Anatomy - CNS

CENTRAL NERVOUS SYSTEM (CNS)

SOMATIC PART of CNS
- Carry conscious sensation from peripheral à CNS
- Innervates voluntary muscles
- Dermatomytome (from somites) : skeletal muscles + dermis
o Migrate to
§ ANTERIOR : Hypaxial muscles (limbs & trunk)
§ POSTERIOR : Epaxial muscles (intrinsic back muscles & dermis)
- Developing nerve cells in anterior neural tube (form CNS) à differentiating dermatomytome [ MOTOR neurons]
- Developing nerve cells in the neural crest (form PNS) à a) Medial process à posterior of NT
- à b) Lateral process à differentiating dermatomytomes [ SENSORY neurons]
Organized segmentally along the NT and form parts of all spinal nerves & some cranial nerves


- Sensory infos à POSTERIOR spinal cord Motor infos àAnterior spinal cord
- Peripheral à CNS Somatic Sensory Afferents/ General Somatic Afferents (GPAs)
· Modalities include pain, touch, temperature & proprioception
- CNS à Peripheral Somatic Motor Efferents/ General Somatic Efferents (GSEs)

Dermatomes (sensory)
- Specific somite develops à dermis at a precise location à associated somatic sensory fibres enter à POSTERIOR spinal cord at a specific level becomes à ONE specific spinal nerve
- Thus, EACH spinal nerve carries somatic sensory infos from a specific area of skin on the surface of the body
Area of skin supplied by a SINGLE spinal cord level/spinal nerve

- Dermatome is usually overlap
o Autonomous Region: Overlap of dermatomes is least likely
§ TESTING TOUCH in conscious patient à localize lesions to a specific spinal nerve
Mytomes (motor)
- Specific somite develops à skeletal muscle at a precise location à associated somatic motor fibres ­+ somatic sensory nerves from the SAME level = SPINAL NERVE
Portion of skeletal muscle innervated by a SINGLE spinal cord level/ spinal nerve

- More difficult to test than dermatomes as each skeletal muscle is usually innervated by > 1 spinal nerve
- However, TESTING MOVEMENT at successive joints à localize lesions to specific spinal nerve, e.g. a) shoulder joint (C5 & C6) b) elbow (C6 & C7) c) hand (C8 & T1)

IMPORTANT CLINICAL USE
Fundamental to carry out neurological examination