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Transcript
THE HUMAN BODY 1 The dura mater (of the meninges) wraps the spinal cord 26: Spinal Cord, Spinal Nerves, White and Grey Matter Cauda equina Spinal cord The spinal cord runs down through the vertebral foramina (singular: vertebral foramen, a hole between the body and vertebral arch of a vertebra) of the vertebrae. It is covered in three layers of connective tissue called the meninges, which are continuous with the brain. Conus medullaris (end of spinal cord proper). At L1 Filum terminale The spinal cord itself ends at the conus medullaris, situated at the first lumbar (L1) vertebra. It is important to learn all of the names on Figure 3.26. Note that ventral is essentially another way of saying anterior, and dorsal is essentially interchangeable with posterior. Spinal nerves The ventral root branches off the anterior aspect of the spinal cord and carries fibres from efferent neurons (which carry information If we took a transverse section of the spinal cord, we would see something like this: Dorsal (sensory) root ganglion Posterior horn Figure 3.25 away from the central nervous system [CNS]) out to effectors in the periphery. These neurons are also known as motor neurons. The dorsal root branches off the posterior aspect of the spinal cord and carries fibres from afferent neurons (which carry information towards the CNS) from sensors in the periphery. These neurons are also known as sensory neurons, and their cell bodies are located in the dorsal root ganglion. The ventral root and dorsal root come together and form a spinal nerve. Spinal nerves are always mixed nerves, as they carry both sensory and motor fibres. Posterior median sulcus These nerves join to make one mixed nerve Posterior column (where the dorsal column tract travels) Lateral column Afferent fibres (from body) Efferent fibres (to body) Nervous The nerves continue in a structure called the cauda equina that terminates at the filum terminale. Anterior column Anterior horn Anterior median fissure Figure 3.26 © aptitute aptitute.co.nz Nervous | 1 THE HUMAN BODY 1 Spinal nerves branch again into dorsal rami and ventral rami (singular: ramus). Dorsal rami innervate the back and ventral rami innervate most other regions of the body except for the head. The ventral rami communicate with the sympathetic chain via sympathetic rami (the white ramus communicans and grey ramus communicans). These axons are arranged into fascicles that are covered in a second layer of connective tissue known as the perineurium. A tough fibrous sheath of connective tissue surrounds collections of fascicles and is called epineurium. Perineurium (wrapping a fascicle) Epineurium Spinal nerves come in pairs, with one nerve on either side of the spinal cord. Nerves exit the spinal cord by passing through spaces between the vertebrae (intervertebral foramina between adjacent vertebral arches). There are 30 vertebrae, but 31 pairs of spinal nerves as there are 8 cervical nerves (in the cervical region nerves exit above the vertebrae, but this changes at the C7 vertebra, below which the C8 nerve exits, therefore the extra cervical nerve). Nervous Dorsal ramus (supplies posteriorally) Axon Endoneurium (wrapping axon) Figure 3.28 White and grey matter Spinal nerve White matter: •Contains myelinated axons (that appear white because of the lipid material in myelin). •Found in the periphery of the spinal cord in regions known as columns (See Figure 3.26 on page 1). •Located in the central region of the brain. Grey matter: White ramus communicans (myelinated/preganglionic) Ventral ramus (supplies anteriorally) Grey ramus communicans (unmyelinated/postganglionic) Figure 3.27 •Contains the cell bodies of neurons and non-myelinated axons. •Found in the centre of the spinal cord in the regions known as horns (See Figure 3.26 on page 1). •Located in the peripheral regions of the brain, and the ganglia (term for a group of cell bodies in the peripheral nervous system) or nuclei (term for same thing in central nervous system). Nerve composition Nerves are made of nervous tissue, and are structurally supported by connective tissue, which also provides stretch resistance. A layer of connective tissue called endoneurium surrounds individual axons. 2 | Nervous aptitute.co.nz © aptitute