Nervous System Lecture Notes PDF

MC_101_: ANATOMY AND PHYSIOLOGY LECTURE LECTURE 02: THE NERVOUS SYSTEM PROFESSOR: Ms. Celisse Esguerra 1ST SEMESTER | A.Y 2022-2023...

MC_101_: ANATOMY AND PHYSIOLOGY LECTURE LECTURE 02: THE NERVOUS SYSTEM PROFESSOR: Ms. Celisse Esguerra 1ST SEMESTER | A.Y 2022-2023 Your glands also. Your NS controls your glands so LECTURE 00 that it secretes hormones or secretions (ex. Sweat Hello ill jus put this after tomorrow :(( para lang rin glands) makapag review na lahat RECEIVING SENSORY INPUTS external and internal · DEFINITION OF NERVOUS SYSTEM Sensory receptors monitor numerous external and A communication system, receiving signal from and internal stimuli sending signals to different areas of the body Examples of Sensory Input or sensations via At its most basic level, nervous communication ○ External Stimuli (outside the body) occurs through electrical signals (arrow) that spread vision over the cell membrane of neurons and cause hearing changes at the synapse, the communication taste junction between the neuron and its neighboring cell. smell Helps coordinate body functions to maintain touch homeostasis Pain Homeostasis = balance Body position Temperature ○ Internal Stimuli (inside the body) blood pH blood gases Blood pressure you usually don't feel these unless they become abnormal (ex. hypertension) these sensations are picked up by what we call as sensory receptors — they receive stimulus INTEGRATING INFORMATION with every action there is reaction Brain and Spine · , a ; means combining all the processed stimuli and in return, initiates a response. Remember the saying in physics = for every action, there is an equal or opposite reaction? ○ Same goes with your nervous system As seen in the picture, we have the CNS which consists of ○ Or since we’re comparing it to a the brain and spinal cord, whereas the PNS (meaning away communication system, an example is from the center) – consists of the nerves. when your talk over the phone. When your caller asks you a question, you obviously NERVOUS SYSTEM FUNCTIONS (CRIME) reply. ○ So the main organs responsible for CONTROLLING MUSCLE AND GLANDS · cardiac Skeletal , smooth , glands integration is your brain and spinal cord. , Nervous system controls major movements of the MAINTAINING HOMEOSTASIS balance - body. It participates in controlling muscles such as Homeostasis is balance. cardiac and smooth and many glands. Too much or too little of anything disrupts that When stimulated, your skeletal muscles control your balance and it obviously makes you sick. body movements So, how does take part in this nervous system? What about when you eat? ○ Your nervous system has the ability to ○ You have smooth muscles in your GI tract. detect, interpret, and respond to changes So they contract as well to push what you in the internal and external conditions. eat down from your esophagus down to your stomach and then towards your intestines until you pass it out then you defecate. Next is your cardiac muscles = Your cardiac muscles are continuously contracting to pump your heart. If it stops contracting, you obviously die. TABANAO | 1NU02 1  signals to your glands, specifically your sweat glands and then your sweat glands reuse all these needs sweat to you skin. And then it cools off your skin. So, these are just one of the few ways, that your nervous system controls your body so that it can maintain homeostasis. ESTABLISHING AND MAINTAINING MENTAL ACTIVITY Your brain is responsible for memory, thinking, your consciousness if you’re awake or asleep and your mental health as well. DIVISIONS OF THE NERVOUS SYSTEM Example: ○ In mid-day when the sun is very high, your body senses temperature. It sends signals to your nervous system and it tells “hey it’s too hot! You need to maintain a normal range for your body temperature.” Otherwise, what will happen? You might get heat stroke. So, what does your nervous system do about it? ○ It reacts by sending signals to your blood vessels so they can dilate. To draw, ○ sun above, skin below, blood vessels underneath it, receptor on the side and brain below. CENTRAL NERVOUS SYSTEM (CNS) brain and spine Consists of brain and spinal cord PERIPHERAL NERVOUS SYSTEM (PNS) nerves and ganglia Includes all nervous tissue outside CNS including nerves and ganglia Serves as the communication link between CNS and various parts of the body Carries information about different tissues of the body to CNS and deliver commands to alter body activities. DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM (PNS) So, what happens? ○ Your sensory receptors perceive heat SENSORY DIVISION afferent division towards the center - - coming from the sun and then it sends Your sensory division is also called as afferent signals to your brain. When your brain division. perceives that sensation, it sends signals Afferent just means towards the center. to your motor. What are your motors? In It conducts action potentials or signals from your this case, it is your blood vessel so it is sensory receptors towards the peripheral nervous smooth muscle. system and eventually to the central nervous system. So, what does it do? So, the afferent neuron is your sensory neuron. ○ It sends signals to your blood vessels so it Afferent (toward) division; conducts action can dilate. potentials from sensory receptors to the CNS. ○ So why does it need to dilate? ○ Sensory neurons - neurons that transmit So that the blood can easily pass action potentials from the periphery to to through your blood vessels. the CNS Faster. Because when it travels faster through your blood vessel, MOTOR DIVISION efferent away from CNS ; effect · - or action it dissipates the heat from your