Exam 3Skeletal Muscle Composition and the NMJ

Question 1

3 types of muscles

Answer 1

Cardiac, Skeletal, Smooth

Question 2

Characteristic of Skeletal muscle

Answer 2

Multinucleated cells
Cells appear striated at the microscopic level due to orientation of contractile proteins
Contraction provides voluntary movement

Question 3

Connective tissue laters of Skeletal Muscle

Answer 3

Epimysium, perimysium, endomysium

Question 4

Epimysium

Answer 4

An external sheath of DENSE connective tissue, surrounds the entire muscle.
Septa of this tissue extend inward, carrying the larger nerves blood vessels and lymphatics of the muscle

Question 5

Perimysium

Answer 5

A thin connective tissue layer that immediately surrounds each bundle of muscle fibers termed a fascicle. Each fascicle of muscle fibers makes up a functional unit in which the fibers work together. Nerves, blood vessels, and lymphatics penetrate the perimysium to supply each fascicle.

Question 6

Endomysium

Answer 6

A very thin, delicate later of reticular fibers and scatter fibroblasts within fascicles surrounding the external lamina of individual muscle fibers. In addition to nerve fibers, capillaries form a rich network in the endomysium bringing oxygen to the muscle fibers

Question 7

Function of collagen in CT layers of muscle

Answer 7

serve to transmit the mechanical forces generates by the contracting muscle cells/fibers

Question 8

Function of CT

Answer 8

Nourishment via rich capillary and lymphatic network
Protection/organization
Transmit forces along muscle fibers (through collagen)

Question 9

Muscle components

Answer 9

Myofilaments
Myofibrils
Muscle Fiber
Muscle fasciculus
Whole Muscle
Myotendinous junction

Question 10

Myofilaments

Answer 10

Protein polymers responsible for contraction (e.g., actin and myosin)

Question 11

Myofibrils

Answer 11

grouping of myofilaments within a muscle cell

Question 12

Muscle fiber

Answer 12

muscle cell, made up of myofibrils

Question 13

Muscle fasciculus/fascicle

Answer 13

bundle of muscle fibers

Question 14

Whole muscle

Answer 14

many fascicles bundled together

Question 15

Cardiac muscle characteristics

Answer 15

composed of irregularly branched cells bound together longitudinally by intercalated discs and shows strong, involuntary contractions

Question 16

Smooth muscle

Answer 16

Composed of grouped, fusiform cells with weak involuntary contractions

Question 17

Myotendinous junction

Answer 17

connection of muscle and tendon
Infoldings of cell membrane of muscle fibers
Provides insertion sites for collagen fibers of tendon into muscle fibers

Question 18

Sarcomere

Answer 18

functional unit of muscle

Question 19

Components of a sarcomere

Answer 19

Thick (myosin) and thin (actin) myofilaments, Titin

Question 20

Titin functions

Answer 20

assists with transmission of force during contraction, limits range of motion of sarcomere in tension, provides passive tension in resting muscle, maintains appropriate positions of actin and myosin (binds Z-disc to M-line)

Question 21

Sarcomere landmarks

Answer 21

Z-line (disk)- boundaries of a sarcomere *actin attaches here
I-band: area of actin molecules only (straddles Z-lines; Z-lines bisect I-band)
A-band: area of myosin and actin overlap
H-band (H-zone): area of myosin only
M-line: anchors central area of myosin within each sarcomere; contains kinase - enzyme that adds high energy phosphates to ADP to make ATP

Question 22

Myofilaments of skeletal muscle

Answer 22

small proteins responsible for muscle contraction (actin and myosin filaments)
Number of myofilaments increases with training hypertrophy while number of muscle fibers is unaltered

Question 23

Thick filament

Answer 23

Myosin

Question 24

Light chain of Myosin

Answer 24

Consists of area of ATPase function (globular head)

Serves as connection sites for actin

Question 25

Globular head

Answer 25

Heavy chain; just beyond the neck/light chain; Functions as an ATPase - enzyme that energizes the process of muscle contraction by facilitating hydrolysis of ATP to release energy

Question 26

Heavy chain of myosin

Answer 26

Consist of helixes of filamentous protein polymers

Question 27

thin filament

Answer 27

Actin

Question 28

Actin

Answer 28

Globular protein polymer, bound to myosin at cross-bridges (on light chain of myosin) Globular proteins polymerized into long chains

Question 29

Tropomyosin

Answer 29

Filamentous protein that exists within the "grooves" of actin filaments

Question 30

Troponin

Answer 30

Complex of three proteins TnT - binds tightly to tropomyosin TnC - contains a calcium binding site TnI - inhibits tropomyosin from uncovering binding sites on actin

Question 31

Sarcoplasmic Reticulum

Answer 31

SER of muscle cells is specialized as a storage area for calcium ions; has terminal cisterns adjacent to T-tubules

Question 32

Transverse tubules

Answer 32

invaginations of the sarcolemma that create a network of membranous tubules at each sarcomere of muscle fibers

Question 33

Triad

Answer 33

complex of two terminal cisterns of SR and one t-tubule; area where sarcolemma depolarization is transmitted to the membrane of the SR

Question 34

Sarcoplasmic Reticulum: function

Answer 34

Motor neuron creates depolarization of the sarcolemma at the neuromuscular junction; Depolarization is transmitted from the sarcolemma to the SR via the T-tubule system of the muscle fiber; SR depolarization stimulates release of calcium from cisterns; Released Calcium binds to TnC (binding allows cross-bridging between actin and myosin); At the end of depolarization, calcium is actively returned from the sarcoplasm to the SR

Question 35

Muscle spindles

Answer 35

Proprioceptors within striated muscle fibers; used reflexively to maintain appropriate muscle tension for posture and regulation of opposing muscle groups

Question 36

Spindles consist of

Answer 36

A CT capsule that surrounds intrafusal muscle fibers (modified muscle fibers): bag fibers (dynamic and static stretch) and chain fibers (static stretch)

Question 37

Spindles monitor...

