A&P ch 12-14

  1. stages of embryonic brain development
    • 1 neural plate forms from surface ectoderm
    • 2 neural plate invaginates. forming neural groove flanked by neural folds
    • 3 neural fold cells migrate to form the neural crest which will form most of the PNS and many other structures
    • 4 neural groove becomes the neural tube, which will form CNS structures
  2. 3 primary brain vesicles
    • 1 prosencephalon (forebrain)
    • 2 mesencephalon (midbrain)
    • 3 rhombencephalon (hindbrain)

    all 3 come from anterior end of neural tube
  3. secondary brain vesicles
    • prosencephalon > telencephalon and diencephalon
    • mesencephalon > mesencephalon
    • rhombencephalon > metencephalon and myelencephalon
  4. adult brain structures development
    • telencephalon > cerebrum, cerebral hemispheres (cortex, white matter, basal nuclei)
    • diencephalon > diencephalon (thalamus, hypothalamus, epithalamus), retina
    • mesencephalon > brain stem, midbrain
    • metencephalon > brain stem, pons
    • cerebellum
    • myelencephalon > brain stem, medulla oblongata
    • spinal cord
  5. adult neural canal regions
    • telencephalon > lateral ventricles
    • diencephalon > third ventricle
    • mesencephalon > cerebral aqueduct
    • metencephalon and myelencephalon > 4th ventricle
    • spinal cord > central canal
  6. cells that line ventricles of the brain
    ependymal cells
  7. lobes of the brain
    • 1 frontal
    • 2 parietal
    • 3 temporal
    • 4 occipital
    • 5 insula
  8. cerebral cortex function
    conscious mind - awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding
  9. functional areas of cerebral cortex
    • 1 motor
    • 2 sensory
    • 3 association
  10. motor areas
    • 1 primary motor cortex
    • 2 premotor cortex
    • 3 Broca's area
    • 4 frontal eye field (voluntary eye movement)
  11. sensory areas
    • 1 primary somatosensory cortex
    • 2 somatosensory association cortex
    • 3 visual areas
    • 4 auditory areas
    • 5 olfactory cortex
    • 6 gustatory cortex
    • 7 visceral sensory area
    • 8 vestibular cortex
  12. multimodal association areas
    • input/output
    • allow us to give meaning to info received, store it as memory, compare it to prvious experience, and decide on an action to take
    • 3 parts
    • 1 anterior association area
    • 2 posterior association area
    • 3 limbic association area
  13. anterior association area (prefrontal cortex)
    • - intellect, cognition, recall and personality
    • - working memory for judgement, reasoning, persistence, and conscience
    • - development depends on social feedback
  14. posterior association area
    • - recognizing patterns and faces and localizing us in space
    • - understanding written and spoken language (wernicke's area)
  15. limbic association area
    • - part of limbic system
    • - provides the emotional impact that helps establish memories
  16. lateralization and dominance
    • division of labor between hemispheres
    • cerebral dominance - one hemisphere is dominant in the action
  17. left hemisphere function
    • language
    • math
    • logic
  18. right hemisphere function
    • insight
    • visual-spacial skills
    • intuition
    • artistic skills
  19. cerebral white matter
    • myelinated fibers and their tracts
    • responsible for communication
  20. cerebral white matter fibers
    • commissures - (corpus collosum) gray matter between the 2 hemispheres
    • association fibers - different parts of the same hemisphere
    • projection fibers - (corona radiata) connect the hemispheres with lower brain or spinal cord
  21. basal nuclei function
    • influence muscle control
    • help regulate attention and cognition
    • regulate intensity of slow or stereotyped movements
    • inhibit antagonistic and unnecessary movements
  22. basal nuclei
    • subcortical nuclei
    • consists of corpus striatum (caudate nucleus + lentiform nucleus (putamen + globus pallidus)
    • functionally associated with subthalamic nuclei (diencephalon) and the substantia negra (midbrain)
  23. primary motor cortex
    • conscious control of precise, skilled, voluntary movements
    • lg pyramidal cells of precentral gyri
    • long axons > pyramidal (corticospinal) tracts
  24. motor humunculi
    upside-down caricatures representing the motor innervation of body regions
  25. premotor cortex
    • controls learned, repetitious or patterned motor skills
    • coordinates simultaneous or sequential actions
    • involved in planning of movements that depend on sensory feedback
  26. Broca's area
    • present in 1 hemisphere (usually left)
    • motor speech area that directs muscles of the tongue
    • active as one prepares to speak
  27. Frontal eye field
    controls voluntary eye movements
  28. Primary somatosensory cortex
    • receives sensory info from the skin, skeletal muscles, and joints
    • capable of spatial discrimination - id of body region being stimulated
  29. somatosensory association cortex
    • integrates sensory input from primary somatosensory cortex
    • determines size, texture, and relationship of parts of objects being felt
  30. visual areas
    • 1 primary visual cortex - most of it is buried in the calcarine sulcus; recieves visual info from the retinas
    • 2 visual association area - surrounds primary visual cortex; uses past visual xp to interpret visual stimuli; complex processing involves entire posterior half of the hemispheres
