Copyright © 2010 Pearson Education, Inc. Spinal Cord Location Begins at the foramen magnum Solid cord ends around L 1 vertebra Filum terminal below that Functions Provides two-way communication to and from the brain Contains spinal reflex centers

Copyright © 2010 Pearson Education, Inc. Spinal Cord: Protection Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space

Copyright © 2010 Pearson Education, Inc. Figure Ligamentum flavum Supra- spinous ligament Lumbar puncture needle entering subarachnoid space Filum terminale Inter- vertebral disc T 12 L5L5 Cauda equina in subarachnoid space Dura mater L5L5 L4L4 S1S1 Arachnoid matter Lumbar puncture

Copyright © 2010 Pearson Education, Inc. Figure 12.29a Cervical enlargement Lumbar enlargement Cauda equina Filum terminale Cervical spinal nerves Lumbar spinal nerves Sacral spinal nerves Thoracic spinal nerves Posterior (dorsal) view of spinal cord Overlying structures (muscle, bone, etc) have been removed

Copyright © 2010 Pearson Education, Inc. Spinal Cord Spinal nerves 31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal

Copyright © 2010 Pearson Education, Inc. Figure 12.31a (a) Cross section of spinal cord and vertebra Epidural space (contains fat) Pia mater Spinal meninges Arachnoid mater Dura mater Bone of vertebra Subdural space Subarachnoid space (contains CSF) Dorsal root ganglion Body of vertebra Cross-Sectional Anatomy

Copyright © 2010 Pearson Education, Inc. Figure 12.31b (b) The spinal cord and its meningeal coverings Dorsal funiculus Dorsal median sulcus Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater Gray commissure Dorsal horn Gray matter Lateral horn Ventral horn Ventral funiculus Lateral funiculus White columns Dorsal root ganglion Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Spinal nerve Cross-Sectional Anatomy

Copyright © 2010 Pearson Education, Inc. Gray Matter Dorsal horns—interneurons that receive somatic and visceral sensory input Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons Dorsal root (spinal) gangia—contain cell bodies of sensory neurons

Copyright © 2010 Pearson Education, Inc. Figure Somatic sensory neuron Dorsal root (sensory) Dorsal root ganglion Visceral sensory neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Dorsal horn (interneurons) Visceral motor neuron Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Cross-Sectional Anatomy

Copyright © 2010 Pearson Education, Inc. White Matter 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 (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) Each spinal tract is composed of axons with similar functions

Copyright © 2010 Pearson Education, Inc. Pathway Generalizations Pathways decussate (cross over) Most consist of two or three neurons (a relay) Most exhibit somatotopy (precise spatial relationships) Pathways are paired symmetrically (one on each side of the spinal cord or brain)

Copyright © 2010 Pearson Education, Inc. Figure Ascending tractsDescending tracts Fasciculus gracilis Dorsal white column Fasciculus cuneatus Dorsal spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Ventral white commissure Lateral corticospinal tract Lateral reticulospinal tract Ventral corticospinal tract Medial reticulospinal tract Rubrospinal tract Vestibulospinal tract Tectospinal tract Ventral spinocerebellar tract

Copyright © 2010 Pearson Education, Inc. Ascending Pathways Consist of three neurons First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as it enters the spinal cord or medulla Synapses with second-order neuron

Copyright © 2010 Pearson Education, Inc. Ascending Pathways Second-order neuron Interneuron Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum

Copyright © 2010 Pearson Education, Inc. Ascending Pathways Third-order neuron Interneuron Cell body in thalamus Axon extends to somatosensory cortex

Copyright © 2010 Pearson Education, Inc. Ascending Pathways Two pathways transmit somatosensory information to the sensory cortex via the thalamus Dorsal column pathways Spinothalamic pathways (Skip spinocerebellar)

Copyright © 2010 Pearson Education, Inc. Dorsal Column Pathways (somatosensory) Transmit input to the somatosensory cortex for discriminative touch and vibrations Composed of the paired fasciculus cuneatus and fasciculus gracilis in the spinal cord and the medial lemniscus in the brain (medulla to thalamus)

Copyright © 2010 Pearson Education, Inc. Figure 12.34a (2 of 2) Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Fasciculus gracilis (axon of first-order sensory neuron) Axon of first-order neuron Muscle spindle (proprioceptor) Joint stretch receptor (proprioceptor) Cervical spinal cord Touch receptor Medial lemniscus (tract) (axons of second-order neurons) Dorsal spinocerebellar tract (axons of second-order neurons) Nucleus gracilis Nucleus cuneatus Lumbar spinal cord (a)Spinocerebellar pathway Dorsal column pathway (skip spinocerebellar) Dorsal column pathway (somatosensory)

Copyright © 2010 Pearson Education, Inc. Figure 12.34a (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons (a)Spinocerebellar pathway Dorsal column–medial lemniscal pathway Dorsal column pathway (somatosensory)

Copyright © 2010 Pearson Education, Inc. Spinothalamic Pathway (somatosensory) Spinothalamic tracts Transmit pain, temperature, and coarse touch impulses within the lateral spinothalamic tract

Copyright © 2010 Pearson Education, Inc. Figure 12.34b (2 of 2) Axons of first-order neurons Temperature receptors Lateral spinothalamic tract (axons of second-order neurons) Pain receptors Medulla oblongata Cervical spinal cord Lumbar spinal cord (b)Spinothalamic pathway Spinothalamic pathway (somatosensory)

Copyright © 2010 Pearson Education, Inc. Figure 12.34b (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons (b)Spinothalamic pathway Spinothalamic pathway (somatosensory)

Copyright © 2010 Pearson Education, Inc. Descending Pathways and Tracts Deliver efferent impulses from the brain to the spinal cord Direct pathways—pyramidal tracts Indirect pathways—all others

Copyright © 2010 Pearson Education, Inc. Descending Pathways and Tracts Involve two neurons: 1.Upper motor neurons Pyramidal cells in primary motor cortex 2.Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles

Copyright © 2010 Pearson Education, Inc. The Direct (Pyramidal) System (corticospinal) Impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal) tracts Axons synapse with interneurons or ventral horn motor neurons The direct pathway regulates fast and fine (skilled) movements

Copyright © 2010 Pearson Education, Inc. Figure 12.35a (1 of 2) Primary motor cortex Internal capsule Cerebral peduncle Midbrain Cerebellum Cerebrum Pons Pyramidal cells (upper motor neurons) Pyramidal (corticospinal) pathways

Copyright © 2010 Pearson Education, Inc. Figure 12.35a (2 of 2) Medulla oblongata Cervical spinal cord Skeletal muscle Pyramids Decussation of pyramid Lateral corticospinal tract Ventral corticospinal tract Lumbar spinal cord Somatic motor neurons (lower motor neurons) Pyramidal (corticospinal) pathways