Physio Midterm II

  1. Neuron
    One nerve cell, includes dendrites, cell body (soma), axon to conduct nerve impulses
  2. Nerve Fibers
    Axons, peripheral and central processes
  3. Nerve
    A bundle of nerve fibers
  4. Ganglia
    A collection of neuron cell bodies located outside the CNS
  5. CNS
    Central Nervous System
  6. PNS
    Peripheral Nervous System
  7. Nuclei
    Clusters of neuron cell bodies in CNS
  8. Gray matter
    Neuron cell bodies
  9. White matter
    myelinated nerve fibers, form tracts in CNS
  10. Neural networks
    Interconnecting circuits of neurons
  11. CNS Organs
    Brain and Spinal Cord
  12. PNS Organs
    Nerves and Ganglia
  13. Divisions of Motor
    • Somatic: supplies motor impulses to skeletal muscles (voluntary)
    • Autonomic (visceral) system: supplies motor impulses to cardiac, smooth muscle, glands (involuntary)
  14. Divisions of Autonomic
    Sympathetic and Parasympathetic-dual innervation of effectors.
  15. Division of Sensory
    • General (body wide) and special (localized)
    • Somatic (body wall, cutaneous) and autonomic (visceral)
    • Visceral-pertaining to internal organs
    • Somatic-pertaining to the body's framework-skin, muscle, tendon, joints
  16. Neuroglia
    • Do not conduct impulses, are supporting cells.
    • Serve to nourish and protect neurons.
    • Some form blood-brain barrier with capillary cell walls.
  17. Schwann Cells
    • Form myelin sheath around axons in PNS
    • Myelin acts as insulator and speeds nerve impulse conduction
    • Breaks between Schwann cells are Nodes of Ranvier-where ions can cross membranes in APs
  18. Afferent or sensory (Classes of Neurons)
    Transmit information from receptors to CNS
  19. Interneurons (Classes of Neurons)
    Connecting, located entirely in CNS
  20. Efferent or motor (Classes of Neurons)
    Transmit info from CNS to effector cells
  21. Graded Potentials
    Dendrites and soma
  22. Action Potentials
    Axon, peripheral process (nerve impulse-a propagated action potential)
  23. Synaptic Transmission
    Neurotransmitters cross a synapse; may include signal transduction
  24. Sensory Transduction
    Sensory recpetors
  25. Potential
    • A voltage difference across a cell membrane
    • The adjectives membrane, resting, graded, action, and post synaptic all define conditions under which a potential is measured or the way it develops in cells; all are used tp define potentials
  26. Polarize
    • Another series of terms is used to describe the direction of membrane potential changes relative to the resting state (-70mV)
    • -Hyperpolarize-inside of cell is more negative than usual
    • -Depolarize-positive charge is added to inside of cell, inside of cell becomes positive
    • -Repolarize-membrane potential returns to resting value after a change
  27. Gating
    Ion channels are gated 3 ways: voltage (electrical), chemical (receptor), mechanically (stretch)
  28. Resting Membrane Potential
    • Neurons are polarized, Na outside, K and protein inside, inside is negative (-70mV)
    • (Neurons are polarized, can be depolarized, repolarized, hyperpolarized)
    • All cells have resting membrane potential, only muscle and nerve cells are excitable:can change membrane potential in response to a stimulus
  29. Action Potential
    • An action potential is a transient, all or none reversal of membrane polarity
    • They constitute an electrical signal which can be propagated by nerve and muscle cells.
    • APs are initiated by graded potentials. If the incoming stimulus is strong enough (reaches threshold)voltage gated Na channels will open-membrane becomes highly permeable to Na
  30. Voltage gated Na channels
    • Are opened by Na from graded potential, as more Na enters cell, more channels open=a positive feedback cycle which causes the cell to depolarize (+50 mV)
    • This localized reversal of membrane polarity is an action potential.
    • The voltage gated channels are found initially at axon hillock, and all along axon.
  31. Conduction
    • Along a neuron
    • Action potentials=brief reversal of membrane polarity in one place; how is message conducted?
  32. Propagation
    • One AP results in Na entry, which is the trigger for voltage gated channels on adjacent membrane to open
    • A series of APs os omitiated down the axon membrane=propagation
    • The propagated action potential is called a nerve impulse
  33. Refractory period
    • time during which neuron cannot respond to a second stimulus.
