[Music] in this animation we want to explain the human nervous system with the help of incredible never-before seen images the body's nervous system is a complex system made up of countless nerve cells that serve among other things to process stimuli from the environment a distinction is generally made between the Central and peripheral nerve nervous system the peripheral nervous system runs through the entire body and is shown here in [Music] yellow the brain and spinal cord are part of the central nervous [Music] system they are well protected by the skull and spinal column our spinal column consists of individual vertebrae that have a spinal canal containing fatty and connective tissue and the spinal cord like the brain the spinal cord is enclosed in three membranes the outer membrane of the spinal cord is called dura moer the arachnoid modder is located directly under the dura modder this arachnoid modder is connected to the P Mo via arachnoid tcul [Music] the spinal nerves of the peripheral nervous system lead into the spinal cord whereby the spinal nerve is divided into afferent and ephant fibers the afferent nerve fibers conduct nerve impulses from the sensory receptors to the central nervous system while ENT nerve fibers carries impulses to affect our organs mainly muscles and glands we will take a close closer look at the thickening that we call spinal gangion or dorsal root gangion in a [Music] moment blood vessels and many nerve fibers are part of a spinal nerve several nerve fibers form a nerve [Music] faasle nerve fibers are enclosed by a connective tissue layer of endorian Schwan cells are located under this protective layer if these cells are wrapped around the axon several times they are able to increase the conduction speed of an Impulse the increase in conduction speed is achieved by regular interruptions which are known as nodes of ronier the cell uses an axon to conduct electrical impulses let us first take a look at the basic structure of a nerve cell nerve cells consist of the nerve fiber mentioned earlier which originates from a cell body inside we see the glowing cell nucleus dendrites mainly used to receive stimuli also originate from the cell [Music] body at the end of an axon are terminal buttons [Music] these small knobs form the first part of a synapse and are therefore called press synaptic terminals terminal buttons possess calcium channels that can open and close these calcium channels open via an electrical impulse as soon as the action potential reaches the terminal button the calcium channels open and allow calcium ions to flow in there are vesicles in the terminal button these vesicles contain neurotransmitters which are shown here as red spheres there are approximately 200 to 500 such vesicles in the synaptic terminal buttons the calcium ions enable these vesicles to fuse with the outer layer that is the membrane of the cell [Music] the fusion of the vesicle with the membrane allows the neurotransmitters to be transported out of the cell this process is known as exocytosis the neurotransmitters are absorbed by receptors located on the post synaptic cell membrane which convert the neurotransmitters back into an electrical impulse with the help of such a chemical synapse a nerve cell can transmit its signal to an another nerve [Music] [Applause] [Music] cell for this purpose the dendrites have spines which possess the post synapses mentioned before spines can take many forms including stubby and [Music] [Applause] thin [Music] terminal buttons can not only transmit impulses via the spines of dendrites they can also transmit their action potential directly to the cell it is also possible for a terminal button to form a synapse with another axon or terminal button nerve cells can and must also be able to transmit impulses to other cells such as our muscle cells so that we can move but now let's get back to the spinal cord and nerves the impulses are transmitted via the nerve fibers on one side impulses come from the spinal cord on the other side they are transmitted to the spinal cord the cell bodies of the sensory neurons are located in the spinal gangion that is why this part of a spinal nerve is thicker than the other part the neurons in the dorsal root gangion are pseudo unipolar neurons in which the Axon is divided into two branches One Branch goes to the periphery for example to the skin and the other to the central nervous system impulses are transmitted from the skin to the central nervous system via the axon depending on the function neurons can also have unmyelinated nerve fibers in that case non-m milina Schwan cells and sheath the axon that means that there is no increase in conduction [Music] speed let's take a look at the process with the help of a highly simplified image on the fingertips in particular we have numerous receptors at the ends of sensory nerve fibers if the receptors of a sensory neuron receive a mechanical stimulus this stimulus is converted into an electrical impulse and transmitted via the a on to another neuron in the spinal cord the neuron in the spinal cord transmits the action potential to the brain where another neuron finally transmits the impulse to the somato sensory cortex the impulse is then [Music] processed as already mentioned there are numerous receptors in the skin some receptors are are located in the upper layer of the skin the epidermis which is made up of dead and living keratinocytes mner cor pusles and Merkel cells are found here other receptors are located in deeper layers of the skin such as rufini cor pusles which are found in the dermis there are many other receptors but only these three will be briefly described here let's start with the meisner's cor pusle as soon as pressure is applied to the er's core pusle for example by pressing on the skin an action potential is triggered this action potential only occurs when there is a change in pressure meisner's cor pusles are therefore rapidly adapting mechano receptors Merkel cells on the other hand belong to the slowly adapting mechano receptors as they trigger an action potential in response to both Dynamic and static stimuli rufini cor pusles trigger an action potential when the tissue is stretched rufini cor pusles also belong to slowly adapting mechano receptors of the skin let's take another look at the spinal cord and the spinal [Music] nerves the axons of the sensory nerves end at nerve cells in the spinal cord nerve fibers which can be seen here as thin threads extending into the brain originate from the cell bodies of these nerve cells the nerve fibers are referred to as white and the cell bodies as gray matter when The receptors of the skin or organs generate an action potential they transmit this action potential via the nerve fibers to the gray matter after which the action potential is transmitted to the brain via the white matter [Music] from above we can see the butterfly-shaped structure of the gray [Music] matter however impulses can also be processed directly in the spinal cord the sensory fibers transmit impulses directly or indirectly to motor nerve fibers which can then contract or relax a muscle this is called [Music] reflex such a reflex occurs when we burn ourselves receptors then transmit impulses via Sensory neurons to interneurons which then cause motor neurons to contract [Music] muscles [Music]