BIOL1191 > Chapter 13 - Spinal Cord & Spinal Nerves > Flashcards

Chapter 13 - Spinal Cord & Spinal Nerves Flashcards

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1
Q

Spinal Cord

A
  • 2 Main Functions: Conduction pathway & reflex center
  • Located within vertebral canal
  • 3 Main Protections: Vertebral column, 3 meninges, cerebrospinal fluid
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2
Q

3 Meninges

A
  1. Dura Mater
  2. Arachnoid Mater
  3. Pia Mater
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3
Q

Denticulate Ligaments

A
  • Supports/protects/centers spinal cord within subarachnoid space
  • Located between anterior & posterior roots of spinal nerves
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4
Q

Cerebrospinal Fluid

A
  • Made by choroid plexuses & secreted by ependymal cells of brain ventricles
  • Circulates in brain ventricles, connecting channels, subarachnoid space & central canal of spinal cord
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5
Q

3 Spaces Between Meninges

A
  1. Epidural: Between Dura & bone
  2. Subdural: Under Dura
  3. Subarachnoid: Between Pia & Arachnoid
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6
Q

Lumbar Puncture

A
  • Insertion of a needle between L3-L4 or L4-L5
  • Used for extraction of CSF/injection of anesthesia
  • Supracristal line identifies L4
  • AKA “Spinal Tap”
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7
Q

External Anatomy of Spinal Cord

A
  • Extends from foramen magnum to the space between vertebrae L1 & L2
  • Conus Medullaris = Tapered end
  • Filum Terminale = Anchoring cord
  • Cauda Equina = Spinal nerve roots
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8
Q

31 Spinal Nerve Pairs (Typing)

A
  • 8 Cervical
  • 12 Thoracic
  • 5 Lumbar
  • 5 Sacral
  • 1 Coccygeal
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9
Q

2 Enlarged Areas of the Spinal Cord

A
  1. Cervical (C4 - T1) = Upper Limbs

2. Lumbar (T9 - T12 L1 & Cauda Equina) = Lower Limbs

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10
Q

Posterior Median Sulcus

A

Divides the posterior side of the spinal cord

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11
Q

Anterior Median Fissure

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Divides the anterior side of the spinal cord

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12
Q

Gray Matter of Spinal Cord

A
  • Contains sensory axon terminals, interneurons, and motor neurons (all unmyelinated)
  • Also contains neuroglia
  • Integrating center for spinal reflexes
  • Is “H-shaped”
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13
Q

Gray Commissure

A

Cross-bar of the gray matter

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14
Q

Central Canal

A
  • Extends the length of spinal cord
  • Continuous w/ 4th ventricle
  • Contains CSF
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15
Q

Sensory Nuclei

A

Cell bodies of interneurons within gray matter

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16
Q

Motor Nuclei

A

Cell bodies of motor neurons within gray matter

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17
Q

3 Types of Gray Horns

A
  1. Anterior Gray Horn: Contains somatic motor neurons (connects to skeletal muscle)
  2. Lateral Gray Horn: Contains visceral motor neurons (connects to visceral smooth muscle)
  3. Posterior Gray Horn: Contains interneurons (connects to incoming sensory axons)
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18
Q

2 Spinal Nerve Roots on Each Side (Gray Matter)

A
  1. Anterior Root & Rootlets

2. Posterior Root & Rootlets

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19
Q

Anterior Root & Rootlets

A
  • Contains axons of lateral & anterior horn motor neurons
  • Motor fibers exit cord via anterior roots
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20
Q

Posterior Root & Rootlets

A
  • Contains axons of sensory neurons & posterior root ganglion
  • Sensory fibers enter cord via posterior roots
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21
Q

Spinal Nerve

A

Combination of both anterior root & posterior root

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22
Q

Spinal Nerve Root Damage

A
  • Most common cause: Spinal disc herniation

- Effects: Loss of sensation, muscle coordination + pain

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23
Q

White Matter of Spinal Cord

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A
  • Contains tracts (Bundles of myelinated axons of motor & sensory neurons)
  • Anterior white commissure = found right in front of the gray commissure
  • 3 White columns: Posterior, Lateral & Anterior (Each representing a sensory or motor fiber tract)
24
Q