  31. auditory areas
    • 1 primary auditory cortex - interprets info from inner ear as pitch, loudness, and location
    • 2 auditory association area - sores memories of sounds and permits perception of sounds
  32. olfactory cortex
    • part of the primitive rhinencephalon, along with olfactory bulbs and tracts (remainder of rhinencephalon in humans is part of the limbic system)
    • conscious awareness of odors
  33. gustatory cortex
    • in the insula
    • involved in perception of taste
  34. visceral sensory area
    conscious perception of visceral sensations (upset stomach, full bladder)
  35. vestibular cortex
    responsible for conscious awareness of balance (position of head in space)
  36. diencephalon
    • thalamus - mediates sensation, motor activities, cortical arousal, learning and memory
    • hypothalamus - visceral control center and maintains homeostasis
    • epithalamus - from where pineal gland extends
    • encloses 3rd ventricle
  37. regions of brain stem
    • midbrain
    • pons
    • medulla oblongata
  38. brain stem
    • similar structure to spinal cord but contains embedded nuclei
    • controls automatic behaviors necessary for survival
    • contains fiber tracts connecting higher and lower neural centers
    • associated with 10 of the 12 pairs of cranial nerves
  39. midbrain
    • cerebral peduncles (pyramidal motor tracts)
    • cerebral aqueduct
    • nuclei that control cranial nerves III and IV
    • corpora quadrigemina - superior colliculi = visual reflex centers, inferior colliculi = auditory relay centers
  40. pons
    • forms part of anterior wall of 4th ventricle
    • fibers of the pons - 1 connect higher brain centers and the spinal cord, 2 relay impulses between the motor cortex and the cerebellum
    • origin of cranial nerves V, VI, and VII
    • some nuclei of the reticular formation
    • nuclei that help maintain normal rhythm of breathing
  41. medulla oblongata
    • joins spinal cord at foramen magnum
    • forms part of the ventral wall of the 4th ventricle
    • contains a choroid plexus of the 4th ventricle
    • cranial nerves VIII, X, and XII
    • autonomic reflex centers - cardiovascular center and respiratory center
    • vestibular nuclear complex - mediates responses that maintain equilibrium
  42. cerebellum
    subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction
  43. anatomy of the cerebellum
    • 2 hemispheres connected by vermis
    • each hemisphere has 3 lobes - anterior, posterior and flocculonodular
    • folia - transversely oriented gyri
    • arbor vitae - distictive treelike pattern of the cerebellar white matter
  44. cerebellar peduncles
    • 3 paired fiber tracts connect the cerebellum to the brain stem
    • -superior - connect cerebellum to midbrain
    • -middle - connect pons to the cerebellum
    • -inferior - connect the medulla to the cerebellum
  45. function of the cerebellum
    • function is cognitive
    • recognizes and predicts sequences of events during complex movements
    • plays a role in nonmotor functions such as word association and puzzle solving
  46. protection of the brain
    • bone
    • membranes (meninges)
    • watery cushion (cerebrospinal fluid)
    • blood-brain barrier
  47. meninges
    • cover and protect the CNS
    • protect blood vessels and enclose venous sinuses
    • contain CSF
    • form partitions in the skull
    • 3 layers -
    • -dura mater
    • -arachnoid mater
    • -pia mater
  48. dura mater
    • strongest meninx
    • 2 layers of fibrous connective tissue (around the brain) separate to form dural sinuses
    • dural septa limit excessive movement of the brain
    • -falx cerebri - in 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
  49. 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
  50. pia mater
    layer of delicate vascularized connective tissue that clings tightly to the brain
  51. cerebrospinal fluid (CSF) constitution
    • watery solution
    • less protein and different ion concentrations than plasma
    • constant volume
  52. CSF functions
    • gives buoyancy to the CNS organs
    • protects the CNS from blows and other trauma
    • nourishes the brain and carries chemical signals
  53. 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
  54. blood-brain barrier
    • helps maintain a stable environment for the brain
    • separates neurons from some bloodborned substances
    • composition -
    • -continuous endothelium of capillary walls
    • -basal lamina
    • -feet of astrocytes - provide signal to endothelium for the formation of tight junctions
  55. function of blood-brain barrier
    • 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 (vomiting center and hypothalamus) where monitoring of the blood chemistry is necessary
  56. homeostatic imbalances of the brain
    • concussion- temporary alteration in function
    • contusion- permanent damage
    • subdural or subarachnoid hemorrhage- may force brain stem through the foramen magnum, resulting in death
    • cerebral edema- swelling of the brain associated with traumatic head injury
    • degenerative brain disorders
    • - alzheimer's disease- progressive, results in dimentia
    • - parkinson's disease- degeneration of the dopamine-releasing neurons of the substantia nigra
