Nervous System Overview

Anatomy Notes

Nervous System

Organizational

Go over organizational chart:

DRAW AND LABEL the neuron.

Brain cells are amitotic. Why can’t brain cells divide?

How can someone get brain cancer if the cells can’t divide?

Neuroglia (Glia)—“Nerve Glue” Support cells

I. CNS

Astrocytes-form a barrier between nerve cell and capillaries, helping to block harmful substances in the blood. Maintain salt concentration.

Microglia- phagocytes that dispose of dead brain cells and bacteria.

Ependymal cells—ciliated to move cerebrospinal fluid in brain

Oligodendrocytes- form insulating myelin sheaths.

II. PNS

Schwann cells- form myelin in PNS

Satellite cells- protect and cushion

Myelination- glial cell (either Schwann cell or oligodendrocyte) wraps around nerve cell. See animation of Schwann cell. MS (multiple sclerosis), defective myelin

3 neuron pathway:

1) Sensory neuron (afferent transmission)

2) Association neuron (interneuron)

3) Motor neuron (efferent transmission)

Resting Membrane Potential of the Nerve Cell

(but not really resting- because it takes energy)

  • Na outside/ K inside
  • + charge outside compared to charge inside
  • Polarized
  • Resting membrane potential –70 mV.
  • Need Na/ Kpump to maintain resting potential.

- (3 Na pumped out to 2 K pumped in)

  • membrane acts like a battery because it separates polar charges.
  • - Resting is “charging” phase

Graded Potentials

  • Changes in membrane permeability (Na+ rushes in)cause graded potential.
  • This change in membrane permeability in sensory neuron brought about by a stimulus

-Chemical Receptor (smell and taste);

-Mechanical Receptor(touch) (hearing);

-Light Receptor- (vision)

-Nociceptors – detect painful -harmful stimuli.

  • If graded potential is too small, no action potential. This is a normal and healthy condition which prevents over-firing (seizure).

Action Potential.

  • If graded pot. is large enough (about –55 mV), all channels open
  • Depolarization occurs. This is an action potential.

-This is known as “all or none” because if fired, it fires fully (like pulling a trigger).

Voltage in the cell increases to about 30mV.

  • After depolarization, pumps act to repolarize.
  • Hyperpolarizition- overshoot of K causes more negative membrane- refractory period

The refractory period is so important that when it is too short, it leads to seizures

Propagation of action potential. Patches of depolarization move down the axon

Depolarization- Na+ enters-inside of cell more positive

A.P. more likely

Hyperpolarization- A.P. less likely

See animation on my Home Page

Raven animations

Neurotransmitters carry the message at the synapse.

Acetylcholine causes EPSP (excitatory post synaptic potential) in the parasympathetic n.s.

GABA causes IPSP (inhibitory psp). Causes hyperpolarization (making depolarization less likely)

Important for regulating movement and brain function.

Glutamate- causes EPSP in the CNS

More about Neurotransmitters

Acetycholine- in addition to EPSP, acetylcholine is important in the neuromuscular junction.

Norepinephrine- Works with hormone epinephrine in the sympathetic NS

Dopamine—bodily movements (imbalance may cause Parkinson’s and schizophrenia), learning, and well-being

Serotonin—well being, sleep

Breakthrough in neurobiology: IQ was always thought to be set. If you take an IQ test when you are 8, it wouldn’t be much different when you are 30. But now, they know with an enriched learning environment, IQ can increase so significantly that a person with an average IQ (100) can see an increase to top 1/3 (127). The inverse is also true. This correlates with a change in the STRUCTURE of the brain. This is really important information for a student or a teacher to know.

Mantis Shrimp Eyes: