Chapter 13 - Lecture notes 13 PDF

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Lecture note for chapter 13....

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BIOL 1303 Lecture Outline Nervous System III- Spinal Cord and Spinal Nerves Chapter 13 I. Functions A. Spinal nerves: carry sensory information to and motor information from the CNS B. Spinal cord: help maintain homeostasis with quick reflexive responses to stimuli and carry sensory and motor information to and from the brain II. Protection of Spinal Cord A. Veterbral column 1. bone of vertebrae provide physical protection 2. spinal cord lies within the vertebral canal (vertebral foramina) B. Meninges: three layered connective tissue covering of the brain and spinal cord 1. epidural space a. between the vertebrae and dura mater b. cushion of fat and CT 2. dura mater a. most superficial b. dense irregular CT 3. subdural space a. between dura mater and arachnoid mater b. filled with interstitial fluid 4. arachnoid mater a. collagen and elastic fibers 5. subarachnoid space a. between arachnoid mater and pia mater

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b. filled with cerebrospinal fluid 6. pia mater a. thin connective tissue b. highly vascular c. adheres to surface of brain and spinal cord d. denticulate ligaments 1. thick extensions of pia mater that fuse with arachnoid and dura mater 2. protect against shock and sudden displacement (hold SC to dura mater) 7. HINT: PAD= Pia, Arachnoid, Dura C. Cerebrospinal fluid (CSF) 1. provides cushioning of CNS 2. in subarachnoid space, ventricles of brain, and central canal of SC 3. ependymal cells produce and circulate CSF III. Structure of Spinal Cord A. Location 1. inferior to brain 2. connect to medulla oblongata 3. within the vertebral canal B. Longitudinal Section 1. cervical enlargement (C4-T1): nerves of upper limbs arise here 2. lumbar enlargement (T9-T12): nerves of lower limbs arise here 3. conus medullaris: between L1 and L2, termination of SC 4. cauda equine: “horse tail” nerve axons that arise from the inferior SC and continue down vertebral canal before exiting

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5. filum terminale: extension of pia mater that anchors SC to coccyx 6. spinal tap done in L3/5 region to avoid damage to SC (to extract CSF or administer medications) C. Cross Section 1. Posterior (dorsal) median sulcus: narrow and deep 2. Anterior (ventral) median fissure: shallow and wide 3. Gray matter: “butterfly” shape in, composed of cell bodies, dendrites, and unmyelinated axons of motor and interneurons a. posterior (dorsal) horn: somatic and autonomic sensory nuclei (interneurons that relay sensory information) b. anterior (ventral) horn: cell bodies of somatic motor neurons and motor nuclei c. lateral horn: 1. only in thoracic, upper lumbar and sacral segments 2. cell bodies of autonomic motor neurons c. gray commissure: surrounds central canal 4. White matter: myelinated/unmyelinated axons of sensory, interneruons, and motor neurons a. posterior (dorsal) white column (funiculus) b. lateral white column (funiculus) c. anterior (ventral) white column (funiculus) d. anterior white commissure: between gray commissure and anterior median fissure e. tracts: distinct bundles of axons, having a common origin or destination and carrying similar types of information (found in all columns) 1. ascending (sensory): conduct impulses toward brain 2. descending (motor): conduct impulses down the SC

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3. most are named according to where their soma are and axons end: i.e. spinothalamic, cerebrospinal 5. Central canal a. surrounded by gray commissure b. runs the length of the SC c. continuous with the 4th ventricle d. filled with CSF IV. Spinal Nerves: (31 pairs) path of communication between SC and body A. Naming paired nerves: based on the vertebrae (intervertebral foamina) where they emerge 1. Cervical C1-C8: a. named for the vertebrae below point of emergence b. EXCEPT C8 (no C8 vertebrae) 2. Throacic T1-T12: named for the vertebrae above point of emergence 3. Lumbar L1-L5: named for the vertebrae above point of emergence 4. Sacral S1-S5: named for the vertebrae above point of emergence 5. Coccygeal Co1 B. Origin and Structure of Spinal Nerves and Related Structures 1. Roots a. dorsal (posterior) root 1. contains sensory axons 2. dorsal (posterior) root ganglia contain cell bodies of sensory neurons b. ventral (anterior) root: axons of motor neurons 2. Common spinal nerve a. where roots join and nerve leaves through intervertebral foramina

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b. mixed nerves (contain motor and sensory information) 3. Rami: branches a. dorsal (posterior) ramus: muscles and skin of dorsal surface of trunk b. ventral (anterior) ramus: muscles and skin of upper and lower limbs and the of lateral and ventral surfaces of trunk c. communicating rami: serve ANS d. sympathetic trunk ganglia: collections of cell bodies that serve the ANS 4. Plexus: networks of anterior rami (except thoracic region) a. cervical plexus (C1-C5): head, neck, diaphragm, superior shoulder and chest b. brachial plexus (C5-T1): shoulder and upper limbs c. lumbosacral plexus 1. lumbar plexus (L1-L4): abdominal wall, lower limb, external genitalia 2. sacral plexus (L4-S4): buttocks and lower limb d. intercostals nerves (T2-T12): 1. do not form plexus but innervate areas directly 2. abdominal region, intercostal region, skin of axilla, anterior and lateral chest walls 5. Connective tissue a. individual axons covered by endoneurium b. fascicles of axons covered by perineurium c. entire nerve covered by epineurium V. Reflex Arc 1. Reflex: fast, involuntary, unplanned sequence of actions that occur in response to a particular stimulus 2. Types of reflexes

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a. innate/acquired b. spinal/cranial c. somatic/autonomic 3. Components of a reflex arc a. stimulus b. receptor: responds to stimulus with graded potential- may reach threshold c. sensory neuron: transmits impulse from receptor to gray matter of SC or brain stem (dorsal root) d. integrating center: one or more regions of gray matter (dorsal horn) 1. monosynaptic: sensory neuron synapses directly with motor neuron 2. polysynaptic: one or more interneurons involved (more common) e. motor neuron: impulses carried from integration center to effector (ventral horn and ventral root) f. effector: part of body that responds (muscle or gland)

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