    • - huntington's disease- fatal hereditary disorder caused by accumulation of the protein huntington that leads to degeneration of the basal nuclei and cerebral cortex
  57. CSF circulation
    • 1 CSF is produced by the choroid plexus of each ventricle
    • 2 CSF flows through the ventricles and into the su barachnoid space via the median and lateral apertures. some CSF flows throught the central canal of the spinal cord
    • 3 CSF flows through the subarachnoid space
    • 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi
  58. spinal cord and function
    • begins at foramen magnum and ends as conus mudullaris at L1 vertebra
    • function-
    • - provides 2 way communication to and from the brain
    • - contains spinal reflex centers
  59. protection of the spinal cord
    • bone, meninges and CSF
    • cushion of fat and a netwo9rk of veins in the epidural space between the vertebrae and spinal dura mater
    • CSF in subarachnoid space
    • 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
  60. anatomical features of spinal cord
    • 31 pairs of spinal nerves
    • cervical and lumbar enlargements - nerves serving the upper and lower limbs emerge here
    • cauda equina - collection of nerve roots at the inferior end of the vertebral canal
    • 2 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
  61. gray matter in spinal cord
    • 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) ganglia - contain cell bodies of sensory neurons
  62. white matter of spinal cord
    • consists mostly of ascending (sensory) and descending (motor) tracts
    • transverse tracts (commissural fibers) cross from one side to the other
    • tracts are located in 3 white columns (funiculi on each side - dorsal (posterior), lateral and ventral (anterior))
    • each spinal tract is composed of axons with similar functions
  63. pathway generalizations
    • pathways decussate (cross over)
    • most consist of 2 of 3 neurons (relay)
    • most exhibit somatotopy (precise spatial relationships)
    • pathways are paired symmetrically (one on each side of the spinal cord or brain)
  64. ascending pathways
    • consist of 3 neurons-
    • -1st order neuron - sensory neuron, cell bodies in ganglion, conducts impulses from cutaneous receptors and proprioceptors
    • synapses with 2nd order neuron
    • -2nd order neuron - interneuron, cell body in dorsal horn of spinal cord or medullary nuclei
    • axons extend to thalamus or cerebellum
    • -3rd order neuron - interneuron, cell body in thalamus, axon extends to somatosensory cortex
  65. transmission of somatosensory info to the sensory cortex (via the thalamus) for conscious interpretation
    • dorsal column-medial lemniscal pathways
    • spinothalamic pathways
  66. transmission of somatosensory info to cerebellum (end of tracts)
    spinocerebellar pathways
  67. dorsal column-medial lemniscal pathways
    • transmit input to the somatosensory cortex for discriminative touch and vibrations
    • composed of the paired fasciculus cuneatus and fasciculus gracilis in the spinal cord and the medial lemniscus in the brain (medulla to thalamus)
  68. spinothalamic pathways
    • lateral and ventral spinothalamic tracts (anterolateral)
    • transmit pain, temp, and coarse touch impulses within the lateral spinothalamic tract
  69. spinocerebellar tracts
    • ventral and dorsal tracts
    • convey info about muscle or tendon stretch to the cerebellum
  70. descending pathways and tracts
    • deliver efferent impulses from the brain to the spinal cord-
    • -direct pathways - pyramidal tracts
    • -indirect pathways - all others
    • involve 2 neurons -
    • -1 upper motor neurons - pyramidal cells in primary motor cortex
    • -2 lower motor neurons - ventral horn motor neurons, innervate skeletal muscles
  71. direct (pyramidal) system for descending pathways
    • impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal) tracts
    • axons synapse with interneurons or ventral horn motor neurons
    • direct pathway regulates fast and fine (skilled) movements
  72. indirect (extrapyramidal) system for descending tracts
    • includes the brain stem motor nuclei, and all motor pathways except pyramidal pathways
    • also called multineuronal pathways
    • complex, multisynaptic pathways that regulate - axial muscles that maintain balance and posture; muscles controlling coarses movements; head, neck and eye movements that follow objects
  73. spinal cord trauma
    • functional losses -
    • - parasthesias - sensory loss
    • - paralysis - loss of motor function
    • - transection - total sensory and motor loss
  74. paralysis
    • flaccid - severe dmg to ventral root or ventral horn cells - impulses don't reach muscles; there is no voluntary or involuntary control of muscles; muscles atrophy
    • spastic - dmg to upper motor neurons of the primary motor cortex - spinal neurons remain intact; muscles are stimulated by reflex activity; no voluntary control of muscles
    • transection - cross sectioning of the spinal cord at any level; results in total motor and sensory loss in regions inferior to the cut; paraplegia - transection between T1 and L1; quadriplegia - transection in cervical region
  75. poliomyelitis
    • destruction of the ventral horn motor neurons by the poliovirus
    • muscles atrophy
    • death may occur due to paralysis of respiratory muscles or cardiac arrest
