Structure of Muscle Tissue

Compare cardiac muscle to skeletal muscle in terms of 1. Striation 2. Nucleation (how much and where) 3. What major feature is in cardiac muscle but not in skeletal muscle? 4. T-tubules 5. Dyads 6. Amount of mitochondria, lipids, glycogen, myoglobin in sarcoplasm 7. Force of contraction 8. Nervous and hormonal control of contraction 9. Branching

1. Both have it 2. Cardiac has one (or two) centrally located nucleus per cell vs. many multinucleate peripherally in skeletal 3. the presence of intercalated discs (noted by arrows below) which are highly specialized attachments that join cardiac muscle fibers together. The structural arrangement of the intercalated discs allows the heart to contract in a wringing fashion. 4/5. The T-tubules are more prominent in association with a reduced SR cisterna, so dyads are formed at the vicinity of the Z-line. 6. There are more mitochondria, lipid droplets, glycogen and myoglobin in the sarcoplasm of cardiac muscle cells. 7/8. The contraction of cardiac muscle is vigorous, rhythmic, and under the control of both the autonomic nervous system innervation and circulating hormones. 9. Cardiac muscle is branched

All muscle fibers in a single x are of the same fiber type. Motor Units are recruited in order of size- called the size principle; as the synaptic drive on the motor neurons increases, x motor units are recruited first, followed by medium sized ones and finally x ones. Allows automatic, smooth increase in force generation.

All muscle fibers in a single motor unit are of the same fiber type. Motor Units are recruited in order of size- called the size principle; as the synaptic drive on the motor neurons increase small motor units are recruited first, followed by medium sized ones and finally large ones. Allows automatic, smooth increase in force generation.

Name the type of muscle fiber

FF (Fast- twitch, fatigable or Type IIB) [c in below diagram) have large MNs, produce large amounts of force for short time periods. Large, white (low myoglobulin content) fibers with few mitochondria; adapted for rapid contraction and fine, precise movements; thus high concentration in extraocular and distal and finger muscles.

FR (Fast-twitch, fatigue resistant or Type IIa) [b in below diagram) 1. have x sized MNs 2. produce x amounts of force for x durations. 3. Medium sized, x fibers with moderate amounts of x; higher content in x muscles of sprinters for example.

FR (Fast-twitch, fatigue resistant or Type IIa) [b in below diagram) have medium sized MNs, produce moderate amounts of force for moderate durations. Medium sized, paler fibers with moderate amounts of myoglobulin; higher content in gastrocnemius muscles of sprinters for example.

What is this an image of?

Muscle spindle

In muscle spindle, which fibers are stimulated by change in length of intrafusal fibers?

Muscle spindle In addition to motor innervation, skeletal muscles also have sensory receptors (proprioceptors) called muscle spindles which detect the amount of stretch of a muscle (i.e length). The muscle spindle has an outer connective tissue capsule, within which an inner capsule contains two types of modified muscle cells (intrafusal fibers) that function to detect stretch. Afferent sensory fibers (Ia afferent) wrapped around these are stimulated by change in length of intrafusal fibers in the spindle. Efferent motor fibers modulate the sensitivity of the spindle by adjusting the tension in the intrafusal fibers, thus maintaining sensitivity to stretch during contraction. Is the basis for the stretch reflex (more in CNS lecture) and allows us to know our position in space (proprioception).

congenital muscle diseases (various types including Duchenne's) with severe weakness, atrophy and destruction of fibers; are caused by genetic mutations in the muscle transmembrane proteins of the dystrophin-glycoprotein complex.

Muscular Dystrophy

How can skeletal muscles adapt to use? What can change in skeletal muscle over time with exercise/repeated use?

Skeletal muscle can also adapt to use by changes in fiber type and fiber size. Increased muscle size includes an increase in muscle fiber and fibril size and number. Insulin Like Growth Factor 1(IGF-1) stimulates protein synthesis in muscle (it is antagonistic to the effects of Myostatin (see below).

Smooth muscle cells are arranged as sheets joined by xto allow intercellular communication regulating contraction of the entire sheet or bundle of smooth muscle. The arrows (right) depict the dense bodies containing x which are associated with the actin filaments.

The cells are arranged as sheets joined by gap junctions (GJ) to allow intercellular communication regulating contraction of the entire sheet or bundle of smooth muscle. The arrows (right) depict the dense bodies containing actinin which are associated with the actin filaments.

