Magic Anatomy

The human body is a masterpiece of engineering, but it’s even cooler when you can see the blueprint from the outside.
​This is a textbook look at surface anatomy. Notice how clearly the muscles define themselves under the skin you can practically trace the origins and insertions. It takes a perfect mix of low body fat, muscle density, and lighting to capture definition like this.
​Can you name the primary muscle group stealing the show here? Drop your anatomy guess below! 👇
​

Anatomy in Action: Let’s talk stretching! 🧘‍♂️
Ever wondered exactly which muscle you’re targeting when you stretch? We’re stripping away the textbook walls and bringing it down to the bare anatomy with these custom hand-drawn diagrams! ✍️✨muscle undergoing lengthened tension during these essential stretches.
🔍 Take a look and tell us: Which of these stretches do you need to add to your daily routine today?

Each slide highlights the exact

MUSCLES OF THE BACK – THE POWERHOUSE OF POSTURE, MOVEMENT & SPINAL STABILITY | COMPREHENSIVE ANATOMY (GRAY’S STYLE)
INTRODUCTION
The muscles of the back form a complex musculoskeletal system responsible for maintaining posture, stabilizing the vertebral column, moving the upper limb, and producing movements of the head, neck, and trunk. Anatomically, they are classified into extrinsic (superficial and intermediate) and intrinsic (deep) muscles.
CLASSIFICATION OF BACK MUSCLES
Extrinsic Back Muscles
• Superficial group (upper limb movements)
• Intermediate group (respiration)
Intrinsic Back Muscles
• Superficial layer (splenius)
• Intermediate layer (erector spinae)
• Deep layer (transversospinalis)
• Minor deep muscles
#️⃣ SUPERFICIAL EXTRINSIC MUSCLES
Trapezius
Origin
• Superior nuchal line
• External occipital protuberance
• Ligamentum nuchae
• Spinous processes C7–T12
Insertion
• Lateral third of clavicle
• Acromion
• Spine of scapula
Actions
• Elevates scapula
• Retracts scapula
• Depresses scapula
• Upward rotation of scapula
Nerve Supply
• Spinal accessory nerve (CN XI)
• C3–C4 proprioceptive fibers
Latissimus Dorsi
Origin
• Spinous processes T7–L5
• Thoracolumbar fascia
• Iliac crest
• Lower ribs
Insertion
Floor of intertubercular sulcus of humerus.
Actions
• Extension of arm
• Adduction of arm
• Medial rotation of arm
Nerve Supply
Thoracodorsal nerve (C6–C8)
Levator Scapulae
Origin
Transverse processes C1–C4.
Insertion
Medial border of scapula above spine.
Actions
• Elevates scapula
• Assists neck lateral flexion
Nerve Supply
Dorsal scapular nerve (C5)
Rhomboid Minor
Origin
Ligamentum nuchae and C7–T1 spinous processes.
Insertion
Root of spine of scapula.
Actions
• Retracts scapula
• Fixes scapula to thoracic wall
Nerve Supply
Dorsal scapular nerve (C4–C5)
Rhomboid Major
Origin
Spinous processes T2–T5.
Insertion
Medial border of scapula below spine.
Actions
• Retracts scapula
• Downward rotation of scapula
Nerve Supply
Dorsal scapular nerve (C4–C5)
#️⃣ INTERMEDIATE EXTRINSIC MUSCLES
Serratus Posterior Superior
Origin
Ligamentum nuchae and C7–T3 spinous processes.
Insertion
Ribs 2–5.
Action
Elevates ribs during inspiration.
Nerve Supply
Intercostal nerves 2–5.
Serratus Posterior Inferior
Origin
Spinous processes T11–L2.
Insertion
Ribs 9–12.
Action
Depresses lower ribs.
Nerve Supply
Intercostal nerves T9–T12.
#️⃣ INTRINSIC (DEEP) BACK MUSCLES
Splenius Group
Splenius Capitis
Origin
Ligamentum nuchae and C7–T4 spinous processes.
Insertion
Mastoid process and superior nuchal line.
Actions
• Extension of head
• Rotation of head to same side
Splenius Cervicis
Insertion
Transverse processes C1–C3/C4.
Actions
• Neck extension
• Ipsilateral rotation
Nerve Supply
Posterior rami of cervical spinal nerves.
#️⃣ ERECTOR SPINAE GROUP
General Features
Largest intrinsic muscle group extending from sacrum to skull.
Components (Lateral → Medial)
Iliocostalis
Most lateral column.
Action
Extension and lateral flexion of vertebral column.
Longissimus
Intermediate column.
Action
Extension of spine and head.
Spinalis
Most medial column.
Action
Extension of vertebral column.
Nerve Supply
Posterior rami of spinal nerves.
#️⃣ TRANSVERSOSPINALIS GROUP
Semispinalis
Action
Extension of head and vertebral column.
Special Feature
Semispinalis capitis forms prominent posterior neck muscle.
Multifidus
Action
Stabilizes vertebrae during movement.
Clinical Importance
Important muscle for spinal stability.
Rotatores
Action
Assist rotation and proprioception.
Nerve Supply
Posterior rami of spinal nerves.
#️⃣ MINOR DEEP MUSCLES
Interspinales
Between adjacent spinous processes.
Action
Assist spinal extension.
Intertransversarii
Between transverse processes.
Action
Assist lateral flexion.
Levatores Costarum
Origin
Transverse processes C7–T11.
Insertion
Rib below.
Action
Elevate ribs.
#️⃣ THORACOLUMBAR FASCIA
GENERAL FEATURES
Strong fascial sheet enclosing intrinsic back muscles.
FUNCTIONS
• Muscle attachment
• Force transmission
• Lumbar stabilization
#️⃣ BLOOD SUPPLY
Arteries
• Posterior intercostal arteries
• Subcostal arteries
• Lumbar arteries
• Deep cervical artery
• Occipital artery
#️⃣ NERVE SUPPLY
Extrinsic Muscles
Supplied by anterior rami or cranial nerves.
Intrinsic Muscles
Supplied exclusively by posterior rami of spinal nerves.
#️⃣ FUNCTIONS OF BACK MUSCLES
• Maintain posture
• Stabilize vertebral column
• Extend spine and head
• Rotate vertebral column
• Laterally flex trunk
• Move scapula and upper limb
• Assist respiration
#️⃣ CLINICAL ANATOMY
Back Strain
Commonly affects erector spinae and multifidus muscles.
Postural Dysfunction
Weak deep back muscles contribute to chronic back pain.
Thoracodorsal Nerve Injury
May weaken latissimus dorsi.
Accessory Nerve Injury
Produces trapezius weakness and shoulder droop.
Lumbar Instability
Associated with multifidus dysfunction.
#️⃣ SUMMARY
The muscles of the back are organized into extrinsic and intrinsic groups. The extrinsic muscles primarily move the upper limb and assist respiration, while the intrinsic muscles maintain posture and produce movements of the vertebral column and head. Together they form the essential muscular framework responsible for spinal stability, locomotion, and posture.

