Anatomy Lecture Exam 2

Myocyte

Muscle cell or muscle fiber

Sarcolemma

The plasma membrane of the muscle fiber

Sarcoplasm

The cytoplasm of a muscle fiber

Sarcoplasmic Reticulum

ER of a muscle fiber

Functional Characteristics of ALL muscles

• Contractibility

• Excitability

• Extensibility

• Elasticity

Contractability

Ability to shorten and generate force

What is the only action muscles do?

Pull

Excitability

Ability to respond to stimuli by producing electrical signals

Extensibility

Ability to stretch without being damaged

Elasticity

Ability to return to its original length/shape following distension

Functions of Muscle

• Movement (contraction)

• Posture and joint stabilization

• Open/close body passageways

• Thermogenesis

What do muscles do to open and close passageways?

• Open- relax

• Close- contract

What muscle contracts to produce heat?

Skeletal muscle

What muscle contracts to prevent heat loss? What are two examples?

• Smooth muscle

• Goosebumps- arrector pili muscles

• Dartos muscles (muscles that line the scrotum in men)

  • Both muscles thicken areas to prevent heat loss

Epimymysium

Connective tissue sheath that wraps a muscle fiber.

Fascicle

A bundle of muscle fibers wrapped by perimysium

Endomysium

Between individual muscle fibers

What is the alignment of skeletal muscle cells?

Parallel

Why are skeletal muscle cells in a parallel alignment?

So they can generate force as a whole

Tendon

Connective tissue attachment of skeletal muscle to a bone’s periosteum

What is the tendon continuous with?

All three connective tissue sheaths of a muscle beyond the length of the muscle fibers

Aponeurosis

Broad, flat tendon

Origin of a muscle

Attachment of a muscle on the stationary/less moveable bone

Insertion of a muscle

Attachment of muscle on the mobile/more moveable bone

Direct attachment

• Connective tissue strands very short

• Muscle may appear to be attached to the bone

Indirect attachment

• Common

• Connective tissue forms tendons/aponeurosis

Strains vs sprains

• Strains- muscle or tendons

• Sprains- ligaments

Nervous Innervation of muscle

• Each muscle innervated by a single nerve which branches extensively within connective tissue sheaths

• Each axon makes up nerve synapses with multiple muscle cells

Blood Supply of Muscles

• Each muscle is supplied by a single artery which branches extensively within connective tissue sheaths

Location and shape of capillary networks and the purpose of its shape.

• Within the endomyosium

• Wavy in the resting muscle

• Allows of extensibility of the tissue

Myofibrils

• Inside muscle fibers

• Specialized contractible organelles

• Proteins

Sarcomere

Individual, basic, contractile units of muscle fibrils

Myofilaments within sarcomere

• Thin filaments (actin)

• Thick filaments (myosin)

Thin (actin) filaments

• Double stranded

• Z disc/Z line to the center of the sarcomere

• Made up of actin, tropomyosin, troponin

Thick (myosin) filaments

• A band length

• Made up of many myosin filaments

H Zone

• Thick filaments only

• No overlap with thin filaments

I band

• Thin filaments only

• No overlap with thick filaments

A band

• Thick filament length

Elastic (titin) filaments

• Tethers/anchors myosin filaments to Z-disc/line

• Can coil up to help contract

• Allows extensibility

3 Types of Proteins that make up Myofibrils

• Contractile Proteins

• Regulatory Proteins

• Structural Proteins

Contractile Proteins

• Actin myofilaments

• Myosin filaments

Regulatory Proteins

• Troponin

• Tropomyosin

Structural Proteins and their Locations

• Titin, inside sarcomere

• Dystrophin, at the ends of the myofibril

Where does the myosin head attach to the actin molecule?

The myosin-binding site on the actin molecule

Relationship of tropomyosin and troponin

Troponin holds the tropomyosin strand in place

Removal of Troponin

• Calcium ion binds to troponin and changes its shape

• Tropomyosin is pulled off the myosin binding site on actin, revealing the binding site for myosin to attach

What stores calcium?

Smooth ER

Dystrophin

Keeps myofibrils in place in the cell

T Tubule

Invagination of the sarcolemma that carries an electrical impulse from surface membrane deep into muscle fiber

Triad

T-tubule positioned between two terminal cisternae of the SR

Terminal cisterns of the sarcoplasmic reticulum

Membranous sacs/folds that store and release calcium ions

Tubules of the sarcoplasmic reticulum

Network of tubules that regulate calcium ion levels and where electrical signals travel down

Steps of Muscle Contraction

1. Calcium is released from terminal cisterns of the sarcoplasmic reticulum

2. Troponin is released from tropomyosin

3. Tropomyosin on actin rolls over and lets myosin heads bind and pivot to pull the thin filaments inward

What changes regarding filaments during contraction?

The overlap of filaments, NOT the length

Describe what happens to the sarcomere, H-zone, and I band during muscle contraction

• No H-Zone

• I band decreases

• sarcomere decreases in size

Motor unit

One nerve fiber and all the muscle fibers innervated by it

Nervous Innervation of Skeletal Muscle

• Each nerve fiber branches out to several muscle fibers

• Each muscle fiber is supplied by only one motor neuron. It will not be innervated by multiple nerves

Where do the axons of motor neurons extend from?

