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Chapter 8: Nervous System (Kahoot 8.4-8.6 (The dural sinuses are located…

- - - - brain & spinal cord
    - - nerves that extend from brain (cranial nerves) and spinal cord (spinal nerves)
  - - - CNS
      - involves interpretation of an incoming sensory impulse (decision is made concerning what is gong to happen next, based on sensory impulse)
      - integration occurs in interneurons
      - a motor pulse beings
    - - PNS
      - involves the response of a body part
      - motor impulses are carried fro the CNS to responsive body parts called effectors
      - a motor impulse is carried on a motor neuron
      - 2 types of effectors
        
        muscle (that contracts)
        
        glands (that secrete a hormone)
    - - sensory receptors (at end of peripheral neurons) detect changes (are stimulated) occurring in their surroundings
      - once stimulated, sensory receptors transmit a sensory impulse to the CNS
      - PNS
      - a sensory impulse is carried on a sensory neuron
- - - - Somatic (effectors: skeletal muscle & conscious control)
      - Autonomic (effectors: smooth muscle & cardiac muscle & glands & unconscious control)
        
        Parasympathetic (Homeostasis, rest and digest & NT: acetocholine)
        
        Sympathetic (fight-or-flight & NT: norepinephrine)
- - - - Each cell has a cell body & many extensions from the cell body called neuron processes or nerve fibers
        
        Cell body = central portion of neuron; contains usual organelles, except centrioles
        
        Neuron processes/ nerve fibers = extensions from cell body; 2 types
        
        Dendrites
        
        short and branched
        
        receptive portion of neuron
        
        many per neuron
        
        carry impulses toward cell body
        
        Axons
        
        long, thin process
        
        carry impulses away from cell body
        
        note terminations of axon branch = axonal terminals; synaptic knobs
        
        one per neuron
        
        Axons in PNS
        
        large axons are surrounded by a myelin sheath produced by many layers of Schwann cells (neuroglial cell)
        
        myelin = lipoprotein
        
        interruptions in the myelin sheath between schwann cells = nodes of ranvier
        
        "myelinated nerve fiber"
        
        small axons do not have myelin sheath
        
        "unmyelinated nerve fibers"
        
        however allaxons (in PNS) are associated with Schwann cells
        
        Axons in the CNS
        
        A bundle of myelinated nerve fibers = white matter
        
        PNS = nerve
        
        CNS = tract/column
        
        This is in contrast to CNS gray matter = a bundle of cell bodies (or unmyelinated nerve fibers)
        
        PNS = ganglia
        
        CNS= nucleus
        
        Myelin is produced by an oligodendrocyte, instead of Schwann cells
    - - cell body injury = death of neuron
      - damage to an axon may allow for regeneration
    - - PNS = schwann cells produce myelin, and satellite cells nourish neurons
      - CNS = 4 types, provide bilk of brain and spinal cord tissue
        
        astrocyte, star shaped, nourishes neurons, largest
        
        microglia, looks like a spider, does phagocytosis
        
        ependymal cells, epithelial-like layer, lines spaces in CNS, brain = ventricles, spinal cord = central canal
        
        oligodendrocytes, looks like eyeball and produces myelin
    - - Functional classification
        
        Interneurons (association)
        
        CNS
        
        link other neurons together (ex. sensory neuron to interneuron to motor neuron)
        
        Motor neurons
        
        efferent neurons
        
        carry motor impulses away from CNS and to effectors
        
        PNS
        
        output information from CNS
        
        effectors = muscles & glands
        
        somatic motor neurons (skeletal muscles)
        
        visceral motor neurons (muscle & glands)
        
        sympathetic (adrenegic)
        
        parasympathetic (cholinergic)
        
        sensory neurons
        
        carry sensory impulses from sensory receptors to CNS
        
        input information to CNS
        
        afferant neurons
        
        location of receptors = skin & sense organs
        
        somatic receptors
        
        external receptors (touch, pressure, temp, sight, smell, hearing, & touch)
        
        Proprioceptors (position & movement)
        
        Visceral receptors (digestive, respiratory, cardiovascular, urinary, reproductive, taste, deep pressure & pain
        
        PNS
      - Structural classification
        
        Bipolar neurons (rare, sight, smell, & hearing)
        
        two extensions
        
        one fused dendrite leads toward cell body, one axon leads away from cell body
        
        unipolar neurons (most PNS sensory neurons)
        
        forms central and peripheral processes
        
        only distal ends are dendrites
        
        one process from cell body
        
        Multipolar neurons (most common neuron in CNS)
        
        many extensions
        
        many dendrites lead toward cell body, one axon leads away from cell body
- - - - 1) more negative = "hyperpolarization" -80 or -90
      - 2) less negative (towards 0) = "depolarization"
        
        the cell membrane of a neuron must be depolarized (to approx. -55 mV) in order far a certain ion channel to open and therefore start a nerve impulse
  - - - this is called action potential
      - the action potential represents the start of the nerve impulse on a neuron
    - - threshold is -55 mV
      - a threshold stimulus = +15 mV
  - - - K+ high outside
      - NA+ high outside
      - Cl- high outside
      - negatively charged proteins or anions, high outside
  - - - an NI is similar to a row of dominos falling
      - a nerve impulse begins on a dendrite, runs towards the cell body, through cell body, and then down the axon
      - The NI is an electrical impulse
    - - refractory period = period following a NI when a threshold stimulus cannot produce another NI
        
