NPB 101

Role of nucleus

contains DNA and code for proteins and other

Role of nucleolus

make RNA

Role of ribosome

make proteins (translation)

Role of rough ER

ribosome and protein production

Role of smooth ER

processing (more than RER)

Role of golgi apparatus

protein modifications, make vacuoles

Role of mitochondria

produce ATP

Role of lysosome

degrade proteins, mitochondria, etc.

• low pH where only specific enzymes (cathepsins) work at this pH

Role of vacuole

stores waste

Role of centrioles

cell replciation and division

Role of microvilli

increase surface area for absorption

Role of cytoplasm

medium for reactions

What are the four primary types of tissues? List each subunit.

• muscle (contraction)

  • skeletal

  • cardiac

  • smooth

• nervous (signals)

  • central

  • peripheral

• epithelial (exchange)

  • epithelial sheets (form boundaries)

  • glands (secretion)

• connective (structural support)

  • tendons

  • bones

  • blood

What is homeostasis? What (8) variables are maintained in homeostasis?

• maintenance of dynamic steady state in the internal environment

  • concentration of nutrients

  • partial pressure of O2 and CO2

  • concentration of metabolic waste products

  • blood pH

  • blood osmolarity

  • concentration of Na+, K+ and other electrolytes

  • blood volume and pressure

  • body temperature

How is homeostasis maintained?

• cells exchange materials from the intracellular fluid, with the interstitial fluid (extracellular space) and blood (specifically plasma)

What kind of mechanism is homeostasis? Describe what this means

• dynamic mechanism

  • detect and respond to deviations in physiological variables from their set point values by initiating effector responses that restore the variables to the optimal physiological range

• example

  • deviations in glucose concentration in blood “dynamic constancy” (vary short term, fairly constant in the long term)

What is the homeostatic control system? Describe each key component (3).

• an interconnected network of body components that work together to maintain a given factor relatively constant

• to maintain homeostasis the control system must be able to:

  • detect deviations from normal

    • sensor detected deviation from set point

  • integrate this information with other information

    • control center

  • make adjustments to restore the factor to normal

    • response involving effectors

What type of feedback are intrinsic and extrinsic control systems? What is the main goal?

• negative feedback

• goal is to remediate an unwanted change

What is an afferent signal? What about efferent signal?

Afferent

• sends the information from the sensor to the control center / integrator

• sometimes it is not needed if the sensor and control center are the same cell

Efferent

• used to send information from the control center to the effectors (cells/organs) that need to perform an action to help restore homeostasis

What are the 3 main components in negative feedback? How does the result affect the different parts?

Sensor

• detects deviation in controlled variable

Integrator / Control Center

• gets information from the sensor and sends these instructions to the effector (through afferent signals)

Effector

• receives instructions from the integrator / control center to bring about compensatory response about said controlled variable

Result

• controlled variable restored to normal, this creates a reaction to shut off sensor

What is the intrinsic control system? What about extrinsic?

Intrinsic

• local system that are “built in” to an organ or tissue

  • ex) increased CO2 production by exercising skeletal muscle leads to relaxation of smooth muscle and dilation of blood vessels, increased blood flow brings more O2

Extrinsic

• contained outside of an organ or system, permitting coordinated regulation of several organs

  • ex) low blood pressure is detected by the nervous system, which causes an increase in heart rate and constriction of blood vessels

What is pathophysiology?

• refers to abnormal functioning of the body associated with disease

• when homeostatic disruption becomes so severe that is no longer compatible with survival, death results

What are the 2 types of direct intercellular communication? What about indirect intercellular communication?

Direct

• Gap Junctions

  • allow small molecules and ions to move from one to another

• Transient Direct Hookup

  • cells directly link up with each other through their surfaces

Indirect

• Paracrine Secretion

  • target cell has a receptor that receives information from another cell

  • used for more local

• neurotransmitter secretion

  • neuron is excited and releases a neurotransmitter, which bind to local target cells to bring about a reaction

What are the two types of endocrine signaling?

