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A system of human body means a collective functional unit made by several organs in which the organs work in complete coordination with one another. Organs cannot work alone because there are certain needs of every organ that need to be fulfilled and the organ itself cannot fulfill those needs. So all organs of human body need the support of other organs to perform their functions and in this way an organ system is formed. Human body is made of ten different systems. All the systems require support and coordination of other systems to form a living and healthy human body. If any one of these systems is damaged, human body will become unstable and this lack of stability will ultimately lead to death. The two coordination systems of the body are the nervous system and the endocrine system, which enable all parts of the body to work together as one.
Endocrine system is the system of glands of human body. Each of these glands secretes one or more different hormones in the blood for different functions. The secretions of endocrine glands are known as hormones. Each endocrine gland may secrete one or more hormones in the blood and these hormones may or may not have related functions. Generally the hormones regulate different functions of human body like growth, mood, development, and metabolism etc. They perform their function by attaching to the target cells and then communicating with them. Endocrine system is a regulatory system of human body. In fact, it associates the nervous system in controlling body functions. The control of body function by the nervous system is called nervous coordination and the control of body functions by the endocrine system is called chemical coordination. The control of body functions by the endocrine system is a long term control system. All the necessary changes and adaptations of the body, required for the long term control of a specific function, are influenced by the hormonal system.
Endocrine glands are ductless glands of human body that pour their secretions (hormones) directly into the blood. They have three characteristic features that are:
1. They are ductless.
2. They are highly vascularized.
3. They possess intracellular vacuoles or granules that store the hormones.
Endocrine glands of human body are divided into two categories : typical endocrine glands and organs having secondary endocrine function.
Typical Endocrine Glands: These glands have the primary function of producing hormones for human body. Typical endocrine glands include:
1. Pituitary Glands
2. Thyroid Glands
3. Parathyroid Glands
4. Adrenal Glands
Organs having secondary endocrine function : These organs primarily belong to some other system of the body but have a secondary function of producing hormones. They include:
1. Pancreas
2. Ovaries (In females)
3. Testes (In males)
4. Kidneys
5. Liver
Nervous system is the chief controlling and coordinating system of the body. It controls and regulates all voluntary and involuntary activities of human body. There are three characteristic properties of nervous system of human body: sensitivity, conductivity and responsiveness. Nervous system of human body is divided broadly into two parts; Central Nervous System (CNS) and Peripheral Nervous System (PNS)
Central Nervous System (CNS): The brain and spinal cord together form the central nervous system, or CNS. The CNS acts as the control center of the body by providing its processing, memory, and regulation systems. The CNS takes in all of the conscious and subconscious sensory information from the body’s sensory receptors to stay aware of the body’s internal and external conditions. Using this sensory information, it makes decisions about both conscious and subconscious actions to take to maintain the body’s homeostasis and ensure its survival. The CNS is also responsible for the higher functions of the nervous system such as language, creativity, expression, emotions, and personality. The brain is the seat of consciousness and determines who we are as individuals.
Peripheral Nervous System: (PNS ) The peripheral nervous system includes all of the parts of the nervous system outside of the brain and spinal cord. These parts include all of the cranial and spinal nerves, ganglia, and sensory receptors.
The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts.
Control of all body functions: Nervous system is the master system of human body. It controls the activity of all other systems in such a way that all the systems collectively make a human being. Without a controlling system, there is no concept of life because in such case there will be no coordination between different body functions and they will all act separately. Nervous system not only controls the voluntary functions of human body that are directed by human will, but it also controls those functions that are below the level of consciousness of human beings. Control of a function means that the intensity of that function can be increased or decreased according to the demands of human body.
Coordination of different body organs: Nervous system not only produces coordination between different systems, but also between different organs of a system. To form an organ system, role of the component organs must also be coordinated. So nervous system is not only important for formation of an organism by different organ systems, but also for formation of a system by different organs of human body.
