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Anatomy-Ch.12
Anatomy-Ch. 12
| discovery of nerve growth factor | |
| alzheimer disease | |
| parkinsons disease | |
| endocrine system | body system that commmunicates by means of hormones (chemical messengers) secreted into the blood |
| nervous system | body system which employs electrical and chemical means to send messages very quickly from cell to cell |
| how does the nervous system carry out its coordinating tasks? | 1 through sense organs/nerve endings it receives info about changes in body & transmits msgs to CNS 2CNS proceses this info, relates it to past experiences & determines the response 3 CNS issues commands to muscle &gland cells to carry out such responses |
| Central Nervous System (CNS) | consits of brain and spinal cord which are protected by cranium and vertebral column |
| Peripheral Nervous System (PNS) | consists of the rest of body; composed of nerves & ganglia. is divided into sensory & motor divisions and each of these is further divided into somatic and visceral subdivisions |
| nerve | bundle of nerve fibers (axons) wrapped in fibrous connective tissue. they emerge from the CNS through foramina of the skull and verterbral column and carry signals to and from organs of the body |
| ganglion | a knot-like swelling in a nerve where the cell bodies of neurons are concentrated |
| sensory division | carries signals from various receptors to the CNS. this pathway informs the CNS of stimuli within and around the body (incoming;into) |
| somatic sensory division | carries signals from receptors in the skin, muscle, bones, and joints (skeletal muscle) |
| visceral sensory division | carries signals mainly from the viscera of the thoracic and abdominal cavities such as heart, lungs, stomach, and urinary bladder |
| sensory vs motor | sensory: incoming/into motor: movement/outgoing |
| motor division | carries signals from the CNS to gland and muscle cells that carry out the body's responses |
| effectors | cells and organs that respond to commands from the nervous system |
| somatic motor division | carries signals to the skeletal muscles which produces somatic reflexes |
| somatic reflexes | muscular contractions that are voluntary and involuntary |
| visceral motor division | is the automatic nervous system (ANS)that carries signals to glands, cardiac muscle, & smooth muscle |
| Visceral reflexes | the responses of the ANS and its effectors |
| Automatic Nervous System (or Visceral motor division) has 2 further divisions | sympathetic division and parasympathetic division |
| sympathetic division | arouses the body for action (fight or flight) , is fast, and prevents digestion |
| parasympathetic divion | has a calming effect, is slower (slowing heartbeat), and stimulates digestion |
| neurons | takes the role of communicating within the nervous system |
| universal properties of neurons | excitability (irritability), conductivity, and secretion |
| excitability | (irritability) all cells are excitable, that is, they respond to environmental changes (stimuli) |
| conductivity | neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations |
| secretion | when the electrical signal reaches the end of a nerve fiber, the neuron secretes a chemical neurotransmitter that crosses the gap and stimulates the next cell |
| 3 general types of neurons | sensory (afferent), interneurons (association neurons), motor (efferent) neurons |
| sensory neurons | (afferent neurons)- specialized to detect stimuli such as light, heat, pressure, chemicals, and transmit info about them to the CNS |
| interneuron | (association neurons) lie entirely within the CNS they receive signals from many other neurons & carry out the integrative function of the nervous system- they process, store & retrieve info & make decisions that determine how the body responds to stimuli |
| motor neuron | efferent neuron that sends signals to muscle and gland cells, the effectors |
| afferent | info is going up to next level, toward the CNS |
| interneuron | lie between and interconnect the incoming sensory pathways and the outgoing motor pathways of CNS; make up about 90% of neurons |
| efferent | info is going down, outgoing away from CNS |
| soma | aka neurosoma, cell body, or perikaryon; is the control center of the neuron |
| what makes up the soma | has a centrally located nucles w/ large nucleolus/ cytoplasm cytoskeleton filled with microtubules & neurofibrils, has nissi bodies, no centrioles, dendrites, & lipofuscin |
| microtubules/ neurofibrils | bundles of actin filaments that make up the cytoskeleton; they compartmentalize the rough ER into Nissl bodies |
