A&P Lecture Test 3 Review - Chap 9,10,11

8/3/2019 A&P Lecture Test 3 Review - Chap 9,10,11

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Chapter 9 Muscles and Muscle Tissuey GP- SHORT DISTANCE; CHEMICALLY OPEN ION CHANNELSy AP- LONG DISTANCE; VOLTAGE OPENS ION CHANNELSy Muscle tissue types PICTURE1,1A

o Skeletal- striated, voluntary 40% of body mass Most responsible to generating heat

o Cardiac- striated, involuntaryo Smooth- NOT striated, involuntary

y Muscles distinguished by their ability to transform chemical energy into directed mechanicalenergy

y When you see prefixes myo, mys, or sarco, the reference is to muscley Characteristics of muscle tissue:

o Excitabilityo Contractibilityo Extensibilityo Elasticity

y Each muscle is served by one artery, on nerve, and one or more veinsy Skeletal muscle

o Connective tissue sheaths: Epimysium- surround entire muscle; dense regular connective tissue Perimysium- surrounds fascicle; fibrous connective tissue Endomysium- surrounds muscle fiber; areolar connective tissue

y Microscopic anatomy of skeletal muscleo Cylindrical cello Multiple peripheral nucleio Many mitochondria-(mitochondria/glycogen-provides energy used during contraction)o Glycosomes for glycogen storage, myoglobin for O2 storageo

Glycosomes- granuales of stored oxygen that provide glucose during periods of muscleactivity

o Myoglobin- red pigment that stores oxygeno Hemoglobin- pigment that transports oxygen in bloodo Myofibrils- densely packed, rod like elements

*80% of cell volume Exhibit striations- perfectly aligned repeating series of dark A bands/light I bands

o Sarcomere- smallest contractile (functioning) unit PICTURE2 Region of myofibril between 2 successive Z discs Composed of thick and thin myofilaments *Thick filaments- contain myosin *Thin filament- contain actin Z disc- coin shaped sheet of protein that anchors thin filaments and connects

myofibrils to bone another

H zone- lighter midregion where filaments do not overlap M line- line of protein myomesin that holds adjacent thick filaments together Ultrastructure of THICK filament- composed of protein Myosin

y Myosin tailsy Myosin heads- act as cross bridges during contraction

o Binding sites for actin of thin filaments and ATP


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Ultrastructure of THIN filament- twisted double strand of fibrous protein F actiny *Tropomyosin and Troponin- regulatory proteins bound to actin

Sarcoplasmic reticulum- surrounds each myofribrily *Functions in the regulation of intracellular Ca levels- at rest Ca stored in

terminal cisternae; released during contraction

y Calcium provides final go signal for contraction T tubules- continuations of the sarcolemma

y Penetrate the cells interior at each A band/I band junctiony Associate with the paired terminal cisternae to form triads that encircle each

sarcomere

Triad relationships:y *T tubules conduct impulses deep into muscle fibery T tubule proteins- voltage sensors

Sarcoplasm- the cytoplasm of a muscle celly Contraction- the generation of force

o Does not necessarily cause shortening of the fiber; shortening occurs when tensiongenerated by cross bridges on the thin filaments > forces opposing shortening

y Sliding filament model of contractiono *Relaxed muscle- thin and thick filaments overlap only slightly PICTURE3o Contraction:

1. Myosin heads bind to actin 2. Detach 3. Bind again- propels the thin filaments toward the M line

o As H zones shorten and disappear: Sarcomeres shorten Muscle cells shorten Whole muscle shortens

y Requirements for skeletal muscle contractiono 1. Activation- neural stimulation at a neuromuscular junctiono 2. Excitation-contraction coupling:

Generation and propagation of an action potential along the sarcolemma Final trigger- a brief rise in intracellular Ca levels

y Events at the neuromuscular junctiono Skeletal muscles are stimulated by somatic motor neuronso *Nerve cells that activate skeletal muscle fibers are called somatic motor neurons

y Neuromuscular junctionso Situated midway along the length of a muscle fibero Axon terminal and muscle fibers are separated by a gel filled space called a synaptic clefto Synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (Ach)o

Junctional folds of the sarcolemma contain ACh receptors

Provide large surface area for the millions of ACh receptors located therey *A resting sarcolemma is polarizedy Events at the neuromuscular junction PICTURE4

o 1. Nerve impulse arrives at axon terminalo 2. ACh is released from synaptic vesicleso 3. Ach diffuses across synaptic clefto 4. Ach binds to receptors on sarcolemmao 5. Action potential generated


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y Destruction of acetylcholineo Ach effects are quickly terminated by the enzyme acetylcholinesteraseo Prevents continued muscle fiber contraction in the absence of additional stimulation

y Events in generation of an Action Potential PICTURE5o 1. Local depolarization

Ach binding open chemically gated ion channels Simultaneous diffusion of Na (inward) and K (outward) More Na diffuses, so the interior of the sarcolemma become less negative Local depolarization- end plate potential

o 2. Generation and propagnation of an action potential End plate potential spreads to adjacent membrane areas Voltage-gated Na channels open Na influx decrease the membrane voltage toward a critical threshold If the threshold is reached, an action potential is generated Local depolarization wave continues to spread, changing the permeability of the

sarcolemma

Voltage-regulated Na channels open in the adjacent patch, causing it to depolarize tothreshold

o 3. Repolarization Na channels close and voltage-gated K channels open K efflux rapidly restored the resting polarity Fiber cannot be stimulated and is in a refractory period until repolarization is

complete

Ionic condition of the resting state are restored by the Na K pumpy *Cross bridge formation- attachment of myosin heads to actiny Excitation-contraction (E-C) coupling PICTURE6

o Sequence of events by which transmission of an AP along the sarcolemma leads to sliding ofthe myofilaments

o Latent period: Time when E-C coupling events occur Time between AP initiation and the beginning of contraction

y Events of E-C couplingo AP is propagated along sarcolemma to T tubuleso Voltage sensitive proteins stimulate Ca release from SR

