3.13pt2 Anatomy Chapter 13

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3.13pt2 Anatomy Chapter 13
2010-10-17 22:56:39
Central Nervous System Brain

Embryonic development, basic parts and organization, ventricles, brain stem, cerebellum, diencephalon, cerebrum, functional brain systems, protection
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  1. Embryonic Development of the Brain
    • During Week 4 of Development,
    • Primary brain vesicles appear at week 5, secondary brain vesicles form (adult brain structures)

    1. Prosencephalon (forebrain) divides into telencephalon (cerebrum: cerebral cortex, white matter, basal nuclei) and diencephalon (thalamus, hypothalamus, epithalamus; retina)

    2. Mesencephalon (midbrain) remains undivided (becomes brain stem: midbrain)

    3. Rhombencephalon (hindbrain) divides into the metencephalon (brain stem: pons; cerebellum) and the myelencephalon (brain stem: medulla oblongata)

    Adult brain divided into four regions: Cerebrum, Diencephalon, Brain Stem, Cerebellum

    • Gray and White Matter in the brain:
    • Gray matter: outlines inner surfaces, surrounding ventricles, also on outer cortex of cerebrum and cerebellum
  2. Ventricles of the Brain
    • - Filled with Cerebral Spinal Fluid (CSF)
    • - Lined with Ependymal cells
    • - Continuous with one another and with central canal of spinal cord

    • Lateral ventricles: lie in the cerebral hemispheres; horseshoe shape reflects bending of hemispheres during development; separated by septum pellucidum
    • Third ventricle: lies in diencephalon; connects to lateral ventricle through intraventricular foramen.

    • Fourth ventricle: lies in the brain stem; connects to the third ventricle via the cerebral aqueduct and caudally connects to the central canal of the spinal cord.
    • *contains three openings: lateral apertures and median aperture that connect the ventricles with the subarachnoid space, supplying it with CSF
  3. Myelencephalon
    Medulla Oblongata
    Most caudal portion of the brain stem

    • Pyramids: two longitudinal ridges formed by the pyramidal tracts (carry voluntary motor output from the cerebrum to the spinal cord).
    • Decussation of the pyramids: point at which pyramidal fibers cross over to the other side of the body

    Olive - lie lateral to a pyramid, contains inferior olivary nucleus (relay station for psensory information traveling to the cerebellum

    inferior cerebellar peduncles - fiber tracts that connect the medulla to the cerebellum dorsally

    Cranial nerves that attach to the Medulla:

    1. Cranial nerve VIII: (vestibulocochlear nerve) attaches where medulla and pons meet; sensory nerve of hearing and equilibrium

    2. Cranial nerve IX: (glossopharyngeal nerve) stick out from olives; innervates part of tongue and pharynx

    3. Cranial nerve X: (vagus nerve) lie behind hypoglossal nerve from Olives; innervates visceral organs in thorax and abdomen

    4. Cranial nerve XI (accessory nerve) four small nerve roots at the rostral part of the Olives; innervates some muscles of the neck

    5. Cranial nerve XII (hypoglossal nerve) in front of glossopharyngeal nerve, between pyramids and olives; innervates tongue muscles

    • *also contains nuclei of reticular formation
    • 1. cardiac center - force and rate of heartbeat
    • 2. vasomotor center - blood pressure regulation
    • 3. medullary respiratory center - controls rhythm and rate of breathing
    • 4. additional centers that control hiccuping, swallowing, coughing and sneezing
  4. Metencephalon
    Pons, Cerebellum
    • Pons: bulge between midbrain and medulla oblongata in brain stem; separated from cerebellum by the fourth ventricle; forms a ventral bridge between brain stem and cerebellum
    • Cranial nerves that attach to the pons: trigeminal (V) innervates skin of face and chewing muscles; abducens (VI) eye moving muscles; facial (VII) supplying muscles of facial expression
    • pontine nuclei - relay brain nuclei from cerebral cortex to cerebellum; involved with coordination of voluntary movement
    • middle cerebellar peduncles: axons from pontine nuclei to cerebellum

    • Cerebellum
    • 11% of brain mass; separated from pons and medulla by fourth ventricle
    • **smooths and coordinates body movements and helps maintain posture and equilibrium
    • divided into two cerebellar hemispheres separated by vermis; folded ridges called folia, grooves called fissures, each hemisphere divided into 3 lobes: anterior and posterior lobes that control balance and equilibrium of limbs, and flocculondular lobe that adjust posture and maintains equilibrium and coordinate head and eye movements

    Three regions: outer cortex of gray matter, arbor vitae "tree of life": internal white matter; consists of axons that relay instructions from cerebellar cortex to other parts of the brain, and deeply situated gray matter called deep cerebellar nuclei

    • **cerebellum also involved in motor memory and practice learning
    • *damage to cerebellum leads to disorders of coordination "drunken gait", etc.
  5. Mesencephalon
    • Most rostral of the brain stem, lies between diencephalon and pons; central cavity is the cerebral aqueduct that divides the midbrain into tectum dorsally and cerebral peduncles ventrally (looks like pillars that hold up the cerebrum). They contain pyramidal motor tracts that descend from the cerebrum to the spinal cord (most ventral part is called the crus cerebri
    • Ventral part also has superior cerebellar peduncles that connect the midbrain to the cerebellum.
    • Around the cerebral aqueduct is a periaqueductal gray matter that is involved in "fight or flight" reaction and mediating the response to visceral pain. Also contains cell bodies of motor neurons contributing to oculomotor and trochlear nerves that control most of the muscles that control the eyes.

