24-25 Stu Nervous System Part 2 PDF

Protection of Brain The Brain is protected by 4 Main Parts: 1. Bone (skull) 2. Membranes (Meninges) 3. Cerebrospinal Fluid 4. Blood Brain Barrier Meninges 3 Connective Tissue membranes that lie externally to the CNS. Fxns: ❖ Cov...

Protection of Brain The Brain is protected by 4 Main Parts: 1. Bone (skull) 2. Membranes (Meninges) 3. Cerebrospinal Fluid 4. Blood Brain Barrier Meninges 3 Connective Tissue membranes that lie externally to the CNS. Fxns: ❖ Cover/Protect CNS ❖ Protect Blood Vessels/ Enclose Venous Sinuses ❖ Contain Cerebrospinal Fluid ❖ Form Partitions within the skull  Meninges (cont’d) 3 Types of “Meninx” (Meninges): 1. Dura Mater 🡪 “Tough Mother”; outermost layer. Strongest of Meninges; double layer sheet of fibrous tissue; encloses dural sinuses that collects venous blood from the brain & directs it into the Jugular Vein of the neck. 2. Arachnoid Mater 🡪 middle, web-like, loose brain covering; filled with cerebrospinal fluid; contains the largest blood vessels serving the brain 3. Pia Mater 🡪”Gentle Mother”; innermost layer composed of delicate connective tissue & richly invested tiny blood vessels; ONLY MENInX THAT CLINGS TO BRAIN WITH EVERY MOVEMENT!!! Cerebrospinal Fluid Found in & around brain & spinal cord Forms a liquid cushion = buoyancy to CNS organs Fxns: 1. Reduces Brain weight by 97% (prevents it from crushing itself) 2. Protects Brain & Spinal Cord from blows/ trauma 3. Helps nourish the brain/ carry chemical signals CSF Interesting Facts… Adults 🡪 Total CSF volume = 150mL (about ½ a cup); Replaced every 8 hours = 500mL of CSF formed EVERY DAY!!! What Happens if you CANNOT Drain CSF? Hydrocephalus 🡪 “Water on the Brain” Babies 🡪 skull bones haven’t fused yet Adults 🡪 Tumor, Brain Damage, Trauma, etc. Solution? Inserting a shunt into brain ventricles that drains fluid into neck Blood Brain Barrier Maintains Homeostasis/ stable environment for the brain Prevents brain exposure to blood-borne substances (i.e. various ions – K+, waste, drugs, & other toxins) that may “Over-excite” neurons. EXTREMELY SELECTIVE, with the help of tight junctions BUT… Ineffective against fats, fatty acids, O2, & CO2 🡪 THUS, nicotine alcohol, and anesthetics affect the brain! But did you know… Stress contributes to increased permeability of BBB, as well as the slight breakdown of the BBB. There are some areas of the brain where the BBB is ABSENT! 1. Vomiting Center of Brain Stem, which monitors blood for harmful substances within the brain 2. Hypothalamus, which regulates water balance, body temperature, and many metabolic activities 3. Newborns – contain incomplete BBB, which could lead to harmful substances entering the brain. 4. Pituitary - needs to secrete hormones into the bloodstream Trauma Head Injuries are the leading cause of accidental death in the US! Brain damage is NOT only localized (i.e. blow to the head), but also caused by the ricocheting effect (i.e. shaking of brain). Two Main Types: Concussions – slight brain injury; mostly mild/short-lived; results in dizziness, “seeing stars”, brief loss of consciousness, but usually no permanent neurological damage*** Contusions – brain tissue destruction; eventually loses consciousness (COMA) for many hours and perhaps, even a lifetime ☹ Trauma (cont’d) Following a head blow, death may result in Subdural or Subarachnoid Hemorrhages Bleeding of ruptured blood vessels into these meningeal spaces. Accumulating blood = ⇑ intracranial pressure = compression on brain tissue = force of brainstem, into foramen magnum = ⇓blood pressure, ⇓ heart rate, ⇓ respiration = death ☹ Solution🡪 Surgery to remove Hematoma, and repair of blood vessels Cerebral Edema Swelling of the brain Caused by increased water uptake of brain Solution 🡪 Anti-inflammatory drugs (prednisone) & other steroids to help reduce injury aggravation. Trauma (cont’d) Video Trauma: Cerebrovascular Accidents (CVAs) AKA 🡪 Strokes or Brain Attacks Most common nervous system disorder & 3rd leading cause of death in the US! Strokes 🡪 blood circulation to brain is deprived/blocked (ischemia) & brain tissue dies. MOST COMMON CVA = blockage of a cerebral artery by a blood clot Other causes include 🡪 compression of brain tissue by hemorrhage or edema OR progressive narrowing of brain blood vessels. 80% die from initial Cerebral Hemorrhage CVA attack; Survivors = partial paralysis (one side; may affect language, speech, etc.) Patients with CVAs caused by blood clots, usually have reoccurring clotting problems Solution Anti-inflammatory drugs (prednisone) & other steroids to help reduce injury aggravation.  