FOUNDATIONS OF PHYSIOLOGY Biology The scientific study of living things How do we know if a thing is a living thing? Life is a process or function, not a substance Characteristics of living things - Organization - Homeostasis - Grow - Adapt/evolve - Reproduce - Require energy and nutrients Homeostasis Process by which organisms maintain equilibrium or internal constancy (temp, bp, blood sugar, pH, water balance) Physiology The study of the processes or functions of organisms Levels of organization - Atom - Molecule - Cells - Tissues - Organ - Organ system - Organism Molecules Assemble into cell structures, regulate cell functions, and catalyze cell reactions Cells Smallest units capable of carrying out the processes of life Tissue Group of cells with similar structures and functions Four types of tissue 1. Epithelial 2. Connective 3. Muscle 4. Nervous Organ Two or more types of tissue organized to perform a particular function Organ system Collection of organs performing related functions and interacting to accomplish a common activity Negative feedback main regulatory mechanism for homeostasis - Occurs when a change in a variable triggers a response that opposes the change - Delayed response Sensor Measures the variable Integrator Compares with set point/ideal Effector Makes corrective response Anticipation/feedforward control Reduces delay and helps overcome fluctuations Anticipator Predicts and counters oncoming disturbance before regulated state is changed Positive feedback output is continually enhanced so that the variable continues to move in the direction of change - occurs when rapid change is needed because homeostatic set point is no longer appropriate - eventually a trigger will end the positive feedback loop - EX: birth Whole body systems Regulate and coordinate homeostasis and other functions for the good of the whole body Nervous system - for activities requiring swift responses - detects external environment changes - Coordinates complex "higher" functions like learning, memory, and consciousness Endocrine system - for activities that require duration rather than speed - Controls internal environment and reproductive cycles Support and movement systems Protect from harm, obtain food, reproduce, etc Skeletal system - support and protection for organs - Enables movement Muscular system - enables movement - Temperature regulation Maintenance systems Maintain the internal environment/homeostasis Circulatory system Transports nutrients, gases, hormones, etc. Around the body Respiratory system - gas exchange - Maintains proper ph Immune system - defends against foreign invaders and cancerous cells - Repairs or replaces injured and old cells Excretory system Removes excess water, salts, acids, and wastes Digestive system - breaks down food to absorbable nutrients - transfers water and salts to internal environment - Eliminates undigested food Integumentary system (hair, skin, and nails) - regulates body temp - Protective physical barrier keeping out microorganisms and keeping in internal contents Reproductive system - produces gametes - delivers gametes - embryo and fetal development - Produces milk MEMBRANE PHYSIOLOGY Cell membrane - encloses cell - maintains differences in ion concentrations inside and out of cells - permits specific substances to pass in and out - Provides surface interactions for cell-to-cell communication Cell membranes have three components 1. Phospholipids 2. Cholesterol 3. Proteins Phospholipids Have hydrophobic and hydrophilic regions Lipophilic (Hydrophobic) repel water Phospholipid bilayer Phospholipid Unsaturated fatty acids Saturated fatty acids Cholesterol Increase fluidity (more flexible) Decrease fluidity (stiffer) Temperature Proteins Some molecules wiggle through on their own Some molecules cannot wiggle through on their own Passive transport Passive transport examples Simple diffusion Facilitated diffusion Cells have watery insides and watery outsides, so phospholipid tails clump in such a way that two layers are formed shape only take their shape because of the clumping of the tails - Constantly moving and wiggling around, exchanging places millions of times per second - This accounts for the membrane's fluidity - don't line up well - Makes phospholipids more flexible/fluid - stack well - Makes phospholipids stiffer hydrophobic lipid that animals make - Wiggles in with the hydrophobic tails to make the cell membrane less fluid (stiffer) - use unsaturated fatty acids - Use no or very little cholesterol - use saturated fatty acids - Use plenty of cholesterol - heat = more fluid - cold = less fluid - cold environments use unsaturated fats - Warm environments use cholesterol - channels/pores or carriers for transport - receptors for communication - enzymes for chemical reactions - adhesion proteins for anchoring and attaching cells - Recognition proteins - Small molecules (water, co2, o2) - Hydrophobic molecules (lipophilic molecules, caffeine, alcohol, hormones, vitamins) - Hydrophilic molecules (sugars, salts) need transport proteins - Large molecules (polysaccharides) need vesicular transport the movement of substances across a cell membrane without the use of energy by the cell - Move down high to low - Simple diffusion - Facilitated diffusion - Osmosis movement of a solute from an area of high concentration to an area of low concentration - O2 in, CO2 out - Wiggle across phospholipids the transport of substances through a cell membrane along a concentration gradient with the aid of transport proteins Osmosis Tonicity Isotonic solution Hypertonic solution Hypotonic solution Isotonic solution Hypertonic Hypotonic Energy-requiring transport Active transport Vesicular transport Cell-to-cell communication Direct cell communication Surface markers Nanotubes Messenger ligands Paracrines - Take up salts and electrolytes Diffusion of water through specialized aquaporins The relative concentration of solutions that determine the direction and extent of osmosis Has the same concentration of nonpenetrating solutes as normal cells A solution in which the concentration of solutes is greater than that of the cell that resides in the solution A solution in which the concentration of solutes is less than that of the cell that resides in the solution No net flow Water flows out, cell shrinks Water flows in, cell expands movement of substances either against their concentration gradient (low to high) or using vesicles - Energy required Use of a protein and energy (ATP) to move molecules against their concentration gradients Allows large things to enter (endocytosis) or leave (exocytosis) the cell Communicate through direct contact or indirectly through extracellular chemical messengers gap junction tunnels that bridge two cells - Allow small molecules and ions to be shared - Especially important for electrical signals (ions) in excitable cells (like neurons) allow for direct linkup between cells - Allows for recognition - Especially important for immune system to recognize and destroy cells that aren't our own cytoskeletal extensions that allow transfer of molecules and also whole organelle - Found between developing mammalian immune cells - paracrines - neurotransmitters - hormones - neurohormones - pheromones - Cytokines local chemical messengers that only affect cells in immediate environment - Rely on diffusion Neurotransmitters Hormones Neurohormones Pheromones Cytokines Intracellular cascades Lipophilic molecules Lipophobic molecules Nuclear receptors Three means of signal transduction upon binding Opening or closing chemically/ligand gated membrane channels Activation of an enzyme that in turn activates a protein Transferring signal to an intracellular chemical messenger molecules used by neurons (brain/nerve cells) to communicate directly with their very close, specific target cells - Released in response to electrical signals - Targets can be other neurons, muscles, or glands long-range messengers secreted into circulation by glands to effect cells at a distance - Only target cells will have appropriate receptors/receive the message Released by neurons in response to electrical signals (like neurons) but are released into blood stream to affect distant target cells (like hormones) released into the external environment and travel through air or water to sensory cells in another animal - Often used for social interactions such as sexual activity and marking territory can have local or distant effects but are not produced by glands - Made by almost anybody cell, generally involved in development and immunity when activated, receptors trigger a biochemical chain of events inside the cell called signal transduction - 2 mechanisms: lipophilic and lipophobic molecules Enter the cell by moving through the membrane Cannot enter the cell and must bind to receptors on the cell surface Receptor recognizes a particular promoter sequence and starts transcription (building new proteins/changing gene expression) 1. Opening or closing chemically/ligand gated membrane channels 2. Activation of an enzyme that in turn activates a protein 3. Transferring signal to an intracellular chemical messenger - "second messenger" regulates movement in and out of the cell - Especially important for ion movement, which causes electrical conduction in brain muscle cells some receptors have a protein kinase enzyme associated which activates other proteins - Common molecules that use this pathway = insulin and growth factors this in turn triggers a cascade of events - Second messenger Amplification of a second-messenger pathway Two categories Antagonists Agonists Membrane potential The majority of the ICF and ECF is electrically neutral and the membrane itself is not charged All cells have a slight excess of positive charges outside and negative charges inside Some excitable cells (brain and muscle) can produce rapid changes in membrane potential when excited Equilibrium potential for K+ G-protein coupled receptor, g protein, second messenger (most common = camp), protein