Lecture: Ch. 13 Nervous Tissue: Monday 10/18

**We now resume our regularly scheduled notes. Sorry about the gap last week, folks, blame the flu.**

Some notes before the actual notes:
1. The suggestion was made that this material is harder than anything we've encountered to date, by virtue of being very conceptual. Adjusting study habits to include reading before class to prepare was strongly suggested. It was also put forth that you want to read this material more than once. So, pre read, read after lecture, then maybe read once or twice more just for kicks.

2. A lot of the lab practical will have to be on pictures/charts and diagrams that are in the text or powerpoints. Using them while you study, very smart. Not referring to them, potentially problematic during the next exam. Your choice.

Neural Tissue/Ch. 13 - starts on p. 341 in the text, powerpoints are available on the computer in the anatomy lab.

Two main divisions of the nervous system: **KNOW THIS**
1. CNS - Central Nervous System
the brain and spinal cord
2. PNS - Peripheral Nervous System
everything else, all the peripheral nerves

Functional Categories
1. Receptors - collect information from internal/external environment and send it back to the CNS via 'receptor pathways' where the brain processes the input.
2. Effectors - signal is sent back down the neural pathways from the CNS, via the PNS, and cells in muscles or glands receive impulses which cause the body to react in a certain way.

Functional Organization
1. The Sensory Nervous System or SNS is "AFFERENT"
stimulus -> CNS ->
a. Somatic Sensory - touch, pain, pressure, vibration
b. Visceral Sensory - involuntary impulses from viscera - a stomach ache, sense of bladder being full, cramps.
2. The Motor Nervous System or MNS is "EFFERENT"
CNS -> PNS -> glands and muscles
a. Somatic Motor - causes contraction of skeletal muscles, running, walking, picking stuff up, scratching your nose in response to an itch (somatic sensory).
b. Autonomic Motor - smooth muscle such as the digestive tract, cardiac tissue, respiration, totally regulated unconsciously by impulses from the CNS.

quick summation/concept check:
Autonomic Nervous System - fight or flight, breathing, digestion
a. sympathetic
b. parasympathetic
Somatic Nervous System - body, causing movement
**REFER TO CHART ON PAGE 343 for flow and detail**

Cellular Organization
1. Neuron - a nerve cell
a. excitable, can be stimulated
b. can initiate, transmit and recieve nerve impulses
c. the basic structural unit of the nervous system
d. high metabolic rate and high O2 needs
e. longevity - some neurons last your entire lifespan
f. non-mitotic - they don't replace themselves.
So when your mom told you you'd totally destroy brain cells so don't do anything stupid, she was right and you should have listened.
Neuron structure is as such:
a. cell body
b. dendrite - directional/afferent - smaller, go into cell body, sensory
c. axon - directional/efferent - leave cell body, larger, motor