efferent neuron, efferent, which means away from body. your central nervous system. This has motor neurons. What else? It sends action potentials or signals from your CNS ○ Glands. When your body perceive that it is to the effector organs. very hot outside, what happens? Efferent is the effect or the reaction You perspire, you sweat. Why? Efferent (away) division; conducts action potentials Because when these receptors from the CNS to effector organs perceive signals that it is hot and goes to your brain and brain send TABANAO | 1NU02 2  ○ Motor Neurons - neurons that transmit CELLS OF THE NERVOUS SYSTEM action potentials from the CNS toward the periphery COMPOSITION OF NEURONS Also called nerve DIVISIONS OF MOTOR DIVISION cells Receive stimuli, SOMATIC NERVOUS SYSTEM CNS to sucletal muscle · conduct action potentials, Transmits action potentials from the CNS to the transmit signals to other skeletal muscles neurons or effector organs “Soma” – the word soma in Greek means body. Remember your Skeletal muscles is involve to your bodily movements, your voluntary body movements. neurons are connected to each other so they either AUTONOMIC NERVOUS SYSTEM (NG cardiac smooth glands (self-governing ;voluntary · to , , receive stimulus or action “Auto” means self-governing. potentials from other neurons It transmits signals(action potentials) from your CNS or can also receive stimuli to your cardiac muscles, smooth muscles, and your from other receptors. glands. Auto is self-governing, these are involuntary so this CELL BODY one nucleus happens automatically. contains single You don’t have conscious effort. This then divide nucleus. further divided into sympathetic and Source of parasympathetic. information for gene Sympathetic - fight or flight system expression Parasympathetic - rest and digest system Nucleus is surrounded by rough ER, ENTERIC NERVOUS SYSTEM intestines (independent ( · mitochondrion and Golgi body Unique subdivision; both sensory and motor that are floating in the side of neurons contained within the digestive tract; can nucleus. function without input from CNS and PNS Enteric means intestines. DENDRITES receive and transmit information - It is very independent of your CNS and PNS. cytoplasmic extension from the cell body. They are expanding from your cell body. They usually receive information from other neurons SUMMARY: and transmits the information to the cell body. AXON single long cell process. In the illustration, it is the long yellow thing. It starts from the axon hillock (the triangular end part). ○ “Hillock” means hill so this looks like hills. Axon are usually unbranched since they are a single long process. But sometimes they form what they call collateral axon. Let’s start with your sensory input: the light, sound, ○ So there is an extra axon. This works just smell, touch, etc. sensory receptors which perceive the same as an unbranched axon. or receive those sensory input. Axons can be surrounded by highly specialized It sends the signals to your sensory divisions. This insulating layer of cells called is still in your peripheral ns. ○ Myelin sheaths — the transparent or Once it receives the stimulus it sends the signal to translucent purple ones that covers the your CNS. axon and they are insulators. ○ First to your spinal cord then to your brain. Once CNS has processed this, it then sends signals to your motor division. NOTE: Your motor division has somatic and autonomic ns. When a neuron dies, it is no longer replaced Somatic means soma which means body so it because it does not divide and does not multiply. controls your body functions this means your skeletal muscles which are responsible for body QUESTION: How does the neuron transmit signals? movement. Your autonomic, auto, is also further subdivided to parasympathetic and sympathetic division. when a neuron dies, it’s no longer replaced, ○ It is responsible for involuntary movements which involves cardiac, smooth muscles because it DOES NOT DIVIDE and MULTIPLY and glands. So what happens?, it affects the metabolism, heart rate, breathing, etc. TABANAO | 1NU02 3  So, it’s like unipolar but its not. ○ Uni means one. ○ So you have a single process extending from your cell body. ○ It then divides into two processes. It branches into two. ○ The cell body transmits action potentials to that one process and then it splits into two directions. ○ One goes to the CNS and one goes to PNS. QUESTION: How does this work compared to the first two which has dendrites connected to the cell body? Your peripheral axon in this, acts as a Through action potentials. dendrite. It receives sensory information What is action potential? and immediately transmit this as an ○ They are a change of the resting action potential to CNS. That’s why the membrane potential. They are like sensory axonal branch it has a sensory electrical impulses. receptor over there. Example: Once you touch your cheek, it starts with the sensory receptor, sending signals to the dendrites towards the neuron cells and then the axons of the sensory neurons transmit action potentials towards your CNS. CNS must process this, then the motor neuron so then it will then conduct action potential away towards your muscle to the effector organ. Take note that the axon may also conduct action potential from one part of the brain to another. Same to the spinal cord. TYPES OF NEURONS The dorsal root- the swelling part. The green part in This depends on either function or structure. the picture is the dorsal root ganglion is an example What we discuss a while ago is based on their of pseudo-unipolar neuron. function. So the axon divides into two branches – the When it comes to the structure there are 3. peripheral