    • survivors often develop postpolio syndrome many years later, as neurons are lost
  76. amyotrophic lateral sclerosis (ALS/Lou Gehrig's disease)
    • involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract
    • loss of ability to speak, swallow and breathe
    • death typically occurs within 5 years
    • linked to glutamate excitotoxicity, attack by the immune system, or both
  77. developmental aspects of the CNS
    • CNS established during 1st month of development
    • gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal testosterone
    • maternal exposure to radiation, drugs, or infection can harm the developing CNS
    • smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damage
    • age brings some cognitive declines, but not significant in healthy individuals until they reach their 80s
    • shrinkage of brain accelerates in old age
    • excessive use of alcohol causes signs of senility unrelated to the aging process
  78. nerve
    • cordlike organ of the PNS
    • bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue
  79. connective tissue covering of nerves
    • endoneurium - loose connective tissue that encloses axons and their myelin sheaths
    • perineurium - coarse connective tissue that bundles fibers into fascicles
    • epineurium - tough fibrous sheath around a nerve
  80. classification of nerves
    • most are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers
    • pure sensory (afferent) or motor (efferent) nerves are rare
    • types of fibers in mixed nerves
    • -somatic afferent and somatic efferent
    • -visceral afferent and visceral efferent
    • peripheral nerves classified as cranial or spinal nerves
  81. ganglia
    • contain neuron cell bodies associated with nerves
    • - dorsal root ganglia (sensory, somatic)
    • -autonomic ganglia (motor, visceral)
  82. regeneration of nerve fibers
    • mature neurons are amitotic
    • if the soma of a dmg nerve is intact, axon will regenerate
    • involves coordinated activity among-
    • -macrophages - remove debris
    • -Schwann cells- form regeneration tube and secrete growth factors
    • -axons - regenerate dmg part
    • CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration
  83. cranial nerves
    • 12 pairs
    • most mixed in function; 2 pair are purely sensory
    • I olfactory - smell
    • II optic - vision
    • III oculomotor - vision
    • IV trochlear - vision
    • V trigeminal - face
    • VI abducens - vision
    • VII facial - face
    • VIII vestibulocochlear - hearing and balance
    • IX glossopharyngeal - tongue and pharynx
    • X vagus - visceral
    • XI accessory - neck
    • XII hypoglossal - tongue
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  84. sensory, motor or both for cranial nerves
    • I sensory
    • II sensory
    • III motor
    • IV motor
    • V both
    • VI motor
    • VII both
    • VIII sensory
    • IX both
    • X both
    • XI motor
    • XII motor
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  85. olfactory nerves
    • arise from olfactory receptor cells of nasal cavity
    • pass through the cribriform plate of the ethmoid bone
    • fibers synapse in the olfactory bulbs
    • pathway terminates in the primary ofactory cortex
    • purely sensory function
  86. optic nerves
    • arise from the retinas
    • pass through the optic canals, converge and partially cross over at the optic chiasma
    • optic tracts continue to the thalamus, where they synapse
    • optic radiation fibers run to the occipital (visual) cortex
    • purely sensory (visual) function
  87. oculomotor nerves
    • fibers extend from the ventral midbrain through the superior orbital fissures to the extrinsic eye muscles
    • functions in raising the eyelid, directin g the eyeball, constricting the iris (parasympathetic), and controlling lens shape
  88. trochlear nerves
    • fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle
    • primarily a motor nerve that directs the eyeball
  89. trigeminal nerves
    • largest cranial nerves (fibers extend from pons to face)
    • 3 divisions-
    • -ophthalmic (V1) passes through the superior orbital fissure
    • -maxillary (V2) passes through the foramen rotundum
    • -mandibular (V3) passes through the foramen ovale
    • convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication
  90. abducens nerves
    • fibers from the inferior pons enter the orbits via the superior orbital fissures
    • primarily a motor, innervating the lateral rectus muscle
  91. facial nerves
    • fibers from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the face
    • chief motor nerves of the face with 5 major branches
    • motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands
    • sensory funtion (taste) from the anterior 2/3 of the tongue
  92. vestibulocochlear nerves
    • afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border
    • mostly sensory function; small motor component for adjustment of sensitivity of receptors
  93. glossopharyngeal nerves
    • fibers from the medulla leave the skull via the jugular foramen and run to the throat
    • motor functions: innervate part of the tongue and pharynx for swallowing and provide parasympathetic fibers to the parotid salivary glands
    • sensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors
  94. vagus nerves
    • only cranial nerves that extend beyond the head and neck region
