Chapter 14 Lecture Outline See separate PowerPoint slides for all figures and tables pre- inserted into PowerPoint without notes. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1 14.1 Spinal Cord Gross Anatomy • Spinal cord – Extends inferiorly from brain’s medulla through vertebral canal – Ends at L1 vertebra with conus medullaris and below extend inferiorly as cauda equina – Two widened regions with greater number of neurons o Cervical enlargement: contains neurons innervating upper limbs o Lumbar enlargement: contains neurons innervating lower limbs 2 14.1 Spinal Cord Gross Anatomy • Spinal cord subdivided into five parts from top to bottom – Cervical part (superiormost part) o 8 pairs of cervical spinal nerves – Thoracic part o 12 pairs of thoracic spinal nerves – Lumbar part o 5 pairs of lumbar spinal nerves – Sacral part o 5 pairs of sacral spinal nerves – Coccygeal part (inferior tip of spinal cord) o 1 pair of coccygeal spinal nerves 3 Gross Anatomy of the Spinal Cord and Spinal Nerves Figure 14.1a, c 4 14.1 Spinal Cord Gross Anatomy • Spinal cord parts do not align with vertebrae names – Vertebrae growth continues after spinal cord growth complete – Rootlets from parts L2 and below extend inferiorly as cauda equina o Filum terminale: thin strand of pia attaching conus medullaris to coccyx • Spinal nerves are named for attached spinal cord part – Superiormost spinal nerve is C1 nerve – Inferiormost spinal nerve is Co1 nerve 5 14.2 Protection and Support of the Spinal Cord • Spinal cord meninges – Pia mater: delicate layer adhering to spinal cord o Made of elastic and collagen fibers o Denticulate ligaments: lateral extensions of pia; help suspend spinal cord o Filum terminale: pia anchoring inferior end of spinal cord to coccyx – Arachnoid mater: web-like layer, external to pia o Arachnoid trabeculae: fibrous extensions of the membrane o Subarachnoid space: area deep to arachnoid through which CSF flows – Dura mater: tough, outermost layer o One layer of dense irregular connective tissue that stabilizes spinal cord o Subdural space is between dura and arachnoid o Epidural space is between dura and vertebra – Houses adipose, areolar connective tissue, blood vessels 6 Spinal Meninges and Structure of the Spinal Cord Figure 14.3a 7 Spinal Meninges and Structure of the Spinal Cord Figure 14.3b 8 Clinical View: Lumbar Puncture • Procedure for obtaining CSF for medical diagnosis • Needle passes through – Skin, back muscles, ligamentum flavum – Epidural space, dura mater – Arachnoid mater into subarachnoid space • Adult spinal cord ends at L1 – Lumbar puncture below this, just above or below L4 – Spinous process of L4 at highest points of iliac crests 9 14.3a Distribution of Gray Matter • Gray matter – Made of neuron’s cell bodies, dendrites, and unmyelinated axons; also glial cells • Masses of grey matter project from center of spinal cord – Anterior horns house cell bodies of somatic motor neurons – Lateral horns house cell bodies of autonomic motor neurons o Only present in parts T1–L2 – Posterior horns house axons of sensory neurons and cell bodies of interneurons 10 14.3a Distribution of Gray Matter • Gray commissure – Horizontal band of gray matter surrounding central canal – Contains unmyelinated axons connecting left and right gray matter • Nuclei: groups of cell bodies – Sensory nuclei in posterior horn contain interneurons o Somatic sensory nuclei receive signals from skin, muscle, joints o Visceral sensory nuclei receive signals from blood vessels, viscera – Motor nuclei in anterior and lateral horns contain motor neurons o Somatic motor nuclei (anterior) innervate skeletal muscle o Autonomic motor nuclei (lateral) innervate smooth muscle, heart, glands 11 Neuron Pathways and Nuclei Locations Figure 14.5 12 14.3b Distribution of White Matter • White matter: myelinated axons to and from the brain • Regions of white matter – Posterior funiculus o Sits between posterior gray horns and posterior median sulcus o Contains sensory tracts (axon bundles called fasciculi) – Lateral funiculus o Sits on lateral sides of spinal cord o Contains ascending (sensory) and descending (motor) tracts – Anterior funiculus o Sits between anterior gray horns and anterior median fissure o Left and right anterior funiculi are interconnected by white commissure o Contains ascending (sensory) and descending (motor) tracts 13 Clinical View: Treating Spinal Cord Injuries • May leave individuals paralyzed and unable to perceive sensations • Prompt use of steroids after injury – May preserve muscle function • Early antibiotics – Have reduced number of deaths due to pulmonary and urinary infections • Neural stem cells – May be used in future to regenerate CNS axons 14 14.4a Overview of Conduction Pathways • Spinal