Three components of the troponin complex

Thin filaments - 3 major proteins Actin - a 42 kD globular protein that polymerizes in a double helical structure forming the thin filament Tropomyosin - a 64 kD protein that also forms a double helical structure lying in the groove of the actin helix. It acts with the troponin complex to regulate myosin-actin binding. Troponin Complex consisting of 3 globular subunits: TnI - An actin binding protein that prevents binding of actin to myosin TnT - A tropomyosin binding protein that holds the troponin complex to actin TnC - A calcium binding protein, the essential step in initiation of muscle contraction.

Muscle type with the least potential for regeneration

cardiac

T/F - TnI, TnT, TnC are all fibrillar proteins

false - all globular

T/F- Like skeletal muscle, cardiac muscle is also striated and multinucleate

false - cardiac muscle only has one or two CENTRALLY located nucleus per cell.

T/F - Smooth muscle has an extensive t-tubule network

false - no t-tubules in smooth muscle

muscle mass is a balance between x protein synthesis and degradation.

muscle mass is a balance between myofibril protein synthesis and degradation.

a thinner layer of dense irregular connective tissue that surrounds individual fascicles

perimysium

The X is the structural and functional unit of skeletal muscle

sarcomere

T/F - The interaction of actin and myosin myofilaments during smooth contraction is somewhat similar to that for skeletal muscle;

true

A tropomyosin binding protein that holds the troponin complex to actin

TnT globular subunit of troponin complex

X is the darker stained band seen in histological slides and is equivalent to the length of the myosin filament. It contains both the thick filament and the portion of the thin filament that overlaps with the thick filament. The extent of overlap depends on the degree of muscle contraction.

A (anisotropic band)

T/F - All muscle fibers in a single motor unit are of the same fiber type. 2. Motor Units are recruited in order of x- called the x principle; as the synaptic drive on the motor neurons increase small motor units are recruited first, followed by medium sized ones and finally large ones. Allows automatic, smooth increase in force generation.

All muscle fibers in a single motor unit are of the same fiber type. Motor Units are recruited in order of size- called the size principle; as the synaptic drive on the motor neurons increase small motor units are recruited first, followed by medium sized ones and finally large ones. Allows automatic, smooth increase in force generation.

Muscle Atrophy- 1. Cast immobilization leads to decreased protein synthesis within x hours. 2. x (also known as GDF-8) expression plays a central role in inhibition of muscle growth (regulating normal development as well as involvement in pathological conditions). It is a cytokine that circulates in an inactive form; proteolytic cleavage is necessary for activation. It down regulates MyoD transcription. Normally its action is antagonized by (IGF-1) activity. 3. Myostatin signaling as well as other pathways are involved in protein loss during atrophy. Disuse also leads to a disuse atrophy from bedrest, lack of exercise or disease states.

Atrophy- Cast immobilization leads to decreased protein synthesis within 24 hours. Myostatin (also known as GDF-8) expression plays a central role in inhibition of muscle growth (regulating normal development as well as involvement in pathological conditions). It is a cytokine that circulates in an inactive form; proteolytic cleavage is necessary for activation. It down regulates MyoD transcription. Normally its' action is antagonized by (IGF-1) activity. Myostatin signaling as well as other pathways are involved in protein loss during atrophy. Disuse also leads to a disuse atrophy from bedrest, lack of exercise or disease states.

Myostatin (also known as x) expression plays a central role in x, as well as involvement in pathological conditions. It is a x that circulates in a x form, where x cleavage in necessary for activation. Myostatin down-regulates x and this action is antagonized by x activity.

Atrophy- Cast immobilization leads to decreased protein synthesis within 24 hours. Myostatin (also known as GDF-8) expression plays a central role in inhibition of muscle growth (regulating normal development as well as involvement in pathological conditions). It is a cytokine that circulates in an inactive form; proteolytic cleavage is necessary for activation. It down regulates MyoD transcription. Normally its' action is antagonized by (IGF-1) activity. Myostatin signaling as well as other pathways are involved in protein loss during atrophy. Disuse also leads to a disuse atrophy from bedrest, lack of exercise or disease states.

Both the x and the x of muscle have specializations that relate to the contractile mechanism of muscle.

Both the plasma membrane and the smooth endoplasmic reticulum of muscle have specializations that relate to the contractile mechanism of muscle.

Cardiac muscle *1. Cardiac muscle fibers are joined together by x. 2. x junctions are at the end of the cells (transverse component), while x junctions are along the side of the cells (lateral component), and attaching x are at the ends and along the sides (i.e. in both locations). 3. The many gap junctions present are responsible for the electrotonic coupling between adjacent cardiac myocytes so the heart muscle contracts as a x.

Cardiac muscle fibers are joined together by intercalated discs shown at the left by arrows. Fasciae Adherens junctions are at the end of the cells (transverse component), while gap junctions are along the side of the cells (lateral component), and attaching desmosomes (Maculae adherens) are at the ends and along the sides (i.e. in both locations). The many gap junctions present are responsible for the electrotonic coupling between adjacent cardiac myocytes so the heart muscle contracts as a syncytium.

