Dermatomes & Segmental Innervation of the Upper & Lower Limbs PDF

Dermatomes & Segmental Innervation of The Upper & Lower Limbs Segmental Innervation of the Skin  Segmental Nerve Supply to The Limbs Nerve Supply to the limbs comes from the Spinal Cord The Spinal Cord is protected by the Vertebral Column Vertebral Col...

Dermatomes & Segmental Innervation of The Upper & Lower Limbs Segmental Innervation of the Skin  Segmental Nerve Supply to The Limbs Nerve Supply to the limbs comes from the Spinal Cord The Spinal Cord is protected by the Vertebral Column Vertebral Column consists 33 Spinal Vertebrae 24 are Discrete (typical) Spinal Vertebrae 9 are fused to form the Sacrum & Coccyx There are 5 Distinct Groups of Spinal Vertebrae 1. Cervical (n=7) 2. Thoracic (n=12) 3. Lumbar (n=5) 4. Sacrum (fused-n=5) 5. Coccyx (fused n=4)  Typical Features of A Vertebral Segment Each Vertebra makes 1 vertebral segment It has the following: A Body A spine 2 Transverse Processes 2 Superior Vertebral Notches 2 Inferior Vertebral Notches A Vertebral Foramen  Features of 2 adjoining Vertebral Segments Each vertebra has an inferior & a superior vertebral notch on each side When any 2 consecutive vertebrae form a common joint, their corresponding inferior and superior vertebral notches form an intervertebral foramen The Spinal cord passes through Vertebral Foramina (most levels) Segmental nerves leave the spinal cord via inter-vertebral foramina  The Spinal Cord+ Vertebral Column + = The spinal cord is a column of millions of nerve cell bodies and neuronal fibres (Ascending, Descending & Crossing) It extends from the Medulla to the Conus Medullaris (where it ends) It runs through vertebral foramina of the vertebral column Vertebral foramina form the spinal canal  The Spinal Cord Rostral The Gross Shape of the spinal cord changes from rostral to caudal Shows two enlargements at the cervical and lumbar levels and ends in a taper (conus Cervical medullaris) The cross sectional appearance of the cord shows changes from rostral to caudal Thoracic In X-section: the spinal cord shows regional specialisations that match the 4 Vertebral Regions Lumbar Distribution of motoneurones varies along the rostro-caudal axis of cord Sacral Caudal  ?What is a Segmental Nerve At Each Vertebral Level the spinal cord gives out a pair of nerves One to the Left One to the Right The nerves exit the vertebral column through intervertebral foramina Each of these nerves is known as a Spinal Segmental Nerve There is an established relationship between a vertebral level and a neuronal spinal level. Composition of a Segmental Nerve Segmental Nerves are known as Mixed Spinal Nerves We need to know what this mixture consists of Functional Modalities of A Segmental Nerve Each Spinal Segmental Nerve comprises of: 1) Dorsal Roots (Sensory) 2) Ventral Roots (Motor) 3) Ventral Roots (Autonomic)  Branching Order of a Segmental Nerve As the mixed spinal nerve emerges through the intervertebral foramen it divides into 2 branches Posterior or Dorsal Ramus (small) The Posterior Ramus Divides further into Medial & Lateral Branches Anterior or Ventral Ramus (Large) All Rami contain all functional modalities for that segmental level Anterior & Posterior Rami of Spinal Nerves  Nerve Supply to The Upper Limb It Receives all its Nerve Supply from The Spinal Cord Most of Its Supply is derived from the Cervical Spinal Segments (C5- T1) The rest comes from T2 Roots Spinal Nerves (except T2) to the Upper Limb form a Network of nerves The Brachial Plexus  Brachial Plexus Roots From Anterior Rami C5-T1 Unite & Divide to give UpperTrunks (C5,C6) Middle Trunks (C7) Lower Trunks (C8,T1) All Trunks Divide into Divisions: Anterior Posterior Divisions give rise to Cords (Axillary Artery): Medial Cord Lateral Cord Posterior Cord  Nerves of The Upper Limb Radial Nerve – C5,6,7,8,T1 Musculocutaneous Nerve – C5,6,7 Ulnar Nerve – C7,8,T1 Median Nerve – C6,7,8,T1  Other Nerves of the Upper Limb Lateral Pectoral Upper Subscapular Lower Subscapular Dorsal Scapular Long thoracic Axillary  Nerve Supply to The Lower Limb The Lower Limb Also Receives all its Nerve Supply from The Spinal Cord It is supplied from the Lumbar and Sacral Spinal Segments (L1-S4) Spinal Nerves to the Lower Limb originate from two separate Networks of nerves The Lumbar Plexus (L1-L4) Sacral Plexus (L4-S4) The Lumbar Plexus It forms behind within the psoas major muscle Nerves emerge either medial or lateral to the borders of the psoas Nerves emerging lateral to psoas 1. The femoral (L2-L4) 2. Iliohypogastric 3. Ilioinguinal 4. Lateral cutaneous nerve of the thigh 5. Nerves emerging medial to psoas 6. The obturator nerve 7. The lumbosacral trunk Lumbar Plexus  The Sacral Plexus Composed of: Lumbosacral trunk (half of L4 & all L5) Sacral spinal segmental outflow Plexus forms within the pelvic cavity Plexus lies in relation to piriformis Sacral plexus supplies:  Pelvic region  Gluteal region  Perineal region  The lower limb (via the sciatic nerve)  Dermatomes of the Upper Limb Why Study Dermatomes? To enable examination of integrity of sensory function of the skin of the body (as a major organ of the body) To accurately pinpoint areas of skin with disturbed function (e.g. anaesthesia; Allodonia) To predict what nerves & spinal segments may be affected (Disturbed Sensory Function above) To anaesthetise segments of nerves and associated skin with accuracy  Dermatomes Remember that: The spinal cord handles both General Categories of Nervous System Function: (Somatic & Autonomic) Somatic Sensory (Inflow) Motor (Outflow to Muscles) Autonomic: Outflow to: – glands and – smooth muscles  ?What is a Dermatome Literally- it translates to skin (derma-) segment (-tome) It is an area of skin supplied by sensory fibers from a single spinal nerve Dermatomes are arranged as highly ordered slices of the skin A spinal nerve root supplies 1 slice of skin (or dermatome) 1 Dermatome receives sensory supply from 1 spinal nerve root  Spinal Nerves - As a general rule: An area of skin is supplied by sensory fibers from a single spinal nerve root (no overlap with others) A spinal nerve is made from nerve fibers coming from a single spinal segment (that corresponds to its vertebral level)  Spinal Nerves What is the reality?: There is functional overlap between adjacent dermatomes Some sections of a dermatome are served by 2 successive spinal nerves Thus, a typical dermatome sandwiched between 2 others will be served by 3 successive sensory nerves Anaesthesia as a result of nerve damage will result for any dermatome only if all its 3 sensory nerves are all damaged together Sensory Supply of Upper & Lower Limbs Sensory Supply of Upper Limb  Sensory Supply of Upper Limb C4- Skin Over The Shoulder Tip C5- Radial side of Upper Arm C6 Radial Side of Forearm C7 skin of the hand C8- Ulnar side of the Forearm T1-Ulnar side of the Upper Arm T2- Skin of the Axilla  Dermatomes of the Lower Limb Sensory Supply of Lower Limb The Front of limb is supplied largely by lumbar segments The Back of limb is supplied largely by Sacral Segments The Saddle Area is supplied by Sacral Segments The Perineal Area is supplied by Sacral Segments To Note The Discontinuity of Deramtomes at the back of the limb (Axial Line)