3 FINAL: 11 05 PNS & Reflexes - PHYL 301

What vertebrae makes up the brachial plexus?

Ventral rami (roots) of C5 to T1 spinal nerves

Brachial Plexus

• Roots (C5 to T1)

• Trunks (superior, middle, and inferior trunk)

• Divisions (anterior and posterior divisions)

• Cords (posterior, lateral, and medial cords)

• Spinal nerve branches

Brachial Plexus Major Branches

• Radial nerve

• Ulnar nerve

• Median nerve

• Musculocutaneous nerve

• Axillary nerve

Erb Palsy

• Caused by damage to C5–C6 roots of brachial plexus

• Frequently due to obstructed labor

• Atrophy of affected arm

Atrophy

Decrease in size or wasting of a tissue

Neurogenic Atrophy

Muscle atrophy due to peripheral nerve damage

Median nerve

• Innervation

  • Forearm flexors

  • Pronator teres & quadratus

  • Digital flexors

  • Digits 1 to 3

    • Thumb, Pointer, Middle

  • Inner ½ of digit 4

    • Half of Ring Finger

Carpal Tunnel Syndrome - Causes & Symptoms

• Many causes, all involve median nerve

• Paresthesia: numbness, tingling, or pain

  • Affects thumb and fingers

• Freq. loss of grip

Innervation of wrist

Carpal Tunnel Syndrome - Diagnosis

• Nerve conduction test

• Tinel sign

• Phalen maneuver

Carpal Tunnel Syndrome - Treatment

• transverse carpal ligament = flexor retinaculum

  • Ligament over median nerve

  • May cut ligament to give median nerve more room

• Wrist splint: Keep wrist in neutral postion to reduce pressure on median nerve

Which spinal nerve levels contribute to the lumbar plexus?

• Branches from L1 to L4 spinal nerve roots (some fibers from T12)

• L4 & L5 fuse to form lumbosacral trunk

Lumbosacral trunk

• L4 & L5 spinal nerve roots

Lumbar Plexus

Major branches:

• liohypogastric nerve: innervates external & internal obliques & transverse abdominis

• Ilio-inguinal nerve: innervates external & internal obliques & transverse abdominis

• Lateral femoral cutaneous nerve: carries sensations from skin of anterior, lateral, & posterior thigh

• Genitofemoral nerve: sensory information from skin of anteromedial surface of thigh and external genitals

• Femoral nerve: innervates quadriceps, sartorius, pectineus, & iliopsoas

• Obturator nerve: innervates gracilis, obturator externus, & adductor magnus

Liohypogastric nerve - Lumbar plexus

Innervates external & internal obliques & transverse abdominis

Ilio-inguinal nerve - Lumbar plexus

innervates external & internal obliques & transverse abdominis

Lateral femoral cutaneous nerve - Lumbar plexus

carries sensations from skin of anterior, lateral, & posterior thigh

Genitofemoral nerve - Lumbar plexus

sensory information from skin of anteromedial surface of thigh and external genitals

Femoral nerve - Lumbar plexus

innervates quadriceps, sartorius, pectineus, & iliopsoas

Obturator nerve

innervates gracilis, obturator externus, & adductor magnus

What spinal nerve roots form the sacral plexus?

Formed from spinal nerve roots L4 to S4

Sacral Plexus

• Major branches:

• Superior gluteal nerve: innervates gluteus minimus, gluteus medius, & tensor fasciae latae

• Inferior gluteal nerve: innervates gluteus maximus

• Sciatic nerve: innervates semimembranosus, semitendinosus, & adductor magnus

• Posterior femoral cutaneous nerve: sensory from perineum, posterior thigh & lower leg

• Pudendal nerve: innervates genitalia, perineum, external anal sphincter, and urethral sphincter

Superior gluteal nerve - Sacral Plexus

innervates gluteus minimus, gluteus medius, & tensor fasciae latae

Inferior gluteal nerve - Sacral Plexus

innervates gluteus maximus

Sciatic nerve - Sacral Plexus

innervates semimembranosus, semitendinosus, & adductor magnus

Posterior femoral cutaneous nerve - Sacral Plexus

sensory from perineum, posterior thigh & lower leg

Pudendal nerve - Sacral Plexus

innervates genitalia, perineum, external anal sphincter, and urethral sphincter

Sciatica

• radiating pain and/or numbness from spine to the back of the leg

• Usually unilateral

• Commonly caused by sciatic nerve compression

  • Herniated disc common cause

  • Spinal compression of the nerve •

  • Piriformis syndrome (related, but not the same as sciatica

Sciatica – Foot Drop

• Caused by compression/lesions of the peroneal/fibular nerve

• Peroneal n. innervates anterior & lateral compartment of the leg

Sciatica – Treatment

• Non-steroidal anti-inflammatory drugs (NSAIDs)

• Corticosteroid injection

• Muscle relaxants

• Physical therapy – strengthening core muscles

• Chiropractic alignment?*

Reflex

Quick, almost immediate involuntary motor response

Reflex arc Definition

• Path from sensory stimulus to motor response

• Begins at sensory receptor and ends at peripheral effector

Reflex arc Pathway

1. Activation of a sensory receptor

2. Relay of information to the CNS

3. Information processing

4. Activation of a motor neuron

5. Response by the effector

Example of parallel processing: girl’s right foot steps in class

• Parallel processing: spinal cord coordaites both responses at same time

• Right leg — ipsilateral withdrawal reflex. She steps on glass with her right foot. The right leg flexes to lift that foot away from the glass.

• Left leg — contralateral crossed-extension reflex. Interneurons in the spinal cord relay the signal to the opposite side. The left leg extends to support her weight and keep her from falling.

Ipsilateral

Same Side

Contralateal

Opposite side

Different Reflex Classifications

• Development: Innate or acquired reflex

• Response: Somatic, visceral, or autonomic reflex

• Circuit complexity: Monosynaptic or polysynaptic

• Processing site: Spinal, cranial (cerebral), or enteric reflex

Innate Reflexes

Instinctive reflex that doesn’t require learning

• Withdrawal reflex

• Crossed-extensor reflex

• Patellar reflex

• Plantar (Babinski) reflex

Learned Reflexes

Reflex acquired through experience and repetition

• Swallowing, micturition, defecation

• Athletic & rehearsed movements

• Transcribing and typing

• Braking at red lights

Positive Babinski Sign

• Poke feet → Toes go up

Normal in infants

Bad for adults

Negative Babinski sign

• Poke feet → Toes curl down

Normal in adults

Monosynaptic Reflex

Involves a single segment of the spinal cord

Polysynaptic Reflex

Integrates motor output from several spinal segments

Stretch Reflex

Examples: patellar reflex, postural reflexes

Stretch reflex arc:

1. Stimulus stretches muscle spindle fibers

2. Activates a sensory neuron

3. Information is processed in the spinal cord

4. Motor neurons are activated

5. Effector muscle(s) contract(s)

Baroreceptor Reflex

• Baroreceptors

• Regulate cardiovascular center activity in medulla oblongata

  • Monitors internal pressure; blood pressure

• Detect pressure changes via stretch & mechanoreceptors

Locations: • Carotid sinus • Aortic arch • Cardiac atria

more representative, if blood pressure drop, baroreceptor fires less, increases sympathetic blood pressure will increase

Sympathetic System

Fight or Flight

Parasympathic System

Rest and digest