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Brain Stem II Basic Neuroscience QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. James H. Baños, Ph.D. Today… Brain Stem Reticular Formation Corticobulbar tract Cranial nerves and their nuclei Major Brain Stem Activities Conduit Ascending and descending pathways Integrative functions Complex motor patterns Respiratory and cardiovascular activity Regulation of arousal and level of consciousness Cranial Nerve functions Integrative Functions: Brain Stem Reticular Formation Brain Stem Reticular Formation Reticular = “netlike” Loosely defined nuclei and tracts Extends through the central part of the medulla, pons, and midbrain Intimately associated with Ascending/descending pathways Cranial nerves/nuclei Input and output to virtually all parts of the CNS Brain Stem Reticular Formation Brain Stem Reticular Formation Can be roughly divided into three longitudinal zones Midline - Raphe Nuclei Medial Zone - Long ascending and descending projections Lateral Zone - Cranial nerve reflexes and visceral functions Brain Stem Reticular Formation Connectivity is extremely complex Many different types of neurons Innervate multiple levels of the spinal cord Numerous ascending and descending collaterals Some have bifurcating collaterals that do both Many have large dendritic fields that traverse multiple levels of the brain stem Brain Stem Reticular Formation QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Reticular Formation Functions I. Participates in control of movement through connections with both the spinal cord and cerebellum Two reticulospinal tracts originate in the rostral pontine and medullary reticular formation Major alternate route by which spinal neurons are controlled Regulate sensitivity of spinal reflex arcs Tonic inhibition of flexor reflexes Mediates some complex “behavioral” reflexes Yawning Stretching Babies suckling Some interconnectivity with cerebellar motor control circuitry Clinical Correlation Pseudobulbar affect (as seen in Amyotrphic Lateral Sclerosis) Degeneration of descending motor pathways from the cortex to the brainstem “Release” of some of complex motor behaviors such as laughing and crying Usually uncontrollable, not consistent with mood May laugh when angry, cry at sad things, etc Conceptually analogous to upper motor neuron hyperreflexia Disinhibited spinal reflexes are very simple Disinhibited brainstem reflexes are very complex Clinical Correlation The Terri Schiavo case Reticular Formation Functions II. Modulates transmission of information in pain pathways Spinomesencephalic fibers bring information about noxious stimuli to the periaqueductal grey Periaqueductal grey also receives input from the hypothalamus and cortex about behavioral and drive states Efferents from the periaqueductal grey project to one of the raphe nuclei and medullay reticular formation These project to the spinal cord and can suppress transmission of pain information in the spinothalamic tract Reticular Formation Functions Cortex Thalamus Spinothalamic Tract Hypothal Periaqueductal Grey Raphe Spinal Cord Level Clinical Correlation Pain Management Periaqueductal grey has high concentration of opiate receptors Natural pain modulation relies on endogenous opiates Exogenous opiates are used for pain management Pause for contemplation! Major recurring theme: LOOPS Many brain functions are represented in loops (usually with a modulatory influence) Muscle tone Reflex loops Pain modulation Pathology and treatment of pathology are often related to modulating these loops Many of the basic pathways are supplemented by more complex pathways that complete this modulated loop architecture …meanwhile, back at the reticular formation… III. Autonomic reflex circuitry Reticular formation receives diverse input related to environmental changes Also receives input from hypothalamus related to autonomic regulation Output to cranial nerve nuclei Intermediolateral cell column of the spinal cord Involved in Breathing Heart rate Blood pressure Etc. Clinical Correlation Damage to the medulla often kills you Horner’s Syndrome Interruption of descending pathways to the intermediolateral cell column Ipsilateral Miosis (small pupil) Ipsilateral Ptosis (drooping eyelid) Ipsilateral Flushing/lack of sweating Reticular Formation Functions IV. Involved in control of arousal and consciousness Input from multiple modalities (including pain) Ascending pathways from RF project to thalamus, cortex, and other structures. Thalamus is important in maintaining arousal and “cortical tone” This system is loosely defined, but referred to as the Ascending Reticular Activating System (ARAS) ARAS is a functional system, not an anatomically distinct structure Clinical Correlation Normal functions Loss of Consciousness Traumatic brain injury Smelling salts, sternal rubs, and the ARAS Coma Sleep/wakefulness Can result from extensive damage to cortex More focal damage to ARAS Coma vs Minimally