pnb exam 2

proprioceptors

" any of the sensory nerve endings that give information concerning movements and position of the body" 1. carry input of sensory neurons to CNS 2. located in skeletal, muscle, joint capsules, and ligaments 1. muscle spindles 2. golgi tendon organs

Sir Charles Sherrington

"father of the nervous system" gave us most of our knowledge of reflexes Integrative Action of the Nervous System, circa 1901

botox (clostridium botulinum toxin)

"the neuromuscular wonder drug" keeps motor neurons from initiating contractions kill neurons (no response) for relaxing localized

alpha-gamma coactivation

1. alpha motor neuron fires (innervates skeletal muscle) and gamma motor neuron fires (innervates muscle spindle) 2. alpha motor action potential = skeletal muscle contracts (extrafusal) 3. gamma motor action potential = ends of muscle spindle contract (intrafusal) = stretch on centers of intrafusal fibers unchanged ( shrinking of ends compensate for the shrinking of the skeletal muscle so the center does not have to shrink) -firing rate of afferent neuron remains constant

steps leading up to muscle contraction

1. events at neuromuscular junction 2. excitation-contraction coupling 3. contraction-relaxation cycle

properties of muscle tissue

1. excitability: outside stimuli initiate electrical changes in muscle fibers leading to its contraction (action potentials, also in neurons) 2. contractility: stimulation of muscle fiber leads to contraction/shortening of muscle fiber 3. elasticity: muscle fiber's ability to return to original length when tension of contraction is released (don't die when stretched) 4. extensibility: ability of muscle fiber to be stretched beyond relaxed length (can still function)

cardiac muscle fibers

1. found almost exclusively in heart wall 2. striated 3. 1 - 2 nuclei 4. Y-shaped branches (bifurcations) 5. join adjacent cells to form intercalated discs (gap junctions) 6. autorhythmic 7. involuntary shared features 1. like skeletal: striated, sarcomere structure 2. unlike skeletal: shorter fibers, branched, single nucleus 3. like smooth: electrically linked, some have pacemaker potentials, sympathetic/parasympathetic/hormone control

smooth muscle fibers

1. found in walls of viscera + blood vessels 2. short fusiform cells (widest in middle, tapered at each end) 3. centrally located nucleus 4. no striations 5. thin filaments attached to dense bodies 6. involuntary control

relaxation in smooth muscle

1. free Ca2+ in cytosol decreases when Ca2+ pumped out of cell or back into sarcoplasmic reticulum 2. Ca2+ unbinds from calmodulin (CaM) 3. myosin phophotase removes phosphate from myosin, decreasing myosin ATPase activity 4. less myosin ATPase results in decreased muscle tension

smooth muscle contraction

1. intracellular Ca2+ concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum 2. Ca2+ binds to calmodulin (CaM) 3. Ca2+-calmodulin activates myosin light chain kinase (MLCK) 4. MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity 5. active myosin cross bridges slide along actin and create muscle tension longer lasting than skeletal, slower but more sustained kind of like a balloon being tightened with string (not just a shortening) @ dense bodies membrane receptors/channels controlled by different ligands (neurotransmitters, hormones, paracrines)

lipid bilayer (cell membrane)

1. made of lipids 2. selectively permeable -impermeable to ions (need ion channels: cross rapidly)

process @ neuromuscular junction

1. motor neuron action potential comes down 2. Ca2+ enters synapse through voltage-gated channels 3. acetylcholine release: cross synapse (some degraded) 4. acetylcholine binding opens Na+ ion channels 5. Na+ entry 6. local current between depolarized end plate and adjacent muscle plasma membrane 7. muscle fiber action potential initiation 8. propogated action potential in muscle plasma membrane lots of neurotransmitters released AChE may break down some ACh, but still enough left to initiate action potential

smooth muscle properties

1. much smaller than skeletal fibers 2. longer actin/myosin filaments 3. myosin ATPase activity slower 4. myosin light chain plays regulatory role 5. not arranged in sarcomeres 6. less/no sarcoplasmic reticulum, no t-tubules, no troponin (uses calmodulin) 7. IP3 receptor = primary calcium channel 8. calcium also enters from extracellular fluid

properties of whole muscles

1. not all muscle cells contract at the same time (only the ones activated by the same neuron) 2. number of activated motor units determines strength of contraction (larger number @ greater frequency = stronger)

electricity review

1. opposite charges attract, like charges repel 2. separating positive + negative charges requires energy 3. conductor (transfers charge: channel, carriers) vs. capacitor (stores charge: lipid bilayer)

neuron pathways + nuclei locations

1. posterior root/horn (somatic/visceral sensory neurons) 2. Lateral horn (autonomic motor neurons) 3. Anterior root/horn (motor neurons)

cardiac action potential

1. rapid depolarization due to opening of voltage-gated fast Na+ channels 2. plateau (maintained depolarization) due to opening of voltage-gated slow Ca2+ channels and close of some K+ channels 3. repolarization due to opening of voltage-gated K+ channels and closing of Ca2+ channels calcim comes in from outside AND SR rest, plateau, back (no hyperpolarization)

molecular basis of muscle contraction

1. relaxed muscle 2. myosin heads bind to actin 2. power stroke (phosphate released) 3. ADP release 4. ATP binding causes cross bridge detachment 5. ATP hydrolysis what you need 1. calcium: binds to troponin to get tropomyosin out of the way (blocks binding to actin) 2. ATP: keep releasing myosin heads and allow cocking

steps of action potential

1. resting membrane potential (-70 mV) 2. depolarizing stimulus 3. membrane depolarizes to threshold (all or none): voltage-gated Na+ channels open quickly and Na+ enters cell (positive-feedback, ended by inactivation), voltage gated K+ channels begin to open slowly 4. depolarization of cell 5. Na+ channels close and slower K+ channels open 6. K+ moves from cell to extracellular fluid 7. K+ channels remain open and more K+ leaves cell, hyperpolarizing it 8. voltage-gated K+ channels close, less K+ leaks out 9. cell returns to resting ion permeability = resting membrane potential ion permeability affects voltage (the lag causes huge spike up, followed by hyperpolarization) peak around +30 (when Na+ channels inactivated, K+ channels open) travel 10-100 m/s