branch, and the central branch They are named after their number of processes. ○ The peripheral branch picks up sensation from your skin, while the central branch transmits the information to the PNS (Spinal Cord and Brain). TYPES OF GLIAL CELLS (NEUROGLIA) Supportive cells of PNS and CNS Non-neuronal cells of the neuroglia or glue nerve CNS + PNS they do not conduct - More numerous than action potentials neurons Retain the ability to divide There are 4 Glial Cells in MULTIPOLAR NEURONS -most ; has many dendrites common but only one axon CNS while 1 in PNS Multi means many. Glial cells are what we So it has many dendrites and only one axon. Most call your neuroglia (or neurons in your CNS and motor neurons are multi nerve glue) they are polar supporting cells. found in sensory organs (retina and naval cavity ( ○ Take note that they do not conduct action BIPOLAR NEURONS - can be Bi means two, so you have one dendrite and one potentials. axon. ○ They are just supportive cells because This can be seen in sensory organs, most they enhance neuron function so they are exclusively in your retina and nasal cavity. like boosters. ○ Retina - eyes (2) Neurons cannot divide but glial cells can divide. ○ Nasal cavity - nostrils (2) These are schwann, microglial, oligodendrocyte, just to name a few. PSEUDO-UNIPOLAR NEURONS dendrites - no more numerous than neurons since they can divide Pseudo means resembling or imitating. It looks true but it’s not. TABANAO | 1NU02 4  IN CENTRAL NERVOUS SYSTEM: ASTROCYTES -blood-brain barrier They are major supporting cells in the CNS. 1. They stimulate or inhibit the signaling activity of nearby neurons—that’s one function. 2. they form the blood-brain barrier( a permeability barrier—a barrier between blood vessels and brain ). Blood barriers are like filters that permits specific substances to enter your brain. 3. Another function, astrocytes also limit further damage of your neural tissue so it does not die. However, it forms a scar—and whatever is damaged can no longer regenerate but that part of the neural tissue will still not die. EPENDYMAL CELL - cells line the cavities in the brain that contains (OF MYELIN SHEATHS Myelin sheaths are specialized layers that are wrap around the axons of some neurons formed by It lines the fluid-filled cavities like the ventricles oligodendrocytes and Schwann cells. L CNS L PNS (third and fourth ventricles, which actually have They are repeatedly wrapped around the segment Cerebrospinal Fluid). of an axon. ○ CSF is produced by your glial cells. It forms a series of tightly wrapped cell membranes ○ CSF is a fluid made of this cell and it helps so it looks like a croissant. protect your brain and spinal cord from it prevents almost all iron movement across the cell sudden impact or injury. membrane. ○ It’s like a cushion or helmet in fluid form. It also increases the speed and efficiency of the ○ Another is that it removes waste products action potential. from your brain and it makes sure it is clean so CNS can work properly. The node of Ranvier however, are gaps between ○ Ependymal cells have cilia that help move myelin sheaths. the CSF through the CNS. ○ So obviously, they are not covered with myelin, they are not insulated and they MICROGLIAL CELL - immune cells ; they remove bacteria and cell debris allow ion movement. This acts as immune cells so it has immune functions. They remove bacteria and cell debris. OLIGODENDROCYTES provides myelin sheet for in CNS axons provide myelin to neurons in the CNS. Myelin is an insulating material that surrounds the axon. Next is unmyelinated neurons. IN PERIPHERAL NERVOUS SYSTEM: ○ They are axons without myelin sheaths PNS that rest in the indentation of glial cells. SCHWANN CELLS provides myelin sheets for axons in Example: Provides myelin that surrounds axons (only in PNS) ○ A small typical nerve that consists of axons of multiple neurons usually contains unmyelinated axons than myelinated. TABANAO | 1NU02 5  CLINICAL PICTURE: MULTIPLE SCLEROSIS Polarized means: to divide into two opposing Multiple sclerosis is an autoimmune disease--the groups (a positive and a negative). A small immune system attacks the myelin sheaths and voltage difference is called potential. destroys it. ○ You have 3 factors that generate the The result is communication problem in brain and resting membrane potential: organs. Because of this, patients have a loss of a higher concentration of muscle function, they cannot walk properly, potassium inside the cell, experience numbness, and feel paralyzed as well a higher concentration of sodium because they cannot transmit action potential. outside the cell, and cell membrane permeability preference to your potassium as compared to your sodium. CELL TYPES DESCRIPTION Neuron Multipolar Many dendrites: 1 axon Bipolar 1 dendrite: 1 axon Glial Cells of CNS Astrocytes BB Highly branched Ependymal Cells CSF Epithelial-like Microglia Immune Small, mobile cells Oligodendrocytes Cell with process that can surround CNS Myelin several axons Glial Cells of PNS Schwann Cell PNelinSingle cell surrounding axons ORGANIZATION OF NERVOUS TISSUE Nervous tissue varies in color due to the location and arrangement of the parts of neurons and glial cells. Sometimes, it depends if they have myelin sheaths. GRAY MATTER outside of the brain little myelin sheets · ; The gray matter consists of neuron cell bodies and ION CHANNELS their dendrites where there is very little myelin. Basis of difference in membrane permeability It is in the cortex or outside of the brain. Proteins embedded in cell membrane Clusters of gray matter located deep within the Example of ion channels is your gated and leak brain are called nuclei. channels. In