Nervous System Part II: Spinal Cord & Peripheral Nervous System

Spinal Cord (General)

• 31 segments:

  • 8 cervical spinal nerves

  • 12 thoracic spinal nerves

  • 5 lumbar spinal nerves

  • 5 sacral spinal nerves

  • 1 coccygeal spinal nerve

Efferent Fibers

Spinal cord provides innervation for the trunk (torso) and limbs via spinal nerves

Afferent fibers

Provides sensory info from peripheral receptors

Spinal Cord (Cell Bodies)

• CB of preganglionic neurons for sympathetic innervations:

  • Cardiac muscles

  • Smooth muscles

  • Secretory glands

Satellite Cell

1. Electrically insulates PNS cell bodies

2. Regulates nutrient & waste exchange for cell bodies in the ganglia

Neurolemmocyte

1. Surround and insulate PNS axons & myelinate those having large diameters

2. Allows for faster action potential propagation along an axon in the PNS

Posterior (dorsal) Horn

• Termination of primary afferent fibers

• Enter via the posterior roots of the spinal nerves

Lateral Horn

Preganglionic sympathetic neurons

Anterior (Ventral) Horn

• Proprioceptive reflex afferent

• Descending motor neurons

• Reflexes: embedded within spinal cord

Spinal Cord White Matter

• Responsible for Ascending & Descending Tract

• Consist of longitudinally running nerve fibers

• Fasciculi: fiber groups together anatomically to form tracts

Ascending tracts

Carry afferent impulses up the spinal cord & to the brain (PNS → CNS)

Descending tracts

Originate from cell bodies in cerebral cortex or brain stem nuclei

Autonomic Nervous System

• Consists of neurons in both CNS & PNS that control internal environment through innervations of secretory glands, cardiac muscle, smooth muscles

• Sympathetic: fight or flight responses

• Parasympathetic: rest & digest

Sympathetic Nervous System

• Constriction of cutaneous & abdominopelvic arteries

  • Increase blood supply to heart, muscles, & brain

  • Vasodilation in skeletal muscles

  • Relaxation of tracheal & bronchial musculature

  • Stimulation of dilatory pupillae

Parasympathetic Nervous System

• Cardiac slowing & reducing force of myocardial contraction

• Contraction of tracheal & bronchial musculature

• Stimulation of secretions of tracheal & bronchial glands

• Stimulation of sphincter pupillae & ciliary muscles

Difference in Gray/White Matter

• Brain: WM (axon) on outside, GM (cell body) inside

• ___: WM on inside, GM on outside (cell bodies)

Autonomic Nervous System

• Preganglionic nuclei located in brain stem & lateral horn

• Preganglionic axons (myelinated), exit CNS via cranial/spinal nerve & synapse to postganglionic neurons (unmyelinated

Cranial Nerves

• 12 paired peripheral nerves

• Serve as conduits of info

• Mediators for motor, sensory, and autonomic functions

Cranial Nerves (Listed)

I. Olfactory

II. Optic

III. Oculomotor

IV. Trochlear

V. Trigeminal

VI. Abducens

VII. Facial

VIII. Vestibulocochlear

IX. Glossopharyngeal

X. Vagus

XI. Accessory

XII. Hypoglossal

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Olfactory (CN I)

Sense of Smell

Optic (CN II)

Visual process transduction

Oculomotor (CN III)

• Innervates superior oblique, medial rectus, inferior rectus, & inferior oblique

• Iris (pupil responses)

• Ciliary Muscle (accomodation)

Trochlear (CN IV)

Innervates superior oblique

Trigeminal (CN V)

• Opthalmic (V1)

• Maxillary (V2)

• Mandibular (V3)

Abducent (CN VI)

Innervate lateral rectus

Facial (CN VII)

• Parasympathetic to lacrimal gland

• Facial muscles & sensations

Vestibulocochlear (CN VIII)

Hearing & Balance

Glossopharyngeal (CN IX)

Muscles, organs near throat

Vagus (CN X)

Paraympathetic nervous system (rest & digest, mucus secretion)

Accessory (CN XI)

• Intrinsic muscle of larynx

• Motor control of trapezius & sternocleidomastoid muscle

(CN XII)Hypoglossal

Intrinsic & extrinsic motor movements of tongue