| Nissl bodies | dark staining regions |
| lipofuscin | golden-brown pigment produced when lysosomes degrade worn-out organelles and other products; accumulates with age and pushes nucleus to one side of the cell; called "wear and tear granules" |
| dendrites | primary site for receiving signals from other neurons; the more dendrites a neuron has the more information it can receive and incorporate into decision making |
| axon hillock | a mound on one side of the soma where axon originate, gives rise to axon collaterals along the way and most axons branch extensivley at their distal end |
| axon | nerve fiber that is specialized for rapid conduction of nerve signals to point remote from the soma. there is never more than one axon in a neuron |
| describe properties of axon | axoplasm-cytoplasm of a axolemma- membrane of a shwan cells & myelin sheath- enclose ax terminal arborization- an extensive complex of fine branches at distal end of a synaptic knob-(terminal button) little swelling that forms a synapse w next cell |
| multipolar neurons | has one axon and multiple dendrites; most common type and includes most neurons of the brain and spinal cord |
| bipolar neurons | has one axon and one dendrite; examples: olfatory cells of nasal caivity, certain neurons of the retina, and sensory neurons of the inner ear |
| unipolar neurons | have only a single process leading away from the soma; represented by neurons that carry sensory signals to spinal cord; then branches like a T into a peripheral fiber & a central fiber |
| anaxonic neurons | have multiple dendrites but no axon; they communicate through their dendrites and do not produce action potentials; some are found in the brain, retina, and adrenal medulla |
| axonal transport | the two way passage of proteins, organelles, and other material along the axon |
| anterograde transport | movement away from the soma down the axon; employs motor protein called kinesin that carry materials to bind repeatedly to the microtubules and crawl along them; has fast and slow axonal transport |
| retorgrade transport | movement up the axon toward the soma; employs a motor protein called dynein that carry materials to bind repeatedly to the microtubules and crawl along them; has fast retrograde transport |
| fast axonal transport | occurs at a rate of 20-400 mm/day and may be either fast anterograde transport or fast retrograde transport |
| fast anterograde transport | moves mitochondria, synaptic vesicles, small molecules and other organelles to the distal end of the axon |
| fast retrograde transport | returns used synaptic vesicles and other materials to the soma and inform the soma of conditions at the axon terminals |
| slow axonal transport | anterograde process that works as fast axonal transport except.5-10 mm a day; moves enzymes & cytoskeletal components down axon, renews worn out axoplasmic components in mature neurons &supplies new axoplasm for developing/regenerating nueron |
| neruroglia | supportive cells aka glial cells; they protect the neuron and help them funcition, binds neurons together and provide a supportive framework for nervous tissue |
| 4 types of neuroglia that occur in CNS | oligodendrocytes, ependymal cells, microglia, and astrocytes |
| 2 types of neuroglia that occur in PNS | shwan cells and satellite cells |
| oligodenderocytes | form myelin in brain and spinal cord |
| ependymal cells | lines cavities of brain ans spinal cord; secrete and circulate cerebrospinal fluid |
| microglia | phagocyte and destroy microorganisms, foreign matter, and dead nervous tissue |
| astrocytes | cover brain surface & nonsynaptic regions of neurons; form supportive framework in CNS; induce formation of blood-brain barrier; nourish neurons, produce growth factors that stimulate neurons, help regulate composition of ECF |
| schwan cells | form neurilemma around all PNS nerve fibers and myelin around most of them; aid in regeneration of damaged nerve fibers |
| satellite cells | surround somas of neurons in the ganglia; provide electrical insulation and regulate chemical environment of neurons |
| perivascular feet | extensions that contact the blood capillaries and stimulate them to form a tight seal called the blood-brain barrier |
| blood-brain barrier | isolates the blood from the brain tissue and limits what substances are able to get to the brain cells |
| astrocytosis/ sclerosis | process when neurons are damaged, astrocytes form hardened scar tissue and fill space formerly occupied by neurons |
| brain tumors arise from | meninges, metastasis, usually glial cells |
