Uploaded January 2022 | Updated September 2026, 1 week ago
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Content
0:00 Introduction
0:23 Division of the Forearm Muscles
0:40 Anterior (Flexor) Group
1:13 Pronator Quadratus
1:41 Flexor Digitorum Profundus
2:11 Flexor Pollicis Longus
2:36 Flexor Digitorum Superficialis
3:14 1st Layer
4:48 Lateral Group
5:28 Brachioradialis
5:55 Extensor Carpi Radialis Longus
6:17 Extensor Carpi Radialis Brevis
6:42 Posterior Group
7:05 Abductor Pollicis Longus
7:25 Extensor Pollicis Brevis
7:45 Extensor Pollicis Longus
8:05 Extensor Indicis
8:35 Extensor Digitorum
8:57 Extensor Digiti Minimi
9:20 Extensor Carpi Ulnaris
Muscles of the forearm
- Anterior (Flexor) group
- Lateral (Radial) group
- Posterior (Extensor) group
Anterior (Flexor) group
- 1st Layer
β Palmaris Longus
β Flexor Carpi Radialis
β Pronator Teres
β Flexor Carpi Ulnaris
- 2nd Layer
β Flexor Digitorum Superficialis
- 3rd Layer
β Flexor Digitorum Profundus
β Flexor Pollicis Longus
- 4th Layer
β Pronator Quadratus
Pronator Quadratus
musculus pronator quadratus
- O: Anterior surface of Ulna
- I: Anterior surface of Radius
- F: Pronation of forearm
Flexor Digitorum Profundus
Musculus flexor digitorum profundus
- O: Anterior surface of Ulna
I: Base of the distal phalanges (2-5 finger)
basis phalangis distalis (II-V)
- F:
Flexion of 2-5th fingers at
metacarpophalangeal and
interphalangeal joints
Accessory flexion of hand
Flexor Pollicis Longus
musculus flexor pollicis longus
- O: Anterior surface of Radius
I: Base of the distal phalanges of the thumb
basis phalangis distalis pollicis
- F: Flexion of thumb at
metacarpophalangeal and
interphalangeal joints
Accessory flexion of hand
Flexor Digitorum Superficialis
musculus flexor digitorum superficialis
O:
Medial epicondyle of humerus
Ulna
Anterior surface of radius
I: Base of the middle phalanges of 2-5th fingers
basis phalangis mediale II-V
F:
Flexion of 2-5 fingers at
metacarpophalangeal and proximal
interphalangeal joints
Accessory flexion of hand
Pronator Teres
musculus pronator teres
- I: Anterolateral surface of Radius
Flexor Carpi Radialis
musculus flexor carpi radialis
- I: Base of 2nd and 3rd metacarpal
Palmaris Longus
musculus palmaris longus
I: Palmar Aponeurosis
aponeurosis palmaris
Flexor Carpi Ulnaris
musculus flexor carpi ulnaris
- I:
Pisiform
Hamatum and
base of 5th metacarpal
Lateral (Radial) group
- Superficial Layer
β Brachioradialis
β Extensor Carpi Radialis Longus
β Extensor Carpi Radialis Brevis
- Deep Layer
Supinator
Supinator
musculus supinator
O:
Lateral Epicondyle
Radial Collateral Ligament
Ulna
- I: Lateral Surface of Radius
- F: Supination of the forearm
Brachioradialis
musculus brachioradialis
- O: Lateral margin of humerus
- I: Radius above Styloid Process
F:
- Supination/Pronation
- Flexion of forearm
- Stabilises elbow joint
Extensor Carpi Radialis Longus
musculus extensor carpi radialis longus
- O: Lateral margin + Lateral Epicondyle of Humerus
I: Base of 2nd metacarpal
basis ossis metacarpalis II
F:
Abduction of hand
Extension of hand
Extensor Carpi Radialis Brevis
musculus extensor carpi radialis brevis
- O: Lateral Epicondyle of Humerus
I: Base of 3nd metacarpal
basis ossis metacarpalis III
F:
Abduction of hand
Extension of hand
Posterior (Extensor) group
- Superficial Layer
β Extensor Digitorum
β Extensor Digiti Minimi
β Extensor Carpi Ulnaris
- Deep Layer
β Abductor Pollicis Longus
β Extensor Pollicis Brevis
β Extensor Pollicis Longus
β Extensor Indicis
Abductor Pollicis Longus
musculus abductor pollicis longus
O:
Posterior surface of Ulna/Radius
Interosseous membrane
I: Base of 1st metacarpal
F: Abduction of thumb
Extensor Pollicis Brevis
O:
Posterior surface of Radius
Interosseous membrane
I: Base of proximal phalanx of thumb
F: Extension and abduction of thumb
Extensor Pollicis Longus
O:
Posterior surface of Ulna
Interosseous membrane
I: Base of distal phalanx of thumb
F: Extension of thumb
Extensor Indicis
O:
