Anatomy Exam 3

Origin

The attachment of a tendon to the more stationary bone

-More stationary/less movable

Insertion

The attachment of the muscle’s other tendon to the more movable bone

-Movable

Belly of origin

“Head” of origin

Action

The main movements that occur during contraction

Ex: Flexion or Extension

Tendon

Connects muscle to bone

Aponeurosis

A thin, flattened sheet of tendon

Retinaculum

a band of thickened deep fascia around tendons that holds them in place. It is not part of muscle. Its function is mostly to stabilize a tendon.

Prime Mover (agonist)

Contracts to cause an action

Synergists

Work with prime mover, prevent unwanted movement or otherwise aid with movement

-Ex: Biceps brachaii & Brachalis (In elbow flexion)

-Ex; Triceps brachaii (In elbow extension)

Fixator

Stabilize the origin of the prime mover

Antagonist

Opposes the action of the prime mover

-Ex: Triceps brachaii (In elbow flexion)

-Ex: : Biceps brachaii & Brachalis (In elbow extention)

Anatagonistic pairs

Most muscles are arranged in opposing pair at joints

-Depending upon the movement, many muscles may act as prime movers, antagonists, synergists, or fixators

Fascicle Arrangement (Power & range of motion)

-The longer the fibers in a muscle, the greater the range of motion it can produce

-The power of a muscle depends not on the length but on its total cros- sectional area

Fusiform

Fascicles nearly parallel to longitudinal axis of muscle; terminate in flat tendons; muscles tapers toward tendons, where diameter is less than at belly

-Ex: Digastric muscle

Parallel

Fascicles parallel to loghitudinal axis of muscle; terminate at either end in flat tendons

-Ex; Stylohyoid muscle

Convergent

Fascicles spread over broad area converge at thick central tendon; gives muscle a triangular appearance

-Ex: Pectoralis major muscle

Unipennate

Fascicles are arranged on only one side of tendon

-Ex: Extensor digitorum longus muscle

Bipennate

Fascicles are arranged on both sides of centrally positioned tendons

-Ex: Rectus femoris muscle

Multipennate

Fasclicles attach obliquely from many directions to several tendons

-Ex: Deltoid muscle

Circular

Fascicles in concentric circular arrangements form sphincter muscles that enclose an orifice(Opening)

-Ex: Orbicularis oculi muscle

Intrinsic muscle

Extrinsic muscle

Originate on a different body part than where they insert and act

Anterior compartment

Muscles dorsiflex the foot at the ankle joint

Lateral compartment

Muscles plantar flex and evert the foot at ankle

Posterior compartment

Muscles are split between superficial and deep groups. Superficial muscles share a common tendon of insertion

-Ex: calcaneal tendon

Hypertrophy

Increase in muscle fiber size

Atrophy

Reduction in muscle size

Fibrosis

The overgrowth, hardening, and/or scarring of various tissues

Myoblast

Are cells that fuse to form single muscle fibers

Satellite Cells

Are myoblast cells that do not fuse with muscle fibers and remain adult skeletal muscle

Moter neuron axon

Is the branch of a moter unit and branches to innervate a number of muscle fibers

Sarcolemma

The plasma membrane of a skeletal muscle fiber

Transverse Tubules

Are deep invaginations of the sarcolemma that extend into the sarcoplasm of muscle fibers as a network of narrow membranous tubules

Sarcoplasmic Reticulum

Stores calcium ions needed to initiate muscle contraction

Terminal Cisternae

Blind sacs of the Sarcoplasmic Reticulum, they are reservoirs and specific sites for calcium ion release

Triad

Two terminal cisternae and the centrally placed t-tubule form a structure

Myofibrils

Are long, cylindrical structures that extend the length of the muscle fiber

-Are 80% of the volume of a muscle fiber

Myofilaments

Are bundles of protein filamentsin a myofibril

Thin Filament

Are 5-6 nanometers in diameter and are primarily composed of two strands of the protein actin twisted around to form a helical shape

