© 2017 Pearson Education, Inc.

Gross Anatomy and Protection
Spinal Cord Gross Anatomy and Protection Spinal cord is enclosed in vertebral column Begins at the foramen magnum Ends at L1 or L2 vertebra Functions Provides two-way communication to and from brain and body Major reflex center: reflexes are initiated and completed at spinal cord © 2017 Pearson Education, Inc.

Gross Anatomy and Protection (cont.)
Protected by bone, meninges, and CSF Spinal dura mater is one layer thick Does not attach to vertebrae Epidural space Cushion of fat and network of veins in space between vertebrae and spinal dura mater CSF fills subarachnoid space between arachnoid and pia maters Dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2 Site of lumbar puncture or tap © 2017 Pearson Education, Inc.

Figure 12.27a Gross structure of the spinal cord, dorsal view.
Cervical spinal nerves Cervical enlargement Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Conus medullaris Cauda equina Lumbar spinal nerves Filum terminale Sacral spinal nerves 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. © 2017 Pearson Education, Inc.

Figure 12.28 Diagram of a lumbar puncture.
Ligamentum flavum Lumbar puncture needle entering subarachnoid space L4 Supra- spinous ligament L5 Filum terminale S1 Inter- vertebral disc Cauda equina in subarachnoid space Arachnoid mater Dura mater © 2017 Pearson Education, Inc.

Spinal cord terminates in cone-shaped structure called conus medullaris Filum terminale extends to coccyx Fibrous extension of conus covered with pia mater Anchors spinal cord Denticulate ligaments Extensions of pia mater that secure cord to dura mater Cervical and lumbar enlargements: areas where nerves servicing upper and lower limbs arise from spinal cord © 2017 Pearson Education, Inc.

Spinal nerves Part of PNS Attach to spinal cord by 31 paired roots Cervical and lumbosacral enlargements Nerves serving upper and lower limbs emerge here Cauda equina Collection of nerve roots at inferior end of vertebral canal © 2017 Pearson Education, Inc.

Figure 12.27a Gross structure of the spinal cord, dorsal view.
Cervical spinal nerves Cervical enlargement Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Conus medullaris Cauda equina Lumbar spinal nerves Filum terminale Sacral spinal nerves 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. © 2017 Pearson Education, Inc.

Figure 12.27b Gross structure of the spinal cord, dorsal view.
Foramen magnum Terminus of medulla oblongata of brain Sectioned pedicles of cervical vertebrae Spinal nerve rootlets Dorsal median sulcus of spinal cord Cervical spinal cord. © 2017 Pearson Education, Inc.

Figure 12.27c Gross structure of the spinal cord, dorsal view.
Vertebral arch (cut) Cut edge of dura mater Dorsal root ganglion Dorsal median sulcus Dorsal root Thoracic spinal cord. © 2017 Pearson Education, Inc.

Figure 12.27d Gross structure of the spinal cord, dorsal view.
First lumbar vertebral arch (cut across) Conus medullaris Cauda equina Filum terminale Inferior end of spinal cord, showing conus medullaris, cauda equina, and filum terminale. © 2017 Pearson Education, Inc.

Spinal Cord Cross-sectional Anatomy
Two lengthwise grooves that run length of cord partially divide it into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Gray matter is located in core, white matter outside Central canal runs length of cord Filled with CSF © 2017 Pearson Education, Inc.

Figure 12.29a Anatomy of the spinal cord.
Epidural space (contains fat) Pia mater Arachnoid mater Spinal meninges Subdural space Dura mater Subarachnoid space (contains CSF) Bone of vertebra Dorsal root ganglion Body of vertebra Cross section of spinal cord and vertebra © 2017 Pearson Education, Inc.

Figure 12.29b Anatomy of the spinal cord.
Dorsal median sulcus Dorsal funiculus Gray commissure Dorsal horn White columns Ventral funiculus Gray matter Ventral horn Lateral funiculus Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into dorsal rootlets) Ventral median fissure Pia mater Ventral root (derived from several ventral rootlets) Arachnoid mater Spinal dura mater The spinal cord and its meningeal coverings © 2017 Pearson Education, Inc.

Spinal Cord Cross-sectional Anatomy (cont.)
Gray matter and spinal roots Cross section of cord resembles butterfly or letter “H” Three areas of gray matter are found on each side of center and are mirror images: Dorsal horns: interneurons that receive somatic and visceral sensory input Ventral horns: some interneurons; somatic motor neurons Lateral horns (only in thoracic and superior lumbar regions): sympathetic neurons © 2017 Pearson Education, Inc.