Ca is final trigger for contractiony Role of calcium in contraction

o At low intracellular Ca concentration: Tropomyosin blocks the active sites on actin Myosin heads cannot attach to actin Muscle fiber relaxes

o At higher intracellular Ca concentration: Ca binds to troponin Troponin changes shape and moves tropomyosin away from active sites Events of the cross bridge cycle occur When nervous stimulation ceases, Ca is pumped back into the SR and contractions

ends

y Cross bridge cycle PICTURE7o Continues as long as the Ca signal and adequate ATP are presento Cross bridge formation- high energy myosin head attaches to thin filament


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o Working (power) stroke- myosin head pivots and pulls thin filaments toward M lineo Cross bridge detachment- ATP attaches to myosin head and the cross bridge detacheso Cocking of the myosin head- energy from hydrolysis of ATP cocks the myosin head into the

high energy state

y Review principles of muscle mechanismso same principles apply to contraction of a single muscle fiber and a whole muscleo contraction: produces tension, the force exerted on the load/object to be movedo Contraction does not always shorten a muscle Isometric contraction- no shortening; muscles tension increases but does not exceed

the load

Isotonic contraction- muscle shortens because muscle tension exceeds the loado Force and duration of concentration vary in response to stimuli of different frequencies and

intensities

y Motor unit: the nerve-muscle functional unito Motor unit= a motor neuron and all muscle fibers it supplieso Small motor units in muscles that control fine movements (fingers, eyes)o Large motor units in large weight bearing muscles (thighs, hips)o Muscle fibers from a motor unit are spread throughout the muscle so that a single motor uni

causes weak contraction of entire muscleo Motor unit in a muscle usually contract asynchronously; helps prevent fatigue

y Myogram- a graphic recording of contractile activityy Muscle twitch

o Response of a single muscle to a single, brief threshold stimuluso Simplest contraction observable in the lab (recorded as a myogram)o **Three phases of a twitch: PICTURE8

1. Latent period- events of excitation-contraction coupling 2. Period of contraction- cross bridge formation; tension increases 3. Period of relaxation- Ca reentry into the SR; tension declines to zero

y Muscle twitch comparisonso *Different strength and duration of twitched are due to variations in metabolic properties

and enzymes in different muscles

y Graded muscles responseso Variations in the degree of muscle contractiono Required for proper control of skeletal movemento Responses are graded by:

1. Changing the frequency of stimulation 2. Changing the strength of the stimulus

y Response to change in stimulus FREQUENCY PICTURE8o A single stimulus results in a single contraction- a muscle twitcho Increase frequency of stimulus (muscle does not have time to completely relax between

stimuli)

o *Ca release stimulates further contraction temporal (wave) summationo Further increase in stimulus frequency unfused (incomplete) tetanuso If stimuli are given quickly enough fused (complete) tetany results; EX- mom lifting car off

her child

o Temporal/wave summation = unfused/incomplete tetanusy Response to change in stimulus STRENGTH

o Threshold stimulus- stimulus strength at which the first observable muscle contractionoccurs


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o Muscle contracts more vigorously as stimulus strength is increased above thresholdo Contraction force is precisely controlled by recruitment(multiple motor unit summation),

which brings more and more muscle fibers to contract

o Size principle- motor units with larger and larger fibers are recruited as stimulus intensityincreases

Size principle important b/c it allows the increases in force during weak contractions *This principle explains how the same hand that pats your check can deliver a

stinging slapy Muscle tone

o Constant, slightly contracted state of all muscleso Due to spinal reflexes that activate groups of motor units alternately in response to input

from stretch receptors in muscles

o Keeps muscles firm, healthy, and ready to respondy Isotonic contractions

o Muscle changes in length and moves the loado Isotonic contractions are either concentric or eccentric:

Concentric contractions- the muscle shortens and does work; EX- bicep curls topickup a book

Eccentric contractions- the muscles lengthens as it contracts; 50%more powerfulthan concentric at the same loadEX- biceps as putting the book downy Isometric contractions- muscle neither shortens nor lengthens; maintaining upright position,

holding joints in place

o The load is greater than the tension the muscle is able to developo *Tension increases to the muscles capacity, but the muscle neither shortens nor lengthens

EX- trying to push down a wally Electrochemical and mechanical events are identical in both isotonic and isometric, HOWEVER, in

isotonic contractions- the thin filaments are sliding, in isometric- the cross bridges are generating

force but are not moving

y ATP supplies the energy for cross bridge movement and detachment and for operation of thecalcium pump in SR

y Muscle metabolism: energy for contraction PICTURE9o ATP- only source used directly for contractiono Available stores of ATP are depleted in 4-6 secondso ATP is regenerated by:

