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Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes
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Outline Introductions Syllabus, Textbooks, etc.
Gross anatomy of sensory and motor systems Reflex anatomy and physiology Case of autonomic regulation (handout to be used throughout term)
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Next Time: Chapters 13 and 14
Prepare to answer the following questions: How are somatic reflexes and autonomic reflexes different? How are they similar? What is the connection between cranial nerves and reflexes? …between spinal nerves and reflexes?
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Biology 232 Human Anatomy and Physiology II
Dieterich Steinmetz (503) Web: Lab:
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Separation of Structure and Function
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General Organization of the Nervous System
Highly organized, very efficient Figure 13–1
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Motor-Sensory Strip of the Cerebral Cortex
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Quick Questions What is the somatic nervous system?
What is the autonomic nervous system? Examples: What are receptor molecules? What are ligands?
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Quick Answers What is the somatic nervous system?
Voluntarily controllable (eg., skeletal muscle control) What is the autonomic nervous system? Sympathetic ANS fight/flight Parasympathetic ANS rest/repose (or rest/digest) What are receptor molecules? Examples: adrenoceptors (alpha1, alpha2, beta1, or beta2), cholinergic receptors (muscarinic or nicotinic) What are ligands? Examples: catecholamines (adrenaline, noradrenaline), ACh, muscarine, nicotine
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Case of the Woman with HT
Name the two parts of the ANS Describe the two major groups of receptors and their subtypes (and their usual ligands.) Distinguish between receptor stimulation and cell stimulation. Explain what “specificity” means when we are referring to a ligand’s specificity for receptors. Provide a background for studying examples of somatic and autonomic reflexes.
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Specialization of the Human Nervous System
The CNS is not homogenous. Review Gray matter and white matter CNS vs. PNS Brain vs. Spinal Cord Cranial Nerves vs. Spinal Nerves
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Motor-Sensory Strip of the Cerebral Cortex
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Motor-Sensory Strip
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Somatosensory Map of Postcentral Gyrus
Relative sizes of cortical areas proportional to number of sensory receptors proportional to the sensitivity of each part of the body Can be modified with learning
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Primary Motor Cortex The precentral gyrus initiates voluntary movement. Cells are called upper motor neurons. Muscles are represented unequally (according to the number of motor units)
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A Somatic Reflex Figure 13–14
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Sectional Anatomy of the Spinal Cord
Figure 13–5a
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Peripheral Distribution of Spinal Nerves
Sensory fibers Figure 13–7b
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5 Steps in a Neural Reflex
Figure 13–14
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Video of Human Nervous System
Meninges Gross brain 12 cranial nerves ….. Don’t fall asleep! Gross spinal cord Examples spinal nerves
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What are the basic structural and organizational characteristics of the nervous system?
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General Organization of the Nervous System
Highly organized, very efficient Figure 13–1
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In lab this week: Spinal Reflexes
Rapid, automatic, predictable response triggered to a specific stimulus Controlled by spinal cord alone; not the brain
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What are the structures and functions of the spinal cord?
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Spinal Cord: Gross Anatomy
Note variations in cross sections. Figure 13-2
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Spinal Cord Protection
the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.
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1. dura 2. arachnoid (transparent) 3. cerebral veins in subarachnoid space, over pia matter
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Spinal Cord Enlarged
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Coverings of the Spinal Cord
Three “meninges”: Dura Mater Arachnoid Mater Ce re bro spi nal Flu id Pia Mater spinal cord (or brain)
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The Adult Spinal Cord About 18 inches (45 cm) long
1/2 inch (14 mm) wide Ends between vertebrae L1 and L2
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Bilateral Symmetry Grooves divide the spinal cord into left and right
Posterior median sulcus: on posterior side Anterior median fissure: deeper groove on anterior side
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Enlargements of the Spinal Cord
Caused by: amount of gray matter in segment involvement with sensory and motor nerves of limbs Cervical enlargement: nerves of shoulders and upper limbs Lumbar enlargement: nerves of pelvis and lower limbs
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Spinal Cord Cervical Enlargement Conus Medularis Cauda Equina
pia matter Filum Terminale
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The Distal End Conus medullaris: Filum terminale: Cauda equina:
thin, conical spinal cord below lumbar enlargement Filum terminale: thin thread of fibrous tissue at end of conus medullaris Cauda equina: nerve roots extending below conus medullaris
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31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Relationships of segments to vertebrae change with age because spine grows longer than spinal cord.
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Naming Spinal Nerves Superior SEVEN spinal nerves: All other nerves:
are named for #___ inferior vertebra All other nerves: are named for superior vertebra Where is spinal nerve C8? ________
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Roots 2 branches of spinal nerves: Dorsal root ganglia: ventral root:
contains axons of motor neurons dorsal root: contains axons of sensory neurons Dorsal root ganglia: contain cell bodies of sensory neurons
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White Matter of the Spinal Cord
Dorsal Ventral Anterior median “fissure” is clearer than the Posterior median “sulcus”
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The Spinal Nerve Each side of spine: dorsal and ventral roots join
to form a “mixed” spinal nerve
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Mixed Nerves Carry both afferent (sensory) and efferent (motor) fibers
Spinal nerves are mixed nerves
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What are the structures and functions of the three meningeal layers that surround the central nervous system?
