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Spinal Cord
- Extends through vertebral canal from foramen magnum to L1
- Each pair of spinal nerves receives sensory information and issues motor signals to muscles and glands
- A component of the Central Nervous System while the spinal nerves are part of the Peripheral Nervous System
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Anatomy of Spinal Cord
- Cylinder of nerve tissue within the vertebral canal (thick as a finger)
- –Vertebral column grows faster so in an adult the spinal cord only extends to L1
- 31 pairs of spinal nerves arise from cervical, thoracic, lumbar and sacral regions of the cord
- –Each cord segment gives rise to a pair of spinal nerves
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Gray Matter
Neuron cell bodies with little myelin
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White Matter
Myelinated axons
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Cervical in the Neck
- C1 to C5
- Supplies neck and phrenic nerve to the diaphragm
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Brachial in the Armpit
- C5 to T1
- Supplies upper limb and some of shoulder & neck
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Lumbar in the Low Back
- L1 to L4
- Supplies abdominal wall, anterior thigh & genitalia
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Sacral in the Low Pelvis
- L4, L5 & S1 to S4
- Supplies remainder of butt & lower limb
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Coccygeal
- S4, S5 and C0
- Not really important
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Oculomotor,Trochlear, Abducens
Eye movement
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Trigemenal
Face: sensory, movement
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Facial
Face: expression and sensory
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Auditory
Hearing and balance
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Glossopharyngeal
Tongue and throat: motor and sensory
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Accesory
Head, neck and shoulder: movement and swallowing
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Hypoglassal
Speech, swallowing, and chewing
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Sensory (Afferent) Neurons
- Conduct signals from receptors to the CNS
- Perephyreal Nervous System
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Interneurons (Association Neurons)
Confined to the CNS
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Motor (Efferent) Neurons
- Conduct signals from the CNS to effectors such as muscles and glands
- Periphyreal Nervous System
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Somatic Reflexes
- Quick, involuntary, stereotyped reactions of glands or muscle to sensory stimulation
- Automatic responses to sensory input that occur without our intent or often even our awareness
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Somatic Reflex Arc
- Stimulation of somatic receptors
- Afferent fibers carry signal to dorsal horn of spinal cord
- Interneurons integrate the information
- Efferent fibers carry impulses to skeletal muscles
- Skeletal muscles respond
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Patellar Tendon Reflex Arc
- 1. Extensor muscle stretched
- 2. Muscle spindle stimulated
- 3. Primary afferent neuron excited
- 4. Primary afferent neuron stimulates alpha motor neuron to extensor muscle
- 5. Primary afferent neuron stimulates inhibitory interneuron
- 6. Interneuron inhibits alpha motor neuron to flexor muscle
- 7. Alpha motor neuron stimulates extensor muscle to contract
- 8. Flexor muscles (antagonist) relaxes
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Sympathetic Ganglion
Carries information for some voluntary feelings or movements such as stress and anger, as well as fight and flight
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