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NERVOUS SYSTEM (8.3 - IN NEURONS, A CHANGE IN THE PLASMA MEMBRANE'S…

- - - - less neg(-) = depolarization
        
        must be depolarized to about -55mV
      - more neg(-) = hyperpolarization
  - - - RESULTS FROM DISTRIBUTION OF IONS ACROSS CELL MEMBRANE
        
        NEGATIVELY CHARGED PROTEINS OR ANIONS HIGH INSIDE
        
        K+ HIGH INSIDE
        
        Cl- HIGH OUTSIDE
        
        Na+ HIGH OUTSIDE
    - - electrically charged (charge on inside is diff from charge on the outside
  - - - threshold potential for neuron is -55mV
      - threshold stimulus is +15mV
  - - - REFRACTORY PERIOD
        
        period following NI when a threshold stimulus cannot produce another NI (RMP must be restored in order depolarize again)
      - ALL OR NOTHING RESPONSE
        
        if a nerve cell responds at all, it responds completely
        
        threshold stimulus (15mV) = yes AP; yes NI
        
        threshold stimulus (20 mV) = yes AP; yes NI, but no greater intensity than above
        
        sub-threshold stimulus (5mV) = no AP; no NI
      - SUMMATION
        
        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 conduction"
        
        NI jumps from node of Ranvier to node of Ranvier; very fast transmission
  - - - SYNAPSE
        
        the junction between 2 neurons where a nerve impulse is transmitted
- - - - provide 2-way system of communication
        
        ascending tracts located in the posterior dorsal columns and conduct senosry (afferent) impulses from body barts to brain
        
        descending tracts located in anterior(ventral) columns and conduct motor (efferent) impulses from brain to effectors
        -general characteristics of nerve tracts
        
        most crossover
        
        most have 2-3 successive neurons
        
        most exhibit somatotrophy (tracts from to upper body are located on outside; tracts from to lower body on inside)
        
        all pathways are paired (right and left)
- - - - contains brain and spinal cord, indicated and coordinates the processing of sensory data and the transmission of motor commands; also the seat of higher function such as intelligence, memory, and emotion
    - - all communication between the CNS and the rest of the body occurs over the PNS, includes all neural tissue outside of CNS
        
        somatic nervous system (SNS) - efferent division; provides control over skeletal muscle contractions
        
        autonomic nervous system (ANS) - aka visceral motor system; efferent division; provides automatic involutary regulation of smooth muscle, cardiac muscle, and glandular secretions
        
        sympathetic division
        
        parasympathetic division (typically opposite from :arrow_double_up: )
        
        somatic and autonomic
        
        action potential
    - - afferent - sensory info detected outside of the nervous system (by receptors) is transmitted by afferent division, where info is processed
      - efferent - CNS then sends motor commands by means of the efferent division of the PNS to smooth and cardiac muscle and glands (called effectors)
- - - - outermost membrane; attached to inner periostem of skull;tough, white fibrous CT; many blood vesssels and nerves; splits into two layers where it encloses dural sinuses
    - - inner layer; clings to brain surface; thin, delicate CT, many nerves and blood vessels (nourishment); dips into grooves and contours; subdural hematoma and meningitis
      - spinal chord - dural mater is not attached to bone of vertebra, epidural space is space between dura mater and bone (filled with loose CT and fat); CSF fills sub arachnoid space and central canal
    - - middle layer; thin, netlike membrane; under it lies a wide space called sub arachnoid space;
        filled with CSF and serves as brain cushion
  - - - csf is secreted by specialized capillaries in choroid plexuses in lateral ventricles (1 and 2)
      - circulates down into 3rd then 4ths ventricle
      - central canal of spinal chord
      - subarachnoid of meninges
      - csf is reabsorbed back into bloodstream through arachnoid granulations that project into dural sinuses
      - csf movement is aided by cilia of epidymal cells
    - - total vol = 150 mL (about 1 liter daily to replenish circulating 150 mL 3-4 hours
      - functions - mehanical protection, chemical protection
- - - - are the basic units of the nervous system; all neural functions involve the communications of neurons with one another and other cells
        
        general structure
        
        several branches
        
        dendrites - receive incoming signals
        
        cell body
        
        most lack centrioles (organelles involved in movement of chromosomes during mitosis; therefore cannot be replaced)
        
        neural stem cells persist in adult nervous system and are typically inactive except in the nose for the sensation of olfactory or sense of smell and the hippocampus (portion of brain involved with memory storage)
        
        large, round nucleus with a prominent nucleolus
        
        Nissl bodies - give gray color to areas containing neuron cell bodies and account for the color of gray matter seen in brain and spinal chord dissections
        
