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Mammalian Physiology

by: TCU2461

Mammalian Physiology 40403

Marketplace > Texas Christian University > Biology > 40403 > Mammalian Physiology

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About this Document

Cell signaling, membrane potentials, graded and action potentials, neurotransmitters, Nervous system structure
Mammalian physiology
Study Guide
Physiology, mammalian physiology, cells, membrane potential, action potentials
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This 6 page Study Guide was uploaded by TCU2461 on Sunday October 16, 2016. The Study Guide belongs to 40403 at Texas Christian University taught by in Fall 2016. Since its upload, it has received 15 views. For similar materials see Mammalian physiology in Biology at Texas Christian University.


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Date Created: 10/16/16
Notes 1 - Homeostasis: • Tendency for body to maintain balance within the internal environment, despite massive changes in external environment. • Mechanisms of changing due to environment: - Physiological - Behavioral - Feedback Loops: • Positive feedback loops: - to push the system away from the homeostatic set point (ex. childbirth, fever, blood clotting, breastfeeding) • Negative feedback loops: - bring system back to the homeostatic set point. - Achange in the system is recognized by the receptor (cells, tissue, organs). The receptor sends signal (input) to controller. The controller compares input to the system set point (checks if input is inside or outside the set point), if outside, sends signal (output) to the effector, which has a response (effect) which is intended to bring system back to set point. - EXAMPLES! - Cell Signaling: • Neural signaling • Endocrine signaling - Hormones which travel in the blood and must have a target cell • Paracrine signaling • Autocrine signaling • Acell’s response to a message depends on: - The chemical message • Lipophilic (nonpolar) • Hydrophilic (polar) - Concentration of chemical - Whether or not receptor is even present - Machinery inside of the cell • Lipophilic Messengers - These messengers can cross membrane and probably bind to receptors inside cell. Transcription factors regulate gene production and that is usually the result of a lipophilic message. • Hydrophilic Messengers - These messengers must bind to membrane-bound receptors since they can’t cross the membrane. The receptors include: • Ligand-gated ion channels • Protein kinase receptors - These have intrinsic enzymatic activity as they undergo autophosphorylation. - The general response is turing on of protein or enzyme • Janus kinase receptors - These have cytosolic proteins that posses enzymatic activity that phosphorylate - Usually, the result is the production of new proteins which is unique • GPCRs - α subunit binds to GDP and GTP— α subunit has higher affinity for GTP when signal is present. The α subunit turns on or off effector proteins. - EXAMPLES! Notes 2 - Membrane Potential • Unequal distribution of ions between interior and exterior of all cells creating a potential. • Resting membrane potential is negative for all cells ranging from -5 to -100 mV. • The more negative resting membrane potential the more excitable—this is because it’s easier to depolarize. • Resting membrane potential depends on two factors: - Differences in permeabilities of specific ions • Ion channels - Differences in specific ion concentrations in intracellular and extracellular fluid • Na and K channels are present in all cells and you will always have more K channels! There is a higher [K ] inside the cell! • + + + • Na /K ATPase pumps m+intain a low [Na ] within the cell. - Movement of K from inside to outside is re+ponsible for negative charge inside cell. Therefore, it is the more important ion (relative to Na ). <—IS THIS TRUE? • Two forces determine concentration of ions across membranes: - Electrochemical forces - Diffusive forces • Donnan Equilibrium describes how ions move across a semi-permeable membrane when such molecules are present. - Equilibrium Potential: • Equilibrium is reached when diffusive forces pushing ions in one direction are equal to electrical forces pushing ions in the other directions—no net movement of ions. • Nernst Equation (at 37ºC): - E ion (61/z) log ([ion]out/ [ionin) • Goldman-Hodgkin-Katz Equation: ⎛ ⎞ V = 61×log P KK ]out [NaNa+ P [out] Cl in m ⎝ PK[K ]inP [NNa]+ PinCl ] Cl out ⎠ - - Note that [Cl ] is flipped because of the negative charge Notes 3 - Chemical Synapses & Neurotransmitter Release • There is a depolarization of the terminal membrane which opens voltage-gated Ca channels allowing Ca to move IN to the cell. Ionotropic (ion channels) receptors are DIRECT activation while metabotropic (GPCRs) receptors • are INDIRECT and are therefore slower. Metabotropic are more prolonged, though. • The number of neurotransmitters in the synapse determines likeliness of signal being transmitted as well as how quickly. The strength of the signal depends on how much neurotransmitter is in synapse as well as for how long. • Autoreceptor: - will always bind to NT being released and is basically a negative feedback loop to slow down NT being released. Axo-axonic synapse: • - Neuron term2+al synapsing with another neuron terminal • The more Ca that moves in, the more neurotransmitter released • Typically excitatory NT: - Ach - Dopamine - Glutamate • Typically inhibitory NT: - Serotonin - GABA - Some endorphins • NTs binding to receptors on the post-synaptic cell can be stopped by: - Enzymatic activity - Reuptake (Ex. Serotonin channels) - Diffusion from synapse - Excitatory NTs result in opening of Na and K channels which causes depolarization of the post- synaptic cell. - Inhibitory NTs result in opening of K channels only and a hyper polarization of the post-synaptic cell. - Summation: The response of the post-synaptic cell to the NT is influenced by temporal and spatial summation • - Temporal summation: If signals on the cell are close enough in time - Spatial summation: Release of NT from two separate sources Notes 4 - Graded Potentials • Alterations in membrane potentials that are: - Local; they are restricted to a small region of the plasma membrane - Graded; they vary in magnitude deleting upon the stimulus - Typically the result from the activation of ligand-gated ion channels • The magnitude of a graded potential: - can be depolarizing or hyper polarizing - varies as a function of stimulus strength - decreases in magnitude over time - decrease