Actin

A protein

G-Actin

Is a singular spherical molecule in a strand of actin

F- Actin

Is a filament composed of a strand of G-actin molecules

Tropomyosin

A short, thin, twisted filament that covers small sections of the actin strands

Troponin

Attaches to actin and tropomyosin, provides a binding site for calcium ions

Thick Filaments

Are assembled from bundles of 200-500 myosin protein molecules

Myosin

Consists of two strands, each strand has a free, globular head and an attached, elongated tail. The heads are Actin and ATP binding sites

Titin

A “cablelike” protein that extends from the z discs to the M line through the core of each thick filament

-Stabilizes the position of the thick filament and maintains thick filament alignment within a sarcomere

Dystrophin

Part of a protein complex that anchors myofibrils that are adjacent to the sarcolemma to proteins within the sarcolemma

-Links internal myofilament proteins of a muscle fiber to external proteins

Muscular Dystrophy

Collective term for hereditary diseases in which the skeletal muscles degenerate, lose strength, and are gradually replaced by adipose and fibrous tissue

Myoglobin

Is a protein found in the muscle cells of animals. It binds iron and oxygen, functioning as an oxygen-storage unit to provide oxygen to working muscles

Glycogen

A multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria.

A-band

Dark band in the middle of the sarcomere: composed of entire thick filaments and in it’s lateral end regions of overlapping thin filaments

I-band

Extends from both directions of a Z-disc and are bisected by the Z-discs. Contain only thin filaments and titin proteins

Z-disc

Dark proteins called titins in the center of the I-band where thin filaments attach

Sarcomere

Is the functional contractile unit of a skeletal muscle fiber

-Myofilaments within myofibrils are arranged in repeating microscopic cylindrical units

H-zone

Is the most central portion of the A-band in a resting sarcomere

-Only thick filaments are present

M-line

A thin transverse protein meshwork structure in the center of the H-zone

-Serves as an attachment site for the thick filaments and keeps thick filaments aligned during contraction and relaxation

Somatic Motor Neurons

Extend from the brain and spinal cord to innervate skeletal muscle fibers

-Control voluntary actions

Motor Unit

Is composed of a single motor neuron and all of the muscles fibers it controls

-Involved in muscle contraction

Neuromuscular Junction

The point where a motor neuron meets a muscle fiber

Synaptic Knob

Is an expanded tip of an axon

-A nerve impulse transfers here from the axon

-Houses numerous synaptic vesicles

Moter-end plate

Is a specialized region of the sarcolemma. It has folds and indentations to increase the membrane surface area

-Has ACh receptors

Synaptic Cleft

IS a narrow space separating the synaptic knob and the motor end plate

Acetylcholine (ACh)

An organic compound that functions in the brain and body of many types of animals (including humans) as a neurotransmitter.

Synaptic Vesicles

Are small membrane sacs filled with molecules of the neurotransmitter acetylcholine (ACh)

Acetylcholinesterase

Resides in the synaptic cleft, rapidly breaks down molecules of ACh that are released into the synaptic cleft

-It is needed so ACh is not continuously stimulating a muscle

ACh Receptors

In the motor neuron plate and act like doors that are normally closed and only ACh is allowed in

Sliding filament mechanism

When a muscle contracts, thick and thin filaments slide past each other and the sarcomere shortens

Excitation-Contraction Coupling

The stimulation of a muscle fiber by a nerve impulse results In a series of events that culminates in muscle fiber contraction

-CA++ release channel in SR

Contraction

When contractile proteins within muscle cells slide past one another and the muscle cell shortens

-Allows muscle movement

Relaxation

Ca++ pumps pn SR

Contraction Cycle

1. A signal is sent from the brain or the spinal cord to the muscle via neurons

2. An action potential is generated in the neuron, releasing Ca⁺⁺ in the neuromuscular junction

3. The influx of caalcium ions causes acetylcholine (AcH) to be released in the synaptic cleft

• AcH binds to the AcH receptors present in the sarcolemma, increasing its permeability