        timulation - action potential which travels along axon; begin at axon hillock; axon may branch - creating collateral; a synaptic terminal is part of a synapse (site where neuron communicates w/ another cell)
        
        axon - carries outgoing signals toward one or more synaptic terminals
        
        in cns ( Myelin is produced by oligodendrocyte ) in pns (Large axons are surrounded by a myelin sheath produced by many layers of Schwann Cells)
        
        structural classification (3 types)
        
        unipolar neuron - dendrites and axon are continuous; cell body lies off to one side; action potential begins at base of dendrites and rest of process is considered an axon; most sensory neurons of the peripheral nervous system are unipolar
        
        bipolar neurons - two processes - one dendrite and one axon with the cell body between them; rare, but occur in special sense organs where they can relay info about sight, smell, or hearing from receptor cells to other neurons
        
        multipolar neuron - has two or more dendrites and a single axon; most common neuron in CNS; all motor neurons that cotrol skeletal muscles are multipolar
        
        functional classification of neurons (3 functional groups)
        
        motor neurons
        
        interneurons
        
        sensory neurons
        
        approx. 10 million sensory neurons in afferent PNS
        
        receptors categories by what info they receive
        
        somatic sensory receptors (sensory neurons)
        
        detect info about the outside world or our physical position
        
        types
        
        3 more items...
        
        motor neurons
        
        .5 billion in efferent division of CNS carry instructions to other tissues, organs, or organ systems
        
        peripheral targets (effectors) - respond by doing something
        
        two efferent divisions
        
        3 more items...
        
        interneurons
        
        20 billion interneurons (association neurons; interconnect othe neurons) are located within the brain and spinal chord; also play role in higher function (such as memory, planning, and learning)
        
        1 more item...
      - organization of neruons in the nervous system
        
        organized in bundles/masses that have distinct anatomical boundaries
        
        neuron cell bodies (gray matter) are located in ganglia
        
        PNS white matter contains axons bundled together in nerves (spinal nerves to spine, cranial nerves to brain); both sensory + motor axons may be present in the same nerve
        
        center - collection of neuron cell bodies w/ common function; center with discrete boundaries = nucleus
        
        neural cortex - portions of brain surface are covered by thick layer of gray matter
        
        white matter of CNS contains bundles (tracts; form larger groups called columns in spinal chord) of axons that share common origins, destinations, and functions
    - - (much smaller than neurons, aka glial cells) outnumber neurons, most retain ability to divide; regulate the environment around neurons, provide a framework for neural tissue, and act as phagocytes
        
        found in CNS (greater variety of glial cells) and PNS
        
        4 TYPES (CNS)
        
        oligodendrites
        
        nodes (of ranvier) - gaps between adjacent cell processes
        
        myelinated axon - each oligodendrite does this to short segments of several axons, many are needed to coat an entire axon with myelin (not everyone is myelinated; aka unmyelinated)
        
        internodes - areas covered in myelin (increases speed at which an action potential travel along axon)
        
        thin, expanded tips wrap around axons - creates membranous sheath of insulation made of myelin
        
        myelin - lipid-rich; appears glossy white on dissection; constitue white matter of CNS
        
        oligo- meaning FEW; have fewer processes (cytoplasmic extensions) than astrocytes
        
        microglia
        
        perform protective functions such as engulfing cellular waste and pathogens
        
        phagocytic cells derived from white blood cells that migrated into the CNS as the nervous system formed
        
        smallest and rarest of the neuroglia in the CNS
        
        astrocytes
        
        create structural frameworks for CNS
        
        largest + most numerous glial cell
        
        perform repairs in damaged neural tissues
        
        secrete chemicals vital to maintenance of the blood-brain barrier(isolates CNS from general circulation); causes capillaries of the CNS to become impermeable to many compounds that could interfere w/ neuron function
        
        ependymal
        
        ependyma produces CSF in some regions of brain and cilia on epidymal cells in other locations - help circulate this fluid within and around CNS
        
        the lining is called the ependyma
        
        line central canal of spinal chord and chambers/ventricles of the brain - cavities filled with cerebrospinal fluid (CSF)
        
        2 TYPES (PNS)
        
        satellite cells
        
        surround and support neuron cell bodies (like astrocytes in CNS)
        
        schwann cells
        
        cover every axon outside of CNS
        
        whenever one covers and axon, outer surface is called the neurilemma
        
        can myelinate only one segment of a single axon unlike oligodendrite in CNS that myelinates portions of several adjacent axons
        
        can endorse portions of several diff unmyelinated axons