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Figure 12.23a

Thalamus. Basal forebrain. Touch. Prefrontal cortex. Hearing. Smell. Taste. Vision. Hippocampus. Sensory input. Thalamus. (a) Declarative memory circuits. Association cortex. Medial temporal lobe (hippocampus, etc.). Prefrontal cortex. ACh. ACh. Basal forebrain.

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Figure 12.23a

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  1. Thalamus Basal forebrain Touch Prefrontal cortex Hearing Smell Taste Vision Hippocampus Sensory input Thalamus (a) Declarativememory circuits Association cortex Medial temporal lobe (hippocampus, etc.) Prefrontal cortex ACh ACh Basal forebrain Figure 12.23a

  2. Brain Structures Involved in Nondeclarative Memory Procedural memory Basal nuclei relay sensory and motor inputs to the thalamus and premotor cortex Dopamine from substantia nigra is necessary Motor memory—cerebellum Emotional memory—amygdala

  3. Sensory and motor inputs Basal nuclei Premotor cortex Association cortex Thalamus Dopamine Premotor cortex Substantia nigra Basal nuclei Thalamus Substantia nigra (b) Procedural (skills) memory circuits Figure 12.23b

  4. Molecular Basis of Memory During learning: Altered mRNA is synthesized and moved to axons and dendrites Dendritic spines change shape Extracellular proteins are deposited at synapses involved in LTM Number and size of presynaptic terminals may increase More neurotransmitter is released by presynaptic neurons

  5. Molecular Basis of Memory Increase in synaptic strength (long-term potentiation, or LTP) is crucial Neurotransmitter (glutamate) binds to NMDA receptors, opening calcium channels in postsynaptic terminal

  6. Molecular Basis of Memory Calcium influx triggers enzymes that modify proteins of the postsynaptic terminal and presynaptic terminal (via release of retrograde messengers) Enzymes trigger postsynaptic gene activation for synthesis of synaptic proteins, in presence of CREB (cAMP response-element binding protein) and BDNF (brain-derived neurotrophic factor)

  7. Protection of the Brain Bone (skull) Membranes (meninges) Watery cushion (cerebrospinal fluid) Blood-brain barrier

  8. Meninges Cover and protect the CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in the skull

  9. Meninges Three layers Dura mater Arachnoid mater Pia mater

  10. Skin of scalp Periosteum Bone of skull Dura mater Periosteal Meningeal Superior sagittal sinus Arachnoid mater Pia mater Arachnoid villus Subdural space Blood vessel Falx cerebri (in longitudinal fissure only) Subarachnoid space Figure 12.24

  11. Dura Mater Strongest meninx Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses

  12. Dura Mater Dural septa limit excessive movement of the brain Falx cerebri—in the longitudinal fissure; attached to crista galli Falx cerebelli—along the vermis of the cerebellum Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure

  13. Arachnoid Mater Middle layer with weblike extensions Separated from the dura mater by the subdural space Subarachnoid space contains CSF and blood vessels Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption

  14. Skin of scalp Periosteum Bone of skull Dura mater Periosteal Meningeal Superior sagittal sinus Arachnoid mater Pia mater Arachnoid villus Subdural space Blood vessel Falx cerebri (in longitudinal fissure only) Subarachnoid space Figure 12.24

  15. Pia Mater Layer of delicate vascularized connective tissue that clings tightly to the brain

  16. Cerebrospinal Fluid (CSF) Composition Watery solution Less protein and different ion concentrations than plasma Constant volume

  17. Cerebrospinal Fluid (CSF) Functions Gives buoyancy to the CNS organs Protects the CNS from blows and other trauma Nourishes the brain and carries chemical signals

  18. Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the choroid plexus of each ventricle. Cerebral aqueduct Lateral aperture 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. Fourth ventricle Median aperture 2 Central canal of spinal cord 3 CSF flows through the subarachnoid space. (a) CSF circulation 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a

  19. Choroid Plexuses Produce CSF at a constant rate Hang from the roof of each ventricle Clusters of capillaries enclosed by pia mater and a layer of ependymal cells Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes

  20. Blood-Brain Barrier Helps maintain a stable environment for the brain Separates neurons from some bloodborne substances

  21. Blood-Brain Barrier Composition Continuous endothelium of capillary walls Basal lamina Feet of astrocytes Provide signal to endothelium for the formation of tight junctions