    • fibers from the medulla exit the skull via the jugular foramen
    • most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera
    • sensory fibers carry impulses form thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx
  95. accessory nerves
    • formed from ventral rootlets from the C1-C5 region of the spinal cord (not the brain)
    • rootlets pass into the cranium via each foramen magnum
    • accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles
  96. hypoglossal nerves
    • fibers from the medulla exit the skull via the hypoglossal canal
    • innervat extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech
  97. spinal nerves
    • 31 pairs of mixed nerves named by point of issue from spinal cord
    • -8 cervical (C1-C8)
    • -12 thoracic (T1-T8)
    • -5 lumbar (L1-L5)
    • -5 sacral (S1-S5)
    • -1 coccygeal (C0)
  98. roots of spinal nerves
    • each spinal nerve connects to cord via 2 roots
    • -ventral roots - contain motor fibers from the ventral horn motor neurons; fibers innervate skeletal muscles
    • -dorsal roots - contain sensory fibers from sensory neurons in the dorsal root ganglia; conduct impulses from peripheral receptors
    • dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foramina
  99. rami of spinal nerves
    • each spinal nerve branches into mixed rami-
    • -dorsal ramus
    • -larger ventral ramus
    • -meningeal branch
    • -rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region
    • all ventral rami except T2-T12 form interlacing nerve networks called plexuses (cervical, brachial, lumbar and sacral)
    • back is innervated by dorsal rami via several branches
    • ventral rami of T2-T12 as intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall
  100. cervical plexus
    • formed by ventral rami of C1-C4
    • innervates skin and muscles of the neck, ear, back of head, and shoulders
    • phrenic nerve - major motor and sensory nerve of the diaphragm (receives fibers from C3-C5)
  101. brachial plexus
    • formed by ventral rami of C5-C8 and T1 (and often C4 and T2)
    • gives rise to the nerves that innervate the upper limb
    • major branches-
    • -roots - 5 ventral rami (C5-T1)
    • -trunks - upper, middle and lower
    • -divisions - anterior and posterior
    • -cords - lateral, medial, and posterior
  102. nerves of the brachial plexus
    • axillary - innervates the deltiod, teres minor, and skin and joint capsule of the shoulder
    • musculocutaneous - innervates the biceps brachii and brachialis and skin of lateral forearm
    • median - innervates the skin, most flexors and pronators in the forearm, and some intrinsic muscles of the hand
    • ulnar - supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand and skin of medial aspect of hand
    • radial - innervates essentially all extensor muscles, supinators, and posterior skin of limb
  103. lumbar plexus
    • arises from L1-L4
    • innervates the thigh, abdominal wall and psoas muscle
    • femoral nerve - innervates quadriceps and skin of anterior thigh and medial surface of leg
    • obturator nerve - passes through obturator foramen to innervate adductor muscles
  104. sacral plexus
    • arises from L4-S4
    • serves the buttock, lower limb, pelvic structures and perineum
    • sciatic nerve -
    • -longest and thickest nerve of the body
    • -innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot
    • -composed of 2 nerves: tibial and common fibular
  105. Peripheral Nervous System (PNS)
    • all neural structures outside the brain
    • -sensory receptors
    • -peripheral nerves and associated ganglia
    • -motor endings
  106. sensory receptors
    • specialized to respond to changes in their environment (stimuli)
    • activation results in graded potentials that trigger nerve impulses
    • sensation (awareness of stimuli) and perception (interpretation of the meaning of the stimulus) occur in the brain
  107. receptor classification
    • stimulus type
    • location
    • structural complexity
  108. classification of receptor by stimulus type
    • mechanoreceptors - respond to touch, pressure, vibration, stretch and itch
    • thermoreceptors - sensitive to changes in temp
    • photoreceptors - respond to light energy
    • chemoreceptors - respond to chemicals (smell, taste, changes in blood chem)
    • nociceptors - sensitive to pain-causing stimuli (extreme heat or cold, excessive pressure, inflammatory chems)
  109. classification of receptors by location
    • 1 exteroreceptors
    • -respond to stimuli arising outside the body
    • -receptors in the skin for touch, pressure, pain and temp
    • -most special sense organs
    • 2 interoceptors
    • -respond to stimuli arising in internal viscera and blood vessels
    • -sensitive to chemical changes, tissue stretch, and temp changes
    • 3 proprioceptors
    • -respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
    • -inform the brain of one's movements
  110. classification of receptors by structural complexity
    • 1 complex receptors (special sense organs)
    • -vision, hearing, equilibrium, smell, and taste
    • 2 simple receptors for general senses
    • -tactile sensations, temp, pain, and muscle sense
    • -unencapsulated (free) or encapsulated dendritic endings
  111. unencapsulated dendritic endings
    • thermoreceptors
    • -cold receptors (10-40degrees C); in superficial dermis
