BHSC MOD.2 SP.CORD

• •Provides a two-way conduction pathway to and from the brain
• •Begins at the foramen magnum
• •Ends as conus medullaris at L1 or L2 vertebral level in most adults

• -fibrous extension from conus medullaris that anchors the spinal cord to the coccyx
• •31pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccyx)

•The cauda equina is a collection of spinal nerves at the inferior end of the spinal cord, below the conus medularis

•Cervical and lumbar enlargements the nerves serving the upper and lower limbs emerge here

• •The spinal cord sits in the vertebral canal
• •The spinal nerves exit from the intervertebral foramen with the exception of C1spinal nerve which exits between the skull and the C1 vertebra

• •Internal gray matter is mostly cell bodies
• •Gray matter surrounds the central canal
• •Central canal is filled with cerebrospinal fluid
• •Exterior white mater
• •conduction tracts

• Dorsal horns (pointed)
• •interneurons that receive somatic and visceral sensory input

• Ventral horns (rounded)
• •somatic motor neurons whose axons exit the cord via ventral roots

• Lateral horns (only in thoracic and lumbar regions)
• •Visceral output via sympathetic neurons visceral motor

• Dorsal root (spinal) ganglia
• •contain cell bodies of sensory neurons one for each spinal level

• •Consists mostly of ascending (sensory) and descending (motor) tracts
• •Transverse tracts (commissural fibers) cross from one side to the other

• Tracts are located in three white columns
• 1.dorsal (posterior)
• 2.lateral
• 3.ventral (anterior)

•Each spinal tract is composed of axons with similar functions

•Spinal nerves leave at the level of each vertebrae

•Spinal nerve consists of:

• Dorsal root
• •Axons carry somatic and visceral sensoryinformation
• •Associated with the dorsal root ganglionat each spinal level of the cord
• •Ganglia are collections of cell bodies ofunipolar neurons outside the central nervous system

• Ventral root
• •Axons that carry motor output

• •Pathways decussate (cross over) 10% go straight down and cross at the spinal cord
• •Most consist of two or three neurons (a relay)
• •Pathways are paired symmetrically (one on each side of the spinal cord or brain)

•Involve two neurons:

• 1.Upper motor neurons (brain)
• •Pyramidal cells in primary motor cortex, can't recieve info

• 2.Lower motor neurons (spinal cord)
• •Ventral horn motor neurons
• •Innervate skeletal muscles, can't carry info to muscles

• •Impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (also called corticospinal) tracts then to appropriate muscle
• •Axons synapse with ventral horn motor neurons
• •The pyramidal system controls fast and fine (skilled) movements

• Endoneurium (inside)
• • surrounds each fiber

• Perineurium (around)
• •Binds groups of fibers into fascicles

• Epineurium (outside)
• •Binds fascicles together

• Mixed nerves
• •Both sensory and motor fibers

• Sensory(afferent) nerves (dorsal)
• •Carry impulses toward the CNS

• Motor (efferent) nerves (ventral)
• •Carryimpulses away from the CNS

• •31 pairs of spinal nerves
• •Formed by the combination of the ventral and dorsal roots of the spinal cord
• •Named for the region from which they arise
• •C8 comes out between C7/T1, T1 comes out between T1/T2 (named for the vertebrae above it)

•Spinal nerves divide soon after leaving the spinal cord into a dorsal ramus and a ventral ramus

• Ramus
• •branch of a spinal nerve
• •contains both motor and sensory fibers

• Dorsal ramus
• •serve the skin and muscles of the posterior trunk
• (feed paravertebral region of muscles)

• Ventral ramus
• •form a complex of networks (plexus) for the anterior
• (thoracic region follows the intercostal space)

• Plexus
• •networks of nerves serving motor andsensory needs of the limbs
• •Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions

• Four plexuses:
• •Cervical
• •Brachial
• •Lumbar
• •Sacral

• •Originates from ventral rami of C1 – C5
• •Serves anterior neck muscles known as the strap muscles

• Important nerve:
• •Phrenic nerve roots from C3,4,5 supplying the diaphragm

•Originates from ventral rami in C5 – C8 andT1(posterior to clavicle and anterior to the 1st rib)

• Important nerves:
• •Radial nerve
• •Terminal branch of radial nerve called the axillary nerve
• •Median nerve
• •Musculocutaneous nerve
• •Ulnar nerve
• Areas served:
• shoulder, arm, forearm, and hand

• •Originates from ventral rami in L1 through L4
• Important nerves:
• •Femoral
• •Obturator
• •L2, L3, L4
• Areas served:
• •Lower abdomen L1 sensory
• •Anterior and medial thighs L2, L3, L4

•Originates from ventral rami in L4-L5 and S1–S4

• Important nerves:
• •Sciatic (huge, a thumb width)
• •Superior and inferior gluteal

• Areas served:
• •Lower trunk and posterior thigh
• •Lateral and posterior leg and foot
• •Gluteal muscles of hip area

• •Twelv epairs of nerves that mostly serve the head and neck
• •Only the pair of vagus nerves extend to thoracic and abdominal cavities
• •Most are mixed nerves, but three are sensory only (CN I, II and VIII)

• •I – Olfactory nerve, smell
• •II – Optic nerve, sight
• •III – Oculomotor nerve
• •IV – Trochlear nerve
• •V – Trigeminal nerve
• •VI – Abducens nerve
• •VII – Facial nerve
• •VIII – Vestibulocochlear nerve, hearing
• •IX – Glossopharyngeal nerve
• •X – Vagus nerve(wanders from head to transverse colon)
• •XI – Accessory nerve
• •XII – Hypoglossal nerve

A patch of skin supplied by one spinal nerve segment.

• •I Olfactory nerve: special sensory for smell
• •II Optic nerve: special sensory for vision
• •III Oculomotor nerve: motor fibers to most eye muscles(2 exceptions) rasies the eye lid
• •IV Trochlear nerve: motor fiber to the superior oblique eye muscle

• •V Trigeminal nerve: all 3 divisions are sensory for the face; the 3rd division also has motor fibers to the muscles for chewing
• •VI Abducens nerve: motor fibers to lateral rectuseye muscles
• •VII Facial nerve: Special sensory for taste; motor fibers to the face; visceral motor fibres to glands of face except for parotidgland
• •VIII Vestibulocochlear nerve: sensory for balance and hearing

• •IX Glossopharyngeal nerve: sensory for taste; motor fibers to the one muscle of the pharynx; visceral motor fibres to parotid gland
• •X Vagus nerves: Visceral sensory and motor fibers for pharynx, larynx, and viscera
• •XI Accessory nerve: motor fibers totrapezius and sternocleidomastoidmuscles
• •XII Hypoglossal nerve: motor fibers to tongue