1. NERVOUS SYSTEM

2. NERVOUS SYSTEM 2 Main Divisions Central NS – brain and spinal cord
Peripheral NS – all other nerves (cranial, spinal)
CNS – median structure; all sensory impulses arrive there, all motor impulses begin there
PNS -- nerves that lie outside (peripheral to) the CNS
– convey all sensations and motor impulses to and from the CNS.
-cranial nerves – originate from the brain and brainstem
-spinal nerves – originate from the spinal cord
both give rise to smaller branches.

4. PERIPHERAL NS 2 Subdivisions
Somatic System (voluntary) – sensory nerves from the skin and sensory organs (ear, eye, nose) and motor nerves to skeletal muscles
Autonomic System (involuntary) – controls blood vessels, gland
further subdivided:
Sympathetic – times of stress (injury, excitement, physical activity)
Parasympathetic – conditions of normal organ functioning

7. NERVOUS TISSUE 2 Types of Nervous Tissue :
Neuroglia – (glial cells) – 90% of the CNS
-Small part of the PNS.
-Provide structural framework for the neurons.
-Non-conducting.
Neurons – Structural and functional unit of the N.S. even though they are outnumbered by glial cells
- Perform the functions of the N.S. – sense changes, integrate information, make a motor response.

9. TYPES OF GLIAL CELLS -Astrocytes (CNS) – most numerous
– form webs that surround capillaries, allowing small molecules (O2 and CO2) to pass through, keep others out.
-Oligodendrocytes (oligodendroglia) (CNS) – help hold nerve fibers together
– produce a myelin sheath, a protective covering
-Microglia (CNS) – engulf and destroy microbes and debris in inflamed/damaged tissue
-Ependymal (CNS) – line cavities of CNS
– form and circulate CSF
-Schwann cells (PNS) – form myelin sheath/neurolemma around peripheral nerves. Have high lipid content

11. NEURONS Classified according to the DIRECTION OF IMPULSE
-Afferent (sensory) – toward brain and spinal cord
-Efferent (motor) – toward muscles/glands/organs
-Interneurons (AKA Association) – CNS only, connect afferent and efferent fibers

14. Classified according to STRUCTURE
-Multipolar – many dendrites, single axon (CNS to skel. muscle)
-Bipolar – single dendrite, single axon (special sensory areas)
-Unipolar – one fiber extending from the body, it splits into two branches (one to the spinal cord (axon); the other to the peripheral body (dendrite) (sensory from skin to sp. cord).

17. NEURON ANATOMY Cell body- has nucleus, cell membrane
At least 2 processes
Dendrites –receivers (impulses from other neurons – go to cell body)
Axon –senders (away from cell body) – 1 per neuron (may have branches, collaterals)
Nissl bodies – extra protein synthesis (Rough ER)

19. Myelin sheath – around axon (fat) insulation
– speeds up transmission (Schwann or oligodendroglia)
myelin – (white matter) inside – medulla
non-myelin (gray matter) outside – cortex
Node of Ranvier- gaps in between that aid in impulse conduction
Neurolemma – outer covering of axons [Schwann]
– helps in regenerating nerves
– none in brain and cord *no regeneration
Loses spindle fibers at about 3yo – no longer able to mitotically divide