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Download University of Jordan Faculty of Medicine L15 –Dr. Loai Physiology
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University of Jordan Faculty of Medicine Physiology || for Pharmacy L15 –Dr. Loai Nervous-System Note: 1) Make sure you understand everything, exams questions will be based on understanding NOT memorizing alone 2) Anything between *** was not mentioned during the lecture (only for your knowledge) 3) make sure you go through the slides for the nervous system by Dr.loai ----------------------------------------------------------------------------------------------------------The central nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. The nervous system has 3 parts: 1) Enteric nervous system which is located in the digestive system that processes in food digestion with minimal control from the CNS 2) Peripheral nervous system nerves that are located in the peripheral part of the body its main function to transport information from the outside (like sensation information) to the CNS & to receive orders from the CNS. Note: all the nerves you learnt about in the anatomy course are peripheral nerves. 3) Central nervous system mainly we will focus on the nerves that are in the core of the body (inside the spinal cord & the brain) its main function is to process the information Q: what does processing mean? To edit the information and to get the main important info, this will be sent as an output order that will go back to the peripheral and also there might be no order! The peripheral nervous system acts as an input device(sensory part) and also an output device(motor part) And between the sensory and the motor there is the integrative part We will focus on the Central nervous system The main function for the CNS processing The Nervous system from the anatomical part The central nervous system is divided into 3 levels: 1) The spinal cord processing (1st level) It will receive info and sensation from the peripheral and will send it to the upper levels of the CNS OR will receive orders from the upper level and after sorting and editing the info (orders) it will deliver it to the peripheral The spinal cord can make motor orders(output) especially those that need a fast reflex and cannot wait until it receives the order from the brain it’s called spinal cord reflexes or general reflexes For example when you touch a very hot cup and you remove your hand directly this is a spinal cord reflex 2) The cerebral cortex it is the highest & the most important level in the CNS (the 3rd level) Responsible for conscious movements & voluntary actions Q: what is the difference between conscious and voluntary? Conscious: analysis and understanding (as a sensation) Voluntary: movement 3) The brain stem and subcortical (the 2nd level) Actually this level is about anything between the cerebral cortex and the spinal cord Its main function is processing and taking orders up to the cortex, because the cortex is the boss of the CNS Also it might make orders mainly unconscious and involuntary actions just like heart rate, pressure, body temp, emotions, and respiration (internal environment conditions and unconscious movements or behavior) Examples on behavior: 1-sexual behavior 2- Hunger behavior 3- Unconscious motor behavior Example 1: If you place your hand on something that causes pain such as a needle reflex will be from the spinal cord directly(without waiting the subcortex or the cortex) in addition to an unconscious feeling of pain that will reach the cortex then you’ll figure out that the pain was from the needle Example 2: If the doctor wants to take blood from you here the cortex will cancel the spinal cord reflex so the cortex will keep telling that you should not move and to relax Functions of the cortex: 1) To receive information from the lower levels of the CNS 2) Processing and editing information 3) Build up a conscious meaning of the information that was received 4) Can send order to the lower levels to work or not to work (voluntary movements) 5) Emotions the cortex will try to relax you when you’re angry 6) Responsible for higher functions that need to be controlled by more than one information, such as personality, language, thoughts, thinking & calculations. 7) Memory ( the most important) As we mentioned that the cortex make processing and translation of the sensations that was received If a new person joint us on the lecture you will ask the doctor if he was new or not because when you saw his face you did not recognize him (lets say the cortex did not recognize him) so as a result of the cortex processing it the result was that he you don’t know him Next time he will come to the lecture the cortex will not tell you that he is new and you will recognize him quickly that is because the cortex saved his face in the memory because processing the cortex is strongly related to the old memory So we can define processing as a comparison with old memory As a conclusion there is no memory without processing and no processing without memory. That’s why the storage of memory is located in the cortex(where processing happens) Q: where is the memory located in the cortex? There are four lopes and each one has its own processing and so each lope has its own memory to use it For example the visual information is processed in the occipital lope so we expect to find the visual memory there As we mentioned the nervous system will have a sensation that will input information processing will occur in the cortex if a motor order is needed the order will be sent from the cortex through lower levels of the CNS until it leaves as a motor output Storage of the Nervous system The nervous system is mainly composed of neurons neurons have 4 parts: -cell body processing -dendrites processing & generating graded potential -axon generates and transports action potentials -axon terminals sends info from one neuron to another neuron As a conclusion the shape of the cell body and the dendrites is very important in processing Types of neurons: 1) Unipolar dendrites-axon-axon terminal (no cell body no processing) So we expect to find it abundantly in the PNS 2) Bipolar small processing It is found in a certain parts of the CNS but mostly in the PNS In the special sensations of the peripheral nervous system 3) Multipolar More than 99% of the CNS neurons It has more than one complex dendritic tree that converge together and enter the cell body for processing There are about 35 different shapes for the multipolar in the CNS Every shape is abundant in a certain part of the CNS and due to different shapes different processing that is what makes it unique and special. Q: what does the word pathway mean? Group of cells of the nervous system that information need to pass by until it reaches its destination For example : Visual pathwayinformation will pass from the eye until it reaches as a special sensation to the cortex and processing will occur Another examplespain pathway, motor pathway, Q:what is faster & easier ?to use one neuron until reaching the cortex OR 3 neurons (1 transfers to 2 and 2 transfers to 3) Any pathway has more than one neuron For example the pain pathway from the finger to the cortex it uses up to 3 neurons The question is that we used 3 neurons while 1 neurons is better !! so why 3 neurons? ITS BECAUSE WE NEED PROCESSING all the way before reaching the cortex Processing means we need to have a synapse So number of neurons during the pathway does not affect the length at all it affect processing only! (type of sensation) More complex more stops (to process) more neurons needed the 1st neuron in the pathway (somatosensory) did not need to make processing so its Unipolar in the special sensations we need A LOT of processing it will be Bipolar Q: what is the difference between somato-sensation and special sensation? Any sensation that is only in the head special sensation Like Vision, hearing, balance, face Any sensation that can be found in the head and the body somato Like pain, temp, movement, touch, pressure & vibration Muscle Movement, muscle length, muscle tension, joint positions proprioceptive sensation *** Proprioceptive sensation: to feel. the feeling of body movement and position, including motion of the arms and legs, resulting from stimuli received by special sense organs in the muscles, tendons, joints, and inner ear*** Other cells that are in the nervous tissue besides neurons: 1) Neuroglia play a supporting role to the neurons There are many types of Neuroglia: the most famous is Oligodendrocytes --> responsible for myelination (myelin sheath: sheet that goes all round the axons to increase speed of axons & decreases consumption of ATP in addition to isolation) The 2nd type is Astrocytes has many functions: - Mechanical support to the neuron - Environmental support (O2 and nutrition) - Forms blood brain barrier Microglia is the 3rd type similar to macrophages in the function its function is phagocytosis Ependymal cells produces cerebrospinal fluid fills internal cavities in the brain and the spinal cord and provides protection to the brain. Done by: Rahaf Mihyar