1. Direct phosphorylation of ADP by creatine phosphate (CP)- fastest 2. Anaerobic(without oxygen) pathway (glycolysis)

y At 70% of maximum contractile activity:o Bulging muscles compress blood vesselso Oxygen delivery is impairedo Pyruvic acid is converted into lactic acido Lactic acid:

Diffuses into the bloodstream Used as fuel by the liver, kidneys, and heart Converted back into pyruvic acid by the liver

3. Aerobic respiration- slowesty Produces 95% of ATP during rest and light to moderate exercisey Fuels: stored glycogen to: blood glucose- pyruvic acid from glycolysisy Aerobic exercise increase # of capillaries surrounding muscle fibers, # of

mitochondria, more myoglobin


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y Muscle fatigueo Physiological inability to contracto Occurs when:

Ionic imbalances (K, Ca, P) interfere with E-C coupling Prolonged exercise damages the SR and interferes with Ca regulation and release

o Total lack of ATP occurs rarely, during states of continuous contraction, and causescontractures

y Oxygen deficito Extra O2 needed after exercise for replenishment of:

y Oxygen reservesy Glycogen storesy ATP and CP reserves

o Lactic acid pyruvic acid glucose glycogeno During oxygen deficit- lactic acid is end product of cellular metabolism of glucose

y Heat production during muscle activityo 40% of the energy released in muscle activity is useful as worko Remaining energy (60%) given off as heato Dangerous heat levels are prevented by radiation of heat from the skin and sweating

y Force of muscle contractiono *The force of muscle contraction is affected by:

1. Number of muscle fibers stimulated (recruitment) 2. Relative size of the fibers- hypertrophy of cells increases strength 3. Frequency of stimulation- increase frequency allows time for more effective

transfer of tension to noncontractile components

4. Length-tension relationship- muscles contract mot strongly when muscle fibers are80-120% of their normal resting length

y Velocity (speed of contraction) and duration of contractiono Influenced by:

Muscle fiber type Load Recruitment

y Muscle fiber typePICTURE10o Classified according to 2 characteristics:

1. Speed of contraction: slow or fast, according to:y Speed at which myosin ATPases split ATPy Pattern of electrical activity of the motor neurons

2. Metabolic pathways for ATP synthesis:y Oxidative fibers- use aerobic pathwaysy Glycolytic fibers- use anaerobic glycolysis

o 3 muscle fiber types: Slow oxidative fibers- marathons Fast oxidative fibers- sprints Fast glycolytic fibers- quick, intense movements (hitting baseball)

y Influence of loado Increase load increase latent period, decrease contraction/duration of contraction

y Influence of recruitmento Increase recruitment faster contraction and increase duration of contraction

Recruitment- more muscle fibers acting together


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y Effects of exerciseo Aerobic (endurance) exercise:

Leads to increased muscle capillaries, # of mitochondria, myoglobin synthesis Results in greater endurance, strength, and resistance to fatigue May convert fast glycolytic fibers into fast oxidative fibers

o Resistance exercise: Results in muscle hypertrophy; increased mitochondria, myofilaments, glycogen

stores, and connective tissuey Overload principle- forcing a muscle to work hard promotes increased muscle strength and

endurance

o Muscle adapts to increased demandso Muscle must be overloaded to produce further gains

y Smooth muscleo In walls of hallow organso Usually in 2 layers (longitudinal and circular)o **Peristalsis- alternating contractions and relaxations of smooth muscle layers that mix and

squeeze substances through the lumen of hollow organs

*Longitudinal layers contracts; organ dilates and shortens *Circular layer contracts; organ contracts and elongates

y Microscopic structure of smooth muscleo Spindle shaped fibers: thin and short compared with skeletal muscle fiberso Connective tissue-endomysium onlyo SR- less developed than in skeletal muscleo Pouchlike infoldings (caveolae) of sarcolemma sequester Cao No sarcomeres, myofibrils, of T tubules

y Innervation of smooth muscleo Autonomic nerve fibers delivers nerve impulses (innervative) smooth muscle at diffuse

junctions

o Varicosities (bulbous swellings)- store and release neuotransmitters; **similar to axonterminal

y Myofilaments in smooth muscleo Ratio of thick to thin is 1:13, which is much lower than skeletal muscle (1:2)o Thick filaments have heads along their entire lengtho *No troponin complex; protein calmodulin binds Ca, similar to troponin in skeletalo Myofilamets are spirally arranged, causing smooth muscles to contract in a corkscrew

manner

o Dense bodies- proteins that anchor noncontractile intermediate filaments to sarcolemma atregular intervals

y Contraction of smooth muscle PICTUREo Slow, synchronized contractions; takes 30X longer to contract and relaxo Cells are electrically coupled by gap junctionso Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for

sheets of muscle

o Very energy efficient(slow ATPases)o Myofilaments may maintain a latch state for prolonged contractionso Relaxation requires:

Ca detachment from calmodulin Active transport of Ca into SR and ECF Dephosphorylation of myosin to reduce myosin ATPase activity


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o 1. Sliding filament mechanismo 2. Final trigger is increase intracellular Cao 3. Ca is obtained from the SR and extracellular space

y Role of calcium ionso Ca binds to and activates calmodulino Activated calmodulin activates myosin kinaseo Activated kinase phosphorylates and activates myosino Cross bridges interact with actin

y Regulation of contractiono Neural regulation:

