Nervous PhysiologyMark Robertson

Professor of BiologyDelta College

Nervous System DivisionsCentral Nervous System (CNS; consists of brain and spinal cord)Peripheral Nervous System (PNS; consists of spinal and cranial nerves)

Sensory Division (afferent neurons into CNS for our 5 senses)Motor Division (efferent neurons out of CNS to muscles and glands)

Somatic Motor (voluntary control of skeletal muscles only)Autonomic Motor (involuntary control of cardiac, smooth, & glands)

Sympathetic (fight or flight)Parasympathetic (rest &

General Design of A NeuronNeuron (an elongated cell with processes that can generate and move action potentials - APs)

Cell Body (largest portion; contains nucleus and most of the organelles)

Multiple Dendrites (stimulated end of the cell; contains receptors and generates AP’s; a ton of sodium channels found here)

Single Branched Axon (move AP over large distance in the body down to terminal buds full of neurotransmitters)

Schwann Cells (often has myelination to insulate it better for increased speeds)

Nodes of Ranvier (openings left in the myelin sheath to allow ion entry/exit)

Neuronal PathwaysNeurons are linked into pathways called arcs to control the body

Myelination will increase nonmyelinated neuronal speeds from 1m/sec (in CNS often) up to about 100m/sec (in CNS and PNS)

Neurons come in three general types:Sensory (5 senses bring information into your brain)

Motor (somatic and autonomic out of your brain)

Interneuron (allows control of responses)

Reflex ArcsInvoluntary (controlled by brainstem or spine without conscious control; works even in coma)

EEG (Electroencephalogram)Resting Potential (RP is about -70mV; Na+/K+ pumps keep the cell polarized; waiting for stimulus)

Graded Potential (GP is a subthreshold response to a weak stimulus; Na+/K+ pumps fighting the Na+ ion entry)

Depolarization (created whenever stimulus moves membrane from - towards + mV; Na+ ions entering the cell to move the charge more positive)

Threshold (about -50 to -55mV normally; this is the point at which Na+ ion channels open wide)

Action Potential (AP is about +30mV; Na+

ion channels close here, K+ channels open, and Na+/K+ pumps turn back on to reverse potential)

Repolarization (created as Na+/K+ pumps move the membrane from + back towards - mV; the Na+/K+ pumps are on and K+ channels are open)

Hyperpolarization (membrane going more

Repolarization Phase

Depolarization

Graded

Action Potential3

Steps for Neuronal Response1. Na+/K+ pumps located in dendrites force 3 Na+ ions

out for every 2 K+ ions pumped into the cell2. K+ channels remain slightly open (leaky) and Na+

channels are closed3. K+ ions slowly equilibrate across the membrane4. Internal charge reaches -70mV (RP) and the cell waits

for stimulus (holding Na+ ions out)5. Stimuli (ex: Light, Pressure, Injury, Heat, and

Chemicals) needed to allow Na+ ion leakage as pumps click on to fight the entry

6. If internal charge = threshold, sodium channels open wide and Na+ ions flood the cell (towards the axon)

7. Internal charge becomes positive (depolarizes) until channels are altered at AP value (Na+ channels close now and K+ channels open wide)

8. Na+/K+ pumps kick on again to repolarize the cell as K+ ions exit the cell

9. Slight hyperpolarization occurs (at about -80mV with excess loss of K+ ions; resists new stimulus)

Excitatory/Inhibitory PotentialsEPSP (Excitatory Post-Synaptic Potential)

Uppers or stimulants

Cause opening of Na+ channelsCell depolarizes

Norepinephrine, epinephrine, and dopamine

IPSP (Inhibitory Post-Synaptic Potential)

Downers or depressants

Cause opening of K+ channels

Cell hyperpolarizes

Seratonin and GABA

Synaptic Physiology1. Action Potential created at dendrite and

moves down to axonal terminal bud2. Calcium channels open3. Extracellular Ca2+ ions enter the bud and

pull vesicles towards presynaptic membrane

4. Vesicles release neurotransmitters by exocytosis

5. Neurotransmitters diffuse across synapse towards postsynaptic dendritic receptors

6. As neurotransmitters bind to enough receptors, either reach threshold or hyperpolarize as specific channels open

7. Either IPSP or EPSP results depending on the relative concentrations of specific neurotransmitters

8. If AP generated, it moves from dendrites towards axon to continue the process

Possible Journal Critique Topics?

Multiple Sclerosis?

Tay Sachs Disease?

Alzheimer’s?

Autism?

Anesthetics and Analgesics?

Fragile X Syndrome