Neural control and coordination

Introduction

Locomotion is a unique feature of many living organisms. Movement occurs as a result of unintended and intended actions produced by the living organisms. The mechanisms of movement between the plants and animals vary. Animals can move the individual part of the body as well as they can transfer the whole body from one place to another. Plants, on the other hand, stationary but a slight movement can be observed while they are stable. Plants growing tall and their developing branches is also a type of natural movement but animals do not grow as tall as trees. 

 

Intended and unintended movement 

Some of the movements in the animal`s body occur as a result of the bodily activities, for example, cows chewing the cud- a natural process rather than intentional.  Whereas few of the movements are intentional, for instance,  animals migrating from one place to another, running, jumping, walking and playing. In order for the movement to be purposeful, systematic control and coordination are necessary and they are mediated by our body systems.  Control and coordination is the consolidated effort of the nervous system, muscular system and the endocrinal system. They are divided into 2 major types, Endocrinal coordination and control and the  Neural coordination and control.

 

Voluntary and involuntary movement

Movement can be purposeful and purposeless. The purposeful movements are the voluntary movements with a specified goal. Imagine you are an athlete and you are assigned to reach 1-kilometre distance in 5 minutes. In this case, you must ascertain the plan of your movement in advance. Some of the things that need to be calculated beforehand are the intention, pace, and method to be adapted to finish the task. So keeping this in mind, you must run at a pace of 200 meters per minute. On the other hand, involuntary movement is the reflexive action as a response to an acknowledged threat. For instance,  what happens when you accidentally touch a hot iron box? In a fraction of second, you will immediately withdraw your hand away from the heating source. Why is this? this is a natural defence to ensure you are safe and this is an involuntary reflex action of the nervous system. So an involuntary movement is an action automatically initiated by the nervous system before you are volunteering. This article aims to describe the role of our body systems in the coordination process.

 

The nervous system 

The nervous system is a very complex system as it is highly connected with the rest of the body. Some of the body systems working in coordination with the nervous system are the muscular system, sense organs, and skeletal system. Our nervous system comprised of nerves capable to detect the sensory feelings from the external environment. Some of the sensory stimulation are heat, cold, pressure and the sharpness of an object. To sense these feelings, we have a specialized cellular system in our body called the sensory-motor system ( a part of the nervous system). Our sensory nerves contain sensitive tips that receive the stimuli from outside. The peripheral stimulus reaches the brain in the form of signals and the brain in response will send a message to other parts of the body. This will help in initiating a movement such as lifting,  moving, hitting, kicking, standing or running.  Let us understand in detail about how the nervous system functions and how it can produce movement and coordination necessary for our lives. 

 

Components of the nervous system

The nervous system is divided into the central nervous system and peripheral nervous system. The central nervous system is again subdivided into the brain and spinal cord. Brain has 12 pairs of cranial nerves coming out of the different parts of the brain. The spinal cord has 31 pairs of spinal nerves connected to the different levels of our backbone and limbs. On the other hand, the peripheral nerves are spread across the periphery ( all over the skin). Peripheral nerves have the sensitive nerve endings spread very close to the layers of skin. Two types of peripheral nerves are sympathetic and parasympathetic nerves. These nerve endings will receive and convey signals from in and out of the body parts like hands, face and legs.

 

 

 

Human Brain

Covering layers of the brain( meninges)

The brain is a curd-like material, very soft and delicate. The layer above the brain and spinal cord are called meninges. There are 3 layers of meninges, namely, dura mater, arachnoid mater, and pia mater. In between these layers, there is a fluid called cerebrospinal fluid which protects the brain by absorbing shock and pressure.

The cerebrum

The human brain is the most amazing creation by the god. We have the largest brain of all vertebrates ( in proportion to their relative body size and weight). The human brain weighs about 1.5 kilograms which is about 2% of the total body weight. The brain is broadly divided into cerebrum or forebrain, midbrain, and the cerebellum or hindbrain.  The cerebrum is the major portion which makes up about  85% of the brain's weight. The brain has approximately 86 billion nerve cells (neurons) form the grey matter and the white matter.  Individual areas of the cerebrum performs specialized sensory functions like hearing, smell, taste, sight and so on. These are involuntary in nature as we cannot control them by personal efforts.  For example, we can’t control hunger, breathing and heart rate but we can very well control writing, walking, reading etc.

 

The Cerebellum

The cerebellum is mainly responsible for the coordination, balance, and control. It will assist in the bodily actions such as walking in a straight line, picking up a pencil, riding a bicycle, drawing a picture and sitting straight. 

 

Spinal cord

The spinal cord has many sub-divisions.In total there are 31 segments ( spinal nerve channels) through the length of the spinal cordAmong these, there are 8 cervical (C) segments, 12 thoracic (T) segments, 5 lumbar (L) segments, 5 sacral (S) segments, and 1 coccygeal (Co) segment. The spinal cord is mainly responsible for movement or motor functions of the body. Any injury to spinal nerves causes paralysis (Permanent disability by losing complete control.)

 

Neurons

Neurons are the structural and functional units of the nervous system responsible for the proper functioning of the nervous system. They receive and send signals from the brain and towards the brain. They look like long fibres, slender and branched at their axonal ends. As seen in the picture below, dendrite is the head or the cell body which is connected down to a structure called the axon.  At the terminal part of the axon, there are hair-like projections which set electrical impulse through chemicals called neurotransmitters. Axons are covered by a protective sheath called myelin sheath. The myelin sheath protects the axon from shock and external threats. Damage to the sheath can interfere with the passage of nerve impulse through it. The information through axons occurs in the form of electric impulse. Electrical conduction is aided by the neurotransmitters and the neurochemicals produced at the synaptic junctions. A synaptic junction is formed when the axonal end of one neuron joins with the dendrites of the next neurons ( tail to head).  In order to pass a signal, neurotransmitters must cross the synaptic junctions. The electrical or chemical impulses should pass through this synapse in order to transfer to the message from one neuron to the next neuron. Many neurons join together to form a nerve. On the other hand, a similar synapse junction from peripheral muscles and body parts will allow signals to travel from the body towards the brain. So overall, nervous tissue is made up of an organized network of nerve cells or neurons specialized in conducting information in the form of electrical impulses via the length of the neuron.

 

Neuron and synaptic junction- image from wiki commons and freepik

 

Mechanism of Reflex Actions

Reflex is an instant and natural action in response to a surprise provocation from the outside environment.  What if a dog suddenly starts running ( stimulus) behind you, naturally you will demonstrate fight or flight response. Because you feel that it might bite or scratch. To react to the obvious threat, you will start running and the act of running is a reflexive action.  Pulling your hand off the lamp, feeling like a watery mouth when you see a delicious dish, etc. are some of the examples of reflexive actions. These actions do not involve a deep thinking process rather,  they just happen like common emotions. 

 

Control and coordination achieved through Reflex Arc

Our coordination and control occur through a path called the reflex arc that takes a sequence of flow of information or signals. The following path takes its action when we come across a threat that is sudden and unexpected.

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