    • -heat receptors (32-48 C); in deeper dermis
    • nociceptors - respond to--pinching-chemicals from dmg tissue-temps outside the range of thermoreceptors-capsaicin
    • light touch receptors-tactile (merkel) discs-hair follicle receptors
  112. encapsulated dendritic endings
    • all are mechanoreceptors
    • -meissner's (tactile) corpuscles - discriminative touch
    • -pacinian (lamellated) corpuscles - deep pressure and vibration
    • -ruffini endings - deep continuous pressure
    • -muscle spindles - muscle stretch
    • -golgi tendon organs - stretch in tendons
    • -joint kinesthetic receptors - stretch in articular capsules
  113. sensation
    awareness of changes in the internal and external environment
  114. perception
    conscious interpretation of those stimuli
  115. sensory integration
    • input comes from exteroceptors, proprioceptors, and interoceptors
    • input is relayed toward the head, but is processed along the way
  116. levels of neural integration in sensory systems
    • 1 receptor level - sensor receptors
    • 2 circuit level - ascending pathways;
    • 3 perceptual level - neuronal circuits in the cerebral cortex
  117. processing at the receptor level
    • receptors have specificity for stimulus energy
    • stimulus must be applied in a receptive field
    • transduction occurs - stimulus energy is converted into a graded potential called a receptor potential
    • in general sense receptors, the receptor potential and generator potential are the same thing
    • - stimulus> receptor/generator potential in afferent neuron> action potential at first node of Ranvier
  118. processing at the circuit level
    • pathways of 3 neurons conduct sensory impulses upward to the appropriate brain regions
    • - 1st order neurons - impulses from receptor lvl to 2nd order neurons in CNS
    • - 2nd order neurons - impulses to thalamus or cerebellum
    • - 3rd order neurons - impuses from the thalamus to the somatosensory cortex (perceptual lvl)
  119. processing at the perceptual level
    id of the sensation depends on the specific location of the target neurons in the sensory cortex
  120. aspects of sensory perception
    • -perceptual detection - ability to detect a stimulus (requires summation of impulses)
    • -magnitude estimation - intensity is coded in the frequency of impulses
    • -spatial discrimination - id'ing the site or pattern of the stimulus
    • -feature abstraction - id of more complex aspects and several stimulus properties
    • -quality discrimination - ability to id submodalities of a sensation (eg. sweet or sour tastes)
    • - pattern recognition - recognition of familiar or significant patterns in stimuli (eg. melody in music)
  121. perception of pain
    • warns of actual or impending tissue dmg
    • stimuli - extreme pressure and temp, histamine, K+, ATP, acids and bradykinin
    • impulse travel on fibers that release neurotransmitters glutamate and substance P
    • some pain impulses are blocked by inhibitory endogenous opioids
  122. innervation of skin
    • dermatome - the area of skin innervated by the cutaneous branches of a single spinal nerve
    • all spinal nerves except C1 participate in dermatomes
    • most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness
  123. innervation of joints
    hilton's law - any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint
  124. motor endings
    PNS elements that activate effectors by releasing neurotransmitters
  125. innervation of skeletal muscle
    • takes place a neuromuscular junction
    • ACh is the neurotransmitter
    • ACh binds to receptors resulting in -
    • -movement of Na+ and K+ across the membrane
    • -depolarization of the muscle cell
    • -an end plate potential, which triggers an action potential
  126. innervation of visceral muscle and glands
    • autonomic motor endings and visceral effectors are simpler than somatic junctions (ie. neuromuscular junctions)
    • branches form synapses via varicosities
    • acetylcholine and norepinephrine act indirectly via second messengers
    • visceral motor responses are slower than somatic responses (neurotransmitter vs ion channels)
  127. levels of motor control
    • segmental
    • projection
    • precommand
  128. segmental level
    • lowest lvl of the motor hierarchy
    • central pattern generators (CPGs) - segmental circuits that activate networks of ventral horn neurons to stimulate specific groups of muscles
    • controls locomotion and specific, oft-repeated motor activity
  129. projection level
    • consists of -
    • -upper motor neurons that direct the direct (pyramidal) system to produce voluntary skeletal muscle movements
    • -brain stem motor areas that oversee the indirect (extrapyramidal) system to control reflex and CPG-controlled motor actions
    • projection motor pathways keep higher command levels informed of what is happening
  130. precommand level
    • neurons in the cerebellum and basal nuclei
    • -regulate motor activity
    • -precisely start or stop movements
    • -coordinate movements with posture
    • -block unwanted movements
    • -monitor muscle tone
    • -perform unconscious planning and discharge in advance of willled movements
    • cerebellum - acts on motor pathways through projection areas of the brain stem; acts on the motor cortex via the thalamus