Extraocular and Intraocular Muscles of the Eye.

The muscles of the eye are divided into two groups:

1. Extraocular Muscles (EOMs)

The extraocular muscles consist of seven skeletal muscles: four re**us muscles, two oblique muscles, and one eyelid muscle.

Re**us Muscles

All originate from the Common Tendinous Ring (Annulus of Zinn).

* Medial Re**us → CN III
* Lateral Re**us → CN VI
* Superior Re**us → CN III
* Inferior Re**us → CN III

Oblique Muscles

* Superior Oblique
* Passes through the trochlea
* Innervation: CN IV
* Inferior Oblique
* Originates from the medial orbital floor
* Innervation: CN III

Eyelid Muscle

* Levator Palpebrae Superioris
* Innervation: CN III

Mnemonic

LR6 SO4 AO3

* Lateral Re**us → CN VI
* Superior Oblique → CN IV
* All Others → CN III

⸻

2. Intraocular (Intrinsic) Muscles

Ciliary Muscle

* Located in the ciliary body
* Innervation: Parasympathetic fibers of CN III

Sphincter Pupillae

* Circular smooth muscle around the pupil
* Innervation: Parasympathetic fibers of CN III

Dilator Pupillae

* Radial smooth muscle of the iris
* Innervation: Sympathetic fibers from the superior cervical ganglion

⸻

Summary of Innervation

* Medial Re**us → CN III
* Lateral Re**us → CN VI
* Superior Re**us → CN III
* Inferior Re**us → CN III
* Superior Oblique → CN IV
* Inferior Oblique → CN III
* Levator Palpebrae Superioris → CN III
* Ciliary Muscle → Parasympathetic CN III
* Sphincter Pupillae → Parasympathetic CN III
* Dilator Pupillae → Sympathetic fibers.