Answer 37

the velocity and degree of muscle stretch and send that information to the CNS (transmit info using *1A and II afferent fibers*)

Question 38

Muscle stretch information from sensory fibers of the spindles synapses at...

Answer 38

the spinal cord to allow reflexive control of the contractile state of muscles

Question 39

When stretched (quickly) spindles

Answer 39

Stimulate reflexive contraction of the muscle to reduce stretch (MSRs)

Question 40

Spindles also stimulate reflexive inhibition...

Answer 40

of antagonist muscles to allow agonist muscles to contract without opposition

Question 41

Gamma motorneuron controls

Answer 41

the sensitive of the spindles to stretch

Question 42

Golgi tendon organ

Answer 42

Sensory nerve ending imbedded in the collagen fibers of the myotendinous junction; monitors the force of contraction of the muscle and sends info to CNS via *1b afferent fibers*; Provides input to CNS about contraction forces to aid in producing appropriate, smooth contractions

Question 43

GTO provides an inhibitory reflex that...

Answer 43

protects muscles from creating too much tension (too much tension in a contracting muscle stimulates reflexive relaxation to prevent muscle damage)

Question 44

glycogen

Answer 44

polymer of glucose; abundant amount stored within the sarcoplasm and serves as a source of glucose for energy production

Question 45

Myoglobin

Answer 45

oxygen binding protein in sarcoplasm; serves as storage site for oxygen for aerobic respiration; concentrated in muscles that maintain activity for prolonged periods

Question 46

Neuromuscular junction

Answer 46

site of connection between the nerve fiber of a motorneuron and the muscle fibers of skeletal muscle (also called "motor end plate"); each nerve contains terminal branches allowing it to synapse with up to several hundred muscle fibers (synapse at midpoint of muscle fiber)

Question 47

Synaptic characteristics

Answer 47

Synaptic trough: invagination of muscle membrane | Subneural clefts: folds within synaptic trough which increase surface area for NT receptors (Ach)

Question 48

Mitochondria of motorneuron of NMJ

Answer 48

within axon terminal of motorneuron; create ATP energy for acetylcholine synthesis and vesicle exocytosis

Question 49

Voltage gated calcium channels of motorneuron on NMJ

Answer 49

Opened by spread of action potential to axon terminal; influx of Ca stimulates vesicle release of Ach

Question 50

How is Ach of motorneuron released? Then what happens?

Answer 50

exocytosis of synaptic vesicles; Ach moves into synaptic cleft and binds nicotinic receptors located in subneural clefts

Question 51

The post-synaptic membrane of the NMJ

Answer 51

muscle fiber

Question 52

characteristics of the post-synaptic NMJ membrane

Answer 52

contains synaptic trough and subneural clefts; Ach binding to nicotinic receptor opens Sodium channels that creates local depolarization (end plate potential); most end plate potentials create and action potential in muscle fibers (for fiber contraction); AP propagates in both directions along muscle fiber (moves along t-tubules within fibers)

Question 53

Neuromuscular contraction

Answer 53

AP is transmitted along the t-tubules and across each sarcomere within the muscle fiber; along t-tubule stimulates depolarization of SR membrane which results in release of Calcium from the cisterns of the SR; ACh is active at receptors for milliseconds, ACh is released from its receptor and is quickly degraded by acetylcholinesterase; Calcium binds with TnC and initiates attractive forces between actin and myosin of muscle fibers; conformation change in Tn causes tropomyosin to "move" and uncover actin binding sites; Once calcium binds, actin and myosin "bridge" together; actin-myosin then slide along side each other, creaing a muscle fiber contraction; following contraction calcium is released from TnC and then pumped back into the SR in preparation for the next depolarization

Question 54

Myasthenia gravis

Answer 54

``` Auto-immune disease in which antibodies "attack" (blocks) ACh receptors and render them non functional; disease creates weakness/paralysis due to inability muscle cell to react to nerve impulses; Treatment: Acetylcholinesterase inhibitors that reduce ACh degradation and increase ACh binding to remain functional receptors. Nerve gas (sarin) - inhibits acetylcholinesterase and creates tonic muscle contraction ```

Question 55

Alpha motor neuron

Answer 55

extrafusal muscle fibers (skeletal muscle fibers); creates muscle fiber contraction

Question 56

Gamma motor neuron

Answer 56

intrafusal muscle fibers (muscle spindle); generates muscle response to sensory input from muscle spindles; causes tightening/relaxation of spindles to alter their sensitivity

Question 57

C-motor neuron

Answer 57

autonomic nervous system fibers to smooth muscle