Cells of the Nervous System
I. there are 2 basic types of cells in the nervous system
1. glia: can duplicate (most brain cancers of glial origin)
A. astrocytes: exist only in the CNS.
B. oligodendrocytes: myelinate axons
in the CNS
a. multiple sclerosis
C. Schwann cells: these serve to myelinate
the PNS
b. Guillain-Barre syndrome
2. neurons:
A. duplication is very limited but they often change
their shape
B. lose these thru out life
C. use primarily glucose for fuel
D. types of neurons
a. interneurons: communicate with other
neurons
b. sensory neurons (receptor): sensitive
to environmental energy (e.g., light)
-sometimes called
afferent neurons
-these are responsible
for transduction
c. motor neurons: carry information
from the CNS to the muscles
a. sometimes called
efferent neurons
II. internal structure of neurons
1. nucleus: this contains chromosomes
2. cytoplasm: jellylike substance inside cells which contains
A. mitochondria: extracts energy
B. endoplasmic reticulum: is involved
in the storage & transport
a. golgi apparatus:
packaging material
C. neurofilaments: long protein fibers
D. microtubules: involved in cell transport
a. axoplasmic transport:
III. external structure of neurons
1. soma (cell body):
2. dendrites: specialized to receive information
A. dendritic spines
3. axon: long thin fiber that transmits electrical signals
A. myelin: forms an insulating sheath
a. nodes of Ranvier:
B. terminal buttons (presynaptic terminal):
small knobs at the end of the axon
a. vesicles containing
neurotransmitter
4. synapse: a space between neurons
IV. Neurons are distinguished by their shape
1. multipolar: one axon & many trunks of dendrites
from soma
2. bipolar: one axon & one dendritic trunk from soma
3. unipolar: one stalk emerges from the soma
V. Blood-Brain Barrier (BBB): a barrier between the blood and the CNS
1. protects fragile brain cells from some substances
2. How does it keep out some stuff?
The Nerve Impulse
I. resting potential of -70 millivolts (mv)
1. axons have a selectively permeable membrane
2. diffusion & electrostatic pressure
3. important charged particles (ions) & concentration gradient
A. organic anions (A-): trapped inside the
axon
B. sodium (Na+): mostly outside the axon
C. potassium (K+): mostly inside the axon
II. action potential (AP): a brief change in the neuron’s electrical
charge
1. when a neuron is stimulated enough to surpass a threshold
of excitation
2. the process
A. Na+ ions pour in causing depolarization
B. depolarization causes K+ ions to pour out
C. Na+ channels then close but K+ continues
to pour out
3. characteristics of Action potential (AP):
A. drugs like Novocain inhibit action potentials
B. all or none:
C. rate law: frequency conveys intensity of
stimulus
D. APs propagate down the axon
a. APs skip from one
node of Ranvier to another (saltatory conduction)
E. when the AP reaches the end of the axon
it causes
a. the contents of
the vesicles (i.e., neurotransmitter) pour into the synapse
F. refractory periods
a. absolute refractory period
b. relative refractory period
(hyperpolarization after an AP)
III. sodium-potassium pump: pushes Na+ back out & K+ back in