Module 5 : Anatomy The nervous system In this module you will learn: The main parts of the nervous system The different sections of the brain and how it functions The structure and function of the spinal cord About nerve cells and how they transmit messages around the body About the effects of exercise on the nervous system 5.1 Anatomy The nervous system All your thoughts, communications, movements and actions are controlled by the nervous system. It is like the CPU of the body that is responsible for all the actions and decisions that we make. For a person looking to have a career in fitness training, it is important to understand the nervous system and its impact on the body.
The Nervous System 5.2 What is nervous system? The nervous system is the system by which all our movements, whether voluntary or involuntary, are controlled.
It transmits impulses and signals between the various parts of the body. If the nervous system fails we would be like vegetables, alive but unable to move or express ourselves. The nervous system comprises of two parts: The Central Nervous System also called the CNS. This comprises of our Brain and Spinal Cord which are the main organs of the nervous system The Peripheral Nervous System is also known as the PNS. This comprises of nerves, which are groups of long tissues known as axons. The axons connect the various parts of the body to the CNS. The Nervous system is made up of nerves and special cells called the glial cells, along with blood vessels and connective tissue. The nerve cells are also called neurons and are the main receptor and transmitters of signals. The glial cells, which are also called neuroglia, are cells that protect and support the neurons in the nervous system and maintain the balance of the system throughout the body. They help to keep the neurons in place, provide nutrients to the neurons and protect neurons from one another. They also help to remove dead neurons and destroy disease causing organisms. 5.3 Central Nervous System The CNS consists of two main organs. We cannot begin to understand the nervous system without
studying the brain and the spinal cord in detail. The CNS is obviously named for its function of integrating information and sensations received from all over the body and responding to it in an appropriate manner. 5.4 The Brain The brain is perhaps the most important organ of our body. It is like the conductor of an orchestra, it has to coordinate all the different parts and guide them to function properly at all times. The brain is encased at the top of our body inside the skull. The cranium protects the brain. The brain consists of three main parts. These are: Cerebrum: this is the front part of the brain and is also known as the front brain. Cerebellum: is the middle part of the brain and is also known as the mid brain. Brain Stem: is the lowermost part of the brain that is connected to the spinal cord. It is also known as the hind brain.
Cerebrum This is divided into four different regions that take care of different functions. Frontal lobes: They are placed directly behind the forehead. This part of the brain controls your behaviour, abstract thoughts, reasoning, problem solving, creativity, judgement, and co-ordination of movements, sense of smell, muscle movement, skilled movement, physical reaction and sexual urges, amongst other things. Parietal Lobes: They lie behind the frontal lobe on the upper part of the brain. This part of the brain is responsible for tactility, stereognosis, response to the senses, they receive and process information about sensations of warmth, touch, movement from the body. In addition to this, they are also responsible for our ability to read and solve arithmetic problems. Occipital Lobes: As the name suggests, this part of the brain is concerned with sight and reading. It processes all that the eyes see. It is located towards the back of the brain. This lobe helps us to understand what we are seeing by linking it to the memory. Injury to the occipital lobes can lead to impaired vision and confusion. Temporal Lobes: It is located in the middle part of the bottom of the brain. This is the part of the brain that is responsible for auditory sensation. It helps us to hear by receiving information from our ears and processing it. It also plays an important role in creating and recollecting memories. This lobe helps us to identify sounds and the different pitches and helps us to understand speech. It also controls the sense of identity and some behaviours and emotions. The Cerebrum is divided into two hemispheres. The brain can be split into two identical parts.