Mandibular Nerve (V₃)

The mandibular nerve (V₃) is the largest branch of the trigeminal nerve (cranial nerve V, CN V). It is a mixed nerve, carrying both sensory and motor fibers. Its primary functions include controlling the muscles of mastication (chewing), transmitting sensory information from the lower face, lower teeth, and tongue, and contributing to certain autonomic functions. Human anatomy, as usual, prefers efficiency wrapped in complexity.

Core Anatomy

Origin

* The mandibular nerve arises from the trigeminal ganglion.
* It exits the cranial cavity through the foramen ovale and enters the infratemporal fossa.

Divisions

After passing through the foramen ovale, the mandibular nerve divides into two main branches:

1. Anterior Division

* Smaller division.
* Predominantly motor in function.
* Supplies most of the muscles of mastication.

2. Posterior Division

* Larger division.
* Predominantly sensory in function.
* Carries sensory information from the lower jaw, mandibular teeth, part of the tongue, and adjacent regions.

Functions

Motor Functions

* Innervates the muscles of mastication:
* Masseter
* Temporalis
* Medial pterygoid
* Lateral pterygoid
* Also supplies:
* Mylohyoid
* Anterior belly of the digastric
* Tensor veli palatini
* Tensor tympani

Sensory Functions

* General sensation from:
* Lower jaw and chin
* Lower teeth and gingiva
* Temporomandibular joint (TMJ)
* Anterior two-thirds of the tongue (general sensation only, not taste)
* Part of the external ear and temporal region

Clinical Significance

Damage to the mandibular nerve may result in:

* Weakness of mastication
* Deviation of the jaw toward the affected side when opening the mouth
* Loss of sensation in the lower face, mandibular teeth, or anterior tongue
* Reduced or absent jaw-jerk reflex (depending on the site of the lesion)