Hormonal Secretion

• extracellular signaling molecule that is released into the blood and act as its receptors in distal tissues to elicit a physiological response

• even though hormones circulate in the blood stream, only specific target cells can respond to them because they express the hormone’s receptor

Neurohormones Secretion

Fill out each part.

Nervous System

• anatomic arrangement

  • a wired system

  • specific structural arrangement between neurons and their target cells, which structural continuity in the system

• type of chemical messenger

  • neurotransmitters released into synaptic cleft

• distance of action of chemical messenger

  • very short distance (diffuses across synaptic cleft)

Endocrine System

• anatomic arrangement

  • a wireless system

  • endocrine glands widely dispersed and not structurally related to one another or their target cells

• type of chemical messenger

  • hormones released into blood

• distance of action of chemical messenger

  • long distance (carried by blood)

Fill out table.

Nervous System

• specificity of action on target cell

  • dependent on close anatomic relationship between neurons and their target cells

• speed of response

  • generally rapid (milliseconds)

• duration of action

  • brief (milliseconds)

• major functions

  • coordinates rapid, precise responses

Endocrine System

• specificity of action on target cell

  • dependent on specificity of target cell binding and responsiveness to a particular hormone

• speed of response

  • generally slow (minutes to hours)

• duration of action

  • long (minutes to days or longer)

• major functions

  • controls activities that require long duration rather than speed

What is positive feedback? Does it contribute to homeostasis?

• amplifies the initial change

• moves the system away from set point

• does not contribute to homeostasis, but to physiological needs

• check image for example

What are feedforward mechanisms? This can be done through what two conditions?

• operate without detectors

• activate homeostatic mechanisms and anticipate when a change is likely to occur

• conditions

  • in response to anticipated, once in a lifetime (or infrequent) event

    • ex) normal anticipatory regulation of heartbeat in advance of actual physical exertion

  • through body rhythms

    • rhythms are internally driven but entrained (timing is set by environmental cues)

How can there be alterations in homeostasis? What are the three types?

• set points can change

• three types

  • in sickness

    • fever

  • as we age

    • BMR

  • throughout the day

    • circadian rhythms

What are the four things that controlled contraction of muscle allow?

• purposeful movement of the whole body or parts of the body

• manipulation of external objects

• propulsion of contents through various hollow internal organs

• emptying contents of certain organs to the external environment

What are the three types of muscles? Describe whether striated / unstriated, or voluntary / involuntary

• skeletal

  • striated

  • voluntary

• cardiac

  • striated

  • involuntary

• smooth

  • unstriated

  • involuntary

• check image

What are the sarcolemma, sarcoplasm, and sarcoplasmic reticulum?

• specific terms for some the intracellular structures

• sarcolemma = plasma membrane

• sarcoplasm = cytoplasm

• sarcoplasmic reticulum = smooth ER

What are the five main characteristics of a skeletal muscle fiber?

• contains many mitochondria

• multinucleated

• has special structures called transverse tubules (T-tubules)

• has myofibrils and sarcomeres

• has sarcolemma, sarcoplasm, and sarcoplasmic reticulum

Describe the 7 step process of the neuromuscular junction (NMJ)

• 1) action potential propagates into the terminal bouton

• 2) depolarization of the terminal bouton opens voltage-gated Ca++ channels

• 3) Ca2+ ions trigger vesicles of Ach to fuse with the plasma membrane

• 4) Ach diffuses across the synaptic cleft and binds with receptors in the motor endplate

• 5) Ach binding with the receptor leads to the opening of cation channels where Na2+ enters and depolarizes the end plate

• 6) depolarizing current flows to adjacent membrane that contains voltage-gated Na2+ channels (action potential)

• 7) Ach is degraded by Ach-esterase, terminating the action of Ach

• check image

Describe the structure of skeletal muscle (4)

• muscle is made up of elongated muscle fibers that are held together by connective tissues and connected at either end of tendons

