4. Afferent and Efferent Division
The afferent division of the PNS, peripheral nervous system, detects stimuli and conveys action po-
tentials to the CNS, central nervous system. The CNS interprets incoming information and initiates
action potentials that are transmitted through the efferent division to produce a response. The effer-
ent division is divided into two systems, the somatic nervous system and autonomic nervous sys-
tem. The efferent division of the nervous system is divided into two subdivisions: the somatic nerv-
ous system and the autonomic nervous system (ANS). The somatic nervous system transmits ac-
tion potentials from the CNS to skeletal muscle. Its neuron cell bodies are located within the CNS,
and their axons extend through nerves to neuromuscular junctions, which are the only somatic mo-
tor nervous system synapses outside of the CNS. The ANS transmits action potentials from the
CNS to smooth muscle, cardiac muscle, and certain glands. The ANS is sometimes called the invol-
untary nervous system because control of its target tissues occurs subconsciously. The ANS is di-
vided further into the sympathetic and the parasympathetic divisions. In general, the sympathetic
division prepares the body for physical activity when activated, whereas the parasympathetic divi-
sion regulates resting or vegetative functions, such as digesting food or emptying the urinary blad-
der.
5. Cells of the nervous System Crossword Puzzle
1
2
3
4 5
6
7
Across Down
4. Provide the insulation (myelin) to neurons 1. Like astrocytes, microglia digest parts of
in the central nervous system. dead neurons.
6. Cells Physical support to neurons in the pe- 2. Star-shaped cells that provide physical and
ripheral nervous system. nutritional support for neurons
7. Cells Provide the insulation (myelin) to 3. neurons These transmit impulses from the
neurons in the peripheral nervous system. central nervous system to the
5. These are found exclusively within the spi-
nal cord and brain. They are stimulated by
signals reaching them from
6. neurons touch odor taste sound vision
7. The Resting Membrane Potential
When a neurone is not sending a signal, it is at ‘rest’. The membrane is responsible
for the different events that occur in a neurone. All animal cell membranes contain a
protein pump called the sodium-potassium pump (Na+K+ATPase). This uses the en-
ergy from ATP splitting to simultaneously pump 3 sodium ions out of the cell and 2 po-
tassium ions in.
The Sodium-Potassium Pump
(Na+K+ATPase)
(Provided by: Doc Kaiser's Mi-
crobiology Website)
Three sodium ions from inside
the cell first bind to the transport
protein. Then a phosphate
group is transferred from ATP to
the transport protein causing it
to change shape and release
the sodium ions outside the cell.
Two potassium ions from out-
side the cell then bind to the
transport protein and as the
phospate is removed, the pro-
tein assumes its original shape
and releases the potassium ions
inside the cell.
If the pump was to continue unchecked there would
be no sodium or potassium ions left to pump, but
there are also sodium and potassium ion chan-
nels in the membrane. These channels are normally
closed, but even when closed, they “leak”, allowing
sodium ions to leak in and potassium ions to leak
out, down their respective concentration gradients.
8. The Action Potential The resting potential tells us about what happens when a neurone is at
rest. An action potential occurs when a neurone sends information down an axon. This involves an
explosion of electrical activity, where the nerve and muscle cells resting membrane potential chang-
es.
In nerve and muscle cells the membranes are electrically excitable, which means they can
change their membrane potential, and this is the basis of the nerve impulse. The sodium and potas-
sium channels in these cells are voltage-gated, which means that they can open and close de-
pending on the voltage across the membrane.
The normal membrane potential inside the axon of nerve cells is –70mV, and since this potential
can change in nerve cells it is called the resting potential. When a stimulus is applied a brief rever-
sal of the membrane potential, lasting about a millisecond, occurs. This brief reversal is called
the action potential:
An action potential has 2 main phases called depolarisation and repolarisation:
At rest, the inside of the neuron is slightly negative due to a higher
concentration of positively charged sodium ions outside the neu-
ron.
When stimulated past threshold (about –30mV in humans), sodi-
um channels open and sodium rushes into the axon, causing a
region of positive charge within the axon. This is calleddepolari-
sation
The region of positive charge causes nearby voltage gated sodium
channels to close. Just after the sodium channels close, the potas-
sium channels open wide, and potassium exits the axon, so the
charge across the membrane is brought back to its resting poten-
tial. This is called repolarisation.
This process continues as a chain-reaction along the axon. The
influx of sodium depolarises the axon, and the outflow of potassi-
um repolarises the axon.