This differentiation is associated with expression of the transcription factors MyoD, myogenin and others

Differentiation of progenitor cells to myoblasts

Each anatomically identifiable skeletal muscle has a three dimensional structure maintained by connective tissue layers. These connective tissue layers also serve as a route for both the x and x supply to access the muscle tissue. There are three connective tissue layers in each muscle: 1. x - dense irregular connective tissue that surrounds all of the fascicles that constitute a muscle 2. x - a thinner layer of dense irregular connective tissue that surrounds individual fascicles 3. x - a fine layer of reticular fibers that surround individual muscle fibers.

Each anatomically identifiable skeletal muscle has a three dimensional structure maintained by connective tissue layers. These connective tissue layers also serve as a route for both the nerve and circulatory supply to access the muscle tissue. There are three connective tissue layers in each muscle: Epimysium - dense irregular connective tissue that surrounds all of the fascicles that constitute a muscle Perimysium - a thinner layer of dense irregular connective tissue that surrounds individual fascicles Endomysium - a fine layer of reticular fibers that surround individual muscle fibers.

FF (Fast- twitch, fatigable or Type IIB) [c in below diagram) 1. have x MNs 2. produce x amounts of force for x time periods. 3. Large, x (low myoglobulin content) fibers with x mitochondria; a 4. adapted for x contraction and fine, precise movements; thus high concentration in extraocular and distal and finger muscles.

FF (Fast- twitch, fatigable or Type IIB) [c in below diagram) have large MNs, produce large amounts of force for short time periods. Large, white (low myoglobulin content) fibers with few mitochondria; adapted for rapid contraction and fine, precise movements; thus high concentration in extraocular and distal and finger muscles.

Name the type of muscle fiber

FR (Fast-twitch, fatigue resistant or Type IIa) [b in below diagram) have medium sized MNs, produce moderate amounts of force for moderate durations. Medium sized, paler fibers with moderate amounts of myoglobulin; higher content in gastrocnemius muscles of sprinters for example.

T/F - Smooth muscle has a sarcomere, but does not have striations

False - smooth muscle does not have sarcomeres

What are the 3 major elements connecting cardiac myocytes to function as a syncytium via the intercalated disc? Where is there approx location.

Fasciae Adherens junctions are at the end of the cells (transverse component), while gap junctions are along the side of the cells (lateral component), and attaching desmosomes (Maculae adherens) are at the ends and along the sides (i.e. in both locations).

Growth- 1. During development myoblasts differentiate from progenitor cells. This differentiation is associated with expression of the transcription factors x, x and others and is associated with up-regulation of myofilament protein gene transcription. 2. Skeletal muscle can also adapt to use by changes in fiber x and fiber x. Increased muscle size includes an increase in x and fibril x and x. 3. x stimulates protein synthesis in muscle (it is antagonistic to the effects of Myostatin (see below).

Growth- During development myoblasts differentiate from progenitor cells. This differentiation is associated with expression of the transcription factors MyoD, myogenin and others and is associated with up-regulation of myofilament protein gene transcription. Skeletal muscle can also adapt to use by changes in fiber type and fiber size. Increased muscle size includes an increase in muscle fiber and fibril size and number. Insulin Like Growth Factor 1(IGF-1) stimulates protein synthesis in muscle (it is antagonistic to the effects of Myostatin (see below).

x Is the lighter stained band seen in histological slides and is equivalent to the portion of thin filaments in adjacent sarcomeres that are not overlapping with thick filaments Z-line or disc

I (isotropic band)

In the sarcomere, during contraction, the x band is always the same length, the x band is what changes During contraction, the x band gets shorter, the x bands also get shorter, and the x bands get closer together.

In the sarcomere, during contraction, the A band is always the same length, the H band is what changes During contraction, the H band gets shorter, the I bands also get shorter, and the Z bands get closer together.

T/F -

Increased muscle size includes an increase in muscle fiber and fibril size and number.

Insulin Like Growth Factor 1(IGF-1) stimulates protein synthesis in muscle (it is antagonistic to the effects of X)

Insulin Like Growth Factor 1(IGF-1) stimulates protein synthesis in muscle (it is antagonistic to the effects of Myostatin

Identify the structure that encompasses the 3 circled elements

Intercalated discs - comprised of asciae Adherens junctions are at the end of the cells (transverse component), while gap junctions are along the side of the cells (lateral component), and attaching desmosomes (Maculae adherens) are at the ends and along the sides (i.e. in both locations).