  22. Capillary Neuron Astrocyte (a) Astrocytes are the most abundantCNS neuroglia. Figure 11.3a

  23. Blood-Brain Barrier: Functions Selective barrier Allows nutrients to move by facilitated diffusion Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood

  24. Spinal Cord Location Begins at the foramen magnum Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers

  25. Spinal Cord: Protection Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space

  26. Spinal Cord: Protection Denticulate ligaments: extensions of pia mater that secure cord to dura mater Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx

  27. T12 Ligamentum flavum L5 Lumbar puncture needle entering subarachnoid space L4 Supra- spinous ligament Filum terminale L5 S1 Inter- vertebral disc Cauda equina in subarachnoid space Arachnoid matter Dura mater Figure 12.30

  28. Cervical spinal nerves Cervical enlargement Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Conus medullaris Lumbar spinal nerves Cauda equina Filum terminale Sacral spinal nerves (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Figure 12.29a

  29. Spinal Cord Spinal nerves 31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal

  30. Cross-Sectional Anatomy Two lengthwise grooves divide cord into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Gray commissure—connects masses of gray matter; encloses central canal

  31. Pia mater Epidural space (contains fat) Arachnoid mater Spinal meninges Subdural space Dura mater Subarachnoid space (contains CSF) Bone of vertebra Dorsal root ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a

  32. Dorsal median sulcus Gray commissure Dorsal funiculus Dorsal horn Gray matter White columns Ventral funiculus Ventral horn Lateral funiculus Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into dorsal rootlets) Ventral median fissure Ventral root (derived from several ventral rootlets) Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b

  33. Gray Matter Dorsal horns—interneurons that receive somatic and visceral sensory input Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons Dorsal root (spinal) gangia—contain cell bodies of sensory neurons

  34. Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Spinal nerve Ventral horn (motor neurons) Ventral root (motor) Somatic motor neuron Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32

  35. White Matter Consists mostly of ascending (sensory) and descending (motor) tracts Transverse tracts (commissural fibers) cross from one side to the other Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) Each spinal tract is composed of axons with similar functions

  36. Pathway Generalizations Pathways decussate (cross over) Most consist of two or three neurons (a relay) Most exhibit somatotopy (precise spatial relationships) Pathways are paired symmetrically (one on each side of the spinal cord or brain)

  37. Ascending tracts Descending tracts Ventral white commissure Fasciculus gracilis Dorsal white column Fasciculus cuneatus Lateral reticulospinal tract Dorsal spinocerebellar tract Lateral corticospinal tract Rubrospinal tract Ventral spinocerebellar tract Medial reticulospinal tract Lateral spinothalamic tract Ventral corticospinal tract Ventral spinothalamic tract Vestibulospinal tract Tectospinal tract Figure 12.33

  38. Ascending Pathways Consist of three neurons First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as it enters the spinal cord or medulla Synapses with second-order neuron

  39. Ascending Pathways Second-order neuron Interneuron Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum

  40. Ascending Pathways Third-order neuron Interneuron Cell body in thalamus Axon extends to somatosensory cortex

  41. Ascending Pathways Two pathways transmit somatosensory information to the sensory cortex via the thalamus Dorsal column-medial lemniscal pathways Spinothalamic pathways Spinocerebellar tracts terminate in the cerebellum

  42. Descending Pathways and Tracts Deliver efferent impulses from the brain to the spinal cord Direct pathways—pyramidal tracts Indirect pathways—all others

  43. Descending Pathways and Tracts Involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles

  44. The Direct (Pyramidal) System Impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal)l tracts Axons synapse with interneurons or ventral horn motor neurons The direct pathway regulates fast and fine (skilled) movements

  45. Indirect (Extrapyramidal) System Includes the brain stem motor nuclei, and all motor pathways except pyramidal pathways Also called the multineuronal pathways

  46. Indirect (Extrapyramidal) System These pathways are complex and multisynaptic, and regulate: Axial muscles that maintain balance and posture Muscles controlling coarse movements Head, neck, and eye movements that follow objects

  47. Indirect (Extrapyramidal) System Reticulospinal and vestibulospinal tracts—maintain balance Rubrospinal tracts—control flexor muscles Superior colliculi and tectospinal tracts mediate head movements in response to visual stimuli

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