Anatomy Lecture Test 3

What is a muscle fiber?

muscle cell

What are the 3 types of muscle tissue?

1. Skeletal ─ striated and voluntary
2. Cardiac ─ striated and involuntary
3. Smooth ─ non-striated and involuntary

What is skeletal muscle?

Skeletal muscle is attached to bones by tendons and is responsible for voluntary movement.
- Multinucleated, striated, unbranched cells.
- All or none contraction

Describe the tissue within skeletal muscle?

Skeletal Muscle has an extensive connective tissue component.
- Optimally arranged for effective transfer of pull of contraction of the muscle attachements.
- Multiple tissue wrappings
- Epimysium
- Perimedium
- Endomesium

Epimysium

a sheath of fibrous elastic tissue surrounding a muscle.

Perimesium

the sheath of connective tissue surrounding a bundle of muscle fibers.

Endomysium

Connective tissue surrounding a muscle fiber

Describe epimysium, perimysium, and endomysium

- The whole muscle is enclosed in the epimysium.
- Partitions extend into the muscle dividing it into bundles of muscle fiber → fascicles
- The fascicles are wrapped in the perimysium
- The perimysium conveys the blood vessels, nerves, and lymphatics from epimysium.
- Delicate, loose connective tissue partitions extend from the perimysium into the individual fascicles.
- Wrap around each fiber in a fascicle
- Contain capillaries and nerve fibers
- This is the endomesium

What is sarcoplasm?

cytoplasm of a muscle cell
- Contains cylindrical striated contractile elements called myofibrils.
- Extend the full length of the fiber
- The bands are made-up of tightly packed segments of myofibrils.

Describe the anatomy of a muscle

What is inside of myofibrils?

Myofibrils
- A-bands: anisotropic bands (dark bands)
- I-bands: Isotropic bands (light bands)
- these make up skeletal muscle striated

Myofibrils

Microscopic protein filaments that make up muscle cells.

What is a sarcomere?

The functional unit of the muscle cell.
The fundamental repeat unit within muscle that is responsible for contraction.
- The contractile elements of the sarcomere are actin (thin filaments) and myosin (thick filaments).
- Cross-bridges are formed between them allowing the actin filaments to slide inward relative to the myosin, thus shortening the length of the sarcomere

Cardiac muscle:

causes the involuntary contractions of the heart.
- Striated and branched cells.
- Contract spontaneously.
- no nerve impulses
- Connected by intercalated discs.

intercalated discs of cardiac muscle

Attachment sites between the transverse lines between cardiac muscle cells

Smooth muscle:

is found in the walls of the digestive tract, urinary bladder, and blood vessels.
- Cells are unstriated, spindle shaped, and cause slow, but involuntary movements.
- Control the diameter of lumens.
- Partial contractions.
- Tonic contractions→ maintain tone

What are tonic contractions?

sustained contractions
- the sustained contraction of different groups of fibers within a muscle to maintain continual muscular tension (tonus)
- necessary for blood vessels that are constantly slightly contracted

Muscle Function

1. Locmotion
2. Produce a great amount of body heat.
3. Digestion and blood circulation and glandular secretion.

What do muscles do?

Muscles can only function by shortening in length.
- They can only contract.

How is muscle contraction for striated muscle?

- Striated muscle fibers must fully contract when stimulated.
- An "all-or-none" response.
- Controlled muscle contraction is achieved by varying the number of muscle fibers recruited in a given contraction

What is the difference between extending and flexing a muscle?

- The actual motion elicited depends on its orientation to the joint.
- If it increases the angle of the joint it when contracted, it is said to extend the joint.
- If it decreases the angle of the joint it when contracted, it is said to flex the joint
Pic just for representation

Synergistic muscles

- Muscles work in conjunction with other muscles in order to elicit a given motion.
- Synergistic muscles cause a similar or ancillary motion when contracted.
nE.g., Brachialis and Biceps brachii work together to flex the elbow.

Antagonistic muscles

Antagonistic Muscle is a muscle that opposes the action of another.
- Antagonistic muscles are enlisted for controlled movement.
For example, when the triceps oppose the contraction of the flexing biceps by relaxing, the triceps would be regarded as the antagonistic muscle to the biceps whereas the biceps, the agonist muscle

What else do muscles do?

Muscles can be used for stability
- Muscles may also have some muscles acting to stabilize a joint or one end of a joint while the muscles eliciting the muscular action contract.
E.g., muscles in the shoulder and pectoral girdle such as Pectoralis major act to stabilize the shoulder while the elbow is flexed.

