Chapter 2: Spinal Cord

• Cylindrical has of nerve tissue
• Extends from foramen magnum in skull continuous with medulla to lower border of 1st lumbar vertebra in conus medullaris
• Divided into 30 segments → 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and a few coccygeal

• 2 anterior (ventral) and 2 posterior (dorsal) horns
• United by gray commissure with central canal
• 2 enlargements (cervical and lumbosacral) for origins of nerves of upper and lower extremities

• Contain cell bodies that give rise to efferent (motor) neurons 
• Alpha motor neurons to affect muscles
• Gamma motor neurons to affect muscle spindles

Contain afferent (sensory) neurons with cell bodies located in dorsal root ganglia

• Found in thoracic and upper lumbar segments
• For preganglionic fibers of ANS

• Anterior (ventral), lateral, and posterior (dorsal) white columns or funiculi
• Ascending fiber systems
• Descending fiber systems

• DCML
• Spinothalamic
• Spinocerebellar
• Spinoreticular

• Proprioception
• Vibration
• Tactile discrimination

Divided into fascicles cuneatus (UE tracts, laterally located) and fasciculus gracilis (LE tracts, medially located)

Neurons ascend to medulla → fibers cross (lemniscal decussation) → form medial lemniscus → ascend to thalamus → somatosensory cortex

• Lateral: pain and temperature 
• Anterior: crude touch

Tracts ascend 1-2 ipsilateral SC segments (Lissauer's tract) → synapse and cross in SC → ascend in ventrolateral spinothalamic system

• Proprioception from muscle spindles and GTO's (unconscious proprioception)
• Touch and pressure receptors to cerebellam for control of voluntary movements

• Dorsal: ascends to ipsilateral inferior cerebellar peduncle
• Ventrospinocerebellar: ascends to contralateral and ipsilateral superior cerebellar peduncle

• Deep and chronic pain
• To reticular formation of brainstem via diffuse, polysynaptic pathways

• Corticospinal 
• Vestibulospinal 
• Rubrospinal 
• Reticulospinal 
• Tectospinal

Arise from primary motor cortex → descend in brainstem → cross in medulla (pyramidal decussation) → via lateral corticospinal tract to ventral gray matter (anterior horn cells)

10% of fibers do not cross and travel in anterior corticospinal tract to cervical and upper thoracic segments 

Important for voluntary motor control

Arise from vestibular nucleus → descend to SC in lateral (uncrossed) and medial (crossed and uncrossed) vestibulospinal tracts

Control of muscle tone, antigravity muscles and postural reflexes

Arise in contralateral red nucleus → descend in lateral white columns to spinal gray

Assist in motor function

Arises in reticular formation of brainstem → descends (crossed and uncrossed) in ventral and lateral columns → terminates both on dorsal gray and ventral gray

• Dorsal gray: modifies transmission of sensation (especially pain)
• Ventral gray: influences gamma motor neurons and spinal reflexes

Arises from superior colliculus (midbrain) → descends to ventral gray

Head turning responses to visual stimuli

• Innervation of involuntary structures: smooth muscle, heart, glands
• Helps maintain homeostasis (constant internal body environment)

• Sympathetic
• Parasympathetic

• Both have afferent and efferent nerve fibers
• Preganglionic and postganglionic fibers

• Thoracolumbar division, T1-L2
• Prepares the body for fight of flight, emergency responses
• Increases HR and BP
• Constricts peripheral blood vessels 
• Redistributes blood
• Inhibits peristalsis

• Craniosacral Division, CN III, VI, IX, X, pelvic nerves 
• Conserves and restores homeostasis
• Slows heart rate and reduces BP
• Increases peristalsis and glandular activity

• Cardiac
• Pulmonary
• Celiac (Solar)
• Hypogastric
• Pelvic

Descending autonomic system: arises from control centers in hypothalamus and lower brainstem (cardiac, respiratory, vasomotor) and projects to preganglionic ANS segments in thoracolumbar (sympathetic) and craniosacral (parasympathetic) segments

Cranial nerves: visceral afferent sensations via glossopharyngeal and vagus nerves; efferent outflow via oculomotor, facial, glossopharyngeal, and vagus nerves