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General information about the nervous system. Structure of the Spinal Cord • Extends from the foramen magnum to the first or second lumbar vertebra. • Ends in the conus medullaris • Filum terminale – Extends from conus medullaris to sacral vertebrae • Cauda equina – = filum terminale + dorsal & ventral roots from spinal nerves that extend below conus Human Anatomy, 3rd edition Prentice Hall, © 2001 medularis Coverings of the Spinal Cord • 3 layers called meninges • Dura mater – Outer layer • Arachnoid – Middle layer • Pia mater – Adheres tightly to the surface of the spinal cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Meninges of the Spinal Cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Meninges of the Spinal Cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Sectional Anatomy of the Spinal Cord • Inner part consists of gray matter – Unmyelinated cell bodies, neuroglia, & dendrites – Organized into “horns” • Outer part consists of white matter – Tracts of myelinated fibers – Ascending tracts are sensory – Descending tracts are motor Human Anatomy, 3rd edition Prentice Hall, © 2001 Example of Ascending Nerve Tracts Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Nerves • Connect to the spinal cord via a dorsal and a ventral root • Dorsal root is sensory – Contains a dorsal root ganglion • Ventral root is motor Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Nerves • The roots unite into the spinal nerve • Spinal nerves exit through intervertebral foramen • Split into branches, or rami. – Dorsal ramus – Ventral ramus – Regions of skin supplied by a spinal nerve = dermatomes (“skin slices”) Human Anatomy, 3rd edition Prentice Hall, © 2001 Dermatomes Human Anatomy, 3rd edition Prentice Hall, © 2001 Nerve Plexuses • Plexus = “braid” • Nerves supplying the limbs form plexuses when they leave the spinal cord – Cervical plexus – Brachial plexus – Lumbosacral plexus • Lumbar plexus • Sacral plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Cervical Plexus • Formed by spinal nerves C1 – C5 – Nerves innervate the neck and shoulder region – Phrenic nerve to the diaphragm Human Anatomy, 3rd edition Prentice Hall, © 2001 Brachial Plexus • Formed by spinal nerves C5 – C8 and T1 – Nerves innervate the arm and shoulder • Radial nerve • Ulnar nerve • Median nerve Human Anatomy, 3rd edition Prentice Hall, © 2001 Brachial Plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Lumbosacral Plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Lumbar Plexus • Formed by spinal nerves T12 and L1 – L4. – Innervates the medial and anterior portions of the thigh and lower abdominal regions – Lateral femoral cutaneous nerve Human Anatomy, 3rd edition Prentice Hall, © 2001 Sacral Plexus • Formed by spinal nerves L4 and L5, and S1 and S2 – Innervates the posterior portion of the hip, thigh, and leg, and the genital region – Sciatic nerve Human Anatomy, 3rd edition Prentice Hall, © 2001 Sacral Plexus Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Reflexes • Reflexes are automatic responses to stimuli • Spinal reflexes result from the stimulation of a spinal reflex arc. Human Anatomy, 3rd edition Prentice Hall, © 2001 Basic Elements of a Reflex Arc Human Anatomy, 3rd edition Prentice Hall, © 2001 • Located btwn the diencephalon and the pons. – 2 bulging cerebral peduncles on the ventral side. These contain: • Descending fibers that go to the cerebellum via the pons • Descending pyramidal tracts Midbrain – Running thru the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain. – The roof of the aqueduct ( the tectum) contains the corpora quadrigemina • 2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli • 2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli Human Anatomy, 3rd edition Prentice Hall, © 2001 •Cranial nerves 3&4 (oculomotor and trochlear) exit from the midbrain •Midbrain also contains the headquarters of the Human Anatomy, 3rd edition reticular activating system Prentice Hall, © 2001 Medulla Oblongata • • Nuclei in the medulla are associated w/ autonomic control, cranial nerves, and motor/sensory relay. Autonomic nuclei: – Cardiovascular centers • • Cardioinhibitory/cardioaccele ratory centers alter the rate and force of cardiac contractions Vasomotor center alters the tone of vascular smooth muscle – Respiratory rhythmicity centers • Receive input from the pons – Additional Centers • Emesis, deglutition, coughing, hiccupping, and sneezing Human Anatomy, 3rd edition Prentice Hall, © 2001 Medulla Oblongata • Sensory & motor nuclei of 5 cranial nerves: – • Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12) Relay nuclei – – Nucleus gracilis and nucleus cuneatus pass somatic sensory information to the thalamus Olivary nuclei relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex. Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Cord • • • • Functions to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter). Tube of neural tissue continuous w/ the medulla at the base of the brain and extends about 17” to just below the last rib. (Ends at L1) Majority of the SC has the diameter of your thumb Thicker at the neck and end of the cord (cervical and lumbar enlargements) b/c of the large group of nerves connecting these regions of the cord w/ the arms and legs. Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Cord • • Surrounded by a single layered dura mater and arachnoid and pia mater. Terminates in cone shaped structure called the conus medullaris. – The filum terminale, a fibrous extension of the pia mater, extends to the posterior surface of the coccyx to anchor the spinal cord. • The cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina. Human Anatomy, 3rd edition Prentice Hall, © 2001 Cross Sectional Anatomy of the Spinal Cord • • • Flattened from front to back. Anterior median fissure and posterior median sulcus partially divide it into left and right halves. Gray matter is in the core of the cord and surrounded by white matter. Human Anatomy, 3rd edition Prentice Hall, © 2001 • • • • • Resembles a butterfly. 2 lateral gray masses connected by the gray commissure. Posterior projections are the posterior or dorsal horns. Anterior projections are the anterior or ventral horns. In the thoracic and lumbar cord, there also exist lateral horns. Human Anatomy, 3rd edition Prentice Hall, © 2001 Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Cord & Spinal Nerves • Spinal cord – Truly the pathway between body and mind – Conducts impulses to and from the brain – Carries out spinal reflexes • Spinal nerves – 31 pairs – All are mixed nerves Spinal Cord Injuries • Can affect sensory perception; motor paralysis • Location affects severity of the injury • Spinal compression results from squeezing the spinal cord within the vertebral canal • Spinal transection is the severing of the spinal cord Human Anatomy, 3rd edition Prentice Hall, © 2001 Spinal Cord Injuries • Quadriplegia • Paraplegia http://www.apparelyzed.com/paralysis.html Spinal ganglia, their structure and functional importance. Part I: Spinal cord 1. Organization - General - Cauda equina - Meninges 2. Structure Grey matter White matter 3. Blood supply 4. Spinal nerves - Typical n. - Components 1. Organization • • Cauda equina Meninges 2. Structure: Grey matter • Components: Nerve cells, Processes, Neuroglia, Blood vessels • Grey columns: Anterior, Posterior, Transverse, Lateral Gray Matter Posterior horns contain interneurons. Anterior horns contain some interneurons as well as the cell bodies of motor neurons. These cell bodies project their axons via the ventral roots of the spinal cord to the skeletal muscles. The amount of ventral gray matter at a given level of the spinal cord is proportional to the amount of skeletal muscle innervated. Gray Matter Lateral horn neurons are sympathetic motor neurons serving visceral organs. Their axons also exit via the ventral root. Afferent sensory fibers carrying info from peripheral receptors form the dorsal roots of the spinal cord. The somata of these sensory fibers are found in an enlargement known as a dorsal root ganglion. The dorsal and ventral roots fuse to form spinal nerves. Grey columns: Anterior: Medial group: skeletal muscles of the neck and trunk Central group: cervical and lumbosacral segments & contains the phrenic, asccessory and lumbosacral nuclei Lateral group: cervical and lumbosacral areas innervating skeletal muscles of the limbs Posterior: Substantia gelatinosa: concerned with pain, temperature and touch Nucleus proprius: fibers from white posterior column associated with proprioception, 2-piont discrimination and vibration Nucleus dorsalis (Clark’s column) from C8 – L3/4 proprioceptive endings in spindles Visceral afferent nucleus from T1– L3 receives visceral afferent information Grey columns (cont.) Transverse: – Contains central canal that starts in the MO, – Inferiorly expands in the conus medullaris as the terminal ventricle: CSF & ependyma Lateral: – From T1–L2/3 – Give rise to preganglionic sympathetic fibers – Similar group in S2-4 give rise to preganglionic parasympathtic fibres 2. Structure: White matter • Mixture of myelinated nerve fibers, neuroglia and blood vessels • Ascending tracts • Descending tracts • Ascending and descending tracts with the same origin, course and termination: Fasciculus • Intersegmental tracts White Matter • Myelinated nerve fibers. • Allows for communication btwn the brain and spinal cord or btwn different regions of the spinal cord. • White matter on each side of the cord is divided into columns or funiculi. – Typically, they are ascending or descending. • What does that mean? Ascending tracts: • Sensory, contain 1st, 2nd and 3rd order neurons • Pathways