muscle fiber terminology

1. sarcolemma: plasma membrane 2. sarcoplasm: cytoplasm 3. sarcoplasmic reticulum: smooth ER, stores Ca2+

myofilaments

1. short bundles that make up myofibrils 2. don't run entire length of cell 3. organized in repetitive groupings types 1. thin: actin + associated proteins 2. thick: myosin

types of muscle

1. skeletal: most widespread 2. cardiac 3. smooth

triad

1. somatic motor neuron releases ACh at neuromuscular junction 2. Net entry of Na+ through ACH receptor-channel initiates muscle action potential 3. action potential in T-tubule alters conformation of DHP receptor 4. DHP receptor (on T-tubule) opens RyR Ca2+ release channels (on sarcoplasmic reticulum) + Ca2+ enters cytoplasm 5. Ca2+ binds to toponin allowing actin-myosin binding 6. myosin heads execute power stroke 7. actin filament slides toward center of sarcomere calcium into cytosol: can also come from outside in cardiac; comes solely from sarcoplasmic reticulum in skeletal can't maintain calcium in cytoplasm forever (has to be exported back into SR/mitochondria): uses a lot of energy for removal: use of secondary and primary transporters, generation of heat

CNS integrates movement

1. spinal cord -integrates spinal reflexes -contains central pattern generators 2. brain stem + cerebellum -control postural reflexes -hand/eye movements 3. cerebral cortex + basal ganglia -voluntary movement

temporal summation

1. synapse receives 2 EPSPs separated in time: no summation 2. synapse receives 2 EPSPs at nearly the same time: summation

neuron

1. synapses (thousands) + dendrites: receive signals (input) 2. cell body (soma): receives EPSPs (add) + IPSPs (subtract): integration 3. axon hillock: decision maker: does depolarization meet threshold? all or none 4. axon: sends action potential: output signal

components of neuromuscular junction

1. synaptic knob: expanded end of neuron 2. synaptic vesicles: membrane bound sacs filled w/ acetylcholine (Ach: neurotransmitter) 3. motor end plate: region of sarcolemma across from synaptic knob: has folds/indentations to increase surface area 4. synaptic cleft: narrow space separating synaptic knob from motor end plate 5. Ach receptors: in motor end plate that binds to ACh 6. acetylcholinesterase (AChE): enzyme in synaptic cleft, rapidly breaks down ACh

electricity history

1786: Luigi Galvani: discovered that if leg of dead frog was touched by metal knife, leg would twitch violently: existence of animal electricity? 1792: Alessandro Volta: disagreed, realized Galvani's discovery was result of 2 different metals, steel knife + plate holding frog (moisture between causes electricity): invention of 1st battery (voltaic pile from copper, zinc, + moist pasteboard separator) 1803: Giovanni Aldini: galvanized executed body of criminal 1818: Andrew Ure: used galvanic battery to shock hanged man after his execution

anesthetics

1846: 27 year old Morton performs tumor removal at Mass General Hospital in front of an audience of doctors + surgeons: 1st successful use of ether as general anesthetic

refractory period

2 kinds 1. absolute (can never generate another action potential): from depolarization to hyperpolarization 2. relative (can only generate action potential if enough stimulation): excitability increases, may not have all Na+ channels active

Compared to skeletal muscle, smooth muscle

A and B -is slower to contract in response to stimulus -sustains contractions longer without fatigue

Suppose you have identified a neuron with sodium equilibrium potential +60 mV and a potassium equilibrium potential of -80 mV. Assume the membrane is only permeable to these two ions. Which of the following is TRUE about this neuron if its membrane potential is +20 mV?

A and C are TRUE -the membrane is more permeable to sodium than potassium ions -if the sodium and potassium permeability is both double, the resting potential of the neuron will remain at +20mV

astrocyte

CNS cell 1. protective: maintain blood-brain barrier 2. scaffold: create 3D framework for CNS 3. repair: damaged neural tissue 4. development: glial cells develop first 5. regulation: control interstitial environment

ependymal cells

CNS cell ciliated cuboidal epithelial cells that line the ventricles of the brain + the central canal of the spinal cord in conjunction with other glial cells, produce/circulate cerebral spinal fluid (CSF) + form the choroid plexus ciliated, stem cell like properties

microglial cells

CNS cell small, motile, important for immune system remove cell debris by phagocytosis

In focal dystonias the use of Botulinum toxin (Botox) alleviates symptoms because:

Botulinum toxins lead to no vesicular release

EBIO is a compound that prevents closure of ryanodine receptors in skeletal muscle. Based on your knowledge of skeletal muscle physiology, what will be the most likely effect of EBIO?

Following stimulation of the skeletal muscle, calcium will be continuously released to the cytoplasm maintaining contractions for prolonged periods, and leading to increase in body temperature.

Which of the following would produce an IPSP under physiological ion concentrations?

Glutamate binding to a ligand gated chloride channel.

Which of the following is TRUE with regard to the relative refractory period?

It could allow an action potential of much smaller amplitude to proceed along the length of an axon.

zombie

Defense Department has a response of armed forces in the case of attack CONOP 8888: unclassified document, military survival plan Wade Davis: Harvard ethnobotanist, claimed a living person could be turned into one by 2 special powders entered into bloodstream 1. tetrodoxin (TTX): fatal neurotoxin from pufferfish, blocks voltage-gated sodium channels (causes paralysis), can go into trance b/c brain still active

Excitation-contraction coupling:

Describes what happens in a muscle fiber between stimulation by acetylcholine and cross-bridge formation.

Little Timmy has a pain sensitivity disorder resulting from a genetic mutation in the activation gate of his voltage gated sodium channel that lowers threshold from -55mV to -65mV. As a result, he is ____________ likely to fire action potentials.His treatment could involve a medication that______________

More; increases the number of leaky potassium channels open at rest

The gamma motor fibers function is to set the firing tone of

Muscle spindle organs

According to the length tension relationship, the force generated in a muscle fiber is determined by:

Number of crossbridges that can be formed.

