1. The Nervous System- Nervous Tissue Chapter 9

2. The Nervous system has 3 major functions:
Sensory – monitors/detects stimuli of internal & external environment through presence of receptors (afferent neurons)
Integration – interpretation of sensory information (information processing); complex/higher order functions (interneurons- most common)
Motor – response to information processed through stimulation of effectors (efferent neurons)
muscle contraction
glandular secretion

3. General Organization Two Divisions of Nervous System
Central nervous system (CNS)
Brain and Spinal cord
Peripheral nervous system (PNS)
All other nervous tissue outside CNS
Somatic nervous system (SNS)
Special senses and skeletal muscles…voluntary
Autonomic nervous system (ANS)
Visceral organs (stomach & lungs), smooth muscle, cardiac muscle, glands…involuntary
Sympathetic and parasympathetic divisions
Enteric nervous system (ENS)= autonomic
Brain of the gut (contractions and secretions)…involuntary

5. Histology of neural tissue
Two types of neural cells in the nervous system:
Neurons - For processing, transfer, and storage of information
Neuroglia – For support, regulation & protection of neurons (generally smaller and more numerous)

6. Neuron structure (3 parts):
Dendrites
Cell Body
Axon (& axon terminal)

8. Schwann cells
surround all axons of neurons in the PNS creating a neurilemma around them. Neurilemma allows for potential regeneration of damaged axons
creates myelin sheath around most axons of PNS; white color
Myelin increases from birth to maturity (responses to stimuli get better)

9. Myelin will get laid down in segments (internodes) along the axon, leaving unmyelinated gaps known as “nodes of Ranvier”
Regions of the nervous system containing groupings of myelinated axons make up the “white matter”
“gray matter” is mainly comprised of groups of neuron cell bodies, dendrites, unmyelinated axons, & neuroglia (shaped like a butterfly)
of Ranvier

10. Neuroglia (glial cells)
CNS neuroglia:
astrocytes
oligodendrocytes
microglia
ependymal cells
PNS neuroglia:
Schwann cells (neurolemmocytes)
satellite cells

11. Astrocytes
create supportive framework for neurons
create “blood-brain barrier”
Play a role in learning and memory
secrete chemicals for embryological neuron formation

12. Oligodendrocytes
Produce & maintain myelin sheath around axons of neurons in the CNS.

13. Microglia
phagocytize cellular wastes/debris & pathogens/microbes

14. Ependymal cells
line ventricles of brain & central canal of spinal cord
produce, monitor & help circulate CSF (cerebrospinal fluid)

15. Conduction across synapses
In order for neural control to occur, “information” must not only be conducted along nerve cells, but must also be transferred from one nerve cell to another across a synapse
2 types of conduction:
continuous (unmyelinated axons)
saltatory (myelinated axons)
*diameter, myelin, and temp of axon determine speed of nerve impulse

17. The Structure of a Typical Synapse
One direction: presynaptic to postsynaptic.
*A typical neuron in the CNS receives input from ,000 synapses

18. Acetlycholine (Ach)- excitatory or inhibitory *nicotine imitates
Most synapses within the nervous system are chemical synapses, & involve the release of a neurotransmitter molecules/receptors
100 substances ? (50 known):
Acetlycholine (Ach)- excitatory or inhibitory
*nicotine imitates
Glutamate
Aspartate
Gamma aminobutyric acid (GABA)
*Barbiturates/depressants/alcohol/THC enhance
Glycine
excitatory
inhibitory

19. Neurotransmitters (cont.)
Norepinephrine (NE)- arousal from sleep, dreaming, moods
Dopamine (DA)- emotional response, addictive behavior, pleasurable experience
*Cocaine/Amphetamines/THC block uptake of dopamine (lasts longer)
*caffeine increases production of dopamine
Serotonin- Sensory perception, temp regulation, control of mood/appetite/onset of sleep
*ecstasy increases
Endorphins- Body’s natural painkillers
* Opiates increase

20. Neurotransmitters in our food?
Chocolate:
Over 300 substances have been identified in small amounts.
caffeine
theobromine (another, less powerful stimulant)
Phenylethylamine (a substance related to a family of stimulants called amphetamines)
Anandamide (the neural receptors for anandamide are the same ones to which THC, the main active ingredient in cannabis)
 you would have to eat well over 30 kilos of chocolate to experience effects comparable to one dose of cannabis!

21. Anatomical organization of neurons
Neurons of the nervous system tend to group together into organized bundles
The axons of neurons are bundled together to form nerves in the PNS & tracts/pathways in the CNS. Most axons are myelinated so these structures will be part of “white matter”
The cell bodies of neurons are clustered together into ganglia in the PNS & nuclei/centers in the CNS. These are unmyelinated structures and will be part of “gray matter”

22. Neural Tissue Organization

23. Anatomical structure of Nerves
Fig. 14.6