Muscle Tissue Flashcards
Muscle Tissue
specialized for contraction
either under voluntary or involuntary control
skeletal - voluntary & striated
smooth - involuntary & nonstriated
cardiac - involuntary & striated
Development of Skeletal Muscle
myoblasts → myotubes → muscle fiber
skeletal muscle fibers are long, clyindrical, & multinucleated
Gross Anatomy of Skeletal Muscle
highly organized; layers of CT surround & organize muscle fibers
tendon, epinysium, perimysium, fasicle, endomysium, muscle fiber
Tendon
connects muscle to bone
collagen fibers of epi, peri, endomysium blend with those of tendon for attachment
collagen fibers of tendon interweave with those of periosteum & cement to matrix bone as perforating fiberss
Microanatomy of Skeletal Muscle
sarcolemma
sarcoplasm
sarcoplasmic reticulum
t-tubules
terminal cisterna
triad
myofilaments
myofibril
Myofilament: Thin Filament
composed of filamentous actin (F-actin)
F-actin composed of 2 rows of 300-400 globular molecules of G-actin
increase Ca++ → conformational change in troponin → tropomyosin shifts → active site of G-actin revealed myosin can bind
Myofilament: Thick Filament
composed of 2 elongated proteins wound together
~300 myosin molecules bundle together to form a thick filament
each has a globular head & elongated tail
myosin head binds with F-actin during contraction creating “cross-bridges”
Organization of Sarcomere
composed of overlapping thick & thin filaments
Z-disc: delineates the sarcomere & attachment for thin filaments, which extend towards the M line
M line: attachment for thick filaments
I band: extend both directions from Z disc; contains only thin filaments, less dense area
A band: extends length of thick filaments & includes parts of thin filaments that overlap
H zone: central portion of A band; thick filaments only
Skeletal Muscle Contraction
starts at neuromuscular junction (NMJ): synapse between somatic motor neuron & muscle fiber
NMJ includes the synaptic knob, synaptic cleft, & motor end plate
Events in Muscle Contraction
- a nerve impulse triggers the release of ACh from the synaptic knob into the synaptic cleft
- ACh binds with ACh receptros on the motor end plate & opens ligand-gated ion channels; Na+ diffuses down concentration gradient → triggers AP
- AP propogates along sarcolemma into system of T-tubules → Ca++ is released from terminal cisternae & muscle fibers contracts; cyclic events continue as long as Ca++ is present
Motor Units & Muscle Control
motor unit: a single motor neuron + all the muscle fibers it controls
most muscles have many motor units; inverse relationship between size of motor unit & degree of control
motor unit contracts as a whole & thus forced development is proportional to # of activated motor units
Muscle Tone
tonos=tension
some motor units are always active; produce tension but not enough tension to cause movement
motor units avoid fatigue by rotating motor unit activation
Muscle tone is the resting tension in muscle; resting tone stabilizes position of bones & joints
Types of Skeletal Muscle
muscle fibers are classified as “slow twitch” or “fast twitch” based on their response to stimulation
slow-twitch muscle fibers use aerobic means to generate ATP, while fast-twitch fibers generate ATP by anaerobic meansH
Hypertrophy of Skeletal Muscle
repeated stimulation near maximal tension will result in:
- more mitochondria
- more glycogen reserves
- more glycolytic enzymes
- increase number of myofibrils with more myofilaments
Cardiac Muscle
cells are short, branched, 1 central nucleus, & connected by intercalated discs
striated, involuntary
lack myosatellite cells & thus cannot regenerate
Intercalated Disc Join Cardiac Muscle Cells
specialized cell junctions found at irregulat intervals
gap junctions: allows for intercellular ionic communication
desmosomes & fascia adherens: provide a strong connection between cells
pace-maker cells set the basic rate of contraction & impulse is conducted between gap junctions
Cardiac Muscle
dependent on aerobic respiration
sarcoplasm contains increase in mitochondria = fatigue resistance
reserves of myoglobin to store O2
lipid droplets & glycogen granules provide energy reserves
Smooth Muscle
specialized for slow, steady contractions
found in walls of blood vessels & digestive respiratory, urinary, & reproductive organs
cells are small, fusiform shape, non-striated, single centrally located oval nucleus
involuntary; pacesetter cells set basic rate of contraction & signals propagate via gap junctions
can hypertrophy and has the capacity to regenerate