The endocrine system works alongside of the nervous system to form the control systems of the body. The nervous system provides a very fast and narrowly targeted system to turn on specific glands and muscles throughout the body. The endocrine system, on the other hand, is much slower acting, but has very widespread, long lasting, and powerful effects. Hormones are distributed by glands through the bloodstream to the entire body, affecting any cell with a receptor for a particular hormone. Most hormones affect cells in several organs or throughout the entire body, leading to many diverse and powerful responses. Once hormones have been produced by glands, they are distributed through the body via the bloodstream. As hormones travel through the body, they pass through cells or along the plasma membranes of cells until they encounter a receptor for that particular hormone. Hormones can only affect target cells that have the appropriate receptors. This property of hormones is known as specificity. Hormone specificity explains how each hormone can have specific effects in widespread parts of the body. Many hormones produced by the endocrine system are classified as tropic hormones. A tropic hormone is a hormone that is able to trigger the release of another hormone in another gland. Tropic hormones provide a pathway of control for hormone production as well as a way for glands to be controlled in distant regions of the body. The levels of hormones in the body can be regulated by several factors. The nervous system can control hormone levels through the action of the hypothalamus and its releasing and inhibiting hormones. Nutrition can also control the levels of hormones in the body. The number of receptors present in cells can be varied by cells in response to hormones. Cells that are exposed to high levels of hormones for extended periods of time can begin to reduce the number of receptors that they produce, leading to reduced hormonal control of the cell.
A neuron is a nerve cell that is the basic building block of the nervous system. Neurons are similar to other cells in the human body in a number of ways, but there is one key difference between neurons and other cells. Neurons are specialized to transmit information throughout the body. These highly specialized nerve cells are responsible for communicating information in both chemical and electrical forms. There are also several different types of neurons responsible for different tasks in the human body. Sensory neurons carry information from the sensory receptor cells throughout the body to the brain. Motor neurons transmit information from the brain to the muscles of the body. Interneurons are responsible for communicating information between different neurons in the body. There are three basic parts of a neuron: the dendrites, the cell body and the axon. However, all neurons vary somewhat in size, shape, and characteristics depending on the function and role of the neuron.
Neurons have specialized projections called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body. Information from one neuron flows to another neuron across a synapse. Synapses are found where nerve cells connects with other nerve cells as well as where nerve cells connect with muscles and glands. For communication between neurons to occur, an electrical impulse must travel down an axon to the synaptic terminal. The synapse contains a small gap separating neurons An electrical impulse travels down the axon of a neuron, and then triggers the release of neurotransmitters. These chemical messengers cross the synaptic cleft and connect with receptor sites in the next nerve cell, triggering an electrical impulse known as an action potential. The synapse consists of:
1. a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles
2. a postsynaptic ending that contains receptor sites for neurotransmitters
3. a synaptic cleft or space between the presynaptic and postsynaptic endings.
The human brain is the most complicated structure known to man. Via billions of nerve cells, it constantly receives signals from outside and from within, processes them, stores them, and passes them on. Nerve cells do not communicate in isolation but in a sort of conference call with thousands of other cells, whereby the participants change all the time in periods of seconds. In this way the brain controls our organs, our movements, our behavior, our thoughts and feelings - all simultaneously and completely automatically, without our assistance, and without us even being aware of it. The brain is our language and learning center with limitless storage capacity for experience, sensation, learning. And it's all interconnected, unlike in a computer, which stores data neatly side by side. The memory grows with every new links, new information becomes old, and is assigned to the familiar. Different tasks and functions are performed by different regions of the brain. As our most active organ, the brain uses an enormous amount of oxygen and energy.
The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain consists of the cerebrum, thalamus, and hypothalamus The midbrain consists of the tectum and tegmentum. The hindbrain is made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla are referred to together as the brainstem.
The cerebrum: The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe
• Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving
• Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli
• Occipital Lobe- associated with visual processing
• Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech
A deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. The corpus callosum is a bundle of axons which connects these two hemispheres.
The cerebellum: The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance.
Limbic system: The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old. This system contains the thalamus, hypothalamus, amygdala, and hippocampus
Brain Stem: Underneath the limbic system is the brain stem. This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure. The brain stem is made of the midbrain, pons, and medulla.
