The Nervous System Spinal Cord Continuation of CNS inferior to foramen magnum Simpler than the brain Conducts impulses to and from brain Two way conduction pathway Reflex actions Passes through vertebral canal Foramen magnum L2 Conusmedullaris= tapered end of the cord Filumterminale= anchors the cord Caudaequina= bundle of lower (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura and arachnoid are cut open and reflected laterally. Dura and arachnoid Conus medullaris Cauda equina Filum terminale Thoracic Sacral Spinal nerves 31 pairs and lumbar s Nerves serving the upper & lower limbs emerge here Dura and arachnoid Conus medullaris Cauda equina Filum (a) The spinal cord and its nerve terminale roots, with the bony vertebral arches removed. The dura and arachnoid are cut open and reflected laterally. Thoracic Sacral Figure 12.29a 1
Protection Bone Meninges CSF Spinal tap-inferior to L2 vertebra T 12 L 5 L 4 Ligamentum flavum puncture needle entering subarachnoid space Supra- spinous ligament L 5 Filum terminale Inter- vertebral disc S 1 Arachnoid matter Dura Cauda equina in subarachnoid space Figure 12.30 Cross section Central gray matter Cortex of white matter Epidural space (contains fat) Subdural space Subarachnoid space (contains CSF) Pia Arachnoid Dura Spinal meninges Bone of vertebra ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a Dorsal funiculus White Ventral funiculus columns funiculus ganglion Spinal nerve (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Dorsal median sulcus commissure Dorsal horn Ventral horn matter horn Central canal Ventral median fissure Pia Arachnoid Spinal dura matter Site of inters& motor cell body synapses All cell bodies in spinal gray matter are multipolar Regions Dorsal (posterior) horns Ventral (anterior)horns horns (only in thoracic and lumbar regions) (b) The spinal cord and its meningeal coverings Figure 12.31b 2
(sensory) ganglion Somatic sensory Visceral sensory Visceral motor Somatic motor Spinal nerve Ventral root (motor) Dorsal horn (inters) Ventral horn (motor s) Inters receiving input from somatic sensory s Inters receiving input from visceral sensory s White matter Myelinatedascending (sensory) & descending (motor) s Also some transverse (commisural fibers) Tracts located in 3 white columns (funiculi) on each side 1. Dorsal (posterior) 2. 3. Ventral (anterior) Visceral motor (autonomic) s Somatic motor s Figure 12.32 Dorsal funiculus White Ventral funiculus columns funiculus ganglion Spinal nerve (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Dorsal median sulcus commissure Dorsal horn Ventral horn matter horn Central canal Ventral median fissure Pia Arachnoid Spinal dura Spinal s Run through the funiculi Multineural pathways Contain axons with similar destinations and functions Most decussate (cross over) Most exhibit somatotopy Pathways are paired symmetrically (b) The spinal cord and its meningeal coverings Figure 12.31b Ventral Pyramids Decussation of pyramid Skeletal muscle spinal cord Naming of s Many are named for origin and termination Example Anterior (ventral) spinothalamic Origin = spinal cord Termination = thalamus Location = anterior funiculus Ascending = must be sensory Somatic motor s (lower motor s) (a) Pyramidal (lateral and ventral ) pathways Figure 12.35a (2 of 2) 3
Consist of two or three s First order Second order Third order First-order s Cell bodies in ganglia (dorsal root or cranial) Carry impulses from sensory receptors in muscle and skin to spinal cord and brain Synapse with second-order s Examples Receptor to medulla Spinothalamic Receptor to spinal cord Second-order s Inters Cell bodies in dorsal horn of spinal cord Synapse with third-order Examples Medulla to thalamus (decussates in medulla) Spinothalamic Spinal cord to thalamus (decussates in spinal cord) Third-order s Inters Cell bodies in thalamus Examples Thalamus to cortex Spinothalamic Thalamus to cortex Ascending pathways Two pathways transmit somatosensoryinformation to the sensory cortex via the thalamus Fine touch, proprioception, vibration Spinothalamic pathways Crude touch, temperature, pain Ascending s Dorsal white column Dorsal spinocerebellar Fasciculus gracilis Fasciculus cuneatus Ventral spinocerebellar spinothalamic Ventral (anterior) spinothalamic Descending s Ventral white commissure reticulospinal Rubrospinal Medial reticulospinal Ventral Vestibulospinal Tectospinal Figure 12.33 4
spinothalamic (axons of second-order s) Primary somatosensory cortex Axons of third-order s Thalamus Pain receptors spinal cord Axons of first-order s Temperature receptors (b) Spinothalamic pathway (b) Spinothalamic pathway Figure 12.34b (2 of 2) Figure 12.34b (1 of 2) Dorsal spinocerebellar (axons of second-order s) Axon of first-order Muscle spindle (proprioceptor) Medial lemniscus () (axons of second-order s) Nucleus gracilis Nucleus cuneatus Fasciculus cuneatus (axon of first-order sensory ) Joint stretch receptor (proprioceptor) Fasciculus gracilis (axon of first-order sensory ) spinal cord Primary somatosensory cortex Axons of third-order s Thalamus (a) Spinocerebellar pathway Dorsal (posterior) column Touch receptor (a) Spinocerebellar pathway Dorsal (posterior) column Figure 12.34a (2 of 2) Figure 12.34a (1 of 2) Descending pathways & s Deliver efferent impulses from the brain to the spinal cord (and from there to an effectormuscle or glad) 1. Direct pathways = pyramidal s 2. Indirect pathways (extrapyramidal) = all others Pyramidal Tracts From primary motor cortex to cord Involve two s: 1. Upper motor s (1 st order) Cortex to cord (decussate in pyramids of the medulla or in the cord) 2. Lower motor s (2 nd order) Spinal cord to muscle Innervate skeletal muscles (voluntary) 5
Pyramidal cells (upper motor s) Primary motor cortex Internal capsule Ventral Pyramids Decussation of pyramid Cerebral peduncle Skeletal muscle spinal cord (a) Pyramidal (lateral and ventral ) pathways Somatic motor s (lower motor s) (a) Pyramidal (lateral and ventral ) pathways Figure 12.35a (1 of 2) Figure 12.35a (2 of 2) Extrapyramidal (indirect) s Various CNS regions (avoiding pyramids) to cord Impulses regarding unconscious motor control Posture and balance Involve two s: 1. Upper motor s (1 st order) Subcortex or pons (decussate) to cord 2. Lower motor s (2 nd order) Spinal cord to muscle Innervate skeletal muscles (involuntary) An extrapyramidal pathway Red nucleus (b) Rubrospinal Figure 12.35b (1 of 2) Rubrospinal Motor damage Damage to LMN Flaccid paralysis Nerve impulses do not reach the affected muscles Cannot move voluntarily or involuntarily Muscles atrophy Damage to UMN Spastic paralysis Spinal motor s remain intact Reflex activity continues (involuntary movement) No voluntary muscle control (b) Rubrospinal Figure 12.35b (2 of 2) 6