Human Anatomy and Physiology Notes 3 PDF

Human Anatomy and Physiology Notes 3 Resting Membrane Potential Electrical potential difference across a cell membrane when the cell is at rest Outside of the cell is positively charged Inside of the cell is negatively charged We have proteins inside the cell that are negatively charg...

Human Anatomy and Physiology Notes 3 Resting Membrane Potential Electrical potential difference across a cell membrane when the cell is at rest Outside of the cell is positively charged Inside of the cell is negatively charged We have proteins inside the cell that are negatively charged and cannot leave the cell We have potassium inside the cell, which is positive, it essentially cancels out the charge of protein. Potassium can leave the cell through potassium leak channels o Potassium leak channels are slow opening and closing ▪ This is because voltage gated potassium channel only has one gate High concentration of potassium inside the cell and a low concentration outside the cell. We also have sodium leak channels, but sodium is more highly concentrated outside the cell, so it leaks in Sodium leak channels are extremely fast opening and closing o This is because voltage gated sodium channels have two gates We have more potassium leak channels than sodium leak channels Electrical gradient will attract the potassium back into the cell when the charge gets too negative Cells are 25-fold more permeable to potassium than sodium Electrochemical Gradient- the charge of inside and outside the cell. Concentration Gradient- has to do with the amount of each molecule inside or outside the cell. *Sodium potassium pump will pump 3 sodium's out for every 2 potassium's in Three Main Types of Ion Channels 1. Leakage (non-gated) channels a. Always open 2. Voltage Gated a. Part of a protein changes shape to open/close channel in response to changes in a charge. 3. Ligand Gated or Chemically Gated a. Part of a protein changes shape to open when ligand or substrate binds Membrane Potential Changes Used as Communication Signals Changes in membrane potential used as signals to receive, integrate, and send information. Changes produce two types of signals Graded Potentials o Incoming signals operating over short distance/start on dendritic side of axon o Can be excitatory or inhibitory Action Potential o Long distance signals of axons o Starts at axon hillocks Depolarizing signal is excitatory. If cell hits threshold at –55mV and it will trigger an action potential The further the potential gets from where it is bound the smaller and smaller the graded potential will get. It will open voltage gated sodium channels at the axon hillocks, sodium rushes in and it keeps happening all the way down the axon. Repolarization happens due to the opening of voltage gated potassium channels This causes the cell to be polarized because the positively charged potassium ion will flow out of the cell causing it to become more negative. Hyperpolarization- cells hyperpolarize when we let chloride in because chloride is negatively charged. Potassium channels cause hyperpolarization because the positive potassium flows out of the cell causing the inside of the cell to become more negative When we hyperpolarize a cell, it causes it to be further from threshold making it harder to create an action potential It is inhbibitory Characteristics of a Graded Potential 1. Hyperpolarizing or depolarizing 2. Decremental 3. Different magnitude 4. Short distance communication 5. Can be summated 6. Can trigger an action potential Action Potential and Ion Permeability Threshold- membrane potential that will trigger an action. Around –55mV Action potentials are always depolarizing, and you can never summate them What causes an action potential to happen is the opening of the voltage gated sodium channels at the axon hillocks. These channels open because of a large, graded potential from the dendritic side of the neuron. This is because the axon hillock has an abundance of voltage-gated sodium channels, which open when the membrane potential reaches a certain threshold. This positive feedback mechanism allows the action potential to move down the axon. At the axon terminus, voltage-gated calcium channels open, allowing calcium to enter the cell and stimulate exocytosis of vesicles containing neurotransmitters, which are then secreted into the synapse to communicate with the next