VERTEBRATE PHYSIOLOGY
Introduction
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 every body part. Motor neurons transmit signals from the brain while afferent or 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 (Nieuwenhuys, Hans and Nicholson, 2014). In this division, the autonomic system is further categorized into the sympathetic and parasympathetic systems. The sympathetic PNS sets in, in times of emergencies so as 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 (Nieuwenhuys, Hans and Nicholson, 2014). 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 (Nieuwenhuys, Hans and Nicholson, 2014). 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, therefore, 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 ECG 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 moved 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
Various experiments were conducted on the eye to demonstrate its functionality. The functioning of the iris was demonstrated by an experiment whereby participants in my group closed their eyes for 10 seconds. Similar to a lens, eyes also reverse images and this was demonstrated by conducting a visualizing experiment using a light bulb and a magnifying lens. The presence of a blind spot was equally 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.
The effect of bleaching visual pigments was also demonstrated in the lab. A provided bright light was gazed upon in the lab for one minute. Quickly thereafter, the participant gazed on a white screen. A similar experiment was conducted simultaneously with a red light.
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 lying down, the electrodes were placed on them. Calibration was then done and ECG readings 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 diameter of the pupils in the eye experiment revealed a quick narrowing. A visualizing experiment resulted in the observation of a reversed image of the light source. 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 demonstrating the effect of bleaching, a negative afterimage was observed in the wall. The subsequent experiment on the red light resulted in the observation of a blue image on the wall.
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 ECG 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 indicates 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. The experiment demonstrating the effect of bleaching produced a negative afterimage because the light receptors in the eye which had previously processed the image where inactivated momentarily. Consequentially, the white wall could not be seen and instead dark shadow was seen. This was the case also for the subsequent experiment on red light. Bleaching of pigments in the cones occurred in both instance resulting in the documented results.
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 test 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 ECG 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 ECG 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.
Work cited
Lab Manual
Nieuwenhuys, R., Hans, J., & Nicholson, C. (2014). The central nervous system of vertebrates. Springer.
