The Spinal Cord & Peripheral Nervous System Lesson 7

Dorsal Ventral Horns

Spinal Cord n Dorsal root ganglion (DRG) l Sensory input n Ventral root l Motor output n Caudal spinal cord l Cauda equina ~

Spinal Cord Tracts n Major descending & ascending tracts n Motor n 1. corticospinal tract l distal muscles l only descending tract with overt effects n 1a. Rubrospinal tract l Red nucleus to spinal cord ~

Spinal Cord Tracts n Sensory n 2. Dorsal column-medial lemniscal tract l touch, vibration, & proprioception l axons ascend ipsilaterally l synapse then decussate at medulla n 3. Spinothalamic tract (anterolateral) l pain & temperature l decussate at SC entry level l ascends contralaterally ~

Medulla Dorsal column-medial lemniscal path Spinothalamic path Corticospinal tract

Dorsal Ventral Spinal Cord

Peripheral N. S. n Cranial Nerves - 12 pair n Spinal Nerves - 31 pair n Somatic Division l Sensory info l Body Movement n Autonomic division - Homeostasis l regulation ~

Cranial Nerves n From ventral surface l numbered anterior  posterior n Sensory, motor, or mixed n Mnemonic ~

Oh To Touch And Feel Very Green Vegetables A H Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulococlear Glossopharangeal Vagus Accessory (Spinal) Hypoglossal I II III IV V VI VII VIII IX X XI XII On Old Olympus’s Towering Top A Famous Vocal German Viewed Some Hops

Spinal Nerves n 1 pair for each vertebral segment n 8 pr. cervical (C1-C8) n 12 pr. thoracic (T1-T12) n 5 pr. lumbar (L1-L5) n 5 pr. sacral (S1-S5) n 1 pr coccygeal ~

Spinal Nerves n Thoracic nerves relatively small back & ribs n Cervical, lumbar, & sacral: large nerves rest of the body n All Interconnect l after leaving vertebral canal l form 4 major plexuses cervical, brachial, lumbar, sacral~

Somatic Nervous System n Sensory input l receptors  DRG  dorsal SC l Dorsal column-medial lemniscal pathway l Spinolthalamic tract n Motor output l Lateral SC  ventral horns  muscles l Corticospinal tract l Rubrospinal tract ~

Dermatomes n Sensory innervation l each spinal nerve has receptive field n Overlap at distal branches l redundancy l retain some sensation even if a complete spinal nerve destroyed ~

The Lateral Pathway n Voluntary movement l distal limbs l 2 tracts n Corticospinal tract about 1 million axons n Rubrospinal tract small part of pathway ~ Somatic N.S.: Motor Output

Motor N.S. n Striate muscle l uninterrupted neuron a motor neuron l nerve-dependent n Excitatory only at neuroeffector synapse l NT is acetylcholine (ACh) cholinergic l Nicotine = direct agonist (AG) l Curare = direct antagonist (ANT) ~

Somatic Motor N. S. Spinal Cord Motor Neuron Effector ACh

Autonomic N. S. n Homeostasis n Effectors l Smooth Muscle l Cardiac Muscle l Glands ~

Autonomic Subdivisions n Not nerve-dependent n Sympathetic l Emergency, flight/fight n Parasympathetic l Conservation / vegetative ~

Effector Ganglion Preganglionic neuron Postganglionic neuron Autonomic N. S.: General Features

Effector Autonomic N. S.: General Features ACh n Ganglionic synapse: Nicotinic (nACh) l different than neuromuscular l Neuroeffector junction l Sympathetic: Norepinephrine l Parasympathetic: nACh & mACh ~

Sympathetic vs. Parasympathetic n Sympathetic l ganglia near spinal cord l interconnected  active together l long-lasting effects n Parasympathetic l ganglia near effector l discrete  active independently l transient effects n Antagonistic regulation ~

Effector Responses Effector Sympathetic Parasympathetic Heart   Respiration   GI   Immune system   Iris  (radial)  (sphincter) Sweat glands  no input Adrenal glands  no input ~

Parasympathetic Post- Pre- Sympathetic Adrenal Glands ACh Glands Smooth muscle NE

Sympathetic Arousal Syndrome n Fight or flight situations l Diffuse sympathetic activation n Adrenal glands l releases NE into blood l maintains sympathetic arousal n Parasympathetic rebound l antagonistic regulation ~