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Anatomy (Fach) / Anatomy IV (Lektion)
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- Nerves of the peripheral nervous system 1. Cranial nerves - 12 pairs (I-XII) which emerge from the brain 2. Spinal nerves - 31 pairs (8 cervical, 12 thoracic, 5 sacral, 5, lumbar, 1 coccygeal) which leave the spinal cord through intervertebral foramina
- Microanatomy of peripheral nerves 1. Nerve fibres (cells) - axon and its supporting Schwann cells - surrounded by endoneurium 2. Bundles/fascicles - contain several nerve fibres and blood vessels - surrounded by perineurium 3. Peripheral nerve - contains several fascicles - surrounded by epineurium
- Structure of the spinal cord - extends from the foramen magnum to the 1st/2nd lumbar vertebrae (ends at the conus medullaris) 1. White matter: nerve fibres (axon + myelin sheath) - white commissure - anterior median fissure 2. Grey matter: cell bodies of neurons - grey commissure - posterior grey horn - lateral grey horn - anterior grey horn - central canal
- Meninges (Structure) - connective tissue layers covering the spinal cord: --> epidural/extradural space 1. Dura mater (outer layer) 2. Arachnoid mater (middle layer) --> Subarachnoid space (CSF) 3. Pia mater (inner layer)
- Spinal nerves (structure) the 31 spinal nerves are made up of: - ventral (motor information) and dorsal rootlets (sensory information) - ventral and dorsal roots - dorsal root ganglion (cell bodies of sensory neurons) - spinal nerve (motor and sensory information) - dorsal ramus and ventral ramus (motor and sensory information)
- Cauda equina Bundle of lumbar and sacral nerves below L2 --> no spinal nerves anymore
- Relation spinal cord segments and vertebrae due to the fact that in embryonic development the spinal cord grows slower than the vertebral column, the spinal cord already ends between the 1st and 2nd vertebrae Consequences: 1. thoracic, lumbar and sacral spinal nerves emerge from the intervertebral foramen below their numerical vertebra 2. Cervical spinal nerves (C1-7) emerge from the intervertebral forman above their numerical vertebra 3. C8 emerges below the 7th vertebra --> 8 cervical spinal nerves but only 7 cervical vertebrae
- Sehmental distribution of spinal nerves - Thoracic spinal nerves and sensory and motor to the trunk, where each spinal nerve divides into a dorsal and ventral ramus: 1. Ventral rami: form intercostal nerves passing anteriorly in the intercostal space between the ribs, innervating the intercostal muscles --> supply the skin via lateral cutaneous branches and anterior cutaneous branches 2. Dorsal rami: supply the erector spinae group of muscles and the areas of skin above it
- Dermatome Def. The area of skin supplied by a single spinal nerve/spinal cord segment --> In the thoracic region the spinal nerves supply the skin in a segmental way --> dermatomes are segmental --> More complex pattern in the limbs
- Def. Myotome "a region of skeletal muscle inntervated by a single spinal nerve/spinal cord segment"
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- Somatic reflex arc the simplest form of of a neural pathway which activates a reflex --> may involve just 2 neurons (sensory neuron, motor neuron), a sensory receptor and a skeletal muscle fibre and sometimes an interneuron
- Peripheral nerve plexuses (2) 1. Somatic plexuses - supply skin, voluntary skeletal muscle and joints - formed from the ventral rami of spinal nerves 2. Autonomix plexuses - innervate blood vessels and viscera (thorax, abdomen, pelvis)
- Somatic plexuses (4) - In the trunk, the ventral rami of the spinal nerves have a segmental pattern --> but some ventral rami come together as 4 somatic plexuses: 1. Cervical plexus - ventral rami of C1-C4 join together - supply of the skin and muscles of the head, neck , shoulder region 2. Brachial plexus - ventral rami of C5-C8, T1 join together - supply skin and muscles of the uüüer limb theough 5 main nerves: a) Axillary - shoulder region b) Radial - posterior aspect arm, forearm, hand c) Musculocutaneous - anterior surfaces arm d) Ulnar - anterior forearm and hand (medially) e) Median - anterior forearm and hand (laterally) 3. Lumbar plexus - ventral rami of L1-L4 join together - supply muscle and skin of anterior and medial aspect of thigh (femoral and obturator nervs) 4. Sacral plexus - ventral rami of L4, L5, S1-S4 join together - supply skin and muscle of posterior aspect of thigh, leg and foot (sciatic nerve)