Like cardiac muscle, smooth control is both x (adrenergic & cholinergic) and x, but the NMJs are simple, no T-system is present, and the innervation tends to x rather than initiate activity.

Like cardiac muscle, control is both autonomic (adrenergic & cholinergic) and hormonal, but the NMJs are simple, no T-system is present, and the innervation tends to modify rather than initiate activity.

M-line located at the center of the sarcomere. The major proteins, x and x stabilize the thick filaments in register at the M line.

M-line located at the center of the sarcomere. The major proteins, C-protein and myomesin stabilize the thick filaments in register at the M line.

x located at the center of the sarcomere. The major proteins, C-protein and myomesin stabilize the thick filaments in register at the x.

M-line located at the center of the sarcomere. The major proteins, C-protein and myomesin stabilize the thick filaments in register at the M line.

Motor Unit 1. A motor unit is a motor neuron and all the x it innervates. 2. a neuron makes contact with muscle fibers of the same x type 3. Small/large number of motor units associated with fine motor control (e.g. finger/hand muscles; extraocular muscles) 4. Small/large motor units associated with gross postural control (e.g. abdominal and back muscles)

Motor Unit -a motor neuron and all the muscle fibers it innervates; a neuron makes contact with muscle fibers of the same histochemical type/ Small number of motor units associated with fine motor control (e.g. finger/hand muscles; extraocular muscles) Large motor units associated with gross postural control (e.g. abdominal and back muscles)

***Muscle Fiber Types - There are different types of skeletal muscle fibers based on differences in contractile speed, metabolic profile and fiber morphology. T/F - Most muscles have all 3 fiber types but proportion depends on function of a particular muscle . Types of muscle fibers: 1. X have small motor neurons (MN), produce small amounts of force for prolonged time periods (hence also called fatigue resistant FR). Have abundant thin, red fibers (high in myoglobulin), numerous mitochondria and contract weakly but for long periods of time; high concentration in back muscles necessary for long, slow contraction necessary for sustained posture. 2. X have medium sized MNs, produce moderate amounts of force for moderate durations. Medium sized, paler fibers with moderate amounts of myoglobulin; higher content in gastrocnemius muscles of sprinters for example. 3. X have large MNs, produce large amounts of force for short time periods. Large, white (low myoglobulin content) fibers with few mitochondria; adapted for rapid contraction and fine, precise movements; thus high concentration in extraocular and distal and finger muscles.

Muscle Fiber Types - There are different types of skeletal muscle fibers based on differences in contractile speed, metabolic profile and fiber morphology. True -Most muscles have all 3 fiber types but proportion depends on function of a particular muscle . Types of muscle fibers: 1. S (Slow-twitch or Type I) have small motor neurons (MN), produce small amounts of force for prolonged time periods (hence also called fatigue resistant FR). Have abundant thin, red fibers (high in myoglobulin), numerous mitochondria and contract weakly but for long periods of time; high concentration in back muscles necessary for long, slow contraction necessary for sustained posture. 2. FR (Fast-twitch, fatigue resistant or Type IIa) have medium sized MNs, produce moderate amounts of force for moderate durations. Medium sized, paler fibers with moderate amounts of myoglobulin; higher content in gastrocnemius muscles of sprinters for example. 3. FF (Fast- twitch, fatigable or Type IIB) have large MNs, produce large amounts of force for short time periods. Large, white (low myoglobulin content) fibers with few mitochondria; adapted for rapid contraction and fine, precise movements; thus high concentration in extraocular and distal and finger muscles.

Muscle Fibers 1. Each muscle cell (also called muscle fiber or x) is a multi-nucleated cell with numerous xly located nuclei just beneath the plasma membrane (called x in muscle). They are unusual cells in that they develop from the end to end fusion of precursor cells called x, resulting in extremely long multinucleated fibers. Cross-striations (seen in b above) are the result of the regular cytoarchitectural arrangement of the x. The cytoplasm of the cells (sarcoplasm) is dominated by the contractile filaments, but is also rich in mitochondria and a well developed x endoplasmic reticulum (called the sarcoplasmic reticulum) surrounding the x.

Muscle Fibers Each muscle cell (also called muscle fiber or myofiber) is a multi-nucleated cell with numerous peripherally located nuclei just beneath the plasma membrane (called sarcolemma in muscle). They are unusual cells in that they develop from the end to end fusion of precursor cells called myoblasts, resulting in extremely long multinucleated fibers. Cross-striations (seen in b above) are the result of the regular cytoarchitectural arrangement of the myofilaments. The cytoplasm of the cells (sarcoplasm) is dominated by the contractile filaments, but is also rich in mitochondria, a well developed smooth endoplasmic reticulum (called the sarcoplasmic reticulum) surrounding the myofilaments (actin and myosin).

