Unit 6 muscular system

11

1. 1

2. Muscular System
2

3. 1. Produce Movements- Muscle pulls tendons to move
the skeleton
2. Maintenance of posture – enables the body to
remain sitting or standing
3. Joint stabilization
4. Guard entrances and exits: Encircle openings to
digestive and urinary tracts. Control swallowing and
urination
5. Heat generation
Muscle contractions produce heat
Helps maintain normal body temperature

4. –Contractility
•Long cells shorten and generate pulling force
–Excitability
•Electrical nerve impulse stimulates the muscle
cell to contract
–Extensibility
•Can be stretched back to its original length by
contraction of an opposing muscle
–Elasticity
•Can recoil after being stretched

5. •Skeletal
–Attached to bones
–Makes up 40% of body weight
–Responsible for locomotion, facial expressions, posture, respiratory
movements, other types of body movement
–Voluntary in action; controlled by somatic motor neurons
•Smooth
–In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
–Some functions: propel urine, mix food in digestive tract,
dilating/constricting pupils, regulating blood flow,
–In some locations, autorhythmic
–Controlled involuntarily by endocrine and autonomic nervous systems
•Cardiac
–Heart: major source of movement of blood
–Autorhythmic
–Controlled involuntarily by endocrine and autonomic nervous systems

6. •Cells of muscles
–Are known as fibers
•Plasma membrane is called a sarcolemma
•Cytoplasm is called sarcoplasm
•Muscle contraction
–Depends on two types of myofilaments (contractile
proteins)
•One type contains actin
•Another type contains myosin
–These two proteins generate contractile force

7. •Connective tissue and fascicles
–Connective tissue sheaths
bind a skeletal muscle and
its fibers together
•Epimysium – dense regular
connective tissue surrounding
entire muscle
•Perimysium – surrounds
each fascicle
(group of muscle fibers)
•Endomysium – a fine sheath
of connective tissue wrapping
each muscle cell
Connective tissue sheaths are continuous with tendons

8. Connective tissue sheaths are continuous with tendons

9. •Nerves and blood vessels
–Each skeletal muscle supplied by branches
of
•One nerve
•One artery
•One or more veins
–Nerves and vessels branch repeatedly
–Smallest nerve branches serve
•Individual muscle fibers

10. •Muscle attachments
–Most skeletal muscles
run from one bone to
another
–One bone will move –
other bone remains
fixed
•Origin – less movable
attachment
•Insertion – more
movable attachment

11. Sarcolemma - cell membrane
–Surrounds the sarcoplasm (cytoplasm of fiber)
•Contains many of the same organelles seen in other cells
•An abundance of the oxygen-binding protein myoglobin
–Punctuated by openings called the transverse tubules (T-
tubules)
•Narrow tubes that extend into the sarcoplasm at right angles
to the surface
•Filled with extracellular fluid
Microscopic Anatomy of Skeletal Muscle

12. 10-12
•System of tubular sacs similar to smooth ER in nonmuscle
cells
•Sarcoplasmic reticulum stores Ca
+2
in a relaxed muscle
•Release of Ca
+2
triggers muscle contraction
•Forms ‘triad’ with T-tubules

13. •A triad consists of a T-tubule and the segments of sarcoplasmic
reticulum on either side.

14. •Myofibrils -cylindrical structures
within muscle fiber
–Are bundles of protein
filaments (=myofilaments)
•Two types of myofilaments
1.Actin filaments (thin
filaments)
2.Myosin filaments (thick
filaments)
–At each end of the fiber,
myofibrils are anchored to the
inner surface of the
sarcolemma
–When myofibril shortens,
muscle shortens (contracts)
Microscopic Anatomy of Skeletal Muscle

15. •Basic unit of contraction of skeletal muscle
–Z disc (Z line) – boundaries of each sarcomere
–Thin (actin) filaments – extend from Z disc toward the center
of the sarcomere
–Thick (myosin) filaments – located in the center of the
sarcomere
•Overlap inner ends of the thin filaments
•Contain ATPase enzymes

16. •A bands – full length of the thick filament
–Includes inner end of thin filaments
•H zone – center part of A band where no thin filaments occur
•M line – in center of H zone
–Contains tiny rods that hold thick filaments together
•I band – region with only thin filaments
–Lies within two adjacent sarcomeres

17. •Myofibrils are built of 3 kinds of protein
–contractile proteins
•myosin and actin
–regulatory proteins which turn contraction on & off
•troponin and tropomyosin
–structural proteins which provide proper alignment,
elasticity and extensibility
•titin, myomesin, nebulin and dystrophin

18. 10-18

19. •Titin – a spring-like molecule in sarcomeres
–Resists overstretching
–Holds thick filaments in place
–Unfolds when muscle is stretched

20. •Composed of one motor
neuron and all the muscle
fibers that it innervates
•There are many motor units
in a muscle
•The number of fibers
innervated by a single motor
neuron varies (from a few to
thousand)
•The fewer the number of
fibers per neuron  the
finer the movement (more
brain power)
Motor Units

21. •Motor neurons innervate skeletal muscle
tissue
–Neuromuscular junction is the point where nerve
ending and muscle fiber meet

