1. THE NERVE OF IT ALL COMMUNICATION CONTROL AND INTEGRATION
COURTESY OF BRAIN, SPINAL CORD (CNS) AND NERVES (PNS)

3. KINDS OF CELLS NEURONS Classified by direction of impulse
Afferent (sensory) – transmit signal to spinal cord
Efferent (motor) – transmit signal away from spinal cord or brain to glands or muscles
Interneurons – lie within CNS; transmit from afferent to efferent

5. CELLS, cont’d Can also be classified by # of processes
Multipolar – (CNS and neurons that carry AWAY from CNS) one axon, several dendrites (brain and spinal cord)
Bipolar – (receptors) one axon, one dendrite (retina, inner ear, olfactory pathways)
Unipolar – (to CNS) sensory neurons

6. CELLS, cont’d
Large myelinated neurons (eg. Those that innervate muscles) conduct AP up to 100 m/sec
Small unmyelinated neurons (visceral organs) ~.5 to 1 m/sec

7. More on Neurons CELL BODIES (gray matter) PROCESSES (white matter)
In CNS = nuclei
Outside CNS = ganglia
PROCESSES (white matter)
In CNS = tracts
Outside CNS = nerves
Epineurium – tough and cordlike; perineurium – around fascicles; endoneurium – delicate CT

8. CELLS, cont’d Neuroglia – CT cells
Astrocytes – largest and most numerous; form sheaths around blood capillaries of brain
Microglia – small phagocytes
Oligodendrocytes – lay down myelin sheath around brain and spinal cord neurons (CNS)
Schwann – form neurolemma and myelin sheath only on neurons OUTSIDE of CNS = PNS
Ependymal – line central canal and ventricles; help produce and circulate CSF in choroid plexus

10. Dendrite – receivers - take impulse to soma
Cell body = soma
Axon – away from soma
Nissl bodies
Myelin sheath
Neurilemma – Sheath of Schwann – only in PNS

11. Myelin sheath – segmented wrapping around an axon – concentric layers
Saltatory conduction
WHY?

12. NEURAL PATHWAYS
Stimulus -> dendrites of sensory neuron -> soma -> axon -> axon terminus -> release neurotransmitters -> synapse -> dendrites of interneuron -> interneuron -> interneuron releases neurotransmitters across synapse to motor neuron -> effect ( contraction or secretion)

15. ACTION POTENTIAL
An electrical gradient exists between inner and outer membrane
At rest, neuron is –70mV inside membrane; courtesy of Na+/K+ pump (3Na+ out/2K+ in)
Membrane is polarized
Stimulus – Na+ rushes into cells – membrane is depolarized – reverse polarization

16. Inside cell membrane is now +30mV
This current flows down membrane to axon terminals
Lasts for a millisecond, then repolarization
Na+ gates close and membrane is impermeable to Na+ again, but very permeable to K+; K+ exits
Absolute refractory period = neuron resists stimulation

18. REFLEX ARC Route traveled by nervous impulses
Afferent neuron -> interneuron in CNS -> efferent neuron
Vesicles in synaptic knob have
~10,000 molecules of neuro-transmitters

19. NEUROTRANSMITTERS
Acetylcholine – autonomic NS and brain - neuromuscular junctions – excite muscles – inactivated by cholinesterase
- flea collars, pest strips, nerve gas contain cholinesterase inhibitors

20. Norepinephrine – sympathetic NS; regulates activity of of visceral organs and controls certain brain functions
3. Dopamine – Brain - motor functions; too little – muscle rigidity, tremors, forward gait (Parkinson’s ); too much – mental disorders (schizophrenia)

21. Serotonin – CNS - mental functions – wakefulness and sleep and other Circadian rhythms
GABA – inhibitory
Glycine – inhibitory in spinal cord
Net effect is what determines if a neuron will fire

22. Neuropharmacological agents
Exogenous substances that can affect neuron excitability by either mimicking or blocking action of neurotransmitter
Curare = blocks Ach receptors
Theobromine, caffeine increase excitability by affecting membrane perm. to Ca++
Strychnine and tetanus toxin inhibit inhibitory neurotransmitters and cause convulsions
Ether = inc K+ perm causing hyperpol. Making membrane less responsive to stimulation

23. Valium enhances inhibitory effects of GABA
LSD mimics serotonin and binds to its receptors – effects are quite different