1. In addition to motor innervation, skeletal muscles also have sensory receptors (proprioceptors) called x which detect the amount of stretch of a muscle (i.e length). 2. The muscle spindle has an outer x, within which an inner capsule contains two types of modified muscle cells (intrafusal fibers) that function to detect x. 3. Afferent sensory fibers (Ia afferent) wrapped around these are stimulated by change in x of intrafusal fibers in the spindle. 4. Efferent motor fibers modulate the x of the spindle by adjusting the tension in the intrafusal fibers, thus maintaining sensitivity to stretch during contraction. 5. Is the basis for the x reflex (more in CNS lecture) and allows us to know our position in space (proprioception).

Muscle spindle In addition to motor innervation, skeletal muscles also have sensory receptors (proprioceptors) called muscle spindles which detect the amount of stretch of a muscle (i.e length). The muscle spindle has an outer connective tissue capsule, within which an inner capsule contains two types of modified muscle cells (intrafusal fibers) that function to detect stretch. Afferent sensory fibers (Ia afferent) wrapped around these are stimulated by change in length of intrafusal fibers in the spindle. Efferent motor fibers modulate the sensitivity of the spindle by adjusting the tension in the intrafusal fibers, thus maintaining sensitivity to stretch during contraction. Is the basis for the stretch reflex (more in CNS lecture) and allows us to know our position in space (proprioception).

Function of the muscle spindle

Muscle spindle In addition to motor innervation, skeletal muscles also have sensory receptors (proprioceptors) called muscle spindles which detect the amount of stretch of a muscle (i.e length). The muscle spindle has an outer connective tissue capsule, within which an inner capsule contains two types of modified muscle cells (intrafusal fibers) that function to detect stretch. Afferent sensory fibers (Ia afferent) wrapped around these are stimulated by change in length of intrafusal fibers in the spindle. Efferent motor fibers modulate the sensitivity of the spindle by adjusting the tension in the intrafusal fibers, thus maintaining sensitivity to stretch during contraction. Is the basis for the stretch reflex (more in CNS lecture) and allows us to know our position in space (proprioception).

Muscular Dystrophy - congenital muscle diseases (various types including Duchenne's) with severe weakness, atrophy and destruction of fibers; are caused by genetic mutations in the muscle x proteins of the x complex.

Muscular Dystrophy - congenital muscle diseases (various types including Duchenne's) with severe weakness, atrophy and destruction of fibers; are caused by genetic mutations in the muscle transmembrane proteins of the dystrophin-glycoprotein complex.

is an autoimmune disease with progressive muscular weakness. It is characterized by a reduction in the number of acetylcholine receptors in the sarcolemma at the NMJ. Circulating antibodies bind to the receptors, which are removed by endocytosis and lysosomal digestion.

Myasthenia gravis

Myasthenia gravis is an x disease with progressive muscular weakness. It is characterized by a reduction in the number of x receptors in the sarcolemma at the NMJ. Circulating x bind to the receptors, which are removed by endocytosis and lysosomal digestion.

Myasthenia gravis is an autoimmune disease with progressive muscular weakness. It is characterized by a reduction in the number of acetylcholine receptors in the sarcolemma at the NMJ. Circulating antibodies bind to the receptors, which are removed by endocytosis and lysosomal digestion.

Individual sarcomeres are joined end to end at x extending more or less from one end of the cell to the other. Each of these long cylindrical strands of sarcomeres is termed a x.

Myofibrils Individual sarcomeres are joined end to end at Z-discs extending more or less from one end of the cell to the other. Each of these long cylindrical strands of sarcomeres is termed a myofibril.

Myofibrils are composed of bundles of myofilaments: these are the individual polymers of x (thick filaments) and x and its associated proteins (thin filaments)

Myofibrils are composed of bundles of MYOFILAMENTS: these are the individual polymers of myosin (thick filaments) and actin and its associated proteins (thin filaments)

Myofilaments are linked into a highly structured organization called the x (sa), a unique structural feature of striated (skeletal and cardiac) muscle. Sarcomeres line up end to end along the length of the muscle fiber in small parallel bundles called x. It is a highly organized arrangement of thin and thick filaments in a specific banding pattern which forms the basis for muscle contraction.

Myofilaments are linked into a highly structured organization called the sarcomere (sa), a unique structural feature of striated (skeletal and cardiac) muscle. Sarcomeres line up end to end along the length of the muscle fiber in small parallel bundles called myofibrils. It is a highly organized arrangement of thin and thick filaments in a specific banding pattern which forms the basis for muscle contraction.

