1. Where’s the beach? Did you buy your tickets?
Muscular System
Where’s the beach?
Did you buy your tickets?

2. Muscle Functions Production of Movement
Movement of body parts and of the environment
Movement of blood through the heart and the circulatory vessels.
Movement of food (and, subsequently, food waste) through the GI tract, of fluids (urine, sperm, bile, etc), of a newborn through the birth canal

3. Muscle Functions Maintenance of posture Thermogenesis
Muscle contraction is constantly allowing us to remain upright.
Right now?
Thermogenesis
Generation of heat. Occurs via shivering – an involuntary contraction of skeletal muscle.

4. Muscle Functions Stabilization of joints
Muscles keep the tendons that cross the joint nice and taut.
Maintains the integrity of the joint.
All the things muscles do fall under one of these 4 categories.

5. 3 Types of Muscle Tissue

6. Characteristics of Muscle Tissue
Excitability
The ability to receive and respond to a stimulus
In skeletal muscle, the stimulus is a neurotransmitter (chemical signal) release by a neuron (nerve cell).
In smooth muscle, the stimulus could be a neurotransmitter, a hormone, stretch, pH, Pco2, or Po2. (the symbol  means “a change in”)
In cardiac muscle, the stimulus could be a neurotransmitter, a hormone, or stretch.

7. Characteristics of Muscle Tissue
Contractility
The ability to shorten forcibly when adequately stimulated.
This is the defining property of muscle tissue.
Extensibility
The ability to be stretched
Elasticity
The ability to recoil and resume original length after being stretched.

8. Skeletal Muscle – the organ
Has nerves and blood vessels
Surrounded by a layer of dense irregular connective tissue known as the epimysium.(epi= ?, mysium=muscle).

9. Skeletal Muscle – the organ
Epimysium surrounds several bundles known as fascicles.
Each fascicle is a bundle of super-long skeletal muscle cells (muscle fibers),
Each muscle cell extends the length of the whole muscle organ
Skeletal Muscle – the organ

10. In this photomicrograph, you should notice: the epimysium on the left, the multiple fascicles, the translucent perimysium partitioning them , and the multiple muscle fibers making up the fascicles.

11. Microanatomy
Each muscle fiber contains rodlike structures called myofibrils that extend the length of the cell.
The myofibrils contain 2 filaments: actin (thin) and myosin (thick)

13. Microanatomy cont. Thick myofilaments are made of the protein myosin
A single myosin protein resembles 2 golf clubs whose shafts have been twisted about one another
About 300 of these myosin molecules are joined together to form a single thick filament

14. Microanatomy cont.
Each thin filament is made up of 3 different types of protein: actin, tropomyosin, and troponin.
This strand is a polymer that resembles a string of beads. Each “bead” is the globular protein actin. On each actin subunit, there is a myosin binding site.

15. Note the relationship between the thin and thick filaments

16. Microanatomy cont.
Each myofibril is made up 1000’s of repeating individual units known as sarcomeres (pictured below)
Each sarcomere is an ordered arrangement of thick and thin filaments..

17. Muscle Contraction: The Sliding Filament Hypothesis
Place your right palm on the back of your left hand. Now slide your right palm toward your left elbow.
What happened to the distance between your elbows?
It got shorter!
This is how muscle contraction occurs.
The thin filaments slide over the thick filaments. This pulls the Z discs closer together. When all the sarcomeres in a fiber do this, the entire fiber gets shorter which pulls on the endomysium, perimysium, epimysium and attached tendon and then pulls on the bone. Voila, we have movement.

18. Skeletal Muscle Attachments
Most span joints and are attached to bones.
The attachment of the muscle to the immoveable bone in a joint is its origin, while the attachment to the moveable bone is its insertion.

19. Here are 2 electron micrographs of the same sarcomere
Here are 2 electron micrographs of the same sarcomere. Do you see the Z discs, A band, H zone, M line, and I bands? How do the 2 pictures differ? What happened?

20. Sliding Filaments
We can actually divide the whole process of muscle contraction into 4 steps:
Excitation
Excitation-contraction coupling
Contraction
Relaxation

21. QUICK THOUGHT QUESTION: In this sculpture, why are the lion’s back legs paralyzed even though they were not injured?

22. Skeletal Muscle Attachments
Most span joints and are attached to bones.
The attachment of the muscle to the immoveable bone in a joint is its origin, while the attachment to the moveable bone is its insertion.

23. Muscle Diagrams
Label major muscles
Label origin and insertion points

32. Muscle Fiber Types
2 main types:
Slow fibers
Fast fibers

33. Slow Fibers Contract slowly because its myosin ATPases work slowly.
Depends on oxygen delivery and aerobic metabolism.
Is fatigue resistant and has high endurance.
Is thin in diameter – large amt of cytoplasm impedes O2 and nutrient diffusion.
Cannot develop high tension – small diameter means few myofibrils.
Has rich capillary supply and lots of mitochondria.
Contains lots of the O2-storing protein, myoglobin which gives it a red color.
Uses lipids, carbs, and amino acids as substrates for it aerobic metabolism.
Best suited for endurance type activities.
A.k.a. red fibers, slow oxidative fibers, type I fibers.