kinase, designated protein 1. cAMP 2. Ca+2 (through DAG and IP3 pathways) 3. cGMP It only takes a small amount of the original messenger to bring about dramatic effects 1. Antagonists 2. Agonists block a step or receptor in a signaling pathway - EX: Viagra blocks the second messenger pathway that restricts blood flow (allowing more blood flow) enhance a step or activate a receptor - EX: heroin and morphine are agonists of opioid receptors (mimicking endorphins) separation of charges across the membrane - Measured in millivolts (mv) - Opposite charges attract each other, causing them to line up against membrane - Na+ and Cl- ions = high outside in ECF - K+ ions = high inside in ICF the magnitude of the membrane potential depends on the number of charges separated - As more separated charges are lined up, the membrane potential rises - Resting membrane potential is negative - Main ions: Na+, K+, and A- A- is a negatively charged intracellular proteins - A- too large to cross membrane, but Na+ and K+ can move through channels if open - K+ is extremely permeable (crosses easily) - The opening of ion channels (transport proteins for ions) to allow Na+ and K+ to flow will quickly alter the resting membrane potential - -90mv - Inside negative relative to outside - If membrane was fully permeable to K+, it would flow out of the cell down concentration gradient - Cell would become more negative because of A- Now K+ is attracted to negative inside and starts to flow back inward down the electrical gradient Nernst equation When the electrical and concentration gradients counterbalance, no net movement occurs = equilibrium potential for K+ eion= 61/z log co/ci Equilibrium potential for Na+ 61 = a constant Z = ion's valence Co = concentration outside Ci = concentration inside Equilibrium potential for Na+ +61mv If membrane was fully permeable to Na+, it would flow into the cell down concentration gradient - Outside becomes more negative because of Cl- But now Na+ is attracted to negative outside and starts to flow back out down the electrical gradient Goldman-hodgkin-katz equation Vm = 61log((pk[k]out+pna[na]out)/(pk[k]in+pna[na]in)) Counterbalancing passive leaks and active Resting potential is not at K+ or Na+ equilibrium, pumping at resting membrane potential so both leak - Continually, K+ leaks out, Na+ leaks in - K+ more because it's so permeable - Na+ more slowly because it's less permeable NEURONAL PHYSIOLOGY Excitable cells Undergo rapid, short-lasting changes in membrane potential Two main types of excitable cells 1. Neurons 2. Muscle cells Neurons Use change in potential to receive, process, initiate, and transmit signals Muscles Use change to contract Polarization Membrane potential other than 0 mv Depolarization Decrease in potential; membrane less negative Repolarization Return to resting potential after depolarization Hyperpolarization Increase in membrane potential; membrane more negative Two main techniques of measuring membrane 1. Microelectrodes potential 2. Patch clamping Microelectrodes Can be inserted into a neuron with little damage; can directly measure voltage - Can also be paired with a voltage clamp technique: membrane potential is held at a constant and specific value - Patch clamping Electric signaling Leak channels Gated channels Four types of gated ion channels Voltage-gated channels Ligand-gated (chemically gated) channels Mechanically-gated channels Thermally-gated channels Channel opening results in one of two forms of electrical signals Graded potentials Stronger event Longer duration of event Current Graded potentials are Allows researchers to measure which ions move in which direction at any given voltage A single tiny pipe gets attached to membrane with gentle suction - Allows measurement of a single ion channel - Can also add substances to pipe the (to block or activate receptors and channels) Generated by ion movement across the membrane - Changes in ion movement are brought about by changes in membrane permeability in response to a triggering event Non-gated and open all the time - Contribute to resting potential Opened or closed in response to a stimulus; changes membrane potential 1. Voltage-gated 2. Ligand-gated 3. Mechanically-gated 4. Thermally-gated Open and close in response to changes in membrane potential; crucial for neural signaling Open or close in response to a specific chemical messenger; also crucial for neural signaling Open or close in response to stretch or touch; important for sensory transduction Respond to local changes in temperature; also important for sensory transduction 1. Graded potentials 2. Action potentials Serve as short distance signals - Usually produced in only one region of membrane - Result in depolarization with a magnitude directly related to the magnitude of the triggering event More channels open = larger graded potential Longer duration of graded potential A flow of electric charge - Once a graded potential is produced in one area, the current spreads in both