in magnitude as they travel along the plasma membrane - Action Potentials • Alterations in membrane potentials that: - are greater in magnitude and are rapid than graded potentials - areALL or NOTHING; they do not vary in magnitude regardless of stimulus strength - propagate over long distances • Na channels: - Closed —> Open —> Inactivated • K channels: - Closed —> Open • PHOTO OFACTION POTENTIAL ON PAGE 2! • Absolute Refractory Period: - When Na channels are inactive. This prevents the potential from going backwards since by not allowing sodium to to move into the cell and create another action potential. No matter what magnitude of stimulus, no action potential ca be generated. Relative Refractory Period: • - Immediately after the absolute refractory period you can have an action potential, but the stimulus must be a little greater and the potential will be slightly lower. This period is still all or nothing! • λ = distance action potential (current) can travel before reduced by 63% - In order to have a high λ, you want to increase R mnd decrease+R. l • R m resistance across the membrane. They help keep Na inside membrane - To increase R m you can myelinate the membrane. • R l resistance along length of membrane. Related to cross sectional area - To decrease R,lyou need a larger diameter neuron. Notes 5 - Feed Forward: • The anticipation that a stimulus is coming (ex. smelling food begins digestive process) - Sensory Receptors • Free afferent nerve endings - Common in skin - Nociceptors - Some mechanoreceptors - Thermoreceptors • Sense organs - Collagen filled with fluid which allows for a wider receptive field compared to that of the free nerve endings. - Some mechanoreceptors • Sensory receptor synapsing with afferent neuron - Some chemoreceptors - Some mechanoreceptors - Some electromagnetic receptors - Receptor Potential • Agraded potential that occurs at the receptor membrane. • The magnitude of the receptor potential: - is proportional to the stimulus intensity - influences the frequency of action potentials - Transient Receptor Potentials + • Non specific cation channels, Na is important though because it depolarizes the cell. They have a gate that opens at specific temperatures and sometimes open upon binding to certain molecules. • Release glutamate as NT - Pain • Nociceptors have TRP associated with them, certain responded to extreme temp, pressure, chemicals. Once detected, ion channels open, Na cause depolarization, action potential that either release glutamate or Substance P NT. Post synaptic cell sends signal to CNS, which then releases pain relieving signal (Opiates—NT released—heorin and morphine are examples of these). Released into terminal end of axon releasing glutamate and substance P (Axo-axoninic cell). • Afferent pain fibers: - A-delta: fast and sharp pains - C-fibers: slow and dull pains - Gustation • Receptors - Salty receptors • Pleasant association with salt, because you need sodium for your body - Sweet receptor • Sugary foods provide energy, so your body likes them - Sour receptor/Bitter • Warning that the food is no good - Umami • Fatty foods rich in amino acids • Tongue —> Papillae —> Taste buds —> Taste cells - Olfaction • Olfactory bulb has olfactory receptor cells, on each recepter cells there is cilia that project from bulb into nasal cavity. Cilia is covered with olfactory receptors, signal goes to receptor cell, off to the nerve, then CNS. • Shape theory - Shape of odorant determines whether or not olfaction receptor is activated • Vibrational theory - Odorant can fit in the receptor (it has the same shape) but it does not chemically bind to receptor. Instead, it’s the vibrational frequency of the complex that sends the signal. This is why two molecules that are very similar in structure can give very different odors. • The combination of shape and vibrational frequencies allow for the smell of specific odors! - The number of pseudo genes determines how many things we can smell. Because we have so many pseudo genes, means we can’t smell as many things (unlike dogs). - The pattern and timing of binding of odorant molecules determines what smell we smell. - ReceptorAdaptation • Sensory receptors are prone to adaption which makes them less sensitive to a stimulus. They can either be: - Slowly: • in response to a constant stimulus, receptor potential increases, then decreases gradually over time. • Ex. receptor allowing you to monitor posture - Rapidly: • in response to a constant stimulus, receptor potential increases, then decreases rapidly. Some rapidly adapting receptors will also generate a receptor potential when stimulus is removed. • Monitors things if we need to know there is a quick change • Ex. wearing a watch or clothes. - Sensory Coding • Three types of information from the receptor that is coded and transmitted to the CNS: - Stimulus modality • the type of stimulus; the five senses - Stimulus intensity • basically spatial summation; the higher the intensity, the more action potentials generated - Stimulus location • Convergence - Not very precise; more convergence = less precision • Site of receptive field - The smaller the receptive field, the more precise you are figuring where the stimulus came from • High density of receptors in receptive field = more precision • Lateral Inhibition - adjacent neurons influences one another to transmit signals Pre-lecture - Components of Nervous System • Receptors - Somatic sensory = position, touch, pressure, temperature - Special sensory = four senses besides touch - Visceral sensory = status of internal organs • Sensory division of PNS - Delivers information from receptors to CNS via afferent neurons • Central Nervous System - Process, integrate, and distribute information • Motor Division - CNS sends commands to peripheral tissue via efferent neurons - Somatic Nervous System • Skeletal muscles - Autonomic Nervous System • Parasympathetic - Rest and digest (slows heart, stimulates digestion, contracts bladder, etc.) • Sympathetic - Fight vs. flight (accelerated heart, dilated pupil, inhibit digestion, etc.) - Parasympathetic Nervous System • Neurons originate from cranial (brainstem) and sacral regions of CNS. • Ganglion lie closer to effector organ. • Postganglionic region are less branched. - Sympathetic Nervous System • Neurons originate from cervical, thoracic and lumbar part of spinal cord. • Ganglion lie close to spinal cord. • Postganglionic neurons are highly branched meaning that they can affect multiple effectors.


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