lecture # 17: muscular tissue (chapter 11) objectives: 1- compare the three types of muscle tissue...
TRANSCRIPT
Lecture # 17: Muscular Tissue(Chapter 11)
Objectives:
1- Compare the three types of muscle tissue with regard to microscopic appearance, location, function, and regulation of contraction. 2- Define epimysium, perimysium, endomysium, and tendon. 3- Describe muscle cell anatomy.4- Describe the arrangement of thin and thick filaments in a sarcomere and its relationship to striations. 5- Define motor unit and describe the anatomy of a neuromuscular junction. 6- Explain the neural, chemical, and mechanical factors involved in the contraction of skeletal muscle. 7- Explain isotonic and isometric contractions.
Skeletal Muscle
Muscle fiber (cell)
Fascicle
Muscle
EndomysiumPerimysium
Epimysium
Tendon
(connective tissue around muscle cells)
(connective tissue around muscle fascicles)
(connective tissue surrounding entire muscle)
(attachments between muscle and bone matrix)
The Muscle Fiber
2 Terminal cisternaeTransverse tubule
Muscle fiber
Openings intotransverse tubules
Triad:
Sarcoplasmic reticulumIt stores and releases calcium for muscle contraction
Terminal cisterna
SarcolemmaSarcoplasm
MitochondriaThey produce the chemical energy (ATP) for muscle contraction
T tubulesThey conduct the nerve impulse from the sarcolemma to the interior of the cell
Myofibrils
Myofilaments
Nucleus
SKELETAL MUSCLEContains: Surrounded by:
MUSCLE FASCICLEContains: Surrounded by:
MUSCLE FIBER (CELL)Contains: Surrounded by:
Muscle fascicles Epimysium
Muscle fibers (cells) Perimysium
Myofibrils Endomysium
MYOFIBRILContains:
Myofilaments
They are organized in sarcomeres
Sarcomere
MYOFILAMENTSThick filaments: myosin
Thin filaments: actin
Thin filament
Myosin molecule
Thick filament
Tropomyosin
HeadHinge region
Tail
G actin
Troponin complex
Myofilaments
Myosin
Actin
Contractile proteinsThey do the work of shortening the muscle fiber
Regulatory proteinsTroponin
TropomyosinThey act like a switch to determine when the fibers can contract
They attach the thin and elastic filaments
They are the smallest functional units of the muscle fiber
Sarcomere
A band (dark)
H band
M line
M line: It consists of proteins that connect each thick filament with its neighbors
H band: It is a lighter region on either side of the M line, which contains only thick filaments
Zone of overlap: It is the region where the thin filaments are situated between the thick filaments
Zone of overlap
Zone of overlap
A band: Its length is equal to the length of the thick filaments. It contains both thin and thick filaments
I band (lighter) It contains thin filaments but not
thick filaments
Z lineI band
Zone of overlap
H band M line
Actin (thin filaments)
Myosin (thick filaments)
Z line Z lineTitin(elastic
filaments)
Striations
I band I band
A band
H band
Zone of overlap
Zone of overlap
M lineZ line Z line
When a skeletal muscle fiber contracts:
1- The H bands and I bands get smaller
2- The zone of overlap get larger
3- The Z lines move closer together
4- The width of the A band remain constant
Active sites
Power stroke; sliding of thin filament over thick filament
Formation of myosin–actin cross-bridgeHydrolysis of ATP to ADP + Pi; activation and cocking of myosin head
Sliding of thin filament over thick filament shorten the sarcomeres and muscle also shorten (contraction)
ATP ADP
Pi
ADP Pi
ADP
Pi
Contraction
Binding site for myosin (active site)
G-actin strand
ATP
ADP + Pi
Hydrolysis of ATP to ADP + Pi; activation and cocking of myosin head
Ca +2
At low intracellular concentration of Ca the tropomyosin blocks the binding sites for myosin in the actin molecules and prevents the formation of cross-bridges
+2
Troponin
F-actin strand
Tropomyosin
ADP + Pi
Cross-bridge
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2
Ca +2Ca +2
At high intracellular concentration of Ca the troponin is activated and undergoes a conformational change that moves the tropomyosin away from actin’s binding sites for myosin heads
+2
Troponin
F-actin strand
Tropomyosin
ADP + Pi
Cross-bridge
The Nerve-Muscle Relationship
It is one nerve fiber and all the muscle fibers innervated by it
Motor unit:
The average motor unit contains 200 muscle fibers for each motor unit
Neuromuscular junction (NMJ): It is the point where a nerve fiber meets a muscle fiber
The Muscle Fiber Muscle fiber
Sarcoplasmic reticulumIt stores and releases calcium for muscle contraction.