Though they may appear identical, the two hemispheres are totally different and perform totally diverse functions. The two hemispheres are called: Left Hemisphere: Controls the right side of our body and performs logical and academic functions. Left brain functions include analysis of thoughts, language, and reasoning, understanding of written information, numbers, science and mathematics. Right Hemisphere: Controls the left side of our body and performs creative functions. It is concerned with spatial and sequential functions, analysing and interpreting nonverbal communication. Its functions also include intuition, insight, creativity, etc. The two hemispheres of the brain are connected with the corpus callosum, which is located under the cortex. Corpus callosum transmits all neural communications between the left and the right brain. Cerebellum This is the middle brain and is located towards the back of the brain and under the cerebrum. It is the most easily recognizable part of the brain, mainly because of its shape and location. It is responsible for all voluntary movements, balance and synchronisation of muscles and body. It helps us with tasks such as running, walking, typing, etc. as well as maintaining balance. Brain Stem This is the lowest part of the brain. It connects the cerebrum to the top of the spinal cord. All the information to and from the body is sent to the cerebrum and the cerebellum through the brain stem. It is formed of the following:
Mesencephalon: also called the mid brain. Metencephalon: which forms a part of the pons. It is located above the medulla oblongata and connects the upper part of the brain to the lower part. It functions as a storage area before the messages are relayed to the various parts of the brain. It is the transmitter of the messages. It also has an important role to play in our sleep. The REM sleep originates from the pons. Medulla Oblongata: it is a part of the spinal cord that extends into the pons. This is the area of the brain through which all information passes. The functions of the brain stem include controlling arousal, breathing, digestion, heart rate, blood pressure and carrying information between the spinal cord and the brain. It is also responsible for autonomous functions of the body. 5.5 The Spinal Cord The second major organ of the CNS is the spinal cord. It is a long cable-like structure that runs from the base of the skull all the way down through the vertebral column. It is composed of nerve tissues or neurons including: Somatic Motor Cells: transmitters for skeletal muscles Autonomic Motor Cells: transmitters for autonomic ganglia Transmission Neurons: help to conduct information between the brain and various points of the spinal cord Interneurons: connect other neurons to the spinal cord and are responsible for reflex and sensory reactions The spinal cord in human beings is roughly about 45 centimetres long. It is protected by the vertebral column which is composed of 31 bony segments called the vertebrae.
Each segment has a pair of spinal nerves emerging from it. The entire length of the vertebral column is about 70 centimetres. The vertebral column is divided into: Cervical Section: comprises of seven vertebrae that form the top of the spine and correspond to the neck. Thoracic Section: made up of 12 bones and supports the chest area. Lumbar Section: made up of 5 bones and forms the lower back. Sacral Section: comprises of 5 bones. Coccygeal Section: made up of 4 bones that are fused together. Other Parts Besides these two major organs, there are other parts that complete the CNS. These are: Meninges These are layers of protective tissue or membranes that protect the brain and the spinal cord. It consists of three layer:. Dura Mater which is the outer most layer. Arachnoid which is the middle layer. Pia Mater which is the innermost layer of the meninges. Cerebrospinal Fluid Is a layer of fluid that surrounds the brain and the spinal cord and protects it from shock and provides nourishment.
5.6 Neurons The cells that constitute the brain are called nerve cells or neurons. There are billions of cells that make up a human brain. Neurons can assimilate and transmit electrochemical signals. Though the neurons are similar in composition to other cells, their ability to transmit electrochemical signals and communicate with one another sets them apart. Each Neuron can be divided into three distinct parts. These are: Soma or the Cell body: contains the nucleus of the cell, mitochondria, endoplasm and ribosomes. Axon: a long tail-like structure that carries the electrochemical messages. It is like an electric wire and transmits the electrochemical message. The axons can be sheathed by a thin layer called myelin sheath. Myelin is composed of proteins and fat. Dendrites: these are the nerve endings and have tiny little branches growing out to create connections with other nerve cells and initiate communication between them. There are several different types of neurons present in a human body. They also vary greatly in length from a few millimetres to several inches. They also vary in shape and function.