Myelin is produced by _____________ in the __________________.

Oligodendrocytes; CNS

What would most likely happen if the concentration of calcium ions outside a neuromuscular junction was decreased?

Less neurotransmitter would be released from a presynaptic terminal in response to an action potential.

Which of the following correctly describes the state of the voltage gated sodium channel at the peak of the action potential (+30mV)?

The activation gate is open, inactivation gate is closed, and the channel is inactive.

Which of the following statements regarding reflexes is CORRECT:

Reflexes preserve homeostasis

Which of the following could result in an EPSP?

Resting potassium channels are closed.

According to the sliding filament mechanism of skeletal muscle contraction, during contraction:

The H-band shortens, whereas the A-band stays the same size.

This question refers to Figure 2. SodiumGLO is a chemical that fluorescently labels voltage gated sodium channels (Nav). In an experiment, a first year graduate student applies SodiumGLO to an isolated motor neuron, but asks you to double check her findings. Which of the following would you expect to see (no backpropagation of action potential can take place)

a

Anna accidentally injected an insectide to herself that increases ATP hydrolysis on the myosin head. What symptoms might Anna exhibit?

a and c is correct -muscle relaxation might be accelerated -muscle contraction will be accelerated

all-or-none principle

a muscle fiber contracts completely or not at all no going half way

neurons

basic unit of the nervous system send + receive electrical + chemical signals/impulses (action potentials) throughout the body excitable characteristics 1. high metabolic rate (produce/consume tons of ATP to drive Na/K pumps + maintain gradients) 2. extreme longevity 3. nonmiotic (hard to replace) components 1. cell body (soma) 2. dendrites (in) 3. axon (out) structural classification (based on processes coming off soma) 1. unipolar (single: T-shape) 2. bipolar (2: axon/dendrite) 3. multipolar (many) functional classification 1. sensory (afferent): receptors to CNS 2. motor (efferent): CNS to muscles/glands 3. interneuron: communication between sensory + motor

terminal cisternae

blind sacs at the end of sarcoplasmic reticulum

dendrites

branched processes protruding from the cell body receive signaling information from multiple sources (facilitate integration) can be lots of variation in structure (more vs. less depending on function)

classifying reflexes

by processing site 1. spinal (in spinal cord) 2. cranial (in brain, lower brainstem) by complexity of circuit 1. monosynaptic 2. polysynaptic: most common by response 1. somatic (skeletal muscle) 2. visceral/autonomic (smooth, cardiac muscle, glands) ex: sweating, feeling of butterflies, involuntary by development 1. innate (genetic) 2. acquired (learned) -ex: driving: muscle memory, don't really think much, becomes automatic -ex: Pavlov: dogs salivate to a bell

Reflexes are classified by each of the following except

by the response they generate

graded potentials

decrease in strength as they spread out from point of origin ex: synaptic potentials

Which of the following changes would increase the probability of cardiac muscle contraction?

decreased rate of calcium reuptake

transverse tubules (T-tubules)

deep invaginations of the sarcolemma that extend into sarcoplasm brings action potentials into interior of muscle fiber 2 per sarcomere

hyperkalemic period paralysis

defect caused by incomplete closure of sodium inactivation gate results in increased level of persistent sodium influx, higher levels of potassium lots of twitching, then exhaustion/weakness/paralysis

measuring potential differences

calculated in reference ex: both electrodes inside the cell: 0 mV ex: recording in cell, reference in saline: -70 mV ex: reference in cell, recording in saline: +70 mV

damage to descending (upper motor neuron) pathways

causes 1. upper motor neuron lesion 2. disinhibition of spinal reflexes by disconnecting corticospinal inputs effects 1. exaggeration of muscle stretch reflexes 2. spread of reflex (to more adjacent body areas) characteristic decorticate posturing (activation of all spinal stretch reflexes) of animal after decapitation

neurotransmitters

chemical messengers released at presynaptic membrane always a lot available, will always dump out more than you need, serve as ligands for ion channel receptors influence receptors of postsynaptic membrane are broken down by enzymes assembled at synaptic knob ex: acetocholine

synaptic transmission

chemical synapses: use neurotransmitters (easier to move across space, but have to be made by ribosomes, can be degraded, modified) electrical synapses: pass electrical signals process 1. action potential depolarizes axon terminal 2. depolarization opens voltage-gated Ca2+ channels and Ca2+ enters cell 3. calcium entry triggers exocytosis of synaptic esicle contents 4. neurotransmitters diffuses across synaptic cleft + binds with receptors on postsynaptic cell 5. neurotransmitter binding initiates a response in postsynaptic cell if you equalize concentrations of K+ inside and outside, then gradient goes to 0 (instead of -75), same effect as closing Na+ channels, so membrane potential goes up, depolarization will cause release of vesicles (as Ca2+ flows in)

cell body (soma)

common features 1. nucleus 2. nucleolus 3. golgi complex specializations 1. mitochondrial number 2. free ribosomes + rough ER (Nissl bodies)

Motor units

consist of a motor neuron and all the muscle fibers it supplies

muscular system

consists of 700+ skeletal muscles (most well-studied, reference point)

motor unit

consists of a single motor neuron + the muscle fibers it controls (all will contract when stimulated) controls only a few muscle fibers in an entire muscle (more in larger muscles)

tetanus

constant/sustained maximum contraction eventually run out of energy (ATP) and get fatigue

muscle tone

continued steady, low level of contraction that stabilizes joints + maintains general muscle health there's always some low level of activity (never 0)

isotonic contractions

create force and move load actions 1. concentric: shortening 2. eccentric: lengthening muscle tension equals or is greater than resistence: elastic elements already stretched, muscle shortens

isometric contractions

create force without moving a load sarcomeres shorten, elastic elements stretch, little change in overall length muscle tension (force able to generate) is less than resistence, muscle doesn't shorten think about trying to lift something that's too heavy for you: you feel the tension, but don't actually move usually happens first

authorhythmic

able to generate muscle impulse without nervous stimulation no motor units no neurons needed to get the process started involuntary control

contraction

creation of tension in muscle 1. events at neuromuscular junction 2. excitation-contraction coupling 3. Ca2+ signal 4. contraction-relaxation cycle 5. sliding filament theory 1. nerve impulse releases ACh in synapse 2. ACh binds motor end plate receptors 3. Muscle impulse along sarcolemma/T-tubule 4. Calcium released into sarcoplasm 5. calcium binds troponin causing tropomyosin to uncover active binding sites 6. myosin heads bind to actin forming crossbridges 7. power strokes + release by ATP