| glial cells and brain tumors | mature neurons have little or no capacity for mitosis and seldom form tumors, gliomas grow rapidly and are highly malignant, blood-brain barrier decreases effectiveness of chemotherapy; treatment: radiation or sugery |
| myelin sheath | an insulating layer around a nerve fiber; formed by oligodendrocytes in CNS and schwan cells in PNS. it consists of plasma membranes of glial cells. it is about 20% protein and 80% lipid |
| myelination | production of the myelin sheath; begins at week 14 of fetal development, proceeds rapidly during infancy, completed in late adolescence, and dietary fat is important to CNS development |
| multiple sclerosis | degenerative disorder of the myelin sheath; oligodendrocyte and myelin sheaths in the CNS deteriorate, myelin replaced by hardened scar tissue, nerve conduction is disrupted, cause may be autoimmune triggered by virus |
| tay-sachs disease | a hereditary disorder of infants of eastern europe jewish ancestry; abnormal accumulation of ganglioside disrupts conduction of nerve signals, blindness, loss of coordination, and dementia, fatal before age of 4 |
| myelinated and unmyelinated nerve fibers | schwan cells hold 1-12 small nerve fibers in grooves on the surface, membrane folds once around each fiber overlapping itself along the edges |
| mesaxon | neurilemma wrapping of unmyelinated nerve fibers |
| conduction speed of nerve fibers | speed at which a nerve signal travels along a nerve fiber depends on diameter of fiber and the presence or absence of myelin |
| signal conduction occurs along the surface of a fiber | larger fibers have more surface area and conduct signals more rapidly; myelin further speeds signal conduction |
| conduction speed | small unmyelinated fibers: .5-2.0 m/s; small myelinated fibers: 3-15 m/s; large myelinated fibers: up to 120 m/s |
| slow signals. fast signals of conduction speed | slow signals supply the stomach and dilate the pupil where speed is less of an issue; fast signals supply skeletal muscles and transport sensory signals for vision and balance |
| when can regeneration of a nerve fiber occur? (1) | can occur if soma is intact & atleast some neurilemma remains |
| injured fiber (2) | fiber distal to the injury cannot survive and degenerates; macrophages clean up tissue debris at the point of injury and beyond |
| degeneration of severed fiber (3) | soms swells, ER breaks up, and nucleus moves off center; due to loss of nerve growth factor from neuron's target cell;axon stump sprouts multiple growth processes; severed distal end continues to degenrate |
| early regeneration (4) | regeneration tube: formed by schwan cells, basal lamina, and the neurolemma near the injury |
| late regeneration (5) | regeneration tube guides the growing sprout back to the original target cells and reestablishes synaptic contact |
| regenerated fiber (6) | nucleus returns to normal shape, regeneration of damaged nerve fibers in the CNS cannot occur at all |
| denervation atrophy | a shrinkage of muscle due to loss of nerve contact by damaged nerve |
| electrophysiology | cellular mechanisms for producing electrical potentials and currents; basis for neural communication and muscle contraction |
| electrical potential | a difference in the concentration of charged particles between one point and another |
| what is an electrical current | a flow of charged particles from one point to another |
| what does electrical current do | in the body, currents r moevements of ions such as Na+ or K+, through gated channels in the plasma membrane;gated channels are opened or closed by various stimuli; enables cell to turn electrical currents on/off |
| polarized | living cells are polarized bc they have a potential |
| resting membrane potential (rmp) | charge difference across the plasma membrane; about -70mV in a resting, unstimulated neuron; negative value means there are more neg chargedparticles on the inside of the membrane than on the outside |
| RMP results from what? | results from the combined effect of • ions diffuse down their concentration gradient through the membrane; plasma membrane is selectively permeable and allows some ions to pass easier than others; electrical attraction of cations and anions to each other |
| the resting membrane potential: K+ | potassium ions have the greatest influence on RMP; plasma membrane is more permeable to K+ than any other ion; leaks out until electrical charge of cytoplasmic anions attracts it back in &equilibrium is reached& net diffusion of K+ stops; |
| the resting membrane potential:cytoplasmic anions | cannot escape due to size or change |
