Peripheral Nervous System & General Senses Lecture

Vocabulary flashcards covering key terms and concepts from the lecture on the peripheral nervous system, sensory receptors, reflexes, cranial and spinal nerves, and related clinical topics.

Peripheral Nervous System (PNS)

All nervous tissue outside the brain and spinal cord, including cranial nerves, spinal nerves, and sensory receptors.

Sensation

Conscious or subconscious awareness of changes in the external or internal environment.

Perception

Interpretation of sensory information, primarily in the cerebral cortex.

Sensory Modality

A specific type of sensation, such as touch, temperature, or pain.

General Senses

Somatic and visceral sensations with receptors scattered throughout the body (e.g., touch, temperature, proprioception).

Special Senses

Smell, taste, vision, hearing, equilibrium—each with dedicated organs.

Somatic Sense: Tactile

Includes light touch, deep touch, pressure, vibration, itch, and tickle.

Proprioception

Sense of body position, movement, and muscle tension.

Visceral Stretch Receptors

Detect pressure or stretch in organs such as stomach, bladder, and blood vessels.

Chemoreceptor

Receptor that detects chemical stimuli (e.g., taste buds, blood CO₂ sensors).

Photoreceptor

Light-sensitive receptor in the eye (rods and cones).

Mechanoreceptor

Receptor responding to mechanical deformation of the membrane (e.g., touch, hearing).

Thermoreceptor

Receptor detecting temperature changes; adapts quickly to constant temps.

Nociceptor

Pain receptor activated by tissue damage; does not undergo peripheral adaptation.

Osmoreceptor

Receptor monitoring osmotic (solute) pressure in body fluids.

Exteroceptor

Receptor that monitors the external environment (e.g., skin, special senses).

Interoceptor (Enteroreceptor)

Receptor that monitors internal environment (e.g., blood pH, organ stretch).

Free Nerve Ending

Bare dendrites that detect pain, temperature, tickle, itch, light touch.

Encapsulated Nerve Ending

Dendrites enclosed in connective tissue; detect deep pressure, vibration.

Hair Cell

Specialized mechanoreceptor of inner ear for hearing and equilibrium.

Gustatory Receptor Cell

Chemoreceptor in taste buds; not a neuron but synapses with one.

Peripheral Adaptation

Decreased receptor response to a sustained stimulus (e.g., clothes on skin).

Central Adaptation

Reduced perception of a stimulus due to CNS inhibition (e.g., ignoring chronic pain).

Substance P

Primary neurotransmitter released by nociceptors for pain signaling.

Dermatome

Skin area supplied by a single spinal nerve.

Cranial Nerves

Twelve pairs of nerves arising from the brain that innervate head, neck, and some visceral organs.

Cranial Nerve I – Olfactory

Purely sensory; conveys smell information from nasal cavity to brain.

Cranial Nerve II – Optic

Sensory; carries visual information from retina.

Cranial Nerve III – Oculomotor

Motor; controls most extra-ocular eye muscles, eyelid, pupil constriction.

Cranial Nerve IV – Trochlear

Motor; innervates superior oblique muscle of eye.

Cranial Nerve V – Trigeminal

Mixed; sensory from face, motor to muscles of mastication; has three branches.

Cranial Nerve VI – Abducens

Motor; controls lateral rectus muscle (abducts eye).

Cranial Nerve VII – Facial

Mixed; motor to facial expression muscles, sensory taste from anterior tongue.

Cranial Nerve VIII – Vestibulocochlear (Acoustic)

Sensory; hearing (cochlear) and equilibrium (vestibular) information.

Cranial Nerve IX – Glossopharyngeal

Mixed; taste from posterior tongue, swallowing, salivation.

Cranial Nerve X – Vagus

Mixed; extensive parasympathetic control of heart, lungs, digestive tract.

Cranial Nerve XI – Accessory

Motor; innervates sternocleidomastoid and trapezius muscles.

Cranial Nerve XII – Hypoglossal

Motor; tongue movements for speech and swallowing.

Phrenic Nerve

Cervical plexus nerve (C3-C5) that innervates the diaphragm; essential for breathing.

Brachial Plexus

Network of nerves (C5-T1) supplying shoulder and upper limb.

Radial Nerve

Brachial plexus branch running along radius; motor/sensory to posterior arm and hand.

Ulnar Nerve

Brachial plexus branch along ulna; motor/sensory to medial hand; "funny bone" nerve.

Median Nerve

Brachial plexus branch down center of forearm; implicated in carpal tunnel syndrome.

Femoral Nerve

Largest lumbar plexus nerve; supplies anterior thigh muscles.

Sciatic Nerve

Largest nerve of body; from sacral plexus, splits into tibial and common fibular nerves.

Reflex

Fast, involuntary response to a stimulus to maintain homeostasis or protect body.

Stretch (Patellar) Reflex

Monosynaptic reflex causing quadriceps contraction when patellar tendon is tapped.

Tendon Reflex

Polysynaptic reflex causing muscle relaxation when tension is excessive in tendon.

Withdrawal (Flexor) Reflex

Polysynaptic reflex that pulls a limb away from painful stimulus.

Crossed-Extensor Reflex

Contralateral reflex aiding balance by extending opposite limb during withdrawal.

Ipsilateral Reflex

Stimulus and response occur on the same side of the body.

Contralateral Reflex

Stimulus on one side produces response on the opposite side.

Peripheral Nerve Connective Layers

Endoneurium (around axon), Perineurium (around fascicle), Epineurium (around whole nerve).

Amyotrophic Lateral Sclerosis (ALS)

Progressive degeneration of motor neurons leading to muscle weakness and paralysis.

Poliomyelitis

Viral infection that can destroy motor neurons; prevented by vaccination.

Shingles (Herpes Zoster)

Reactivation of varicella-zoster virus along a dermatome, causing painful rash.

Reticular Activating System (RAS)

Brain network maintaining wakefulness; depression leads to sleep or coma.

REM Sleep

Sleep phase with rapid eye movement and vivid dreaming; important for memory formation.

Non-REM Sleep

Sleep stages without rapid eye movement; restorative for the body.

Peripheral Somatic Pathway

Three-neuron chain (first-, second-, third-order) conveying sensory input to cerebral cortex.

Precentral Gyrus

Primary motor cortex in frontal lobe controlling voluntary movements.

Postcentral Gyrus

Primary somatosensory cortex in parietal lobe receiving body sensations.

Cerebellum

Brain region coordinating movement, posture, and balance via sensory-motor comparison.

Adaptation (Sensory)

Decrease in receptor or CNS responsiveness to continuous stimuli.