Physical exercise causes x (increase in cell size) of x and x muscle fibers, whereby the increase in cell volume is due to the formation of new x. 2. Smooth muscle fibers (eg. uterus) are in addition capable of x (increase in cell number). An inhibitor to "x" can increase muscle mass, but the tendons are smaller and can rupture. Following injury, skeletal muscle can regenerate new fibers via myoblastic cells nearby called x cells; these cells are surrounded by a x (laminin), which is outside the sarcolemma. If the basal lamina is disrupted, x repair the injury site and a scar results. Regenerated skeletal muscle has x nuclei. Smooth muscle has modest regenerative potential, but x muscle for the most part cannot regenerate; therefore myocardial infarcts are replaced by connective tissue scars.

Physical exercise causes hypertrophy (increase in cell size) of skeletal and cardiac muscle fibers, whereby the increase in cell volume is due to the formation of new myofibrils. Smooth muscle fibers (eg. uterus) are in addition capable of hyperplasia (increase in cell number). An inhibitor to "myostatin" can increase muscle mass, but the tendons are smaller and can rupture. Following injury, skeletal muscle can regenerate new fibers via myoblastic cells nearby called satellite cells; these cells are surrounded by a basal lamina (laminin), which is outside the sarcolemma. If the basal lamina is disrupted, fibroblasts repair the injury site and a scar results. Regenerated skeletal muscle has central nuclei. Smooth muscle has modest regenerative potential, but cardiac muscle for the most part cannot regenerate; therefore myocardial infarcts are replaced by connective tissue scars.

S (Slow-twitch or Type I) [a in diagram below] 1. have x motor neurons (MN) 2. produce x amounts of force for x time periods (hence also called fatigue resistant FR). 3.Have abundant thin, red fibers (high in x), numerous/few? mitochondria and contract x for long periods of time; high concentration in x muscles necessary for long, slow contraction necessary for sustained posture.

S (Slow-twitch or Type I) [a in diagram below] have small motor neurons (MN), produce small amounts of force for prolonged time periods (hence also called fatigue resistant FR). Have abundant thin, red fibers (high in myoglobulin), numerous mitochondria and contract weakly but for long periods of time; high concentration in back muscles necessary for long, slow contraction necessary for sustained posture.

Name the type of muscle fiber

Slow twitch of Type I -have small motor neurons (MN), produce small amounts of force for prolonged time periods (hence also called fatigue resistant FR). Have abundant thin, red fibers (high in myoglobulin), numerous mitochondria and contract weakly but for long periods of time; high concentration in back muscles necessary for long, slow contraction necessary for sustained posture.

*Name the hierarchical organization of skeletal muscle from the smallest component to the muscle. (5 stages)

Smallest 1. Myofilaments (actin and myosin contractile myofilaments) 2. Myofibril (organelle with repeating sarcomere units) 3. Muscle fiber (cell, myofiber) 4. Muscle fascicle (a bundle of fibers) 5. Muscle (deltoid, for example)

Smooth muscle cells are xform, lack cross-striations (myofibrils) and x, and have a single centrally located nucleus. 2. They are found in the x of tubular organs (in two planes); the iris and ciliary body of the eye, the scrotum, blood vessels and hair follicles (specific names given later). 3. The cell length can range from 20 m (arteriole) to 200 m (gut wall) and 500 m (pregnant uterus)

Smooth muscle cells are fusiform, lack cross-striations (myofibrils) and T-tubules, and have a single centrally located nucleus. They are found in the wall of tubular organs (in two planes); the iris and ciliary body of the eye, the scrotum, blood vessels and hair follicles (specific names given later). The cell length can range from 20 m (arteriole) to 200 m (gut wall) and 500 m (pregnant uterus)

The Xis the critical location of certain diseases (Myasthenia Gravis, Lambert Eaton syndrome) or toxins (Botulism) Loss of stimulation to the muscle cell through the X leads to muscle atrophy (Denervation Atrophy).

The NMJ is the critical location of certain diseases (Myasthenia Gravis, Lambert Eaton syndrome) or toxins (Botulism) [these will be discussed in the CNS block]. Loss of stimulation to the muscle cell through the neuromuscular junction leads to muscle atrophy (Denervation Atrophy).

The Neuromuscular Junction 1. Skeletal muscle is stimulated to contract by the release of the neurotransmitter X. 2. In muscle this synaptic connection is called a neuromuscular junction (NMJ) or X which includes specializations of the muscle cell. 3. The plasma membrane of the muscle cell has extensive X where the axon terminates on the muscle cell. 4. The NMJ is also responsible for a X effect on the target muscle cell.