After death, when metabolism stops, which step of the contractile cycle will be impaired?

crossbridge breaking

membrane potential (Vm)

defined as potential inside the cell relative to potential outside the cell where net flux of ALL ions together equals 0 a steady state, not an equilibrium voltage caused by separation of charge at the membrane... 1. Ions unequally distributed across membrane -small variations by species, cell type -gradients dependent on ATP-driven pumps 2. Membranes unequally permeable to various ions -at rest, easier for K+ to move than Na+ influenced by... 1. concentration gradient 2. membrane permeability basis of neuronal/muscle signaling between the ceiling (most positive you can go) and floor (most negative you can go) based on the concentrations of your ions (Eion) ions with greater permeability have greater influence (larger influence of X = closer to Ex): at rest, close to EK+, during depolarization, gets closer to ENa+

Z discs are to skeletal muscle as ____________ are to smooth muscle.

dense bodies

electrochemical gradient

dependent on... 1. concentration: movement from high to low (down) 2. charge of ions: move to equally distribute -may act as opposing forces in opposite directions (think: tug o war)

excitatory post-synaptic potential (EPSP)

depolarization (promotes action potential generation) if the membrane potential is more positive than Vm

Nernst equation

describes membrane potential that a single ion would produce if membrane were permeable to only that ion Ex = (58/z) log (Xo / Xi) Eion = (61/z) log (out/in) Ex = equilibrium potential of ion x (in mV) z= charge on ion x (valence) X = concentration of ion x (in mM) o = moving out i = moving in so... no concentration gradient if Xo = Xi or Ex = 0

Excitation-contraction coupling in skeletal muscles:

describes what happens in a muscle fiber between stimulation by acetylcholine and cross-bridge formation.

graded potential

differences from normal action potential 1. no minimum level required to initiate 2. 2 signals close together in time will sum 3. initial strength indicated by frequency of a series 4. can also use mechanical/chemical gated ion channels

other NMJ disorders

different causes, often same phenotypes 1. myasthenia gravis 2. myasthenic syndrome (Eaton Lambert Disease) 3. muscular dystrophies (Duchenne) 4. myotonias 5. multiple sclerosis 6. guillain-barre (acute idiopathic polyneuritis) 7. amoyotrophic lateral sclerosis (ALS)

The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________

smooth muscles use calmodulin, whereas skeletal muscles uses troponin as calcium sensors

neuroglia (glial cells)

support + protect neurons: help them do their job (ex: by helping to control ion concentrations) may play a role in signal transduction a major sink for neurotransmitters (disruption causes lots of dysfunction + disease) can be very complex 1. located in CNS and PNS 2. half volume of nervous system 3. smaller + more abundant than neurons 4. mitotic 5. physically protect/nourish neurons 6. brain tumors 7. contact capillaries (unlike neurons)

guillain-barre (acute idiopathic polyneuritis)

symptoms come fast can't move, numbness, weakness, tingling usually happens after viral infection: attacks nerves (myelin insulation): slower conduction, can't propogate signals treatment with plasmaphoresis: washing blood infusion of immunogobulin

synaptic potentials

synaptic potentials process... 1. Ca2+ signal helps vesicles fuse to pre-synaptic membrane + release neurotransmitters into synaptic cleft 2. neurotransmitters (chemical) cross the cleft and bind to receptor sites on ion channels 3. ligand-gated ion channels open, depolarization propagates the action potential notes... 1. travel from synapse in all directions 2. get smaller and slower over distance (graded) 3. passive membrane properties (like an electric cable)

You identify a new creature from Mars. You are investigating its cardiac action potential and you notice that its cardiac action potential is similar to the cardiac action potential in humans. The ONE difference is that these muscle cells also have potassium channels that are activated quickly by high concentrations of intracellular calcium. How would this change the properties of the Martian cardiac action potential?

the Martian action potential will have a shorter plateau phase

muscle fiber

the cell of a muscle

synapse

the junction between adjacent neurons, or neurons/muscles (NMJ) location of communication between neurons + muscles

equilibrium potential (Eion, Ex)

the membrane potential at which the concentration gradient + electrical potential forces are equal and opposite (for the ion of interest) ions move, but no net movement of ion across the membrane what do the values mean... 1. positive = causes positive charge inside cell (due to passive influx/efflux of ions) 2. negative = causes negative charge inside cell clarifying some misconceptions... 1.no significant change in ion concentrations 2. small percent of ions move to generate a sufficient Vm to balance diffusion force Ex: K+ (more concentrated inside cell, flows out, makes inside of cell more negative)= -75 mV Na+ (outside, flows in)= +58 mV Cl- (outside, flows in) = -59 mV Large Anions (inside, no flow) = none

malignant hyperthermia

disorder caused by certain anesthetics (usually happens in OR): impossible to know who will have this reaction massive stiffness (complete contraction of muscles), temperature skyrockets, death excessive activation: massive dump of calcium in system (massive contraction), lots of ATP used and heat produced drug to prevent (injection settles down receptor)

myasthenia gravis

disorder caused by post-junctional alteration (auto-immune response blocks ACh receptors preventing maintenance of contraction) onset pharyngeal + ocular weakness, muscle fatigue worsens with exercise treatment: anticholinesterases (prevent break down of ACh, more available to bind to receptors)

dystonia

disorder characterized by involuntary sustained muscle contractions resulting in twisting + repetitive movements or abnormal postures

multiminicore disease

disorder primarily affecting skeletal muscles muscle weakness + related health problems (mild to life-threatening), increased risk of malignant hyperthermia due to mutations in RYR1 + SEPN1 receptor genes