• these muscle fibers are made up of myofibril that have A bands and I bands

• these myofibrils contain sarcomeres that contain Z lines, M lines, and the H zone

• this sarcomere is made up of thick (myosin filaments) and thin (actin) filaments

• check image

[Skeletal muscle] Describe key parts of a muscle fiber that surround myofibrils (5)

• T-tubules

  • act as an extension of membrane through the muscle cell

• sarcoplasmic reticulum

  • modified endoplasmic reticulum composed of a fine network of interconnected tubules into which Ca2+ is actively transported and stored

• lateral sacs

  • enlarged regions of the sarcoplasmic reticulum that come into close contact with the transverse tubules

• foot proteins

  • proteins that span the gap between lateral sacs and the transverse tubules and mediate a change in permeability to Ca2+ by the lateral sacs

  • also known as ryanodine receptors because they are locked open by the plant chemical ryanodine

• dihydropyridine receptor

  • proteins in the transverse tubule membrane that come into contact with the foot proteins

  • they are voltage-dependent and gate the change in permeability of the foot proteins to Ca2+

• check image

[Skeletal muscle] What is the sarcomere? Describe the structure of a sarcomere and its structural components (5)

• smallest unit of a muscle cell containing all the elements necessary for contraction

• composed of interdigitating and partially-overlapping thick and thin filaments

• components

  • Z line

    • defines boundary of sarcomere where thin filaments attach

  • H zone

    • lighter area within middle of A band where thin filaments do not reach

  • I band

    • consists of remaining portion of thin filaments that do not project into A band

  • A band

    • made up of thick filaments along with portions of thin filaments that overlap

  • M line

    • extends vertical down middle of A band within center of H zone

• check image

[Skeletal muscle] Describe the thick and thin filaments of the sarcomeres. Define myosin, actin, tropomyosin, and troponin.

Thick Filament

• special assemblies of hundreds of myosin protein molecules organized into elongated fibers

• myosin is a cytoskeletal protein composed of two interwoven subunits, each with a long tail and a globular head region

• it has an actin binding site which is a specialized region of the myosin head that is capable of binding to actin

• has a myosin ATPase site which is a specialized region of the myosin head that is capable of ATP hydrolysis

Thin Filament

• specialized assemblies of three proteins (actin, tropomyosin, and troponin), arranged to form an elongated double helical strand

• actin is a globular cytoskeletal protein linked to form two long chains arranged in a double helical strand

• tropomyosin are pairs of threadlike filamentous proteins that lie alongside the groover formed by the actin helix

• troponin is a protein complex composed of three subunits, where one can bind to actin, one can bind to tropomyosin, and one that binds Ca2+

  • multiple copies of this complex are bound to the strands of actin and tropomyosin

[Skeletal muscle] Describe the cross bridge activity of sarcomeres. (4 steps)

• 1) binding

  • myosin cross bridge binds to actin molecules

• 2) power stroke

  • cross bridge bends, pulling thin myofilament inward

• 3) detachment

  • cross bridge detaches at end of power stroke and returns to original conformation

• 4) binding

  • cross bridge binds to more distal actin molecule; cycle repeats

• check image for visualization

[Skeletal muscle] What are the consequences of cross bridge activity? (5)

• sarcomere shortens

• H zone shortens

• I band shortens

• A band is same width

• individual actin and myosin fibers maintain a constant length

[Skeletal muscle] What is the role of Ca2+ in cross bridge activity in the relaxed vs excited state of muscle fiber?

• relaxed muscle fiber

  • troponin - tropomyosin complex covers the cross bridge binding site

• excited muscle fiber

  • Ca2+ binds troponin, pulling the troponin - tropomyosin complex aside to expose cross-bridge binding sites

[Skeletal muscle] Describe the 6 steps of cross bridge cycling.

