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Lecture 2

BIOM 2000 Lecture Notes - Lecture 2: Neural Tube, Salivary Gland, Cerebral Hemisphere


Department
Biomedical Sciences
Course Code
BIOM 2000
Professor
N.Campbell
Lecture
2

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Physiology — Unit 2
Expectations:
Explain how resting membrane potential is established
Identify components of neuron + describe roles in neurotransmission
Discuss processes involved with nerve transmission + signal transduction
Compare/contrast structures + functions of central + peripheral nervous systems
Identify major regions of brain + provide example of function in each
Describe importance of reflexes + how they differ from other impulses
List ways that nervous system is protected from damage
Terms:
Neuron — cells of nervous system specialized to transmit messages throughout the body
Dendrite — branching extensions of neutrons that carry electrical signals to cell body;
receptive portion of a nerve cell
Axon — neuron process that carries impulses away from nerve cell body; efferent process; the
conducting portion of nerve cell
Synapse — region of communication between neurons, or neuromuscular junction between
neutron + a muscle cell
Resting membrane potential — voltage (charge) difference across the cell membrane when
cell is at rest
Depolarization — loss of a state of polarity; the loss of a negative charge inside plasma
membrane
Action potential — electrical event occurring when stimulus of sufficient intensity is applied
to neutron or muscle cell, allowing sodium ions to move into cell + reverse polarity
Repolarization — restoration of membrane potential to the initial resting (polarized) state
Saltatory conduction — propagation of action potentials along myelinated axons from node
of Ranvier to next node, increasing conduction velocity of action potentials
Electrical Properties of Cell Membranes:
Cell membrane acts like battery — because there is unequal distribution of
Na+ and K+ on outside and inside of cell
Inside plasma membrane of cells are more negatively charged compared to
outside
Charge difference called resting membrane potential (RMP) + is very
small (approx. -70mV)
Discharges of RMP result in nerve impulses (aka action potentials)
Discharge of RMP refers to depolarizations/electrical signals across
membrane
Depolarization occurs when stimulus causes Na+ channels in membrane
(which are normally closed) to open

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As result Na+ rapidly enters cell down its concentration gradient
Propagation of depolarization of membrane is what refers to action
potential
Repolarization is transient — causes K+ channels to open and allows K+ to
move out of cell thru ion specific channel
Repolarization of membrane occurs w/in 1-3 milliseconds, then RMP is
reinstated — de/repolarization events move as wave along nerve cell
Unequal distribution established by sodium-potassium pump
Review: Pump moves Na+ from inside to outside of cell and K+ from
outside to inside of cell
RMP has been established (slightly negative)
Yellow/green arrow on figure represents Na (yellow) + K (green) channels
mentioned above
When channels open, ions move to other side of membrane down
concentration gradient (established by pump)…Na+ rushes out of cell and
K+ rushes into
Neurons and Nerve Impulses:
Neurons (nerve cells) —> cells of nervous system involved with
transmitting signals + known as nerve impulses
4 parts: cell body, dendrites, axon + synapses

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Cell body contains nucleus +
has dendrites (projections
acting as docking sites to make
connections w/ other neurons)
Single axon carries nerve
impulse (action potential)
along length of cell + synapses
at end of axon contain
neurotransmitter substance,
used to activate other cells
Axons of some neurons
insulted by myelin sheath
Myelin sheath formed by
Schwann cells around axon of
neuron
Myelinated axons — action
potentials only found at nodes
of Ranvier + action potential moves by
process called saltatory conduction
Involves action potential jumping from one
node to next, this permits rapid transfer of
signal + also reduces energy needed to re-
instate resting potential bc not as many
sodium-potassium pumps required
Terminal region of axon called synapse
Synapses contain vesicles of chemicals called neurotransmitter substance
Action potentials arriving at synapse cause controlled release of
neurotransmitter
Synapse closely associated with cell that it stimulates — cell could be
dendrites of another neuron or an effector such as muscle cell
Neurotransmitters —> released into space between synapse + cell to be
stimulated and bind to receptor proteins on membrane
Diagram illustrates events taking place between synapse and cell that is
stimulated
Structural Classification of Neuron:
Neurons —> classified by # of processes extending from cell body
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