5 Generalizations About Spinal Tracts

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A
  1. Multi-neuron pathways between brain & periphery
    - Pyramidal Tract = CNS->UMN->LMN->Skeletal Muscle
    - Spinothalamic Tract = Periphery->Neurons->CNS
  2. Axons w/ similar destinations & functions
  3. Purely motor tracts OR purely sensory tracts
  4. Come in pairs
  5. Most decussate/cross over
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2 Main Spinal Cord Functions
1. Information transmission (Via sensory & motor white matter tracts) 2. Information integration (Reflexes & reflex arcs)
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3 Main Sensory Tracts
1. Spinothalamic Tract: Located in the anterior & lateral white columns 2. Posterior White Column Sensory Tracts (Gracile & Cuneate): Located in the posterior white column 3. Anterior & Posterior Spinocerebellar Tracts: Located in the lateral white column
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2 Types of Motor Tracts
1. Direct Motor Pathways | 2. Indirect Motor Pathways
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Direct Motor Pathways
- 2-neuron Pathways: Upper motor neuron (UMN) & Lower motor neuron (LMN); the starting points of the pathways - Anterior & Lateral Corticospinal Tracts: Located in the Anterior & Lateral White Columns
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Indirect Motor Pathways
- UMN arises from motor nuclei in brainstem - Rubrospinal & Vestibulospinal Tracts: Located in the Lateral White Column - Tectospinal Tract: Located in the Anterior White Column - Lateral & Medial Reticulospinal Tracts: Located in the Lateral & Medial White Columns
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Neural Reflex
- Automatic motor response by nervous system to changes in external/internal environment in order to preserve homeostasis - Examples: Somatic reflexes (withdrawal reflex) & Autonomic reflexes (heartbeat regulation)
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5 Components of a Neural Reflex Arc
1. Stimulus activates receptor (specialized cell/tissue that monitors internal/external environment) 2. Receptor activates sensory neuron 3. Integrating center (CNS info processing site; can be monosynaptic or polysynaptic) 4. Integrating center activates motor neurons 5. One ore more effectors respond
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6 Classifications of Reflexes & Reflex Arcs
1. Spinal Reflexes 2. Cranial Reflexes 3. Somatic Reflexes 4. Visceral Reflexes 5. Ipsilateral Reflex Arc 6. Contralateral Reflex Arc
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Spinal Reflex vs. Cranial Reflex
- Spinal = Process of the spinal cord; mostly innate | - Cranial = Processed in the brain; mostly learned reflexes
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Somatic Reflex vs. Visceral Reflex
- Somatic = Controls skeletal muscles | - Visceral = Controls visceral organs
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Ipsilateral vs. Contralateral
- Ipsilateral: Sensory stimulus & motor response on the same side of the body - Contralateral: Motor response on side opposite to the stimulus
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Monosynaptic vs. Polysynaptic
- Monosynaptic = Sensory neuron synapses directly on motor neuron (E.g, Stretch Reflex) - Polysynaptic = Reflex involving at least one interneuron between sensory & motor neurons (3 Main Examples)
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5 Features of a Polysynaptic Reflex
1. Interneuron involvement 2. May be intersegmental 3. May involve reciprocal innervation (if there are opposing muscles) 4. May use reverberating circuits (prolonged exposure) 5. Several reflexes may cooperate
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Stretch Reflex
Regulates skeletal muscle length & muscle tone; sensory receptors = muscle spindles - Sensory Nerve endings wrapped around intrafusal fibers - Example: Patellar reflex (AKA "Knee Jerk"); CNS sets muscle tone
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Steps of a Stretch Reflex
1. Generator potential 2. AP in sensory neuron 3. EPSPs in motor neuron 4. AP in motor neuron 5. ACh release 6. EPSPs in extrafusal fibers 7. AP in extrafusal fibers 8. Muscle contraction 9. Relieved strain of stretch
40