contrast to your peripheral nervous system, a Also, there is a fact that there are negatively cluster of cell body is called ganglion or a swelling. charged molecules such as proteins inside the cell that are too large to exit the cell that’s why the WHITE MATTER has myelin sheet that's why it's · white inside is more negative as compared to your outside. White matter are bundles of parallel axons with their white myelin sheaths that’s why they are white. TWO BASIC TYPES OF ION CHANNELS In the CNS, it forms nerve tracts. Remember, white tracts are conduction LEAK CHANNELS always open potassium leak channels · ; pathways propagating action potentials from one area of the CNS to another. It is truly channel’s that the resting membrane And the PNS is bundles of axons plus your potential is established because it’s always open connective tissue forms the nerves. that’s why it leaks. Remember from high school chemistry what is the rule, substances tend to go from higher ELECTRICAL SIGNALS AND NEURAL PATHWAYS concentration to lower concentration, that is how it always is. POLARIZED CELL MEMBRANE Okay, from higher concentration gradient to lower Uneven distribution of charge concentration gradient. RESTING MEMBRANE POTENTIAL Potassium contributes the most to the resting Membrane potential is the difference in the membrane potential because there are 50 to 100 times more potassium leak channels than your electrical charge between the inside and the outside sodium. of the cell/neuron So, since there are more channels, it is easier for The inside is usually negative, while the outside is them to just in and out of the cell membrane as usually positive. That is when it is at rest. compared to your sodium. So the unstimulated, unevenly distributed charge is called the resting membrane potential. GATED CHANNELS Take note that it is the time when your cell Gated Channels only opened via a specific signal, membrane is polarized. that is why it is called gated, it has a gate. It does TABANAO | 1NU02 6  not just let substances in and out like the leaky Now, remember because of the many potassium channels. leaky channels, the positively charge potassium ○ Your chemically gated channels are goes outside the cell, why? opened by neurotransmitters, or ○ Because it has a lower concentration sometimes other chemicals, but mostly there, so it goes from higher concentration your neurotransmitters. to lower concentration. There’s a receptor on these gates ○ What happens? one a neurotransmitter attaches The inside becomes more to that receptor, it opens up. So, negative because your potassium it’s like a hotel key, you tap it, and is going out, it’s a positive charge. the door opens. Your However, since the opposite neurotransmitter is the hotel key. charges attracts, again your ○ Another gated channel is the potassium has no choice but to voltage-gated channel as compared to move back in. your chemically gated channel that is What happens it just goes in and opened by neurotransmitters, your out of the leaky channels. voltage-gated channels are opened by a change in your membrane potential. That’s Again, when we are talking about resting membrane why it is voltage-gated, it's opened by the potential, everything is at rest, this is the norm. change in the charge or the voltage of the There is a point of equilibrium since the potassium membrane. is going out of the cell and its balanced by the negative ions inside the cell in which it attracts the When there is a change in the membrane potential, this is potassium to go back in. also what we called the Depolarization ○ Think of these ions, as a negative and polarized means its divided into two completely strict parent, you badly want to go out, it is opposing roots, negative in positive out. in your nature, you can’t help it, that is just how you are. Depolarization means the difference decreases, so instead ○ So, you go from higher to lower of all of this is negative inside and then everything is positive concentration, you want to go out. outside it becomes mixed or the inside becomes more Whenever you are out, partying with your positive, and the outside becomes more negative. friends, the negative ions pull you back - inside becomes more positive outside , becomes negative home. How does this happen, how does depolarization ○ The strict parent, your negative parent and happen? you have no choice but to follow. Okay, remember you have sodium leak channel, ○ But then you will ask, but Doc if there’s right? Even if there only a few, it has more potential also sodium leaky channels, even if there to go inside the cell than backout because it goes only a few won’t then negatively charge from higher concentration to lower concentration, ions prevent the sodium from going back okay that is one. out. Another is the inside of the cell is originally more negative as opposed to the outside. What is the And also, you can’t go from lower concentration to second factor? higher concentration right. Won’t there be ○ Opposite charges attract, so again your eventually become more potassium outside the cell sodium which is positive is being sucked than inside if these keeps going on or there will be inside your cell because it's negative more sodium ions inside the cell. inside. To answer that question, you have the sodium ○ So what happens?, since more sodium is potassium pump to help. going in, coming in the inside of the cell ○ To compensate for the potassium leakage, becomes more positive than usual. the membrane has to make sure that there is greater concentration of sodium outside So the membrane no longer has that much and potassium in. difference in charge, right? ○ You have to maintain that, that’s normal, ○ It becomes more depolarized. that’s the balance of this cell. ○ Due to this depolarization the channel opens, the voltage-gated channels opens. When activated by the ATP Adenosine Triphosphate, ATP is basically energy, so just If your leak channels are responsible for imagine you prompt to pump into a socket or you maintaining the resting membrane potentials, put batteries on it, it becomes activated. opening your voltage-gated channels starts an With every 2 potassium ions that comes back inside action potential. the cell, it pumps out 3 potassium ions. ○ It's no longer resting, it's already an action So, this how it compensates and helps the sodium because you depolarized the membrane. ion to go back outside the cell where it has higher concentration. SODIUM-POTASSIUM PUMP Now remember this pump will only work when you The reason why the inside of the cell is negative is have ATP or energy. Especially in neurons where it because there is more negatively charge molecules requires 70% ATP. like your proteins, they are impermeable in the Does it makes sense? That even if you are just membrane. sitting and don’t move around much when you study, you feel like you as if you become more tired than usual is because posture frame consumes a Impermeable means its not permitting to passed lot of energy ‘when its working. through, so it stays inside. So again, to summarize this, leaky channels, potassium is going out from higher concentration TABANAO | 1NU02 7  but its pulled back in due to the negative charge of leaky channel are open because the inside of the cell. they don’t have gates. The sodium goes in the cell because it goes from So just think the leaky channels higher concentration to lower concentration; at the are back door passes, so it is only same time the positive charge of the sodium is for party staff. attracted to the negative side of the cell. They can go inside more easily So it is going to have a difficult time going back and earlier than the rest. outside the cell because the force inside of the cell So they are hyped up, they carry is very strong. positive vibes inside the house Higher to lower concentration plus negatively because the potassium carries charge pa siya; so this is controlled by your positive vibes inside the house. sodium-potassium pump to help the sodium get out Then it is time to start the party, it of the cell to maintain the normal balance. is already 7 pm. That every 2 potassium it discharges, or it brings So upon stimulus, the cell is out 3 sodium ions. So that is how you make sure to stimulated, upon the stimulus of keep the resting membrane potential. the nerve cell or the muscle cell with the neurotransmitter (hotel ACTION POTENTIALS keys or the VIP tickets), it briefly opens your sodium channels and some sodium diffuses quickly into the cell. So only the VIP guests gets to go inside because the door only opens for a while. This is what we call local current when the sodium channels briefly open and some sodium ions come in. So the party gets more hyped because the VIP guests arrived, more positive vibes so this local current process the depolarization because it makes the inside of the cell more positive or less negative. This depolarization in turn causes a local potential. This usually occurs in your dendrites – or in your soma. ○ If the depolarization isn’t strong enough, the sodium channels close and this local potential disappears. So imagine: ○ Your VIP guests didn’t attract too much attention – the party was a flop, ended early and gates were closed. ○ However, if the depolarization is strong enough because of the stimulus, more sodium enters the cell because it keeps the channels open. ○ The channels don’t close. The channels are open until it reaches a threshold value. This threshold is most often reached at the axon Your muscles and nerve cells are excitable cells, as hillock. long as there is a stimuli, the resting membrane ○ This is called your all or none law. potential can change via the gated channels The action potential either occurs It allows permeability of some substances which will or it doesn’t – depending on previously de-permeable and then eventually it whether it reaches the threshold produces an action potential because you So the party either flies or flops. depolarized the cell. That’s what the all or none law ○ Let us apply what we learned a while ago means. to explain action potential, let us also So more guests with positive vibes come in compare this to a house party so that you because the gates were opened longer. can understand better. ○ More depolarization Situation, before the party the ○ More positive charge inside the cell house is resting right? It is silent, ○ Because of this, it triggers the opening of there has no guest, there is no your voltage-gated channels. that much people. So the house gates are closed Because the party was fun the staff says “Hey, hey because the party has not started we need to open more gates!” So aside from the yet. sodium-gated channels, the So at the rest the voltage-gated sodium-voltage-gated channels also open. channel were closed, only the TABANAO | 1NU02 8  The inside of the cell becomes more and more positive in a faster pace. So even your sodium-potassium pump can’t complete. During this time, however, your potassium-voltage-gated channels also open. ○ The exit doors: ○ So you have guests with curfew so they have to leave early. But there are just a few of these doors opening. ○ More guests are still coming in. This occurs until it reaches a brief time when the inside of the cell is now more positive than the outside. 