Nerve Impulse Transmission and Caffeine

This assignment explores the intricate workings of the nervous system, focusing on the mechanisms of nerve impulse transmission. It differentiates between voluntary and involuntary actions controlled by the central and autonomic nervous systems respectively. The text delves into the roles of various neurons and neurotransmitters in signal propagation. Finally, it examines the impact of caffeine on nerve impulse transmission, highlighting its stimulatory effects and influence on dopamine production.

1 STRUCTURE AND FUNCTION OF NERVOUS SYSTEM
STRUCTURE AND FUNCTION OF NERVOUS SYSTEM

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Table of Contents
Introduction......................................................................................................................................3
Structure of the Central Nervous System........................................................................................3
Transmission of nerve impulses......................................................................................................4
Comparison of voluntary and reflex actions....................................................................................6
Effects of caffeine on nerve impulse transmission..........................................................................7
Conclusion.......................................................................................................................................7
References........................................................................................................................................8

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Introduction
The nervous system is a fundamental part of the body. Its functions rank among the most
important, and life as we know it is impossible without it in most life forms. Since it is
responsible for all voluntary actions, in addition to innumerable other complicated tasks, its
structure is bound to be a complex network, spanning the entire body. It is classified into
different subtypes, based on different criteria. Transmission of nerve impulses fulfills all
voluntary tasks, including those involving limbs, movement, and reactions. Descriptions
regarding the aforementioned have been given. Detailed studies of the nervous system also lead
to gaining a proper understanding of Central and Autonomic Nervous Systems as well. Herein,
this study is about the nervous system, with details about its structure and functions.
Structure of the Central Nervous System
The Central Nervous System is the main control unit of the body. It consists of two
physiologically important structures known as the brain and the spinal cord. The brain is
considered as the most imperative organ of the body that handles all the regulation system, being
responsible for the efficient function of all other organs and organ systems of the body (2). It is
encased in the skull, which provides it with protection from external injuries. The part of the
skull specifically responsible for protecting this organ is known as the cranium.

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Figure 1: Central Nervous System of human
(Source: (1))
The spinal cord, as its name suggests, is located within the spinal cord region along the vertebral
column of most animals including humans. It is continuous with the brain and lies in a position
caudally to it. Vertebral bones are responsible for its protection, and damage to it may hasten
death. It extends from the base of the skull, comprising nearly the entire span of the vertebral
column (it occupies upper sections of the vertebral canal) and finally terminates within the first
or second lumbar vertebra.
Sensory neurons are a type of neuron that is responsible for converting certain types of stimulus
into their action or graded potentials. They perform their functions using their receptors and
finish their tasks in a very short span of time. It consists of a cell body (known as soma), an axon
(a projection that actually performs the task of conducting electrical signals away from the cell
body), dendrites (tree-like structures) and synapses (junctions located between different
neurons).
Connector neurons, is also termed as interneurons, are a diverse class of neurons responsible for
aids in maintaining communication among central nervous system and sensory neurons (5). They
consist of the basic parts of a neuron including axon, dendrites, and cell body, with slight
modifications that differentiate them from the other classes.
Motor neurons are termed as neurons wherein cell tissues are specifically located in the spinal
cord. Their axons are situated in a particular manner, where they exist outside the spinal cord in
order to facilitate controlling on effector organs such as muscles and glands. They can control
these organs in a direct or indirect manner. Since they are responsible for controlling organs that
help in movement, they are known as motor neurons.
The central nervous system has number of excitable nerve cells which are also called as
neurons and which are huge support from specialized tissue called as neuroglia. However, the
long processes of a nerve cell are called as axons or nerve fibers. However, at the same time, the

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nervous system is categorized into three different areas such as the hindbrain, the midbrain and
the forebrain. Hindbrain is made up of cerebellum, the pons and the medulla which exists near
the spinal cord and which also manages regulation of cells. There are certain chemicals produced
in the pons that helps in maintaining the sleep- wake cycle in a person. The peripheral nervous
system has many parts of neurons that brings signals to the central nervous system and motor
neurons. Some motor neurons are also helpful in controlling skeletal muscle.
Transmission of nerve impulses
Transmission of nerve impulses along the neurons from one to another is possible due to the
development of electrical charges across neuron membrane. Once a neuron is unstimulated, there
is a marked difference between electrical charges of its inside and outside, with the inside one
being of a negative value.
Positively charged sodium ions provide a net positive charge to the outside region. The
negatively charged proteins and nucleic acids provide a net negative charge to the inside
environment, despite the presence of positively charged potassium ions. Once a neuron is
stimulated, its gated ion channels open up and allow sodium ions inside, resulting in an overall
positive charge. Eventually, this leads to the generation of a specific action potential, when a
stimulus exceeds a particular threshold level (7).
Complete depolarization happens as a result, and the entire stimulus is transmitted.
Repolarization and eventually, the refractory period make sure that the original balance of
sodium and potassium ions on the outside and inside is achieved. Synaptic cleft separates
neurons and the transmitted signal transverses it in order to reach the next dendrite. Chemical
transmitters known as neurotransmitters aid in this process, becoming active in these situations
and binding to receptors of next neuron’s dendrites.

