HEAD AND NECK PART 2 INTEGRATED CURRICULUM = Integrate Basic Science and Clinical Training 1- ENT PATIENT EXAM IN ICS COURSE - Today and next week - Review/Preview Anatomy underlying ENT exam 2- NEUROANATOMY/NEUROLOGY - tomorrow Dr. Jeanette Norden - review Spinal Cord, everything else. etc. - Integrate with Gross Anatomy of Cranial Nerves, Hematomas, 3. ANATOMY OF NECK - Dissection of Neck - Thursday 1/5/17 - see Thyroid Gland, Muscles of Neck, Carotid Arteries, Jugular Veins, Lymph Nodes
1. REVIEW GROSS ANATOMY OF SPINAL CORD 2. GROSS ANATOMY OF BLOOD SUPPLY TO SPINAL CORD 3. SPINAL REFLEXES 4. REFLEX CHANGES IN LOWER AND UPPER MOTOR NEURON DISORDERS
1) GROSS ANATOMY OF SPINAL CORD Dorsal root - sensory grey matter - cells, etc. white matter - axons (tracts) PIA MATER - closely adherent to Spinal Cord Ventral root - motor ARACHNOID - closely adherent to inner side of Dura DURA MATER - tube around spinal cord; separate from vertebral canal
2) ARTERIES OF SPINAL CORD Posterior spinal arteries - paired on dorsal surface Anterior spinal artery - single artery on ventral (anterior surface)
BASILAR ARTERY ARTERIES OF SPINAL CORD ARISE FROM VERTEBRAL ARTERY (OR ITS BRANCHES) LEFT AND RIGHT VERTEBRAL ARTERIES
ARTERIES OF SPINAL CORD ARISE FROM VERTEBRAL ARTERY (OR ITS BRANCHES)
VERTEBRAL ARTERY BASILAR ARTERY VERTEBRAL ARTERY VERTEBRAL ARTERY Vertebral artery courses on ventral surface of brainstem (medulla) Vertebral artery gives rise to Anterior and Posterior Spinal arteries ANTERIOR SPINAL ARTERY
ARTERIES OF SPINAL CORD Radicular arteries Posterior spinal arteries - branches of Vertebral or Posterior Inferior Cerebellar artery (branch of Vertebral) Anterior spinal artery - branch of Vertebral A. Radicular arteries (Lateral Spinal Arteries) - enter vertebral canal via intervertebral foramina; reinforce supply to Anterior and Posterior Spinal Arteries
3) AND 4) SPINAL REFLEXES AND DIAGNOSIS OF UPPER AND LOWER MOTOR NEURON LESIONS DEFINITION OF A REFLEX - SENSORY STIMULUS PRODUCES STEREOTYPED MOTOR RESPONSE SENSORY STIMULUS MOTOR RESPONSE FOR REFLEX TO OCCUR ALL ELEMENTS MUST BE FUNCTIONAL; PATHWAYS MUST BE INTACT
THREE CLASSIC SPINAL REFLEXES 1) Stretch reflex - produced by activating muscle spindles 2) Autogenic inhibition - produced by activating Golgi tendon organs 3) Flexion reflex - produced by activating cutaneous, pain afferents
FUNCTIONS OF SPINAL REFLEXES 1) Stretch reflex - produced by activating muscle spindles - contributes to maintaining postural stability, countering sudden loads 2) Autogenic inhibition - produced by activating Golgi tendon organs - aids in regulating muscle tension, prevents damage to tendon, bone 3) Flexion reflex - produced by activating cutaneous, pain afferents - avoid obstacle or painful stimulus (stepping on nail)
STRETCH (DEEP TENDON) REFLEX SENSORY STIMULUS Two methods: 1) Rapidly Stretch muscle (change muscle length) Activate- Muscle spindle (Group Ia and II); monosynaptically excite Alpha (Lower) motor neuron to same muscle. Muscle spindle - Sensory neurons (Ia, II) SIGNAL MUSCLE LENGTH Excites Lower (Alpha) motor neuron in Ventral Horn MOTOR RESPONSE Stretched muscle contracts rapidly 2) TAP ON MUSCLE TENDON Note: Response large because also excite motor neurons to muscles with similar action and inhibit muscles with opposite action
MUSCLE TONUS = resting tension in muscle Tonus reflects firing of alpha motor neurons at rest REFLEXES CHANGED BY GAMMA MOTOR NEURONS - GET PATIENT TO RELAX BEFORE TESTING TONUS OR STRETCH REFLEX GAMMA MOTOR NEURONS - innervate muscle cells in muscle spindles ALPHA MOTOR NEURONS - innervate regular skeletal muscle cells TONUS - Tested by physician slowly extending or flexing joints (stretching patient's muscle) Activity in muscle spindles at rest is important in determining Tonus because connection is monosynaptic Gamma motor neurons innervate muscle cells in muscle spindles; Gamma motor neurons can heighten stretch reflexes (Gamma dynamic motor neurons specifically effect Ia sensory neurons)