1. This stimulus causes or initiates the depolarization ○ Because of this, the cell thinks: “Oops, this of the cell. If the depolarization is not strong is too much. Full house na” enough, it will have failed initiations. ○ So what happens? The cell membrane This is what we call the “all or none law” now then closes your sodium channels to stop more sodium from entering. 2. However, if it reaches the threshold, the ○ During this time, they are not letting other depolarization will become higher and higher guests in. More potassium channels are because more sodium ions are coming in. So the opening. inside of the cell becomes more positive. Remember, it didn’t open at the same time as the sodium 3. Until it reaches the peak where the inside of the cell channels. What happens here is: is now more negative than the outside of the cell. Potassium ions goes What happens? outside where there is Your sodium-ion channels start to close lesser potassium and then more potassium ions start to concentration open. What happens then? Since there are no more sodium ions going ○ The inside of the cell becomes more in, the inside of the cell will become less negative again. positive or more negative ○ Kasi labas na siya nang labas eh At the same time, the inside of the cell will ○ All the positive potassium ions are already again be more negative because positive going outside, and none of the sodium ions potassium ions are going out of the cell are going in ○ And this is what we call ○ This occurrence repolarizes your cell. repolarization because you’re ○ Cell membrane goes back to its resting trying to put the membrane membrane potential potential back to its resting state. ○ Depolarization and repolarization constitute an action potential 4. However, there is also a short period of time where Everything that happened in this hyperpolarization occurs. Because more and more party is the action potential. potassium are going out of the cell. At the end of 5. But then again, this becomes balanced and goes repolarization, the back to its resting state once the potassium ions charge on the cell become closed. membrane briefly becomes more ACTION POTENTIAL UNMYELINATED AXON negative than the Action potentials are conducted slowly in resting membrane unmyelinated axons, and more rapidly in potential. myelinated axons. UNMYELINATED AXONS slower - You call this hyperpolarization. It is beyond the resting membrane potential. Naked ones Nasobrahan because the potassium channels were Here we can see that in this part of the axon, the open. cell membrane stimulates local currents in the adjacent part of the cell membrane. Elevated permeability of this potassium lasts only a Local current very short time. This hyperpolarization is also only ○ Is when the sodium flows into the cell. for a short time. ○ It’s that brief period where the sodium channels were open. So it depolarizes that Do take note that ALL action potentials have the part. same magnitude. So a stronger stimulus does not ○ That part in return, produces an action produce a stronger action potential but it produces potential and then that new part again more action potentials. stimulates local currents in the next part and depolarizes it. This goes again and Stronger stimulus = more action potentials. It again. increases the frequency of the potential generation. This is what we call as (continuous conduction). TABANAO | 1NU02 9  Because the action is ○ Sodium ions come in which makes it more continuously conducted or positive and then it depolarizes this area passed along the axon. resulting in another action potential. ○ Again it bumps positive ions in the myelin MYELINATED AXONS faster · sheets (second rectangle), and then it The action potential is propagated faster. reaches another node. And, it jumps from The myelin sheath acts as an insulator. It does not one node to another. have ion channels which means depolarization cant occur in this area SYNAPSE If you see the orange one above, that area is the Node of Ranvier. It produces an action potential because it does not have any myelin. Once there is an action potential in that space, the sodium ions bump other positive ions until this wave depolarizes the next node over here. Neuronal synapse is a junction where the axon of one neuron interacts with another neuron or effector organ. The end of the action forms a presynaptic terminal. The membrane of the next neuron forms the Since this node has ion channels, it causes local postsynaptic membrane, with a synaptic cleft in current through extracellular fluid and then through between. the cytoplasm of the next axon in the next node, ○ Cleft - means a division, fissure, or a split causing another action potential. ○ So it sort of jumps from node to another The round ones in the presynaptic terminals are node. called vesicles. ○ This is called your saltatory conduction ○ within the synaptic vesicles there are Saltatory = to leap neurotransmitters. ○ note: action potentials are being conducted Advantages of Myelinated axon; along the axon, once it reaches the end of ○ Because of the jumping of action the axon (or the presynaptic terminal), the potentials, conduction velocity is voltage-gated channels of the calcium increased. Through the ions are conducted opens. along the cell membrane just to produce There is a new ion involved here, calcium, the influx an action potential. of calcium causes the synaptic vesicles to latch on ○ Note: Ions are only conducted in the nodes the cell, and then release the neurotransmitters via and not where there is myelin. exocytosis. ○ Because of this, lesser energy is required for the sodium potassium pump to The neurotransmitter then crosses the cleft and binds to the receptor molecule over the maintain iron distribution postsynaptic neurons. ○ Sodium