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?