Conscious State Intact sleep/wake patterns in brain activity The Corticobulbar Tract The Corticobulbar Tract Corticospinal tract Descending motor pathways to ventral horn of the spinal cord Includes only fibers for torso, arms, legs (i.e., headless HAL) Decussates at a single point in the pyramids of the medulla (pyramidal decussation) The Corticobulbar Tract Corticobulbar tract Descending motor pathways to cranial nerve nuclei Includes descending fibers for HAL’s head Fibers for each CN nucleus decussate at the level of that nucleus (i.e., multiple points of decussation) QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Cranial Nerves and Their Nuclei A word about organization… Sensory and motor spinal nerves can be divided into Sensory (dorsal) Somatic - pain, temperature, mechanical stimuli Visceral - from receptive endings Motor (ventral) Somatic - Innervate skeletal muscle Visceral - To visceral autonomic ganglia A word about organization… Cranial Nerves also include: Special Sensory fibers Hearing, equilibrium, etc Special motor fibers Branchial motor Muscles of the head and face Different embryologic origin and location Otherwise, structurally and functionally the same as other muscle Autonomic fibers A word about organization… All of these fiber types organize predictably around the sulcus limitans QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. See p. 292 A word about organization… QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. See p. 294, 296 Starting from the top…CN I Starting from the top…CN I - Olfactory Fiber types: Special Sensory -- Smell The olfactory bulb and tract aren’t really CNI The fibers of CNI originate in the olfactory mucosa of the nasal cavity, pass through the cribiform plate, and synapse onto the olfactory bulb Note that there is no brain stem nucleus for CNI Cribiform plate Olfactory bulb CN I Clinical Correlation Olfactory nerve dysfunction is often reported as altered taste and smell Conditions affecting CNI include: Upper respiratory tract infection Traumatic Brain Injury (TBI) Subfrontal meningioma Dementia Clinical Correlation Anosmia - Total loss of smell Hyposmia - Partial loss of smell Hyperosmia - Exaggerated sense of smell Dysomia - Distorted sense of smell Olfactory hallucinations - Associated with seizures CN II - Optic CN II - Optic Fiber Types Special Sensory -- Vision Retinal ganglion cells to: Thalamus (lateral geniculate nucleus) -- Primary visual pathway Superior colliculus -- Reflexes involving vision and light Hypothalmus -- Light-dependent behavioral cycles Does not have a specific nucleus in the brain stem CN III - Oculomotor CN III - Oculomotor Somatic Motor - Eye movement Superior, inferior, medial recti Inferior oblique Levator palpebrae superioris Autonomic - Pupillary constriction Edinger-Westphal nucleus to pupillary sphincter CN III - Oculomotor Nucleus of III Edinger-Westphal QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. CN III - Oculomotor Eye movement Superior rectus - elevation Inferior rectus - depression Medial rectus - adduction Inferior Oblique - extorsion/elevation Levator palpebrae superioris? CN III - Oculomotor III 7 CN III Oculomotor “Pillars” that hold the eye open CN VII Facial “Hook” that pulls the eye closed CN III - Oculomotor Edinger-Westphal nucleus Receives bilateral projections from superior colliculi (which had received unilateral projections from CN II) This is the efferent component of the pupillary light reflex Also involved in pupillary accomodation Clinical Correlation Damage to CN III or nucleus of III “Down and out” eyeball Diplopia Ptosis Dilated and fixed pupil Paralysis of pupillary accommodation Can be cause by… Uncal/transtentorial herniation Aneurysm Clinical Correlation Pupillary light reflex Direct Consensual II - left III - left II - right III - right Clinical Correlation II - left III - left II - right III - right Clinical Correlation II - left III - left II - right III - right Clinical Correlation II - left III - left II - right III - right CN IV - Trochlear CN IV - Trochlear Somatic Motor Superior Oblique - Intorts, depressed, adducts the eye CN IV - Trochlear Nucleus of IV QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. CN VI - Abducens CN VI - Abducens Somatic Motor Lateral Rectus CN VI - Abducens III III IV IV VI VI Finally, lets add a pathway What muscles are being used when we look left or right? What cranial nerves? Is the same thing happening on each side? Finally, lets add a pathway During horizontal conjugate eye movements, each eye is doing the opposite of the other Adduction (CN III) on one side Abduction (CN VI) on the other side This is accomplished by “cross wiring” the nuclei via the medial longitudinal fasciculus (MLF) Finally, lets add a pathway III III IV IV VI VI Learn More… University of California -- Davis Eye Simulation Website: http://cim.ucdavis.edu/eyes/version15/eyesim.html Coming Up… Tomorrow More cranial nerves Thursday Diencephalon