Gray matter and spinal roots (cont.) Gray commissure: bridge of gray matter that connects masses of gray matter on either side Encloses central canal Ventral roots: bundle of motor neuron axons that exit the spinal cord Dorsal roots: sensory input to cord Dorsal root (spinal) ganglia: cell bodies of sensory neurons Spinal nerves: formed by fusion of dorsal and ventral roots © 2017 Pearson Education, Inc.

Gray matter and spinal roots (cont.) Gray matter divided into four groups based on of somatic or visceral innervation Somatic sensory (SS), visceral sensory (VS), visceral (autonomic) motor (VM) and somatic motor (SM) © 2017 Pearson Education, Inc.

Figure 12.30 Organization of the gray matter of the spinal cord.
Dorsal root (sensory) Dorsal horn (interneurons) Dorsal root ganglion SS Somatic sensory neuron VS VM Visceral sensory neuron SM Visceral motor neuron Somatic motor neuron Spinal nerve Ventral horn (motor neurons) Ventral root (motor) SS Interneurons receiving input from somatic sensory neurons VS Interneurons receiving input from visceral sensory neurons VM Visceral motor (autonomic) neurons SM Somatic motor neurons © 2017 Pearson Education, Inc.

White matter Myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain Run in three directions Ascending: up to higher centers (sensory inputs) Descending: from brain to cord or lower cord levels (motor outputs) Transverse: from one side to other (commissural fibers) © 2017 Pearson Education, Inc.

White matter (cont.) White matter is divided into three white columns (funiculi) on each side Dorsal (posterior) Lateral Ventral (anterior) Each spinal tract is composed of axons with similar destinations and functions © 2017 Pearson Education, Inc.

Figure 12.29b Anatomy of the spinal cord.
Dorsal median sulcus Dorsal funiculus Gray commissure Dorsal horn White columns Ventral funiculus Gray matter Ventral horn Lateral funiculus Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into dorsal rootlets) Ventral median fissure Pia mater Ventral root (derived from several ventral rootlets) Arachnoid mater Spinal dura mater The spinal cord and its meningeal coverings © 2017 Pearson Education, Inc.

Ascending tracts Descending tracts Ventral white commissure
Figure Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view. Ascending tracts Descending tracts Ventral white commissure Dorsal white column Corticospinal tracts (pyramidal tracts) • Fasciculus gracilis • Fasciculus cuneatus • Lateral • Ventral Spinocerebellar tracts Rubrospinal tract • Dorsal • Ventral Reticulospinal tracts Spinothalamic tracts • Medial • Lateral • Lateral • Ventral Vestibulospinal tract Tectospinal tract © 2017 Pearson Education, Inc.

Spinal Cord Trauma and Disorders
Localized injury to spinal cord or its roots leads to functional losses Paresthesias: caused by damage to dorsal roots or sensory tracts Leads to sensory function loss Paralysis: caused by damage to ventral roots or ventral horn cells Leads to motor function loss Two types of paralysis: flaccid or spastic © 2017 Pearson Education, Inc.

Spinal Cord Trauma and Disorders (cont.)
Spinal cord trauma (cont.) Flaccid paralysis: severe damage to ventral root or ventral horn cells Impulses do not reach muscles; there is no voluntary or involuntary control of muscles Muscles atrophy Spastic paralysis: damage to upper motor neurons of primary motor cortex Spinal neurons remain intact; muscles are stimulated by reflex activity No voluntary control of muscles Muscles often shorten permanently © 2017 Pearson Education, Inc.

Spinal cord trauma (cont.) Transection (cross sectioning) of spinal cord at any level results in total motor and sensory loss in regions inferior to cut Paraplegia: transection between T1 and L1 Quadriplegia: transection in cervical region Spinal shock: transient period of functional loss caudal to lesion © 2017 Pearson Education, Inc.

Poliomyelitis Destruction of ventral horn motor neurons by poliovirus Muscles atrophy Death may occur from paralysis of respiratory muscles or cardiac arrest Survivors often develop postpolio syndrome many years later from neuron loss © 2017 Pearson Education, Inc.

Amyotrophic lateral sclerosis (ALS) Also called Lou Gehrig’s disease Destruction of ventral horn motor neurons and fibers of pyramidal tract Symptoms: loss of ability to speak, swallow, and breathe Death typically occurs within 5 years Caused by environmental factors and genetic mutations involving RNA processing Involves glutamate excitotoxicity © 2017 Pearson Education, Inc.