Terminal cisterna
MitochondriaThey produce the chemical energy (ATP) for muscle contraction.
T tubulesThey conduct the nerve impulse from the sarcolemma to the interior of the cell.
Myofibrils
Myofilaments
Nucleus
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
. .
..
. . ..
. ...
Action potential
Neurotransmitter
Action potential
Synaptic knob or axon
terminal
Synaptic cleft
Motor nerve fiber
Synaptic knob
Sarcolemma
T tubule
Junctional folds
Synaptic vesicle
Synaptic cleft
Sarcolemma
Mitochondrion
Myelin
The Neuromuscular Junction
Myofilaments
Sarcoplasm
Synaptic knob
They have ACh receptors which bind Ach
They contain acetylcholine (Ach)
Chemically gated ion channels:
+ + + + + + + _ _ _ _ _ _ _+ + + + +
_ _ _ _
Voltage gated ion channels:
Ligands
(Neurotransmitters, hormones)
They open in response to a voltage change in the plasma membrane.
They open when the specific ligand binds to the receptor.
Two Types of Ion Channels
+ + +
_ _ _ + + +
_ _ _
Acetylcholine Na+
End plate Potential
Resting Membrane Potential
Chemically Gated ion Channels
Axon of motor neuron
Action potential
Synaptic terminal
Sarcolemma
T tubule
Junctional folds
Synaptic vesicle
Ca 2+
Fusing synaptic vesicle
Synaptic cleft
Action potential
Voltage gated ion channels
open
Excitation1- The Arrival of an Action Potential
Mitochondrion
2- The Release of Acetylcholine
Sarcolemma
+ + + + + + + +
_ _ _ _ _ _ _ _ _ _ _Acetylcholine
Na
K
Acetic acid
Choline
Axon terminal
Motor End Plate
Chemically gated ion channels+
+
End-plate potentialIt is rapid fluctuation in the membrane potential that falls back to a level close to the resting membrane potential
3- Binding of Ach to the receptors
4- Opening of ligand-gated ion channels and creation of end plate potential
+ + + + + + + +
_ _ _ _ __ _ _
Voltage-gated ion channels
+ + + +
_ _ _ _
End-plate potential
Action Potential
5- Opening of voltage-gated ion channels and creation of action potential
Ligand- gated ion channels
It is a rapid voltage change in which a plasma membrane reverses its electrical polarity
Action potential have self-propagating effect that produce a traveling wave of excitation in the nerves and muscles cells
Action Potential:
- - + + + + + + + + + +
+ + - - - - - - - - - - - -
ATP
Acetylcholine
Ca+2
Na +
1 & 2- Nerve signal stimulates voltage-gated calcium channels that result in exocytosis of synaptic vesicles containing ACh = ACh release
3 & 4- Binding of ACh to the surface of muscle cells opens Na+ and K+ channels resulting in an end-plate potential (EPP)
5- Voltage change in end-plate region (EPP) opens nearby voltage-gated channels in plasma membrane producing an action potential
6 & 7- Action potential spreading over sarcolemma reaches and enters the T tubules -- voltage-gated channels open in T tubules causing calcium gates to open in SR
8 & 9- Calcium released by SR binds to troponin. Troponin-tropomyosin complex changes shape and exposes active sites on actin
10 - Myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and “cocking” it in an extended position. It binds to an active site on actin
11 – Myosin releases the ATP and P and flexes into a bent , tugging the thin filaments along with it (POWER STROKE).
12 & 13- Nerve stimulation ceases and acetylcholinesterase removes ACh from receptors so stimulation of the muscle cell ceases14- Active transport pumps calcium from sarcoplasm back into SR where it binds to calsequestrin. ATP is needed for muscle relaxation as well as muscle contraction
15 & 16- Loss of calcium from sarcoplasm results in troponin-tropomyosin complex moving over the active sites which stops the production or maintenance of tensionMuscle fiber returns to its resting length due to stretching of series-elastic components and contraction of antagonistic muscles
Active transport
Stiffening of the body beginning 3 to 4 hours after death -- peaks at 12 hours after death & diminishes over next 48 to 60 hours
Deteriorating sarcoplasmic reticulum releases calciumActivates myosin-actin cross bridging & muscle contracts, but
does not relax.Muscle relaxation requires ATP & ATP production is no longer
produced after deathFibers remain contracted until myofilaments decay
Rigor Mortis