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The Nervous System SPINAL CORD Spinal Cord Continuation of CNS inferior to foramen magnum (medulla) Simpler Conducts impulses to and from brain Two way conduction pathway Reflex actions Spinal Cord Passes through vertebral canal Foramen magnum L2 Conus medullaris Filum terminale Cauda equina Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Figure 12.29a Spinal Cord Spinal nerves 31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Figure 12.29a Spinal Cord Protection Bone, meninges, and CSF Spinal tap-inferior to second lumbar vertebra T12 Ligamentum flavum Lumbar puncture needle entering subarachnoid space L5 L4 Supraspinous ligament Filum terminale L5 S1 Intervertebral disc Arachnoid matter Dura mater Cauda equina in subarachnoid space Figure 12.30 Spinal Cord Cross section Central gray matter Cortex of white matter Epidural space (contains fat) Subdural space Subarachnoid space (contains CSF) Pia mater Arachnoid mater Dura mater Spinal meninges Bone of vertebra Dorsal root ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a Dorsal median sulcus White columns Dorsal funiculus Ventral funiculus Lateral funiculus Dorsal root ganglion Gray commissure Dorsal horn Ventral horn Lateral horn Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Gray matter Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b Gray Matter Association neurons and motor neuron cell bodies site of synapses Dorsal (posterior) horns Ventral (anterior)horns Lateral horns (only in thoracic and lumbar regions) Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32 White Matter Myelinated ascending (sensory) and descending (motor) tracts Tracts are located in three white columns (funiculi) on each side Dorsal (posterior), lateral, and ventral (anterior) Dorsal median sulcus White columns Dorsal funiculus Ventral funiculus Lateral funiculus Dorsal root ganglion Gray commissure Dorsal horn Ventral horn Lateral horn Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Gray matter Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b Spinal Tracts Multineural pathways Decussate (cross over) Most exhibit somatotopy Pathways are paired symmetrically Ventral corticospinal tract Pyramids Decussation of pyramid Lateral corticospinal tract Medulla oblongata Cervical spinal cord Skeletal muscle Lumbar spinal cord Somatic motor neurons (lower motor neurons) (a) Pyramidal (lateral and ventral corticospinal) pathways Figure 12.35a (2 of 2) Naming of tracts Many are named for origin and termination Example Anterior (ventral) spinothalamic tract Ascending Pathways Consist of two or three neurons First-order neuron Receptor to spinal cord Synapses with second-order neuron Examples Posterior (Dorsal) Column Receptor to medulla Spinothalamic Tract Receptor to spinal cord Ascending Pathways Second-order neuron Interneuron Synapse with third-order neuron Examples Posterior (Dorsal) Column Medulla to thalamus (decussates in medulla) Spinothalamic Spinal cord to thalamus (decussates in spinal cord) Ascending Pathways Third-order neuron Interneuron Examples Posterior (Dorsal) Column Thalamus to cortex Spinothalamic Thalamus to cortex Ascending Pathways Two pathways transmit somatosensory information to the sensory cortex via the thalamus Posterior (Dorsal) column Spinothalamic pathways Ascending tracts Fasciculus gracilis Dorsal white Fasciculus cuneatus column Dorsal spinocerebellar tract Ventral spinocerebellar tract Lateral spinothalamic tract Ventral (anterior) spinothalamic tract Descending tracts Ventral white commissure Lateral reticulospinal tract Lateral corticospinal tract Rubrospinal tract Medial reticulospinal tract Ventral corticospinal tract Vestibulospinal tract Tectospinal tract Figure 12.33 Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Lumbar spinal cord Axons of first-order neurons Temperature receptors (b) Spinothalamic pathway Figure 12.34b (2 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons (b) Spinothalamic pathway Figure 12.34b (1 of 2) Dorsal spinocerebellar tract (axons of second-order neurons) Medial lemniscus (tract) (axons of second-order neurons) Nucleus gracilis Nucleus cuneatus Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Axon of first-order neuron Muscle spindle (proprioceptor) (a) Spinocerebellar pathway Joint stretch receptor (proprioceptor) Cervical spinal cord Fasciculus gracilis (axon of first-order sensory neuron) Lumbar spinal cord Dorsal (posterior) column Touch receptor Figure 12.34a (2 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons (a) Spinocerebellar pathway Dorsal (posterior) column Figure 12.34a (1 of 2) Descending Pathways and Tracts Deliver efferent impulses from the brain to the spinal cord Direct pathways—pyramidal tracts Indirect pathways (extrapyramidal) —all others Pyramidal Tracts From primary motor cortex to cord Involve two neurons: 1. Upper motor neurons (1st order) 2. Cortex to cord (decussate in pyramids) Lower motor neurons (2nd order) Spinal cord to muscle Innervate skeletal muscles (voluntary) Pyramidal cells (upper motor neurons) Primary motor cortex Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons (a) Pyramidal (lateral and ventral corticospinal) pathways Figure 12.35a (1 of 2) Ventral corticospinal tract Pyramids Decussation of pyramid Lateral corticospinal tract Medulla oblongata Cervical spinal cord Skeletal muscle Lumbar spinal cord Somatic motor neurons (lower motor neurons) (a) Pyramidal (lateral and ventral corticospinal) pathways Figure 12.35a (2 of 2) Extrapyramidal (Indirect) Tracts Various CNS regions (avoiding pyramids) to cord Impulses regarding unconscious motor control Posture and balance Involve two neurons: 1. Upper motor neurons (1st order) 2. Subcortex or pons (decussate) to cord Lower motor neurons (2nd order) Spinal cord to muscle Innervate skeletal muscles (involunatry) An extra pyramidal pathway Cerebrum Red nucleus Midbrain Cerebellum Pons (b) Rubrospinal tract Figure 12.35b (1 of 2) Rubrospinal tract Medulla oblongata Cervical spinal cord (b) Rubrospinal tract Figure 12.35b (2 of 2) Motor neuron damage Damage to LMN=flaccid paralysis Damage to UMN=spastic paralysis Questions?