| the resting membrane potential: sodium (Na+) | membrane is much less permeable to high concentration of sodium found outside of cell; some leaks and diffuses into the cell down its concentration gradient;Na+ is about 12 times as concentrated in the ECF as in the ICF |
| Na+/K+ pump | 3 Na+ out for every 2 K+ it brings in;works continuously to compensate for Na+ and K+ leakage & requires great deal of ATP;70% of the energy requirement of the nervous system; necessitates glucose& oxygen be supplied to nerve tissue |
| local potentials | disturbances in membrane potential when a neuron is stimulated by chemicals, light, heat, or mechanical disturbances; neuron response begins at the dendrite, spreads through the soma, travels down the axon, and ends at the synaptic knobs |
| depolarization | case in which membrane voltage shifts to a less negative value |
| graded | vary in magnitude with stimulus strength • stronger stimuli open more Na+ gates |
| difference of local potentials and action potentials | local potentials are graded, decremental, reversible, and excitatory or inhibitory while action p are all or none, nondecremental, and irreversible |
| decremental | vary in magnitude with stimulus strength • stronger stimuli open more Na+ gates |
| reversible | when stimulation ceases, K+ diffusion out of cell returns the cell to its normal resting potential |
| excitory or inhibitory | some neurotransmitters (glycine) make the membrane potential more negative (hyperpolarize it) so it becomes less sensitive and less likely to produce an action potential |
| action potential | more dramatic change produced by voltage-regulated ion gates in the plasma membrane; only ccur where there is a high enough density of voltage-regulated gates; soma cannot generate it, trigger zone is where the action potential is generated |
| characteristics of action potential | all or none law: • if threshold is reached, neuron fires at its maximum voltage • if threshold is not reached, it does not fire; nondecremental: do not get weaker with distance; irreversible: once started goes to completion |
| action potential is a rapid.. | up and down shift in the membrane and occurs in 7 steps |
| action potential step 1 | • sodium ions arrive at the axon hillock • depolarize the membrane at that point |
| action potential step 2 | • threshold: critical voltage to which local potentials must rise to open the voltage-regulated gates • −55 mV |
| action potential step 3 | • when threshold is reached, neuron “fires” and produces an action potential • more and more Na+ channels open in the trigger zone in a positive feedback cycle creating a rapid rise in membrane voltage, called spike |
| action potential step 4 | • when rising membrane potential passes 0 mV, Na+ gates are inactivated • begin closing; when all closed, the voltage peaks at +35 mV • membrane now positive on the inside and negative on the outside • polarity reversed from RMP (depolarization) |
| action potential step 5 | • by the time the voltage peaks, the slow K+ gates are fully open • K+ repelled by the positive intracellular fluid now exit the cell • their outflow repolarizes the membrane; shifts the voltage back to negative numbers returning toward RMP |
| action potential step 6 | • K+ gates stay open longer than the Na+ gates • slightly more K+ leaves the cell than Na+ entering • drops the membrane voltage 1 or 2 mV more negative than the original RMP (negative overshoot, hyperpolarization, afterpotential) |
| action potential step 7 | Na+ and K+ during action potential switch places |
| refractory period | the period of resistance to stimulation that during an action potential and for a few milliseconds after, it is difficult or impossible to stimulate that region of a neuron to fire again |
| hyperpolarize | make membrane more negative |
| refractory period has 2 phases | absolute refractory and relative refractory period |
| absolute refractory period | no stimulus of any strength will trigger AP as long as Na+ gates are open |
| relative refractory period | • only especially strong stimulus will trigger new AP • K+ gates are still open and any effect of incoming Na+ is opposed by the outgoing K+ |
| signal conduction in nerve fibers: communication | for communication to occur, the nerve signal must travel to the end of the axon |
| unmyelinated fibers | has voltage regulated ion gates along its entire length; action potential from trigger zone causes Na+ 2 enter the axon & diffuse into adjacent regions beneath membrane;depolarization excites voltage-regulated gates immediately distal to action potential |
| unmyelinated fibers cont... | • Na+ and K+ gates open and close producing a new action potential • by repetition the membrane distal to that is excited • chain reaction continues to the end of the axon |