potassium pump requires ATP but in the areas (internode) where there is ○ Note: Neurotransmitters are like keys to myelin it doesn't have any channels. the channels. The receptors are the lock. Ligand-gated channels for sodium, potassium, As compared to unmyelinated all the areas will chloride are delegated to the postsynaptic need ATP because of the ion channels. membrane and then they either open or close, they So, having myelinated also conserves energy. are either stimulated or inhibited by the neurotransmitters. Do neurotransmitters always activate action potential? No. It depends on what type of neurotransmitter it is, and what type of receptor there is. If the neurotransmitter opens sodium channels depolarization occurs because it causes the inside cetamine to be more positive or less negative. If the potassium or chloride channel opens it hyperpolarizes because your chloride ions which are negative contain and the positive potassium ions go out. so both of them go down their concentration gradient. Therefore, the action potential is generated. When there is an action potential (on the first circle), From the chapter of the cells extra cell uni-ions myelin sheets (first rectangle) don't have ion (means outside of the cell), sodium, calcium, channels, positive charges are getting bumped until chloride they reach the area (second circle), this area has ○ intracellular ions are mainly your ion channels. potassium, few sodium, few chloride, but What happens? mostly the negative ion proteins. TABANAO | 1NU02 10  Simplest reflex act don't include interneurons Neurotransmitters don't usually remain in the ○ When you touch something hot, the heat synaptic class indefinitely, it doesn't stay there. stimulates pain receptors in skin. Thus, Thus their effect on postsynaptic membranes are producing an action potential towards your short in duration. These substances are either sensory neurons (at the back). rapidly broken down by enzymes. ○ This conducts an action potential to the ○ ex. Enzymatic degradation - these happen spinal cord where it synapses with the also in the synaptic or they are transported interneurons and then towards the motor back into the presynaptic terminal. neuron, conducting action potentials to the flexor muscles (in the upper limb). These MOST COMMON NEUROTRANSMITTERS limbs then react by contracting and pulling Acetylcholine (Ach) the hand away from the hot object. Norepinephrine ○ Reflex arc doesn't go up the CNS. Acetylcholinesterase - enzyme that breaks down NEURONAL PATHWAY (CONVERGING) the acetylcholine and these products go back to the 2 or more presynaptic to one postsynaptic presynaptic terminal for recycling. ○ Aside from being broken down by enzymes, Norepinephrine can also be actively transported back into the presynaptic terminal. So this transfer of your transmitter occurs rapidly countless times per second and these are affected by numerous diseases on drugs. ○ so these are very fast REFLEX involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS. A converging pathway - simple pathway in which ○ This allows a reaction faster than two or more neurons synapse with the same conscious thought. postsynaptic neuron react to stimuli more quickly than conscious thought This allows information transmitted in more than occur in the spinal cord or brainstem(rather than the one neuronal pathway to converge into a single higher brain centers) pathway. REFLEX ARC NEURONAL PATHWAY (DIVERGING) ↑ presynaptic to 2 postsynaptic A reflex arc is the neuronal pathway by which a reflex occurs. basic functional unit of the nervous system because it's the smallest, also the simplest pathway capable of receiving a stimulus and then giving a response. A diverging pathway - (also a simple pathway) an axon from one neuron divides and synapses with more than one other postsynaptic neuron. This allows information transmitted in one neuronal pathway to diverge into two or more pathways. SUMMATION A single presynaptic action potential usually doesn't cause efficient postsynaptic local potential to reach a threshold, it's too weak. So obviously a single 1. A sensory receptor presynaptic action can't achieve a threshold and 2. A sensory neuron can't produce an action potential. 3. Interneurons (in some reflexes, located between and dominacating with two other neurons that's why How to achieve a threshold? it's called interneurons) ○ Many presynaptic action potentials are 4. A motor neuron needed, this is what you call summation. 5. An effector organ (muscle or glands) TABANAO | 1NU02 11  ○ Multiple subthreshold local potentials are added or integrated to cause a local potential enough to trigger an action potential. SPATIAL SUMMATION multiple inputs - Occurs when the local potentials come from different locations of the postsynaptic neurons. Multiple locations For example, converging pathways TEMPORAL SUMMATION single input but fired rapidly - It occurs when the local potential overlaps in time, like when a single input fires rapidly. The local Cervical, Thoracic, Lumbar, Sacra potentials then overlap briefly. Gray matter is a collection of neuronal cell bodies. The result of this summation depends on the type of It looks like an 'H' or a butterfly. signal given whether it is stimulatory or inhibitory. ○ Posterior horn that contains interneuron Only one location but action potentials fired rapidly. ○ Anterior horn contains Somatic motor neuron ○ Lateral horn is responsible for Autonomic THE NERVOUS SYSTEM Nervous System (ANS) ○ Central canal, the hole in the middle, is CENTRAL NERVOUS SYSTEM where your cerebral spinal fluid flows from Brain (located in skull) your brain. (CSF the fluid that protects spinal cord (located in