neuron. Characteristics of Action Potentials 1. Generated from graded potentials that cause the cell to reach threshold 2. Action potential is always the same regardless of the magnitude of the stimuli. No summation 3. They are an all or nothing phenomenon 4. Are always excitatory 5. Are not decremental 6. We code for strength by action potential frequency. Called rated coding Refractory Periods Period where it’s harder for a neuron to provide an action potential Absolute Refractory Period- the cell cannot produce another action potential This happens because the voltage gated activation gates are still open and haven’t reset Relative Refractory Period- neuron can fire another action potential but it takes a larger stimulus since it’s further from threshold. This happens because the voltage gated activation gates have reset Propagation of Action Potentials Movement of an action potential down the axon The amount of neurotransmitter binding to the ligand gated ion channel determines the size of the action potential. If the potential is large enough, it reaches the threshold, causing voltage-gated sodium channels to open and sodium ions to flow into the cell, initiating an action potential. This potential then propagates down the axon due to a positive feedback loop involving voltage-gated channels. When the action potential reaches the axon terminal, voltage-gated calcium channels open, causing the release of neurotransmitters. These neurotransmitters can either excite or inhibit the next neuron, depending on the type of neuron. Hyperpolarization- where an inhibitory neurotransmitter makes it harder for a neuron to fire again. Events of an Action Potential 1. Voltage gated Na+ channels open 2. Na+ permeability of plasma membrane increases 3. Depolarization ends 4. Voltage gated K+ channels open 5. K+ permeability of plasma membrane increases 6. Hyperpolarization occurs Events of an Action Potential from Synapse ACh is released on the axon terminis and then binds to neurotransmitter receptor of the dendrites. This ion channel is opened which allows sodium in. This causes graded potentials. The amount of neurotransmitter that binds dictates how big the graded potential is. If the graded potential is big enough it will reach threshold and then open sodium channels at the axon hillocks. This causes propagation of the axon down the cell. When it reaches the axon terminis it opens voltage gated calcium channels which causes exocytosis on vesicles containing ACh. Post Synaptic Potentials Are synonymous with graded potentials. Excitatory Post Synaptic Potential – graded potentials that depolarize the cell. Inhibitory Post Synaptic Potential – graded potentials that hyperpolarize the cell. Some drugs hyperpolarize our neurons o Alcohol o Xanax Spatial Summation Action potentials 1 and 2 cause the production of graded potentials at two different dendrites. These graded potentials summate at the trigger zone to produce a graded potential that reaches threshold resulting in an action potential. Temporal Summation Two action potentials arrive in close succession at the presynaptic membrane. The first action potential causes the production of the graded potential that does not reach threshold at the trigger zone. The second action potential results in the production of a second graded potential that summates with the first to reach threshold, resulting in an action potential. Synapses Different neurons store their respective neurotransmitters in their axon terminis Adrenergic neurons store norepinephrine and epinephrine Cholinergic neurons contain ACh GABA – main inhibitory neuron neurotransmitter released from neurons in your central nervous system Controls memory, learning, and anxiety Gaba neurotransmitter receptor is a major pharmaceutical target for anti-anxiety medication. Inhibitory When GABA binds it opens its ligand gated ion channel which then allows negatively charged chloride to come in. Take it further away from threshold  *Alcohol acts like GABA Glutamate – major excitatory neurotransmitter released from CNS Will indirectly cause motor neurons to activate Has several different types of receptors o Calcium gated ion channels o Sodium gated ion channels Astrocytes mop up glutamate when its levels become too high Plays role in learning, memory, cognition Dopamine – important in controlling motor movement. It inhibits motor movement. Dopamine is the