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Meninges,Cerebrospinal Fluid, and the Spinal Cord

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Meninges,Cerebrospinal Fluid, and the Spinal Cord 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 Cervical spinal nerves enlargement Dura and arachnoid Thoracic mater spinal nerves Lumbar enlargement Conus medullaris Lumbar Cauda spinal nerves equina Filum (a) The spinal cord and its nerve terminale Sacral roots, with the bony vertebral spinal nerves arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Figure 12.29a Spinal Cord Spinal nerves 31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cervical Cervical spinal nerves enlargement Dura and arachnoid Thoracic mater spinal nerves Lumbar enlargement Conus medullaris Lumbar Cauda spinal nerves equina Filum (a) The spinal cord and its nerve terminale Sacral roots, with the bony vertebral spinal nerves arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Figure 12.29a Spinal Cord Protection Bone, meninges, and CSF Spinal tap-inferior to second lumbar vertebra T12 Ligamentum flavum L5 Lumbar puncture needle entering subarachnoid space L4 Supra- spinous ligament L5 Filum terminale S1 Inter- Cauda equina vertebral Arachnoid Dura in subarachnoid disc matter mater space Figure 12.30 Spinal Cord Cross section Central gray matter Cortex of white matter Epidural space Pia mater (contains fat) Arachnoid mater Spinal Subdural space meninges Dura mater Subarachnoid space Bone of (contains CSF) vertebra Dorsal root ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a Dorsal median sulcus Gray commissure Dorsal funiculus Dorsal horn White Ventral funiculus Gray Ventral horn columns Lateral funiculus matter Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into Ventral median dorsal rootlets) fissure Ventral root (derived from several Pia mater ventral rootlets) 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 Spinal nerve neuron Ventral horn Ventral root (motor neurons) Somatic (motor) motor neuron 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 Gray commissure Dorsal funiculus Dorsal horn White Ventral funiculus Gray Ventral horn columns Lateral funiculus matter Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into Ventral median dorsal rootlets) fissure Ventral root (derived from several Pia mater ventral rootlets) 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 Medulla oblongata Pyramids Decussation of pyramid Lateral corticospinal Cervical spinal cord tract 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 Descending tracts Fasciculus gracilis Ventral white Dorsal commissure white Fasciculus cuneatus column Lateral reticulospinal tract Dorsal Lateral spinocerebellar corticospinal tract tract Rubrospinal tract Ventral spinocerebellar Medial tract reticulospinal Lateral tract spinothalamic tract Ventral corticospinal Ventral (anterior) tract spinothalamic Vestibulospinal tract Tectospinal tract tract Figure 12.33 Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature Lumbar spinal cord 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 Medial lemniscus (tract) spinocerebellar (axons of second-order neurons) (axons of tract Nucleus gracilis second-order Nucleus cuneatus neurons) Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor Axon of (proprioceptor) first-order Cervical spinal cord neuron Fasciculus gracilis Muscle spindle (axon of first-order sensory neuron) (proprioceptor) Lumbar spinal cord Touch receptor (a) Spinocerebellar Dorsal (posterior) pathway column Figure 12.34a (2 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons (a) Spinocerebellar Dorsal (posterior) pathway 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) Cortex to cord (decussate in pyramids) 2. Lower motor neurons (2nd order) Spinal cord to muscle Innervate skeletal muscles (voluntary) Pyramidal cells (upper motor Primary motor cortex neurons) Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons (a) Pyramidal (lateral and ventral corticospinal) pathways Figure 12.35a (1 of 2) Ventral corticospinal tract Medulla oblongata Pyramids Decussation of pyramid Lateral corticospinal Cervical spinal cord tract 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) Subcortex or pons (decussate) to cord 2. 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? .
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