1. 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.

3. Skeletal Muscle Tendon Muscle Fascicle Muscle fiber (cell) Epimysium
(attachments between muscle and bone matrix)
Muscle
Fascicle
Epimysium
Muscle fiber (cell)
Endomysium
Perimysium
(connective tissue surrounding entire muscle)
(connective tissue around muscle cells)
(connective tissue around muscle fascicles)

4. The Muscle Fiber T tubules Nucleus Muscle fiber
They conduct the nerve impulse from the sarcolemma to the interior of the cell
Muscle fiber
Terminal cisterna
Sarcoplasmic reticulum
It stores and releases calcium for muscle contraction
Mitochondria
They produce the chemical energy (ATP) for muscle contraction
Openings into transverse tubules
Triad:
Myofibrils
2 Terminal cisternae
Transverse tubule
Sarcolemma
Sarcoplasm
Myofilaments

5. SKELETAL MUSCLE MUSCLE FASCICLE MUSCLE FIBER (CELL) MYOFIBRIL
Contains:
Surrounded by:
MUSCLE FASCICLE
Muscle fascicles
Epimysium
Contains:
Surrounded by:
MUSCLE FIBER (CELL)
Muscle fibers (cells)
Perimysium
Contains:
Surrounded by:
Myofibrils
Endomysium
MYOFIBRIL
Contains:
Myofilaments
MYOFILAMENTS
They are organized in sarcomeres
Thick filaments: myosin
Sarcomere
Thin filaments: actin

6. Myofilaments Troponin Thick filament Thin filament Myosin molecule
G actin
Thin filament
Tail
Head
Hinge region
Tropomyosin
Troponin complex
Myosin molecule
Contractile proteins
Regulatory proteins
Troponin
Tropomyosin
Myosin
Actin
They do the work of shortening the muscle fiber
They act like a switch to determine when the fibers can contract

8. Striations M line Z line Titin Sarcomere Myosin (thick filaments)
They attach the thin and elastic filaments
Z line
Titin
(elastic filaments)
Sarcomere
They are the smallest functional units of the muscle fiber
M line
Myosin (thick filaments)
Actin (thin filaments)
I band (lighter)
It contains thin filaments but not thick filaments
Zone of overlap
A band (dark)
H band
A band: Its length is equal to the length of the thick filaments. It contains both thin and thick filaments
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
I band
Z line
Zone of overlap
Zone of overlap: It is the region where the thin filaments are situated between the thick filaments
H band
M line

10. When a skeletal muscle fiber contracts:
A band
H band
I band
Z line
M line
Z line
Zone of overlap
When a skeletal muscle fiber contracts:
1- The H bands and I bands get smaller
3- The Z lines move closer together
2- The zone of overlap get larger
4- The width of the A band remain constant

11. Contraction
ADP Pi
Active sites
ADP
ATP Pi
Hydrolysis of ATP to ADP + Pi; activation and cocking of myosin head
Formation of myosin–actin cross-bridge
ADP Pi
Sliding of thin filament over thick filament shorten the sarcomeres and muscle also shorten (contraction)
Power stroke; sliding of thin filament over thick filament

12. Hydrolysis of ATP to ADP + Pi; activation and cocking of myosin head
Binding site for myosin (active site)
G-actin strand
ADP + Pi
ATP

13. Troponin
Tropomyosin Ca +2
F-actin strand
Cross-bridge
ADP + Pi
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

14. Troponin Ca +2 Ca +2
Tropomyosin Ca +2 Ca +2 Ca +2
F-actin strand Ca +2 Ca +2 Ca +2
Cross-bridge Ca +2
ADP + Pi Ca +2 Ca +2 Ca +2 Ca +2 Ca +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

15. The Nerve-Muscle Relationship
Motor unit:
It is one nerve fiber and all the muscle fibers innervated by it
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

16. Synaptic knob or axon terminal
The Muscle Fiber
Nucleus
T tubules
They conduct the nerve impulse from the sarcolemma to the interior of the cell.
Muscle fiber
Terminal cisterna
Sarcoplasmic reticulum
It stores and releases calcium for muscle contraction.
Action potential
Mitochondria
Ca2+
They produce the chemical energy (ATP) for muscle contraction.
. . ..
. ...
Neurotransmitter
Myofibrils
Synaptic cleft
Synaptic knob or axon terminal
Action potential
Myofilaments

17. The Neuromuscular Junction
Myelin
The Neuromuscular Junction
Motor nerve fiber
Synaptic knob
Sarcolemma
Mitochondrion
Synaptic knob
Sarcolemma
T tubule
Synaptic vesicle
Junctional folds
They have ACh receptors which bind Ach
Synaptic cleft
Sarcoplasm
They contain acetylcholine (Ach)
Myofilaments

19. Two Types of Ion Channels Voltage gated ion channels:
Ligands
(Neurotransmitters, hormones)
_ _ _ _
+ + +
_ _ _
_ _ _ _
Chemically gated ion channels:
Voltage gated ion channels:
They open when the specific ligand binds to the receptor.
They open in response to a voltage change in the plasma membrane.

20. _ _ _ + + + _ _ _ + + + Chemically Gated ion Channels Acetylcholine
Na+
+ + +
_ _ _
+ + +
_ _ _
Resting Membrane Potential
End plate Potential

21. Excitation 1- The Arrival of an Action Potential
Axon of motor neuron
Action potential
1- The Arrival of an Action Potential
2- The Release of Acetylcholine
Synaptic terminal
Sarcolemma
Action potential
Mitochondrion Ca 2+
Voltage gated ion channels open
Sarcolemma
T tubule
Synaptic vesicle
Junctional folds
Fusing synaptic vesicle
Synaptic cleft

22. Chemically gated ion channels
Axon terminal
3- Binding of Ach to the receptors
4- Opening of ligand-gated ion channels and creation of end plate potential
_ _ _ _ _ _ _ _ _ _ _
Motor End Plate
Acetylcholine
End-plate potential
Chemically gated ion channels +
It is rapid fluctuation in the membrane potential that falls back to a level close to the resting membrane potential Na + K
Acetic acid
Choline

23. End-plate potential Action Potential
5- Opening of voltage-gated ion channels and creation of action potential
Action Potential:
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
_ _ _ _
+ + +
_ _ _ _ _
_ _ _
End-plate potential
Voltage-gated ion channels
Action Potential
Ligand- gated ion channels

24. Acetylcholine Ca Na Active transport ATP - - + + + + + + + + + +
1 & 2- Nerve signal stimulates voltage-gated calcium channels that result in exocytosis of synaptic vesicles containing ACh = ACh release
Acetylcholine Ca +2 Na +
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
3 & 4- Binding of ACh to the surface of muscle cells opens Na+ and K+ channels resulting in an end-plate potential (EPP)
12 & 13- Nerve stimulation ceases and acetylcholinesterase removes ACh from receptors so stimulation of the muscle cell ceases
8 & 9- Calcium released by SR binds to troponin. Troponin-tropomyosin complex changes shape and exposes active sites on actin
14- 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
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
Active transport
11 – Myosin releases the ATP and P and flexes into a bent , tugging the thin filaments along with it (POWER STROKE).
15 & 16- Loss of calcium from sarcoplasm results in troponin-tropomyosin complex moving over the active sites which stops the production or maintenance of tension
Muscle fiber returns to its resting length due to stretching of series-elastic components and contraction of antagonistic muscles
ATP

25. Rigor Mortis
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 calcium
Activates myosin-actin cross bridging & muscle contracts, but does not relax.
Muscle relaxation requires ATP & ATP production is no longer produced after death
Fibers remain contracted until myofilaments decay