What is the orientation of muscle fibers?

- Muscle fibers are either parallel to the line of pull of the tendon or oblique to the tendon.
- Long parallel fibers occur in muscles that need to be flexed a lot.
- Muscles with a lot of short fibers that are oblique (slanted) to the line of pull (pennate muscles) are adapted to lift heavy weights short distances.

What are the different shapes of muscles cells?

1) Fusiform
2) Pennate
- unipennate
- bipennate
- multipennate
3) Strap muscles
4) Sheets
5) Sphicters

Fusiform muscles cells

(cylindrical) are modified spindles. E.g., Biceps brachii
- Occur in muscles that need to be flexed a lot.
- Fibers are long and parallel to the line of pull.
- They are long, but relatively few fibers.
- The muscle contracts 1/3 to ½ its length.
- Relatively weak.

pennate muscles

have short fascicles oblique to the long tendon or tendons running the length of the muscle.
- "feather shaped".
- More fascicles attached directly to tendons than other muscle types.
- Generally more powerful than other muscles.
- tend to be antigravity muscles

What are the 3 types of pennate muscles?

unipennate, bipennate, multipennate

unipennate muscle

Direction of pull is toward the side of the tendon.
- all the muscle fibers are on the same side of the tendon

ex of unipennate muscle

Flexor pollicis longus

bipennate muscle

muscle fibers on both sides of the tendon; rectus femoris
- Oblique fascicles on both sides of the tendon.
- Equal pull on both sides of the tendon.
- Adapted to lift heavy weight short distances.
- Contract a short distance.
e.g., Rectus femorus or Triceps brachii

multipennate muscle

- Many oblique fascicles arranged along several tendons.
- Allows movement in multiple
directions in a flexible joint

Strap Muscles

- Fascicles are parallel to the long axis.
- Allow for a wide range of movement, but are not very powerful/strong.
e.g., Sternohyoid

sheets of muscle

- Similar to strap muscles, but also can be used as constrictors.
e.g., External and internal obliques.

Valsalva maneuver

Any forced expiratory effort against a closed airway such as when an individual holds his or her breath and tightens his or her muscles in a concerted, strenuous effort to move a heavy object or change positions in bed.
- constricting sheet muscles.
- allows us to compress the abdomen
*don't need to know*

Sphicters

- Fascicles arranged in circular pattern around and opening of a structure.
e.g., Obicularis oris or External anal sphincter

Describe muscle structure and attachment

- Muscles attach to bone via tendons.
- Tendons are extensions of the epimysium.
- The tendon is continuous with the periosteum of the bone.
- The periosteum inserts into the CaCO3 of the bone via Sharpey's fibers.
- When a tendon forms a broadsheet it is called an aponeurosis.
- a thin sheath of connective tissue that helps connect your muscles to your bones

sharpey's fibers

connect periosteum to compact bone
- a matrix of connective tissue consisting of bundles of strong collagen fibres connecting periosteum to bone.

aponeurosis

A broad, flat tendon

Origin

the least movable point of attachment.
- The site where bone and muscle are attached, but do not move during contraction.

Insertion

the most moveable point of attachment (moves during contraction).
- Usually insert in the proximal end of the bone to produce rapid movement at the distal end of the bone.

Ex of origin and insertion with biceps brachii

Origin ─ Short head: tip of coracoid process of scapulaLong head: supraglenoid tubercle of scapula
Insertion ─ radial tuberosity of the radius

What are the different types of muscle actions?

The action of a muscle usually refers to its prime action.
Types of actions:
- Flexion and extension
- Plantar flexion and dorsi-flexion.
- Protraction and retraction
- Abduction and adduction
- Inversion and eversion
- Pronation and supination
- Levitation and depression

Which actions are the movements of the foot?

- Inversion and eversion
- Dorsiflexion and Plantar Felxion

pronation and supination

palms down to palms up

elevation and depresion

elevation (levitation)- moving a sturcture superior
depression - moving a structure down

cicumduction

moving arm in loop

opposition

Movement of the thumb to touch the fingertips

lateral flextion

bending the vertebral column to the side

Describe tension and load

- The strength of the muscle is proportional to its cross-sectional area.
- Tension: the force muscle exerts on something.
- Load: the force a exerted on the muscle..
- Force drops off as the muscle gets shorter.
- Muscles only operate fully to move the lever at a 90 degrees.

describe isotonic contractions muscles

- Isotonic muscles produce both work and heat.
- If load and tension are not equal the contractions are isotonic.

