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PowerPoint® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community Ninth Edition College Human Anatomy & Physiology CHAPTER 12 The Central Nervous System: Part D © Annie Leibovitz/Contact Press Images © 2013 Pearson Education, Inc. 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. Spinal Cord: Gross Anatomy and Protection • 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. Figure 12.27 Diagram of a lumbar tap. T12 L5 Ligamentum flavum Lumbar puncture needle entering subarachnoid space L4 Supraspinous ligament Filum terminale L5 S1 Intervertebral disc © 2013 Pearson Education, Inc. Arachnoid mater Dura mater Cauda equina in subarachnoid space Figure 12.26a Gross structure of the spinal cord, dorsal view. Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale © 2013 Pearson Education, Inc. Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves 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. 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. 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. 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. Figure 12.28a Anatomy of the spinal cord. Epidural space (contains fat) Subdural space Subarachnoid space (contains CSF) Pia mater Arachnoid mater Dura mater Spinal meninges 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 funiculus White columns Ventral funiculus Lateral funiculus Dorsal median sulcus Gray commissure Dorsal horn Gray Ventral horn matter Lateral horn Dorsal root ganglion Spinal nerve Dorsal root (fans out into dorsal rootlets) Central canal 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. 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. Figure 12.30 Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view. Ascending tracts Dorsal Fasciculus gracilis white Fasciculus cuneatus column Dorsal spinocerebellar tract Ventral spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Descending tracts Ventral white commissure Lateral reticulospinal tract Lateral corticospinal tract Rubrospinal tract Medial reticulospinal tract Ventral corticospinal tract Vestibulospinal tract Tectospinal tract © 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. 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) Axon of first-order neuron Muscle spindle (proprioceptor) Joint stretch receptor (proprioceptor) Cervical spinal cord Fasciculus gracilis (axon of first-order sensory neuron) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway © 2013 Pearson Education, Inc. 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. Spinocerebellar Tracts • Ventral and dorsal tracts • Convey information about muscle or tendon stretch to cerebellum – Used to coordinate muscle activity © 2013 Pearson Education, Inc. Indirect (Multineuronal) System • 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. Spinal Cord Trauma • Functional losses – Paresthesias • Sensory loss – Paralysis • Loss of motor function © 2013 Pearson Education, Inc. 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 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. 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. Developmental Aspects of the CNS • 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. Developmental Aspects of the CNS • 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. Developmental Aspects of the CNS • 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.