    The inferior (important auditory reflex center) and superior (important visual reflex center) colliculi together form the corpora quadrigemina of the tectum.
  6. Diencephalon
    Thalamus, Hypothalamus
    • Borders the third ventricle and consist primarily of gray matter
    • Thalamus: egg-shaped, 80% of the diencephalon, left/right halves joined together by the interthalamic adhesion or (intermediate mass). Major synapse site for afferent fibers going to the cortex
    • *Every part of the brain that communicates with the cerebral cortex must relay its signals through a nucleus of the thalamus.

    • Hypothalamus: inferior portion of the diencephalon; lies between the optic chiasma (point of crossover of cranial nerves II (optic nerves) and the posterior border of the mammillary bodies. pituitary gland also projects inferiorly to the hypothalamus
    • **Main visceral control center of the body:
    • - control of ANS
    • - control of emotional responses (limbic system)
    • - regulation of body temperature
    • - regulation of hunger and thirst sensations
    • - control of motivational behavior (pleasure seeking center)
    • - regulation of sleep-wake cycles
    • - control of the endocrine system
    • - formation of memory

    Epithalamus: The third, most dorsal part of the diencephalon; consists of one tiny group of brain nuclei and the pineal gland that secretes melatonin (involved in circadian rhythm) under the control of the hypothalamus
  7. Telencephalon: Cerebrum
    Structure and Overview
    Account for 83% of total brain mass.

    • gyrus: twisted ridges of the brain tissue (bumps)
    • sulcus: shallow grooves on surface of cerebrum (depressions)
    • longitudinal fissure: divides cerebral hemispheres into right and left
    • transverse cerebral fissure: separates cerebrum from cerebellum
    • central sulcus: separates the frontal and parietal lobe
    • - precentral gyrus: anterior to central gyrus; involved in voluntary movement of skeletal muscles
    • - postcentral gyrus: posterior to central gyrus; involved in somatosensory information
    • lateral sulcus: (acutally a fissure) separates the temporal lobe from parietal and frontal lobes
    • insula: lobe buried deep within the lateral sulcus
    • corpus callosum: largest commissure that lies superior to the lateral ventricles and connects the left and right hemispheres
  8. Telencephalon: Cerebrum
    Frontal Lobe Structure and Function
    Prefrontal cortex: anterior part of the frontal lobe, "executive function"; involved in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior

    Broca's area: motor area lies anterior to the inferior part of the premotor cortex in the left cerebral hemisphere (language-dominant); controls motor movements necessary for speaking. In the right hemisphere (intuitive-emotional), it controls the emotional overtones given to spoken words

    Primary Motor Cortex: brings about precise voluntary movements of the body; responsible for conscious and voluntary movement
  9. Telencephalon: Cerebrum
    Parietal Lobe Structure and Function
    Primary somatosensory area: the primary sensory cortex that receives information from the general somatic senses; located along the postcentral gyrus of the parietal lobe; involved with general somatic senses, provides spatial discrimination or the ability to localize a stimulus to specific areas of the body

    Wernicke's area: located generally in the left hemisphere, at posterior portion where temporal lobe meets the parietal lobe, within the auditory association area; involved in recognizing and understanding spoken words (damage interferes with ability to comprehend speech)
  10. Telencephalon: Cerebrum
    Occipital Lobe Structure and Function
    Located at the posterior end of the cerebrum.

    Primary visual cortex: on the posterior and medial part of the occipital lobe; receives visual information from the retina of the eye contralaterally

    ventral stream: "what" pathway; extends through inferior part of temporal lobe; responsible for recognizing objects, words during reading and faces (right hemisphere)

    dorsal stream: "where" pathway; extends through posterior parietal cortex to postcentral gyrus; perceives spatial relationships among various objects
  11. Telencephalon: Cerebrum
    Temporal Lobe
    Primary auditory cortex: functions in conscious awareness of sound; located on superior edge of the temporal lobe (mostly inside lateral sulcus)
  12. Protection of the Brain
    • Dura mater: two-layered sheet in the brain made of fibrous connective tissue
    • - periosteal layer: more superficial layer, attaches to the internal surface of the skull bones (periosteum)
    • - meningeal layer: deeper layer; forms true external covering of the brain, continuous with dura mater of the spinal cord.
    • **two layers are fused except at dural sinuses

    arachnoid mater forms knoblike projections called arachnoid villi that project superiorly through dura mater into dural sinuses and act as valves that allow CSF to pass from subarachnoid space into dural blood sinuses

    pia mater: highly vascularized, clings tightly to the brain surface, following its contours
  13. Protection of the Brain
    Cerebral Spinal Fluid
    Most CSF is produced in the choroid plexuses (capillary rich membranes located in the four ventricles)

    Each plexus consists of a layer of ependymal cells covered by pia mater. CSF is continually made through filtration of blood plasma through the ependymal cells into the ventricles.

    CSF travels through the ventricles, some pass through to the central canal of the spinal cord, most enters subarachnoid space through medial and lateral apertures of the fourth ventricle. CSF from there bathes the outer surfaces of the brain and spinal cord and then passes through the arachnoid villi and enters the blood of the dural sinuses

    **CSF is recirculated through the blood at ~500mls/day
  14. Disorders of the Central Nervous System: Brain
    Cerebrovascular accidents (strokes)
    Alzheimer's Disease
    Cerebral Palsy
    • CVAs or strokes occur when either blockage or interruption of blood flow (ischemia) to a brain area causes brain tissue to die from lack of oxygen
    • 20% are caused by burst or torn cranial vessels, 80% by blood clots
    • *Damage is dependent on localization of stroke

    Alzheimer's Disease: a progressive degenerative disease of the brain that ultimately results in dementia; associated with structural changes in the basal forebrain nuclei, the hippocampus, and association areas of cerebral cortex: areas involved in memory and thought

    Cerebral Palsy: when voluntary muscle movements are poorly controlled or paralyzed; caused by infections of the placenta or trauma during birth