• activated cross bridge bends toward center of thick filament, “rowing” in thin filaments to which it is attached

• Ca2+ released into sarcoplasm

• Myosin head binds to actin

• Myosin heads swivel toward center of sarcomere (power stroke)

• ATP binds to myosin head and detaches myosin from actin

• hydrolysis of ATP transfers energy to myosin head and reorients it

• contraction continues of ATP is available and Ca2+ level in sarcoplasm is high

[Skeletal muscle] Draw out how the muscle would contract vs its normal state (sarcomere level)

check image

[Skeletal muscle] What is excitation-contraction coupling? What is it mediated by?

• muscular contraction occurs when the thick and thin filaments within a sarcomere slide past one another

• sliding action is mediated by a complex sequence of chemical reactions called the power stroke that utilizes the hydrolysis of ATP as an energy source and is dependent on the release of intracellular stores of Ca2+ from the sarcoplasmic reticulum

[Skeletal muscle] List the 7 steps for excitation contraction coupling.

• 1) Ach released by axon of motor neuron binds to receptors on the motor end plate

• 2) Action potentials generated in response to binding of Ach and subsequent end plate potential is propagated across surface of membrane and down T tubule of muscle cell

• 3) action potential triggers Ca2+ release from sarcoplasmic reticulum

• 4) Ca2+ ions released from lateral sacs bind to troponin on actin filaments

  • tropomyosin physically moved aside to uncover cross-bridge binding sites on actin

• 5) Myosin cross bridges attach to actin and bend, pulling actin filaments toward center of sarcomere

  • powered by energy provided by ATP

• 6) Ca2+ actively taken up by sarcoplasmic reticulum when there is no longer local action potentials

• 7) With Ca2+ no longer bound to troponin, tropomyosin slips back to its blocking position over the binding sites on actin

  • contraction ends

  • actin slides back to original resting position

• check image

[Skeletal muscle] What are muscle mechanics? What are the three important concepts related to this?

• whole muscles are groups of muscle fibers bundled together by connective tissue and attached to bones by tendons

• contains the motor unit, motor unit recruitment, and muscle tension

[Skeletal muscle] What is a motor unit? What are the three rules? What are the number of fibers precise vs powerful muscles have?

• motor neuron and all of the muscle fibers it innervates

• rules

  • 1) one motor neuron innervates multiple muscle fibers, but each muscle fiber is supplied by only one motor neuron

  • 2) When a motor neuron is activated, all of the muscle fibers it innervates are stimulated to contract simultaneously

  • 3) muscle fibers innervated by a given motor neuron are distributed throughout the muscle

    • thus their simultaneous contraction results in an evenly distributed (although weak) contraction of the whole muscle

• check image

• type

  • precise, delicate movement muscles contain fewer fibers per motor unit

  • powerful, coarsely controlled movement muscles have larger numbers of fibers per motor unit

[Skeletal muscle] Describe motor unit recruitment. How are motor units recruited to prevent fatigue? Describe the number of motor units recruited for weak vs strong contractions.

• the process of increasing the number of motor units that participate in muscle contraction

• to delay or prevent fatigue, asynchronous recruitment of motor units takes place

• weak

  • only a few motor units are activated

• strong

  • more and more motor units are recruited in large incremental increases in whole-muscle tension

  • single muscle motor unit contains many muscle fibers

• check image

[Skeletal muscle] Describe muscle tension. What are the four factors that influence the extent to which tension can be developed in a fiber? Draw the two graphs that are associated with this (contractile activity vs action potentials, and muscle fiber length vs resting length)

• depends not only on the number of motor units recruited, but also on the tension developed by each contracting fibers

• 4 factors

  • frequency of stimulation

  • length of the fiber at the onset of contraction

  • extent of fatigue

  • thickness of fiber

[Skeletal muscle] What are the mechanics of single-fiber contractions (2).

• muscle fiber generates force called tension in order to oppose a force called the load, which is exerted on the muscle by an object

• the mechanical response of a muscle fiber to a single action potential is known as a twitch

[Skeletal muscle] What is twitch summation? How is this possible, and what does it result in?