The characteristic of muscles that allows them to return to their original resting shape after changing size is known as:

elasticity

deep brain stimulation

electrodes work like a pacemaker for the brain helps stabilize neuromuscular problems used with Parkinson's instantaneous difference when turned on vs. off

myasthenic syndrome (eaton lambert syndrome)

pre-junctional alteration decreased ACh release affects peripheral + pelvic muscles improves w/ exercise: forces contractions, keep flooding system with as much calcium as possible doesn't improve w/ anticholinesterases (just don't have enough neurotransmitter)

goldman-hodgkin-katz (GHK) equation

predicts membrane potential resulting from the contribution of all ions crossing the membrane: a weighted average note... 1. value is somewhere between largest and smallest Ex 2. ions with greater permeability have a greater influence on Vm (brings it closer to Ex): at rest, mostly permeable to K+, so Vm close to Ek similar set up to Nernst equation 1. take averages of P (permeability) x E (equilibrium potential) for all ions 2. in/out vs. out/in shows that you can change Vm by changing permeability of ions (implications in a neuron)

muscle tension

force created by muscle

propogation

forwards: 1 segment of axon triggers depolarization of the next (refractory = resistance = needs time to recover = won't go backwards) one cell rising, one falling, one at rest: travelling down the line can go in both directions (right and left) if trigger zone is in the middle, but won't travel back to the middle

a-Bungarotoxin

from snake venom binds irreversably + competitively to ACh receptors @ neuromuscular junction can cause paralysis

sarcomere

functional contractile unit in skeletal muscle fiber combo of thick + thin filaments 1. defined as area between 2 adjacent Z discs 2. shorten towards M line as muscle fibers contract (thin filaments move, thick filaments don't) Parts: (lateral to medial) 1. Z line: boundaries, attach thin filaments 2. I band: region of just thin filaments 3. A band: extends length of thick filament (includes some overlap with thin) 4. H zone: region of just thick filaments 5. M line: center, attach thick filaments

nuclei

functional groups of neuron cell bodies within grey matter types (in spinal cord) 1. sensory -in posterior horns -contain interneuron cell bodies of somatic sensory nuclei and visceral sensory nuclei 2. motor -in anterior horns -contain somatic motor nuclei 3. autonomic motor -in lateral horns

PNS terminology

ganglia: neuron cell bodies (NOT the same as glia) peripheral nerves: neuronal axons neuroglia 1. satellite cells 2. schwann cells -cover axons, myelin, 1 per segment

oligodendrocytes

in CNS only wrap themselves around the axons like electrical tape wrapped around a wire produce myelin the only glial cells that can form synapses with neurons (as progenitor cells)

inhibitory post-synaptic potential (IPSP)

hyperpolarization potential (prevents generation of action potential), occurs when membrane potential more negative than Vm

central nervous system (CNS)

includes 1. brain 2. spinal cord 3. sensory receptors of sense organs (eyes, ears, nose) 4. nerves connecting nervous system with other systems many subdivisions cell types 1. astrocyte 2. ependymal cell 3. microglial cell 4. oligodendrocyte

muscle hypertrophy

increase in muscle fiber size (not increase in number of fibers) results from repetitive stimulation of muscle fibers mitochondria increase in number, so amount of ATP increases myofibrils + myofilaments increase in number, causing increase in size can be caused by some mutations ex: in athletes, bodybuilders (physiological)

disorders in sodium channel 1.7

increased function: pain absence: feel no pain (not actually a good thing: unaware of injuries): congenital insensitivity to pain (CIP) scorpion bites: venom opens channels (massive pain): grasshopper mice are resistent b/c they have a different/modified channel that will close instead of open (don't feel any pain)

familial thoracic aortic aneurysm and dissection

inherited condition that predisposes individuals to the development of aneurysms, dilations in a blood vessel, particularly in thoracic aorta smooth muscles relax (don't provide tone)

flexion reflex + crossed extensor reflex

more complex, polysynaptic, crosses over from one side to the other 1. painful stimulus activates nociceptor 2. primary sensory neuron enters spinal cord + diverges 3. one collateral activates ascending pathways for sensation (pain) + postural adjustment (shift in center of gravity) 4. withdrawal reflex pulls foot away from painful stimulus (relaxes extensors, contracts flexors: leg flexes) 5. crossed extensor reflex supports body as weight shifts away from painful stimulus (contracts extensors, relaxes flexors: leg extended)

current

movement of ions changes membrane potential

muscle fatigue

multiple mechanisms cause this in many locations central 1. CNS: psychological effects, protective reflexes peripheral 1. neuromuscular junction: decrease in neurotransmitter release + receptor activation 2. excitation-contraction coupling: change in muscle membrane potential 3. Ca2+ signal: SR Ca2+ leak, decreased Ca2+ release, decreased Ca2+ troponin interaction 4. contraction-relaxation: depletion theories (PCr, ATP, glycogen), accumulation theories (H+, Pi, lactate)

What takes place when a skeletal muscle is stretched,

muscle tone is increased and more motor units are recruited to the contraction.

axons

output, starts at hillock neurons have one or none at all transmit nerve impulse away from the soma (toward the synapse) associated structures 1. collaterals 2. synaptic knobs types 1. unipolar: 1 process, very long, fused to dendrites, not common in humans 2. bipolar: relatively small, common in retina (has lots of inputs + processing) 3. multipolar: includes multiple dendrites, most common

hyperpolarization

overshoot polarizing past the resting state (due to K+ rushing out) Vm becomes even more negative

myotonic dystrophy

part of a group of inherited disorders called muscular dystrophies (Most common form beginning in adulthood) 1. myotonia (prolonged muscle contractions) 2. can't relax certain muscles after use (ex: can't release grip on doorknob) could be b/c NMJ or something more downstream: can't be completely explained (cause unknown)