REFLEXES CAN ALSO BE CHANGED BY ACTIVITY IN UPPER MOTOR NEURONS UPPER MOTOR NEURONS - all descending inputs that affect Lower Motor Neurons (ex. Corticospinal or Reticulospinal neurons) MUSCLE SPINDLE MUSCLE LOWER MOTOR NEURONS = Alpha motor neurons that innervate muscle Upper motor neurons can modulate (change) reflexes by: 1) Changing excitability of alpha motor neurons 2) Pre-synaptic Inhibition of Ia terminals; reduces the amount of transmitter release at the synapse upon motor neuron
LOWER MOTOR NEURON DISORDERS UPPER MOTOR NEURONS - descending systems Examples: 1) Compression of spinal nerve 2) Poliomyelitis - viral infections affecting motor neurons LOWER MOTOR NEURON Flaccid Paralysis - muscle is effectively denervated (can affect single muscles) 1) Decreased stretch (tendon) reflexes - no activation of muscle 2) Decreased tonus - no tonic alpha motor neuron activity 3) Muscle atrophy - Fasciculations (twitches) precede atrophy - Alpha motor neurons fire spontaneously 4) No Babinski sign - no effect descending control
UPPER MOTOR NEURON DISORDERS UPPER MOTOR NEURONS - descending systems Example: Damage to Corticospinal (Corticobulbar) tracts - can occur at all levels from cortex to spinal cord (brainstem) LOWER MOTOR NEURON Spastic Paralysis - affect groups of muscles 1) Increased stretch (tendon) reflexes - No modulation, remove inhibition of reflex pathways 2) Increased tone - Remove inhibition of reflex pathways 3) No Fasciculations 4) Babinski sign - effect descending control of Flexor reflex 5) Clasped Knife Reflex - high forces activate Golgi tendon organs
HYPERREFLEXIA: INCREASED STRETCH REFLEX ON ONE SIDE [used by permission of Paul D. Larsen, M.D., University of Nebraska Medical Center; http://library.med.utah.edu/neurologicexam]
AUTOGENIC INHIBITION: GOLGI TENDON ORGANS DECREASE FORCE GOLGI TENDON ORGANS SIGNAL MUSCLE FORCE - when force is high, activate Golgi Tendon Organ reflexes (Autogenic inhibition); inhibits alpha motor neurons, DECREASE FORCE GOLGI TENDON ORGAN (GTO) GTO (Ib) AUTOGENIC INHIBITION CLASP-KNIFE PHENOMENON stretch muscle Hand of clinician GTO (Ib) muscle tendon SENSORY STIMULUS: FORCE ON MUSCLE TENDON Alpha motor neuron (inhibited) MOTOR RESPONSE: FORCE DECREASES Physician applies, gradual forceful stretch of muscle: resistance to stretch builds until it suddenly gives way.
CLASPED KNIFE REFLEX: is an example of Autogenic inhibition. It is elicited in patients with UMN lesions due to high tonus in muscle. 1) PHYSICIAN TRIES TO FLEX ELBOW JOINT OF PATIENT WITH UPPER MOTOR NEURON LESION 2) KEEP TRYING AND TENSION ON TRICEPS TENDON EXCITES GOLGI TENDON ORGANS 3) TRICEPS RELAXES AND RESISTANCE SUDDENLY DECREASES: ELBOW JOINT FLEXES PHYSICIAN HOLDS WRIST AND PUSHES HERE AFTER TELLING PATIENT TO RELAX ENCOUNTERS HIGH RESISTANCE DUE TO HIGH TONUS IN TRICEPS AND HIGH STRETCH REFLEXES HIGH IMPOSED FORCE EXCITES GOLGI TENDON ORGANS IN TRICEPS TENDON WHICH INHIBITS MOTOR NEURONS TO TRICEPS MUSCLE ELBOW JOINT SNAPS SHUT LIKE A POCKET KNIFE = CLASPED KNIFE REFLEX
FLEXOR REFLEX SENSORY STIMULUS - painful, irritating stimulus to skin MOTOR RESPONSE - Cutaneous afferent synapse onto Interneurons Cutaneous afferent Interneurons - Interneurons make excitatory synapse onto Flexor motor neurons - Note: Also excite extensor motor neurons in opposite leg (not fall down) Flexor motor neuron Lift leg Extend Opposite leg KNEE JOINT Step on nail
FLEXOR REFLEXES ALSO CHANGE IN UPPER MOTOR NEURON LESIONS: BABINSKI SIGN NORMAL RESPONSE BABINSKI SIGN (EXTENSOR PLANTAR RESPONSE) STIMULUS TO SKIN OF SOLE OF FOOT FLEX TOES (DOWN) EXTEND BIG TOE, FANNING (ABDUCTION) OF OTHER TOES Babinski sign - seen after Upper Motor neuron lesion -direction of movement changes from flexing toes to extending and fanning (abducting) toes
PLANTAR REFLEX: ABNORMAL, (POSITIVE) BABINSKI SIGN ON ONE SIDE [used by permission of Paul D. Larsen, M.D., University of Nebraska Medical Center; http://library.med.utah.edu/neurologicexam]