Muscle Tissue (Exam 2) Flashcards
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Excitable tissue
Only contracts in response to electrical activity on the surface of the muscle cell membrane
General characteristics
Excitable tissue
Contracts
Relaxes
Makes up about 40% of the average persons body mass
General functions
Body movement (skeletal)
Maintenance of posture (skeletal)
Production of heat as a by product of activity (all)
Constriction of organs and blood vessels (smooth)
Production of heart beat (cardiac)
Gross anatomy
Connective tissue
Neural innervation
Connective tissue
Epimysium
Perimysium
Endomysium
Epimysium
Dense connective tissue layer around the whole muscle
Also called fascia
Perimysium
CT covering around the bundles of muscle fibers called fasciles
Endomysium
Reticular CT that surrounds each of the fibers in the fascile
Motor neuron
Specialized nerve cells
Somas are in the spinal cord
Axons extend to muscle fibers
Function: electrically stimulate the muscles to contract
Neuromuscular junction
The contact between the axon terminal and the muscle
Motor unit
One motor neuron + all the muscle fibers it innervates
Sarcolemma
Plasma membrane
Sarcoplasm
Intracellular fluid
Contains glycosomes and myoglobin
Glycosomes
Store glycogen for energy
Myoglobin
Red pigmented oxygen storing protien
Microscopic general characteristics
Each fiber is a long cylindrical cell with multiple oval nuclei
Each muscle fiber is made of many myofibrils
Myofibrils
Thread like structures that extend from one end of the muscle to the other
Made of myofilaments
Myofilaments
Action (thin filament)
Myosin (thick filament)
Actin
Each myofilament is made of:
Tropomyosin
Troponin
F-actin
F-actin
Fibrous actin
Coiled to form a double helix
Made of 200 G-actin
G-actin
Small globular protiens
Has an active site to which myosin binds during contraction
Tropomyosin
Stabilizing protien that winds along a groove in the F-actin strand
Troponin
3 polypeptide complex
TnI bonds to G-actin
TnT binds to tropomyosin, anchoring it to the F-actin strand
TnC binds to Ca+2
Myosin
Each filament has:
a rod like tail consisting of two entwined polypeptide chains
Two heads that have three components each
Binding site for actin
Binding site for ATP
Hinge region
Binding site for actin
Has ATPase activity
Splits an ATP to yield ADP, Pi, and energy
Hinge region
Junction of the head and the tail
Allows the head to bend and straighten during contraction
Z-disk/line
Protien attachment site for the actin
Sarcomer
Structural units of actin and myosin
Functional unit of a muscle
Extends from one Z-disk to another
Striations can be seen under a microscope due to alternating light and dark bands
A bands
I bands
H zone
M line
A bands
Dark bands consisting of actin and myosin
I bands
Light bands consisting of actin only
H zone
Band in the middle of the A band
Myosin only
M line
One in the middle of the H zone that holds the myosin in place
Sarcoplasmic reticulum (SR)
Surrounds each myofibril
Upon electrical stimulation it releases Ca+2 from the lateral sacs
Transverse tubule (T-Tubule)
Invagination of the muscle cell sarcolemma
Runs between lateral spaces to form a triad (1 t tubule+2 lateral sacs= a triad)
Functions to quickly transmit AP through out the muscle cell
The AP signals the release of Ca+2 from the lateral sacs
Functions of ATP
Contraction
Relaxation
Contraction
Powers the ratcheting movement of the myosin head
After each ratcheting movement a new ATP molecule binds to the myosin head so it can detach, then bind again to the next G-actin molecule
Relaxation
Powers the pump that removes Ca+2 from the sarcomere
Muscle metabolism
Continuous muscle contraction requires continuous ATP production
Accomplished via 3 pathways:
Direct phosphorylation
Anaerobic respiration/glycolysis
Aerobic respiration/oxidative phosphorylation
Direct phosphorylation of ADP by creatine phosphate (CP)
CP is an extremely high energy molecule that is stored in muscle 1st source of energy Reaction: Creatine phosphate + ADP= creatine + ATP Enzyme: creatine kinase Yield: 1 ATP per creatine phosphate About 15 seconds of activity
Anaerobic respiration/glycolysis
Does not require O2
Involves catabolism of glucose that has been obtained from the blood stream or from the breakdown of glycogen stores in the muscles (within glycosomes)
Reaction: the glucose is broken down into ATP and pyruvic acid
Yield: 2 ATP per 1 glucose
About 30-60 seconds of activity
Aerobic respiration/oxidative phosphorylation
Requires O2
Pyruvic acid from glycolysis is transferred to the Kreb’s cycle
Within mitochondria high energy bonds are broken and ATP is released
Yield: 34 ATP per 1 glucose
Hours at activity
+ the 2 from glycolysis
Skeletal muscle fiber types
Slow oxidative fibers
Fast glycolytic fibers
Fast oxidative fibers
Most muscles are a mixture of fiber types
The predominant type can change based on need/use
Slow oxidative fibers
Myosin ATPases work slow, therefore speed of contraction is slow
Uses oxidative phosphorylation for ATP production
Red in color due to high myoglobin stores
Relatively fatigue resistant and have high endurance
Uses: long distance running and posture
Fast glycolytic fibers
Myosin ATPases work fast therefore speed of contraction is fast
Uses glycolysis to generate ATP
White in color because there is no need for oxygen so no need for myoglobin
Very susceptible to fatigue because of limited glycogen stores
Uses: short term intense movements like lifting a large load
Fast oxidative fibers
Intermediate between slow oxidative and fast glycolytic
Myosin ATPases work fast therefore speed of contraction is fast
Uses oxidative phosphorylation and glycolysis for ATP production
Has both myoglobin and glycogen stores
Pink in color
Moderately fatigue resistant
Uses: walking