The afferent (sensory) and efferent (motor) axons together form the

peripheral nervous system.

golgi tendon reflex

prevents damage when there's too much tension by relaxing the muscle (ex: if something is too heavy, you'll drop it: protective mechanism 1. golgi tendon organs are... -nerve endings -located within tendons near muscle-tendon junction -in series with contracting extrafusal muscle 2. as muscle contracts, force is exerted on its tendon -result: increased tension in tendon + activation of golgi tendon organ 3. nerve impulses signal interneurons in spinal cord, which inhibit actions of motor neurons -relax the muscle to prevent injury when load is too great process 1. neuron from golgi tendon organ fires 2. motor neuron is inhibited 3. muscle relaxes 4. load is dropped

nervous system

processes + coordinates... 1. sensory data from in/out of body 2. higher brain functions (IQ, memory, learning, emotion) 3. motor functions (activity of organs, skeletal muscles) cytology 1. neurons 2. neuroglia

titin

provides elasticity + stabilizes myosin involved in isometric contractions (when stretched out completely, moves to isotonic contraction)

axon hillock

region where the axon connects to the cell body

white matter

regions of CNS tissue containing myelinated axons lots of communication going on

muscle contraction duration

shortest to longest 1. skeletal (fastest rise/fall) 2. cardiac (fast rise/fall) 3. smooth (takes a long time to generate tension/contract, stays contracted for longer b/c have to wait for 2nd messenger calmodulin)

axon collaterals

side branches of the main axon

muscle spindle

works like a thermostat: brain can "set" it to any degree of desired tension (variations from setpoint send contraction signals to motor units) 1. lots embedded in a muscle 2. in parallel with contracting extrafusal muscle muscle stretches: sensory input goes to spinal cord, motor neurons cause contraction in a negative feedback-like mechanism -reflex will counteract stretching of muscle by contracting muscle 1. extrafusal muscle fibers at resting length 2. sensory neuron is tonically active 3. spinal cord integrates fuction 4. alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles 5. extrafusal fibers maintain certain level of tension even at rest: muscle tone

myelinated

wrapping of axon (10-160 of these internodes) leaving nodes of ranvier (places where action potentials happen) can increase speed of conduction by 100 w/out: get multiple sclerosis (lots of different problems): exposure to more potassium channels (block for longer action potentials, need to have just the right dosage)

reflex arc

the neural wiring of a single reflex 1. always begins at PNS receptor 2. communicates with CNS 3. ends at peripheral effector ex: patellar tendon (knee jerk): usually described as monosynaptic (but actually, it's polysynaptic b/c multiple neurons/synapses) 1. stimulus (stretches muscle) 2. afferent path (sensory neurons) 3. integration (CNS) 4. efferent path (somatic motor neurons) 5. response (by effectors) a feedback system 1. controlled condition disrupted 2. sensory neuron receptors relay nerve impulses to central control center 3. control center integrates + relays info 4. motor neurons initiate response by effector (muscle/gland) to counteract disrupting stimulus 5. return to homeostasis types 1. monosynaptic: direct communication between sensory + motor neuron -2 neurons, 1 synapse 2. polysynaptic: interneuron facilitates sensory-motor communication -3+ neurons 2+ synapses

sliding filament theory (model)

thin filaments slide across thick filamens toward the center of the sarcomere (M-line) result 1. H zone + I zone shorten 2. A-band doesn't change 3. Z-lines get closer together

length-tension relationships in contracting skeletal muscle

too close: no contraction increase distance: reach optimum (2-2.3 micrometers) go futher away: doesn't work think in terms of sliding: you want to optimize cross-bridge formation mutations can cause huge effects/problems

synaptic vesicle

type of secretory vesicle transported from soma to axon terminal clustered at active zone (sites of release) ~40 nm diameter, contain neurotransmitter release is fast (ATP + Ca2+ dependent steps), coordinated with action potential arrival, repeatable at high frequencies, highly regulated

glial cells of PNS

types 1. satellite cells 2. schwann cells (neurolemmocytes)

Neurons in which dendritic and axonal processes are continuous and the soma lies off to one side are called

unipolar

This question refers to Figure 3. This neuron would be structurally classified as a:

unipolar neuron

Na+-K+ pump

uses ATP to maintain ion concentrations of Na+ and K+ at constant levels (gradients run down over hours/days) pumping against the gradients (3 Na+ out, 2 K+ in)

resting potential

usually ~ -70mV

muscle atrophy

wasting of tissue that results in reduction of muscle size, tone, and power can be caused by lack of stimulation (exercise) ex: after you get a cast off

load

weight that opposes contraction

gray matter

when you're looking at cell bodies, dendrites, synaptic knobs

trigger zone

where action potential is initiated (axon hillock) has high density of voltage gated sodium channels doesn't have to be right next to soma

myofibrils

where contractions actually happen 1. 100-1000 contained in sarcoplasm of muscle fiber 2. shorten --> contraction --> motion 3.cylindrical structures, extend entire length of cell 4. made of different kinds of filaments (thick + thin: myosin + actin) 5. contain multiple + repeating sarcomeres

intravenous muscle relaxants

work by binding to ACh receptors @ neuromuscular junction and blocking them nondepolarizing blocker: closed blocked (competitive binding: prevents agonist) ex: mivacurium, rocuronium, pancuronium depolarizing blockers: open blocked (persistent depolarization at motor end plate causes desensitization) ex: succinycholine

Which of the following statements about the equilibrium potential for an ion are TRUE?

If the concentration gradient of the ion changes, the equilibrium potential will also change.