*Response depends on neurotransmitter released and type of receptor molecules Hormones and local chemicals:

y May bind to G protein-linked receptorsy May either enhance or inhibit Ca entry

y *Special features of smooth muscle contractiono Stress relaxation response:

Responds to stretch only briefly, then adapts to new length Retains ability to contract on demand Enables organs such as the stomach and bladder to temporarily store contents

o Length and tension changes- can contract when between half and twice its resting lengtho Hyperplasia- Smooth muscle cells can divide and increase their numbers. EX- estrogen

effects on uterus at puberty and during pregnancy

y Types of smooth muscleso Single unit(visceral)

Sheets contract rhythmically as a unit Often exhibit spontaneous action potential Arranged in opposing sheets and exhibit stress relaxation response

o Multi unit Located in large airways, large arteries, arrector pili muscles, and iris of eye

y Developmental aspectso *Muscular development reflects neuromuscular coordinationo Development occurs head to toe, proximal to distalo Female skeletal muscle make up 36% of body masso Male skeletal muscle makes up 42% of body mass, due to testosteroneo *Body strength per unit muscle mass is the same in both sexeso With age, connective tissue increase, muscle fiber decreaseo By age 30, loss of muscle mass (sarcopenia) begins

Regular exercise reverses sarcopeniay Muscular dystrophy

o Group of inherited muscle-destroying diseaseo Muscles enlarge due to fat and connective tissue depositso Duchenne muscular dystrophy (DMD)

Most common and severe type *Cause- diseased muscle lacks dystrophin Victim becomes clumsy and fall frequently; usually die of respiratory failure in their

20s

y Connective tissue sheaths contribute somewhat to the natural elasticity of muscle tissue, and alsoprovide entry and exit routes for the blood vessels and nerve fibers that serve the muscle


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y Because of their small size, more tendons than fleshy muscle can pass over a joint- so tendons alsoconserve space

y The more motor units that are recruited, the grater the muscle forcey In brief twitch contractions- the external tension is always less than the internal tensiony A severely stretched muscle cannot develop tensiony **Muscles of marathoners have high percentage of slow oxidative fibers (about80%), while those o

sprinters contain a high percentage (60%) of fast oxidative and glycolytic fibers

y Increased muscle bulk is an increase of size of muscle fibers rather than number of muscle fibersy Satellite cells help repair injured fibers and allow very limited regeneration of dead skeletal muscle

fibers

y Smooth muscles are able to regenerate throughout life


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Chapter 10 the muscular systemy Insertion moves toward originy 4 functional groups of muscles

o Prime movers- has major responsibility for producing a specific movemento Antagonists- muscles that oppose, or reverse, a particular movemento Synergists- help prime movers by:

Adding a little extra force to the same movement Reducing undesirable/unnecessary movement that might occur as the prime mover

contracts

o Fixators- when synergists immobilize a bone so that prime mover has a stable base on whichto act, they are called fixators. Muscles that help to maintain upright posture are fixators

y Naming skeletal muscles:o 1. Locationo 2. Shapeo 3. Size- Maximus- largest; minimums- smallest; longus- long; brevis- shorto 4. Direction- rectus- straight; transverse/obliqueo 5. # of originso 6. Location of attachmentso 7. Action

y Arrangements of fascicles- circular, convergent, parallel, pennateo Circular- fascicles arranged in concentric rings; sphincters; orbicularis oriso Convergent- broad origin, converge toward single tendon of insertion; pectoralis majoro Parallel- long axis of the fascicles run parallel to the long axis of the muscle; sartoriouso Pennate- fascicles are short and attach obliquely to a central tendon that runs the length of

the muscle

Unipennate- fascicles insert into only one side of tendon; extensor digitorum longus Bipennate- fascicles into tendon on opposite sides, resembling feather; rectus femori Multipennate- all fasicles insert into one tendon; deltoid

o *The arrangement of muscle fascicles determine its ranges of motion and its powero *Muscle power depends more on the total number of muscle fibers in the muscle

y Lever systemso Lever- rigid bar that moves on a fixed point called a fulcrum. The applied force, or effort, is

used to move a resistance, or load.

o ***In body- joints are fulcrums, bones act as levers, muscle contraction provides the effort,which is applied at the muscles insertion point on a bone. The load is the bone itself**

y Mechanical advantage (commonly called a power lever)o Effort X length of effort arm = load X length of load armo (Force X distance) = (resistance X distance)

yMechanical disadvantage (speed lever)

y All levers follow same basic principleo Effort farther than load from fulcrum = lever operates at a mechanical advantageo Effort nearer than load to fulcrum = lever operates at a mechanical disadvantage

y 1stclass levers- load-fulcrum-effort- effort applied at one end of lever and load is at the other, withfulcrum somewhere between. EX- raising your head off your chest. Seesaws and siccors

y 2nd class levers- fulcrum-load-effort-effort is applied at one end of the lever and the fulcrum islocated at the other, with the load between. EX- standing on toes, wheelbarrow

o All 2nd class levers in the bodywork at a mechanical advantage b/c the muscle insertion isalways farther from the fulcrum than is the load.


