A&P Chapter 13: Spinal cord, spinal nerves and spinal reflexes
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What are the 3 meninges that surround the spinal cord?
- 1. Dura mater: most superficial; tough and fibrous; continuous with the cranial dura mater; joins the film terminal in the coccygeal ligament
- 2. Arachnoid mater: middle layer; fine feathery projections, simple squamous epithelia
- 3. Pia mater: deepest layer; attached to the surface of the spinal cord, delivers blood to the spinal cord
What type of information enters the spinal cord?
- -Sensory information run on afferent fibers into the spinal cord
- -Sensory information enters through the dorsal root
What type of information exits the spinal cord?
- -Motor command information run on efferent fibers exiting the spinal cord
- -Motor commands exit through the ventral root
How is gray matter organized?
- 1. Cell bodies of neurons form functional groups (nuclei)
- 2. Sensory nuclei: dorsal, connect to peripheral receptors (posterior horn)
- 3. Motor nuclei: ventral, connect to peripheral effectors (anterior horn)
- 4. Lateral gray horn: contains visceral motor nuclei in the lumbar and thoracic regions of the spine
How is white matter organized?
- 1. Posterior white columns: between posterior gray horns and posterior median sulcus
- 2. Anterior white columns: between anterior gray horns and anterior median fissure
- 3. Lateral white columns: located on each side of the gray matter
- 4. Fasciculi or tracts: bundles of axons in the white matter that relay the same information in the same direction
What are the four major plexuses of the spinal cord?
- 1. Cervical plexus: innervates neck, thoracic cavity, diaphragmatic muscles, and phrenic nerve
- 2. Brachial plexus: innervates pectoral girdle (shoulder) and upper limbs
- 3. Lumbar plexus: innervates pelvic girdle and lower limbs
- 4. Sacral plexus: major nerves are pudendal and sciatic
What are neuron pools?
- 1. Functional groups of interconnected neurons
- 2. Each has limited input sources and output destinations
- 3. May excite or inhibit parts of the brain or spinal cord
What is a reflex arc?
- 1. The wiring of one specific reaction to one specific stimulus
- 2. Begins at a receptor and ends at an effector
- 3. Generally opposes original stimulus (negative feedback)
How are reflexes classified?
- 1. Development: innate or acquired
- 2. Motor response: somatic or visceral
- 3. Complexity of circuit: Monosynaptic or polysynaptic
- 4. Processing site: spinal or cranial
What is the difference between monosynaptic and polysynaptic reflexes?
- 1. Monosynaptic reflexes: faster, simpler; sensory neuron synapses directly onto motor neuron
- 2. Polysynaptic reflexes: slower and sophisticated; at least one interneuron between sensory and motor neurons
What happens in an ipsilateral reflex arc?
- -Sensory and effector neurons on the same side of the body
- 1. Stimulus activates a receptor
- 2. Activation of sensory neuron
- 3. Information processing by postsynaptic cell
- 4. Activation of motor neuron
- 5. Response of peripheral effector
What happens in a contralateral reflex arc?
- -Sensory and effector neurons are on opposite sides of the body
- -Same steps as ipsilateral reflex arc
- -Some reflexes may involve both ipsi- and contralateral arcs
- -Some reflexes inhibit some motor neurons and excite others
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