| myelinated fibers | volatage-gated channels needed for APS are fewere than 25 per μm2 in myelin-covered regions (internodes)&up to 12,000 per μm2 in nodes of Ranvier; much faster than conduction in unmyleniated fibers |
| fast Na+ diffusion occurs between nodes- | signal weakens under myelin sheath, but still strong enough tostimulate an action potential at next node |
| saltatory conduction | nerve signal seems to jump up from node to node |
| comparison of local potentials and action potentials | table 12.2 page 454 |
| synapses | nerve signal can go no further when it reaches the end of the axon;triggers the release of a neurotransmitter and stimulates a new wave of electrical activity in the next cell across the synapse |
| synapses between 2 neurons | • first neuron in the signal path is the presynaptic neuron • releases neurotransmitter • second neuron is postsynaptic neuron • responds to neurotransmitter |
| presynaptic neuron | may synapse with a dendrite, soma, or axon of postsynaptic neuron to form axodendritic, axosomatic, or axoaxonic synapses |
| neuron can have an enormous number of synapses | • spinal motor neuron covered by about 10,000 synaptic knobs from other neurons • 8,000 ending on its dendrites • 2,000 ending on its soma in the cerebellum of brain, one neuron can have as many as 100,000 synapses |
| synaptic cleft | gap between neurons was discovered by Ramón y Cajal through histological observations |
| Otto Loewi, in 1921, | demonstrated that neurons communicate by releasing chemicals(chemical synapses); • later renamed acetylcholine, the first known neurotransmitter |
| how did otto loewi demonstrate that neurons communicate by releasing chemicals? | •he flooded exposed hearts of two frogs with saline, stimulated vagus nerve of the first frog & the heart slowed, removed saline fromfrog & found it slowed heart of 2nd frog • named it Vagusstoffe “vagus substance” |
| electrical synapses | where adjacent cells are joined by gap junctions and ions diffuse through the gap junctions from one cell to the next |
| electrical synapse junctions advantage | have advantage of quick transmission bc there is no delay for release & binding of neurotransmitter |
| electrical synapse junctions disadvantage | they cannot integrate info and make decisions, which is a property of chemical synapses in which neurons communicate by releasing neurotransmitters |
| synaptic knob of presynaptic | contains synaptic vesicles containing neurotransmitter many which are docked on release site on plasma membrane, ready to release neurotransmitter on demand |
| presynaptic neurons | have synaptic vesicles with neurotransmitter and postsynaptic have receptors and ligand-regulated ion channels |
| neurotransmitters fall into 4 categories according to chemical composition | acetylcholine, amino acid, monoamines, and neuropeptides |
| acetylcholine | class by itself, formed from acetic acid and choline |
| amino acid neurotransmitters: | include glycine, glutamate, aspartate, and g-aminobutyric acid (GABA) |
| monoamines | synthesized from amino acids by removal of the –COOH group, retaining the –NH2 (amino) group; major monoamines:• epinephrine, norepinephrine, dopamine (catecholamines) • histamine and serotonin |
| neuropeptides | chains of 2 to 40 amino acids such as beta-endorphin &substance P; they act at lower concnetrations, have longer lasting efffects, stored in axon terminal as larger secretory granules, some function as hormones |
| 3 types of synapses | • excitatory cholinergic synapse • inhibitory GABA-ergic synapse • excitatory adrenergic synapse |
| synaptic delay | time from the arrival of a signal at the axon terminal of a presynaptic cell to the beginning of an action potential in the postsynaptic cell • 0.5 ms for all the complex sequence of events to occur |
| cholinergic synapse | employs ACh as its neurotransmitter, ACh excites some postsynaptic cells-skeletal muscle and inhibits others |
| inhibitory GABA-ergic synapse | employs g-aminobutyric acid as its nrtmtr;nerve signal trgers release of GABA in2 synaptic cleft;GABA receptors r chloride channels;Cl enters cell & makes inside more (-)than resting membrane potential; postsynaptic neuron is inhibited& less likely 2 fire |
| excitory adrenergic synapse | employs neurotransmitter norepinephrine (NE), aka noradrenaline; receptor is not an ion gate but a transmembrane protein assctd w/ G protein; slower to respond; has advantage of enzyme amplification |
| enzyme amplification | single molecule of NE can produce vast numbers of product molecules in the cell |