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o 2nd class levers are levers of strength, speed and range of motion are sacrificedy 3rd class levers- load-effort-fulcrum- effort is applied between the load and the fulcrum. EX- flexing

forearm, tweezers, forceps

o These levers are speedy and always operate at mechanical disadvantageo Most skeletal muscles in the body are 3rd class levers

y Mechanical disadvantage (speed levers)- force is lost but speed and range of motion are gained.y Mechanical advantage (power levers)- slower, more stable, used where strength is priority


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Chapter 11 Nervous system and nervous tissuey Functions of nervous systems

o Sensory input- info gathered by sensory receptors about internal/external changeso Integration- interpretation of sensory inputo Motor output- activation of effector organs produces a response

y Divisions of nervous system **STUDY PICTURE**PICTURE 11y Histology of nervous tissue

o 2 cell types: Neurons- excitable cells that transmit electrical signals PICTURE 12 Neuroglia (glial cells)- supporting cells

y Can be distinguished by smaller size and darker staining nuclei; theyoutnumber neurons 10:1

y CNS- astrocytes, microglia, ependymal cells, oligodenrocyteso Astrocyte

*Most abundant Help determine capillary permeability Guide migration of young neurons Control the chemical environment Participate in information processing in the brain **Mop up leaked potassium ions

o Microglia-**defensive cells; migrate toward injured neuronso Oligodendrocytes- processes wrap CNS fibers, forming insulating

myelin sheaths

o Ependymal cells- line cerebrospinal fluid-filled cavitiesy PNS- satellite cells, Schwann cells PICTURE 12

o Satellite cell- surround neuron cell bodies in the PNSo Schwann cell- surround peripheral nerve fibers and form myelin

sheaths; vital to regeneration of damaged peripheral nerve fibers

y Neurons (nerve cells)o Special characteristics:

Long lived (100 years or more) Amitotic- no ability to divide High metabolic rate Plasma membrane functions in:

y Electrical signalingy Cell to cell interactions during development

o Cell body (soma) Biosynthetic center of a neuron Spherical nucleus with nucleolus Well developed Golgi apparatus Rough ER called Nissl Bodies Network of neurofibrils Axon hillock- cone shaped area from which axon arises Clusters of cell bodies:

y In CNS- Nucleiy In PNS-Ganglia

o Processes


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Dendrites and axons Bundles of process called:

y Tracts in the CNSy Nerves in the PNS

Dendrites- short, tapering, and diffusely branchedy Receptive region of a neurony Convey electrical signals toward the cell body as graded potentials

The axon- one axon per cell arising from axon hillocky Numerous terminal branches (telodendria)y Knob like axon terminals

o Synaptic region of neurono Release neurotransmitters to excite or inhibit other cells

y Function: conducting region of a neuron; generate and transmits nerveimpulses (action potentials) away from the cell body

y Molecules/organelles moved along axons by motor molecules in 2 directionso Anterograde- away from cell bodyo Retrograde- toward cell body

o Myelin sheath PICTURE 12 Segmented protein-lipoid sheath around most long or large diameter axons **Functions to:

y Protect and electrically insulate the axony Increase speed of nerve impulse transmission

In PNS- Schwann cell wraps many times around the axony Nodes of ranvier- myelin sheath gaps between adjacent Schwann cells; sites

where axon collaterals can emerge

y Unmyelinated axons- one Schwann cell may incompletely enclose 15 or moreunmylenited axons

**In CNS- formed by process of oligodendrocytesy W

hite/grey mattero White matter- dense collections of myelinated fiberso Gray matter- mostly neuron cell bodies and unmyelinated fibers

y Structural classification of neurons PICTUREo 1. Multipolar- 1 axon, several dendrites

Most common type in human body, major neuron type in the CNS Most abundant **Motor neurons and interneurons

o 2. Bipolar- 1 axon, 1 dendrite; sensory neuronso 3. Unipolar- single, short process that has 2 branches

Found chiefly in ganglia in the PNS, where they function as sensory neuronsy Functional classification of neurons

o 1. Sensory (afferent)- transmit impulses from sensory receptors towards CNS Virtually all sensory neurons are unipolar

o 2. Motor (efferent)- carry impulses from the CNS to effectors Most are unipolar

o 3. Interneurons (association neurons)- shuttle signals through CNS pathways; most areentirely within the CNS

Make up 99% of neurons in the bodyy Neuron function


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o Neurons: irritable or excitableo Stimulus may yield action potential (nerve impulse)o Impulse is always the same regardless of stimulus

y Principles of electricityo *Human body is electrically neutralo Opposite charges attracto Energy is required to separate opposite charges across a membraneo Energy is liberated when the charges move toward one anothero If opposite charges are separated, the system has potential energy

y Definitionso Voltage V- measure of potential energy generated by separated chargeo Potential difference- voltage measured between two points

**The greater the difference in charge between two point, the higher the voltageo Current I- the flow of electrical charge between two pointso Resistance R- hindrance to charge flow (provided by plasma membrane)o Insulator- substance with high electrical resistanceo Conductor- substance with low electrical resistance

y *OHMs law-the relationship between voltage, current, and resistanceo Current = voltage/resistanceo **Tells us:

Current is directly proportional to voltage; greater the voltage, greater the current There is no net current flow between points that have the same potential Current is inversely related to resistance; greater the resistance, smaller the current

y **The resistance to current flow is provided by the plasma membraney Role of membrane ion channels

o Proteins serve as membrane ion channels; membrane channels are large proteinso *2 main types of ion channels:

