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Lecture 14

Lecture 14. CNS – Gross Anatomy Bio-5 Anatomy JPHubbard Hartnell College. Brain: 4 regions 12 pairs Cranial nerves Spinal Cord Begins at foramen magnum ~18 inches Cervical/thoracic/lumbar Cervical + lumbar enlargements Conus medullaris – tapered end 31pairs spinal nerves

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Lecture 14

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  1. Lecture 14 CNS – Gross Anatomy Bio-5 Anatomy JPHubbard Hartnell College

  2. Brain: • 4 regions • 12 pairs Cranial nerves • Spinal Cord • Begins at foramen magnum • ~18 inches • Cervical/thoracic/lumbar • Cervical + lumbar enlargements • Conusmedullaris – tapered end • 31pairs spinal nerves • Caudaequina • Filumterminale: fibrous extension into sacral canal – part of coccygeal ligament

  3. Coverings of CNS: Meninges • Continuous over brain and spinal cord • Dura mater – single layer • dense irregular CT + simple squamous • Epidural space: adipose + blood vessels • Subdural space filled with interstitial fluid • Dural sinuses - • Arachnoid mater = • Subarachnoid space = CSF • Extends to ~ S2 • Spinal tap – L1-L2 • Pia mater • thin layer covers BV • denticulate ligaments hold in place

  4. Medulla

  5. Organization of Gray Matter - Nuclei: • Posterior Horn: • somatic and visceral (autonomic) sensory association nuclei – association or interneurons • Anterior Horn: • somatic motor nuclei (efferent: to skeletal muscles) • Lateral gray horns (only in thoracic & upper lumbar regions): • Autonomic motor : to viscera • Sympathetic outflow • Gray commissures • Axons of interneurons crossing spinal cord

  6. Anterior median fissure Ventral horn Gray commissure Central canal Lateral horn Spinal nerve Dorsal horn Posterior median sulcus

  7. Sensory nuclei: Somatic Visceral Motor Nuclei Autonomic (in lateral horn) Somatic Gray Commissure

  8. White matter • 3 paired Columns (funiculi) – named for location • Contain Tracts – similar origin/destination • Ascending: sensory information – largely dorsal and lateral • Descending: motor information – ventral or lateral • Transverse: commissural tracts • Generalities: • Cross (decussate) • Involve 2 or 3 neurons • Exhibit somatotopy • paired

  9. Posterior funiculus (column) Lateral funiculus White commissure Anterior funiculus

  10. Spinal Nerves: • 31 pairs • Named: point of issue – • Cervical – 8 pairs • Thoracic – 12 pairs • Lumbar – 5 pairs • Sacral – 5 pairs • Coccygeal – 1 pair

  11. Dorsal Root – sensory information Dorsal Root Ganglion – cell bodies of sensory neurons Ventral root - outgoing motor fibers Spinal Nerves Mixed nerves – sensory + motor information

  12. Reflex Arcs • Monosynaptic: • single synapse in CNS • Simple, fast • sensory • motor neuron • Polysynaptic: • Multiple synapses – two or more • Sensory neuron • Motor neuron • 1 or more interneurons – • Complex control – more than one effector may be stimulated

  13. 4 Principal Parts of the Brain Cerebrum Cerebellum Diencephalon Brain Stem

  14. Fissure: deep groove • Longitudinal fissure • Transverse fissure • Gyri (gyrus): ridges • Sulci (sulcus): furrow, shallow groove

  15. Dura mater • Cranial dural septa – stabilize and support • Falxcerebri = in longitid. fissure • Incl. superior and inf. sagital sinuses • Attaches to cristagalli and internal occipital crest • Tentoriumcerebelli – transverse fissure • Falxcerebelli = between hemispheres of cerebellum • Diaphragmasellae – over sellaturcica • Dural sinuses: between endosteal and meningeal layers of dura mater • Superior sagital sinus • Transverse sinus • Collect blood from circulation around brain + CSF • CSF drains via arachnoid granulations

  16. Ventricles • Hollow spaces within brain – 4 • 2 lateral ventricles (1 & 2) : cerebrum • Separated by septum pellucidum • Third ventricle: within diencephalon • Interventricular foramen connects to lateral ventricles • Forth ventricle: in brain stem • Cerebral aqueduct = aqueduct of midbrain connects to 3rd ventricle • Aperatures communicate with subarachnoid space • Lateral + median aperatures • Contain cerebrospinal fluid • Communicate with each other, central canal of spinal cord and with subarachnoid space

  17. Cerebral Spinal Fluid • 20 ml/hr from plasma at choroid plexus • Composition regulated by ependymal cells – • Flow: ventricles  Central canal of spinal cord  sub-arachnoid space  returned to dural sinuses via arachnoid granulations

  18. Hydrocephalus – failure to reabsorb CSF • Genetic • Birth defects • Disease – meningitis • Aneurism • Trama • tumors

  19. Blood Brain Barrier • Provides constant environment in CNS • Endothelium of capillaries form tight junctions • Thick basal lamina • Bulbous feet of astrocytes • Specialized transport characteristics • In: • Glucose, essential AA, certain electrolytes • Not in: • Drugs, proteins, toxins, metab. Wastes • Pumped out: • Non-essential AA, K+ • Get in anyhow: • Lipid soluble substances • Not uniform – more permeable in certain retgions

  20. CSF is produced at ______________________ which are located (where?)____________________. • What regulates its composition? • Where does it go? • How does interstitial fluid in the brain differ from that in other tissues?