• is the increase in tension accompanying repetitive stimulation of a muscle fiber

• possible because the duration of the action potential is much slower than the duration of a the resulting twitch

• results from sustained elevation of cytosolic calcium upon repetitive stimulation

[Skeletal muscle] What is tetanus? How does it occur?

• smooth, sustained contraction of maximal strength

• occurs if muscle fiber is stimulated so rapidly that it does not have a chance to relax between stimuli

• contraction is usually three to four times stronger than single twitch

[Skeletal muscle] Describe the length tension relationship.

• fiber tension also depends on the length of the fiber at the onset of contraction

• there is an optimal muscle length (lo) at which maximal tension can be developed

• less tension is develop at shorter or longer lengths

• attachment of muscles to bones limits muscle shortening and lengthening

What is the sole energy source for muscular activity? Give examples of the which muscular activities.

• ATP

  • provides sole energy source for muscular activity including power stroke and active transport of Ca2+

What are the three metabolic sources the energy source for muscle activity comes from? Describe each of the metabolic sources, which one is tapped first, where they occur, and what type of exercise is associated.

Creatine Phosphate

• provides reserve of high-energy phosphate for synthesis of ATP through hydrolysis of creatine phosphate (first source tapped)

  • supply ATP for up to first minute of exercise

• during rest, excess ATP generated by glycolysis and oxidative phosphorylation is converted to creatine phosphate and stored by muscle cells as an energy reserve

  • creatine phosphate + ADP ←creatine kinase→ creatine + ATP

Oxidative Phosphorylation (mitochondria)

• slow process of making ATP

• requires oxygen (aerobic)

• produces large amounts of ATP

• metabolism of glucose and fatty acids

  • uses the high myoglobin content of muscle

• during light to moderate exercise, can supply muscle cells with ATP for prolonged periods

Glycolysis (cytosol)

• occurs when O2 delivery or oxidative phosphorylation can’t keep pace with ATP demand

• no O2 needed (anaerobic)

• metabolism of glucose

• excess pyruvic acid is converted to lactic acid, which is removed by the bloodstream

  • can produce ATP quickly

• high-intensity exercise

check image (specifically skeletal muscle)

What is fatigue? Describe the 3 types of fatigue. What are the two primary factors of fatigue?

• inability of muscle to maintain tension

  • can result from muscle fatigue or neuromuscular fatigue

• three types

  • muscle fatigue

    • occurs when an exercising muscle can no longer respond to stimulation with the same degree of contractile activity

  • neuromuscular fatigue

    • inability of the NMJ to synthesize Ach rapidly enough to sustain chemical transmission of action potentials from the motor axon to the muscle cell

  • central fatigue

    • occurs when the CNS no longer adequately activates motor neurons

• 2 primary factors

  • depletion of glycogen reserves

  • local increases in inorganic phosphate from ATP breakdown

How would you recover from fatigue? How about specifically central fatigue?

• replenishment of muscle glycogen and creatine phosphate following intense activity

• central fatigue

  • excess post-exercise oxygen consumption is needed for elevated O2 uptake uptake during recovery from exercise

What are the three types of skeletal muscle? Describe each type, and what level of components each type has. Draw the graph that is associated for each type.

• slow oxidative (type I)

  • slow contraction and reliance on oxidative phosphorylation for ATP

  • high in mitochondria, blood supply, and myoglobin

• fast oxidative (type IIa)

  • fast contraction and reliance on oxidative phosphorylation for ATP

  • high in mitochondria, blood supply, and myoglobin

• fast glycolytic (type IIb)

  • very fast contraction and reliance on glycolysis for ATP

  • low in mitochondria, blood supply, and myoglobin

  • high in muscle glycogen

• check image

Fill out this table

check image

Where are smooth muscles located? Describe the structure of smooth muscles.

