Lecture CNS 2

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Lecture CNS 2
2012-05-03 22:34:17
functional brain systems spinal cord homeostatic imbalances developmental aspects LCCC lecture Bio 163

functional brain systems, spinal cord, homeostatic imbalances, developmental aspects LCCC lecture Bio 163
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  1. Functional Brain systems
    Limbic system

    Reticular formation
  2. Limbic System (limbic means ring)
    Structures on the medial aspects of the cerebral hemispheres and the dienchephalon

    include parts of the diencephalon and some cerebral structures that encircle the brain stem

    • Emotional of affective brain
    • -Amygdala--recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response
    • -Cingulate Gyrus--plays a role in expressing emotions via gestures, and resolves mental conflict

    • Puts emotional response to odors (like skunk=bad smell)
  3. Limbic System: Emotion and cognition
    • the limbic system interacts with the prefrontal lobes, therefore:
    • -we can react remotionally to things we consciously understand to be happening
    • -we are consciously aware of emotional richness in our lives

    Hippocampus and amygdala--play a role in memory
  4. Reticular formation
    • Three broad columns along the length of the brain stem
    • 1. Raphe nuclei (midline)
    • 2. medial (large cell) group of nuclei
    • 3.Lateral (small cell) group of nuclei

    has far flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord (reticular neurons govern the arousal of the brain as a whole)
  5. reticular formation: RAS and motor function
    • RAS: reticular activating system
    • -sends impulses to the cerebral cortex to keep it conscious and alert
    • -filters out repetitive and weak stimuli (about 99% of all stimuli)
    • - severe injurt results in permanent unconcsiousness (coma)

    • Motor Function:
    • -helps control course limb movements
    • -reticular automonic centers regulate visceral motor functions
    • *vasomotor
    • *cardiac
    • *respiratory centers
  6. Electroencephalogram (EEG)
    Records electrical activity that accompanies brain function

    measure electrical differences between various cortical areas
  7. Brain Waves
    Patterns of neuronal electrical activity

    Generated by synaptic activity in the cortex

    Each person's brain waves are unique

    Can be grouped into four classes based on frequency measures as Hertz (Hz)
  8. Types of brain waves
    Alpha waves (8-13Hz): regular and rhythmic, low-amplitude, synchronous waves indicating an "idling" brain

    Beta waves (14-30 Hz)- rythmic, less regular waves occuring when mentally alert

    Theta Waves (4-7 Hz): More irregular; common in children and uncommon in adults

    • Delta waves (4 or less)- high amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage
  9. Brain waves: state of the brain
    -Change with age, sensory stimuli, brain disease, and the chemical state of the body

    EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epilecptic regions

    A flat EEG (no electrical activity) is clinical evidence of death
  10. Epilepsy
    A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable leg jerking

    Epilepsy is not associated with intellectual impairments

    occurs in 1% of the population

    • Absent Seizures (petit mal)
    • -mild seisures seen in young children where expression goes blank

    • Tonic-clonic (grand mal) seizures
    • -victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and sever biting of tongue
    • -sometimes precursed by an "aura"

    • Controlling epilepsy:
    • -anticonvulsive drugs
    • - vagus nerve stimulators implanted under the skin of the chest can keep electrical activity of the brain from becoming chaotic
  11. Consciousness
    -Conscious perception of sensation

    -voluntary initiation and control of movement

    -capabilities associated with higher mental processing (memory, logic, judgement, etc)

    -loss of consciousness (fainting, coma) is a signal that brain function is impaired

    • -Clinically defined on a continuum that grades behavior in response to stimuli
    • 1. Alertness
    • 2. Drowsyness (lethargy)
    • 3. Stupor
    • 4. Coma
  12. Sleep
    State of Partial unsconcniousness from which a person can be aroused by stimulation

    • Two major types of sleep (defined by EEG patterns)
    • 1. Nonrapid eye mvoement (NREM)
    • 2. rapid eye movement (REM)

    First two stages of NREM occur during the first 30-45 minutes of sleep

    Fourth stage is achieved in about 90 minutes, and then REM sleep begins abruptly
  13. Sleep patterns
    • Alternating cycles of sleep and wakefulness reflect a natural circadian (24 hour)
    • -hypothalamus is responsible