| ways to turn off the stimulus to keep postsynaptic neuron from firing indefinitely | • neurotransmitter molecule binds to its receptor for only 1 ms or so; then dissociates from it • if presynaptic cell continues to release neurotransmitter, one molecule is quickly replaced by another and the neuron is restimulated |
| diffusion | • neurotransmitter escapes the synapse into the nearby ECF • astrocytes in CNS absorb it and return it to neurons |
| reuptake | • synaptic knob reabsorbs amino acids and monoamines by endocytosis • break neurotransmitters down with monoamine oxidase (MAO) enzyme • some antidepressant drugs work by inhibiting MAO |
| degration in synaptic cleft | • enzyme acetylcholinesterase (AChE) in synaptic cleft degrades ACh into acetate and choline • choline reabsorbed by synaptic knob |
| 2nd way of stopping synaptic transmission | diffusion, reuptake, and degration in synaptic cleft |
| neruromodulators | hormones, neuropeptides& other messengers that modify synaptic transmission |
| what can neuromodulators do | that may stimulate a neuron to install more receptors in the postsynaptic membrane adjusting its sensitivity to the neurotransmitter& may alter the rate of neurotransmitter synthesis, release, reuptake, or breakdown |
| enkephalins | a neuromodulator family • small peptides that inhibit spinal interneurons from transmitting pain signals to the brain |
| nitric oxide (NO) | simpler neuromodulator; a lightweight gas released by postsynaptic neurons in some areas of brain concerned w/ learning & memory;diffuses in2 presynaptic neuron; stimulates it to release more nrtsmtr•neuron’s way of telling the other to “give me more” |
| neurotransmitter and their locations and actions | table 12.3 pg 463 |
| synaptic delay | slows the transmission of nerve signal; the more synapses there are in a neural pathway, the longer it takes info to get from its origin to its destination |
| gap junctions | allow some cells to communicate more rapidly than chemical synapses |
| why do we have synapses | to process info, store it & make decisions; the more synapses a neuron has the greater its info processing capabilities; |
| how many synapses does cerebral cortex have | 100 trillion |
| cerebral cortex | main information-processing tissue of the brain |
| what is a neural integration | the ability of your neurons to process information, store it, recall it, and make decisions; it is based on the postsynaptic potentials produced by neurotransmitters |
| a neuron has... | a resting membrane potential of -70 mV and threshold of about -55 mV |
| Excitatory postsynaptic potential EPSP | any voltage change in direction of thrshold that makes a neuron more likely to fire; results from Na+ flowing into cell canceling some of the - charge on inside of the membrane; glutamate & aspartate r excitatory brain neurotransmitters that produce ESPSs |
| inhibitory postsynaptic potential (IPSP) | any voltage change away from threshold that makes a neuron less likely to fire; neurotransmitter hyperpolarizes the postsynaptic cell & makes it more negative than the RMP making it less likely to fire; |
| inhibitory postsynaptic potential IPSP (pt. 2) | produced by neurotransmitters that open ligand-regulated chloride gates • causing inflow of Cl− making the cytosol more negative |
| glycine and GABA | produce IPSPs and are inhibitory |
| acetylcholine (ACh) and norepinephrine | are excitatory to some cells and inhibitory to others; • depending on the type of receptors on the target cell • ACh excites skeletal muscle, but inhibits cardiac muscle due to the different type of receptors |
| summation, facilitation, and inhibition | one neuron can receive input from thousands of other neurons; some incoming nerve fibers may produce EPSPs while others produce IPSPs; neuron’s response depends on whether the net input is excitatory or inhibitory |
| summation | the process of adding up postsynaptic potentials and responding to their net effect; occurs in the trigger zone; the balance between EPSPs and IPSPs enables the nervous system to make decisions` |
| temporal summation | occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades • allows EPSPs to add up over time to a threshold voltage that triggers an action potential |
| spatial summation | occurs when EPSPs from several different synapses add up to threshold at an axon hillock • several synapses admit enough Na+ to reach threshold • presynaptic neurons cooperate to induce the postsynaptic neuron to fire |
| facilitation | a process in which one neuron enhances the effect of another one • combined effort of several neurons facilitates firing of postsynaptic neuron |
