Spinal Cord: Gross Anatomy and Protection

Name: Spinal Cord: Gross Anatomy and Protection
Uploaded: 2017-07-04T19:14:03+00:00
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Description: Spinal Cord: Gross Anatomy and Protection

Spinal Cord: Gross Anatomy and Protection
Location Begins at the foramen magnum Ends at L1 or L2 vertebra Functions Provides two-way communication to and from brain Contains spinal reflex centers © 2013 Pearson Education, Inc.

Bone, meninges, and CSF Epidural space Cushion of fat and network of veins in space between vertebrae and spinal dura mater CSF in subarachnoid space Dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2 Site of lumbar puncture or tap © 2013 Pearson Education, Inc.

Terminates in 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 © 2013 Pearson Education, Inc.

T12 L5 Ligamentum flavum Lumbar puncture needle entering subarachnoid
Figure Diagram of a lumbar tap. T12 L5 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 © 2013 Pearson Education, Inc.

The spinal cord and its nerve roots, with the bony
Figure 12.26a 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. © 2013 Pearson Education, Inc.

Cranial dura mater Terminus of medulla oblongata of brain Sectioned
Figure 12.26b Gross structure of the spinal cord, dorsal view. Cranial dura mater Terminus of medulla oblongata of brain Sectioned pedicles of cervical vertebrae Spinal nerve rootlets Dorsal median sulcus of spinal cord Cervical spinal cord. © 2013 Pearson Education, Inc.

Thoracic spinal cord, showing denticulate ligaments.
Figure 12.26c Gross structure of the spinal cord, dorsal view. Spinal cord Vertebral arch Denticulate ligament Denticulate ligament Dorsal median sulcus Arachnoid mater Dorsal root Spinal dura mater Thoracic spinal cord, showing denticulate ligaments. © 2013 Pearson Education, Inc.

Inferior end of spinal cord, showing
Figure 12.26d Gross structure of the spinal cord, dorsal view. Spinal cord Cauda equina First lumbar vertebral arch (cut across) Conus medullaris Spinous process of second lumbar vertebra Filum terminale Inferior end of spinal cord, showing conus medullaris, cauda equina, and filum terminale. © 2013 Pearson Education, Inc.

Spinal nerves (Part of PNS) Cervical and lumbosacral enlargements
Spinal Cord Spinal nerves (Part of PNS) 31 pairs Cervical and lumbosacral enlargements Nerves serving upper and lower limbs emerge here Cauda equina Collection of nerve roots at inferior end of vertebral canal © 2013 Pearson Education, Inc.

Cross-sectional Anatomy
Two lengthwise grooves partially divide cord into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Gray commissure—connects masses of gray matter; encloses central canal © 2013 Pearson Education, Inc.

Cross section of spinal cord and vertebra
Figure 12.28a 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 © 2013 Pearson Education, Inc.

Figure 12.28b 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 © 2013 Pearson Education, Inc.

Gray Matter Dorsal horns - interneurons that receive somatic and visceral sensory input Ventral horns - some interneurons; somatic motor neurons; axons exit cord via ventral roots Lateral horns (only in thoracic and superior lumbar regions) - sympathetic neurons Dorsal roots – sensory input to cord Dorsal root (spinal) ganglia—cell bodies of sensory neurons © 2013 Pearson Education, Inc.

Zones of Spinal Gray Matter
Per relative involvement in innervating somatic and visceral regions of body Somatic sensory (SS) Visceral sensory (VS) Visceral (autonomic) motor (VM) Somatic motor (SM) © 2013 Pearson Education, Inc.

Figure 12.29 Organization of the gray matter of the spinal cord.
Dorsal root (sensory) Dorsal horn (interneurons) Dorsal root ganglion SS VS Somatic sensory neuron 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 © 2013 Pearson Education, Inc.

Run in three directions
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) © 2013 Pearson Education, Inc.

Divided into three white columns (funiculi) on each side
White Matter Divided into three white columns (funiculi) on each side Dorsal (posterior), lateral, and ventral (anterior) Each spinal tract composed of axons with similar destinations and functions © 2013 Pearson Education, Inc.

Neuronal Pathway Generalizations
Major spinal tracts part of multineuron pathways Decussation – Pathways cross to other side Relay – Consist of two or three neurons Somatotopy – precise spatial relationship Symmetry – pathways paired symmetrically © 2013 Pearson Education, Inc.

spinocerebellar tract Lateral corticospinal tract
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 Fasciculus gracilis Fasciculus cuneatus Lateral reticulospinal tract Dorsal spinocerebellar tract Lateral corticospinal tract Ventral spinocerebellar tract Rubrospinal tract Medial reticulospinal tract Lateral spinothalamic tract Ventral corticospinal tract Ventral spinothalamic tract Vestibulospinal tract Tectospinal tract © 2013 Pearson Education, Inc.

