Human Anatomy & Physiology Ninth Edition PowerPoint ® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College C H A P T E R © 2013 Pearson Education, Inc.© Annie Leibovitz/Contact Press Images The Central Nervous System: Part D 12

© 2013 Pearson Education, Inc. Spinal Cord: Gross Anatomy and Protection Location –Begins at the foramen magnum –Ends at L 1 or L 2 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 L 1 or L 2 –Site of lumbar puncture or tap

© 2013 Pearson Education, Inc. Spinal Cord: Gross Anatomy and Protection 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. T 12 Ligamentum flavum Lumbar puncture needle entering subarachnoid space Supra- spinous ligament Filum terminale Cauda equina in subarachnoid space Dura mater Arachnoid mater Inter- vertebral disc L5L5 S1S1 L5L5 L4L4 Figure Diagram of a lumbar tap.

© 2013 Pearson Education, Inc. Figure 12.26a Gross structure of the spinal cord, dorsal view. Cervical enlargement Dura and arachnoid mater Conus medullaris Cauda equina Filum terminale Sacral spinal nerves Lumbar spinal nerves Thoracic spinal nerves Cervical 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. Lumbar enlargement

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

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

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

© 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. 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 Figure 12.28a Anatomy of the spinal cord.

© 2013 Pearson Education, Inc. Dorsal median sulcus Gray commissure Dorsal horn Ventral horn Lateral horn Gray matter Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater White columns Dorsal funiculus Ventral funiculus Lateral funiculus Dorsal root ganglion Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) The spinal cord and its meningeal coverings Figure 12.28b Anatomy of the spinal cord.

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

© 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. 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. Dorsal white column Fasciculus gracilis Fasciculus cuneatus Dorsal spinocerebellar tract Ventral spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Ventral white commissure Lateral reticulospinal tract Lateral corticospinal tract Rubrospinal tract Medial reticulospinal tract Ventral corticospinal tract Vestibulospinal tract Tectospinal tract Descending tractsAscending tracts Figure Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view.

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

© 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. Figure 12.31b Pathways of selected ascending spinal cord tracts. (2 of 2) Medulla oblongata Pain receptors Cervical spinal cord Lumbar spinal cord Axons of first-order neurons Temperature receptors Spinothalamic pathway Lateral spinothalamic tract (axons of second-order neurons)

© 2013 Pearson Education, Inc. 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. 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 Muscle spindle (proprioceptor) Fasciculus gracilis (axon of first-order sensory neuron) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway Cervical spinal cord

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

© 2013 Pearson Education, Inc. Ventral corticospinal tract Pyramids Decussation of pyramids Lateral corticospinal tract Skeletal muscle Pyramidal (lateral and ventral corticospinal) pathways Medulla oblongata Cervical spinal cord Lumbar spinal cord Somatic motor neurons (lower motor neurons) Figure 12.32a Three descending pathways by which the brain influences movement. (2 of 2)

© 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. Indirect (Multineuronal) System 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. 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. Cerebrum Midbrain Cerebellum Pons Rubrospinal tract Red nucleus Figure 12.32b Three descending pathways by which the brain influences movement. (1 of 2)

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

© 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 T 1 and L 1 –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 4 th week Differentiates to CNS

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

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

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

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

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

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