    RAS actively is inhibited during, but RAS also mediates, dreaming sleep

    A typical sleep pattern alternates between REM and NREM sleep

    • The brain uses more O2 during REM than when awake
  14. Importance of Sleep
    NREM stages 3 and 4 are presumed to be the restorative stage

    People deprives of REM sleep become moody and depressed

    REM sleep may be a reverse learning process where superfluous information is purged from the brain (we dream to forget)

    Daily sleep requirements decline with age

    Stage 4 sleep declines steadily and may disapear after age 60
  15. Sleep disorders
    • Narcolepsy
    • - lapsing abruptly into sleep from the awake state

    • Insomnia
    • -chronic inability to obtain the amount or quality of sleep

    • Sleep apnea
    • -temporary cessation of breathing during sleep
  16. Language
    • Language implementation system:
    • -basal nuclei
    • -Broca's areas and Wernicke's areas (in association cortex on the left side)
    • -Analyzing incoming word sounds
    • -Produces outgoing word sounds and grammatical structures

    Corresponfing areas on the right side in involved with nonverbal language components
  17. Memory
    Storage and retrieval of information

    • Two stages of storage:
    • 1. Short term memory (STM, or working memory)--temporary holding of information; limited to seven or eight pieces of information
    • 2. Long term memory (LTM) has limitless capacity
  18. Transfer from STM to LM
    Factors that affect transfer from STM to LM

    1. Emotional State: best if alert, motivated, surprise, and aroused

    2. rehearsal- repetition and practice

    3. association- tying new information with old memories

    4. automatic memory- subconcious information stored in LTM
  19. Categories of Memory
    • 1. Declaritive Memory (factual knowledge)
    • -explicit information
    • -related to our conscious thoughts and our language ability
    • -stored in LTM with context in which it was learned

    • 2. Nondeclarative Memory
    • -less conscious or unconscious
    • -aquired through experience and repetition
    • -best remembered by doing; hard to unlearn
    • -includes procedural (skills) memory (like piano), motor memory (riding a bike), and emotional memory (fear)
  20. Brain structures involved in declarative memory
    -hippocampus and surrounding temporal lobes function in consolidation and acees to memory

    • ACh from basal forebrain is necessary for memry formation and retrieval (primes the area for making memories)
  21. 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
  22. Molecular Basis for learning
    During learning
    • During learning:
    • -altered mRNA is synthesized and move to axons and dendrites
    • -Dendrinic spine changes shape
    • -Extracellular protiens are depositied at synapses involved in LTM
    • -Number and ize of presynaptic terminals may increase
    • -More neurotransmitter is released by presynaptic neurons

    Increase in synaptic strength (long term potentiantion, or LPT) is crucial
  23. Molecular basis for learning
    Neurotransmitter (glutamate) binds to NMDA receptors, opneing calcium channels in postsynaptic terminal

    Ca influx triggers enzymes that modufy protiens of the postsynaptic terminal and presynaptic terminal (via release of retrograde messengers)

    Enzymes trigger postsynapticgene activation for synthesis of synaptic protiens, in presence of CREB (cAMP respnse-element binding protien) and BDNF (brain derived neutotrophic factor)
  24. Protection of the Brain
    Bone (skull)

    Membranes (meninges)

    Watery cushion (CSF)

    Blood-brain barrier
  25. Meninges
    Cover and protect the CNS

    Protect blood vessels and enclose the venous sinuses

    Contain CSF

    Form partitions in the skull

    • Three layers:
    • Dura matter
    • Arachnoid Matter
    • Pia matter
  26. Dura Matter
    Strongest meninx

    Twolayers of fibrous connective tissue around the brain seperate to form dural sinuses