1. Leakage (nongated) channels- always open 2. Gated channels: 3 types

y Chemically gated- open with binding of a specific neurotransmittery Voltage gated- open/close in response to changes in membrane potentialy Mechanically gated- open/close in response to physical deformation of

receptors

y When gated channels are open: PICTURE 13o Ions diffuse quickly across the membrane along their electrochemical gradients

Along chemical concentration gradients from higher concentration to lowerconcentration

Along electrical gradients toward opposite electrical chargeo **Ion flow creates an electrical current and voltage changes across the membrane

yVoltmeter- measures the potential difference between 2 points

y Resting membrane potential PICTURE 13o Potential difference across the membrane of a resting cell

Approx. -70 mV in neuronsy Minus sign indicates that the cytoplasmic side (inside) of membrane is

negatively charged relative to the outside

o Generated by: Differences in ionic makeup of ICF and ECF Differential permeability of the plasma membrane


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o Negative interior of the cell is due to much greater diffusion of K out of the cell than Nadiffusion into the cell

o Sodium-potassium pump stabilizes the resting membrane potential by maintaining theconcentration gradients for Na and K

o ***Potassium plays the most important role in generating the membrane potentialo **At resting membrane potential, the negative interior of the cell is due to much greater

diffusion of K out of the cell than Na diffusion into the cell

o Sodium potassium pump stabilizes the resting membrane potential by maintain theconcentration gradients for sodium and potassiumy Membrane potentials that act as signals

o Membrane potential changes when: 1. Concentrations of ions across the membrane change 2. Permeability of membrane to ions change Only permeability changes are important for information transfer

o *Changes in membrane potential are signals used to receive, integrate, send informationo *2 types of signals:

Graded potentials- incoming short distance signals Action potentials- outgoing long distance signals of axons

y Changes in membrane potentialo Depolarization- a reduction in membrane potential (toward zero, -70 to -60)

Inside the membrane become less negative than the resting potential **Increases the probability of producing an action potential or nerve impulse

o Hyperpolarization- an increase in membrane potential (away from zero, -70 to -80) **Reduces the probability of producing an action potential or nerve impulse

o Above 2 terms describe membrane potential relative to resting membrane potentialo **Depolarization increases probability of producing nerve impulse, hyperpolarization

reduces probability

y Graded potentials- short lived, localized changes in membrane potential that can be eitherdepolarization of hyperpolarization PICTURE 16, 16A

o **Triggered by some change (a stimulus) in the neurons environment that causes gated ionchannels to open

o Graded potential spreads as local currents change the membrane potential of adjacentregions

o B/c graded potentials dissipate quickly with increasing distance from site of initialdepolarization, graded potential can act as signals only over very short distances

o 1. Occur when stimulus opens gated channelso 2. Stronger the stimulus, higher the gradeo 3. Decrease in magnitude with distance away from initial depolarizationo 4. Short distance signals

y Action potential (nerve impulse)- a brief reversal of membrane potential with a total amplitude of100mV

o **Principle way neurons send signals over long distances PICTURE 14o **Only cells with excitable membranes (neurons/muscle cells) can generate AP

y Properties of gated channels PICTURE 13o **Each Na channel has 2 voltage sensitive gates

1. Activation gate- closed at rest, opens with depolarization 2. Inactivation gate- open at rest, closes shortly after depolarization

o **Each K channel has one voltage sensitive gate- closed at rest, opens slowly withdepolarization


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y Generation of an action potentialo Step 1- resting rate

Only leakage channels for Na and K are open All gated Na and K channels are closed

o Step 2- depolarizing phase 1. Depolarizing local currents open voltage gated NA channels 2. Na influx; more depolarization At threshold (-55 to -50mV) positive feedback leads to opening of all Na channels, anda reversal of membrane polarity to +30mV

o Step 3- repolarizing phase 1. Na channel slow inactivation gates close 2. Membrane permeability to Na declines to resting levels 3. Slow voltage-sensitive K gates open 4. K exits the cell and internal negativity is restored Repolarization restores resting electrical conditions, but not resting ionic condition.

Sodium potassium pump restores ion distribution

o Step 5- hyperpolarization 1. Some K channels remain open, allowing excessive K efflux 2. This cause after hyperpolarization of the membrane

y Once initiated, an AP is self propagating and continues along axon at a constant velocity-dominoeffect

y Nerve impulse not really conducted in same way insulated wire conducts current. Neurons arepoor conductors. The expression propagation of a nerve impulse is more accurate b/c the AP is

regenerated anew at each membrane patch

y **Role of the sodium potassium pumpo Repolarization restores the resting electrical conditions of the neuron where as sodium

potassium pump restores ionic conditions

y At Threshold:o Membrane is depolarized by 15 to 20 mVo Na permeability increaseso Na influx exceeds K effluxo Strong stimuli depolarize the membrane to threshold quickly, weaker stimuli must be

applied for longer periods to provide the crucial amount of current flow

y Subthresholdo Subthreshold stimulus- weak local depolarization that does not reach thresholdo Threshold stimulus- strong enough to push the membrane potential toward and beyond

threshold

o AP is an all-or-none phenomenon- action potentials either happen completely, or not at ally Coding for stimulus intensity

o All action potentials are alike and are independent of stimulus intensityo **CNS determines stimulus intensity by the frequency of impulses

y Absolute refractory period PICTURE 14o Time from the opening of the Na channels until the resettling of Na channelso Ensures that each AP is an all or none evento Enforces one way transmission of nerve impulses

y Relative refractory period PICTURE 14o Follows the absolute refractory periodo Threshold for AP generation is elevated


