Peripheral Nervous System – Flashcards (Video Notes)

Flashcards cover PNS structure, sensory receptors classification, nerve organization, cranial/spinal nerves, plexuses, dermatomes, and reflexes as described in the notes.

What are the two principal divisions of the nervous system and their primary components?

CNS: brain and spinal cord; PNS: cranial and spinal nerves.

What composes the input (afferent) component of the PNS?

Sensory (afferent) neurons that carry impulses from sensory receptors to the CNS.

What composes the output (efferent) component of the PNS?

Motor (efferent) neurons that carry impulses from the CNS to muscles and glands.

Differentiate Somatic and Autonomic divisions in terms of what they innervate.

Somatic: skeletal muscles; Autonomic: smooth/cardiac muscle and glands (viscera).

What are the two branches of the autonomic motor system?

Sympathetic and Parasympathetic.

Objective 1 – What does the PNS include?

All neural structures outside the brain and spinal cord: sensory receptors, peripheral nerves and ganglia, efferent motor endings.

How are sensory receptors classified by location?

Exteroceptors, Interoceptors, Proprioceptors.

What do Exteroceptors sense and where are they located?

Stimuli arising outside the body; near or at the body surface.

What do Interoceptors sense?

Stimuli from within the body (chemical, stretch, temperature).

What do Proprioceptors detect?

Internal stimuli about body position and movement in the musculoskeletal system.

What are the five stimulus-detection classes of receptors?

Mechanoreceptors, Thermoreceptors, Photoreceptors, Chemoreceptors, Nociceptors.

What is the difference between simple and complex receptors?

Simple: modified dendritic endings; Complex: specialized sense organs for special senses.

What are free vs encapsulated nerve endings?

Free endings lack a CT capsule; Encapsulated endings are enclosed in CT capsules and are largely mechanoreceptors.

Meissner's corpuscles: location and function?

Located just beneath the epidermis in the dermal papillae; discriminative touch.

Pacinian corpuscles: location and function?

Located deep in the dermis and subcutaneous tissue; detect deep pressure.

What do muscle spindles detect?

Muscle stretch (stretch reflex).

What do Golgi tendon organs detect?

Tendon stretch and tension (tendon reflex).

What are joint kinesthetic receptors?

Proprioceptors in articular capsules that monitor joint stretch.

Describe nerve structure in the PNS: endoneurium, perineurium, epineurium.

Endoneurium surrounds each axon; Perineurium surrounds fascicles; Epineurium surrounds the whole nerve.

What are the three functional nerve classifications by direction?

Mixed nerves (sensory and motor), Sensory (afferent), Motor (efferent).

What are dorsal root ganglia?

Cell bodies of sensory neurons in the afferent fibers; sensory nerve cell bodies.

What defines visceral efferent vs somatic efferent?

Visceral efferent to autonomic targets (smooth/cardiac muscle and glands); Somatic efferent to skeletal muscles.

Where do cranial nerves originate?

First two originate from the forebrain; the rest originate from the brain stem.

Name three purely sensory cranial nerves.

Olfactory (I), Optic (II), Vestibulocochlear (VIII).

Name cranial nerves mainly motor but with proprioceptive fibers.

Oculomotor (III), Trochlear (IV), Abducens (VI).

Which cranial nerve is the major sensory nerve of the face and has motor fibers to chewing muscles?

Trigeminal (V).

Which cranial nerve abducts the eye?

Abducens (VI).

Which cranial nerve controls face muscles and conveys taste from the anterior tongue?

Facial nerve (VII).

Which cranial nerve is responsible for hearing and balance?

Vestibulocochlear (VIII).

Which cranial nerve supplies the pharynx and larynx with parasympathetic fibers to thoracic/abdominal organs?

Vagus (X).

Which cranial nerve innervates neck muscles and why is the phrenic nerve clinically important?

Accessory (XI); phrenic nerve (from C3-C5) innervates the diaphragm; injury can paralyze the diaphragm.

Which cranial nerve controls tongue movements?

Hypoglossal (XII).

What are spinal nerves and how many pairs exist?

31 pairs; fusion of dorsal and ventral roots; mixed nerves.

Spinal nerve branching: what are ventral ramus, dorsal ramus, and meningeal branch?

After exiting, each nerve divides into ventral ramus, dorsal ramus, and meningeal branch; each ramus is mixed.

What are the dorsal vs ventral rami functions?

Dorsal rami: posterior trunk; Ventral rami: form intercostal nerves (T2-T12) and all plexuses for limbs.

What are the cervical, brachial, lumbar, and sacral plexuses and major nerves?

Cervical plexus (phrenic); Brachial plexus (axillary, musculocutaneous, median, ulnar, radial); Lumbar plexus (femoral, obturator); Sacral plexus (sciatic via tibial and common fibular).

What is the sciatic nerve and what happens when injured?

Sciatic nerve from the sacral plexus; leaves pelvis via greater sciatic notch; supplies hamstrings; injury causes sciatica; divides into tibial and common fibular.

Describe dermatomes.

Skin area innervated by branches of a single spinal nerve.

Describe the reflex arc components.

Receptor, sensory neuron, integration center, motor neuron, effector.

How are reflexes classified functionally?

Somatic reflexes (skeletal muscles) and Autonomic reflexes (viscera).

Give examples of spinal reflexes.

Patellar (knee-jerk) stretch reflex; Flexor (withdrawal) reflex; Crossed extensor; Plantar (superficial) reflex.

Describe the stretch reflex mechanism.

Initiated by the muscle spindle; stretched muscle contracts; reciprocal inhibition of antagonists.

Describe the deep tendon reflex mechanism.

Initiated by the Golgi tendon organ; increased tension causes the contracting muscle to relax and reciprocal activation of antagonists.

What is the rate of axon regeneration in the PNS?

1 to 5 mm per day.

Do axons in the CNS regenerate?

No; CNS fibers do not regenerate beyond about 1 mm; brain/spinal cord damage is typically irreversible.

What is a neuromuscular junction?

The synapse between a somatic motor neuron ending and a skeletal muscle fiber.

What are varicosities in autonomic endings?

Bead-like swellings along autonomic nerve endings that release neurotransmitters to smooth muscle or glands.