The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________

Smooth muscles requires phosphorylation of myosin, whereas skeletal muscles requires calcium to bind to troponin.

organization of skeletal muscle

(big to small) 1. Skeletal Muscle 2. Connective Tissue, Muscle Fasciles (bundles), Nerves, Blood Vessels 3. Connective Tissue + Muscle Fibers 4. Myofibrils 5. sarcomeres 6. myofilaments: actin/myosin

without gamma motor neurons

1. alpha motor neuron fires 2. muscle contracts 3. less stretch on center of intrafusal fibers 4. firing rate of spindle sensory neuron decreases

thick filaments (myosin)

1. 11 nm in diameter (2x thicker than thin) 2. composed of bundled molecules of myosin (has 2 heads and elongated tail) 3. heads from crossbridges, which bind to thin filaments during contraction

thin filaments (actin + associated proteins)

1. 5-6 nm in diameter 2. comprised of 2 strands of molecules twisted around each other -filamentous-actin (F-actin): multiple components - globular actin (bead-shaped G-actin): individual component 3. contains 2 regulatory proteins: controlled by calcium -tropomyosin -troponin

Benipidine is a drug that inhibits voltage gated calcium channels. Applying benipidine within the neuromuscular junction would:

Prevent the release of neurotransmitter from presynaptic neurons

__________ is made of strings of multiple globular molecules polymerized to form long chains or filaments.

Actin

Cellular respiration (ATP production) stops following death, which results in rigor mortis. This phenomenon is best explained by the fact that:

Actin myosin cross-bridges cannot be broken

Which of the following is a unique property of muscle fibers (and tissue)

All of the above -They are excitable such that outside stimuli can initiate electrical changes in the muscle fiber leading to contraction of that muscle fiber -They are contractile such that stimulation of muscle fiber can lead to contraction or shortening of the muscle fiber -They are elastic such that they have the ability to return to their original length when the tension of contraction is released

By increasing twitch frequency, muscles can generate:

All of the above -greater tension -unfused tetanus -fused tetanus

Which of the following is true of synaptic potentials?

All of the above are true -they can induce a depolarization -they can induce a hyperpolarization -they are graded diminishing over time

Which of the following statements is FALSE about resting membrane potential in neurons?

All of the above are true statements -Ions enter the cell via passive diffusion -Ions leave the cell via passive diffusion -Ions are being moved by active transport

An overdose with dantrolene (a ryanodine receptor blocker) could produce effects to skeletal muscle most similar to those of

Alpha-bungarotoxin poisoning (an acetylcholine receptor inhibitor)

Lidocaine is a local anesthetic used to dampen neuronal excitability. Lidocaine blocks voltage-gated Na+ channels in the axon. You carry out an experiment where you locally apply Lidocaine to a node of Ranvier that is midway along the axon. You apply Lidocaine in such a way that it does not spread to neighboring nodes. Based on what you know about action potentials, what will happen if you then stimulate the axon hillock with an above threshold stimulus?

An action potential will be initiated, but when it reaches the midway point, voltage-gated sodium channels will not open, although some voltage-gated potassium channel might open.

A closer look at the muscle fiber subtypes in skeletal muscles responsible for supporting posture rather than sprinting would likely reveal:

An increased number of type I fibers & more myoglobin

This question refers to Figure 1. If the concentration of Na inside the cell was changed to 150mM, equilibrium the equilibrium potential for sodium would _____________ and resting membrane potential would _____________________.

Become more negative, become hyperpolarized

Reflexes are classified by each of the following except

By the response they generate

Which of the following statements correctly explains the relationship between Ca2+ and the contractile proteins found in skeletal muscle?

Calcium binds to TroponinC. This removes tropomyosin from the myosin binding site on actin filaments.

Which of the following is most likely to depolarize the membrane of a typical neuron?

Changing the concentration of sodium inside the cell from 10mM to 0mM

The region of the sarcomere containing only actin filaments is known as the:

I band

Which of the following is FALSE about neurons?

In adults, the CNS contains a fixed amount of neurons for the duration of an individuals life.

All of the following are presynaptic disorders except:

Myasthenia Gravis

Which of the following is a postsynaptic disorder?

Myasthenia Gravis

Which of the following statements are true about myelinated axons?

Myelin insulates the axon leading to saltatory conduction

EGTA is a slow calcium chelator that binds calcium, preventing it from binding to its targets. What will be the most likely effect if you apply high levels of EGTA to the intracellular side of a skeletal muscle cell?

No muscle contraction will take place because calcium released from the sarcoplasmic reticulum will bind to EGTA preventing binding of calcium to troponin.

Which of the following is an important function of ATP in muscle? (A) It is required for the dissociation of myosin from actin. (B) It is hydrolyzed by the ATPase that pumps calcium ions into the sarcoplasmic reticulum. (C) It is used for the phosphorylation of myosin in smooth muscle. (D) it directly activates ryanodine receptors.

Only A, B and C is correct

satellite cells (amphicytes)

PNS cells surround ganglia regulate environment around neuron

neurolemmocytes (Schwann cells)

PNS only wrap themselves around the axons like electrical tape wrapped around a wire, insulateds myelinated axons produce myelin comparable to oligodendrocyte, except more cells are required, only make single myelin segments increases speed of action potentials makes nerves appear white

During the repolarization phase of the action potential:

Potassium permeability is mostly increasing

Calcium is essential for signal propagation through the NMJ because:

Signals vesicle docking to the presynaptic membrane

In a motor neuron, in which region of the cell would you expect to find the least number of voltage gated sodium channels?

Synaptic Knob

Which of the following statements are FALSE about resting membrane potential?

The cell membrane is very permeable to sodium ions.

Which of the following events are FALSE about the peak of the action potential when Vm is most depolarized (~ +30mV)?

The inactivation gate of voltage gated sodium channels is OPEN

You are recording a muscle twitch from a cardiac muscle. How would its time course change as a result of a mutation that results in a cardiac muscle lacking voltage-gated calcium channels?

The plateau phase of action potential will be most likely shortened leading to a smaller contraction.

Which of the following statements are FALSE about the Na/K ATPase pump:

The pump contributes to Vm by driving the Vm to more positive values

A student working in a lab accidentally injects himself with a drug that inhibits the L-type calcium channel (DHP) resident in skeletal muscles. Which of the following processes will be most affected?