• Na⁺⁺enter the sarcolemma, changing its polarity, and creating an action potential 

• Ca⁺⁺ are released by the sarcoplasmic reticulum, as the action potential travels down the T-tubules in the muscle fiber

• Ca⁺⁺ bind with troponin C, causing the tropomyosin to shift, and expose the myosin binding sites on actin

• ATP is hydrolyzed into ADP and phosphorus, releasing energy for myosin power stroke

• Myosin binds to actin

• Myosin head bends and actin slides over the myosin surface

• Myosin releases the ADP molecule 

• As the myosin head swivels, another ATP molecule binds to myosin, breaking the actin-myosin bridge.

• When the nervous impulse stops, the calcium gates close, and the sarcoplasmic reticulum is no longer permeable. The Ca⁺⁺ return to the sarcoplasmic reticulum, and troponin and tropomyosin are reverted to their original positions. With the binding sites blocked, myosin cannot form cross-bridges with actin, and the muscle relaxes.

Muscle tone

Is the resting tension in a skeletal muscle

Isometric Contraction

The length of the muscle does not change because the tension produced by this contacting muscle never exceeds the resistance.

Isotonic contraction

The tension produced equals or is greater than the resistance , and then the muscle fibers shorten resulting movement

Concentric Contractions

Actively shorten a muscle

-Ex: lifting something up

Eccentric Contraction

Actively lengthen a muscle

Ex: Putting something down

Slow Twitch

• slow oxidative (SO), red, or “Dark Meat”

• Abundant mitochondria, myoglobin and capillaries - deep red color

• Adapted for aerobic respiration and fatigue resistance

• Ex: soleus of calf and postural muscles of the back

Fast Twitch

• Fast glycolytic (FG), “White Meat”

• QUICK & STRONG response, but fatigue very rapidly

• Rich in enzymes that generate lactic acid causing fatigue

• Poor in mitochondria, myoglobin, and blood capillaries which gives pale
  appearance

• Ex: extrinsic eye muscles, gastrocnemius and biceps brachii

Intermediate Fibers

• Fast myosin ATPase

• Produce a fast and powerful contraction

• Used for medium duration like walking or biking

• Has a high resistance

Endurance Exercise

Long distance running or maintaining posture

Resistance exercise

Short duration, intense movement

Ex: sprinting, lifting weights

Functions of muscle tissue

1. Body movements → moving the skeleton
2. Stabilizing body position → keeping the skeleton stable
3. Storing, and movement, of materials within the body
4. Generating heat

Excitability

The ability for a cell to respond to a stimulus

Conductivity

Involves an electrical change that travels along the plasma membrane during a muscle or nerve impulse

Elasticity

the tendency to return to their initial shape

Extensibility

the ability to be stretched without
damage

Skeletal Muscle

-Voluntary

-Striations

-Attached to bones

Cardiac Muscle

• Voluntary control
   Short, branching cells
   Striated appearance
   Cells are attached at their ends by intercalated discs:
   Gap Junctions – “pores”; electrically link cells together, thus action potentials
  spread from cell to cell
   Desmosomes = strongest cellular junctions!

Smooth muscle

Smooth muscle fibers have thin and thick filaments that are not
arranged in sarcomeres
 Contractions are also activated by Ca2+ ions, but are slower and last
longer
 Two Types/Arrangements of Cells & How They’re Innervated:
 Single Unit or Visceral (sheets of cells, all cells act together)
 Multiunit smooth muscle (cells individually innervated so
individual cells act independently of one another)
 Two types differ in the pattern of innervation
 Smooth muscle fibers shorten more than striated muscle fibers
 Smooth muscle is under involuntary control by autonomic neural
input, as well as multiple other factors (hormones, paracrines, stretch
response)