Posterior surface of Ulna
Interosseous membrane
I: Base of middle/distal phalanx of index finger
F: Extension of Index finger
Extensor Digitorum
O: Lateral Epicondyle of Humerus
I: Base of middle and distal phalanges of 2-5th fingers
F:Abduction of Fingers
Extension of hand
Extensor Digiti Minimi
musuclus extensor digiti minimi
O: Lateral Epicondyle of Humerus
I: Base of middle and distal phalanges of 5th fingers
F:Extension of 5th finger
Extensor Carpi Ulnaris
musculus extensor carpi ulnaris
O:
Lateral Epicondyle of Humerus
Posterior surface of Ulna
I: Base of 5th metacarpal bone (medial side)
basis ossis metacarpalis V
F:Extension of hand
Adduction of hand
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Content
0:00 Introduction
0:23 Division of the Forearm Muscles
0:40 Anterior (Flexor) Group
1:13 Pronator Quadratus
1:41 Flexor Digitorum Profundus
2:11 Flexor Pollicis Longus
2:36 Flexor Digitorum Superficialis
3:14 1st Layer
4:48 Lateral Group
5:28 Brachioradialis
5:55 Extensor Carpi Radialis Longus
6:17 Extensor Carpi Radialis Brevis
6:42 Posterior Group
7:05 Abductor Pollicis Longus
7:25 Extensor Pollicis Brevis
7:45 Extensor Pollicis Longus
8:05 Extensor Indicis
8:35 Extensor Digitorum
8:57 Extensor Digiti Minimi
9:20 Extensor Carpi Ulnaris
Muscles of the forearm
- Anterior (Flexor) group
- Lateral (Radial) group
- Posterior (Extensor) group
Anterior (Flexor) group
- 1st Layer
β Palmaris Longus
β Flexor Carpi Radialis
β Pronator Teres
β Flexor Carpi Ulnaris
- 2nd Layer
β Flexor Digitorum Superficialis
- 3rd Layer
β Flexor Digitorum Profundus
β Flexor Pollicis Longus
- 4th Layer
β Pronator Quadratus
Pronator Quadratus
musculus pronator quadratus
- O: Anterior surface of Ulna
- I: Anterior surface of Radius
- F: Pronation of forearm
Flexor Digitorum Profundus
Musculus flexor digitorum profundus
- O: Anterior surface of Ulna
I: Base of the distal phalanges (2-5 finger)
basis phalangis distalis (II-V)
- F:
Flexion of 2-5th fingers at
metacarpophalangeal and
interphalangeal joints
Accessory flexion of hand
Flexor Pollicis Longus
musculus flexor pollicis longus
- O: Anterior surface of Radius
I: Base of the distal phalanges of the thumb
basis phalangis distalis pollicis
- F: Flexion of thumb at
metacarpophalangeal and
interphalangeal joints
Accessory flexion of hand
Flexor Digitorum Superficialis
musculus flexor digitorum superficialis
O:
Medial epicondyle of humerus
Ulna
Anterior surface of radius
I: Base of the middle phalanges of 2-5th fingers
basis phalangis mediale II-V
F:
Flexion of 2-5 fingers at
metacarpophalangeal and proximal
interphalangeal joints
Accessory flexion of hand
Pronator Teres
musculus pronator teres
- I: Anterolateral surface of Radius
Flexor Carpi Radialis
musculus flexor carpi radialis
- I: Base of 2nd and 3rd metacarpal
Palmaris Longus
musculus palmaris longus
I: Palmar Aponeurosis
aponeurosis palmaris
Flexor Carpi Ulnaris
musculus flexor carpi ulnaris
- I:
Pisiform
Hamatum and
base of 5th metacarpal
Lateral (Radial) group
- Superficial Layer
β Brachioradialis
β Extensor Carpi Radialis Longus
β Extensor Carpi Radialis Brevis
- Deep Layer
Supinator
Supinator
musculus supinator
O:
Lateral Epicondyle
Radial Collateral Ligament
Ulna
- I: Lateral Surface of Radius
- F: Supination of the forearm
Brachioradialis
musculus brachioradialis
- O: Lateral margin of humerus
- I: Radius above Styloid Process
F:
- Supination/Pronation
- Flexion of forearm
- Stabilises elbow joint
Extensor Carpi Radialis Longus
musculus extensor carpi radialis longus
- O: Lateral margin + Lateral Epicondyle of Humerus
I: Base of 2nd metacarpal
basis ossis metacarpalis II
F:
Abduction of hand
Extension of hand
Extensor Carpi Radialis Brevis
musculus extensor carpi radialis brevis
- O: Lateral Epicondyle of Humerus
I: Base of 3nd metacarpal
basis ossis metacarpalis III
F:
Abduction of hand
Extension of hand
Posterior (Extensor) group
- Superficial Layer
β Extensor Digitorum
β Extensor Digiti Minimi
