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VII. The Nervous System
A. Cells of the Nervous System
1. ____________________________- cells specialized for transmitting chemical and
electrical signals from one location in the body to another
a) ________________________________-contains most of the cytoplasm, the
nucleus and other organelles
b) ________________________- convey signals to the cell body, Usually short,
numerous and extensively branched
c) ____________________- conducts impulses away from the cell body.
They are tipped with ___________________________ which release
neurotransmitters
1) ___________________________- chemicals that cross the synapse to
relay a message to a new neuron
2) ___________________________- gap between a synaptic terminal and
the dendrites of another neuron
2. Types of Neurons:
a) ______________________________- convey information about the external
or internal environment to the central nervous system
b) ______________________________- convey impulses from the CNS to the
effector cells
c) _______________________________- integrate sensory input and motor
output (located in the CNS)
3. _________________________________- structurally support, protect insulate and
assist neurons. They do not conduct impulses. They out number neuron 10-50X
a) ____________________- supporting cells of the central nervous system
1) _________________________________- encircle capillaries in the brain
to control the ionic environment around neurons
2) _________________________________- form myelin sheaths that
insulate nerve processes
b) __________________________________- form myelin sheath in the
peripheral nervous system to provide electrical insulation and speed the rate of
nerve impulse transmission.
B. Transmission of Electrical Signals along a Neuron
1. The Origin of Electrical Membrane Potential
a) _______________________________- the difference in charge between the
cytoplasm and extracellular fluid due to a differential distribution of ions
b) _______________________________- about 70 mV in a non-transmitting neuron
c) Ion Distribution:
1) Inside the cell: ____________________________________= negative charge
2) Outside the cell: ___________________________________= positive charge
d) ___________________________________- actively move ions against their
concentration gradient to maintain proper resting potential and counteract
diffusion
2. ___________________________________ rapid change in membrane potential caused by
selective opening and closing of ion gates
a) _________________________________allow neurons to change their membrane
potential in response to stimuli
b) Different ion channel affect the neuron:
1) ___________________________________gates allow K+ to leave the cell
causing the inside to become more negative
2) ___________________________________ gates allow Na+ to enter the cell
making the inside less negative
c) An action potential has four phases:
1) _______________________________- no ion channels are open
2) ___________________________________- Na+ gates are opened. K+ gates are
closed. The influx of Na+ causes the interior of the cell to become positively
charged
3) ____________________________________- Na gates close. K+ gates open.
Loss of K+ causes cell interior to return to a negative state
4) _____________________________________is a time when membrane potential
is temporarily more negative than resting state due to the lag in closing K+ gates
There is a _____________________________- during undershoot phase. During
this period the neuron is insensitive to stimulus and will not fire. This limits the
maximum rate at which a neuron can fire
3. Propagation of the action potential
a) Strong depolarization in one area results in the depolarization of the neighboring area
b) Action potential does not travel down the axon but is regenerated at each position
c) The impulse travels in one direction due to the refractory period at the previous
position
4. Speed of Propagation of Action Potential
a) The larger the diameter of a neuron, the faster the impulse
b) ___________________________________________- the impulse jumps from one
node of Ranvier to the next, skipping myelinated refions
c) ____________________________________- gaps in the myelinated sheath where ion
gates are concentrated
C. The Synapse: Transmission between Cells
1. ____________________________- tiny space between neurons that control
communication between those neurons
a) ____________________________- is the transmitting cell
b) _____________________________- is the receiving cell
2. _____________________________________-action potential spreads directly from
presynaptic to postsynaptic cell via gap junction. Very uncommon.
3. ______________________________________- a chemical called a
______________________________ is released from the presynaptic cell and binds to
receptors on a postynaptic cells causing it to fire
a) An action potential arriving at the _________________________________at the end
of an axon causes Ca+2 to rush through voltage sensitive channels
b) The sudden in rush of Ca+2 causes ______________________________ which
contain neurotransmitters to fuse with the presynaptic membrane releasing
neurotronsmitters into the ________________________ (the space between neurons)
c) Neurotransmitters diffuse to the postsynaptic membrane where they bind to specific
receptors and trigger the opening of ion gates
d) This may cause _____________________________ or ________________________
depending on which ion gates are opened
e) The neurotransmitter is quickly degraded by enzymes and recycled to the presynaptic
cells
4. Nervous Integration
a) One neuron receives signals from numerous adjacent neurons
b) _________________________________________________ (EPSP) are caused by
neurotransmitters that open Na+ gates triggering depolarization
c) _________________________________________________ (IPSP) are caused by
neurotransmitters which open K+ or Cl- gates causing hyperpolarization
d) A single EPSP is rarely strong enough to trigger an action potential, although and
additive effect, _______________________________, from several terminals can
trigger a neuron to fire
1) __________________________________ is when chemical transmission from
one or more synaptic terminals occur so close in time that the additive effect
causes the neuron to fire
2) __________________________________ occurs when several neurons stimulate
the postsynaptic cell at the same time and cause it to fire
3) EPSPs and IPSP can summate also, but each counters the other’s affect
preventing the neuron from firing
D. The Vertebrate Nervous System
1. ________________________________________ consists of sensory and motor neurons
a) _____________________________________________ (voluntary) carries messages
from the central nervous system to skeletal muscles
b) _____________________________________________ controls involuntary
functions and is divided into:
1) ______________________________________________increases function
2) ______________________________________________decreases function
2. The Central Nervous System
a) _________________________________ - the part of the brain below the back of the
cerebrum. It regulates balance, posture, movement, and muscle coordination.
b) __________________________________ - a large bundle of nerve fibers that connect
the left and right cerebral hemispheres. In the lateral section, it looks a bit like a "C" on
its side.
c) ________________________________________________- the top, front regions of
each of the cerebral hemispheres. They are used for reasoning, emotions, judgment, and
voluntary movement.
d) _________________________________________________ - the lowest section of the
brainstem (at the top end of the spinal cord); it controls automatic functions including
heartbeat, breathing, etc.
e) _________________________________________________- the region at the back of
each cerebral hemisphere that contains the centers of vision and reading ability (located
at the back of the head).
f) ___________________________________________ - the middle lobe of each cerebral
hemisphere between the frontal and occipital lobes; it contains important sensory centers
(located at the upper rear of the head).
g) ______________________________________ - a gland attached to the base of the brain
(located between the Pons and the Corpus Callosum) that secretes hormones.
h) _____________________ - the part of the brainstem that joins the hemispheres of the
cerebellum and connects the cerebrum with the cerebellum. It is located just above the
Medulla Oblongata.
i) __________________________________ - a thick bundle of nerve fibers that runs from
the base of the brain to the hip area, running through the spine (vertebrae).
j) ______________________________________________- the region at the lower side of
each cerebral hemisphere; contains centers of hearing and memory (located at the sides of
the head).