💀🧠 THE HUMAN SKULL – THE ARCHITECTURAL FORTRESS OF THE BRAIN & FACE | COMPREHENSIVE ANATOMY
INTRODUCTION
The skull is the bony framework of the head forming the skeleton of the face and cranium. It protects the brain, supports sensory organs, forms the cavities of the nose, orbit, oral cavity, and ear, and provides attachment for muscles of mastication, facial expression, and head movement.
The adult skull consists of 22 bones united mainly by sutures and is divided into:
• Neurocranium (cranial skeleton)
• Viscerocranium (facial skeleton)
#️⃣ DIVISIONS OF THE SKULL
1. Neurocranium
Forms protective case around the brain.
Bones of Neurocranium
• Frontal bone
• Parietal bones (2)
• Temporal bones (2)
• Occipital bone
• Sphenoid bone
• Ethmoid bone
2. Viscerocranium (Facial Skeleton)
Forms facial framework.
Bones of Face
• Maxillae (2)
• Zygomatic bones (2)
• Nasal bones (2)
• Lacrimal bones (2)
• Palatine bones (2)
• Inferior nasal conchae (2)
• Vomer
• Mandible
#️⃣ GENERAL FEATURES OF THE SKULL
Calvaria (Skullcap)
Upper dome-like part composed mainly of frontal, parietal, and occipital bones.
Base of Skull
Forms floor of cranial cavity and contains numerous foramina for neurovascular structures.
#️⃣ CRANIAL FOSSAE
Anterior Cranial Fossa
Supports frontal lobes.
Main Bones
• Frontal bone
• Ethmoid bone
• Sphenoid bone
Middle Cranial Fossa
Supports temporal lobes.
Main Bones
• Sphenoid bone
• Temporal bones
Posterior Cranial Fossa
Contains cerebellum, pons, and medulla.
Main Bones
• Occipital bone
• Temporal bones
#️⃣ IMPORTANT SUTURES OF THE SKULL
Coronal Suture
Between frontal and parietal bones.
Sagittal Suture
Between two parietal bones.
Lambdoid Suture
Between parietal and occipital bones.
Squamous Suture
Between temporal and parietal bones.
#️⃣ FONTANELLES
GENERAL FEATURES
Membranous gaps between fetal skull bones.
Anterior Fontanelle
• Diamond-shaped
• Closes around 18 months
Posterior Fontanelle
• Triangular
• Closes within first few months
#️⃣ IMPORTANT BONES OF THE SKULL
FRONTAL BONE
Forms forehead, roof of orbit, and anterior cranial fossa.
Features
• Frontal sinus
• Supraorbital foramen
• Glabella
#️⃣ PARIETAL BONES Form sides and roof of skull.
Features
• Parietal eminence
• Temporal lines
#️⃣ TEMPORAL BONE
PARTS
• Squamous part
• Petrous part
• Mastoid part
• Tympanic part
Features
• External acoustic meatus
• Mastoid process
• Styloid process
#️⃣ OCCIPITAL BONE
Features
• Foramen magnum
• Occipital condyles
• External occipital protuberance
#️⃣ SPHENOID BONE
GENERAL FEATURES
Keystone bone of skull base.
Important Structures
• Sella turcica
• Greater and lesser wings
• Pterygoid processes
#️⃣ ETHMOID BONE
Features
• Cribriform plate
• Crista galli
• Ethmoidal air cells
#️⃣ FACIAL BONES
MAXILLA
Forms upper jaw and contributes to orbit, nasal cavity, and hard palate.
Features
• Maxillary sinus
• Infraorbital foramen
• Alveolar process
MANDIBLE
Largest and strongest facial bone.
Parts
• Body
• Ramus
• Angle
• Condylar process
• Coronoid process
#️⃣ FORAMINA OF THE SKULL
Optic Canal
Transmits optic nerve and ophthalmic artery.
Superior Orbital Fissure
Transmits CN III, IV, V1, and VI.
Foramen Rotundum
Transmits maxillary nerve (V2).
Foramen Ovale
Transmits mandibular nerve (V3).
Foramen Spinosum
Transmits middle meningeal artery.
Jugular Foramen
Transmits CN IX, X, XI and internal jugular vein.
Hypoglossal Canal
Transmits CN XII.
Foramen Magnum
Transmits medulla, vertebral arteries, and spinal roots of CN XI.
#️⃣ BLOOD SUPPLY OF THE SKULL
Arterial Supply
Mainly from:
• External carotid artery
• Internal carotid artery
Venous Drainage
Through diploic veins and dural venous sinuses.
#️⃣ SCALP LAYERS Mnemonic: SCALP
• Skin
• Connective tissue
• Aponeurosis
• Loose areolar tissue
• Pericranium
#️⃣ CLINICAL ANATOMY
Pterion
Weak junction of frontal, parietal, temporal, and sphenoid bones.
Clinical Importance
Fracture may rupture middle meningeal artery causing epidural hematoma.
Basilar Skull Fracture
May cause:
• CSF leakage
• Cranial nerve injury
• Battle sign
Hydrocephalus
May enlarge infant skull due to open sutures.
Craniosynostosis
Premature fusion of sutures causing abnormal skull shape.
#️⃣ SUMMARY
The skull is a complex osteological structure protecting the brain and supporting facial anatomy and sensory organs. It is divided into neurocranium and viscerocranium and contains numerous foramina, sutures, and cranial fossae of major anatomical and clinical importance. Understanding skull anatomy is fundamental in neurology, neurosurgery, radiology, maxillofacial surgery, and clinical medicine.

Can you identify the muscles labeled A and B in the diagram below?