Describe isometric contractions

- Isometric muscles just produce a lot of heat.
- If load and tension are equal the contractions are isometric

how do muscles work to be able to accomplish tasks?

Muscles work in conjunction with bones and joints to form a lever system

What are the 3 classes of levers?

first class, second class, third class

first-class levers

Fulcrum in the middle like a see-saw(nodding the head)
- the fulcrum is betweeen the force and the weight

ex of first class levers

the head
- the occipital condyle is the fulcrum
- the nuchal muscles are the force
- the head is the weight

Second class lever

the weight is between the force and the fulcrum.

ex of second class lever

foot
- metatarsals are the fulcrum
- force is muscles in back of leg
- weight is leg

third class lever

the force is between the weight and the fulcrum.

ex of third class lever

arm
- weight in hand
- elbow joint is the fulcrum
- forearm flexors are force

What happens when you move your muscles alot?

Hyperactivity causes hyperplasia of muscle fibers (more fibers) and hypertrophy of red muscle fibers.

hypertrophy

increase in cell size

hyperplasia

increase in number of cells

What are the 2 main types of muscle fibers

1) Red muscle fibers are Type I muscle fibers (slow twitch fibers)
2) White muscle fibers are Type II muscle fibers (fast twitch fibers)
- Most vertebrate muscles are a mixture of red and white muscle fibers.

Red Fibers

- Aerobic (don't fatigue as rapidly)
- Less myofibrils
- More myoglobin
- Contract just a little more slowly
- Very vascular
- A lot of mitochondria
- Good for tonic contractions to maintain posture.
- slow twitch fibers
- very aerobic & needs lots of oxygen

white muscle fiber

- More myofibrils
- Less myoglobin
- Contract fast and fatigue fast
- Less vascular
- Less mitochondria
- Basically anarobic
- fast twitch

type 3 muscle fiber

- fast twitch, fatigue resistant fibers.
- seen in flight muscles of migratory birds
- Contract fast, but not as fast as white fibers.
- Don't fatigue as quickly as white fibers.
- Contain many mitochondria and blood vessels (similar to red fibers).
- Store more oxygen and lipids, and less glycogen than other muscle fibers.
- Particularly prominent in flight muscles of migratory birds.

What muscles have each type of fiber?

- Most muscles have all types of fibers.
- The relative abundance gives the muscle its overall characteristics.
-White meat vs. red meat.
- Twitch times vary with body size and mode of locomotion.
- Faster in smaller animals

What is the embryological origin of muscles?

- Muscles develop from myotomes of somites.
- Paraxial mesoderm gives rise to the somites.
- Runs along each side of the neural tube and notochord.
- Segmentation begins in the initial stages of neurulation.
- The segments are called somitomeres.

what is a myotome?

the dorsal part of each somite in a vertebrate embryo, giving rise to the skeletal musculature.

How do somites develop?

- somites derived from paraxial mesoderm
- somitomeres develop into somites
- box-like structures

What are somitomeres?

collections of cells that are derived from the loose masses of paraxial mesoderm that are found alongside the developing neural tube.

Do somitomeres form somites?

Yes but the First 7 somitomeres do not form somites.
- They remain in the head region.
- May contribute to the bones and muscles of the base of the skull.
- Extraoccular eye muscles are thought to form from these cranial somitomeres.
* extraoccular eye muscles move the eye
- alot of chondrocranium will come from

when/where do somitomeres form somites?

The 8th pair of somitomeres form the first pair of somites.

What are the different types of somites?

Sclerotome: forms bone (,vertebrae, and ribs)
Dermatome: forms the dermis of the skin
Myotome: forms muscle

Review somite formation photo on slide 57

How are myotomes initially interacting in the development of muscle?

- Myotomes are divided into epimeres and hypomeres.

How do te epimeres and hypomeres interact after being developed?

- Epimeres and hypomeres are separated from one another by a lateral septum of connective tissue.
- Epimeres give rise to the epaxial muscles (the "true back"muscles).
- Hypomeres give rise to the hypaxial muscles.
- Virtually all muscles of the body are hypaxial muscles.

Epaxial muscles

Epaxial muscles dorsiflex the spine and are innervated by dorsal rami of spinal nerves.

hypaxial muscles

Hypaxial muscles ventroflex the spine and are innervated by ventral rami of spinal nerves.