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o Exceptionally strong stimulus may generate an AP, but a stimulus that would normallygenerate AP would no longer do so

y Conduction velocityo Rate of impulse propagation depends largely on 2 factors:o 1. Effect ofaxon diameter- larger diameter fibers have less resistance to local current flow

and have faster impulse conduction; larger the axons diameter, faster it conducts impulses

o 2. Effect ofmyelination- myelin sheath increase rate of AP propagation b/c myelin act asinsulator. Continuous conduction in unmyelinated axons is slower than salutatoryconduction in myelinated axons

Myelin sheaths insulate and prevents leakage of charge Salutatory conduction in myelinated axons is about 30X faster

y APs appear to jump rapidly from node to nodey Multiple sclerosis

o Myelin sheaths in the CNS become nonfunctional scleroseso Shunting and short circuiting or nerve impulses occurso Impulse conduction slows and eventually ceases

y Nerve fiber classification: classified according to:o Diametero Degree of myelinationo Speed of conductiono 1. Group A fibers- large diameter, myelinated somatic sensory and motor fiberso 2. Group B fibers- intermediate diameter, lightly myelinated ANS fiberso 3. Group C fibers- smallest diameter, unmyelinated ANS fibers

y **Anesthesia acts by blocking voltage gated Na channels; cold and continuous pressure interruptblood circulation, which impairs ability to conduct impulses

y The synapse- a junction that mediates information transfer from one neuron to another neuron orto an effector cell PICTURE 15A

o Presynaptic neuron- conducts impulses toward the synapseo Postsynaptic neuron- transmit impulses away from the synapse

y Types of synapseso Axodendritic- between the axon of one neuron and the dendrite of anothero Axosomatic- between the axon of one neuron and the soma of another

y Electrical synapses- provide simple means of synchronizing the activity of all interconnectedneurons

o Less common than chemical synapses Neurons are electrically coupled (joined by gap junctions) Communications is very rapid, and may be unidirectional or bidirectional Important in:

y Embryonic nervous tissuey

Some brain regionsy Chemical synapses- specialized for the release and reception of neurotransmitters PICTURE 15

o Typically composed of 2 parts: 1. Axon terminal of the presynaptic neuron, which contains synaptic vesicles 2. Receptors region on the postsynaptic neuron

y Synaptic cleft- fluid filled space separating the presynaptic and postsynaptic neuronso Prevents nerve impulses from directly passing from one neuron to the nexto Transmission across the synaptic cleft:

*Is a chemical event(as opposed to an electrical one) Involves release, diffusion, and binding of neurotransmitters


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Ensures unidirectional communication between neuronsy Information transfer at synaptic cleft

o 1. AP arrives at axon terminal of presynaptic neurono 2. Voltage gated Ca channels openo 3. Synaptotahmin protein binds Cao 4. Synaptic vesicles fuse with axon membraneo 5. Excocytosis of neurotransmitter occuro 6. Neurotransmitter diffuses across cleft, binds to receptors on postsynaptic neurono 7. Channels open causing an excitatory or inhibitory event

y Synaptic delayo Neurotransmitter must be

1. Released 2. Diffuse across synapse 3. Bind to receptors

o **Synaptic delay is the rate-limiting step of neural transmissiony Chemical synapse either excitatory/inhibitory depending on how they affect the membrane

potential of postsynaptic neuron

y Postsynaptic potentials PICTURE 15Bo Graded potentials

*Strength determined by:y 1. Amount of neurotransmitter releasedy 2. Time the neurotransmitter is in synapse

o Types of postsynaptic potentials: EPSP- excitatory postsynaptic potentials IPSP- inhibitory postsynaptic potentials

y EPSP and IPSP are Graded Potentialsy Excitatory synapse and EPSP DEPOLARIZATION PICTURE 15

o 1. Neurotransmitter binds, opens chemically gated channelso 2. Simultaneous flow of Na and K in opposite directiono 3. Na influx > K efflux, net depolarizationo 4. EPSP helps trigger AP at axon hillock if EPSP is of threshold strength, opens voltage gated

channels

o An EPSP is a local depolarization of the membrane that brings the neuron closer to APthreshold. Neurotransmitter binding opens chemically gated ion channels, allowing the

simultaneous passage of NA and K

o **Only function of EPSPs is to help trigger an AP distally at the axon hillock of thepostsynaptic neuron

y Inhibitory synapses and IPSP HYPERPOLARIZATION PICTURE 17o 1. Neurotransmitter bindso

2. Opens channels for K or Clo 3. Causes hyperpolarizationo 4. Reduces the postsynaptic neurons ability to produce an action potentialo An IPSP is a local hyperpolarization of the postsynaptic membrane and drives the neuron

away from AP threshold. Neurotransmitter binding opens K or Cl channels

y Integration: summationo A single EPSP cannot induce an action potentialo EPSPs can summate to reach thresholdo *IPSPs can also summate with EPSPs, canceling each other out