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The Meninges Specialized membranes isolate spinal cord from surroundings Spinal meninges: protect spinal cord carry blood supply continuous with cranial meninges Meningitis: viral or bacterial infection of meninges
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Spinal Meninges Figure 13–3
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The 3 Meningeal Layers Dura mater: Arachnoid mater: Pia mater:
outer layer of spinal cord Arachnoid mater: middle meningeal layer Pia mater: inner meningeal layer
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The Spinal Dura Mater Are tough and fibrous Cranially: Caudally:
fuses with periosteum of occipital bone is continuous with cranial dura mater Caudally: tapers to dense cord of collagen fibers joins filum terminale in coccygeal ligament
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The Epidural Space Between spinal dura mater and walls of vertebral canal Contains loose connective and adipose tissue Anesthetic injection site
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The Arachnoid Mater Middle meningeal layer Arachnoid membrane:
simple squamous epithelia covers arachnoid mater
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Inter-Layer Spaces Subdural space: Subarachnoid space:
between arachnoid mater and dura mater Subarachnoid space: between arachnoid mater and pia mater contains collagen/elastin fiber network (arachnoid trabeculae attach to arachnoid membrane of arachnoid mater) filled with cerebrospinal fluid (CSF)
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Cerebrospinal Fluid (CSF)
Is found in subarachnoid space Carries dissolved gases, nutrients, and wastes Spinal tap: withdraws CSF
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The Pia Mater Is the innermost meningeal layer
Is a mesh of collagen and elastic fibers Is bound to underlying neural tissue
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Structures of the Spinal Cord
Paired denticulate ligaments (image): extend from pia mater to dura mater stabilize side-to-side movement Blood vessels: along surface of spinal pia mater within subarachnoid space
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The Spinal Cord Figure 13–4
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Gray Matter The amount of ventral gray matter at a given level of the spinal cord is proportional to the amount of skeletal muscle innervated.
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Gray Matter of the Spinal Cord
Note: colors in reverse due to staining of tissue (common stains)
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What are the roles of white matter and gray matter in processing and relaying sensory information and motor commands?
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Sectional Anatomy of the Spinal Cord
Figure 13–5a
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Back Front
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Dorsal Roots (Sensory)
Spinal Cord Ventral Roots (Motor) Dorsal Roots (Sensory) Spinal Nerve (this is where sensory and motor mix) Dorsal Ramus (mixed) Ventral Ramus (mixed) Rami communicantes (mixed) Nerve Plexuses Sympathetic ganglia
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Sectional Anatomy of the Spinal Cord
Figure 13–5b
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White Matter Is superficial Contains myelinated and unmyelinated axons
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Gray Matter Surrounds central canal of spinal cord
Contains neuron cell bodies, neuroglia, unmyelinated axons Has projections (gray horns)
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The Gray Horns Posterior gray horns: Anterior gray horns:
contain somatic and visceral sensory nuclei Anterior gray horns: contain somatic motor nuclei Lateral gray horns: are in thoracic and lumbar segments contain visceral motor nuclei
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Gray Commissures Axons that cross from one side of cord to the other before reaching gray matter
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Nuclei Nuclei: Sensory nuclei: Motor nuclei:
functional groups of cell bodies Sensory nuclei: dorsal (posterior) connect to peripheral receptors Motor nuclei: ventral (anterior) connect to peripheral effectors
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Posterior White Columns
Lie between posterior gray horns and posterior median sulcus
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Anterior White Columns
Lie between anterior gray horns and anterior median fissure
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Anterior White Commissure
Area where axons cross from 1 side of spinal cord to the other
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Lateral White Columns Located on each side of spinal cord
Between anterior and posterior columns
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Tracts Tracts or fasciculi: Ascending tracts: Descending tracts:
in white columns bundles of axons relay same information in same direction Ascending tracts: carry information to brain Descending tracts: carry motor commands to spinal cord
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Descending Motor Tracts
Corticospinal (Pyramidal) Tract: Carry motor signals from the primary motor cortex of the brain to the skeletal muscles of the body
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Descending Motor Tracts
Medial Pathways (vestibulospinal, tectospinal, reticulospinal): muscle tone and gross movements of the neck, trunk and proximal limb muscles Lateral Pathway (rubrospinal tract): muscle tone and precise movements of the distal parts of the limbs.
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Ascending Sensory Tracts
Anterior Spinothalamic Tract: crude touch and pressure sensations from the body to the thalamus Lateral Spinothalamic Tract: pain and temperature sensations from the body to the thalamus
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Ascending Sensory Tracts
Posterior columns (gracile fasciculus and cuneate fasciculus) fine touch, vibration, pressure and proprioception from the body to the thalamus
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KEY CONCEPT (1 of 3) Spinal cord has a narrow central canal
surrounded by gray matter containing sensory and motor nuclei Sensory nuclei are dorsal Motor nuclei are ventral
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KEY CONCEPT (2 of 3) Gray matter: White matter:
is covered by a thick layer of white matter White matter: consists of ascending and descending axons organized in columns containing axon bundles with specific functions
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KEY CONCEPT (3 of 3) Spinal cord is so highly organized:
it is possible to predict results of injuries to specific areas More on this later…
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continues with part 2
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