    • basal nuclei - inhibit various motor centers under resting conditions
  131. reflexes
    • inborn (intrinsic) reflex - rapid, involuntary, predictable motor response to a stimulus
    • learned (acquired) reflexes result from practice or repetition
  132. reflex arc
    • 1 receptor - site of stimulus action
    • 2 sensory neuron - transmits afferent impulse to CNS
    • 3 integration center - either monosynaptic or polysynaptic region within the CNS
    • 4 motor neuron - conducts efferent impulse from the integration center to an effector organ
    • 5 effector - muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
  133. spinal reflexes
    • spinal somatic reflexes
    • -integration center is in the spinal cord
    • -effectors are skeletal muscle
    • testing of somatic reflexes is important clinically to assess the condition of the nervous system
  134. stretch and golgi tendon reflexes
    • for skeletal muscle activity to be smoothly coordinated, proprioceptor input is necessary
    • -muscle spindles inform the nervous system of the length of the muscle
    • -golgi tendon organs inform the brain as to the amount of tension in the muscle and tendons
  135. stretch reflexes
    • maintain muscle tone in lg postural muscles
    • cause muscle contraction in response to increased muscle length (stretch)
    • how it works -
    • -stretch activates the muscle spindle
    • -sensory neurons synapse directly with motor neurons in the spinal cord
    • -motor neurons cause the stretched muscle to contract
    • all stretch reflexes are monosynaptic and ipsilateral
    • reciprocal inhibition also occurs - fibers synapse with interneurons that inhibit the motor neurons of antagonistic muscles
  136. flexor reflex
    • withdrawal reflex
    • initiated by a painful stimulus
    • causes automatic withdrawal of the threatened body part
    • ipsilateral and polysynaptic
  137. crossed extensor reflex
    • occurs with flexor reflexes in weight-bearing limbs to maintain balance
    • consists of an ipsilateral flexor reflex and a contralateral extensor reflex
    • -stimulated side is withdrawn
    • -contralateral side is extended
  138. superficial reflex
    • elicited by gentle cutaneous stimulation
    • depend on upper motor pathways and cord-lvl reflex arcs
    • plantar reflex
    • babinski's sign
  139. plantar reflex
    • stimulus - stroking lateral aspect of the sole of the foot
    • response - downward flexion of the toes
    • tests function of corticospinal tracts
  140. babinski's sign
    • stimulus - stroking lateral aspect of the sole of the foot
    • response - dorsiflexion of hallux and fanning of toes
    • present in infants due to incomplete myelination
    • in adults, indicates corticospinal or motor cortex dmg
  141. developmental aspects of PNS
    • spinal nerves branch from the developing spinal cord and neural crest cells
    • -supply both motor and sensory fibers to developing muscles to help direct their maturation
    • -cranial nerves innervate muscles of the head
    • distribution and growth of spinal nerves correlate with the segmented body plan
    • sensory receptors atrophy with age and muscle tone lessens due to loss of neurons, decreased numbers of synapses per neuron, and slower central processing
    • peripheral nerves remain viable throughout life unless subjected to trauma
  142. autonomic nervous system (ANS)
    • involuntary nervous system
    • general visceral motor system
    • consists of motor neurons that
    • -innervate smooth and cardiac muscle and glands
    • -make adjustments to ensure optimal support for body activities
    • operate via subconscious control
  143. differences between somatic and autonomic nervous systems
    • effectors: somatic - skeletal muscles; ANS - cardiac muscle, smooth muscle, glands
    • efferent pathways (and their neurotransmitters): somatic - thick, heavily myelinated somatic motor fiber makes up each pathway from the CNS to the muscle; ANS pathway is a 2 neuron chain- 1 preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon, 2 ganglionic neuron in autonomic ganglion has an unmyelinated post ganglionic axon that extends to the effector organ
    • target organ responses to neurotransmitters: somatic - all somatic motor neurons release ACh, effects are always stimulatory; ANS - preganglionic fibers release ACh; postganglionic fibers release norepinephrine or ACh at effectors; effect is either stimulatory or inhibitory, depending on type of receptors
  144. divisions of the ANS
    • sympathetic
    • parasympathetic

    dual innervation - almost all visceral organs are served by both divisions, but they cause opposite effects
  145. role of the parasympathetic division
    • promotes maintenance activities and conserves body energy
    • -blood pressure, heart rate and respiratory rates are low
    • -gastrointestinal tract activity is high
    • -pupils are constricted and lenses are accommodated for close vision
  146. role of the sympathetic division
    • mobilizes the body during activity
    • fight or flight system
    • promotes adjustments during exercise or when threatened
    • -blood flow is shunted to skeletal muscles and heart
    • -bronchioles dilate
    • -liver releases glucose
  147. ANS anatomy
    • sympathetic -
    • -origin of fibers - thoracolumbar region of the spinal cord
    • -length of fibers - short preganglionic and long postganglionic
