Central Nervous System Lab Report

The central nervous system (CNS) and the peripheral nervous

system (PNS) constitute the two main parts of the vertebrate nervous

system. Whereas the brain and the spinal cord form part of the CNS,

nerves, which are enclosed bundles of axons, form part of the PNS and

functions to link the CNS to each body part. Motor neurons transmit

signals from the brain while afferent are the sensory function to transmit

information from the body to the CNS. However, majority of the nerves

perform this dual functionality and these are referred to as mixed nerves.

Three divisions of the PNS are documented and this includes the

somatic, the autonomic and the enteric nervous system. In this division,

the autonomic system is further categorized into the sympathetic

and
parasympathetic systems. The sympathetic PNS sets in, in times of
emergencies to produce energy whereas the parasympathetic system is
activated when a person is relaxed. The enteric PNS on the other hand
plays a role in regulating the gastrointestinal system (GIS). While the
enteric and the autonomic systems perform their roles involuntarily, the
somatic nervous system (SoNS) functions voluntarily. Both the afferent
and the efferent nerves are constituents of the SoNS. The afferent nerves
function to transmit responses from the body to the CNS while the
efferent nerves send signals from the body to the central nervous system.
This action results in muscle contraction and results in body movements.
Background
The nervous system is a constituent of the human body’s
physiology responsible for coordinating voluntary and involuntary
actions as well as the transmission of signals to and from different body
parts. Both the PNS and the CNS work together in transmitting signals.
Whereas the PNS’s sensory neurons transmit information to the CNS,
brain signals are transmitted to motor neurons which are responsible
muscle activity.

In this lab experiment, Comparisons will be made regarding the
rate at which sensory neurons can cause responses via the motor
neurons. The density of sensory neurons in the skin will also be mapped
out. Mapping the blind spot will also be done as well as conducting
acoustic tests. Finally, a tasting test will be conducted.
Objective
The objective of this report is to identify diverse responses of the
PNS and the CNS. Practical experimentations in this regard are
conducted and they include the EEG experiment, experimentation on
reaction time, presence cutaneous receptors, eye tests, ear tests, the taste
bud test and the Rinne Test.

Method

Cutaneous receptors

Four diverse types of sensations mediated by their own receptors

can be felt in the epidermis. These sensations include warmth, touch,

cold and pain. The receptors of these sensations are however unevenly

distributed in the epidermis. This experiment demonstrates this varied

epidermal distribution pattern. The experiment involved drawing of a

2cm square on the upper side forearm of selected group members. The

subjects then closed their eyes while diverse bristle points within the

square were touched. Areas where pain was felt were then marked with a

small X. The bristle was moved methodically across the whole marked

zone using different stimuli. Dry rods, ice cold rods and a probe were all

used while all the sensitive areas were marked. This record of the X

spots and the mapped triangles was kept.

Patellar reflex

The patellar reflex or knee jerk reaction was conducted to

demonstrate simple reflexes. A group member was selected to sit on an

elevated stool in the lab with their legs suspended in the air freely. A

rubber mallet was then used to firmly and gently strike their patellar

tendon.

Eye

An experiment was conducted on the eye to demonstrate

its
functionality. The presence of a blind spot was demonstrated
experimentally using the results from the visualizing experiment. In this
test, the left eye was closed and the page containing the circle held a foot
away from the eye. The circle was then brought closer to the eye in a
slow motion while focusing on it.
Ear
Various experiments were carried out to demonstrate the
functionality of the ear in response to stimuli. In, order to demonstrate
the detection of sound waves, group members blocked their ear canals in
turn using a wad of sterile cotton to prevent vibrations from reaching the
tympanic membrane. A tuning fork was then struck and placed on the
bone prominence behind the ear. The Rinne Test was also conducted to
determine the hearing capacity of the ears. The procedure above was
repeated without the cotton wad.
Taste Buds experiment
The taste buds experiment was carried out to establish the different
distribution of taste buds on the surface of the human tongue. The
tongue was dried with a paper towel and while holding the nose, a dab of
the sweet solution was applied at the tongue’s tip. This procedure was
repeated in various sections of the tongue while different solutions of
bitter and salty dabs were applied to the tongue.
The ECG experiment
Experiments on the brain where conducted to reveal its sensory
functionality. The brains electric activity or the electroencephalogram
was performed. This experiment was carried out using the Bipac Student
Lab. With one group member, the electrodes were placed on them.
Calibrations were then done and EEG readings were recorded.

Results
Low level pains were felt in areas with pain receptors in the touch
experiment where bristles were touched using dry rods, ice cold metal
and a probe.
In the knee jerk reflex experiment, the knee of the participant
responded to the mallet strike by rising.
The cross in the page disappeared while it was brought closer to
the eye. The cross then reappeared after a short while.
In the experiment to demonstrate the detection of sound waves, the
tuning fork’s sound were heard. The Rinne Test produced conflicting
results since some people could hear the tuning forks vibration while
others could not.
The taste bud experiment revealed different zones for different
tastes buds for sweetness were at the tip of the tongue, sour at the
tongue’s sides, saltiness spread across the edges of the tip while bitter
test at the tongues end.

The EEG readings produced mingled alpha, beta, delta and theta

readings. Alpha waves for my group was 8.5 waves per second (Hz), the

beta wave had a frequency of 15 Hz, Delta had 2.5Hz while Theta had a

6.5 frequency.

Discussion

The recorded results indicated varying distribution of sensory

receptors. Regions with a high presence of receptors had more X and

triangles. The knee jerk reaction produced a stretch of knee muscles as

the patellar tendon stretched pulling the spindles in the quadriceps

femoris.

In the blind spot experiment, the disappearance of the cross

occurred as the image passed the blind spot in the eye. The re-

appearance of the cross occurred since the image had passed the blind

spot.

In the experiment to demonstrate the detection of sound waves, the

bones of the skull were responsible for transmitting vibrations to the

cochlea hence the sounds could be heard. The Rinne Test results were

indicative of plausible middle ear defects in some participants in the

experiment.

The taste bud experiment was informative in revealing that the

vertebrate tongue has varying receptor areas for diverse

tastes.
Results from the electroencephalogram indicate that the cerebral
cortex’s activities are continuous throughout a person’s life and its
absence is an indication of death. The recorded EEG readings were
mingled as discussed. However, the wave amplitudes decreased when
the participants opened their eyes indicative of brain activity.
Significance of results
The conducted results on the ear, the eye, the taste buds, cutaneous
receptors, Patellar reflex and the EEG experiment all reveal the role of
the nervous system in humans. Through the results of the experiments,
this functionality is evident.
Conclusion
Conclusively, the documented results illustrate the importance of
the nervous system in daily activities. The knee jerk reflex experiment
for instance, demonstrates the importance of the knee reflexes in
protecting a person in response to a possible fall for instance. This
together with the other conducted experiments reveals the unique role of
the nervous system in the physiology of vertebrates.