directions due to neighboring voltagegated channels - Called passive conduction Decremental: they gradually die out over short distances - This is because of leaks in the current (membrane has no good insulators here) - Graded potentials generate Action potentials Triggering an action potential Explosive depolarization Action potential Voltage-gated ion channels Two types of channels important for action potentials Voltage-gated Na+ channels Voltage-gated K+ channels Changes in permeability underlying an AP This is why they are only useful at signaling over short distances - Postsynaptic potentials (neural function) - Receptor potentials (sensory/neural function) - End place potentials (muscle function) - Pacemaker potentials (cardiac function) - Slow wave potentials (muscle and cardiac function Brief, rapid, large changes in membrane potential during which the cell becomes more positive than the outside - Involved only a portion of membrane - But APs are nondecremental - Great for long distance signaling - Graded potentials in a cell create currents that depolarize portions of the cell - These can summate, causing even more depolarization, eventually reaching threshold - Usually, ~+10 or 15 mv above resting potential +30 to +40mv - Just as rapidly, the membrane repolarizes dropping to resting, but the forces behind this push too far, causing a transient hyperpolarization (~-80mv) The entire rapid change from threshold to peak and then back to resting - An AP is an all-or-none event: if threshold isn't reached, an AP doesn't fire Responsible for permeability changes during the action potential 1. Voltage-gated Na+ channels 2. Voltage-gated K+ channels Have two gates - Activation gate guards the channel (hinge) - Inactivation gate blocks the channel (ball and chain) Both gates must be open to allow Na+ through Only has one gate • Hinge - Unlike Na+ channels, which open rapidly at threshold, K+ have a delayed onset to opening 1. At rest, all voltage-gated channels are closed 2. At threshold, Na+ activation gate opens and Na+ moves in After an AP Anatomy of a neuron Cell body Dendrites Axon Axon hillock Axon terminals Contiguous conduction 3. Na+ moving in causes explosive depolarization 4. At peak of AP, Na+ inactivation gate closes, ending movement in. At same time, K+ activation gate finally opens and K+ starts moving out (down it's concentration gradient) 5. Positive K+ flows out, repolarizing the cell (making it more negative) 6. On return to resting potential, Na+ activation gate closes and inactivation gate opens. Does not cause a change in Na+ flux here but allows it to reset for the next threshold. 7. K+ keeps moving out, causing a brief hyperpolarization 8. K+ gate closes and resting potential - The resting potential is restored by the closing of na and K channels but ion concentration is altered slightly. - The cell can fire another AP right away but it will eventually reach equilibrium concentration - Needs Na+/K+ pump A single AP involves only a small membrane portion of an excitable cell, but it must travel in order to serve as a long-distance signal - Plus, there must be a way for the signal to be transmitted from one cell to the next - Neurons and muscle cells = excitable Houses the nucleus and organelles of a normal cell, but has unique offshoots: dendrites and axons Project like antennae to increase surface area for receiving signals from other neurons - Dendrites and cell body = "input zone" because they receive and integrate incoming signals - Also, where graded potentials occur in response to triggering events "Conducting zone" A single extension that conducts APs away from the cell body and communicates with other cells "Trigger zone" Site where APs is triggered by a graded potential "Output zone" Branch at the end of the axon where they pass on information to other cells - Involves spread of AP down every patch of membrane along the axon - Refractory period Absolute refractory period Relative refractory period Coding the strength Stronger stimulus = frequency of APs Saltatory conduction Myelin Oligodendrocytes Schwann cells Nodes of ranvier Increasing speed by increasing axon diameter Synapse AP cycle repeats in a chain reaction until it has spread to the end Time during which a new AP cannot fire in a region that just fired an AP - The refractory period prevents "backward" current flow. During an AP and slightly after, an area cannot be restimulated to undergo another AP, ensuring it can be propagated forward along the axon Membrane is completely incapable of firing another AP no matter how much it is stimulated by a triggering event - When channels are already open, they can't be stimulated to open again Membrane can only be stimulated by a strongerthan-usual triggering event - Some lingering inactivation of Na+ channels and the slowness to close of K+ channels = fewer channels in resting potential and ready If a stimulus is too weak to get the membrane to threshold, no AP fires - Helps to not clutter up the nervous