Neuronal Pathways Major spinal tracts are part of multineuron pathways Four key points about spinal tracts and pathways: Decussation: Most pathways cross from one side of CNS to other at some point Relay: Consist of chain of two or three neurons Somatotopy: precise spatial relationship in CNS correspond to spatial relationship in body Symmetry: pathways are paired symmetrically (right and left) © 2017 Pearson Education, Inc.

Ascending Pathways Conduct sensory pathways upward through a chain of three neurons: First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as it enters spinal cord or medulla Synapses with second-order neuron © 2017 Pearson Education, Inc.

Ascending Pathways (cont.)
Second-order neuron Interneuron Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum Third-order neuron Also an interneuron Cell bodies in thalamus Axon extends to somatosensory cortex No third-order neurons in cerebellum © 2017 Pearson Education, Inc.

Somatosensory signals travel along three main pathways on each side of spinal cord: Two pathways transmit somatosensory information to sensory cortex via thalamus Dorsal column–medial lemniscal pathways Spinothalamic pathways Provide for discriminatory touch and conscious proprioception Third pathway, spinocerebellar tracts, terminate in the cerebellum © 2017 Pearson Education, Inc.

Dorsal column–medial lemniscal pathways Transmit input to somatosensory cortex for discriminative touch and vibrations Composed of paired fasciculus cuneatus and fasciculus gracilis in spinal cord and medial lemniscus in brain (medulla to thalamus) Spinothalamic pathways Lateral and ventral spinothalamic tracts Transmit pain, temperature, coarse touch, and pressure impulses within lateral spinothalamic tract © 2017 Pearson Education, Inc.

Figure 12.32a Pathways of selected ascending spinal cord tracts.
Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Medial lemniscus (tract) (axons of second-order neurons) Dorsal spinocerebellar 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 Joint stretch receptor (proprioceptor) Cervical spinal cord Muscle spindle (proprioceptor) Fasciculus gracilis (axon of first-order sensory neuron) Lumbar spinal cord T ouch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway © 2017 Pearson Education, Inc.

Figure 12.32b Pathways of selected ascending spinal cord tracts.
Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature receptors Lumbar spinal cord Spinothalamic pathway © 2017 Pearson Education, Inc.

Table 12.2-2 Major Ascending (Sensory) Pathways and Spinal Cord Tracts (continued)

Table 12.2-3 Major Ascending (Sensory) Pathways and Spinal Cord Tracts (continued)

Descending Pathways and Tracts
Deliver efferent impulses from brain to spinal cord Two groups Direct pathways: pyramidal tracts Indirect pathways: all others Motor pathways involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles © 2017 Pearson Education, Inc.

Descending Pathways and Tracts (cont.)
Direct (pyramidal) pathways Impulses from pyramidal neurons in precentral gyri pass through pyramidal (lateral and ventral corticospinal) tracts Descend directly without synapsing until axon reaches end of tract in spinal cord In spinal cord, axons synapse with interneurons (lateral tract) or ventral horn motor neurons (ventral tract) Direct pathway regulates fast and fine (skilled) movements © 2017 Pearson Education, Inc.

Figure 12.33a Three descending pathways by which the brain influences movement.
Pyramidal cells (upper motor neurons) Primary motor cortex Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons Ventral corticospinal tract Medulla oblongata Pyramids Decussation of pyramids Lateral corticospinal tract Cervical spinal cord Skeletal muscle Lumbar spinal cord Somatic motor neurons (lower motor neurons) Pyramidal (lateral and ventral corticospinal) pathways © 2017 Pearson Education, Inc.

Indirect pathways Also referred to as multineuronal pathways Complex and multisynaptic Includes brain stem motor nuclei and all motor pathways except pyramidal pathways These pathways regulate: Axial muscles, maintaining balance and posture Muscles controlling coarse limb movements Head, neck, and eye movements that follow objects in visual field © 2017 Pearson Education, Inc.

Indirect pathways (cont.) Consist of four major pathways: Reticulospinal and vestibulospinal tracts: maintain balance by varying tone of postural muscles Rubrospinal tracts: control flexor muscles Tectospinal tracts: originate from superior colliculi and mediate head movements in response to visual stimuli © 2017 Pearson Education, Inc.

Cerebrum Red nucleus Midbrain Cerebellum Pons Rubrospinal tract
Figure 12.33b Three descending pathways by which the brain influences movement. Cerebrum Red nucleus Midbrain Cerebellum Pons Rubrospinal tract Medulla oblongata Cervical spinal cord Rubrospinal tract © 2017 Pearson Education, Inc.

Table 12.3-1 Major Descending (Motor) Pathways and Spinal Cord Tracts

Table 12.3-2 Major Descending (Motor) Pathways and Spinal Cord Tracts (continued)

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