β Extensor Carpi Ulnaris
- Deep Layer
β Abductor Pollicis Longus
β Extensor Pollicis Brevis
β Extensor Pollicis Longus
β Extensor Indicis
Abductor Pollicis Longus
musculus abductor pollicis longus
O:
Posterior surface of Ulna/Radius
Interosseous membrane
I: Base of 1st metacarpal
F: Abduction of thumb
Extensor Pollicis Brevis
O:
Posterior surface of Radius
Interosseous membrane
I: Base of proximal phalanx of thumb
F: Extension and abduction of thumb
Extensor Pollicis Longus
O:
Posterior surface of Ulna
Interosseous membrane
I: Base of distal phalanx of thumb
F: Extension of thumb
Extensor Indicis
O:
Posterior surface of Ulna
Interosseous membrane
I: Base of middle/distal phalanx of index finger
F: Extension of Index finger
Extensor Digitorum
O: Lateral Epicondyle of Humerus
I: Base of middle and distal phalanges of 2-5th fingers
F:Abduction of Fingers
Extension of hand
Extensor Digiti Minimi
musuclus extensor digiti minimi
O: Lateral Epicondyle of Humerus
I: Base of middle and distal phalanges of 5th fingers
F:Extension of 5th finger
Extensor Carpi Ulnaris
musculus extensor carpi ulnaris
O:
Lateral Epicondyle of Humerus
Posterior surface of Ulna
I: Base of 5th metacarpal bone (medial side)
basis ossis metacarpalis V
F:Extension of hand
Adduction of hand







![CN 4: Trochlear Nerve (Scheme, Pathway, Clinical Relevance) | Neuroanatomy
π Website: https://taimtalksmed.com/
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Content:
0:00 Introduction
00:52 Trochlear Nerve Scheme
02:08 Course of the Trochlear Nerve
06:07 Functions of the Superior Oblique
07:55 Trochlear Nerve Palsy
09:32 Recap
Trochlear Nerve Scheme / Overview:
- Trochlea is Latin for Pulley, due to the function of the superior oblique muscle
- Nucleus of the trochlear nerve located in the midbrain, at the level of inferior colliculi
- Emerges from the posterior surface of the midbrain, and turns anteriorly
- Enter and run on the lateral wall of the cavernous sinus
- Enters the orbit via the superior orbital fissure, to innervate the superior oblique
- Exclusively a somatomotor nerve.
Course of the Trochlear Nerve:
- Nucleus of the Trochlear nerve (nuclei nervi trochlearis) is located in the midbrain, at the level of the inferior colliculus (coliculi inferiores)
- Nucleus is located at the same area as the oculomotor nerve nuclei, just a level lower.
- The trochlear nerve crosses to the contralateral side, leaves from the posterior surface of the midbrain, and turns anteriorly.
- Pierces the dura mater, and then runs through the lateral wall of the cavernous sinus.
- Goes through the superior orbital fissure, to innervate the superior oblique.
Functions of the Superior Oblique Muscle:
- Origin: Body of the sphenoid bone medial to the common tendinous ring.
- Runs anteriorly, muscle tendon hooks around the trochlea of the superior oblique
- Then takes a sharp posterior lateral turn
- Insertion; Posterior Superolateral aspect of eyeball (deep to rectus superior, via trochlea orbitae)
- Causes: Abduction, depression, internally rotation of the eyeball
Clinical Relevance:
- Damage to the trochlear nerve can be caused by either congenital or acquired causes.
- When the nerve is damaged, it causes the eye to naturally shift upwards and externally rotate leading to diplopia (double vision)
- To compensate and reduce the diplopia, patients usually get a head tilt and chin tuck.
- Congenital: Malformations of nucleus or nerve
- Acquired: Trauma, or stroke in the midbrain.
Sources:
- Singh, I. (2017). Human neuroanatomy (10th ed.). Helwany M, Bordoni B. Neuroanatomy, Cranial Nerve 1 (Olfactory) [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-
- Kozlowski, T. (2017). Memorix Anatomy: The Complete Study Guide. 2nd ed. Thieme Medical Publishers.
Pictures and visuals:
- Complete Anatomy
- Biorender
- Powerpoint
- Camtasia 2021 CN 4: Trochlear Nerve (Scheme, Pathway, Clinical Relevance) | Neuroanatomy](https://i.ytimg.com/vi/WLdIkJlvakQ/mqdefault.jpg)


