T1 Nerve Root (T1)

Authors
Affiliations

Doctor of Physical Therapy

B.S. in Kinesiology

Doctor of Physical Therapy

B.A. in Neuroscience

Figure 1: Nerve roots extending from the spinal cord

Motor Innervation

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Muscle Origin Insertion Innervation Action
1st Dorsal interossei (hand) 1-2nd MCP adjacent sides 2nd dorsal digital expansion
2nd Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
2nd digit: MCP Flexion, PIP & DIP Extension & Abduction
1st Lumbrical (hand) Tendon of flexor digitorum profundus 2nd dorsal digital expansion Median n.
C8 - T1
2nd digit: MCP Flexion, PIP & DIP Extension
1st Palmar interossei (hand) 2nd MCP (ulnar side) 2nd dorsal digital expansion
2nd Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
2nd digit: MCP Flexion, PIP & DIP Extension & Adduction
2nd Dorsal interossei (hand) 2-3rd MCP adjacent sides 3rd dorsal digital expansion
3rd Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
3rd digit: MCP Flexion, PIP & DIP Extension & Abduction
2nd Lumbrical (hand) Tendon of flexor digitorum profundus 3rd dorsal digital expansion Median n.
C8 - T1
3rd digit: MCP Flexion, PIP & DIP Extension
2nd Palmar interossei (hand) 4th MCP (radial side) 4th dorsal digital expansion
4th Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
4th digit: MCP Flexion, PIP & DIP Extension & Adduction
3rd Dorsal interossei (hand) 3-4th MCP adjacent sides 4th dorsal digital expansion
4th Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
4th digit: MCP Flexion, PIP & DIP Extension & Abduction
3rd Lumbrical (hand) Tendon of flexor digitorum profundus 4th dorsal digital expansion Median n.
C8 - T1
4th digit: MCP Flexion, PIP & DIP Extension
3rd Palmar interossei (hand) 5th MCP (radial side) 5th dorsal digital expansion
5th Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
5th digit: MCP Flexion, PIP & DIP Extension & Adduction
4th Dorsal interossei (hand) 4-5th MCP adjacent sides 5th dorsal digital expansion
5th Proximal Phalanx (radial border)
Ulnar n.
C8 - T1
5th digit: MCP Flexion, PIP & DIP Extension & Abduction
4th Lumbrical (hand) Tendon of flexor digitorum profundus 5th dorsal digital expansion Median n.
C8 - T1
5th digit: MCP Flexion, PIP & DIP Extension
Abductor digiti minimi (hand) hand_flexor_retinaculum Base of 1st proximal phalanx (radial sesamoid) Median n.
C8 - T1
CMC: Abduction
Abductor pollicis brevis Scaphoid
Trapezium
Flexor retinaculum
1st proximal phalanx via radial sesamoid Median n.
C8 - T1
CMC: Abduction
Adductor pollicis 3rd MCP (plantar surface)
Capitate
2-3rd metacarpal base
Base of 1st proximal phalanx (ulnar sesamoid) Ulnar n.
C8 - T1
CMC: Adduction
1st MCP: Flexion
Flexor carpi ulnaris Medial epicondyle
Olecranon
Hook of Hamate
Base of 5th metacarpal
Ulnar n.
C7 - T1
Wrist: Flexion, Ulnar deviation
Flexor digiti minimi brevis (hand) Hook of Hamate
hand_flexor_retinaculum
Base of 5th Proximal Phalanx Ulnar n.
C8 - T1
5th MCP: Flexion
Flexor digitorum profundus Proximal 2/3 of Ulna
Interosseous_membrane
Palmar surface of Distal phalanges 2-5 Median n. (digits 2-3)
Ulnar n. (digits 4-5)
C8 - T1
Wrist: Flexion
MCP, PIP, & DIP 2-5: Flexion
Flexor digitorum superficialis Medial epicondyle
Coronoid process
Anterior proximal half of Radius
Sides of middle phalanges 2-5 Median n.
C8 - T1
Elbow: Weak flexion
Wrist: Flexion
2-5 MCP & PIP: Flexion, Flexion
Flexor pollicis brevis Flexor retinaculum
Capitate
Trapezium
1st proximal phalanx via radial sesamoid Median n.
Ulnar n.
C8 - T1
CMC: Flexion
Flexor pollicis longus Midanterior Radius
Adjacent Interosseous membrane
Distal phalanx of thumb Median n.
C8 - T1
Wrist: Flexion, Radial deviation
1st CMC, IP, MCP: Flexion
Iliocostalis cervicis Ribs 3-7 C4-C6 TP Spinal nn. Posterior rami (lateral br.)
C8 - L1
Bilateral: Extends spine
Unilateral: Spine ipsilateral sidebend
Iliocostalis lumborum Sacrum
Iliac crest
Thoracolumbar fascia (posterior layer)
Ribs 6-12
Upper lumbar TP
Thoracolumbar fascia (posterior layer)
Spinal nn. Posterior rami (lateral br.)
C8 - L1
Bilateral: Extends spine
Unilateral: Spine ipsilateral sidebend
Iliocostalis thoracis Ribs 7-12 Ribs 1-6 Spinal nn. Posterior rami (lateral br.)
C8 - L1
Bilateral: Extends spine
Unilateral: Spine ipsilateral sidebend
Opponens digiti minimi (hand) Hook of Hamate
hand_flexor_retinaculum
5th Proximal Phalanx (ulnar border) Ulnar n.
C8 - T1
5th MCP: Opposition
Opponens pollicis Trapezium 1st metacarpal (radial border) Median n.
C8 - T1
CMC: Opposition
Pectoralis major Clavicle (medial half)
Sternum
Costal cartilages 1-6
Rectus sheath (anterior layer)
Humerus (crest of greater tubercle) Lateral pectoral n.
Medial pectoral n.
C5 - T1
Entire muscle: Adduction, IR
Clavicular & Sternocostal parts: Flexion, Aids in respiration when shoulder is fixed
Pectoralis minor 3-5 ribs Coracoid process Medial pectoral n.
C8 - T1
Scapula: Depression, Downward rotation, Protraction
Respiration: Assists in respiration
Pronator quadratus Distal 1/4 of anterior Ulna Distal 1/4 of anterior Radius Median n.
C8 - T1
Elbow/Forearm: Pronation
Distal RUJ: Stabilization

Dermatome

Figure 2: Dermatomal cutaneous distribution
Figure 3: Dermatomal cutaneous distribution (Posterior)

Lesion

“Sensory disturbances occur on the medial arm. Paresis occurs variably in the following muscles: abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, all lumbricals and interossei, abductor digiti minimi, opponens digiti minimi, flexor digiti minimi, and adductor pollicis [16]. The finger flexor reflex (C8 T1) may be depressed. Sympathetic fibers destined for the superior cervical ganglia are interrupted, resulting in an ipsilateral Horner syndrome.”

Examination

Muscle Strength

“Hand Intrinsics (T1) The patient is asked to squeeze the clinician’s fingers between their fingers while the clinician tries to pull their fingers away (Fig. 25-30). Based on the findings from the history, systems review, and key muscle testing, a sensory examination may be necessary (see Chapter 3).”

References

1.
Gray H. Anatomy of the Human Body. 20th ed. (Lewis WH, ed.). Lea & Febiger; 1918. https://www.bartleby.com/107/
2.
Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8th ed. Wolters Kluwer Health; 2022.
3.
Dutton M. Dutton’s Orthopaedic Examination, Evaluation, and Intervention. 5th ed. McGraw Hill Education; 2020.

Citation

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