NOTES: NERVOUS SYSTEM Key Characteristics of Nervous System Functions of Nervous System Divisions of Nervous System & Key Parts Neurons Key Characteristics of the Nervous System… Master controlling and communicating system of the body Controls behavior, thought, actions, and emotions Cells communicate by electrical signals, which are rapid, specific, and cause immediate responses  3 Main Functions of Nervous System: 1. Sensory Input: Driving 🡪 See a red light (stimuli) 2. Integration – Red light = Stop 🡪 Nerves INTEGRATE information 3. Motor Output – Activates effector organs 🡪 muscle in foot hits the brake = MOTOR INPUT Divisions of Nervous System 2 main Divisions: 1. Central Nervous System (CNS) 2. Peripheral Nervous System (PNS) Division I: Central Nervous Sys. (CNS) Made up of BRAIN & SPINAL CORD Integrating & Command Center of Nervous System Interprets incoming sensory info & dictates motor movement Division II: Peripheral Nervous System (PNS) Nervous Sys. Outside of CNS 🡪 nerves extending from Brain & Spinal Cord Cranial Nerves – to & from brain Spinal Cord Nerves – to & from spine Two Divisions of PNS: 1. Sensory Afferent Division – brings information toward the CNS from sensory receptors (i.e. skin, skeletal muscles, joints, etc.) 2. Motor Efferent Division – transmits info away from CNS to effector organs…causing an effect! (**Efferent = Exit) The Motor EFFERENT Nervous system is broken up into 2 Groups: 1. The Somatic Nervous Sys. – transmits motor nervous signals from the CNS 🡪 skeletal muscle; also called voluntary nervous system b/c = voluntary movement! 2. The Autonomic Nervous Sys. – transmits motor nervous impulses from CNS 🡪 smooth muscle, cardiac muscle, & glands; autonomic = automatic = movement that CANNOT be controlled (involuntary)! The Autonomic “ INVOLUNTARY” Nervous Sys. (ANS) is divided into 2 subdivisions:  2 Types of Autonomic Nervous Systems: 1. Sympathetic Nervous System – known as “Fight or Flight” response; mobilizes motor movement during an emergency 2. Parasympathetic Nervous System – known as the “Rest & Digest” response; conserves energy, promoting non-emergency functions of the body Your Nerves are similar to every other cell in the body… Made up of a main cell = Neuron excitable sends signals/communicates (neurons, muscles, glands) Made up of supporting cell structures = Neuroglia or “Glial Cells” Most abundant type of cell in nervous tissue  Glial Cells: Astrocytes Astrocytes are the most abundant, versatile, and highly branched glial cells. There are twice as many astrocytes as there are neurons. They cling to neurons and their synaptic endings, and cover capillaries making sure neurons get all the nutrition they need. Figure 11.3a Microglia and Ependymal Cells Microglia – small, oval shaped cells with spiny processes They are phagocytes (cells that engulf things) that monitor the health of neurons Ependymal cells –line the cranial cavity and central canal of the spinal cord. They produce and circulate cerebrospinal fluid Figure 11.3b, c Oligodendrocytes, Schwann Cells, and Satellite Cells Oligodendrocytes and Schwann cells: branched cells that wrap nerve fibers to insulate nerve impulses. Oligodendrocytes are found in the CNS Schwann cells are found in the PNS Satellite cells are similar to astrocytes in the CNS. They make sure the cell bodies have all the chemicals, etc. they need. Figure 11.3d, e Oligodendrocytes vs Schwann Cells Your Nerves are similar to every other cell in the body… Neuron Made up of 3 Main Sections: 1. Cell Body 2. Dendrites 3. Axon (dark part = nucleus) Cell Body (Soma) Contains transparent, spherical nucleus, with nucleolus Contains usual organelles, minus centrioles Most neuronal cell bodies are located within the CNS, and are protected by bones & vertebrate. Cluster of cell bodies in the CNS = nuclei Fewer collections of bodies in the PNS = ganglia Dendrites Branch-like extensions from the cell body that receive electrical messages from other neurons Many dendrites in the brain receive specialized information These messages are NOT nerve impulses, but GRADED POTENTIALS (short distance signals sent between nerve cells) Axons long “tail” from the cell body over which electrical signals are passed/ transported Axons vary in length, with the longest traveling from 3-4 ft to control your big toe! Myelin Sheath In PNS, made of Schwann Cells wrapped around axon. Waxy/fatty coating - protects signal from being lost If nervous tissue is myelinated, then called WHITE MATTER If unmyelinated, then called GRAY MATTER In CNS, Oligodendrocyte Cells provide insulation and protection for axons in the white matter. These are like Schwann Cells, but in the CNS and they can attach to multiple axons at a time where Schwann cells can only attach to the axon of one neuron in the PNS  Myelin Sheath If myelinated, then electrical signals pass more rapidly down an axon. Signals jump from the indentation between cells to the indentation between the next two cells. What is the name of the indentation? In Multiple Sclerosis (MS), the body