The Neuromuscular Junction Skeletal muscle is stimulated to contract by the release of the neurotransmitter acetylcholine. You will hear about the mechanisms of signal transduction in the Synapse lecture. In muscle this synaptic connection is called a neuromuscular junction (NMJ) or motor end-plate which includes specializations of the muscle cell. The plasma membrane of the muscle cell has extensive junctional folds (JF) where the axon terminates on the muscle cell. The NMJ is also responsible for a trophic effect on the target muscle cell.

The muscle spindle has an outer connective tissue capsule, within which an inner capsule contains two types of modified muscle cells (x fibers) that function to x. Afferent sensory fibers (Ia afferent) wrapped around these are stimulated by x. Efferent motor fibers modulate x.

The muscle spindle has an outer connective tissue capsule, within which an inner capsule contains two types of modified muscle cells (intrafusal fibers) that function to detect stretch. Afferent sensory fibers (Ia afferent) wrapped around these are stimulated by change in length of intrafusal fibers in the spindle. Efferent motor fibers modulate the sensitivity of the spindle by adjusting the tension in the intrafusal fibers, thus maintaining sensitivity to stretch during contraction.

The proteins x and x are present in the intermediate filaments of smooth muscle; cytoplasmic dense bodies contain - x and serve to anchor thin filaments to the sarcolemma in order to transmit contractile force.

The proteins desmin and vimentin are present in the intermediate filaments of smooth muscle; cytoplasmic dense bodies contain alpha actinin and serve to anchor thin filaments to the sarcolemma in order to transmit contractile force.

Thick filaments - three major proteins 1. Myosin Heavy Chain - a large protein with two portions, an x "rod" portion and a x "head" portion that has an x and x binding site. 2. Myosin Light Chain 1 3. Myosin Light Chain 2 Phosphorylation of both light chains helps regulate calcium stimulation of contraction. This is more important in x muscle

Thick filaments - three major proteins 1. Myosin Heavy Chain - a large protein with two portions, an alpha helical "rod" portion and a globular "head" portion that has an ATP and actin binding site. 2. Myosin Light Chain 1 3. Myosin Light Chain 2 Light chain phosphorylation helps regulate calcium stimulation of contraction. This is more important in smooth muscle

What do the arrows point to?

They point to the intercalated discs, this is cardiac muscle.

An actin binding protein that prevents binding of actin to myosin

TnI globular subunit of troponin complex

Thick filaments - three major proteins 1. x chain - a large protein with two portions, an alpha helical "rod" portion and a globular "head" portion that has an ATP and actin binding site. 2. Myosin Light Chain 1 3. Myosin Light Chain 2 Light chain x helps regulate calcium stimulation of contraction. This is more important in smooth muscle

Thick filaments - three major proteins 1. Myosin Heavy Chain - a large protein with two portions, an alpha helical "rod" portion and a globular "head" portion that has an ATP and actin binding site. 2. Myosin Light Chain 1 3. Myosin Light Chain 2 Light chain phosphorylation helps regulate calcium stimulation of contraction. This is more important in smooth muscle

The three major proteins comprising thick filaments - of muscle

Thick filaments - three major proteins 1. Myosin Heavy Chain - a large protein with two portions, an alpha helical "rod" portion and a globular "head" portion that has an ATP and actin binding site. 2. Myosin Light Chain 1 3. Myosin Light Chain 2 Light chain phosphorylation helps regulate calcium stimulation of contraction. This is more important in smooth muscle.

Name the three major proteins comprising the thin filaments of muscles

Thin filaments - 3 major proteins Actin - a 42 kD globular protein that polymerizes in a double helical structure forming the thin filament Tropomyosin - a 64 kD protein that also forms a double helical structure lying in the groove of the actin helix. It acts with the troponin complex to regulate myosin-actin binding. Troponin Complex consisting of 3 globular subunits: TnI - An actin binding protein that prevents binding of actin to myosin TnT - A tropomyosin binding protein that holds the troponin complex to actin TnC - A calcium binding protein, the essential step in initiation of muscle contraction.

Thin filaments - 3 major proteins 1. x - a 42 kD globular protein that polymerizes in a double helical structure forming the thin filament 2. x - a 64 kD protein that also forms a double helical structure lying in the groove of the actin helix. It acts with the troponin complex to regulate myosin-actin binding. 3. Troponin Complex consisting of 3 globular subunits: x - An actin binding protein that prevents binding of actin to myosin x - A tropomyosin binding protein that holds the troponin complex to actin x - A calcium binding protein, the essential step in initiation of muscle contraction.

