Chapter 13 – Spinal Cord and Spinal Nerves 1 Chapter 13 The Spinal Cord and Spinal Nerves 2 SECTION 13-1 The brain and spinal cord make up the central nervous system, and the cranial nerves and spinal nerves constitute the peripheral nervous system 3 Grouping of Neural Tissues (1 of 3) White matter • Myelinated (and unmyelinated) neuron processes • Schwann cells in PNS • Oligodendrocytes in CNS Gray matter • Nerve cell bodies and dendrites • Unmyelinated axons • Neuroglia (e.g. astrocytes) Nerve • Bundle of nerve fibers (axons) outside the CNS • Has associated CT layers
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Chapter 13 – Spinal Cord and Spinal Nerves!
1!
Chapter 13!The Spinal Cord and Spinal Nerves!
2!
SECTION 13-1 !The brain and spinal cord make up the central nervous system, and the cranial nerves and spinal nerves constitute the peripheral nervous system!
3!
Grouping of Neural Tissues (1 of 3)!White matter!• Myelinated (and unmyelinated) neuron processes!• Schwann cells in PNS!• Oligodendrocytes in CNS!
Dura mater = “tough mother”!• Not firmly attached to bone (as in cranium)!• Dense irregular CT!• Inner lining of simple squamous EPI!• Tubular portion runs from F. Magnum to S2!
Fuses to form coccygeal ligament (with filum terminale) that extends to coccyx!Fuses with CT coverings of spinal nerves!
Pia mater = “soft” or “delicate” mother!• Adheres to surface of brain and cord!• Delicate collagen and elastin fibers!• Highly vascular!• Runs to coccyx as filum terminale (with dura,
forms coccygeal ligament)!Denticulate (dentate) ligaments (Fig. 13-5)!• Formed from pia mater!• Extend through arachnoid to attach to dura!• Suspend cord within subarachnoid space!
Chapter 13 – Spinal Cord and Spinal Nerves!
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The Spinal Cord and Spinal Meninges!
Figure 13-3b!
Note orientation compared to that in Figure 13-5!
20!
SECTION 13-3 !Gray matter is the region of integration and command, and white matter carries information from place to place!
21!
Sectional Organization of Cord Figure 13-5b!
Note orientation compared to that in Figure 13-3!
Chapter 13 – Spinal Cord and Spinal Nerves!
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Internal Anatomy of the Cord!
• Ventral (anterior) median fissure !(A fissure is larger than a sulcus.)!
• Dorsal (posterior) median sulcus !(smaller than fissure)!
• Gray commissures!Commissure = crossing from one side of the
body to the other!Gray = gray matter!
• Central canal!Contains CSF!
23!
Gray Matter in the Cord see Figure 13-5a!
Nuclei - collections of cell bodies with a similar function!
Ventral (anterior) gray horns!• Somatic motor nuclei!• Efferent information to skeletal muscles!
Lateral gray horns!• Visceral (autonomic) motor nuclei!• Only in thoracic and lumbar segments!
Dorsal (posterior) gray horns (see slide #63)!• Sensory area!• Somatic and autonomic (visceral) nuclei!
24!
Sectional Organization of Cord Figure 13-5a!
Note interneurons in dorsal horns!
Chapter 13 – Spinal Cord and Spinal Nerves!
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White Matter – Columns and Tracts!
Columns:!• Large collections of fibers conveying
information to or from the brain!• Have similar origin and similar destinations!
Tracts:!• Collections of fibers within a column!• Carry same type of information in the same
direction to the same destination!
26!
Examples of Columns and Tracts!
Posterior columns!• Sensory (ascending)!
Spinothalamic tracts!• Sensory (ascending)!
Corticospinal tracts!• Motor (descending)!• Voluntary movements!
Vestibulospinal tracts!• Motor (descending)!• Automatic (involuntary) movements!
Note that the name usually tells you the direction of information
flow.!
27!
Sensory Columns and Tracts Figure 15-4!
Note organization and direction. Do not try to memorize locations.!
Posterior column pathway
Spinothalamic pathway
Chapter 13 – Spinal Cord and Spinal Nerves!
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Motor Columns and Tracts Figure 15-8!
Lateral corticospinal tract
Vestobulospinal tract
Anterior corticospinal tract
Note organization and direction. Do not try to memorize locations.!
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SECTION 13-4 !Spinal nerves form plexuses that are named according to their level of emergence from the vertebral canal!
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Spinal Nerves!
Spinal nerves are mixed nerves!• Contain both sensory and motor fibers!
