<p>Chapters 13 & 16: Spinal Cord; Sensory and Motor Pathways </p><p>Chapter Objectives</p><p>SPINAL CORD ANATOMY</p><p>1. Describe the external features of the spinal cord and the Cauda equina. Discuss its relative length within the vertebral column. 2. Describe the characteristics and purpose of the three layers and spaces of the meningeal structures. 3. Match each horn of gray matter with the type of cell body it contains. 4. Match each column of white matter and the type of tracts it contains. 5. Describe where sensory information enters the spinal cord and where motor information leaves the spinal cord. SPINAL NERVES 6. Define a nerve and discuss the connective tissue layers that surround and protect nerves. 7. Discuss the naming and numbering of spinal nerves, the arrangement of spinal nerves relative to the vertebrae, and the attachment of the spinal nerves to the spinal cord. 8. Discuss the branching of the spinal nerves once they emerge from the vertebral column. 9. Define a plexus; then list the names of major nerves of the cervical, brachial, lumbar, and sacral plexuses. 10. Define a dermatome. SOMATIC SENSATIONS 11. Identify the sensations and the receptors involved. 12. Describe the types of receptors in terms of microscopic features, location, and stimulus type. SOMATIC SENSORY PATHWAYS 13. Discuss the location of first order, second order and third order neuons. 14. Discuss the functions of the anterolateral pathway and where its ascending tracts are located. 15. Discuss the functions of the posterior column-medial lemniscus pathway and where its ascending tracts are located. 16. Discuss the functions of the cerebellar pathway and where its ascending tracts are located. SOMATIC MOTOR PATHWAYS 17. List the neural circuits that are part of the somatic motor pathways. 18. Describe the origin and destination for the descending, motor tracts. REFLEXES AND REFLEX ARC 19. Define a reflex. 20. Describe the components of a reflex arc and their specific functions.</p><p>Chapter Lecture Notes</p><p>Spinal Cord</p><p>Spinal cord - extends from foramen magnum to the level of the second lumbar vertebra (Fig </p><p>13.2)</p><p>Shorter than vertebral column because vertebral column grows faster than spinal cord</p><p>Cauda equina - nerves from lower cord don't leave vertebral column immediately, but instead</p><p> look like coarse hairs of a horse tail</p><p>Has grooves on surface – anterior median fissure and posterior median sulcus</p><p>Central canal – passageway for cerebrospinal fluid; flows from ventricles in brain (Fig 13.3)</p><p>Lined with ependymal cells that help circulate cerebrospinal fluid</p><p>The spinal cord is surrounded by meninges (Fig 13.1)</p><p>Dura mater – outermost layer which is single layered and not attached to the bony vertebrae</p><p> epidural space – space between dura mater and vertebrae</p><p> filled with adipose and blood vessels</p><p>Arachnoid mater – middle layer inside of dura mater</p><p>Pia mater – innermost layer bound very tightly to surface of spinal cord</p><p>Subarachnoid space – space between arachnoid mater and pia mater</p><p> contains cerebrospinal fluid</p><p> lumbar puncture – into subarachnoid space between L3 and L4 or L4 and L5 for </p><p> cerebrospinal fluid diagnosis or to introduce anesthetics</p><p>Gray Matter of the Spinal Cord</p><p>Gray matter (cell bodies and dendrites) - organized into horns and commissures Posterior (dorsal) gray horn - contains cell bodies of interneurons which have synapsed with </p><p> sensory neurons (Fig 13.3 & 13.4)</p><p>Lateral gray horn - contains cell bodies of neurons from autonomic nervous system</p><p>Anterior (ventral) gray horn - contains cell bodies of motor neurons </p><p>Anterior gray commissure - gray communication between right and left section of cord </p><p> anterior to the central canal</p><p>Posterior gray commissure - gray communication between right and left section of cord </p><p> posterior to the central canal</p><p>White Matter of the Spinal Cord</p><p>White matter (myelinated axons) - organized into columns and commissures (tracts travel in </p><p> columns) (Fig 13.3 & 13.12)</p><p>Posterior white column - has ascending tracts only</p><p>Lateral white column - has both ascending and descending tracts</p><p>Anterior white column - has both ascending and descending tracts</p><p>Anterior white commissure</p><p>Posterior white commissure</p><p>Nerves</p><p>Nerves – bundles of axons in the PNS (Fig 13.5)</p><p>Surrounded by connective tissue</p><p>Epineurium – around whole nerve</p><p>Perineurium – around a fascicle of nerve fibers</p><p>Endoneurium – around a single axon</p><p>Mixed nerves – contain both afferent and efferent neurons</p><p>Ganglia – cell bodies of neurons in the PNS</p><p>Spinal Nerves Spinal nerve - has bundles of axons of both motor and sensory neurons, therefore it is a mixed </p><p> nerve</p><p>The anterior root and the posterior root combine to form the spinal nerve </p><p>Posterior (dorsal) root - connection to spinal cord from the peripheral nervous system that</p><p> carries only sensory