Monday March 15, 1999
Announcements: Review Session tonight at 110 Wartick Lab, from 6:30-7:30

Lecture notes:

The RDA is .8 gm. of protein per kilogram (2.21 lb.) of body weight for non-athletes.

Estimates: * for athletes add .4 g/k to get 1.2 g/k/day. (50% more)
* for a 150 lb. Athlete (68 kg) the means approx. 82 gm. of protein per day.
* 1/2 a chicken breast is 30 gm. of protein
* 1/4 hamburger is 25 gm. of protein
* 1 cup of milk is 8 gm. of protein.

*** Rule of thumb: 1 oz. of meat is 7 gm. of pure protein.***

"Energy in" should equal "Energy out"

Too much in = weight gain
Too much out = weight loss

There are 3,500 kcal worth of energy in one pound of fat.

To lose one pound of fat you must:
a) take in 3,500 fewer kcal
b) use up an excess of 3,500 kcal
c) a combination of both

It is better to combine calories restriction with exercise the to use calorie restriction alone.

Aerobic exercise: exercise performed under conditions where oxygen is supplied to muscles in sufficient quantities to carry
glucose (or any other energy source) through aerobic respiration (electron transport system)

Anaerobic exercise: exercise performed under conditions where oxygen is not supplied . Glucose converts to lactate.

Training:
1. Results in more efficient delivery of oxygen to muscles and more mitochondrion.
2. Creates stimulus for muscle building.
3. Increases the body's efficiency at using fatty acids for energy.

Definitions:

Sensory Stimuli: different forms of energy in the internal or external environment that can be detected by receptor cells.
Examples: patterns of light waves, sound waves, pressure, temperature.

Sensory Neurons: the receptors for specific stimuli. (Hearing sensors can't detect light waves.) These include the
receptors in the eyes, ears, mouth, and tongue, skin, nose as well as those that receive messages from
the internal environment.

Interneurons: combine, sort and integrate incoming messages, then influence outgoing messages.
Examples: brain and spinal cord.

Motor Neurons: relay outgoing messages to muscle or gland cells which are the body's effectors.

Neuroglia (nerve glue): These cells make up half of the bulk of the nervous system - the rest being neurons.

These cells provide: a. physical support - packing
b. structure
c. metabolic assistance
d. protection and insulation
e. segregation of groups of neurons

• The peripheral neuron axons and dendrites (those not in the brain or spinal cord) are wrapped by special neurogial cells called Schwann cells. This wrapping is called either the myelin sheath or the Sheath of Schwann.

The spaces between these Schwann cells are call Nodes of Ranvier and are important in conduction of electrical impulses.

A nerve is a bundle of the axons motor neurons, dendrites of sensory neurons of both.

These communication lines connect the brain and spinal column with the rest of the body.

In the brain and spinal cord, clusters of cell bodies are called nuclei.

In other parts of the body, they are called ganglia.

1. In the resting neuron, there are many more sodium (Na+) ions outside the cell than inside.
2. There are many more potassium ions (K+) inside the cell than outside.
3. This situation is maintained by active transport.
4. Overall, the cytoplasm of the neuron is more negatively charged than the "extracellular fluid".

Outside: 5K+ + Charge 150 Na+ Extracellular Fluid
-------------------------------------------------------------------------------
Membrane
-------------------------------------------------------------------------------
Inside: 150 K+ -Charge 15Na+ Cytoplasm

5. The difference in charge on either side of the membrane comes as a result of movement of K+ (potassium ions) down the concentration gradient. This movement results in a net charge differential of 70 millivolts between the inside and the outside of the neuron.

THE RESTING MEMBRANE POTENTIAL IS THE STEADY VOLTAGE DIFFERENCE ACROSS THE MEMBRANE OF THE NEURON AT REST.

1. The resting neuron has a polarized membrane. (The inside is more negative than the outside.) The difference is 70 millivolts.
2. During an action potential (nerve impulse) the membrane is depolarized by the inflow of Na+ (sodium ions) which causes the inside to become more positive than the outside.
3. The membrane is repolarized by outflow of K+ ( potassium ions) to make the inside negatively charges again with respect to the outside.
4. The ion concentrations get back to the way they are supposed to be by active transport usin th "sodium/potassium pump".
   
   ***Here there is a refractory period***
5. The action potential (nerve impulse) travels down the axon because each electrical disturbance triggers the nest down the line.
6. The flow of ions during action potentials is regulated by gated channels.
7. This occurs only if the membrane threshold is met. (the stimulus must be of sufficient strength and/or duration to depolarize the trigger zone.) If not, there is only a local depolarization.

What happens at the Synapse?

Chemical synapses are junctions: between two neurons
between a neuron and a muscle cell
between a neuron and a gland cell

Events:

1. Action potential (nerve impulse) arrives at the axon terminals of the presynaptic neuron.
2. This causes and inflow of Ca++ (calcium ions) into the presynaptic neuron.
3. The Ca++ in the presynaptic neuron causes release of transmitter chemicals into the synaptic cleft by exocytosis.
4. The transmitter chemicals diffuse across the synaptic cleft.
5. Transmitter molecules bind to receptors on postsynaptic neuron.
6. Binding causes channel proteins to open and action potential results.
7. Whether the neuron "fires" or not depends upon the amount of the transmitter released and how close the neuron is to the threshold.
8. There are excitatory and inhibitory chemicals released at the synapse.
9. Some transmitter chemicals are broken down by degradative enzymes in the cleft to prepare the synapse for the next transmission.