system A stronger stimulus doesn't cause a stronger AP, but it does cause more APs per second - Stronger stimulus will also cause more neurons to reach threshold, thus increasing total amount of info sent The spread of APs jumps from node to node AP conduction down insulated axons where AP only happens at nodes instead of along entire length ~ 50 times faster than contiguous A lipid made by cells that tightly wrap around the axon Myelin in CNS Myelin in PNS The bare spaces between myelinated regions - Voltage-gated Na+ and K+ channels are at nodes, so this is where current flows and APs can fire When axon diameter increases, inner resistance decreases allowing for faster conduction Region where info transfer takes place - Info is transferred across the synapse from presynaptic cell to postsynaptic cell When an AP signal reaches the end of an axon, it must transmit information to the next cell Two types of synapses 1. Electrical 2. Chemical Electrical synapse APs are transmitted across electrical synapses unperturbed, as if the synapse wasn't present - The cytoplasm of both cells is in contact via gap junctions - Ions flow right through continuing the signal - Negligible time delay Chemical synapse Pre- and postsynaptic cells don't actually make contact at chemical synapses - The gap, called the synaptic cleft, is too large for electrical impulses to travel past - Instead, chemical messengers called neurotransmitters carry the message across Chemical diffusion advantages • Operate in one direction only • Allow for signaling other than just excitatory APs Synapses can occur between two neurons or In neuron-to-neuron signaling, usually an axon between a neuron and a muscle cell terminal synapses onto the dendrite or cell body of the postsynaptic neuron - Axon-to-axon synapse is far less common - Most neurons receive thousands of synaptic inputs from the axon terminals of other neurons Synaptic knob Swollen end of nerve fiber Synaptic vesicles Store neurotransmitter An AP triggers neurotransmitter release from the NTs bind to receptors on the postsynaptic cell, presynaptic cell usually opening ion channels Synaptic delay Converting the signal from electrical (presynaptic) to chemical (synapse) to electrical (postsynaptic) takes time Each presynaptic neuron usually releases only one NT Excitatory Inhibitory Each NT-receptor combo always produces the same excitatory or inhibitory response ~0.5 - 1 msec Different NTs cause different changes in the postsynaptic cell Cause Na+ channels to open, generating an excitatory post-synaptic potential (EPSP) Cause K+/Cl- channels to open, generating an inhibitory postsynaptic potential (IPSP) - IPSPs cause slight hyperpolarization of the postsynaptic cell - EX: glutamate + glutamate receptor = excitatory - EX: GABA + GABA receptor = inhibitory - Some NTs bind to several different types of receptors though, so can excite or Three ways NTs lose power in the synapse Reuptake Some NTs simply diffuse out of synapse Enzymes Fast synapses Slow synapses Slow synapses ar enot quite as common Neuromuscular synapses Terminal bouton Motor end plate Acetylcholine (ACh) ACh receptors Signal transduction at a neuromuscular synapse inhibit depending on the postsynaptic receptors 1. Neurotransmitters can be returned to axon terminals for reuse or transported into glial cells 2. Enzymes inactivate neurotransmitters 3. Neurotransmitters can diffuse out of the synaptic cleft Cariers can pump certain NTs back into presynaptic cell Removed by blood stream Can inactivate NTs - Acetylcholinesterase (AChE) inactivates and destroys acetylcholine (ACh) Where NT opens ion channels Where NT binds to a receptor that sets off 2nd messenger cascade in postsynaptic cell - Can sometimes trigger long-term changes - Useful for neuronal growth and development, plus learning and memory Junctions between neurons (“motor neurons”) and muscle cells - Muscle cells or “fibers” = long and cylindrical - The axon terminal enlarges into the terminal bouton, forming chemical synapses with muscle fibers Bulge at the end of an axon from which the axon releases a neurotransmitter The area that the terminal bouton synapses onto The terminal bouton is loaded with vesicles carrying the NT ACh Motor end plate loaded 1. An AP in motor neuron travels to terminal bouton 2. Triggers Ca+2 channels to open; Ca+2 enters 3. Ca+2 triggers release of ACh from vesicles 4. ACh diffuses across synaptic cleft and binds to ACh receptor channels on the motor end plate 5. Binding causes channels to open: Na+ moves in, K+ moves out causing current flow 6. Current flow = end-plate potential (EPP) which flows to nearby membrane too 7. Na+ channels in nearby membrane open 8. Na+ entering brings cell to threshold causing an AP (the AP spreads Summation Two types of summation Temporal summation Spatial summation Neuromodulators Modulating neural pathways Presynaptic facilitation Presynaptic inhibition Retrograde messengers Convergence Divergence Many external agents affect neural