The removal of tropomyosin from myosin binding sites

While working in an electrophysiology laboratory, an undergraduate student measures the resting membrane potential (Vm) of a mammalian cell to be +70mV rather than the typical -70 mV. This discrepancy is likely be due to:

The student is measuring the potential outside the cell relative to the inside

When a motor neuron stimulates a muscle fiber to contract, the latent period refers to:

The time between the firing of a neural action potential and a muscle action potential

How would the action potential waveform (time course) change as a result of a mutation that results in a neuron having twice as many voltage-gated sodium channels?

There will be little change to the action potential waveform.

The classical action potential only propagates in one direction because:

Voltage gated sodium channels are inactivated while forward membrane segments are depolarizing

If an electrode is placed in the middle of an axon at rest and an above-threshold voltage (stimulus) is applied, action potentials:

Will start at that point and travel in both directions in the axon.

reflex

a rapid automatic involuntary motor response to internal or external stimuli doesn't require higher processing: stimulus = response 1. some inborn (ex: pull away from heat), some learned/acquired 2. generally protective of the body 3. preserve homeostasis: adjusts organs + systems 4. requires few neurons, minimal synaptic delay: need for speed 5. response is the same every time 6. foundation of nearly all movements (through activation/modulation of underlying circuitry by higher brain centers) types: 1. spinal (ex: pain response) -bypasses brain: integration/processing in the spinal cord at level of info input 2. cranial (ex: eye tracking) -if integration in the brainstem 3. somatic (ex: skeletal muscle contraction) 4. autonomic/visceral -involuntary examples... 1. auditory (loud noise, eyes turn) 2. corneal (touch of cornea, eye blink) 3. cough (food/liquid in pharynx, clear airway) 4. gag (stimulate back of tongue) 5. pupillary (light causes constriction) 6. muscle (stretching 7. movement (walking?)

twitch

a single contraction-relaxation cycle add together to get full contraction of a muscle (summation): eventually reach maximum tension (maximum force)

muscle tone is:

a state of sustained partial contraction

permeable

a surface that allows another substance to pass through it

saltatory conduction

action potentials jumping from node to node (of ranvier) over myelinated internodes faster propogation, allows for smaller fibers

SNARE proteins

affected by toxins like botox which increase/decrease the number of docked/primed vesicles

voltage-gated Na+ channels

allow Na+ to come into the cell (down gradient) states 1. activation (closed @ rest, opens @ depolarization, resets @ repolarization) 2. inactivation (closes @ peak, resets @ repolarization) 3. closed 9 kinds, found in different places, problems can be very bad

alpha + gamma motor neurons

alpha motor neuron: innervate extrafusal muscle (which are what contract) -control skeletal muscle contractions gamma motor neuron: innervate muscle spindles, intrafusal muscle -adjust stretch sensitivity

The sensory fibers of the muscle spindle organs synapse with _____ to form a monosynaptic circuit

alpha motor neurons.

When a neurotransmitter binds to its receptor on a ligand gated sodium channel:

an EPSP is produced

multiple sclerosis

an example of a demyelinating disease

The purpose of cisternae, specializations of the sarcoplasmic reticulum that border the t-tubule, is to:

ensure a supply of Ca2+ ions to the muscle fiber.

peripheral nervous system (PNS)

everything outside of CNS cranial nerves, spinal nerves, ganglia

synaptic knobs

expanded regions at the tip of telodendria

neurogenesis

generation of neurons: probably from stem cells b/c neurons are non-mitotic look at a mouse before and after seizure: it's possible to increase number of neurons

depolarizaion (opposite of repolarization/hyperpolarization)

getting further away from setpoint (mV) causes opening of Na+ channels

repolarization

going back to resting potential after an action potential by re-establishing a greater membrane potential Vm decreases

depolarization

going from resting potential to action potential -70 mV --> more positive value (0): Vm

volatile anesthetics

halothanes/ethers stop firing of action potentials by lowering membrane potential (hyperpolarize closer to Ek by opening voltage gated potassium channels) stay far away from action potential threshold

nebulin

helps align actin

K+, large anions (exclusively)

ions that are more concentrated inside the cell

Na+, Cl-

ions that are more concentrated outside the cell

A contraction that generates force and moves a load is known as __________, whereas one that generates force without movement is known as __________.

isotonic, isometric

post-translational modifications

may dictate protein shape, activity, stability, binding partners, or localization on vs. off (ex: phosphorylation) 1. kinases: add a phosphate (activate) 2. phosphatases: remove a phosphate (deactivate)

passive electrical signal

membrane potential that dissipates as it propogates (in time + space) degrades

active electrical signal

membrane potential that is augmented/transmitted w/out decrement as it propogates (in time + space) doesn't degrade with distance

Naomi's father suffers a stroke that leaves him partially paralyzed on his right side. What type of glial cells would expect to find in increased numbers in the damaged area of the brain that is affected by the stroke?

microglia

The glial cells responsible for phagocytosis of cell debris are:

microglia

For which of the following disorders would an Acetylcholinesterase inhibitor be the most effective?

myasthenia gravis

The concentration of ion X(+) inside the cell is 250mM, and itâ s concentration outside the cell is 75mM. According to the Nernst equation, the equilibrium potential for ion X is:

negative

A person with hyponatremia has lower than normal extracellular Na+ concentration shifting the Ena from +58mV to +10 mV. Based on your knowledge of ion movement in neurons, the main problem(s) that hyponatremia could causes are

neurons can still fire action potentials in response to EPSPs, but the AP amplitude will be smaller.

anaxonic neurons

neurons with small, relatively uniform processes

A motor unit consists of:

one neuron and the muscle fibers it controls

relaxation

release of tension

steady state vs. equilibrium

steady state: going in and going out, volume constant equilibrium: static, volume constant

rigor mortis

stiffening of muscles once a person dies no more ATP, can't get myosin heads to break off of actin, so muscles still contracted takes 48-72 hours for muscle proteins to breakdown + for muscle to relax