    • Dural septa limit excessive movment of the brain
    • -Falx cerebri--in the longitudinal fissure attached to the crista gali
    • -Falx cerebelli-- along the vermis of the cerebellum
    • -Tentorium cerebelli- horizontal dural fold over cerebellum and in the transverse fissure
  27. Arachnoid matter
    Middle layer with weblike extensions

    separated from dural mater by the subdural space

    subarachnoid space contains CSF fluid and blood vessels

    Arachnoid vili protrude into the superior sagittal sinus and permit CSF reabsorption
  28. Pia matter
    layer of delicate vascularized connective tissue that clings tightly to the brain
  29. CSF functions
    gives buoyancy to the CNS organs

    Protects the CNS from blows and other trauma

    nourishes the brain and carries chemical signals

    about 500 mL formed daily
  30. Choroid Plexus
    Produces CSF at a constant rate hang from the roof of each ventricle

    clusters of cappularies enclosed by pia mater and a layer of ependymel cells

    ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing waste

  31. Blood Brain barrier
    helps maintain a stable enviornment for the brain

    separates neurons from some bloodborne substances

    • Composition
    • 1. continyous endothelium of capillary walls
    • 2. basal lamina
    • 3. feet of astrocytes (provides signal to endothelium for the formation of tight junctions)
    • *astrocytes are the most abundant CNS neuroglia
  32. 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, eg, vomiting center of the hypothalamus where it is necessary to monitor the chemical composition of the blood
  33. Homeostatic Imbalances of the Brain
    Traumatic brain injuries
    concussion- temporary alteration in function

    contusion- permanent damage

    subdural or subarachnoid hemorrhage- may force brain stem through the foramen

    cerebral edema-- swelling of the brain associated with traumatic head injury
  34. Homeostatic Imbalances of the Brain
    Cerebrovascular accident (CVAs)/strokes
    blood circulation is blocked and brain tissue dies

    typically leasd to hemilegia (paralization of one side), or sensory and speed deficits

    transient ischemic attackes (TIAs)- temporary episode of reversivle cerebral iscemia--> red flag for CVAs

    tissue plaminogen activator (TPA) is the only approved treatment for stroke
  35. Homeostatic Imbalances of the Brain
    Degenerative Brain disorder
    Alzheimers disease (AD): a progressive degenerative disease of the brain that results in dimentia

    Parkinsons disease: degeneration of the dopamine-releasing neurons of the substantia nigra

    Huntington's disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex
  36. Embryonic development of the spinal cord
    • by week 6, there are two clusters of neuroblasts
    • -Alar plate: will become interneurons; axons form white matter of cord
    • -basal plate: will become motor neurons; axons will grow into effectors

    • Neural crest cells form the dorsal root ganglia sensory neurons; axons grow into the dorsal aspect of the cord
  37. Spinal cord
    location and function
    • Begins at the foramen magnum
    • ends at conus medullarus at L1 vertebrae

    • Functions:
    • -provides two way communication to and from the brain
    • -contains spinal reflex centers
  38. Protection of the spinal cord
    Bone, meninges, and CSF

    Cushion of fat and a network of beins in the epidural space between the vertebrae and spinal dura mater

    CSF in subarachnoid space

    Denticulate ligaments: extensions of the pia mater that secure cord to the dura mater

    • Filum terminale: fibrous extension from conus medullaris; achors the spinal cord to the coccyx
  39. Spinal cord
    31 pairs of spinal nerves

    • 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
  40. Cross sectional anatomy of the spinal cord
    • two lengthwise groove divide cord into right left halves
    • 1. Ventral (anterior) median fissure
    • 2. Dorsal (posteriot) median sulcus

    • Gray commisure: connects the masses of gray matter; encloses the central canal
  41. gray matter of spinal cord
    Dorsal horns: interneurons that recieve somatic and visceral sensory input

    Ventral horns: somatic motor neurons whose axons exit the cord via ventral roots

    Lateral horns (only in T and L regions)- sympathetic neurons

    Dorsal Root (spinal) ganglia- contain cell bodies of senory neurons
  42. white matter of spinal cord
    consists mostly of ascending (Sensory) (to the brain) and descending (motor)(from the brain) tracts

    transverse tracts (commissural fibers) cross from one side to the other

    tracts are located in three white columns (funiculi on each side- posterior, anterior, and lateral)

    each spinal tract is composed of axons with similar functions
  43. Pathway generalizations
    pathways decussate (Cross over)

    most consist of two ir three neurons (a relay)

    most exhibit somatotopy (precise spatial relationships which reflect orderly mapping)