pathways are sensory or motor – Sensory pathways ascend toward brain – Motor pathways descend from brain • Common pathway characteristics – Cell locations: axons are in spinal cord tracts; cell bodies are in ganglia, spinal cord gray horns, and brain gray matter – Each pathway is made of a chain of two or more neurons – Pathways are paired: there is a left and a right tract – Most pathways decussate: axons cross midline so brain processes information for contralateral side o Uncrossed pathways work on the ipsilateral side of body 15 14.4b Sensory Pathways • Sensory (ascending) pathways – Signals for proprioception, touch, temperature, pressure, pain – Somatosensory pathways carry signals from skin, muscles, joints – Viscerosensory pathways carry signals from viscera – Use a series of neurons to relay signal to brain o Primary (1st order) neuron has peripheral ending, cell body in posterior root ganglion, and axon leading to secondary neuron o Secondary (2nd order) neuron is an interneuron; receives primary input and extends to tertiary neuron or to cerebellum o Tertiary (3rd order) neuron is an interneuron; receives secondary neuron input and extends to somatosensory cortex of parietal lobe of cerebrum 16 14.4b Sensory Pathways • Posterior funiculus–medial lemniscal pathway – Signals about proprioception, touch, pressure, and vibration with a three neuron chain – Primary neuron relays signal from skin to brainstem o Peripheral receptor has axon in spinal nerve, posterior root, spinal cord o Within the cord, axon is in the posterior funiculus o In the medulla the axon contacts a secondary neuron – Secondary neuron relays signal from medulla to thalamus o Cell body in either nucleus cuneatus or nucleus gracilis of medulla o Axon decussates and joins medial lemniscus o In thalamus, the axon contacts a tertiary neuron – Tertiary neuron relays signal to primary somatosensory cortex (postcentral gyrus) 17 Posterior Funiculus– Medial Lemniscal Pathway Figure 14.7 18 14.4b Sensory Pathways • Anterolateral spinothalamic pathway – Signals related to crude touch, pressure, pain, and temperature with a three-neuron chain – Primary neuron relays signal from skin to spinal cord o Axon is in spinal nerve and posterior root o Axon contacts secondary neuron in spinal cord’s posterior horn – Secondary neuron relays signal from spinal cord to thalamus o Axon decussates and ascends in contralateral white matter (either the anterior spinothalamic tract or the lateral spinothalamic tract) o Axon contacts tertiary neuron in thalamus – Tertiary neuron relays signal from thalamus to cerebral cortex o Axon contacts target neuron in appropriate part of primary somatosensory cortex 19 Anterolateral Pathway Figure 14.8 20 14.4b Sensory Pathways • Spinocerebellar pathway – Signals about proprioception with a two-neuron chain – Primary neuron relays signal from skin to spinal cord o Axon is in spinal nerve and posterior root o Axon contacts secondary neuron in spinal cord’s posterior horn – Secondary neuron relays signal from spinal cord to cerebellum o Some secondary neuron axons cross, while others remain ipsilateral o Axon ascends in either the anterior spinocerebellar tract or posterior spinocerebellar tract o Axon contacts cell within the cerebellum 21 Spinocerebellar Pathway Figure 14.9 22 Sensory Pathways in the Spinal Cord Figure 14.6 23 14.4c Motor Pathways • Motor (descending) pathways – Control effectors such as skeletal muscles – Start in brain and include at least two neurons o Upper motor neuron in motor cortex, cerebral nucleus or brainstem nucleus; contacts lower motor neuron o Lower motor neuron in cranial nerve nucleus or spinal cord anterior horn; Figure 14.10 excites muscle 24 14.4c Motor Pathways • Direct (pyramidal) pathway – Begins with upper motor neurons in primary motor cortex – Axons end in brainstem (corticobulbar tracts) or spinal cord (corticospinal tracts) – Corticobulbar tracts o Axons extending to brainstem where they synapse with lower motor neurons in cranial nerve nuclei – Corticospinal tracts o Synapse on lower motor neurons in anterior horn o Lateral corticospinal tracts – Lower motor neurons innervate limb muscles for skilled movements o Anterior corticospinal tracts – Lower motor neurons innervate axial skeletal muscle 25 Corticospinal Tracts Figure 14.11 26 14.4c Motor Pathways • Indirect pathway – Upper motor neurons originate in brainstem nuclei – Rubrospinal tracts originating in midbrain (red nucleus) o Regulates precise movement and tone in flexor limb muscles – Reticulospinal tracts from reticular formation o Help control reflexes related to posture and balance – Tectospinal tracts from superior and inferior colliculi o Regulate reflexive orienting responses to visual and auditory