  21. White matter: transmission of information in tracts • Gray matter: integration • Centers: aggregates of cell bodies • Nuclei: centers with defined borders

  22. Cerebrum • Cortex: gray matter – 5 lobes • Contains: • Motor areas • Sensory areas • Association areas • Contralateral • Lateralization • Diff. areas involved in actions – communication

  23. Longitudinal fissure (green) Frontal lobe Central sulcus (yellow) precentral & postcentral gyrus Parietal lobe Parieto-occipital sulcus Occipital lobe Lateral sulcus (blue) Temporal lobe Insula Lobes and Fissures

  24. White Matter of Cerebrum • Myelinated fibers in tracts – 3 types • Commissures – transverse – connect corresponding areas in different hemispheres • Corpus callosum • Anterior commissure • Posterior commissure • Association fibers • Long and short – connect w/i hemisphere • Projection fibers: run vertically – tie to lower brain stem • Tie to sensory receptors/motor effectors • Internal capsule – fans out from top of brain stem (corona radiata)

  25. Basal Nuclei • 3 masses • Caudate nucleus • Putnam + globus passidus = lentiform nucleus • Influence muscle movement • Disorders associated with Huntington’s Chorea, Parkinson’s Dosease

  26. Limbic System • System of tracts • Learning – retention and utilization of past memories • Blends emotions with higher mental functions • Hippocampus – modifies behavior based on prior experience • Amygdala – emotions/past experiences

  27. Limbic System

  28. Diencephalon • Thalamus • Paired lateral, egg shaped masses • Hypothalamus • Mammillary bodies • Homeostatic regulatory functions • Epithalamus • Pineal gland

  29. Functions of Hypothalamus • Controls and integrates activities of the ANS which regulates smooth, cardiac muscle and glands • Synthesizes regulatory hormones that control the anterior pituitary • Contains cell bodies of axons that end in posterior pituitary where they secrete hormones • Regulates rage, aggression, pain, pleasure & arousal • Feeding, thirst & satiety centers • Controls body temperature • Regulates daily patterns of sleep

  30. Hypothalamus • Dozen or so nuclei in 4 major regions • mammillary bodies are relay station for olfactory reflexes;infundibulum suspends the pituitary gland • Major regulator of homeostasis • receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood

  31. Cerebellum • Functions • Receives/acts on proprioception (muscle status) input • Sends motor impulses to skeletal muscles that maintain posture and balance.

  32. 2 cerebellar hemispheres and vermis (central area) • 3 lobes w/I each hemisphere • Anterior lobe • Posterior lobe • Flocculonodular lobe

  33. Cerebellar cortex (folia) & central nuclei are grey matter • Arbor vitae = tree of life = white matter • Purkinje cells – extend from gray matter to cerebellar nuclei • Tracts in cerebellar peduncles carry info to other brain regions

  34. Brain Stem • Midbrain (= mesencephalon) • Medulla oblongata (medulla) • Pons (‘bridge’) • Nuclei assoc. with CN III  XII

  35. Midbrain: • Cerebral peduncles ‘little feet’ of cerebrum • Ventral • Connect to sp. cord motor tracts • Cerebellar peduncles – dorsal • Nuclei • Corpora quadregemina – dorsal domelike • Superior colliculi – eye movements • Inferior colliculi – auditory relay centers • Substantia nigra – prod. of dopamine • Red necleus – relay motor pathways

  36. Pons • One inch long • White fiber tracts ascend and descend • Pneumotaxic & apneustic areas help control breathing • Middle cerebellar peduncles carry sensory info to the cerebellum • Cranial nerves 5 thru 7

  37. Medulla Oblongata • Ascending sensory/ Descending motor tracts VIII-XII • Nuclei of 5 cranial nerves • Cardiovascular center • force & rate of heart beat • diameter of blood vessels • Respiratory center • medullary rhythmicity area sets basic rhythm of breathing • Information in & out of cerebellum • Reflex centers for coughing, sneezing, swallowing etc

  38. Reticular Formation • Scattered nuclei in medulla, pons & midbrain • Reticular activating system • alerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleep • maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles • Motor function is involvement with maintaining muscle tone

  39. Brain Injuries • Causes of damage • displacement or distortion of tissue at impact • increased intracranial pressure • infections • free radical damage after ischemia • Concussion---temporary loss of consciousness • headache, drowsiness, confusion, lack of concentration • Contusion--bruising of brain (less than 5 min unconsciousness but blood in CSF) • Laceration--tearing of brain (fracture or bullet) • increased intracranial pressure from hematoma

  40. Cranial Nerves • "On Old Olympic Towering Top A Finn And German Viewed A Hop.” • Olfactory- smell. • Optic- vision. • Oculomotor- eyelid & eyeball movement. • Trochlear-innervates superior oblique, turns eye downward and laterally. • Trigeminal- face & mouth touch & pain, chewing. • Abducens- turns eye laterally. • Facial-controls most facial expressions, tears & saliva secretion, taste. • Auditory (Vestibulocochlear)- hearing, equilibrium sensation. • Glossopharyngeal- taste, senses carotid blood pressure. • Vagus- senses aortic blood pressure, slows heart rate, stimulates digestive organs, taste, coughing, swallowing, voice production. • Accessory- controls trapezius, sternocleidomastoid, swallowing • Hypoglossal- controls tongue movement.

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