The Muscular System


The Muscular System

The Muscular System is provides the ability to move to living things. Although the muscular system is under the control of the nervous system in vertebrates, some muscles can work completely autonomously.

Thinking About Muscles

Architecture
– general information
– fiber
– tendon, fascia etc.
Naming
General
Function
Muscles by region

General Information Of Muscular System


~700 muscles
Muscle fiber: structural unit
Motor unit: motor neuron + the muscle fibers it control (1- several 100)
Origin
Insertion
Innervation*
Function
The forces developed by skeletal muscles are transferred to bones by;
Tendon
Aponeurosis
Fascia

Naming Muscles


Shape: quadratus, rhomboids
Location: subclavius, occipitalis
Number of heads: biceps, quadriceps
Primary action: flexor digitorum, supinator
Size: gluteus magnus, medius, minimus
Course: rectus abdominis, obliquus superior
Length: longus, brevis
Origin-insertion: coracobrachialis, sternohyoideus

Architecture of Muscles

>> Fibers parallel to tendon >> Fibers oblique to tendon
– short, flat, straplike or fusiform – pennate, semipennate or multipennate
Greater Range of Motion Greater Power

The Role of Fascia

Protection / Connection / Compartmentalization
Superficial Fascia Deep Fascia
– subcutaneous tissue more fibrous & ordered compartmentalizes muscles
– hypodermis invests muscles
Individuality can be site of attachment
Storage spread of fluid & infection
Muscles of facial expression variable thickness

Attachments & Pull Angles
Attachments
DYNAMIC
– cord like (biceps)
– strap like (lat dorsi)
– sheet like (bicipital aponeurosis)
Single pull point ?
multiple pull points (fan shaped muscles) ?
Why long tendon vs short ?
What is the effect of the pull on attachment sites ?
What different leverage systems are created by attachments?

Muscles By Region

Regions are typically between joints or groups of similar joints.
Regions are further divided into muscle groups by similar locations or functions

Region Groups/Compartments
back superficial and deep
trunk pectoral, intercostal, abdominal
arm/forearm flexor & extensor (deep & superficial)
hand thenar, hypothenar, central
thigh flexor, adductor, extensor
leg anterior, posterior, lateral
foot layer 1, 2, 3, 4
head facial, masticators, orbital

MUSCLES OF APPENDICULAR SKELETON


MM. OF SHOULDER AND ARM
Deltoid
Subscapularis
Infraspinatus
Supraspinatus
Teres major
Teres minor
Biceps brachii
Brachialis
Coracobrachialis
Triceps brachii

Deltoid


O: 3 parts
-clavicular, acromial, spinal
I: humerus (deltoid tuberosity)
Inn: axillary nerve
F: the strongest abductor of the arm***
-clavicular part: add+med. rot.
-acromial part: abd**********
(15-90 degrees)
-spinal: add+lat. rot

Subscapularis


O: subscapular fossa
I: humerus (greater tuberosity)
Inn: subscapular nerve
F: med. rot.**

Supraspinatus


O: supraspinous fossa
I: humerus (greater tuberosity)
Inn: suprascapular nerve
F: abd. (0-15 degrees)*****

Infraspinatus


O: infraspinous fossa
I: humerus (greater tuberosity)
In: suprascapular nerve
F: lat. rot.

Teres minor


O: lateral border of the scapula
I: humerus (greater tuberosity)
Inn: axillary nerve
F: lat. rot, add.

Teres major


O: inferior angle of scapula
I: crest of lesser tuberosity
Inn: subscapular nerve
F: med. rot, add, ext.

Rotator Cuff Muscles


They form a musculotendinous cuff around the glenohumeral joint.
They resist displacement of the head of the humerus from the glenoid cavity.

Anterior arm = Flexor muscles of the arm and forearm
Biceps brachii
Brachialis
Coracobrachialis
Inn: Musculocutaneous nerve
Biceps brachii
O: 2 heads
– long: supraglenoid tubercle
– short: coracoid proc.
I: radial tuberosity
F: flex, med. rot (supination)
Brachialis
O: humerus
I: ulnar tuberosity
F: flex. (only forearm)
Coracobrachialis
O: coracoid proc.
I: humerus
F: add, med. rot

Muscles of the Forearm


Radius, ulna and the interosseous membrane connecting them divide into anterior (flexor-pronator) and posterior (extensor-supinator) compartments
Ant: flex.
Inn: median and ulnar nerves
Post.: ext.
Inn: radial nerve

MUSCLES OF THE LOWER EXTREMITY


Gluteal Muscles
Gluteus maximus:
– ext**, lat. rot, abd/add
– inf. gluteal nerve
Gluteus medius:
– abd**, flex/ext, med/lat. Rot
– sup. gluteal nerve
Gluteus minimus:
– abd, flex/ext, med/lat rot
– sup. gluteal nerve
External Rotators
Piriformis
Obturator internus
Obturator externus
Gemelli sup, and inf
Quadratus femoris

Muscles of the Anterior Thigh


uscles-of-the-Anterior-Thigh

Quadriceps femoris
O: 4 heads
I: patella, tibial tuberosity
Inn: femoral nerve
F:
– hip: flex (rectus femoris)
– knee: extension

Sartorius
~62 cm
O: ASIS
I: Tibia (pes anserius)
Inn: femoral nerve
F:
– Hip: flex+abd+lat. rot
– Knee: flex+med. rot