| presynaptic inhibition | rocess in which one presynaptic neuron suppresses another one; opposite of facilitation;reduces or halts unwanted synaptic transmission;neuron I releases inhibitory GABA |
| presynaptic inhibition prevents | voltage-gatedcalciumchannelsfromopeninginsynaptic knob and presynaptic neuron releases less or no neurotransmitter |
| neural coding | the way in which the nervous system converts information to a meaningful pattern of APs |
| qualitative information | depends upon which neurons fire- labeled line code |
| labeled line code | each nerve fiber to the brain leads from a receptor that specifically recognizes a particular stimulus type |
| quantitative inormation | information about the intensity of a stimulus; is encoded in two ways |
| first way of encoding quantitative information | depends on fact that dif neurons have dif thresholds of excitation; stronger stimuli causes a more rapid firing rate; excitement of sensitive, low-threshold fibers gives way to excitement of less sensitive, high-threshold fibers as intensity of stimuli + |
| 2nd way of encoding quantitative information | depends on the fact that the more strongly a neuron is stimulated, the more frequently it fires • CNScanjudgestimulusstrengthfromthefiringfrequency of afferent neurons |
| neural pools | neurons function in large groups, each of which consists of millions of interneurons concerned with a particular body function • control rhythm of breathing • moving limbs rhythmically when walking |
| process of neural pools and circuits | info arrives at a neural pool through one or more input neurons, branch repeatedly & synapse w/ numerous interneurons in pool; some input neurons form multiple synapses with a single postsynaptic cell |
| some input neurons form multiple synapses with a single postsynaptic cell | that can produce EPSPs in all points of contact with that cell through spatial summation, make it fire more easily than if they synapsed with it at only one point |
| discharge zone | neuron acting alone can make the postsynaptic cells fire |
| broader facilitated zone | it synapses with still other neurons in the pool • fewer synapses on each of them • can only stimulate those neurons to fire with the assistance of other input neurons |
| diverging circuit | • one nerve fiber branches and synapses with several postsynaptic cells • one neuron may produce output through hundreds of neurons |
| converging circuit | • input from many different nerve fibers can be funneled to one neuron or neural pool • opposite of diverging circuit |
| reverberating circuits | • neurons stimulate each other in linear sequence but one cell restimulates the first cell to start the process all over • diaphragm and intercostal muscles |
| parallel after-discharge circuits | • input neuron diverges to stimulate several chains of neurons • each chain has a different number of synapses • eventually they all reconverge on a single output neuron • after-discharge: continued firing after the stimulus stops |
| memory trace (engram) | physical basis of memory is pathway through brain; along this pathway, new synapses were created or existing synapses modified to make transmission easier |
| synaptic plasticity | the ability of synapses to change |
| synaptic potentiation | the process of making transmission easier |
| kinds of memory | immediate, short, and long term memory; that correlate with different modes of synaptic potentiation |
| immediate memory | the ability to hold something in your thoughts for just a few seconds; essential for reading ability; feel for the flow of events; our memory of what just happened "echoes" in our minds for a few seconds(reverberating circuits) |
| short term memory | last from a few sec to few hours; quickly forgotten if distracted; reverberating circuits; facilitation causes memory to last longer |
| tetanic stimulation | rapid arrival of repetitive signals at a synapse • causes Ca2+ accumulation and postsynaptic cell more likely to fire |
| posttetanic potentiation | to jog a memory • Ca2+ level in synaptic knob stays elevated • little stimulation needed to recover memory |
| types of long term memory | declarative and procedural |
| declarative memory | retention of events that you can put into words |
| procedural memory | retention of motor skills |
| physical remodeling of synapses | new branching of axons or dendrites |
| long-term potentiation | • changes in receptors and other features increase transmission across “experienced” synapses • effect is longer-lasting |
| synaptic facilitation | causes memory to last longer |
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