DIAPHRAGM – THE POWERHOUSE OF RESPIRATION & THE GREAT MUSCULAR PARTITION OF THE BODY | COMPREHENSIVE ANATOMY
INTRODUCTION
The diaphragm is a dome-shaped musculotendinous partition separating the thoracic cavity from the abdominal cavity. It is the principal muscle of respiration and plays a vital role in breathing, venous return, abdominal pressure regulation, and thoracoabdominal mechanics.
The diaphragm consists of peripheral muscular fibers converging toward a central tendon and possesses multiple openings transmitting major neurovascular structures between thorax and abdomen.
#️⃣ GENERAL FEATURES
• Chief muscle of inspiration
• Forms floor of thoracic cavity
• Forms roof of abdominal cavity
• Right dome lies higher than left due to liver
• Supplied mainly by phrenic nerve
#️⃣ PARTS OF THE DIAPHRAGM
1. Sternal Part
Arises from posterior surface of xiphoid process.
2. Costal Part
Arises from inner surfaces of lower six ribs and costal cartilages.
3. Lumbar Part
Arises from upper lumbar vertebrae through crura and arcuate ligaments.
#️⃣ CENTRAL TENDON
GENERAL FEATURES
Strong aponeurotic central part into which muscular fibers insert.
RELATIONS
• Fused superiorly with fibrous pericardium
• Contains caval opening
#️⃣ CRURA OF THE DIAPHRAGM
Right Crus
• Larger and longer
• Arises from bodies of L1–L3 vertebrae
Left Crus
• Arises from bodies of L1–L2 vertebrae
FUNCTION
Form esophageal hiatus and anchor diaphragm to vertebral column.
#️⃣ ARCUATE LIGAMENTS
Median Arcuate Ligament
Connects right and left crura over aorta.
Medial Arcuate Ligament
Extends over psoas major muscle.
Lateral Arcuate Ligament
Extends over quadratus lumborum muscle.
#️⃣ OPENINGS OF THE DIAPHRAGM
1. Caval Opening (T8 Level)
LOCATION
Within central tendon.
TRANSMITS
• Inferior vena cava
• Terminal branches of right phrenic nerve
2. Esophageal Hiatus (T10 Level)
LOCATION
Within right crus.
TRANSMITS
• Esophagus
• Anterior and posterior vagal trunks
• Esophageal vessels
3. Aortic Hiatus (T12 Level)
LOCATION
Posterior to diaphragm beneath median arcuate ligament.
TRANSMITS
• Descending aorta
• Thoracic duct
• Azygos vein
#️⃣ MINOR OPENINGS Additional structures passing through diaphragm include:
• Sympathetic trunks
• Greater, lesser, and least splanchnic nerves
• Superior epigastric vessels
• Musculophrenic vessels
#️⃣ BLOOD SUPPLY
ARTERIAL SUPPLY
Superior Surface
• Pericardiacophrenic artery
• Musculophrenic artery
Inferior Surface
• Inferior phrenic arteries
VENOUS DRAINAGE
Drains into:
• Inferior vena cava
• Azygos system
#️⃣ NERVE SUPPLY
Motor Supply
Phrenic nerves (C3, C4, C5)
Mnemonic
“C3, 4, 5 keep the diaphragm alive.”
Sensory Supply
Central Part
Phrenic nerve
Peripheral Part
Lower intercostal nerves and subcostal nerve
#️⃣ RELATIONS OF THE DIAPHRAGM
Thoracic Surface
Related to:
• Lungs and pleura
• Heart and pericardium
Abdominal Surface
Right Side
• Liver
• Right kidney
• Right suprarenal gland
Left Side
• Stomach
• Spleen
• Left kidney
#️⃣ FUNCTIONS OF THE DIAPHRAGM
Respiration
Main muscle of inspiration.
During contraction:
• Domes descend
• Thoracic volume increases
• Intrathoracic pressure decreases
Increases Intra-Abdominal Pressure
Important in:
• Defecation
• Micturition
• Vomiting
• Childbirth
Venous and Lymphatic Return
Assists blood flow toward heart.
#️⃣ EMBRYOLOGY OF THE DIAPHRAGM
DEVELOPMENTAL COMPONENTS
• Septum transversum
• Pleuroperitoneal membranes
• Dorsal mesentery of esophagus
• Body wall musculature
#️⃣ CLINICAL ANATOMY
Diaphragmatic Paralysis
Usually due to phrenic nerve injury causing paradoxical movement.
Hiatal Hernia
Part of stomach herniates through esophageal hiatus.
Congenital Diaphragmatic Hernia
Failure of pleuroperitoneal membrane closure.
Referred Pain
Diaphragmatic irritation may refer pain to shoulder through phrenic nerve (C3–C5).
Eventration of Diaphragm
Abnormal elevation due to muscle weakness.
#️⃣ SUMMARY
The diaphragm is the principal muscle of respiration and an essential musculotendinous partition separating thoracic and abdominal cavities. It consists of sternal, costal, and lumbar parts converging into a central tendon and contains major openings for passage of vital structures. Its anatomy, innervation, vascular supply, and clinical significance make it one of the most important structures in thoracoabdominal anatomy.