    • It is due to nature of gated channel, ensures one way conduction of impulses
  34. All-or-none Principle
    • If threshold is reached, an AP is stimulated
    • APs are all the same size=all or none
  35. Saltatory Conduction
    • AP jumps from one node to next in myelinated fibers
    • Increases speed of conduction
  36. Coding
    • The information that is transmitted is in the frequency of APs generated
    • APs are frequency modulated; graded potentials are amplitude modulated
  37. General Properties of APs
    • 1. occur only in excitable membranes (they are only ones with voltage gated channels)
    • 2. requires a minimal (threshold) potential for initiation
    • 3. upstroke of AP is result of a positive feedback loop, is explosive, self-perpetuating
    • 4. APs are all-or-none phenomena; amplitude of response is independent of stimulus intensity
    • 5. APs are propagated without a decline in amplitude
    • 6. Refractory period- membrane has diminished excitability immediately after an AP; this prevents fushion or impulses, permits propagation of discrete impulses
    • 7. APs rapidly conduct information over long distances
  38. Graded Potential
    • A stimulus is a physical, chemical or electrical event that alters neuron membrane permeability, makes neuron permeable to ions which diffuse in (depolarization) or out (hyperpolarization)
    • The event that alters the membrane permeability is gating of an ion channel (stretch, chemical, voltage)
    • This event occurs in sensory receptors, dendrites, soma
    • The change in membrane permeability is a graded potential
  39. Graded Potential
    • Changes in membrane potential confined to a small region of the membrane.
    • They are graded in magnitude, the size of the graded potential reflects size of stimulus
    • Gated channels open to initiate GPs, the resulting current flow spreads passively
    • GPs are important in signaling over short distances
  40. Receptor Potentials (GP)
    Generated by sensory stimuli
  41. Postsynaptic Potentials (GP)
    Generated in dendrites and soma by neurotransmitters; can be excitatory (EPSP); depolaraization or inhibitory (IPSP); hyperpolarization
  42. Pacemaker potentials (GP)
    Spontaneous oscillations in membrane potentials that trigger APs (heart)
  43. Temporal summation
    repeated stimuli over time=larger graded potentials
  44. Spatial summation
    GPs initiated at many sites in a neuron=larger graded potential
  45. GPs are used in these situations
    • Initiate info flow in sensory cells
    • Conduct info from dendrites to axons
    • Represent the entire information transfer in neurons with very short axons (CNS)
    • Initiate action potentials in cardiac muscle cells
  46. Synaptic Transmission
    Conduction across a synapse
  47. Synapse
    • Region of communication between two neurons
    • Consists of synaptic knob, synaptic cleft, postsynaptic membrane
  48. Electrical Synapse
    • Ions pass through gap junction between cells
    • Useful to synchronize electrical events rapidly, found in heart and smooth muscle
  49. Chemical Synapse
    A chemical called a neurotransmitter is released from presynaptic neuron, influences postsynaptic neuron, initiates a GP via chemical gating of ion channels
  50. Presynaptic release of neurtransmitter
    • Propagated APs open Ca voltage gated channels at axon terminals
    • Ca enters axon and effects exocytotic release of neurotransmitter from synaptic vesicles
    • Release is quantal-number of vesicles released relates to frequency of APs
  51. Postsynaptic receptors
    • Neurotransmitters bind to specific receptors in post-synaptic membranes; there are 2 possible effects:
    • 1. the binding gates (opens or closes) an ion channel which is an integral part of receptor protein, ions move driven by concentration gradients, either into or out of cells
    • 2. the binding of NT to receptor initiates a complex mechanism called signal transduction; the off switch is removal of neurotransmitter molecules-by enzymatic degradation or reuptake
  52. PSPs (postsynaptic potentials, graded potentials)
    • Can be excitatory or inhibitory
    • Depends on nature of ion channel, not neurotransmitter
    • EPSP-excitatory= Na/K channels open, Na ions will enter cell and depolarize it
    • IPSP-inhibitory=Cl or K channels will hyperpolarize cell (Cl- flows in, K+ flows out)
    • A particular synapse is always either excitatory or inhibitory
    • Each presynaptic neuron makes only one kind of neurotransmitter
  53. Neurotransmitters
    • Chemicals released from presynaptic membrane
    • They bind to postsynaptic membrane receptors and usually gate ion channels
    • Quickly inactivated by enzymes or removed by presynaptic reuptake pumps
    • Acetylcholine and norepinephrine are usual PNS neurotransmitters
    • Others in CNS include dopamine, seratonin, endorphins, GABA, glutamate, glycine
  54. The binding of neurotransmitters to postsynaptic membranes can cause the following..
    • Block Na voltage gated channels in axons-tetrodotoxin
    • Stimulate release of NT-amphetamine, black widow venom
    • Prevent NT release-botulism toxin prevents ACH release, tetanus toxin blocks release of inhib NT
    • Block enzymatic degradation-malathion, sarin, flea collar, MAO inhibitors
  55. Reflex
    • An automatic, involuntary repsonse to a stimulus; it is mediated by a reflex arc
    • Reflexes include knee jerks, withdrawal, homeostatic adjustments, postural adjustments
    • (The reflex is the observed action; the reflex arc is the wiring that accomplishes the reflex)
  56. Reflex Arc
    • A conduction pathway, the most basic neural pathway
    • The neuron is the structural unit of the NS, the reflex arc is the functional unit
  57. 5 basic components of a reflex arc
    • Sensor, sensory neuron, interneuron, motor neuron, effector
    • Note that in some relfex arcs there is no interneuron, in some there are more than one
    • Information flow has a specific directionality in reflex arcs
    • This is ensured by refractory period in axons and postsynaptic receptors in synapses
Card Set
Physio Midterm II
Physio Midterm II Wilson SRJC