    • -location of ganglia - close to spinal cord
    • parasympathetic -
    • -origin - brain and sacral spinal cord (craniosacral)
    • -length - long preganglionic and short postganglionic
    • -location of ganglia - in visceral effector organs
  148. parasympathetic (craniosacral) division outflow
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  149. sympathetic (thoracolumbar) division
    • preganglionic neurons are in spinal cord segments T1-L2
    • sympathetic neurons produce the lateral horns of the spinal cord
    • preganglionic fibers pass through the white rami communicantes and enter sympathetic trunk (paravertebral) ganglia
    • rami communicantes are associated with the sympathetic division (not parasympathetic)
  150. sympathetic trunks and pathways
    • upon entering a sympathetic trunk ganglion a preganglionic fiber may do one of these
    • 1 synapse with a ganglionic neuron within the same ganglion
    • 2 ascend or descend the sympathetic trunk to synapse in another trunk ganglion
    • 3 pass through the trunk ganglion and emerge without synapsing
  151. visceral reflexes
    • visceral reflex arcs have the same components as somatic reflexes
    • main difference - visceral reflex arc has 2 neurons in the motor pathway
    • visceral pain afferents travel along the same pathways as somatic pain fibers, contributing to the phenomenon of referred pain
  152. referred pain
    • visceral pain afferents travel along the same pathway as somatic pain fibers
    • pain stimuli arising in the viscera are perceived as somatic in origin
  153. neurotransmitters in ANS
    • cholinergic fibers release the neurotransmitter ACh
    • -all ANS preganglionic axons
    • -all parasympathetic postganglionic axons
    • adrenergic fibers release the neurotransmitter NE
    • -most sympathetic postganglionic axons
    • -exceptions - sympathetic postganglionic fibers secrete ACh at sweat glands and some blood vessels in skeletal muscles
  154. receptors for neurotransmitters in ANS
    • 1 cholinergic receptors for ACh
    • -nicotinic
    • -muscarinic
    • 2 adrenergic receptors for NE
    • -alpha (subtypes alpha1 and alpha2)
    • -beta (subtypes beta1, beta2, beta3)
  155. interactions of autonomic divisions
    • most visceral organs have dual innervation
    • dynamic antagonism allows for precise control of visceral activity
    • -sympathetic division increases heart and respiratory rates, inhibits digestion and elimination
    • -parasympathetic division decreases heart and respiratory rates, and allows for digestion and the discarding of wastes
  156. sympathetic tone
    • sympathetic division controls blood pressure, even at rest
    • sympathetic tone (vasomotor tone)
    • -keeps blood vessels in a continual state of partial constriction
    • sympathetic fibers fire more rapidly to constrict blood vessels and cause blood pressure to rise
    • sympathetic fibers fire les rapidly to prompt vessels to dilate to decrease blood pressure
    • alpha-blocker drugs interfere with vasomotor fibers and are used to treat hypertension
  157. parasympathetic tone
    • parasympathetic division normally dominates the heart and smooth muscle of digestive and urinary tract organs
    • -slows the heart
    • -dictates normal activity levels of the digestive and urinary tracts
    • sympathetic division can override these effects during times of stress
    • drugs that block parasympathetic responses increase heart rate and block fecal and urinary retention
  158. control of ANS functioning
    • hypothalamus - main integrative center of ANS activity
    • subconscious cerebral input via limbic lobe connections influences hypothalamic function
    • other controls come from the cerebral cortex, the reticular formation and the spinal cord
  159. functional brain systems
    • networks of neurons that work together and span wide areas of the brain
    • -limbic system
    • -reticular formation
  160. limbic system
    • structures on the medial aspects of cerebral hemispheres and diencephalon
    • includes parts of the diencephalon and some cerebral structures that encircle the brain stem
  161. reticular formation
    • 3 broad columns along the length of the brain stem
    • -raphe nucle
    • -medial (lg cell) group of nuclei
    • -lateral (sm cell) group of nuclei
    • has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum and spinal cord
  162. reticular formation - motor function
    • helps control coarse limb movements
    • reticular autonomic centers regulate visceral motor functions
    • -vasomotor
    • -cardiac
    • -respiratory centers
  163. hypothalamic control
    • control may be direct or indirect (through the reticular system)
    • centers of the hypothalamus control
    • -heart activity and blood pressure
    • -body temp, water balance, and endocrine activity
    • -emotional stages (rage, pleasure) and bio drives (hunger, thirst, sex)
    • reactions to fear and the "fight or flight" system
  164. developmental aspects of ANS
    • preganglionic neurons are derived from the embryonic neural tube
    • autonomic structures located in the PNS are derived from the neural crest
    • during youth ANS impairments are usually due to injury
    • in old age, ANS efficiency declines, partially due to structural changes at preganglionic axon terminals
Card Set
A&P ch 12-14
A&P ch12-14