Nervous System

Nervous System Definition

Considering how important the nervous system is, it's important we understand the definition of it overall. We can define the nervous system as:

Our nervous systems are crucial to supporting bodily functions and coordinating movements in response to the environment (stimuli).

The nervous system allows you to respond to the environment, clipart.me

Nervous System Structure

To understand the different parts of the nervous system, we must differentiate between the central nervous system and the peripheral nervous system. They are made up of different components, so it's important you remember their differences.

The Central Nervous System (CNS)

The central nervous system comprises the brain and the spinal cord and controls communications between the brain and the body, acting as a command centre of sorts. The peripheral nervous system connects the CNS to the body to allow the CNS to enact commands.

How does this work?

Parts of our body, such as muscles, skin, and organs, have sensory neurons (when grouped, these are known as nerves). These neurons have receptors that detect stimuli, which leads to messages being sent directly to the CNS.

• Sensory neurons are responsible for sending messages to the brain from the body.
• Once our brains have gathered and processed this information, it sends messages back to these body parts via the spinal cord to effectors, which prompt movement or responses.
• Motor neurons are responsible for sending these messages back to the body.

The spinal cord facilitates the transfer of messages to and from the brain to the peripheral nervous system. It is also involved in reflex actions e.g. startle response.

The Peripheral Nervous System (PNS)

The peripheral nervous system consists of all the nerve cells which are not in the central nervous system. The spinal cord activates the peripheral nervous system, which is collectively responsible for gathering and sending information to different body parts through nerves.

This is how our body controls automatic functions such as heartbeat, blood flow, and stimulus responses which seem 'automatic' to us.

The peripheral nervous system can be split into two sections:

Think of the autonomic nervous system as one that helps us react to situations, particularly those considered an 'emergency'.

It connects our brain to our endocrine system, which is a network of glands and organs that secrete hormones into the blood.

Nervous System Function: The Function of The Central and Peripheral Nervous System

It may help to clearly underline and distinguish how both parts of the nervous system function.

Central Nervous System

The CNS is responsible for receiving information from the sensory neurons and powering and regulating psychological processes. Any adequate responses are passed to the body via the peripheral nervous system.

• Think of the brain and the spinal cord. The brain is the centre of consciousness, receiving messages from the sensory receptors and sending messages to our glands and muscles.

It may help to think of the spinal cord as an extension of the brain down the body, directing and aiding the brain to control the voluntary movements of the body.

Peripheral Nervous System

The somatic nervous system in the PNS comprises nerves that function by sending messages to and from the senses (external stimuli) and muscles (internal) to and from the spinal cord (CNS).

• It receives directions from the CNS for body movement.

The autonomic nervous system in the PNS functions by regulating involuntary bodily actions such as rises in temperature, arousal, heart rate, and more. It has two divisions: the sympathetic and parasympathetic nervous systems:

• If someone is experiencing a fight or flight response, the autonomic nervous system shifts from the parasympathetic system to the sympathetic system. Energy is readily available to use, and our heart rates increase, as well as our breathing and body temperature.

• When the threat is no longer evident, the ANS returns to the parasympathetic system in control.

The human nervous system is composed of multiple divisions, freepik.com/macrovector

Neurotransmitters

Neurotransmitters are the chemicals that are released from nerve cells in the nervous system. They function by passing chemical messages between neurons across a very small gap between the neurons, known as the synapse. This is called synaptic transmission.

An electrical impulse is triggered and travels down to the end of the neuron, where vesicles containing neurotransmitter molecules release them into the synapse. The molecules are grasped by receptors on the next neuron so that the impulse can be passed onwards.

The James-Lange Theory of Emotion

In the 1880s, William James and Carl Lange came up with a theory of emotion. In short, they proposed that bodily changes to external events instigate emotional responses.

Thus, they believed that stimulus led to physiological reactions to occur.

It is an important early study investigating the fight or flight response.

Evaluating the James-Lange Theory

Whilst it was one of the earliest theories of a emotion in modern psychology, not everyone has been convinced of its accuracy.

• The theory may be criticised as there is an inconsistency in emotional responses. For the theory to be exact, there would have to be a specific emotion that equates to a physical reaction, which we know is not the case. Whilst someone's heart rate may increase, this could insight fear, excitement, or even irritation. Similarly, the action of crying does not always signify one singular emotion.
• Schachter and Singer also challenged the basis of the theory by suggesting that not only physiological changes occur when an individual spots a threat, but also cognitive altercations occur. ANS stimulation can result in a deeper understanding of the threatening environment.
• in 1927, the Cannon-Bard theory of emotion was proposed as an alternative by Walter B. Cannon and Philip Bard. The theory states that external stimuli trigger feelings and physical reactions to occur simultaneously and independently of one another.

Nervous System Disorders

Parts of the nervous system can become damaged, which is considered neurological damage. If someone is a victim of this damage, it can have a direct effect on the way they think, feel, and behave. Some disorders are listed below.

• Spinal Cord Injury: If someone is to suffer from any damage to their spinal cord, it can disrupt electrical impulses, thus signals, from being transmitted throughout the body which prohibits movement. Depending on the severity, this can result in partial or complete paralysis.

• Prefrontal Cortex Damage: the prefrontal cortex control impulses and helps us to make rational decisions. If damage is done to this area, it can cause a shift in behaviour for people who can become more impulsive and even potentially violent.

• Agnosia: Agnosia is a rare disorder where someone cannot process sensory information. With visual agnosia, whilst they may be able to see an object, such as a chair, they cannot recognise that it is a chair. This is because the information sent from the eyes (organ) to the brain (CNS) cannot be comprehended.

• Prosopagnosia: this is an extremely rare form of agnosia where an individual cannot recognise faces despite being able to see them. Around 1 in 50 people suffer with some form of prosopagnosia. It can be caused by damage to part of the frontal lobe known as the fusiform face area.