2. Glial Cells
do not conduct impulses and are not excitable. They are the staid, boring cells of the nervous system.
Neuroglia or neural cells are:
a. found in both the CNS and PNS
b. smaller than neurons
c. mitotic
d. protect and nourish neurons - worker bee cells
e. more numerous than neurons by a factor of 10
f. tumors are more likely to be made up of neuroglia
Types of neuroglia - see page 345 for helpful diagram -
In the CNS:
a. astrocytes
- most abundant glial cells
- help form the blood/brain barrier (**know what this is**)
- regulate fluids
- structural network
- makes repairs
- development of fetal neurons
- have perivascular feet, take 02 and nutrients from blood and transfers this to the neuron. **KNOW this - there's a great diagram/pic in powerpoint and a decent one in the text on page 346**
b. ependymal cells
- line the ventricles of the brain and central canal of spinal cord
- makes CSF - cerebrospinal fluid - in conjuction with other glial cells
- forms choroid plexus
c. microglial
- motile, they move around and do stuff, wander through CNS
- phagocytic activity, remove dead or dying material, etc.
d. oligodendrocyte
(same as neurolemmocytes, but slightly different function, know the difference and which goes to what system.)
- myelinate CNS axons ONLY **KNOW THIS KNOW THIS KNOW THIS**
- wrap around axons like electrical tape (the cell membrane) to make the myelin sheaths
- produce myelin which is a membranous coating around the axon made up of a phospholipid bilayer or the neurolemma of the oligodendrocyte
- myelin sheath improves speed of neural impulses
- Myelinated nodes - the "bumps" of myelin coated axon
- Nodes of Ranvier **KNOW THIS KNOW THIS KNOW THIS** - the unmyelinated part of an axon between myelinated nodes.
- white matter - made of myelinated axons
- grey matter - no myelin here! axons or cell bodies.
- one oligodendrocyte will coat 1mm of several different axons
Glial cells in the PNS:
a. Schwann cells or neurolemmocytes
(are the same as oligodendrocytes, except they do some slightly different things. Know which goes to which system.)
- myelinate PNS axons only
- same function and structure as oligodendrocytes
- nucleus gets sort of squished to the side as it wraps around the axon.
- one neurolemmocyte will coat one mm of one axon only
b. Satellite cells -
(know they exist and which system. Know that they're flattened around neural cells and ganglia. Don't need to know much more.)

Neuron - cell body or "soma" **note, this is where my brain began to glaze over due to saturation of information, so you will want to go over the powerpoint from this point, and fill in any gaps**
a. recieve/send/process impulses
b. have multiple components
c. have organelles
d. **KNOW "Nissl bodies"

Axons:
a. **KNOW** the "axon hillock" which is a slightly thickened area where the axon meets the body of the neural cell.
b. transmits away from cell body
c. at the far end -
d. axon collaterals - side branches
e. telodendria - tree like structures
f. synaptic knobs - at end of telodendria
g. terminal boutons

Classification - see page 350 in text
1. unipolar
2. bipolar
3. multipolar
4. pseudounipolar
5. anaxonic (no axon)
Functional Classification
1. sensory - "afferent" to the CNS
2. motor - "efferent" from the CNS
3. Interneuron - facilitate communication between sensory and motor neurons, fine tune responses, both working at once. 99% of these are in the CNS, mostly brain, a little in spinal cord.

Conduction:
**KNOW** the bigger the axon, the faster the conduction**
1. Nodes of Ranvier - neurofibril node - space in myelin sheath
2. Saltatory Conduction - nerve impulses from node to node, the fastest impulse
3. Continuous Conduction - slow, needs more ATP, pain/cold reception

Regeneration of the PNS
a neuron may regenerate if some neurolemma remains after being damaged
it depends on the amount of damage
certain factors stimulate regrowth and must be present
it also depends on the distance between the area of damage and the effector organ, if there is too much distance, regeneration is nearly impossible.

Wallerian Regeneration **KNOW THIS ONE**
1. trauma happens
2. proximal end of the axon seals itself by fusion and it swells
3. regeneration of the tube/new tube forms
4. axon growth and remyelinization occurs, 5mm per day
5. innervation is restored with the original effector.
Regeneration of the CNS
Not so much with that. Very limited.
why? Oligodendrocytes - no growth factor
Axons - too tightly packed
**check powerpoint, there were other points on this slide that I missed and he went too fast for me to get them down**

Nerve structure:
Endoneurium - a fibrous sheath that wraps around several fascicles of nerves
Perineurium - fibrous sheath wrapping around individual fascicle
Epineurium - fibrous sheath wrapping around one bundle of axons, a cablelike bundle of parallel axons, several within a fascicle.

Vesicular Synapses - the most common type of synapse
axons terminate at a synapse, branch at the telodendria, end in a synaptic knob which makes contact with the synaptic cleft of the tissue it is connected to.
Electrical Synapse
Chemical Synapse - (same as vesicular)

Neuronal Circuits - see p. 355
divergent - walking
convergent - appetite
serial -
parallel - math calculations, anatomy tests
reverberating - breathing at night (a feedback loop, positive reinforcement)