Consist of three neurons First-order neuron
Ascending Pathways Consist of three neurons First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as enters spinal cord or medulla Synapses with second-order neuron © 2013 Pearson Education, Inc.

Ascending Pathways Second-order neuron Interneuron
Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum © 2013 Pearson Education, Inc.

Ascending Pathways Third-order neuron Interneuron
Cell body in thalamus Axon extends to somatosensory cortex No third-order neurons in cerebellum © 2013 Pearson Education, Inc.

Ascending Pathways Three main pathways:
Two transmit somatosensory information to sensory cortex via thalamus Dorsal column–medial lemniscal pathways Spinothalamic pathways Provide discriminatory touch and conscious proprioception Spinocerebellar tracts terminate in the cerebellum © 2013 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) © 2013 Pearson Education, Inc.

Medial lemniscus (tract) (axons of second-order neurons)
Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 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) Joint stretch receptor (proprioceptor) Axon of first-order neuron Cervical spinal cord Fasciculus gracilis (axon of first-order sensory neuron) Muscle spindle (proprioceptor) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway © 2013 Pearson Education, Inc.

Spinocerebellar pathway Dorsal column–medial lemniscal pathway
Figure 12.31a Pathways of selected ascending spinal cord tracts. (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinocerebellar pathway Dorsal column–medial lemniscal pathway © 2013 Pearson Education, Inc.

Spinothalamic Pathways
Lateral and ventral spinothalamic tracts Transmit pain, temperature, coarse touch, and pressure impulses within lateral spinothalamic tract © 2013 Pearson Education, Inc.

Spinothalamic pathway
Figure 12.31b Pathways of selected ascending spinal cord tracts. (2 of 2) 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 © 2013 Pearson Education, Inc.

Spinothalamic pathway
Figure 12.31b Pathways of selected ascending spinal cord tracts. (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinothalamic pathway © 2013 Pearson Education, Inc.

Spinocerebellar Tracts
Ventral and dorsal tracts Convey information about muscle or tendon stretch to cerebellum Used to coordinate muscle activity © 2013 Pearson Education, Inc.

Medial lemniscus (tract) (axons of second-order neurons)
Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 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) Joint stretch receptor (proprioceptor) Axon of first-order neuron Cervical spinal cord Fasciculus gracilis (axon of first-order sensory neuron) Muscle spindle (proprioceptor) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway © 2013 Pearson Education, Inc.

Spinocerebellar pathway Dorsal column–medial lemniscal pathway
Figure 12.31a Pathways of selected ascending spinal cord tracts. (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinocerebellar pathway Dorsal column–medial lemniscal pathway © 2013 Pearson Education, Inc.

Descending Pathways and Tracts
Deliver efferent impulses from brain to spinal cord Two groups Direct pathways—pyramidal tracts Indirect pathways—all others © 2013 Pearson Education, Inc.

Descending Pathways and Tracts
Motor pathways involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles © 2013 Pearson Education, Inc.

The Direct (Pyramidal) Pathways
Impulses from pyramidal neurons in precentral gyri pass through pyramidal (corticospinal)l tracts Descend without synapsing Axons synapse with interneurons or ventral horn motor neurons Direct pathway regulates fast and fine (skilled) movements © 2013 Pearson Education, Inc.

Pyramidal (lateral and ventral corticospinal) pathways
Figure 12.32a Three descending pathways by which the brain influences movement. (1 of 2) Pyramidal cells (upper motor neurons) Primary motor cortex Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons Pyramidal (lateral and ventral corticospinal) pathways © 2013 Pearson Education, Inc.

Pyramidal (lateral and ventral corticospinal) pathways
Figure 12.32a Three descending pathways by which the brain influences movement. (2 of 2) 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 © 2013 Pearson Education, Inc.

Indirect (Multineuronal) System
Complex and multisynaptic Includes brain stem motor nuclei, and all motor pathways except pyramidal pathways © 2013 Pearson Education, Inc.

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 © 2013 Pearson Education, Inc.

Reticulospinal and vestibulospinal tracts—maintain balance Rubrospinal tracts—control flexor muscles Superior colliculi and tectospinal tracts mediate head movements in response to visual stimuli © 2013 Pearson Education, Inc.

Cerebrum Red nucleus Midbrain Cerebellum Pons
Figure 12.32b Three descending pathways by which the brain influences movement. (1 of 2) Cerebrum Red nucleus Midbrain Cerebellum Pons Rubrospinal tract © 2013 Pearson Education, Inc.

