Chapter 6 Muscular System Flashcards
Muscles
Responsible for all types of body movement
3 types of muscle
Skeletal
Cardiac
Smooth
Muscle charactoristics
skeletal and smooth are elongated
contraction is due to movement of microfilaments
myo and mys refers to muscle
Skeletal Muscle
attached by tendons
cells are multinucleated striated,
have visible banding voluntary
connective tissue wrappings
cells surrounded and bundled by connective tissue
Endomysium
Perimysium
Epimysium
Fascia
Endomysium
encloses a single muscle finber
Perimysium
wraps around a fascicle (bundle) of muscle fiber
Epimysium
covers entire skeletal muscle
Fascia
on the outside of the epimysium
Skeletal muscle attachments
epimysium blends into tendons
Tendons
cord like structures that connect muscle to bone
mostly collogen fibers
Smooth muscle chacteristics
lack striations
spindle shaped cells
singel nucleus
involuntary
mainly in wall of hollow organs
Cardiac muscle characteristics
Striations
usually single nucleus branching cells
joined by intercalated disc
involuntary
found only in heart
Muscle functions
produce movement
maintain posture
stabilize joints
generate heat
Skeletal muscle fiber
thin elongated cylindrical cell with rounded ends
extends length of muscle
sarcolemma
transverse tubules
myofibrils
sarcoplasmic reticulum
striation pattern
sarcomere
Sarcolemma
plasma membrane
transverse tubules
invaginations of sarcolemma
entend all through fiber
myofibrils
bundle of contractile proteins
think filament-myosin
thin filament-actin
sarcoplacsmic reticulum
modified ER
sacs and tubes that surround each myofibril
stores Ca+2
striation pattern
due to arrangement of thin and thick fibers
A band: dark think filament
I band: thin filament anchored to Z lines
Sarcomere
contractile unit of muscle
segment of myofirbril between 2 Z lines
Sarcomere organization
myosin
myosin
2 twisted proteins with globular heads (cross bridges) projecting outwards
myosin cross bridge head has ATPase enzymes
energy released cocks myosin head to prepare for binding wtih actin
thick filaments
composed of many myosin molecules
located in center of sarcomere
Actin
double stranded helical molecule
each actin monomer has binding site for myosin
troponin and tropomyosin are regulatory proteins found on thin filament
thin filament
actin is the main protein
anchored to the Z disc
H zone
region in the center of “A” band that contains only myosin at rest
M line
proteins that hold myosin molecules in place
Excitability
ability to receive and respond to a stimulus
Contractabillity
ability to shorten when an adequate stimulus is received
Extensibility
ability of muscle cells to be stretched
Elasticity
ability to recoil and resume resting length after stretching
muscle contraction
skeletal muscles must be stimulated by a motor neuron to contract
Motor unit
one motor neuron
all of skeletal muscles cells are stimulated by that neuron
Neuromuscular Junction
connection between axon terminal of the motor neuron and muscle
Motor Neuron
Axon terminal contains the synaptic vesicles
vesicles contain neurotransmitters
transmitters are chemicals taht transmit signal from neuron to next cell
Motor End Plate
folded region of the sarcolemma under the axon terminal
contains Ach receptors
Synaptic Cleft
gap between nerve and muscle
filled with interstitial fluid
transmission of Nerve Impulse to Muscle
Nerve impulse reaches axon terminals of motor neuron
synaptic vesicles release acetylcholine (ACh)
ACh diffuses across cleft and binds to receptors on motor end plate
sarcolemma becomes permeable to Na+
Na+ rushes into the cell generating an action potential
action potential travels on sarcolemma and stimulates muscle fiber to contract
sliding filament theory
muscle contraction involves the shortening of all the sarcomeres within a muscle fiber
sliding filament theory
myosin pulls the thin filaments intothe center of the sarcomere
thin filaments slide past the think filaments
Main events in skeletal muscle contraction
once stimulated an action potential travels along sarcolemma down t-tublules
causes SR to release Ca+2
Ca+2 binds to troponin
troponin and tropomyosin move exposing binding site for myosin on actin
myosin cross bridge binds to actin
phosphate and SDP are released from cross bridge
myosin cross bridge changes and pulls actin in (power stroke)
new ATP binds to myosin and cross bridge detaches from actin
ATP is hydrolysed and energy is used to “cock” myosin head so it is ready to bind with actin
cross bridge cycle continues if ATP and Ca+2 are present
Skeletal muscle Relaxation
ACh is degraded
muscle fiber is no longer stimulated
Ca+2 is pumped back into the SR
new ATP causes cross bridge to detach from actin
Troponin-tropomyosin move so tropomyosin covers myosin binding site on actin
muscle fiber relaxes
ATP is hydrolysed and energy is used to “cock” myosin cross bridge
ready for further stimulation
Contraction of Skeletal muscle
All or None
not all fibers may be stimulated during same interval
different combinations may give different responses
graded responses different degrees of contraction strength
contractoin graded responses
frequency of stimulation
number of motor units being stimulated at one time
Energy for contraction
stored ATP
only 4-6 secons is stored
other pathways to produce ATP
Direct Phosphorylation of ADP
muscle cells store CP (high energy molecule)
CP supplies are exhausted in less than 15 seconds
Anerobic glycolysis and lactic acid formation
occurs when O2 is limited or absent
produces 2 ATP and lactic acid
not as efficient but fast
about 40 seconds of energy
Aerobic Respiration
Main source of ATP
can provide hours of energy
Cell oxygen source
blood
hemoglobin in RBC carries oxygen from lungs
Myoglobin
found in skeletal muscle
temporary storage site for oxygen
muscle fatigue
Muscle unable to contract even with a stimulus
muscle fatigue causes
build up of lactic acid
lack of ATP
depletion of muscle glycogen stores
lack of acetylcholine