        The RMP has to be restored before it can be depolarized again, dominos must be set up in order to be knocked down again.
      - All or nothing response = if a nerve cell responds at all, it responds completely
      - Summation = many subthreshold stimuli received one after another may allow threshold potential to be reached, triggered an AP and begin an NI on a neuron
      - Conduction = the manner in which the NI runs down the neuron/nerve fiber
        
        unmyelinated nerve fibers: NI must travel the length of the nerve fiber, slow
        
        myelinated nerve fiber: "Saltatory condution" NI jumps from node of ranvier to node of ranvier, very fast
  - - - at least 30 different produced by CNS
      - some neurons produce/release only one while released many
      - most typical NT is acetocholene (ACh)
        
        ACh is released by all motor neurons and some CNS neurons
      - Other NTs include:
        
        monoamines (modified amino acids)
        
        are widely distributed in the brain where they play a role in emotional behavior and circadian rhythm
        
        are present in some motor neurons of the ANS
        
        include epinephrine, norepinephrine, dopamine, serotonin, histamine
        
        unmodified amino acids
        
        glutamate
        
        aspartate
        
        GABA
        
        glycine
      - Fate of neurotransmitter in synaptic cleft
        
        destruction of neurotransmitter: enzymes that are present in cleft destroy NT
        
        reuptake of NT: NT is transported back into pre-synaptic knob
        
        both prevent continual stimulation of post-synaptic membrane
    - - include enkephalins
        
        synthesis is increased during painful stress
        
        bind to same receptors in brain as the narcotic morphine
        
        relieve pain
      - include endorphines
        
        same as above, but with more potent and longer lasting effect
      - act as NTs or neuromodulators that either alter a neuron's response to a NT or block the release of a NT
      - synthesized by CNS neurons
    - - synaptic vesicles to release NT via exocytosis into the synaptic cleft
      - NT diffuses across celft and depolarizes the post-synaptic neuron's membrane
      - AP is triggered and a NI begins in the post-synaptic neuron
      - Ca+ channels open and calcium ions rush into axonal terminal causing
      - NI reaches axonal terminal of pre-synaptic neuron causing depolarization of synaptic knob
    - - Insomnia = deficient serotonin
      - Mania = excess norepinephrine
      - Epilepsy = excess GABA leads to excess norepinephrine & dopamne
      - SIDS = excess dopamine
      - Alzheimer's = deficient ACh
    - - note that two neurons do not touch. there is a gap between them = synaptic cleft
      - occurs between the axon of one neuron and dendrite or cell body of a second neuron
- - - - Arachnoid mater
        
        middle layer
        
        thin net-like membrane
        
        beneath the anarchnoid mater lies a wide space called sub-arachnoid space, its filled with cerebrospinal fluid and serves as a cushion for brain
      - Pia mater
        
        inner layer that clings to brain surface
        
        very thin delicate CT
        
        many nerves & blood vessels = nourishment
        
        dips into grooves & contours
      - Dura mater
        
        tough, white fibrous CT
        
        contains many blood vessels & nerves
        
        outermost membrane that is attached to the inner periosteum of skull
        
        DM splits into 2 layers where it encloses the dural sinuses)
    - - the space between the DM and the bone is called the epidural (subdural) space and is with loose CT and fat
      - CSF fills the subarachnoid space and central canal
      - note that the DM is not attched to bone of the vertebra (like in the brain where it is attached to skull)
  - - - CSF is secreted by specialized capillaries in charoid plexus into the lateral ventricles (1 & 2)
      - CSF circulates down into the 3rd and then 4th ventricle and then into either the central canal of spinal coed or the subarachnoid space of meninges
      - CSF is reabsorbed back into the bloodstream through arachnoid granulations that project into dural sinuses
      - CSF movement is aided by cilia of ependymal cells
    - - Total volume in above spaces = 150 mL
        
        about 1 liter is secreted daily to replenish the circulating 150 mL every 3-4 hours
      - Functions as mechanical protection, like cushion, and chemical protection, like ions and hormones.
- - - - starts at foramen megnum and ends at a tapered point called the conus medullaris and terminates near the intervertebral disc that separates L1 and L2
  - - - locations: posterior (dorsal) funiculi or white column, lateral funculi or white column and anterior (ventral) funiculi or white column
      - white matter of the spinal cord represents the location of out major nerve pathways called "nerve tracts", they provide a 2-way system of communication
        
        in general, descending tracts are located in anterior columns and conduct motor or efferent impulse from brain to effectors
        
        General characteristics of nerve tracts: most cross over, most consist of 2-3 successive neurons, most exhibit somatotropy, and all pathways are paired
        
        in general, ascending tracts are located in posterior columns and conduct sensory or afferent impulse from body parts to brain
    - - ventral root
      - dorsal root
        
        dorsal root ganglion (DRG)
        
        ganglion = a bundle of cell bodies outside the CNS
        
        DRG contains the cell bodies of sensory or afferent neurons bringing impulses to CNS
      - the fusion of the dorsal and ventral roots designates the beginning of spinal nerve which then passes through its intervertebral foramen
    - - lateral horns
      - anterior (ventral) horns
      - posterior (dorsal) horns