Rubrospinal tract Medulla oblongata Cervical spinal cord
Figure 12.32b Three descending pathways by which the brain influences movement. (2 of 2) Rubrospinal tract Medulla oblongata Cervical spinal cord Lumbar spinal cord Rubrospinal tract © 2013 Pearson Education, Inc.

Spinal Cord Trauma Functional losses Paresthesias Paralysis
Sensory loss Paralysis Loss of motor function © 2013 Pearson Education, Inc.

Flaccid paralysis—severe damage to ventral root or ventral horn cells
Spinal Cord Trauma 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 © 2013 Pearson Education, Inc.

Spinal Cord Trauma 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 © 2013 Pearson Education, Inc.

Spinal shock – transient period of functional loss caudal to lesion
Spinal Cord Trauma 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 © 2013 Pearson Education, Inc.

Destruction of ventral horn motor neurons by poliovirus
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 © 2013 Pearson Education, Inc.

Amyotrophic Lateral Sclerosis (ALS) (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 five years Caused by environmental factors and genetic mutations involving RNA processing Involves glutamate excitotoxicity Drug riluzole interferes with glutamate signaling – only treatment © 2013 Pearson Education, Inc.

Assessing CNS Dysfunction
Reflex tests Imaging techniques CT, MRI, PET, radiotracer dyes for Alzheimer's, ultrasound, cerebral angiography © 2013 Pearson Education, Inc.

Developmental Aspects of the CNS
Ectoderm thickens, forming neural plate Invaginates, forming neural groove flanked by neural folds Neural crest forms from migrating neural fold cells Neural groove deepens  neural tube by 4th week Differentiates to CNS © 2013 Pearson Education, Inc.

Both sides of spinal cord bear a dorsal alar plate and a ventral basal plate Alar plate  interneurons Basal plate  motor neurons Neural crest cells form dorsal root ganglia © 2013 Pearson Education, Inc.

Dorsal root ganglion: sensory neurons from neural crest
Figure Structure of the embryonic spinal cord. Dorsal root ganglion: sensory neurons from neural crest Alar plate: interneurons White matter Basal plate: motor neurons Neural tube cells Central cavity © 2013 Pearson Education, Inc.

Gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal testosterone Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm developing CNS Smoking decreases oxygen in blood, which can lead to neuron death and fetal brain damage © 2013 Pearson Education, Inc.

Hypothalamus one of last areas of CNS to develop Premature infants poor body temperature regulation Visual cortex develops slowly over first 11 weeks Neuromuscular coordination progresses in superior-to-inferior and proximal-to-distal directions along with myelination © 2013 Pearson Education, Inc.

Age brings some cognitive declines, but not significant in healthy individuals until 80s Shrinkage of brain accelerates in old age Excessive alcohol use and boxing cause signs of senility unrelated to aging process © 2013 Pearson Education, Inc.

Figure 12.33 Development of the neural tube from embryonic ectoderm.
Slide 1 Neural fold forming Head Surface ectoderm Neural plate Tail The neural plate forms from surface ectoderm. It then invaginates, forming the neural groove flanked by neural folds. 1 Neural crest Neural groove Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. 2 Head Surface ectoderm Neural tube Tail The neural groove becomes the neural tube, which will form CNS structures. 3 © 2013 Pearson Education, Inc.

The neural plate forms from surface ectoderm. It then
Figure Development of the neural tube from embryonic ectoderm. Slide 2 Neural fold forming Surface ectoderm Head Neural plate Tail The neural plate forms from surface ectoderm. It then invaginates, forming the neural groove flanked by neural folds. 1 © 2013 Pearson Education, Inc.

Neural fold cells migrate to form the neural crest, which
Figure Development of the neural tube from embryonic ectoderm. Slide 3 Neural crest Neural Groove Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. 2 © 2013 Pearson Education, Inc.

The neural groove becomes the neural tube, which will
Figure Development of the neural tube from embryonic ectoderm. Slide 4 Head Surface ectoderm Neural tube Tail The neural groove becomes the neural tube, which will form CNS structures. 3 © 2013 Pearson Education, Inc.

Figure 12.33 Development of the neural tube from embryonic ectoderm.
Slide 5 Neural fold forming Head Surface ectoderm Neural plate Tail The neural plate forms from surface ectoderm. It then invaginates, forming the neural groove flanked by neural folds. 1 Neural crest Neural groove Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. 2 Head Surface ectoderm Neural tube Tail The neural groove becomes the neural tube, which will form CNS structures. 3 © 2013 Pearson Education, Inc.

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