Deep View Anterior & Medial Thigh
pectineus
adductor longus (cut)
adductor brevis
adductor magnus***
gracilis
Inn: obturator nerve Hamstring Muscles
(Ischiocrural Muscles)
Biceps femoris (long and short heads)
Semitendinosus
Inn: sciatic nerve (tibial and common fibular divisions)
F:
– Hip: ext
– Knee: flex
Triceps surae
Gastrocnemius Soleus
– O: 2 heads, lat and med femural condyles – O: fibula, tibia
– I: calcaneus (tendo calcanei-achilles) – I: calcaneus
– Inn: tibial nerve – Inn: tibial nerve
– F: plantar flex***, raises heel during walking and flexes leg at knee joint – F: plantar flexes ankle and steadies leg on ankle

Deep posterior compartment
Inn: tibial nerve
F: flexion

Muscles of the Foot


Extensor hallucis brevis Extensor digitorum brevis (medial 4 digits)
Muscles in the sole of the foot: 4 layers
17 muscles

MUSCLES OF AXIAL SKELETON


MM. OF FACE
MM. OF MASTICATION
NECK MM.
MM. OF ABDOMINAL WALL
MM. OF BACK

MUSCLES OF FACE

(FACIAL EXPRESSION MUSCLES)

Located in subcutaneous tissue; they move the skin.
Surround the orifices of mouth, eyes and nose; act as sphincters or dilators.
Change facial expressions to convey mood.
All are innervated by the facial nerve
Orbicularis oculi: closes eyelids.
Orbicularis oris: compresses and protrudes lips (whistling, sucking).
Buccinator: presses cheek against molat teeth (aid chewing), Expels air from oral cavity (wind instrument), sucking
Corrugator supercilii: frowns
Levator labii superioris: smiles
Levator anguli oris: makes a big smile
Levator labii superioris alaeque nasi:
Zygomaticus major ve minor: smiles
Risorius: grins
Depressor labii inferioris: sulks
Depressor anguli oris: pouts

MUSCLES OF MASTICATION


Temporalis: closes the jaw
Masseter: closes the jaw
Medial pterygoid: closes the jawTemporalis
Lateral pterygoid: opens the jawMasseter
All are innervated by the trigeminal nerve

NECK MUSCLES


Platysma: muscle of fascial expression, draws corners of mouth inferiorly (fascial nerve)
Sternocleidomastoideus: tilts head to one side, flexes neck and rotates it so face is turned superiorly toward opposite side; actinh together, flex the neck (cranial accessory nerve)
Infrahyoid muscles
Suprahyoid muscles

PECTORAL MUSCLES (ANT. THORACOABDOMINAL MUSCLES)


Pectoralis major:
3 PARTS:
– clavicular
– sternocostal
– abdominal
* inserts on humerus
* add and medial rotation of the arm
* med. and lat. pectoral nerves
Pectoralis minor:
* 3-5 ribs-coracoid process
* Stabilizes scapula by drawing it inferiorly
* If insertion is fixed, helps inspiration
* Inn: med. pectoral nerve

THORACOABDOMINAL MUSCLES


Serratus anterior:
– 1st to 8th ribs-medial border of scapula
– rotates scapula, holds it against thoracic wall
– long thoracic nerve
Subclavius:
– Anchors and depresses clavicle

Intercostal muscles


External intercostal:
– superficial layer, inferomedial
– elevates the ribs (inspiration)
Internal intercostal:
– middle layer, inferolateral
– depress ribs (expiration)
Innermost intercostal:
– deepest layer
– depress ribs (expiration)

MUSCLES OF ANTEROLATERAL ABDOMINAL WALL


external oblique: superficial, inferomedial
internal oblique: intermediate
transverse abdominal: innermost, horizontal
rectus abdominis: long, broad, strap-like, tendinous
intersections
• pyramidalis: small triangular muscle
Actions:
Compresses (urination, defecation, vomiting, parturition etc) and support abdominal viscera
Flex the trunk.
Rotate the trunk.
Innervated by the anterior rami of thoracic spinal nerves

MUSCLES OF POSTERIOR ABDOMINAL WALL


psoas major*/minor:
– flexes and externally rotates the thigh
– inn : anterior rami of lumbar nerves
iliacus:
– flexes and externally rotates the thigh
– inn : femoral nerve
( psoas + iliacus = iliopsoas: also classified in anterior thigh muscles )
quadratus lumborum:
– helps inspiration, laterally rotates the trunk
– inn : anterior rami of lumbar nerves

PELVIC DIAPHRAGM


levator ani: 2 parts
pubococygeus
iliococygeus
cocygeus
Actions:
resists increases in intra-abdominal pressure
helps to support pelvic viscera

UROGENITAL DIAPHRAGM


superficial/ deep*** transverse perineal muscles
external urethral sphincter
bulbospongiosus-ischiocavernosus

MUSCLES OF THE BACK


muscles of the back
Two Layers
Superficial = extrinsic = migratory
Deep = intrinsic
Superficial muscles act on upper limb
Deep muscles act on vertebral column

Superficial Muscles of the Back


Trapezius
– 3 parts: ascending, descending, transverse
– Functions according to fiber alignment (elevates, retracts and rotates scapula)
– spinal accessory n./ascending transverse cervical a.
Latissimus dorsi
– Raises the arm to trunk (chin-ups), adducts, medially rotates and extends the arm
– thoracodorsal n./a.
Rhomboid major/minor
– Abducts the scapula, fixing the scapula during movements of the arm
Levator scapulae – Elevates scapula
– dorsal scapular n./descending branch transverse cervical a.
Serratus posterior superior
Serratus posterior inferior
– Intercostal nerves/intercostal arteriesSuperficial Muscles of the Back

Deep Muscles of the Back

Splenius capitis/cervicis
Erector spinae
Transversospinalis
Minor Deep Group
Stabilizes spine
Extend head, cervical and thoracal regions accordingly,
rotate head, cervical and thoracal regions contralaterally
Innervated by the post. rami of spinal nerves

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