The sodium/potassium pump restores the resting concentrations of
sodium and potassium ions
9. Membrane Potential-Membrane poten-
tial (or transmembrane potential) is the
difference in voltage (or electrical po-
tential difference) between the interior
and exterior of a cell
10. The local potential is the depolariza-
tion of a cell below threshold. After
the cell is sufficiently depolarized (and
reaches threshold), it fires an action
potential down the axon.
11. Synapse
1. Summation- The potentials spread far enough to
reach the axon hillock, where they add together. When
they add together and reach threshold pontential, they
produce an actional potential called Spatial Summa-
tion. When in rapid succession they produce an action
potential it is called temporal summation.
2. Nuerotransmitters- some trigger the opening or
closing of ion channels directly. They will bind to re-
ceptors linked to G proteins. Small-molecule neuro-
transmitters are amino acids or are derived from ami-
no acids. Large-molecule neurotransmitters are two
chains of 2-40 amino acids.
12. Neuromuscular Reflex lab Graphs
5
4
3 Delta T (s) striking
Delta T(S) sound
2
1
0 0.2 0.4 0.6 0.8 1
5
4
Reflex with reinforcement
3
Relex without
reinforcement
2
1
0 1 2 3 4
13. DATA ANALYSIS FOR NEOMUSCULAR REFLEX LAB
1. Compare the reaction times for voluntary vs. involuntary activation of the quadriceps mus-
cle. What might account for the observed differences in reaction times?
The voluntary times are substantially higher due to the test subject being aware of the
need for his leg to move in order to collect data. Because the test subject could focus
more on voluntarily moving his leg when the table was hit, he could in fact increas the
time of stimulous. While involuntarily, his nervous system took over and was being
tested. He was given no warning for when his knee was to be hit so he did not have
time to contol any outcome of the time of stimulus.
2. Using data from Table 2, calculate speed at which a stimulus traveled from the patellar ten-
don to the spinal cord and back to the quadriceps muscle (a complete reflex arc). To do this,
you must estimate the distance traveled. Using a cloth tape measure, measure the distance
in cm from the mark on the patellar tendon to the spinal cord at waist level (straight across
from the anterior-superior iliac spine–see Figure 9). Multiply the distance by two to obtain
the total distance traveled in the reflex arc. Once this value has been obtained, divide by the
average ∆t from Table 2 and divide by 100 to obtain the speed, in m/s, at which the stimu-
lus traveled.
41.58 m/s
3. Nerve impulses have been found to travel as fast as 100 m/s. What could account for the
difference between your answer to Question 2 and this value obtained by researchers?
Possible miscalculations could have caused our answer to question two, along with the
differenciating intenisties of the subjects knee being hit.
4. Assume the speed of a nerve impulse is 100 m/s. How does this compare to the speed of
electricity in a copper wire (approx. 3.00 ´ 108 m/s)?
The speed of the electricity of a copper wire is 300,000,000,000 x faster than the speed
of a nerve impluse.
5. Compare the data you obtained in this experiment with other members of your group/class.
Can individual differences be attributed to any physical differences (body shape/size, mus-
cle mass, physical fitness level)?
Yes, because the physiology of humans are all diffirent. All of the data collected
throughout the class is all diverse as well due to each test subject being anatomical
ly diverse.
14. DATA NAME: ZACH
Table 1
Kick 1 Kick 2 Kick 3 Kick 4 Kick 5 Average
Time of muscle contraction (s) 12.27 15.39 18.23 21.11 23.86
Time of stimulus (s) 12.09 15.19 17.53 20.30 23.17
∆t (s) 00.18 00.20 00.70 00.81 00.69 .516
Table 2
Reflex 1 Reflex 2 Reflex 3 Reflex 4 Reflex 5 Average
Time of muscle contraction (s) 8.00 11.27 17.74 21.85 25.98
Time of stimulus (s) 7.91 11.25 17.71 21.83 25.95
∆t (s) 0.09 0.02 0.03 0.02 0.03 .038
Table 3
Reflex without reinforcement Reflex with reinforcement
Reflex response Max (mV) Min (mV) ∆mV Max (mV) Min (mV) ∆mV
1 2.158 .716 1.442 2.61 .633 1.988
2 3.442 .535 2.907 2.101 .726 1.375
3 1.982 .676 1.306 2.281 .687 1.594
4 2.379 .612 1.767 2.212 .729 1.483
5 2.776 .679 2.1 2.558 .575 1.983
Average values 1.904 1.684