for temperature, pain, proprioception • Examples: Spinothalamic tract (lateral & anterior, fasciculus gracilis and cuneatus); Spinocerebellar tract (anterior & posterior); Cuneocerebellat tract. • Other: Spinotectal, spinoreticular, spino-olivary, visceral sensory Descending tracts: • White matter from the supraspinal centers with 1st, 2nd and 3rd order motor neurons • Examples: Corticospinal, reticularspinal, tectospinal, rubrospinal, vestibulospinal, olivospinal, descending autonomic 3. Blood supply: Spinal arteries • • • From vertebral, posterior intercostal, lumbar, lateral sacral, ascending cervical, deep cervical, iliolumbar aa. Posterior spinal a. in close association to posterior spinal roots, but is insufficient to supply the spinal cord alone Anterior spinal a. unite to for a single artery on the median fissure of the spinal cord. Spinal arteries (cont.) • Radicular a. reinforce the spinal arteries by entering through the intervertebral foramina • Larger anterior radicular arteries: A. radicularis magna (artery of Adamkiewicz) from the left an intersegmental branch of the descending aorta, that supplies 2/3rds of the spinal cord 3. Blood supply: Venous drainage • Internal (anterior & posterior) venous plexus • External venous plexus (anterior & posterior) • Basivertebral and intervertebral veins. 4. Typical spinal nerve • Posterior (dorsal) root: Supplies synovial joints of the vertebral column, deep muscles of the back & overlying skin. Posterior root ganglia: Sensory, unipolar with satellite cells. • Anterior (ventral) root: Supplies the remaining areas: anterior & lateral regions of the trunk and limbs What brainstem structures are visible here? Reticular Formation Extensive network of neurons that runs thru the medulla and projects to thalamic nuclei that influence large areas of the cerebral cortex. Midbrain portion of RAS most likely is its center Functions as a net or filter for sensory input. Filter out repetitive stimuli. Such as? Allows passage of infrequent or important stimuli to reach the cerebral cortex. Unless inhibited by other brain regions, it activates the cerebral cortex – keeping it alert and awake. How might the “sleep centers” of your brain work? Why does alcohol make you tired? Protection • • What is the major protection for the brain? There are also 3 connective tissue membranes called the meninges: • Cover and protect the CNS • Protect blood vessels • Contain cerebrospinal fluid • The 3 meninges from superficial to deep: • Dura mater • Arachnoid mater • Pia mater Skin Galea Aponeurotica Connective Tissue Bone Dura Mater Arachnoid mater Spinal Cord Functions to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter). Tube of neural tissue continuous w/ the medulla at the base of the brain and extends about 17” to just below the last rib. (Ends at L1) Majority of the SC has the diameter of your thumb Thicker at the neck and end of the cord (cervical and lumbar enlargements) b/c of the large group of nerves connecting these regions of the cord w/ the arms and legs. Spinal Cord Surrounded by a single layered dura mater and arachnoid and pia mater. Terminates in cone shaped structure called the conus medullaris. The filum terminale, a fibrous extension of the pia mater, extends to the posterior surface of the coccyx to anchor the spinal cord. The cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina. Spinal Cord • • Notice the gross features of the spinal cord on the right. 31 pairs of spinal nerves attach to the cord by paired roots and exit from the vertebral canal via the intervertebral foramina. Resembles a butterfly. 2 lateral gray masses connected by the gray commissure. Posterior projections are the posterior or dorsal horns. Anterior projections are the anterior or ventral horns. In the thoracic and lumbar cord, there also exist lateral horns. Spinal Nerves 31 nerves connecting the spinal cord and various body regions. 8 paired cervical nerves 12 paired thoracic nerves 5 paired lumbar nerves 5 paired sacral nerves 1 pair of coccygeal nerves Spinal Nerves Each connects to the spinal cord by 2 roots – dorsal and ventral. Each root forms from a series of rootlets that attach along the whole length of the spinal cord segment. Ventral roots are motor while dorsal roots are sensory. Spinal Nerves The 2 roots join to form a spinal nerve prior to exiting the vertebral column. Roots are short and horizontal in the cervical and thoracic regions while they are longer and more horizontal in the sacral and lumbar regions. • Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a meningeal branch that reenters and innervates the meninges and associated blood vessels. Each ramus is mixed. Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes. These are sympathetic fibers that we’ll deal with shortly. Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs. Thank you for attention !