Postural Reflexes
- Stretch reflexes used to maintain upright posture | - An example of reciprocal innervation: normally, when a stretched muscle (agonist) contracts, its antagonists relax
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3 Examples of Polysynaptic Reflexes
1. Tendon Reflex 2. Flexor (Withdrawal) Reflex 3. Crossed Extensor Reflex
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Tendon Reflex
- Golgi tendon organ prevents stretching damage to tendons when muscles contract vigorously - Relaxation of stimulated muscle (via inhibitory interneuron) & contraction of antagonist (via excitatory neuron) - Tendon reflex overrides stretch reflex
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Flexor (Withdrawal) Reflex
- Move affected body part away from stimulus - Usually initiated by pain stimuli - Ipsilateral - Polysynaptic - Intersegmental - Reciprocal innervation
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Crossed Extensor Reflex
- Complements withdrawal reflex - Polysynaptic - Intersegmental - Contralateral - Example: Step on a nail, flexor reflex pulls away right foot, crossed extensor reflex stiffens left leg
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3 Reflexes for Diagnosing Disease
1. Babinski Sign 2. Patellar Reflex 3. Achilles Reflex
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Babinski Sign
- Positive: Dorsiflexion of great toe when lateral sole is stroked (+ possible fanning of other toes); normal spinal reflex for infants under 18 months; may be sign of CNS injury of oldar than 18 months - Negative: Plantar flexion reflex; represents modification of the spinal reflex due to influences of myelinated descending corticospinal tract fibers; normal in children older than 18 months & adults
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Patellar & Achilles Reflexes
If either reflex is diminished or exaggerated, CNS damage may have occured
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Spinal Nerve Anatomy
- Spinal nerves = union of posterior & anterior spinal roots - Mixed sensory/motor nerves - 3 connective tissue sheaths
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3 Spinal Nerve Sheaths
1. Endoneurium: Wraps fibers 2. Perineurium: Wraps fascicles 3. Epineurium: Wraps whole nerve; continuous w/ dura mater
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4 Branches (Rami) of Spinal Nerves
1. Posterior Rami: Connects to muscles & skin of back 2. Anterior Rami: Connects to limbs & muscles of lateral/ventral trunk - Thoracic Anterior Rami = Intercostal Nerves - Other Anterior Rami = Nerve Plexuses 3. Meningeal Rami 4. Rami Communicantes
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4 Spinal Nerve Plexuses
1. Cervical Plexus 2. Brachial Plexus 3. Lumbar Plexus 4. Sacral & Coccygeal Plexuses
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Cervical Plexus
- Anterior rami of C1-C5 - Innervate skin & muscles of neck, head & shoulders * Phrenic nerve emerges from cervical plexus (specifically C3, C4, C5
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Brachial Plexus
- Anterior rami of C4-T12 - Subdivided into roots, trunks, divisions & cords - Nerves include: radial, median & ulnar nerves - Innervate skin & muscles of shoulder, arm & hand
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Lumbar Plexus
- Anterior rami of T12-L4 - Subdivided into roots & divisions - Nerves include: femoral & obturator nerves - Innervates muscles of anterolateral abdominal wall, external genitals & parts of thigh, leg & foot
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Sacral Plexus
- Anterior rami of L4-S4 - Subdivided into roots & divisions - Nerves include: sciatic nerve (common peroneal + tibial) - Innervate skin & muscle of buttocks, pelvis. thigh, leg & foot
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Coccygeal Plexus
- Anterior rami of S4 & S5 - Nerves include: anococcygeal nerve - Innervate skin & muscle of buttocks, pelvis. thigh, leg & foot
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Dermatomes
- Skin areas supplied by a spinal nerve - Branches of cranial nerve V (trigeminal) has dermatomes w/ little overlap - Help to identify damaged spinal nerves or spinal cord segments * The C1 spinal nerve has no dermatomes
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