attacks and removes the myelin sheath from the nerves. Slows signal transmission. Other nerves try to pick up the slack, but ultimately cannot replace all the damaged neurons. Label: axon, myelin sheath, dendrite, Node of Ranvier, cell body, nucleus, Schwann Cell, axon terminal Action Potentials & Synaptic Transmission  So where is all of this “electricity” coming from? Electricity in the body is known as a Transmembrane Potential (membrane potential) This is the potential energy generated by the separation of positive & negative charges, both inside & outside of the cell membrane. These “charges” are caused by IONS. Cells of the body are POLAR, this means they carry a slight charge Intracellular Fluid contains high amounts of Potassium (K+) & LARGE proteins with a negative charge; thus the inside of the cell is NEGATIVE!!! Extracellular Fluid contains high sodium (Na+) & small amounts of chloride (Cl -); thus the outside of the cell is POSITIVE.  Cell’s Makeup Na+ Na+ Cl- K+ Na+ Cl- PRO- K+ Na+ K+ PRO- Na+ PRO- PRO- Na+ -70 mV Na+ Na+  So what does this mean? The inside of the cell membrane contains a slightly negative charge, when compared to the outside! This charge is -70mV (millivolts are 10-3 volts)  What controls this “happy charge” of the cell? ACTIVE TRANSPORT!!! The Sodium Potassium Pump is a protein that pushes these ions AGAINST their concentration gradient (movement of particles from L 🡪 H concentration). For every 2 K+ moved into the cell; 3 Na+ ions are pushed out! Remember there is more K+ inside the cell, so if you move K+ inside (where it is highly concentrated) you are going against the concentration gradient (moving L 🡪 H…thus ACTIVE TRANSPORT!!!)  The change in the Membrane Potential (Electricity) is influenced by different Ion Channels in the Cell Membrane 1. Leak (passive) Channels always open 2. Gated Channels Chemically Regulated Channels Voltage-Regulated Channels Mechanically Regulated Channels  Chemically Regulated (Controlled) Channels: Chemicals, such as neurotransmitters (NTs), bind receptors and trigger proteins to allow ions in/out of cell Ex. AcH & muscle cell receptors Allows sodium in (positive ion) Sodium carries a positive charge with it this changes the membrane potential to be less negative and more positive (depolarization) Chemically Regulated Ion Channel  Two other Gated Channels Voltage-Regulated Mechanically-Regulated Channels Channels Open in response to Open and close in distortion in the response to membrane changes in the Nerve receptors for voltage - slow to touch and pressure open and close - once the membrane gradient is more positive, sodium channel shuts, this allows voltage gated potassium channels to open and K+ out of the cell, making the intracellular more negative (repolarization) Action Potentials = spread of electricity!!! Changes in the transmembrane potential that is spread over excitable membranes STEP 1: Depolarization Some stimulus hits the initial segment of a nerve This then causes a shift and allows small amount of Na+ into the cell Transmembrane potential rises from -70mV to threshold value (usually -60 to -55mV) When a charge becomes more + = Depolarization! STEP 2: Repolarization Once cell hits threshold, Na+ voltage-regulated channels open Large rush of Na+ into cell Interior voltage rises to +30mV Inactivation gates on Na+ channels close K+ voltage-gated channels are opening and allowing K+ to moves out of the cell Driven out of the cell by the flood of + charges brought by the Na+ and the concentration gradient Drops interior voltage back toward -70mV Step 3: Hyperpolarization Na+ channels remain inactivated until about -60mV Na+ channels stay closed, but capable of reopening status K+ channels start to close at about -70mV, but can’t close fast enough, so K+ moves out and drops interior of cell to -90mV (hyperpolarization) Gates return to normal position and cell goes to -70mV (this is the transmembrane/ resting potential)  Facts about Action Potential An action potential doesn’t get bigger with a bigger stimulus….it is all or nothing (It either happens or it doesn’t) What does change is the frequency of the action potential. – more pain=more frequent transmission Step 1: Review Draw and label a neuron with the markers at your table. Use these terms: Nucleus, axon, nodes of ranvier, dendrites, axon terminals, cell body, myelin sheath Step 2: Connect a Neuron Add a second neuron and show where synaptic transmission is occurring Step 3: What is resting potential? Resting Potential is???? Draw and describe WHILE watching the video Step 4: Voltage Gated Ion Channels Draw and describe what an ion channel is. Action potential summarized Stimulus occurs, small Na+ enters cell. Now more positive. (From resting potential changes due to stimulus from graded potential) Once threshold reached=Na+ voltage channels open and Na+ floods in. (Depolarization) Now positive over all. Na+ channels close and K+ channels open to allow K+ to leave = making more negative. (repolarization) Once about -70mV, K+ close slowly until about -90mmV (hyperpolarization) and then goes back to -70mV (back at resting potential) What does an action potential graph look like? Step 2 Step 3 Step 1 Step 4 Action Potential graph with ion movement pictures  Label the graph hyperpolarization, depolarization, resting potential/state, threshold, repolarization, action potential, refractory period  Label the graph Now add in where the stimulus would be. Also add in the correct mV in the correct spots. Also add in where Na+ in and K+ out) Action potential graph and what is happening at each step. Hyperpolarization  Breakdown Graph vs Cell Membrane  Synaptic Transmission Within the same neuron: Voltage Gated As Sodium floods into the first section of the nerve, it diffuses down the axon, carrying a positive charge As the positive charge flows down the axon, threshold value is reached At threshold, the sodium gates open and the action potential happens in this next section of neuron In this way, the action potential is passed down (propagated) the entire length of the neuron Transmission down a Neuron  Chemically-Regulated Chanel From one neuron to the next: When the action potential reaches the synaptic knobs, the vesicles fuse with the membrane and dump their neurotransmitter into the synapse The neurotransmitter flows across synapse to the next neuron’s dendrites and triggers them to rise to threshold Action potential flows down the “new” neuron Step 5: Action Potential Draw and describe what is happening in the video. Give a summary of what an action potential actually is.  What do you think action potential is? The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell. Transmission between Synapse Propagation of Action Potential in Myelinated neurons vs Unmyelinated neurons  Neurotransmitters 🡪 Chemical messengers between nerve cells ☺ Different nerves use different neurotransmitters Brain uses serotonin, dopamine, etc. Muscles use acetylcholine Imbalance in brain neurotransmitters has been linked to mental disorders, such as anxiety and depression  Neurotransmitters of the Brain Excitatory neurotransmitters are chemicals that increase the likelihood of a neuron firing an action potential, essentially “exciting” the neuron and promoting signal transmission. Inhibitory neurotransmitters decrease the likelihood of a neuron firing, essentially “calming” the neuron and preventing further signal transmission.  Neurotransmitters of the Brain 1. Dopamine – pleasure system; roles in behavior and cognition, voluntary movement, motivation and reward, inhibition of prolactin production (involved in lactation), sleep, mood, attention, and learning * more of a neuromodulator-has both excitatory and inhibitory effects 2. Serotonin – controls mood, consciousness/sleep, depression, and anxiety; only 1-2% is found in the brain (originating from brainstem neurons); influences the functioning of the cardiovascular, renal, immune, and gastrointestinal systems; partly responsible for certain manifestations of schizophrenia, depression, compulsive disorders, panic attacks and learning problems. Also controls how you feel pain 3. Glycine – Inhibitory neurotransmitter found only in vertebrates; released into synapse allowing Cl- to enter the nerve cell; it hyperpolarizes the synaptic membrane, making it less likely to depolarizes, when attempting to deliver a nerve impulse. Participates in processing of motor & sensory info for movement, vision, audition  More NTs…. 4. Gamma-aminobutyric (GABA) - inhibitory neurotransmitter that blocks certain nerve signals from passing on the message to the next neuron. (calms the nervous system down) This is so you don’t become overly anxious, afraid, etc. Helps regulate mood. Abnormal fluctuations of GABA are found in Parkinson’s, epilepsy, schizophrenia, depressive disorders, anxiety, Huntington’s, etc 5. Aspartate (Aspartic Acid)- excitatory neurotransmitter localized in the spinal cord, which increases the likelihood of depolarization in the postsynaptic membrane (does the opposite of glycine) 6. Glutamate (Glutamic Acid) - most common neurotransmitter in the brain; excitatory, usually due to simple receptors that increase the flow of positive ions by opening ion-channels; key role in long-term potentiation (increase in strength of nerve impulses along pathways - at the synapse - that have been used previously) and is important for learning and memory. The correct level of glutamate is important. Monosodium glutamate(MSG) is a flavor additive used in foods that increases this level and can cause issues for some people. Headache, chest pain, fluttering heartbeats, etc)