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spinal cord
- extension of the brain stem from foramen magnum to L1/L2 vertebrae
- 17" long, 3/4" diameter
- 2 enlargements: cervical and lumbar
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cervical enlargement
- between C4 and T1
- nerves for arms and hands enter/exit the cord
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lumbar enlargement
- between T9 and T12
- nerves for legs and feet enter/exit the cord
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conus medullaris
tapered, inferior end of the spinal cord
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denticulate ligaments
filum terminale
- help attach cord to coccyx
- keep cord from moving around in vertebral cavity
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meninges
- group of membranes that surround and protect the spinal cord
- dura, arachnoid, pia
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dura mater
- outer membrane
- dense irregular tissue
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arachnoid
- middle membrane
- spider web-like
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pia mater
- inner membrane
- tightly fused to cord
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epidural space
- between vertebrae and dura mater
- composed of adipose
- protects cord
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subdural space
- between dura mater and arachnoid
- filled with CSF
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subarachnoid space
- between arachnoid and pia mater
- filled with CSF
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posterior root (1)
contains only sensory fibers that carry sensory info into the cord
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dorsal root ganglion (2)
bulge containing cell bodies of sensory neurons
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anterior root (3)
caries motor impulses out to effectors
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spinal nerve (4)
- mixed nerve fibers
- start at intervertebral foramen
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central canal (5)
CSF filled space that runs the length of the cord
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lateral gray horns (6)
unmyelinated neurons that run up and down the cord
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gray commisure (7)
unmyelinated region that connects the lateral gray horns
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posterior white column (8)
anterior white column (9)
lateral white columns (10)
groups of myelinated neurons that run up and down the cord
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posterior medial sulcus
groove that divides cord into right and left posteriorly
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anterior median fissure
groove that divides cord into right and left anteriorly
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spinal nerves
- groups of nerves that connect the CNS to muscle and glands (and vice versa)
- 31 pair - named for where the exit the cord
- exit through intervertebral foramen
- surrounded by connective tissue membranes
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pairs of spinal nerves
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
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epineurium
membrane that covers entire nerve
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perineurium
membrane that covers nerve fascicles
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endoneurium
membrane that covers individual nerve fibers
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fascicle
bundle of nerve fibers
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rami
first division of a spinal nerve immediately after it exits the intervertebral foramen
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plexus
nerves braided together
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ventral ramus
- all nerves that supply arms, hands, legs, feet, lateral and ventral trunk/head
- except for T1/T2, they form plexuses to route to structures
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cervical plexus
- from C1-C4/C5
- supplies skin and muscles of the head, neck, shoulders
- contains phrenic nerve (diaphragm)
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brachial plexus
- from C5-C8 to T1
- supplies hands and arms
- contains ulnar nerve (upper arm)
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lumbar plexus
- from L1 to L4
- supplies anterior and lateral abdomen, external genitalia, upper legs
- contains femoral nerve (upper leg)
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sacral plexus
- from L4/L5 to S1/S4
- supplies buttocks, lower legs, perineum
- contains sciatic nerve (lower leg)
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dorsal ramus
supplies back of head and dorsal trunk
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meningeal raums
supplies meninges, vertebrae, and spinal cord
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rami communicantes
supplies all autonomic structures
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dermatome
- region/band of skin that sends info to the spinal cord
- all spinal nerves except C1 supply dermatomes
- used mostly during anesthesia
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reflex
- an automatic response to a stimulus that is usually interpreted in the spinal cord
- 2 classes: somatic and autonomic
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somatic reflex
causes muscle contraction
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autonomic reflex
- smooth and cardiac muscle contraction
- gland secretion
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reflex arc
- pathway that every reflex travels
- receptor, sensory neuron, integration center, motor neuron, effector
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receptor (reflex)
1. sensory dendrite that responds to a stimulus and generates an AP
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sensory neuron (reflex)
2. ascending neuron that carries AP to spinal cord
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integration center (reflex)
3. region in spinal cord where incoming sensations are converted to motor responses
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motor neuron (reflex)
4. descending neuron that carries AP out to muscle/gland
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effector (reflex)
5. muscle or gland that responds to original stimulus
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five classes of reflexes
- monosynaptic
- polysynaptic
- ipsilateral
- contralateral
- intersegmental
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monosynaptic reflex
two neurons, one synapse
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polysynaptic reflex
multiple neurons, multiple synapses
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ipsilateral reflex
impulse enters and exits on the same side of the body
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contralateral reflex
impulse enters on one side of the body and exits on the other
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intersegmental reflex
incoming sensory neuron splits and synapses in different segments of the cord
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stretch reflex
- aka patellar/knee-jerk
- monosynaptic and ipsilateral
- receptors: muscle spindle cells
- response: extension of the leg
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flexor reflex
- polysynaptic, ipsilateral, intersegmental
- receptors: pain receptors
- response: withdrawal of structure receiving pain
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golgi tendon reflex
- polysynaptic, ipsilateral
- when a tendon is stimulated, the attached muscle relaxes
- prevents muscle damage
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crossed extensor reflex
- polysynaptic, contralateral
- when an unexpected or painful stimulus is received, limb withdraws and opposite limb extends
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