vertebral column or spine) your brain) PERIPHERAL NERVOUS SYSTEM White matter is superficial. Nerves and ganglia outside the brain and spinal ○ consistent of myelinated axons (white cord because of myelin sheets. ○ 12 pairs of Cranial nerves Divided into three columns ○ 31 pairs of spinal nerves ○ Dorsal -posterior column ○ Ventral - anterior column SPINAL CORD ○ Lateral - contains ascending and Extends from foramen (hole, opening) magnum descending tracts (bake) to hole means Tract - there are axons in your (CNS) ○ foramen magnum is located at the base If it's in PNS the name is different. of the skull ↳ big ○ extends to the second lumbar vertebra and Ascending tract/pathway - up towards the brain ends in the conus (looks like a cone) Descending tract/pathway - going away from the medularis. brain ○ filum terminale - long tail or strand (part of the spinal cord). Cervical, Thoracic, Lumbar, Sacral, Coccyx communicates with the body through Spinal nerves. SPINAL CORD DIVERGING PATHWAYS from sensory neurons to ascending path (brain · For the muscle contraction to occur a stimulus must be present. This stimulus is picked up by the pain paying receptors and activates the sensory fibers and the sensory neurons carries the action potential towards the spine. The axons of the sensory neurons branch within the spinal cord. One branch produces a reflex by synapting in interneuron, then interneuron synapses to motor neurons without any stimulus coming from the brain, because it occurs without conscious talk This produces a jerking movement of the muscle away from the stimulus. Other branch carries action potentials synapses with the ascending neuron where it ascends towards the brain and the pain is perceived. TABANAO | 1NU02 12  Reflex- if the sensory neurons synapses it diverges Arise from numerous outlets (form the root where (one in the interneuron and one in the ascending they are located) tract, towards the brain) Spinal nerves allow movements and if it's damaged it can cause paralysis. CONVERGING PATHWAYS from drain to motor (descending) neuron Dorsal and Ventral roots join to form the Spinal When the interneuron synapses with the motor nerve. neuron to produce an action from the muscle (reflex ○ Dorsal root ganglion (swelling) arc); there are also signals coming from the ○ contains cell bodies Pseudounipolar cerebral cortex, this controls the conscious sensory neurons movement. These neurons also synapses with the Pseudounipolar axons have a peripheral branch same motor neuron, this is coming from the axons and an ascendal branch. This axon originated in the from the descending tracts. periphery or the side of the body and it passes ○ Motor neuron - can be stimulated by either through the spinal nerves up to the sensory neuron conscious thought or reflex arc. to the dorsal root and to the posterior horn where it synapses to the interneuron. Interneuron synapses REFLEXES to motor neurons pass through the ventral root out tomonosynaptic A stretch reflex occurs when muscles contract in to the spinal nerve towards the effector organ. response to a stretching force applied to them. (Reflex arc) The knee-jerk reflex, or patellar reflex is a classic If it passes into the white matter it either descends example of a stretch reflex. or ascends in your spinal cord. (where the Withdrawal reflex, or flexor reflex descending and ascending tracts are) ↳ poly synaptic The Dorsal area picks up the outside stimulus (sensory neurons), located in the back portion of the spinal cord) ○ ex: When someone wants to catch your attention they tap you on the shoulder from your back. And then you sense their presence. The motor neurons are located towards the Ventral or the anterior portion of the cord. ⑪ ○ ex: By shaking hands as a greeting, you offer your hand forward. Arise along the spinal cord from union of dorsal roots and ventral roots. Contain axons sensory and somatic neurons called mixed nerves Located between vertebra (spine) Categorized by region of vertebral column from which it emerges (C for cervical) KNEE-JERK REFLEX 31 pairs patellar (knee) ○ 8 pairs of Cervical roots leg bone (femur, long bone in the leg) ○ 12 pairs of Thoracic roots quadriceps femoris - rior anterior of thigh muscles, ○ 5 pairs of Lumbar roots flexor muscles ○ 5 pairs of Sacral roots flexor muscles: ○ 1 pair of Coccygeal roots ○ Semitendinosus ○ Organized in 3 plexuses ○ Semimembranosus ○ long and short head of biceps femoris (located in posterior) Once the patellar ligament is tapped with a hammer the interior muscles and its tendon stretched. Then reflex occurs. When quadriceps femoris muscle contracts it becomes shorter and then it lifts the lower leg forward. ○ when you tap your leg, you see your lower leg kick (knee-jerk reflex) Clinically, this is used as physical activity to test if the CNS is functional (descending neurons converge then synapse with the neurons of the DERMATOMES stretched reflex your inteneuron to modulate the activity for posture, coordination, etc.) What happens when you fall? And received a blunt trauma on your back. It becomes inflamed then causes damage to the spinal cord tissue. If the spinal cord tissue is damaged you lose all reflexes below the level of injury. Once it recovers it becomes hyper excitable. SPINAL NERVES Exits at cauda equina (looks like a tale) TABANAO | 1NU02 13  (sensory innervation in the skin ) C1 is the only spinal nerve that doesn't have sensory distribution to the skin. How do dermatomes supply the skin? ○ bend forward, stand in all force SPINAL PLEXUSES (GRADE) In these plexuses neurons from different spinal nerves and segments intermingle. For sensory neurons provide sensory innervation from the skin in that area,