Thin filaments - 3 major proteins Actin - a 42 kD globular protein that polymerizes in a double helical structure forming the thin filament Tropomyosin - a 64 kD protein that also forms a double helical structure lying in the groove of the actin helix. It acts with the troponin complex to regulate myosin-actin binding. Troponin Complex consisting of 3 globular subunits: TnI - An actin binding protein that prevents binding of actin to myosin TnT - A tropomyosin binding protein that holds the troponin complex to actin TnC - A calcium binding protein, the essential step in initiation of muscle contraction.

A calcium binding protein, the essential step in initiation of muscle contraction.

TnC globular subunit of troponin complex

Transverse tubule - or T-tubule is a tubular invagination of the muscle cell x. These invaginations of the plasma membrane (see text figure below) are normally aligned with the myofibrils at the boundary between x and x bands. They are closely associated with the x of the Sarcoplasmic Reticulum, which is a highly specialized smooth endoplasmic reticulum. The T-tubules and SR allow for contraction of myofibrils throughout the muscle cell quickly, despite the very large X of the cells. The T-tubule allows for changes in the membrane x to extend into the center of the cell and by virtue of the close linkage of the T-tubule, with the terminal cisternae of the Sarcoplasmic Reticulum, whose function is to serve as a reservoir for x ions. The regulation of x calcium concentration is central to the mechanism of muscle contraction and is covered in detail in the muscle physiology lecture. Triad: triple structure seen in cross section consisting of x

Transverse tubule - or T-tubule is a tubular invagination of the muscle cell plasma membrane. These invaginations of the plasma membrane (see text figure below) are normally aligned with the myofibrils at the boundary between A and I bands. They are closely associated with the terminal cisternae of the Sarcoplasmic Reticulum, which is a highly specialized smooth endoplasmic reticulum. These two structures allow for contraction of myofibrils throughout the muscle cell quickly, despite the very large diameter of the cells. The T-tubule allows for changes in the membrane electrical potential to extend into the center of the cell and by virtue of the close linkage of the T-tubule, with the terminal cisternae of the Sarcoplasmic Reticulum, whose function is to serve as a reservoir for calcium ions. The regulation of cytoplasmic calcium concentration is central to the mechanism of muscle contraction and is covered in detail in the muscle physiology lecture. Triad: triple structure seen in cross section consisting of two terminal cisternae flanking a T-tubule at the A-I band.

What are the functions of alpha-actinin, titin, and nebulin in sarcomere contraction?

Z-line or disc The Z-line serves as an anchor for thin filaments by the protein alpha-actinin. The protein Titin anchors the thick filaments to the Z-line. Along the length of the thick filament it may have the function of maintaining appropriate spacing of these filaments in the sarcomere. The protein Nebulin may have this function in relation to the thin filaments. From the end of the thick filament to the Z-line it functions as a molecular spring which provides for passive elasticity of muscle and keeps thick filaments centered in the sarcomere.

Z-line or disc The Z-line serves as an anchor for thin filaments by the protein x. The protein x anchors the thick filaments to the Z-line. Along the length of the thick filament it may have the function of maintaining appropriate spacing of these filaments in the sarcomere. The protein x may have this function in relation to the thin filaments. From the end of the thick filament to the Z-line it functions as a molecular spring which provides for passive elasticity of muscle and keeps thick filaments centered in the sarcomere.

Z-line or disc The Z-line serves as an anchor for thin filaments by the protein alpha-actinin. The protein Titin anchors the thick filaments to the Z-line. Along the length of the thick filament it may have the function of maintaining appropriate spacing of these filaments in the sarcomere. The protein Nebulin may have this function in relation to the thin filaments. From the end of the thick filament to the Z-line it functions as a molecular spring which provides for passive elasticity of muscle and keeps thick filaments centered in the sarcomere.

a 42 kD globular protein that polymerizes in a double helical structure forming the thin filament

actin

function of alpha actinin in smooth muscle

cytoplasmic dense bodies contain alpha actinin and serve to anchor thin filaments to the sarcolemma in order to transmit contractile force.

What serves to anchor thin filaments to the sarcolemma in order to transmit contractile force in smooth muscle?

dense bodies containing alpha actinin

a fine layer of reticular fibers that surround individual muscle fibers.

endomysium

dense irregular connective tissue that surrounds all of the fascicles that constitute a muscle

epimysium

Skeletal and cardiac muscle are striated, and exhibit cross striations at the x microscopic level.

light microscopic

Do smooth muscles have striation, t-tubules, multinucleation?

no

Which muscle types are involuntary muscle, voluntary?

only skeletal muscle is voluntary, cardiac/smooth are involuntary

Describe how smooth muscle is oriented in most organs

outer longitudinal and inner circular layers

a 64 kD protein that also forms a double helical structure lying in the groove of the actin helix. It acts with the troponin complex to regulate myosin-actin binding.

tropomyosin