reward neurotransmitter that gives you motivation and euphoric feeling We know its inhibitory because of Parkinson's disease Cocaine – inhibits the reuptake of dopamine from the synapse. Also does it to norepinephrine and serotonin Norepinephrine Released from adrenergic nerves, these nerves are critical to our ability to learn and control behavior Excitatory neurotransmitter Aderol acts like norepinephrine Has alpha and beta receptors Serotonin Plays a big role in regulating mood, sleep, appetite, and sometimes body weight Main target for treating depression Has several different receptors so it’s hard to tell what it actually does. Autonomic Nervous System Sympathetic: Preganglionic neuron is cholinergic and shorter Postganglionic neuron is adrenergic and secretes NE Can be excitatory or inhibitory Parasympathetic: Preganglionic neuron is cholinergic and longer Target tissues are going to have muscarinic ACh receptors Can be excitatory or inhibitory The synapse in the autonomic nervous system is always excitatory Autonomic nervous system acts on organs, Glands, and smooth muscle Adrenal Gland: Secretes epinephrine The preganglionic neurons that go to the adrenal gland extend all the way to the gland. There is no post-ganglionic neuron Cholinergic Receptors: Two types of receptors bind ACh 1. Nicotinic ▪ Always excitatory ▪ Found on skeletal muscle ▪ On pre and post sympathetic and parasympathetic synapse 2. Muscarinic ▪ Located on target tissue ▪ Excitatory or inhibitory Adrenergic Receptors:  Two major classes 1. Alpha (a) [Subtypes a, a2] 2. Beta (B) [Subtypes B1, B2, B3] Effects of NE depend on which subclass of receptor predominates on the target organ Excitatory or inhibitory Located on the target tissue Role of Parasympathetic Division: Also called craniosacral division because cranial and sacral regions are where these nerves come from Role of Sympathetic Nervous System: All of the gangleons are connected Also called thoracolumbar Sympathetic Trunk Pathways: 1. Synapse at the same level (sympathetic trunk ganglion) 2. Synapse at a higher or lower level 3. Synapse in a distant collateral ganglion anterior to the vertebral column a. Adrenal gland The Endocrine System It controls growth and development, metabolism, and reproduction Important Terms: Endocrine glands o Gland that is going to secrete a hormone into the blood o Doesn’t have ducts o Form of long-distance communication Exocrine Glands o Glands that have ducts o Salvatory glands, some glands in pancreas Hormone o Typically released from endocrine glands o Chemical messages sent through the blood o Long distance communication Autocrine o Cell secretes a factor that acts on the cell it was secreted from ▪ Muscles Paracrine o Factor secreted from the cell that acts on neighboring cells Tropic Hormones – hormones that cause the secretion of other hormones  1. Pineal – melatonin 2. Hypothalamus – dopamine, tropic hormones 3. Pituitary – Growth hormone, tropic hormones 4. Thyroid – thyroid hormones 5. Parathyroid – parathyroid hormone 6. Thymus –DON'T NEED TO KNOW 7. Adrenal gland – epinephrine, cortisol, aldosterone 8. Pancreas – insulin, glucogen 9. Ovary – estrogen, progesterone 10. Testis – testosterone Hormones: Two main classes: 1. Peptide Hormones ▪ Made of amino acids and proteins ▪ Fast acting ▪ Bind to a recptor on cell surface 2. Steroid Hormones ▪ Made of cholesterol ▪ Not water soluble ▪ Need a carrier protein ▪ Typically, slow acting Hours to days ▪ Biond to intracellular receptor Target Cell Specifity Hormones go everywhere but only act on cells with their specific receptors  o All cells have thyroid hormone receptor Control of Hormone Release Endocrine glands stimulated to synthesize and release hormones in respones to: 1. Tropic hormone ▪ Growth Hormone releasing hormone ▪ Growth hormone 2. Humoral – blood effect, substance in the blood that will stimulate the release of a hormone ▪ Glucose levels ▪ Calcium levels 3. Nervous ▪ Sympathetic nervous system causes the release of epinephrine from the adrenal gland Pituitary Gland: Is connected to the hypothalamus Has two major lobes 1. Posterior Lobe ▪ Neural tissue that has neural connection ▪ Secretes ADH Hormone that helps conserve body water o Inhibited by caffeine and alcohol ▪ Secretes oxytocin 2. Anterior Lobe ▪ Glandular tissue ▪ Releases lots of tropic hormones like growth hormone ▪ Does not have a neural connection