Review slide 61

Extrinsic Muscles of the Eye

Three epaxial myotomes form the extrinsic eye muscles.
- Move the eyes
- Innervated by cranial nerves III, IV, and VI (Occular motor, Trochlear, and Abducens).
- These myotomes are derived from somitomeres (not somites)

Axial Muscles

Muscles of the body wall and spine.
- Derived from epimeres and hypomeres of somites

Branchial Muscles

Muscles associated with the visceral arches.
- Derived from posterior somitomeres and anterior somites.
- Innervated by cranial nerves V, VII, IX, X, and XI (Trigeminal, Facial, Glossopharyngeal, Vagus, and Spinal Accessory nn)
- Includes muscles of facial expression and muscles of mastication.

Hypobranchial Muscles:

Develop from hypaxial myotomes that stretch under the pharynx.
- Form the coracoarcuals in fishes.
- Form the strap muscles of the neck and tongue in tetrapods.
- muscles after the gills
slide 67 for pictures

Appendicular Miuscles

Muscles of the appendages.
- In fishes they form from the hypaxial muscles of the body wall. Innervated by ventral rami of spinal nerves.
- In tetrapods they develop as condensations in the mesenchyme of the limb bud; not from myotomes.

homology

structures inherited from common ancestors

How do we look at the evolution of muslces?

- Homology of muscles can be traced within orders, but it is difficult to establish homologies between classes.
- Can look at position and relationship relative to other muscles and the skeleton.
E.g., supraspinatus is always above the scapular spine.

Explain the evolutionary difference in muscles on attachment

- Muscle attachments will sometimes change during evolution.
- This alters action.
- Sometimes muscles of similar action fuse.
- More often ancestral muscles split to form several muscles.

How do we determine homology of muscles?

- Embryology can be useful in determining homology of muscles.
- Nerve supply is the best indicator.
- Nerve supply is the most conservative aspect of anatomy.
- Does not always stay consistent, so it is not foolproof.

What is the difference between fish and mammal muscles

Differentiation from fish to mammals is progressive.
- The number of muscles is related to the precision of movement possible in a particular region.
- Myotomes split when muscles are differentiated.
- Results in changes in the direction of the muscle fibers.

Can we determine homologies of muscles?

- Often get degeneration of certain myotomes during evolution.
- This make homologies of muscles virtually impossible to establish.
- They may even be non-existent

Which parts of the bodies of fishes and tetrapods typically have enlarged muscles?

- In fishes the axial musculature is propulsive and therefore makes up the bulk of their musculature.
- In tetrapods the limbs take over the propulsive function, therefore the axial muscles diminish and the limb muscles enlarge.

What are the muscles that are only found in mammals?

Diaphragm: made up partly from rectus abdominus m. and partly from the cervical myotomes (the phrenic nerve is a cervical nerve).
- This isn't muscular in reptiles and amphibians. Known as septum transversum in reptiles and amphibians.

Cutaneous trunci mm.: superficial splitting of myotomes derived from the latissimus dorsi m. and pectoralis muscles.
- muscles that move the skin

Platysma: derived from the splitting off of branchial muscles in the facial region.

How do muscles and electricity relate?

- Muscles need to depolarize in order to contract.
- Some fishes have exploited this fact.
- Electric organs are usually derived from muscle cells.
- Some electrical organs may be of glandular or nervous tissue origin.

Electrical Fishes

- The electric organ is built like a battery with neurons and electroplaxes.
- It is formed from axial muscle.
- Cells are specialized to develop an ion current flow (they don't contract).
- They discharge in about 3 milliseconds.
- Live in freshwater which doesn't conduct electricity well.
- Therefore need a lot of voltage.

electroplaxes

specialized muscle cells

What do fishes use electrical organs for?

1) Fishes use electric organ for feeding, orientation and defense.
- Ampullary organs are receptive to the electrical field in water and therefore can detect objects.
- Objects are detected because they disrupt the electrical current.
- The ampullary organs are derived from the lateral line system.
2) Can generate shocks for predation or defense.
3) Some can recognize members of their own species by the variations in the electrical pulses.
- Specific Mate Recognition system (SMRs)

What is electroplax?

It is the functional unit of an electrical organ.
- These are large, multinucleated cells.
- Have a folded surface on the cell membrane that contains a high concentration of mitochondria.
- Hundreds of thousands of electroplaxes are stacked to form columns.