22. ·Neurotransmitter – chemical released by
nerve upon arrival of nerve impulse
·The neurotransmitter for skeletal muscle is
acetylcholine
·Neurotransmitter attaches to receptors on the
sarcolemma
·Sarcolemma becomes permeable to sodium
(Na
+
)
·Sodium rushing into the cell generates an action
potential
·Once started, muscle contraction cannot be
stopped

23. •When an action potential reaches the presynaptic terminal of the motor neuron
acetylcholine is released in synaptic cleft

24. Mechanism of Contraction

27. Titin

28. •Ach is removed from the
receptors by
acetylcholinesterase
•Ligand-gated Na+ channels close
•Na/K pumps reestablish the RMP
•Ca++ ions leave troponin and are
brought back into the cisternae
(this process needs energy)
•Tropomyosin moves back over
the actin active site
•The myosin heads release their
binding to actin
•The filaments passively move
back into resting position
Muscle relaxation

29. It has the following steps:
1.Before contraction begins, An ATP molecule binds to the
myosin head of the cross-bridges.
2.The ATPase activity of the myosin head immediately
cleaves the ATP molecule but the products (ADP+P)
remains bound to the head. Now the myosin head is in a
high energy state and ready to bind to the actin molecule.
3.When the troponin-tropomyosin complex binds with
calcium ions that come from the sarcoplasmic reticulum, it
pulls the tropomyosin so that the active sites on the actin
filaments for the attachment of the myosin molecule are
uncovered.
4.Myosin head binds to the active site on the actin
molecule.
SLIDING FILAMENT THEORY

30. Figure 12.7

31. 5.The bond between the head of the cross bridges(myosin) & the
actin filaments causes a the bridge to change shape bending 45°
inwards as if it was on a hinge, stroking towards the centre of the
sarcomere, like the stroking of a boat oar. This is called a POWER
STROKE.
6.This power stroke pulls the thin filament inward only a small
distance.
7.Once the head tilts, this allows release of ADP & phosphate ions.
8.At the site of release of ADP, a new ATP binds. This binding
causes the detachment of the myosin head from the actin.
9.A new cycle of attachment-detachment-attachment begins.
10.Repeated cycles of cross-bridge binding, bending and
detachment complete the shortening and contraction of the
muscle.
SLIDING FILAMENT THEORY

32. Comparison of Skeletal, Cardiac and Smooth Muscle

33. Comparison of Skeletal, Cardiac and Smooth Muscle

35. •Skeletal muscle fibers are categorized according
to
–How they manufacture energy (ATP)
–How quickly they contract
•Skeletal muscle fibers
–Are divided into 3 classes
•Slow oxidative fibers (Type I)
–Red Slow twitch
•Fast glycolytic fibers (Type IIx)
–White fast-twitch
•Fast oxidative fibers (Type IIa)
–Intermediate fibers

36. ·Isotonic contractions
·Myofilaments are able to slide
past each other during
contractions
·The muscle shortens
·Isometric contractions
·Tension (forces) in the muscles
increases
·The muscle is unable to shorten
(not appear to be moving)

38. The presence of INTERCALATED DISKS allow cardiac
muscle fibers to transmit impulses faster among themselves.
The INTERCALATED DISKS are special cell junctions
between cardiac fibers that allow them to exchange
chemicals and function as a group.

39. Smooth Muscle
•Does not contain
sarcomeres.
•Contains > content of
actin than myosin
(ratio of 16:1).
•Myosin filaments
attached at ends of the
cell to dense bodies.
•Contains gap junctions.

40. Smooth Muscle Contraction
•Depends on rise in free intracellular Ca
2+
.
•Ca
2+
binds with calmodulin.
–Ca
2+
calmodulin complex joins with and activates
myosin light chain kinase.
•Myosin heads are phosphorylated.
–Myosin heads binds with actin.
•Relaxation occurs when Ca
2+
concentration
decreases.

41. In smooth muscle, calcium ions combine with CALMODULIN
to allow the actin and myosin cross-bridges to form.
CALMODULIN is found in smooth muscle and takes the
place of troponin; a calcium-calmodulin complex initiates the
sequence leading to the formation of the cross-bridges.

42. •Rigor mortis is a state of muscular stiffness that begins
3-4 hours after death and lasts about 24 hours
•After death there is Excessive release of calcium out of
the sarcoplasmic reticulum in muscle that allow myosin
heads to bind to actin
•Since ATP synthesis has stopped, crossbridges cannot
detach from actin until proteolytic enzymes begin to
digest the decomposing cells.

43. 1.Write the functions of muscles?
2.How many types of muscles are found in human body?
3.State the difference between the 3 types of muscle
present in human body
4.Write the names and locations of different connective
tissue wrappings of skeletal muscle?
5.Write about the microscopic anatomy of skeletal
muscle?
6.What is myofibrils?
7.What is sarcomere?
8.Draw the picture of sarcomere?
9.Name the protein and its location found in sarcomere?
10.Write short notes on sliding filament theory?
11.What is the difference between isometric and isotonic
contraction?

44. 12. Write the characteristics of muscles?
13. Define neuromuscular junction?
14. What is neurotransmitter?
15. Write the difference between the following?
supine and prone position
abduction and adduction
Flexion and extension
16 . What is the reason for muscle fatigue?