CH 13 - The Peripheral Nervous System

Sensory (Afferent) Division

Detects sensory stimuli and transmits to CNS.

Somatic sensory division

Detects external and internal stimuli from skin, muscles, and special sense organs.

Visceral sensory division

Transmits information from internal organs.

Motor (Efferent) Division

Carries out motor functions.

Somatic motor division

Controls voluntary movements via lower motor neurons.

Autonomic Nervous System (ANS)

Maintains homeostasis by controlling cardiac muscle, smooth muscle, and glands.

Sympathetic division

"Fight or flight" response.

Parasympathetic division

"Rest and digest" response.

Anterior root

Motor neurons from anterior horn.

Posterior root

Sensory neurons from posterior horn.

Posterior root ganglion

Contains sensory neuron cell bodies.

Spinal nerves

Mixed nerves formed by the fusion of anterior and posterior roots.

Epineurium

Outermost connective tissue layer.

Perineurium

Surrounds fascicles (axon bundles).

Endoneurium

Surrounds individual axons.

Olfactory

Smell (Sensory)

Optic

Vision (Sensory)

Oculomotor

Eye movement, pupil constriction (Motor)

Trochlear

Eye movement (Motor)

Trigeminal

Facial sensation, chewing muscles (Both)

Abducens

Eye movement (Motor); Moves the eye laterally (abduction)

Facial

Facial expression, taste (Both)

Vestibulocochlear

Hearing, balance (Sensory)

Glossopharyngeal

Swallowing, taste (Both)

Vagus

Parasympathetic control of heart, digestion (Both)

Accessory

Shoulder and neck movement (Motor)

Hypoglossal

Tongue movement (Motor)

Phrenic nerve

Innervates diaphragm (C3-C5, "3-4-5 to stay alive").

Axillary nerve

Deltoid, teres minor.

Radial nerve

Posterior arm, forearm extensors.

Musculocutaneous nerve

Biceps brachii, brachialis.

Median nerve

Wrist flexors, thumb movement.

Ulnar nerve

Intrinsic hand muscles.

Femoral nerve

Anterior thigh, and foot, knee extension, serves quadriceps femoris group.

Obturator nerve

Medial thigh, hip adduction.

Sciatic nerve

Largest nerve, splits into tibial and common fibular nerves.

Tibial nerve

Posterior thigh, leg, foot.

Common fibular nerve

Anterior and lateral leg, dorsum of foot.

Sensory Transduction

Conversion of stimuli into electrical signals.

Mechanoreceptors

Detect touch, vibration, pressure.

Thermoreceptors

Detect temperature changes.

Chemoreceptors

Detect chemical stimuli.

Photoreceptors

Detect light.

Nociceptors

Detect pain.

Dermatome

Skin area innervated by a single spinal nerve; skin sensation (sensory function)

Myotome

Muscle group innervated by a single spinal nerve; muscle movement is motor function

Exteroceptors

External stimuli (skin, special senses).

Interoceptors

Internal stimuli (organs).

Proprioceptors

Body position (muscles, joints).

Muscle spindle

Detects muscle stretch; initiates contraction.

Golgi tendon organ

Detects tension; triggers muscle relaxation.

Simple Stretch Reflex

Prevents overstretching (e.g., patellar reflex).

Golgi Tendon Reflex

Prevents muscle overloading by relaxing muscle.

Flexion (Withdrawal) Reflex

Rapid limb withdrawal from painful stimuli.

crossed-extension reflex

Supports body when opposite limb withdraws.