being releases and transported back to presynaptic neuron to combine with acetate.

Amines Synthesized from amino acid molecules Found in the various parts of the brain

Amino Acids Most common neurotransmitter Stored in synaptic vesicles in the PNS

Other small transmitters Nitric Oxide derived from an amino acid NO from a postsynaptic cell signals the presynaptic neuron, providing feedback in a neutral pathway.