transmission Ouabain Tetrodotoxin (TTX) Antagonists Agonists throughout muscle cell in contiguous fashion (no myelin), causing contraction) 9. ACh is destroyed by AChE, terminating the muscle contraction The basis of decision making for an excitable cell - Graded potentials can be of varying magnitudes and can be EPSPs or IPSPs - Not all-or-none like APs, can be summed 1. Temporal summation 2. Spatial summation The same input causes de- or hyper-polarization very close in time - No refractory period for graded potentials Several inputs cause de- or hyper-polarization - EPSPs summate to depolarize cell - IPSPs summate to hyperpolarize cell - Both can cancel each other out Chemical messengers that bring about longterm changes to a synapse - Do not cause EPSPs/IPSPs - Often activate 2nd messenger cascades that can alter sensitivity of cell or alter enzyme levels Sometimes a 3rd neuron influences activity at a synapse Messages generally travel in one direction Altering so that more NT is released Altering so that less NT is released Diffuse backward (B to A) and modify synapse sensitivity A neuron will often have many other neurons synapsing onto it Neuron will often synapse onto several other cells Drugs, toxins, pollutants, medicines, diseases, temperature, and even pressure Comes from a tree - Blocks the Na+/K+ pump - Can be lethal Comes from blowfish - Blocks Na+ channels, thereby blocking APs - Very potent and very lethal Chemicals that block an effect - Symptoms: convulsions, muscle spasticity, and death Chemicals that enhance an effect - Symptoms: lowered inhibitions, memory loss, difficulty with movement, unconsciousness, eventually death Caffeine Cocaine SSRIs Lead exposure Multiple sclerosis (MS) Black widow venom Myasthenia gravis Even temperature and pressure can alter signaling Whole-body regulation Nervous system Organized into two different systems Central nervous system Peripheral nervous system Afferent Efferent Afferent neurons Antagonist of an inhibitory NT (adenosine) Blocks the dopamine reuptake pump, increasing dopamine (reward signaling) in synapse Selective serotonin reuptake inhibitors - Increase synaptic serotonin, involved in sleep, sexual behavior, appetite, memory, mood, etc. Breaks down the myelin sheath, preventing proper communication Disease with unknown cause that also leads to demyelination - Problems with memory, development, sensation, coordination, muscle weakness, digestion, etc. Agonist, causing huge release of all ACh: muscles can’t relax - No relaxed muscles = respiratory paralysis (need contract/relax diaphragm cycle to breathe) An autoimmune disease in which ACh receptors are blocked - No ACh signaling = extreme muscle weakness Extreme pressure and cold temps can make membranes too rigid, plus proteins open and close too slowly - Cold also slows diffusion in synapse Extreme heat can make membrane too fluid and thus far more permeable, and speeds up diffusion NERVOUS SYSTEM 1. Nervous 2. Endocrine Allows rapid responses, detects the external environment, and coordinates complex functions such as memory and consciousness 1. Central nervous system 2. Peripheral nervous system Brain and spinal cord Nerve fibers extending to other parts of the body Carry information to the CNS from sensors - The afferent division carries info about the external and internal environment Carries information from CNS to organs, muscles, glands, etc. Have a distinct shape with a sensory receptor instead of dendrites - Cell body lies in PNS while axons reach into CNS Efferent neurons Interneurons Interneurons have two main roles Skeletal muscles controlled by Autonomic nervous system Enteric nervous system Sympathetic nervous system Parasympathetic nervous system Central nervous system Glial cells Astrocytes Oligodendrocytes Have cell bodies in the CNS, but axons reach into PNS to affect organs and muscles - Match typical neuronal anatomy - Lie entirely in CNS - 99% of neurons are interneurons 1. Integrate peripheral info and responses 2. Responsible for abstract phenomena such as planning, memory, creativity, intellect, etc. Motor neurons in the somatic nervous system - Often thought of as the voluntary system Part of the efferent division and sends info to three possible systems 1. Enteric nervous system 2. Sympathetic nervous system 3. Parasympathetic nervous system Governs the walls of the digestive tract (which are also influenced by stimuli within the tract) Dominates in fight-or-flight responses and others that prepare us for stress Dominates in rest-and-digest actions Only ~10% of human brain cells = excitable neurons - Other 90% of cells are glial cells Serve as connective tissue and support neurons - Do not branch as extensively, so only take up about half the volume of neurons though The most abundant glia and have many functions: - Hold neurons together - Establish blood-brain barrier (BBB) - Transfer nutrients to neurons - Repair brain injuries and form neural scars - Serve as scaffold and guide during fetal