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o 1. Temporal summation- one or more presynaptic neurons transmit impulses in rapid fireorder

o 2. Spatial summation- postsynaptic neuron is stimulated by many axonal terminals at thesame time

y Partially developed neurons are facilitated- more easily excited by successive depolarization eventsb/c they are already nearer threshold.

y ***B/c EPSPs and IPSPs are graded potentials that diminish in strength the farther they spread, themost effective synapses are those closest to the axon hillock

o **Specifically, inhibitory synapses are most effective when located between the site ofexcitatory inputs and the site of action potential generation

o **Accordingly, inhibitory synapses occur most often in cell body, excitatory synapses occurmost often on the dendrites

y Integration: synaptic potentiationo *Repeated use of the same synapse > efficiency of neurotransmission

y Integration: presynaptic inhibitiono Release of excitatory neurotransmitter by one neuron may be inhibited by the activity of

another neuron via an axoaxonis synapse

o End result- Less neurotransmitter is released and smaller EPSP are formedy Neurotransmitter

o Most neurons make 2 or more neurotransmitters, which are released at different stimulationfrequencies

o *Most factors that affect synaptic transmission do so by enhancing or inhibitingneurotransmitter release or destruction, or by blocking their binding to receptors

y CHEMICAL classification of neurotransmitterso Acetylcholine- released at neuromuscular junction and some AND neurons

Functionally: excitatoryo Biogenic amines include:

Catecholamines- dopamine, norepinephrine, epinephrine Indolamine- serotonin and histamine Play roles in emotional behavior and biological clock Functionally: all but serotonin are + or

o Peptides include: Substance P- mediator of pain signals Endorphins- act as natural opiates; reduce pain perception Gut brain peptides-

o Purines such as ATP- provoke pain sensationo Gases and lipids:

Nitric oxide (NO)- involved in learning Carbon monoxide- regulator of cGMP in the brain

o Endocannabinoids- involved in learning and memoryy FUNCTIONAL classification of neurotransmitters

o Neurotransmitter effects may be excitatory (depolarizing, +) and/or inhibitory(hyperpolarizing, -)

*Determined by the receptor type of the postsynaptic neuron Acetylcholine

y Excitatory at neuromuscular junctions in skeletal muscley Inhibitory in cardiac muscle

o EXCITATORY- CAUSE DEPOLARIZATIONo INHIBITORY- CAUSE HYPERPOLARIZATION


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y Actions of neurotransmitterso Direct action (channel-linked receptors)- neurotransmitter binds to channel linked receptor

and opens ion channels

Promotes rapid response EX- ACh and amino acids

o Indirect action (G-Protein linked receptors)- neurotransmitter binds to a G protein linkedreceptor and acts through an intracellular second messenger

**Promotes long lasting effects EX- biogenic amines, neuropeptideso Neuromodulator- chemical messenger that doesnt directly cause EPSP or IPSP but instead

affects the strength of synaptic transmission

y Transmitter receptor types: PICTURE 18o 1. Channel-linked receptors- direct; mediate fastsynaptic transmission

Ligland-gated ion channels Action is immediate and brief

o 2. G protein-linked receptors- indirect; mediate slow synaptic responses Transmembrane protein complexes Responses are indirect, slow, complex, and often prolonged and widespread

y Neural integration: neuron pools PICTURE 19o Functional groups of neurons that integrate incoming information and forward the

processed info to other destination

o Simple neuron pools- single presynaptic fiber branches and synapses with several neurons Discharge zone- neurons most likely to generate impulse and are closely associated

with the incoming fiber

Facilitated zone- neurons farther away from incoming fibery Circuit types in neuron pools PICTURE 19

o Circuit determine the pools functional capabilitieso Diverging circuit- 1 incoming fiber stimulates an ever increasing number of fibers, often

amplifying circuits

o Converging circuits- opposite of diverging, resulting in either strong stimulation orinhibition

o Reverberating circuit- chain of neurons containing collateral synapses with previousneurons in the chain; controls rhythmic activities

o Parallel after discharge circuit- incoming fiber stimulates several neurons in parallel arraysto stimulate a common output cell

y Patterns of neural processingo Serial processing- input travels along one pathway to a specific destination

Works in all-or-none manner to produce specific response EX- reflexes- rapid, automatic response to stimuli that cause same response

y Reflex arcs 5 essential components: 1. Receptor 2. Sensory neuron 3. CNS 4.Integration center 5. Motor neuron 6. Effecter

o Parallel processing- input travels along several pathway; one stimulus promotes numerousresponses

***Brain derives its power from its ability to process in parallel Important in higher level mental functioning; puts the parts together to understand

the whole

EX- a smell may remind one of the door and associated experiencesy Developmental aspects of neurons

o The nervous system originates from the neural tube and neural crest formed from ectoderm


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o The neural tube becomes the CNS 1. Neuroepithelial cells of the neural tube undergo differentiation to form cells

needed for development

2. Cells become amitotic and migrate 3. Neuroblasts sprout axons to connect the targets and become neurons

o **Axonal growth-astrocytes provide physical support and cholesterol essential forconstruction of synapses

y Cell deatho About 2/ of neurons die before birth

Death results in cells that fail to make functional synaptic contacts Many cells also die due to apoptosis (programmed cell death) during development

A&P Lecture Test 3 Review - Chap 9,10,11

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