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Figure 2: Transmission of nerve impulses
(Source: (8))
A neurotransmitter is stored in the form of granules or vesicles in the axon terminal. Calcium
then enters this terminal, which causes its release. It moves across the synapse and binds to its
receptors, which may trigger short-term changes. Once the signal has been transmitted, the
neurotransmitter is released and deactivated. This helps in transmitting impulses.
Comparison of voluntary and reflex actions
Voluntary Actions Reflex Actions
 Involves prior thought and thinking
 It is prolonged
 It is under control of will
 Involves many nerve cells
 Does not involve planned thinking or
prior thoughts
 It is sudden and not prolonged
 It is not under control of will
 Involves a minimal number of nerve

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 Its responses to particular stimuli may
vary greatly
cells
 Its response does not vary greatly to
particular stimuli, being sudden
movements
Table 1: Differences between Voluntary and Reflex Actions
(Source: (3))
The autonomous nervous system (ANS) performs extremely important functions. Its role is to
control functions of all of our internal organs including intestines, stomach, liver and even the
heart. It functions involuntarily and controls several muscles within our body. Some aspects of
ANS such as heart rate can be controlled via intense training (4).
According to comparison between reflex and voluntary actions, reflex action is a
response that does not need proper planning and thought process. Reflex happens naturally and it
also gives quick response to stimuli which is usually not controlled by the brain. However, on the
other hand voluntary actions involves prolonged response and it is also controlled by the brain. It
involves many nerves cells and accordingly it is coordinated by the brain.
Reflex arc is a neural pathway that is engaged in controlling an action’s reflex and it
holds major importance because it conducts or transmits nerve impulses from the sensory cells to
the spinal cord. It also includes motor or efferent neurone which is engaged in transmitting
impulses from the intermediate neurone to the effector. However, on the other hand voluntary is
based upon the action that is initiated by a person’s own conscious state. In this, the cerebral
cortex transfers impulses to the effectors through spinal cord and this also involves the use of
relay neurons.

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Effects of caffeine on nerve impulse transmission
Caffeine stimulates a particular part of the brain, known as the cortex, to produce more
neurotransmitters such as adenosine. Production of more neurotransmitters results in an increase
in the rate of nerve impulse transfers. This explains why coffee is able to keep people awake, and
why it is used as an energizing drink (6).
Caffeine has a direct impact on cardiac health and it also changes the functioning of
central nervous system. Caffeine is the chemical related xanthines, therophylline and
theobromine which decreases the order of the stimulatory action. This could be included in some
of the over counter drugs. The action of caffeine is to block receptors and it also has similar
structure which means that caffeine will fit the adenosine receptors. Nonetheless, there are fewer
receptors available to the natural braking action of adenosine; hence at the same time it speeds up
the neural activity. It can also be said that caffeine increases the production of dopamine in the
brain’s pleasure circuits which also aids in maintaining the dependency the drug.
Conclusion
The importance of the nervous system cannot be underestimated. Mother Nature has ensured
that all complex processes necessary for its effective functioning work in a systematic manner.
The Central; Nervous System controls all voluntary actions, whereas the Autonomous Nervous
System controls the functioning of all internal organs reflexively. Different types of neurons are
responsible for transmitting signals and impulses across different organs, with a complex process
ensuring correct transmission of a signal from one neuron to the next.

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References
1. Bacq, Z. M. (2013). Chemical transmission of nerve impulses: a historical sketch.
Elsevier.
2. Caon, M. (2016). Nervous system. In Examination Questions and Answers in Basic
Anatomy and Physiology (pp. 347-403). Springer Singapore.
3. Eccles, J. C. (2013). The physiology of synapses. Academic Press.
4. Gundersen, V., Storm-Mathisen, J., & Bergersen, L. H. (2015). Neuroglial
transmission. Physiological reviews, 95(3), 695-726.
5. Kimura, J. (2016). Nerve conduction studies. Oxford Textbook of Clinical
Neurophysiology, 49.
6. Lima, P. M., Ford, N. J., & Lumb, P. M. (2014). Computational methods for a
mathematical model of propagation of nerve impulses in myelinated axons. Applied
Numerical Mathematics, 85, 38-53.

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7. Louveau, A., Smirnov, I., Keyes, T. J., Eccles, J. D., Rouhani, S. J., Peske, J. D., ... &
Harris, T. H. (2015). Structural and functional features of central nervous system
lymphatic vessels. Nature, 523(7560), 337-341.
8. Pannese, E. (2015). Neurocytology: fine structure of neurons, nerve processes, and
neuroglial cells. Springer.