Exist in 31 pairs!Exit vertebral canal via intervertebral foramina!• Named for where they exit vertebral column!
Cord stops at level of L2!• Nerves exiting below this level form the cauda
Ramus = “branch”; plural = rami!1. Dorsal ramus!• Information to and from skin, skeletal muscles
of back!• Somatic and visceral, both motor and sensory!
!2. Ventral ramus!• Information to and from ventrolateral body
surface, body wall and limbs!• Somatic and visceral, both motor and sensory!• Form plexuses or thoracic (intercostal) nerves!
Chapter 13 – Spinal Cord and Spinal Nerves!
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Nerve Roots and Rami modified from Fig. 13-3b!
Dorsal!
Ventral!
Dorsal root!Dorsal root
ganglion!
Ventral root! Denticulate ligament!
Sympathetic chain ganglion!
Ventral ramus!
Dorsal ramus!
Rami communicantes!
35!
Rami Communicantes (much more in Ch. 16)!
3. Rami communicantes!• Communicate between ventral rami and
sympathetic ganglia!• Visceral sensory and visceral motor!• Information to and from interoceptors, smooth
muscle, visceral organs, glands!3a. White ramus!
• Myelinated preganglionic fibers!3b. Gray ramus!
• Unmyelinated postganglionic fibers!Gray and white rami unite at sympathetic ganglia!
• Form sympathetic nerves!
36!
Thoracic nerves
Thoracic (Intercostal) Nerves!
• Formed by ventral rami of T2 - T12 spinal nerves!
• Go directly to innervated structures.!
• Most axons from these segments do NOT join plexuses!
Chapter 13 – Spinal Cord and Spinal Nerves!
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Distribution of Sensory Nerve Fibers Fig. 13-8a!
Exteroceptors in skin are:!• Ambient
temperature!• Pain!• Light touch,
pressure!
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Distribution of Motor Nerve Fibers Fig. 13-8b!
39!
Dermatomes Figure 13-7!
Dermatome = specific region of skin innervated by a single pair of spinal nerves.!!!Clinically important for diagnoses of specific neuropathies.!
Chapter 13 – Spinal Cord and Spinal Nerves!
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Nerve Plexuses!
Plexus = “network”!Formed from ventral rami !• T2 - T12 do not participate in plexuses!
Plexuses are formed by nerve fibers from different spinal nerves.“During development, small skeletal muscles
innervated by different ventral rami fuse to form larger muscles with compound origins. The anatomical distinctions between the component muscles may disappear, but separate ventral rami continue to control each part of the compound muscle.” p. 439!
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Peripheral Nerves and Nerve Plexuses!
Figure 13-9!
Cervical plexus!Brachial plexus!
Lumbar plexus!
Sacral plexus!
42!
Brachial Plexus – 1 Figure 13-11a!
Chapter 13 – Spinal Cord and Spinal Nerves!
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The Brachial Plexus – 2 See your copy of Netter!
Netter Plate 416
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Brachial Plexus – 3 Figure 13-11b!
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SECTION 13-5!Interneurons are organized into functional groups called neuronal pools!
Chapter 13 – Spinal Cord and Spinal Nerves!
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The Organization of Neuronal Pools!
Figure 13-13!
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SECTION 13-6 !Reflexes are rapid, automatic responses to stimuli!
2. Predictable!• Absence indicates damage to N.S.!
Chapter 13 – Spinal Cord and Spinal Nerves!
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Reflex Arc – 1!
Spinal cord is the integrating center.!Components of a Reflex Arc:!1. Sensory receptor!• Responds to stimulus!• Generates signal to be sent to integrator!
2. Sensory neuron!• Cell body in dorsal root ganglion!• Carries info to integrating center!• Info enters via dorsal root!
50!
Reflex Arc – 2!
3. Integrating center = spinal cord!• Usually involves interneurons!
Polysynaptic reflex (most reflexes)!• May not involve interneurons!
Monosynaptic reflex!4. Motor neuron!
• Transmits impulses to muscle or gland!5. Effector!
Characteristics – responds to PAIN1. Polysynaptic!2. Ipsilateral!3. Intersegmental!
• Synapses occur within multiple cord segments!
• Activates several muscle groups!(i.e. stimulates more than one effector)!
4. Reciprocal innervation!(i.e. flexors and extensors)!
62!
Flexor Reflex – a.k.a. Withdrawal Reflex – 2!
Mechanism:!1. Stimulate pain-sensitive sensory neuron!2. Message sent to cord!3. Activate interneurons!4. Relay to several segments!5. Several flexors activated, extensors inhibited!