Human Body: The Nervous System (1950s)

system coordinates the complex actions involved in speaking thank you hearing and seeing what is about to happen will show us one of the simplest actions of the nervous system have you ever touched a hot cup let's watch that in slow motion such an action immediately pulling your hand away from a hot surface is called a reflex it is the simplest action of the nervous system what caused the reflex knowing the functions and parts of the nervous system will give us the answer very important parts of this system are the brain and spinal cord the central coordinators of all the functions of our bodies branching out from the brain and certain points along the spinal cord are many nerves that interconnect the brain and spinal cord with every tissue and organ of the body in addition to these nerves another set of nerves located alongside the spinal cord helps regulate the activities of some of the organs inside our bodies the basic function of the nervous system is to make responses to immunoly that may occur inside the body clear example of a response to a stimulus remember hot cup is a stimulus the response was to pull a waneful stimulus nerves in the hand and other parts of the body are the means by which we receive stimuli what are these nerves like this is one of the nerves found in the human leg it is a long string like piece of tissue we have cut off a portion of the nerve and will place a section of it under the microscope in this microscopic view we see that the nerve actually consists of a bundle of fine threads or fibers shown as white circles in cross-section these fibers are covered by an insulating sheath much like electric wires in a cable each of these fibers is attached to a specialized nerve cell drawn here highly magnified a nerve cell with attached fibers is called a neuron there are three kinds of neurons in the human nervous system these neurons look different since each kind of neuron has a specialized function here we've drawn the three kinds of neurons or nerve cells with attached fibers they are sensory neurons associative neurons and motor neurons the function of sensory neurons is to carry impulses made by stimuli inside or outside the body sensory or stimuli carrying nerves carry these stimuli impulses to the brain and spinal cord there are many sensory or stimuli carrying nerves around the sense organs of the body sensory nerves may be found around the eyes nose ears mouth and skin all sensory nerves terminate in the spinal cord or brain branching out from the spinal cord and brain are other nerves called motor nerves motor or response carrying nerves are made up of motor neurons the function of motor neurons is to carry response impulses from the spinal cord or brain to the various muscles and organs of the body that carry out responses motor and sensory nerves are associated by another kind of neuron found in the brain and spinal cord these neurons are called associative neurons associative neurons receive stimuli impulses from sensory nerves they determine the responses to be made to stimuli then they pass response impulses onto the motor nerves thus they associate stimuli and motor impulses how do sensory associative and motor neurons work together let's look again at our example of a reflex response the stimulus is transferred as a nerve impulse to the sensory nerves in the fingertips the nerve impulse travels at the approximate rate of more than 200 feet per second across the sensory nerve toward and into the spinal cord since the end of the sensory nerve does not touch the associative neuron ends in the spinal cord the nerve impulses pass over an open area called a synapse the associative neuron determines the response the response is transferred as a nerve impulse across another synapse to the motor nerve leading from the spinal cord the nerve impulse causes the muscle to contract and a response is made reflex responses happen before you know it you don't think about moving your hand away from a painful stimulus but later you realize what it was that caused your pain why at the same time stimulus impulses entered the spinal cord and a muscular response was caused the same stimulus impulses continued traveling up the spinal cord to the brain it takes a fraction of a second longer for stimulus impulses to reach the brain than to reach the spinal cord here is an actual human brain this complex organ weighing about three pounds coordinates your thinking seeing feeling and thousands of other activities by looking at this section of the brain we see there is an outer gray covering and an inner white matter the outer gray covering is composed of several billions actually billions of cells of associative neurons the inner white matter is composed of the fibers of these neurons the fibers interconnect all portions of the brain and spinal cord and are the pathways which connect all parts of the body to the brain different parts of the brain have different activities each portion of the brain has a name the cortex and cerebrum are the top most portions the cerebellum lies directly under the cerebrum the lowest portion of the brain is called the brain stem this area of the brain stem the medulla is directly connected to the spinal cord are some of the functions of the medulla the medulla controls many body activities the medulla regulates such organs as the stomach which helps digest food the heart which pumps blood and the functions of most body organs let's say then that many of the internal activities of your body that enable you to continue living are controlled by the medulla a part of your brain no larger than a radish just as the medulla coordinates the organs of your body the cerebellum coordinates the muscles of your body the many complex movements your body performs every day whether playing a fast game of basketball or simply walking whether diving swimming or merely standing or just picking up something you've dropped the hundreds of muscles involved in body activities are coordinated by this amazing portion of the human brain the cerebellum the cerebellum coordinates the activity of the muscles put into action by the cerebrum the cerebrum with its cortex is the most complex portion of the human brain stimuli impulses from all parts of the body converge here and connect with associative neurons in the cortex for example that book you dropped that became a stimulus impulse transferred perhaps by sensory nerves in the eye to the cortex and cerebrum you wanted to pick it up this was the response of the cortex which sent stimuli impulses to the cerebellum which coordinated the many muscles involved in picking up the book this action began in the cortex and cerebrum that portion of the brain which enables you to perform many activities among which the most important is thinking and understanding how the cortex of the brain thinks and understands is a mystery that has yet to be solved we do know however that neurons in certain areas of the cortex called associative areas store a vast number of stimuli impulses these areas of the cortex enable you to associate a steaming cup with a feeling of hot and further enable you to think of ways to avoid the painful hot stimulus in the same way associative areas of your cortex are enabling you to associate the stimulus of this word with a variety of mental images of what the word stands for the wonderful cortex of the human brain enables you to think of ways this problem for example can be solved and the solution itself reading and understanding this sentence is a basic example of the function of the human cortex and an example of the nervous system in action we found out that the human nervous system carries stimuli from outside and within our bodies and coordinates our responses to these stimuli the coordinating organs of the system are the brain and spinal cord joining the brain and spinal cord to all organs and muscles of the body is a network of nerves another network of nerves alongside the spinal cord interconnects some of the internal organs of the body all parts of the human nervous system are made up of thread-like organs called neurons sensory neurons carry stimuli impulses associative neurons determine the responses to be made to various stimuli motor neurons carry response impulses the three kinds of neurons functioning together in the brain spinal cord and nerves the organs of the human nervous system enable us to do all the things we do every day simple but vital processes such as breathing and digesting food depend upon the proper functioning of the nervous system body movements also depend upon the workings of the nervous system perhaps the process of thinking is the most amazing of all the functions of the human nervous system but it is only one of many functions [Music] for every day thousands of stimuli are being received by your body and thousands of coordinated responses are being made to these stimuli by the organs of your nervous system