• muscle fibers are located in the walls of hollow organs and tubes such as blood vessels and intestines

• structure

  • thin filaments are anchored either to the plasma membrane or to cytoplasmic structures known as dense bodies

  • smooth muscle contraction occurs by a sliding-filament mechanism

  • thick and thin filaments are not organized into myofibrils, and there are NO sarcomeres, which accounts for the absence of a banding pattern

• check image

Describe the smooth muscle excitation / contraction coupling process (8). Draw this process and include location of where this occurs.

• 1) self or neuronal excitation leads to Ca2+ entry from the extracellular space through voltage-gated Ca2+ channels

• 2) Ca2+ entry triggers the internal release of more Ca2+ from the sarcoplasmic reticulum

• 3) Ca2+ binds with calmodulin, an intracellular protein similar to troponin

• 4) Ca2+ - calmodulin complex activated myosin kinase which phosphorylates myosin

• 5) phosphorylated myosin binds to actin to form the activated cross-bridges

• 6) removal of Ca2+ leads to dephosphorylation of myosin and the dissociation of myosin from actin

• 7) gap-junctions enable excitation of one cell to propagate rapidly to all the coupled cells in a network

• 8) contraction strength is graded in proportion to the cytosolic Ca2+ concentration

• check image

Compared smooth muscle and skeletal muscle cross-bridge activation.

• check image

What are the two functionally distinct types of smooth muscle? List examples for each on where they are located. Describe how each type responds to stimuli.

Multi-unit smooth muscle

• smooth muscle cells that are activated by neuronal input

• examples

  • walls of large blood vessels

  • large airways to the lungs

  • muscles of the eyes that adjust the lens

  • iris of the eye

  • at the base of hair follicles (goose bumps)

• stimuli

  • respond as a single unit because cells are connected by gap junctions

Single-unit smooth muscle

• smooth muscle cells capable of generating pacemaker activity that are coupled into a functional syncytium by gap-junctions

• examples

  • walls of digestive tract

  • walls of the reproductive tract

  • walls of the urinary tract

  • walls of small blood vessels

• stimuli

  • respond to stimuli independently and they contain few gap junctions

Describe the 2 forms of spontaneous electrical activity. Draw the graphs associated.

Pacemaker potential

• gradual depolarization until threshold is reached

Slow wave potential

• alternating depolarizing and hyperpolarizing swings in membrane potential

check image

Describe the structure of cardiac muscles.

• thin filaments contain tropomyosin and troponin

• contains abundance of mitochondria and myoglobin

• possess t-tubules and sarcoplasmic reticulum

Describe the excitation-coupling process of cardiac muscle (4)

• 1) Ca2+ enters the cytosol from voltage-gated Ca2+ channels in the plasma membrane and triggers internal release of Ca2+

• 2) displays pacemaker activity initiating its own action potentials connected by gap-junctions

• 3) innervated by autonomic neuronal fibers

• 4) action potentials are longer in duration than both smooth and skeletal muscle

What are the three principal components that make up the circulatory system? What is the circulatory system function (5)?

• heart (pump)

• blood vessels (pipes)

• blood (fluid to be moved)

• functions

  • supply oxygen and nutrients

  • remove wastes

  • temperature regulation

  • distribute hormones

  • immuno-vigilance

Draw the anatomy of the heart including the paths to organ systems and lung. Describe the pathways

• dual-pump system composed of four chambers

  • left and right atria, left and right ventricles

• chambers on the right pump oxygen-poor blood through pulmonary circulation to the lungs

• chambers on the left pump oxygen-rich blood through the systemic circulation to the body tissues

  • remember that the image is flipped because we’re looking at it from the outside POV

Describe the four heart valves, label which chamber they’re in, and where they receive blood and pump blood to. Draw these valves in their locations.

• right AV valve (right atrium)

  • tricuspid

  • receives oxygen-poor blood from the systemic venous circulation via the inferior and superior vena cava veins

  • pumps to right ventricle

• pulmonary valve (right ventricle)

  • semilunar

  • receives oxygen-poor blood from the right atrium

  • pumps to pulmonary artery

• left AV valve (left atrium)

  • bicuspid and mitral

  • receives oxygen-rich blood from the pulmonary circulation via the left and right pulmonary veins

  • pumps to left ventricle

• aortic valve (left ventricle)

  • semilunar

  • receives oxygen-rich blood from the left atrium

  • pumps to aorta

• check image

Draw the blood flow of the heart including the different types of blood.