information and ends at the posterior gray horn</p><p>Posterior (dorsal) root ganglia - cell bodies of sensory neurons (unipolar neurons)</p><p>Anterior (ventral) root - connection from the spinal cord to the peripheral nervous system </p><p> that carries only motor information</p><p>Motor neurons = multipolar neurons</p><p>Exits from vertebral column at the intervertebral foramen</p><p>31 pairs of spinal nerves (Fig 13.2)</p><p>8 cervical</p><p>12 thoracic</p><p>5 lumbar</p><p>5 sacral</p><p>1 coccygeal each has 3 branches (rami) (Fig 13.6)</p><p>Visceral (Rami communicantes, part of autonomic nervous system)</p><p>Posterior (dorsal)</p><p>Anterior (ventral) branch (anterior rami) divides into plexus (braids) except thoracic (T1 and </p><p> possibly T2 exception)</p><p>Cervical plexus (C1-C5) - Phrenic nerve (phren = diaphragm) (Fig 13.7)</p><p>Brachial plexus (C5-C8, T1) (Fig 13.8)</p><p>Radial </p><p>Ulnar </p><p>Median nerve Median nerve is compressed in carpal tunnel syndrome causing numbness, </p><p> tingling, and pain in the palm and fingers</p><p>Lumbar plexus - (L1-L4) femoral nerve (Fig 13.9)</p><p>Sacral plexus - (L4-S4) sciatic nerve (Fig 13.10)</p><p>Dermatomes</p><p>Dermatomes - letter and numbers indicating spinal nerve innervating a given region of skin (area</p><p> of the skin that supplies sensory input to the dorsal roots of one pair of spinal nerves) (Fig</p><p>13.11)</p><p>Sensations</p><p>Crude touch – can tell something has contacted skin but where and what can’t be determined</p><p>Fine touch – can tell where and what has contacted skin</p><p>Meissner’s corpuscles</p><p>Pressure – deformation of deeper tissues felt over larger area than touch</p><p>Pacinian corpuscles</p><p>Vibration</p><p>Itch</p><p>Tickle</p><p>Thermal sensations – warm and cold</p><p>Pain – nociceptors</p><p>Proprioceptive</p><p>Sensory Receptors Classified by Microscopic Features </p><p>Free (unencapsulated) nerve endings (Fig 16.1 & Table 16.1)</p><p>Bare dendrites associated with pain, thermal, tickle, itch, and some touch sensations</p><p>First-order neurons – conduct impulses from the PNS into the CNS</p><p>Encapsulated nerve endings</p><p>Dendrites enclosed in a connective tissue capsule Meissner’s corpuscle or Pacinian corpuscle</p><p>First-order neuron</p><p>Receptor cell synapses with first-order neuron</p><p>Photoreceptors of the eye</p><p>Inner ear hair cells</p><p>Taste buds of the tongue</p><p>Sensory Receptors Classified by Location and Activating Stimuli</p><p>Exteroceptors – located near or at the external surface of the body</p><p>Hearing, vision, smell, taste, touch, pressure, vibration, temperature, and pain</p><p>Interoceptors – located in blood vessels, visceral organs and nervous system</p><p>Proprioceptors – located in muscles, tendons, joints, and inner ear</p><p>Body position, muscle length and tension, and the position and movement of joints</p><p>Sensory Receptors Classified by Stimulus Detected</p><p>Mechanoreceptors – mechanical pressure</p><p>Touch, pressure, vibration, proprioception, hearing and equilibrium, and stretch of blood </p><p> vessels and internal organs</p><p>Thermoreceptors – changes in temperature</p><p>Nociceptors – physical or chemical damage to tissues</p><p>Photoreceptors – light detection in retina</p><p>Chemoreceptors – taste and smell</p><p>Osmoreceptors – osmotic pressure of body fluids</p><p>Somatic Sensory Pathways</p><p>Ascending pathways</p><p>Neuronal composition</p><p>First-order neurons – body to spinal cord</p><p>Second-order neurons – spinal cord and brain stem to thalamus Third-order neurons – thalamus to primary somatosensory of cerebral cortex </p><p>Pathways</p><p>Anteriolateral – pain, thermal, tickle, itch, crude touch, and pressure (Fig 16.6)</p><p>Uses spinothalamic tracts</p><p>Posterior column-medial lemniscus (lemniscus = ribbon) (Fig 16.5)</p><p>Uses spinothalamic and spinoreticular tracts</p><p> fine touch, stereognosis (recognize objects by touch) proprioception, and vibratory </p><p> sensations</p><p>Cerebellar – posture, balance, and coordination of skilled movements (Table 16.3 & </p><p>16.12) </p><p>Uses spinocerebellar tracts</p><p>Somatic Motor Pathways</p><p>Upper motor neurons – located in cerebral cortex (Fig 16.9)</p><p>Basal ganglia neurons</p><p>Cerebellar neurons (Fig 16.12)</p><p>Local circuit neurons – interneurons synapse on lower motor neurons in brain stem and spinal </p><p> cord – coordination of rhythmic activity</p><p>Descending tracts (Table 16.4 & Fig 16.10)</p><p>Corticospinal – cerebral cortex to spinal cord (crosses in decussation of pyramids)</p><p>Rubrospinal – red nucleus to spinal cord</p><p>Reticulospinal – reticular formation to spinal cord</p><p>Tectospinal – Corpora quadragemini to spinal cord</p><p>Reflexes</p><p>Reflex - quick involuntary response to an internal or external stimulus (results in either somatic </p><p> or visceral reflex) </p><p>Parts (Fig 13.13 – 13.17) Receptor</p><p>Sensory neuron</p><p>CNS – integration center</p><p>Motor neuron</p><p>Effector - muscle or gland that responds to motor neuron impulse</p>