34. Fast Fibers
So named because they can contract in 0.01 seconds or less after stimulation.
Fast fibers are large in diameter; they contain densely packed myofibrils, large glycogen reserves, and relatively few mitochondria.
Able to develop a great deal of tension b/c they contain a large number of sarcomeres.
Use ATP in massive amounts. Supported by anaerobic metabolism. Fatigue rapidly.
A.k.a., fast fatigue (FF) fibers, fast glycolytic (FG) fibers, white fibers.
Best suited for short term, power activities.

36. Thought questions: why do chickens have white breast meat and dark leg meat? What does this say about the activities of the associated muscles? Why do ducks have dark breast meat?

37. Myasthenia Gravis My=muscle, asthen=weakness, gravi=heavy
Autoimmune disease where antibodies attack the ACh receptors on neuromuscular junctions.
Results in progressive weakening of the skeletal muscles. Why?
Treated w/ anticholinesterases such as neostigmine or physostigmine. These decrease the activity of acteylcholinesterase.
Why would this help someone with myasthenia gravis?

38. Muscular Dystrophy
Group of inherited muscle-destroying diseases that generally appear during childhood.
Dys=faulty; Troph=growth
Most common is Duchenne muscular dystrophy
DMD is caused by an abnormal X-linked recessive gene
Diseased muscle fibers lack the protein dystrophin which normally links the cytoskeleton to the ECM and stabilizes the sarcolemma
Age of onset is btwn 2 and 10. Muscle weakness progresses. Afflicted individuals usually die of respiratory failure, usually by age 25.
Here is a slide of skeletal muscle from someone with DMD. Look how much connective tissue there is. Lots of adipose tissue too. Why do you think there’s so much?

39. Other Important Terms Flaccid paralysis Spastic paralysis Spasm
Weakness or loss of muscle tone typically due to injury or disease of motor neurons
Spastic paralysis
Sustained involuntary contraction of muscle(s) with associated loss of function
How do flaccid and spastic paralysis differ?
Spasm
A sudden, involuntary smooth or skeletal muscle twitch. Can be painful. Often caused by chemical imbalances.

40. Other Important Terms Cramp Hypertrophy
A prolonged spasm that causes the muscle to become taut and painful.
Hypertrophy
Increase in size of a cell, tissue or an organ.
In muscles, hypertrophy of the organ is always due to cellular hypertrophy (increase in cell size) rather than cellular hyperplasia (increase in cell number)
Muscle hypertrophy occurs due to the synthesis of more myofibrils and synthesis of larger myofibrils.

41. Other Important Terms Atrophy Fibrosis
Reduction in size of a cell, tissue, or organ
In muscles, its often caused by disuse. Could a nerve injury result in disuse? Why might astronauts suffer muscle atrophy?
Fibrosis
Replacement of normal tissue with heavy fibrous connective tissue (scar tissue). How would fibrosis of skeletal muscles affect muscular strength? How would it affect muscle flexibility?

42. Smooth Muscle Involuntary, non-striated muscle tissue
Occurs within almost every organ, forming sheets, bundles, or sheaths around other tissues.
Cardiovascular system:
Smooth muscle in blood vessels regulates blood flow through vital organs. Smooth muscle also helps regulate blood pressure.
Digestive systems:
Rings of smooth muscle, called sphincters, regulate movement along internal passageways.
Smooth muscle lining the passageways alternates contraction and relaxation to propel matter through the alimentary canal.

43. Smooth Muscle Integumentary system: Respiratory system Urinary system
Regulates blood flow to the superficial dermis
Allows for piloerection
Respiratory system
Alters the diameter of the airways and changes the resistance to airflow
Urinary system
Sphincters regulate the passage of urine
Smooth muscle contractions move urine into and out of the urinary bladder

44. Smooth Muscle Reproductive system Males Females
Allows for movement of sperm along the male reproductive tract.
Allows for secretion of the non-cellular components of semen
Allows for erection and ejaculation
Females
Assists in the movement of the egg (and of sperm) through the female reproductive tract
Plays a large role in childbirth

45. Smooth Muscle Smooth muscle cells:
Are smaller: 5-10um in diameter and um in length
Are uninucleate: contain 1 centrally placed nucleus
Lack any visible striations
Lack T-tubules
Have a scanty sarcoplasmic reticulum
Smooth muscle tissue is innervated by the autonomic nervous system unlike skeletal muscle which is innervated by the somatic nervous system (over which you have control)
Only the endomysium is present. Nor perimysium or epimysium.

46. Smooth Muscle Contraction
Myosin and actin are present and crossbridge formation powers contraction, but the thick and thin filaments do not have the strict repeating arrangement like that found in skeletal muscle.
There are no Z discs, instead thin filaments are attached to protein structures called dense bodies which attach to the sarcolemma.

47. Cardiac Muscle Striated, involuntary muscle
Found in walls of the heart
Consists of branching chains of stocky muscle cells. Uni- or binucleate.
Has sarcomeres & T-tubules
Cardiac muscle cells are joined by structures called intercalated discs – which consist of desmosomes and gap junctions.
Why do you suppose these are necessary?
Notice the branching and the intercalated disc, indicated by the blue arrow.