We can classify them as: Sensory Neurons: Also called the Afferent Neurons which carry signals from the peripheral parts of the body to the CNS. Motor Neurons: Also known as the Efferent Neurons which carry messages from the CNS to the outer parts of the body like muscles, skin, sense organs, etc. Interneurons: Connect different neurons in the brain and spinal cord together. Point to Remember The neuron cells are unlike other cells in the body. While other cells can regrow after being damaged, once neurons have been damaged, most of them cannot regrow. Neurons from the hippocampus can regrow, but the others cannot. Since there are about 100 billion neurons in our brain, it should not worry you too much. 5.7 Peripheral Nervous System Peripheral nervous system, or PNS, comprises of all the parts of the nervous system that are not covered by the CNS. So, all nerves and their functions, outside of the brain and the spinal cord, are part of the PNS. It includes the spinal and the cranial nerves, sensory receptors and ganglia. The peripheral nervous system has two major parts. These are: Somatic Nervous System: this consists of the voluntary sensory neurons. It controls all the skeletal muscle tissues. Autonomic nervous system: this consists of the involuntary neurons. It controls the involuntary muscles like the cardiac muscle, the digestive tract and tissues
that form other organs of the body. Autonomic nervous system is further divided into three parts. These are: Sympathetic Nervous System This controls all our instinctive responses and emotions, including reflex action and fight or flight reaction. This system, in response to stimuli, can alter the rate of respiration, the heart rate, and releases stress hormones and adrenaline. Parasympathetic Nervous System This system controls our normal response when the body is in a resting and relaxed state. The parasympathetic system helps to heal the body from the effects of sympathetic nervous system. It helps to decrease the respiration and heart rate, and helps in eliminating wastes from the body. Enteric Nervous System This controls and regulates digestive organs and the process of digestion. It receives messages from the CNS via the sympathetic and the parasympathetic nervous system to control its functions. Mostly, the enteric system works independently without any intervention from CNS. 5.8 How Neurons Function
Neurons in the nervous system function via electrochemical signals that are called action potential. This is generated by movement of potassium and sodium ions through the neural membranes. This causes the following conditions: Resting Potential: the potassium and sodium ions are kept separated. The potassium ions are inside the cell and the sodium ions outside. Creating a negative charge within the cell. Threshold Potential: if a stimulus allows positive ions to enter the cell, the cell lets sodium ions from outside enter the cell. The threshold potential has to be achieved for this to happen. Depolarization: As sodium ions enter they create a positive charge and depolarize the cell. The depolarization of the cell is the action potential that is transmitted by the neuron as a signal or a message. Repolarization: After the depolarization, the cell has to return back to its resting potential so it allows potassium ions to diffuse through and the sodium ion to diffuse out and come back to its original state. Take a Quick Recap Test 5.9 Fitness and Nervous System
What we have learned about the nervous system makes it clear to us that each and every part of our body is controlled by some part of the nervous system. It is the source of communication between the various parts of the body and controls all our body functions, responses and emotions. The ANS controls the heart rate, and rate of respiration as well as all reflex responses. When faced with danger or stress, the heart and breathing rate increases. This leads to a change in blood pressure and rate of digestion of food. We go through these reflex responses several times a day. This increases the risk of heart diseases. With exercise, it is possible to increase the response to the parasympathetic nervous system that helps to decrease the reaction to the sympathetic system and helps to bring down the stress levels. As a fitness instructor, you can help your clients to reduce their stress level. A regular exercise schedule helps to reduce stress and lower the blood pressure while increasing the blood flow in your body and heart function. Together, these can help to lower the response of the sympathetic nervous system, thus preventing over-stressing the body and decreasing the risk of heart problems.
It has been observed that the more you exercise, the better its effect on your nervous system. Module Summary Lessons learned The nervous system comprises of two parts: The Central Nervous System and Peripheral Nervous System The brain consists of three main parts: Cerebrum, Cerebellum and Brain Stem The spinal cord is a major organ of the CNS and comprises of nerve tissues, or neurons Nerve cells transmit messages from one part of your body to another Regular exercise is good for the nervous system and helps decrease stress levels. [Tweet I just completed Module 5 of the Fitness Diploma Course ]