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PYC1501/Human nervous system/OER/2022Unit 1: Human nervous system
Learning objectives
This learning section will help you to:
understand the two important parts of the nervous system and their functions.
understand how the components of the nervous system fit together.
understand the process of impulse conduction.
explain the interconnection of neurons in the brain.
1.1 Introduction
The human nervous system is an important aspect of human functioning and is responsible for all human
behaviours. Comparative studies of physiological functioning in the nervous systems of different animals
lend insights to their behaviour and their mental processing and make it easier for us to understand
human brain and behaviour. This learning section outlines different aspects of the human nervous system
and how they coordinate together to produce human behaviour. The section will cover the structure of
the neuron, the process of impulse conduction in the neuron and the structure of the human nervous
system.
1.2 Human nervous system: structure and functions
The mammalian nervous system is a complex biological organ which enables many animals, including
humans, to function in a coordinated fashion. The original design of this system is preserved across many
animals through evolution. Thus, adaptive physiological and behavioural functions show similarity across
many animal species. The human nervous system is divided into the Peripheral Nervous System (PNS)
and the Central Nervous System (CNS) that interact with one another. The peripheral nervous system
controls volitional (somatic nervous system) and non‐volitional (autonomic nervous system) behaviours
using cranial and spinal nerves. The central nervous system consists of the brain, the brain stem, and the
spinal cord, and each division performs a variety of tasks.
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1.2.1 The peripheral nervous system
Figure 1.1: The structure of the peripheral nervous system. The Nervous System | Noba (nobaproject.com)
The peripheral nervous system carries the signals necessary for the body to survive and some of the signals
are related to voluntary actions. The peripheral nervous system is divided into somatic and autonomic
nervous systems.
The somatic nervous system
The somatic nervous system is associated with conscious and voluntary activities. It is involved in the relay
of sensory and motor information to and from the central nervous system. Therefore, it consists of motor
neurons and sensory neurons. The motor neurons that carry information from the CNS to the muscles,
are called efferent neurons (efferent means ‘moving away from’). The sensory neurons that carry sensory
information to the CNS are called afferent neurons (afferent means ‘moving toward’). Each nerve is
basically a two‐way process containing thousands of both efferent and afferent neurons.
The autonomic nervous system
The autonomic nervous system controls involuntary functions of our internal organs and glands. It is
divided into the sympathetic and parasympathetic divisions.
(i) The sympathetic nervous system on one hand, is involved in preparing the body for stress related
activities. For example, when a person encounters any fear‐inducing stimuli like a snake, the
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sympathetic division generally energises many muscles (e.g., heart) and glands (e.g., adrenals),
causing the release of hormones that lead the individual to negotiate the fear‐causing stimuli with
fight‐or‐flight response. Whether the individual decides to fight the snake or run away from it,
either action requires energy.
(ii) The parasympathetic nervous system on the other hand, is associated with returning the body to
routine, day‐to‐day operations. In other words, the parasympathetic nervous system restores and
calms down the physiological responses so as to maintain homeostasis ‐ a state of equilibrium, in
which biological conditions (such as body temperature) are maintained at optimal levels. The two
systems have complementary functions, operating in tandem to maintain the bodily homeostasis.
1.2.2 The central nervous system (CNS)
The central nervous system is made up of the brain, the brainstem, and the spinal cord. This system
performs mainly the ‘information synthesising’ function. During this process, the brain and spinal cord use
appropriate motor output, which is based on the type of sensory input. The CNS regulates everything from
organ function and high‐level thought to purposeful body movement. Thus, it is the control centre of the
body. It is referred to as ‘central’ because it is the brain and spinal cord that are primarily responsible for
processing sensory information. The information is relayed from the spinal cord to the brain and vis‐à‐vis.
The brain and the spinal cord (see figure 1.2 below) communicate largely by sending electrical signals
through individual nerve cells that make up the fundamental building blocks of the nervous system called
neurons. There are approximately 100 billion neurons in the human brain and each has many contacts
with other neurons (Brodel, 1992).
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