The spinal cord

What is the part of the axon that branches out into the muscle fibers called?

Axon terminals

What is the name of the synapse an axon terminal forms with muscle fibers?

Neuromuscular Junction

Function of Neuromuscular Junction

Serves as a communication site between neuron and muscle

Three Main Components of Neuromuscular Junction

1. Axon Terminal

2. Junctional Folds of the Sarcolemma

3. Synaptic Cleft

Function of Junctional Folds of the Sarcolemma

Increases surface area- allowing more receptors to enter

Steps of Muscle Stimulation at Neuromuscular Junction

1. Nerve impulse stimulates the release of the neurotransmitter acetylcholine (ACh) into the synaptic cleft (space between axon terminal and muscle fiber)

2. ACh stimulates changes in the sarcolemma that excite the muscle fiber

3. Stimulus is carried down to the T tubules to release calcium that is stored in the terminal cistern of sarcoplasmic reticulum, initiating muscle contraction

4. Enzymes in the synaptic cleft break down ACh

3 Skeletal Muscle Fiber Types

1. Slow Oxidative Type I

2. Fast Ox-Glycolytic Type IIa

3. Fast-Glycolytic Type IIb/IIx

Myoglobin

Carrying oxygen in muscle cell

Contraction Velocity

Speed of shortening of muscle fibers

What does a larger size fiber allow?

More fibrils and sarcomeres can be packed in more contraction

Slow Oxidative Type I Characteristics

• High myoglobin content

• Slow contraction velocity

• Aerobic metabolic process for ATP production

• High fatigue resistance

• Red in color

• Small fiber diameter

• Function: Maintain posture and endurance activities

Fast Ox-Glycolytic Type IIa

• High myoglobin content

• Fast contraction velocity

• Aerobic + anaerobic (predominant) metabolic process for ATP production

• Intermediate fatigue resistance

• Pink color

• Intermediate fiber diameter

• Function: Walking and sprinting

Fast-Glycolytic Type llb/llx

• Low myoglobin content

• Fast contraction velocity

• Anaerobic Metabolic Process of ATP Production

• Low fatigue resistance

• White color

• Large fiber diameter

• Function: Rapid, intense movements of very short duration

What does fascicle arrangement reflect?

Function

What does the orientation of fascicles represent?

Strength of the muscle and the direction of its pull

What do longer fibers in fascicles reflect?

Greater range of motion

What do more fibers in fascicles represent?

Greater strength

Types of muscle shapes

• Fusiform

• Parallel

• Convergent

• Unipennate

• Bipennate

• Multipennate

• Circular

Circular Muscle Shape

• Fascicles arranged in concentric circles

• Always found external body openings

Convergent Muscle Shape

• Fascicles converge toward a tendon of insertion

• Origin is braod

Pennate Muscle Shape

• Short fascicles that attach obliquely to a tendon that runs the length of the muscle

• Unipennate, bipennate, multipennate

Fusiform Muscle Shape

Fascicles run parallel to the long axis of the muscle

What does a lever system represent?

Bone-muscle relationships

Parts of the lever system and what they are

1. Effort: Force being produced by contracted muscle

2. Fulcrum: Where movement stems from

3. Load: Weight of what is trying to be moved (same direction) or weight that is acting as a resistance (countering)

4. Lever

First-Class Lever

Fulcrum is in the middle

Second-Class Lever

Load is in the middle

Third-Class Lever

• Effort in the middle

• Most common

Muscle and Joint Interaction

• Muscle that crosses a joint, acts at that joint

• Muscle that produces opposite actions lie on opposite sides of a joint

Agonist

• Prime Mover

• Contracts to cause an action

Antagonist

• Stretches and yields to the effects of the agonist

• Relaxes and lets the agonist take control

Synergist

• Acts to assist an agonist by:

  • adding extra force

  • reducing undesirable movements

  • Acting as a fixator: fixing a bone in place during movement

How can you infer the action of a muscle?

By looking at the position of the muscle as it crosses the joint

Action of muscle that crosses the anterior side of a joint

Flexion

Action of muscle that crosses the posterior side of a joint

Extension

Action of muscle that crosses the lateral side of a joint

Abduction

Action of muscle that crosses the medial side of a joint

Adduction

Fascial Compartments

• Groups muscles of similar origin and function

• Innervated by a single nerve

Limb Muscle Compartments

• Upper Limb Compartments

  • Anterior/Posterior Brachial

  • Anterior/Posterior Antebrachial

• Lower Limb Compartments

  • Anterior/Posterior/Medial Thigh

  • Anterior/Posterior/Lateral Leg

Anterior Brachial Compartment

• Muscles: Coracobrachialis, Brachialis, Biceps Brachii

• Action: Flexes the elbow, flexes shoulder

• Innervation: Musculocutaneous nerve

Posterior Brachial Compartment

• Muscles: Triceps Brachii, Anconeus

• Action: Extends the elbow, extends shoulder

• Innervation: radial nerve