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What are the three different types of heart valves? What is a major characteristic of them? Draw these valves.

Types

• tricuspid

• bicuspid

• semilunar

Characteristic

• ensures a one-way flow of blood

  • when pressure is greater behind the valve it opens

  • when pressure is greater in front of the valve, it closes (thus one way)

What is the chordae tendineae? Describe the function.

• tendonous fibers attached to the inside of the AV valves and the interior base of the ventricles via papillary muscles

• prevent the AV valves from everting (inside out) during the pressure wave that occurs during ventricular contraction

T / F: Heart valve disease occurs only in those who are born with defects in their heart valves.

False

• can be a product of age-related changes, infection, etc.

Describe the connective tissue of the heart. Draw where this is located.

• separates the atria from the ventricles and provides a rigid base for attachment of the heart valves and the cardiac muscle

• ring of dense fibrous connective tissue surrounds each of the valves of the heart

• check image

What are the three types of heart walls?

Endocardium

• thin layer of endothelial tissue lining the interior of each chamber

Myocardium

• middle layer of the heart wall, composed of cardiac muscle

Epicardium

• thin external membrane covering the heart and is filled with a small volume of pericardial fluid

What connects muscle cells together? What are the two types of contacts that are formed through this connection? Which wall type do these connections occur? Draw these connections.

Connected end-to-end by intercalated disks where two types of contacts are formed

• desmosomes

  • mechanically hold the cells together

• gap junctions

  • provide paths of low resistance to the flow of the electrical current between muscle cells

  • enable the cardiac muscle to form a functional syncytium

occur in the myocardium

• check image

What is the electrical activity of the heart? What kind of cardiac muscle cells are involved? Describe their role / function.

Electrical activity

• heart muscle is capable of generating its own rhythmic electrical activity referred to as auto rhythmicity

• this occurs because of the unique electrophysiological properties of a subset of specialized cardiac muscle cells that generate pacemaker activity

Pacemaker cells

• grouped together into specialized regions called nodes that together control the rate and coordination of cardiac contractions

What is the pacemaker activity? What controls this?

• 99% of cardiac muscle cells are contractile and do not initiate their own action potentials

• the remaining 1% of the cells are autorhythmic and intrinsically initiate their own action potentials at a regular frequency

• this process is referred to as pacemaker activity and is controlled by the generation of pacemaker potentials

Describe the steps of action potentials in cardiac autorhythmic cells. Draw the graph associated.

First Half

• rising phase

  • there is simultaneous opening of unique funny channels

  • permits inward Na+ current

  • closes K+ channels which reduces outward K+ current

• falling phase

  • opens K+ channels

Second Half

• opening of T-type Ca2+ channels

Heart valve disease is often discovered during an exam when ____.

an echocardiogram is performed

Describe the 7 components involved in the pacemaker activity of the heart. Draw their locations and the spread of cardiac excitation.

Nodes

• specialized cardiac cells capable of pacemaker activity are grouped together to form nodes

Sinoatrial Nodes (SA)

• bundle of specialized cardiac pacemaker cells located in the wall of the right atrium near the opening of the superior vena cava

• this node exhibits an auto rhythmicity of 70 action potentials per minute and leads the activity of the other pacemaker structures in the heart

Atrioventricular Nodes (AV)

• bundle of specialized, cardiac pacemaker cells located at the base of the right atrium

• exhibits an auto rhythmicity of 50 action potentials per minute

• under normal conditions, this node allows the faster SA node at 70 AP / min

Bundle of His

• tract of specialized cardiac pacemaker cells that originates at the AV node and divides and projects into the left and right ventricles

Purkinje Fibers

• small terminal fibers of specialized, cardiac pacemaker cells that extend from the bundle of His and spread throughout the ventricular myocardium

• these fibers exhibit an auto rhythmicity of 30 action potentials per minute

• under normal conditions, they follow the faster SA node (and AV node) at 70 AP / min

Interatrial Pathway

• pathway of specialized, cardiac cells that conducts pacemaker activity from the right atrium to the left atrium

Internodal Pathway

• pathway of specialized cardiac cells that conducts pacemaker activity from the SA node to the AV node

What is the AV nodal delay?