    • pathways are paired symmetrically (one on each side of the spinal cord or brain)
  44. Ascending pathways
    3 neurons
    • consist of three neurons:
    • 1. First order neurons
    • -conducts impulses from cutaneous receptors and proprioceptors
    • -branches diffusely as it enters the spinal cord or medulla
    • -synapses with second-order neuron

    • 2. Second order neurons
    • -interneuron
    • -cell body in dorsal horn of spinal cord or medullay nuclei
    • -axons externd to thalamus or cerebellum

    • 3. Third order neuron
    • -Interneuron
    • -cell body in thalamus
    • -axon extends to somatosensory cortex
  45. Ascending pathways
    via the thalamas
    • Two pathways transmit somatosensory information to the sensory cortex via the thalamus
    • 1. dorsal column-medial lemniscal pathways
    • 2. Spinalthalamic pathways

    Spinocerebral tracts terminate in the cerebellum
  46. Dorsal Column-Medial Lemniscal Pathways
    Transmit input to the somatosensory cortex for discriminative touch and vibrations

    • composed of paired fasiculus cuneatus and fasciculus gracilis in the spinal cord and the medial lemniscus in the brain (medulla to thalamus)
  47. Anterolateral Pathways
    Lateral and ventral spintothalamix tracts

    • transmit pain, temperature, and course touch impulses within the lateral spinothalamic tract
  48. Spinocerebral pathways
    ventral and dorsal tracts

    • convey information about muscle or tendon stretch to cerebellum
  49. 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
  50. The Direct (pyramidal) system
    Impulses from the pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal) tracts

    Axons synapse with interneurons or ventral horn motor neurons

    • The direct pathway refulates fast and fine (skilled) movements)
  51. Indirect (extrapyramidal) system
    includes the brain stem motor nuclei, and all motor pathways except pyramidal pathways

    also called the multineruonal pathways

    These pathways are complex and multisynaptic

    • regulate:
    • -axial muscles that maintain balance and structure
    • -muscles controlling course movments
    • -head, neck, and eye mvoements that follow objects

    -Reticulospinal and vestibulospinal tracts--maintain balance

    Rubrospinal tracts--control flexor muscles

    • Superior colliculi and tectospinal tracts mediate head movements in reponse to visual stimuli
  52. Spinal cord trauma
    • Functional Losses:
    • -Parasthesias-sensory loss
    • -Paralysis- loss of motor function

    • Flaccid Paralusis: sever damage to the ventral root or ventral horn cells
    • -impulses do not reach muscles; there is no voluntary or involuntary control of muscles
    • -muscles astrophy

    • Spastic Paralysis: damage 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 the cerivical region
  53. Poliomyelitis
    destruction of the ventral horn motor neurons by the poliovirus

    muscles astrophy

    death may occur due to paralysis of respiratory muscles or cardiac arrest

    survivors often develop postpolio syndrome many years later, as neurons are lost
  54. Amyotrophic Lateral Sclerosis (ALS)
    Also called Lou gehrigs disease

    Involves progressive destruction of ventral horn motor neurons and the fibers of the pyramidal tract

    Symptoms: loss of the ability to speak, swallow, or breathe

    Death typically occurs within 5 years

    linked to glutamate excitotoxicity, attack by the immune system, or both
  55. Developmental aspects of the CNS
    CNS is established within the first month of development

    gender-specific areas appear both in the brain and spinal cord, depending on the prescense or absence of fetal testosterone

    maternal exposure to radiation, drugs, or infection can hard the developing CNS

    Smoking decreases O2 in blood, which can lead to neuron death and fetal brain damage

    the hypothamalus is one of the last areas of the CNS to develop

    visual cortex develops slowly over the first 11 weeks

    neuromuscluar coordination progresses in superior to inferior and proximal to distal directions along with myelination

    age brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s

    shrinkage of the brain accelerates in old age

    excessive use of alcohol causes signs of senility unrelated to the aging process