Nervous system Magazine 1

Look Inside!

CNS and PNS

Nervous Cells

Nerve Impulses

Synapse

Reflex Lab

©3

CNS The Central Nerv-

ous Systems is the

structural and func-

tional center of the

nervous system. This

system includes the

brain and spinal cord,

and it integrates in-

coming pieces of sen-

sory information, eval-

uates the information,

and then starts an out-

going response. Neu-

robiologists only in-

clude those cells who

begin and end with

the brain or spinal

cord, as part of CNS. ©1

PNS The peripheral nervous system consists of nervous tis-

sues in the “outer” or periphery of the nervous system.

Nerves that originate from the brain are called cranial

nerves, and from the spinal cord, spinal nerves. There are

two types of cells in the PNS sensory nervous cells and mo-

tor nervous cells. The motor nervous cells carry information

from the CNS to organs, muscles, and glands. The sensory

sends information to the CNS from internal organs or from

external stimuli. The PNS is divided into 4 other regions; so-

matic– controls skeletal muscles and external sensory or-

gans,

autonomic– controls

involuntary muscles,

sympathetic– controls

activities that increase

energy, parasympa-

thetic– controls activi-

ties that control ener-

gy.

©2

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.

Cells of the nervous System Crossword Puzzle

Across

4. Provide the insulation (myelin) to neurons

in the central nervous system.

6. Cells Physical support to neurons in the pe-

ripheral nervous system.

7. Cells Provide the insulation (myelin) to

neurons in the peripheral nervous system.

Down

1. Like astrocytes, microglia digest parts of

dead neurons.

2. Star-shaped cells that provide physical and

nutritional support for neurons

3. neurons These transmit impulses from the

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

1

2

3

4

5

6

7

Image of Neuron

© 4

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.

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

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

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.

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.

0 0.2 0.4 0.6 0.8 1

1

2

3

4

5

Delta T (s) striking

Delta T(S) sound

0 1 2 3 4

1

2

3

4

5

Reflex with reinforcement

Relex withoutreinforcement

Neuromuscular Reflex lab Graphs

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.

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