• pacemaker activity is conducted relatively slowly through the AV node, resulting in a delay of approximately 100ms

• this delay ensures that the ventricles contract after atrial contraction

What are the three steps of action potentials for contractile cardiac muscle cells? Draw the graph associated.

• 1) prolonged plateau phase

  • result of slow Ca2+ entry on opening of L-type Ca2+ channels, coupled with reduced K+ efflux on closure of several types of K+ channels

• 2) rapid falling phase

  • result of K+ efflux on opening of ordinary voltage-gated K+ channels, as in other excitable cells

• 3) resting potential maintained by opening of leaky K+ channels

Draw the two cardiac action potentials for the different cells.

check image

Describe the excitation-contraction coupling for the heart (4). What is different compared to skeletal muscle cells?

• 1) t-tubule membranes in cardiac muscle cells contain dihydropyridine receptors that act as voltage-gated Ca2+ channels

• 2) when an action potential invades the T-tubule membranes, these channels open and allow Ca2+ to flow into the cytosol

• 3) Ca2+ entry triggers further release of Ca2+ from the sarcoplasmic reticulum

• 4) these two sources of cytosolic Ca2+ activate the power stroke of contraction

• Difference

  • unlike skeletal muscle cells, the number of activated cross-bridges is proportional to the cytosolic Ca2+ concentration

Draw the relationship of an action potential and the refractory period to the duration of the contractile response in cardiac muscle.

check image

Check image

A

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C

What is an electrocardiogram?

• electrical currents generated by coordinated action potentials of the heart muscle can reach the surface of the body and be detected as voltage differences between two points on the body surface

• record resulting from measuring these voltage changes is referred to as ECG (electrocardigram)

• disturbances in heart function can be detected as changes in the ECG

Draw the electrocardiogram waveforms and describe the four key components of it.

P wave

• represents depolarization of the atria

QRS complex

• represents depolarization of the ventricles

T-wave

• represents repolarization of the ventricles

PR Segment

• represents the AV node delay

Draw a time line of the waveforms and the locations of the heart.

check image

What type of electrocardiogram waveform?

normal rate and rhythm

What type of electrocardiogram waveform?

tachycardia

• abnormality in rate

What type of electrocardiogram waveform?

extrasystole

• premature ventricular contraction

• abnormality in rhythm

What type of electrocardiogram waveform?

ventricular fibrillation

What type of electrocardiogram waveform?

complete heart block

What type of electrocardiogram waveform?

myocardial infarction

• heart attack

Describe the two main mechanical events of the cardiac cycle. Draw the diagram that connects these concepts to the ECG.

Systole

• alternate periods of contraction and emptying

Diastole

• alternate periods of relaxation and filling

What are the three types of volumes associated with the mechanical events? List the formula associated.

EDV

• volume of blood in the chamber at the end of diastole

• equivalent to the max amount of blood that the chamber will hold during cycle

ESV

• amount of blood remaining in the chamber at the end of systole when ejection is complete

Stroke Volume

• amount of blood pumped out of the chamber with each contraction

• SV = EDV - ESV

Describe the contraction and relaxation phase of heart. Draw the pressure graphs for the phases.

Isovolumetric ventricular contraction

• period of time during contraction when the chamber remains closed, and therefore no blood can enter or leave

• chamber pressure increases during this period

Isovolumetric ventricular relxation

• period of time during relaxation when the chamber remains closed, and therefore no blood can enter or leave

• chamber pressure decreases during this period