development - Take up NTs (halting/reducing neural signaling) - Take up excess K+ from ECF, helping to maintain proper ECF concentration for APs to fire - Enhance synapse formation physically and chemically through released substances - Have gap junctions between neurons and other astrocytes – allows communication - Have glutamate (NT) receptors, allowing for further communication and synapse modification Form myelin sheaths around axons in the CNS Ependymal cells Microglia Skull Meninges Cerebrospinal fluid (CSF) Blood-brain barrier (BBB) Plasticity Somatosensory information Somatosensory cortex Homunculus Motor homunculus Most cortical areas are equally distributed across the right and left hemispheres Research suggests each hemisphere is somewhat specialized Learning Memory Two forms of memory Declarative/explicit memory - Done by Schwann cells in PNS Line the ventricles of the brain and central canal of the spinal cord - Form and distribute cerebrospinal fluid (CNF) - Serve as neural stem cells, forming new glial cells, and new neurons - Release some nerve growth factor, helping neurons and glia survive - Serve as immune system in brain, migrating to infection or injury sites to destroy invaders and help with healing Bone that encases the brain Three nourishing membranes between skull and brain Cushioning fluid the brain “floats” in Highly selective barrier that only allows some blood-borne material into vulnerable brain tissue The ability to change in response to demands; when an area is destroyed, other areas of the brain can often assume the responsibilities Body feelings: touch, pressure, body position, heat, cold, pain Receives sensory input from a specific area of the body “Little man” Largest portions represent proportion of motor cortex devoted to controlling muscles in each area - Exception = language areas - The dominant hemisphere for fine motor control is usually the left side, thus most humans and other primates are righthanded - In humans, the left hemisphere excels in logic, math, language, and philosophy - The right excels in spatial perception, art, and music, plus big picture, holistic things Acquisition of abilities or knowledge as a result of experience or instruction - The ability to learn is made possible by the nervous system, the more complex the learning allowed for The storage of acquired knowledge or abilities for later recall 1. Declarative/explicit memory 2. Procedural/implicit memory Events, places, pieces of information, etc. - Often split into semantic (facts) and episodic (events) Procedural/implicit memory Episodic (declarative) Semantic (declarative) Skill learning (procedural) Priming (procedural) Conditioning (procedural) Working memory Short-term memory Long-term memory Memory trace Where in the brain does memory trace occur? How does memory trace occur? Sleep is a universal phenomenon in all vertebrates Restoration and recovery Plasticity and memory processing Stage 1 Stage 2 Stage 3 and 4 REM sleep Skilled motor movements, conditioning, etc. Remembering your first day of school Knowing the capital of France Knowing how to ride a bicycle Being more likely to use a word you heard recently Salivating when you see a favorite food Immediate perceptual and linguistic processing It lasts seconds to hours and has a limited capacity Retained days to years and has a vastly larger capacity - Info lost from short-term is often lost forever, but info from long-term is often lost only temporarily The neural change responsible for retention and storage There is not one center, it’s distributed through several regions: hippocampus, limbic system, temporal lobes, prefrontal cortex, cerebellum, etc. - The molecular mechanisms underlying memory differ for short- vs. long-term - Short-term memory is caused by temporary modification to pre-existing synapses - Long-term memory is caused by relatively permanent functional or structural changes between neurons, which requires changes in gene expression and formation of new synapses Characterized by several features - Periods of minimal movement - Reduced responsiveness to external stimuli - Rapid reversibility Restore biochemical processes that degrade during wakefulness, repair damage caused by free radicals, restore receptor sensitivity Sleep aids in memory consolidation and brain development Light sleep, brain waves start to slow Slower waves and “sleep spindles”; conscious awareness disappears “Slow-wave” or “deep” sleep - Thought to be most restful portion - When sleeping, walking and night terrors can occur - Recently combined into just stage 3 sleep Rapid eye moment sleep - 1 full sleep cycle Consciousness Heart rate, breathing, and body temp no longer well-regulated - “Paradoxical” sleep because EEG looks like waking, though hardest to arouse in REM - Most vivid dreams here - Likely important for memory consolidation - 90 mins - S1, S2, S3, S2, REM, repeat with S3 lessening and REM increasing as cycles continue Subjective awareness of the external world and self
