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A&P Lab Quiz 4 Cheat Sheet by

Muscle Overview

• The majority of the muscle in the body is skeletal muscle since it is attached to the skeleton.
•Main function is to provide movement
• Main Types:
- Cardiac and Smooth (Invol­untary)
Function: transport materials within the body
- Skeletal (Volun­tary)
Main features:
Appear striped (striated)
Contain multiple nuclei (multi­nuc­leate)
Functions:
Gives body contour and shape
Allow movement
Ability to manipulate enviro­nment

The Cells of Skeletal Muscle

• Muscles are composed of long, cylind­rical cells called fibers
• Muscle cells are arranged into myofibrils
- Long, filame­ntous organelles
- Give skeletal muscle its striated appearance
• Myofibrils are composed of thread­-like myofil­aments
- Contain 2 types of contra­ctile proteins
~ Actin or Myosin
- Slide past one another to produce muscle shortening or contra­ction
•Sarco­meres: actual contra­ctile units of muscle which extend from the middle of one I band (its z disc) to the middle of the next along the length of the myofibrils
•Cross section where thick and thin filaments of sarcomeres overlap show thick filaments surrounded by 6 thin filaments; each thin filament is enclosed by 3 thick filaments

Organi­zation of Skeletal Muscle Cells into Muscles

•Endom­ysium: thin areolar connective tissue surrou­nding each fiber
•Perim­ysium: collagenic membrane sheathing bundles of fibers
•Fascicle: bundle of muscle fibers
•Epimy­sium: dense overcoat of connective tissue around entire muscle
•Deep Fascia: connective tissue that bind muscles into functional groups
-Tendons: connect muscle to bone (strong, cordlike)
- Aponeu­roses: connect muscle to muscle or bone (flat, sheet-­like)

The Neurom­uscular Junction

Skeletal muscle cells are stimulated by motor neurons via nerve impulses

Neurom­uscular junctions are found between nerve fibers (axon) and muscle cells

A single neuron may stimulate many muscle cells

A motor unit is composed of the muscle cells and stimul­ating neuron

Synaptic cleft is the gap separating the neuron and muscle fiber

Types of Muscles

Agonists are primarily respon­sible for producing movement

Antago­nists oppose or reverse a movement, provides resistance

- When one is active, the other is relaxed

Synergists aid antago­nists by reducing undesired movement (stabi­lize)

Fixators are specia­lized synerg­ists, immobilize and allow you to “pose”

Muscles of the Head

Epicranius
Orbicu­laris oculi
Corrugator supercilii
Levator labii superioris
Zygoma­ticus (major and minor)
Risorius
Depressor labii inferioris
Depressor anguli oris
Orbicu­laris oris
Mentalis
Buccinator
Masseter
Temporalis
Medial pterygoid
Lateral pterygoid

Muscles of the Head

Zygoma­ticus
O: zygomatic bone
I: corners of mouth
Action: smiling

Muscles of the Head

Mentalis
O: mandible below incisors
I: Skin of chin
Action: Protrudes lower lip; wrinkles chin
 

The Cells of Skeletal Muscle

• At each junction of A and I bands, the sarcolemma indents into the muscle cell, forming a transverse tubule (T tubule).
•These tubules run deep into the muscle cell between the terminal cisternae, of the smooth ER, called the sarcop­lasmic reticulum.
•Regions where the SR terminal cisternae abut a T tubule on each side are called triads.

The Cells of Skeletal Muscle

•The sarcolemma is the covering of each muscle fiber
• The sarcoplasm is the cytoplasm of a muscle fiber
• The sarcosomes are mitoch­ondria of muscle tissue
•The sarcop­lasmic reticulum is the endopl­asmic reticulum of a muscle tissue
• A sarcomere is the contra­ctile unit of a muscle

Organi­zation of Skeletal Muscles Cells

•Epimy­sium: dense overcoat of connective tissue around entire muscle
•Perim­ysium: collagenic membrane sheathing bundles of fibers
•Fascicle: bundle of muscle fibers
•Endom­ysium: thin areolar connective tissue surrou­nding each fiber
• Deep Fascia: connective tissue that bind muscles into functional groups
- Tendons: connect muscle to bone (strong, cordlike)
- Aponeu­roses: connect muscle to muscle or bone (flat, sheet-­like)

The Neurom­uscular Junction

In axon terminal:
neurot­ran­smitter signals muscle
Acetyl­choline (ACh)
leaves axon terminal, goes to synaptic cleft, binds to receptors on sarcolemma

Origins and Insertions

A muscle’s origin is it’s fixed attachment

A muscles insertion is it’s movable attachment

For example: the Triceps

Origin: Humerus

Insertion: Ulna

Muscles of the Head

Orbicu­laris oculi
Sphincter muscle of eyelid
O: frontal & maxillary bones
I: tissue of eyelid
Action: closes eye

Muscles of the Head

Risorius
O: Fascia of masseter muscle
I: Skin at angle of mouth
Action: Draws corner of lip laterally

Muscles of the Head

Masseter

O: zygomatic arch
I: angle & ramus of mandible
Action: elevate mandible
 

The Cells of Skeletal Muscle

• Myofil­aments:
• contra­ctile proteins
• actin- thin
• myosin- thick
• I band: only actin
• A band: actin and myosin
• H-zone: only myosin (between actin). Only thick filaments

Anatomy of a Skeletal Muscle

• Thick Filaments: composed of myosin
• Thin Filaments: composed of actin
• A Bands: dark bands, both actin and myosin (thick). Thick and thin overlap at outer edges
• I Bands: light bands, only actin (thin). Contains thin only
• H Zone: portion of A Band where thick and thin do not overlap
Z Line: bisect I Bands, compose one sarcomere
• T Tubule: indent of sarcolemma at junction of A and I bands

Organi­zation of Skeletal Muscle Cells into Muscles

Tendons provide durability and conserve space
Are rough collagenic connective tissue that span rough bony promin­ences; this would destroy more delicate muscle tissue
Are small so more tendons can pass over a joint then muscle tissue
Connective Tissue Wrappings
Support and bind muscle fibers
Provide strength to the total muscle
Provide a route for the entry and exit of nerves and blood vessels
The larger the muscle, the more connective tissue

The Neurom­uscular Junction

lots ACh released → sarcolemma channels open → K+ and Na+ flow across membrane → action potential → muscle contra­ction

Naming Muscles

Muscles are named by:

Direction of muscle fibers (in reference to an imaginary line)
- rectus (straight) - transverse (at a right angle)
- oblique (irreg­ular)

Relative size of muscle
- maximus (largest) - longus (long)
- minimus (smallest) - brevis (short)

Location of muscle, or bone its associated with

Number of origins
- bi (2) -tri (3) - quad (4)

Location of origin or insertion

Shape of muscle
- orbit (circular) - del (trian­gular)

Action of muscle
- adductor (bring closer) - extensor (move away)

Muscles of the Head

O: zygomatic bone and infrao­rbital margin of maxilla
I: skin and muscle of upper lip and boarder of nostril
Action: opens lip; raises and furrows upper lip

Muscles of the Head

Buccinator
O: molar region of maxilla & mandible
I: Orbicu­laris oris
Action: Draws corners of the mouth

Muscles of the Head

Temporalis
O: temporal fossa
I: coronoid process of mandible
Action: elevate and retract mandible

Muscles of the Head

Temporalis
O: temporal fossa
I: coronoid process of mandible
Action: elevate and retract mandible

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