Download THE NERVOUS SYSTEM - Fox Valley Lutheran High School

THE NERVOUS SYSTEM
 NERVOUS SYSTEM: Receives & relays info. About activities
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w/in the body & monitors & responds to internal & external
changes.
NEURONS: Cells that carry messages throughout the NS.
Impulses- Messages taking the form of electrical signals
Sensory- from sense organs to brain & spinal cord
Motor- from brain & spinal cord to muscles or glands
Interneurons- connect sensory & motor neurons
Parts: Cell body-Lgst. Part w/ nucleus & cytoplasm; ATP
Dendrites-Short branched extensions carrying impulses
from environment or other neurons toward cell body.
Axon- Long fiber carrying impulses away from cell body
Axon terminals- series of small swellings at the end of the
axon; located some distance from cell body. (fig. 37-3)
THE NERVE IMPULSE-1
 Luigi Galvani: Found that nerves work with electrical charges
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along the cell membrane due to mov’t of ions across membranes.
RESTING POTENTIAL (Figure 37-4)
Nerve cells have an electrical potential of 70 mV. Due to the
difference of + & - charged ions on each side of the cell mem.
Na+-K+ pumps move Na+ ions out of cell and actively pump K+
ions into the cell. This Active transport causes the cytoplasm to
have more K+ ions and fewer Na+ ions than the surrounding
medium.
The cytoplasm has negatively charged protein molecules &
ions. The K+ ions leak back out more easily than Na+ ions leak
in, and the – charged molecules don’t leak in or out.
The net result is a – charge on the inside of the cell membrane.
This is known as resting potential. Causing it to be polarized.
(fig. 37-4) (- chgd. On the inside & + chgd. On the outside)
THE NERVE IMPULSE 2
 The moving impulse (like the mov’t. of water rippling in a pond)
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Cell membrane has “gates” that allow Na & K to go through
At impulse, gates open so Na+ flow inside the membrane
causing the cell membrane to be depolarized. As impulse passes,
K+ gates open allowing + chgd. K+ ions to flow out. (repolarized)
Action Potential: The depolarization and repolarization of a
membrane.
Several impt. Facts:
Not an electric current; it’s a wave of depolarization and
repolarization passing along a neuron.
Much slower than an electric current. (10cm to 1m/sec.)
The strength of an impulse is always the same.
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THE SYNAPSE
 Receptor: Sensory neurons in sense organs that receive stimuli
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from their external environment.
Effector: Muscles or glands that bring about a response.
Synapse: Points of contact at which impulses are passed from
one cell to another.
Neurotransmitters: substance used by neurons to signal each
other located within tiny vesicles at axon terminals.
Impulse moves down axon & vesicles discharge the
neurotransmitters into gap between which diffuse into special
receptors on next neuron.
Permeability of the membrane changes, Na+ ions diffuse
through membrane which can depolarize the neuron. Threshold
is reached and an impulse begins in 2nd cell.
Neurotransmitter detaches, is remove or destroyed halting the
effect.
THE NERVE IMPULSE-3
 Propagation of the impulse
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An impulse at one point of the membrane causes the impulse
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at the next point of the membrane
Unlike dominoes, it can restore itself. The mov’t. is only in
one direction because Na gates will not open.
The Role of Myelin
Made of lipids & proteins, it forms an insulated sheath,
wrapping around the the axon.
Myelin has small nodes, gaps, between adjacent sheaths along
axons. This allows the impulse to jump from node to node
greatly increasing the speed of the impulse.
The Threshold: Minimal level of a stimulus that is required to
activate a neuron. (All or none; dominos)
Not restricted to impulses as they travel along neurons. It
also occurs when they move from one neuron to another.