Chapter 11 Test Flashcards
Functions of the nervous system
Sensory input, integration, motor output
Divisions of the nervous syste
Central nervous system(CNS), peripheral nervous system (PNS)
CNS includes
Brain and spinal cord; integration and command center
PNS involves
Paired spinal and cranial nerves carry messages to and from the CNS
Sensory PNS functions
Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints
Visceral afferent fibers—convey impulses from visceral organs
Motor PNS functions
Transmits impulses from the CNS to effector organs
Neuron functions
Plasma membrane functions in:
Electrical signaling
Cell-to-cell interactions during development
Tracts are in
CNS
Nerves are in
PNS
Neurons structural classification
Multipolar, bipolar, unipolar
Multipolar
1 axon and several dendrites
Most abundant
Motor neurons and interneurons
Bipolar
Bipolar—1 axon and 1 dendrite
Rare, e.g., retinal neurons
Unipolar
single, short process that has two branches:
Peripheral process—more distal branch, often associated with a sensory receptor
Central process—branch entering the CNS
Functional classification of neurons
Sensory, motor, interneurons
Sensory
Transmit impulses from sensory receptors toward the CNS
Afferent
Motor
Carry impulses from the CNS to effectors(efferent)
Interneurons
Shuttle signals through CNS pathways; most are entirely within the CNS ( association neurons)
Neuroglia supporting cells
Astrocytes (CNS) Microglia (CNS) Ependymal cells (CNS) Oligodendrocytes (CNS) Satellite cells (PNS) Schwann cells (PNS)
Astrocytes location
Cling to neurons, synaptic endings, and capillaries
Astrocytes functions
Support and brace neurons Help determine capillary permeability Guide migration of young neurons Control the chemical environment Participate in information processing in the brain
Microglia location
Migrate toward injured neurons
Microglia functions
Defensive cells in the CNS
Ependymal location
Line the central cavities of the brain and spinal column
Ependymal functions
Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
Oligodendrocytes location
Processes wrap CNS nerve fibers, forming insulating myelin sheaths
Oligodendrocytes functions
Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers
Satellite cells location
Surround neuron cell bodies in the PNS
Schwann cells location
Surround peripheral nerve fibers and form myelin sheaths
Schwann cells function
Vital to regeneration of damaged peripheral nerve fibers
The synapse
A junction that mediates information transfer from one neuron:
To another neuron, or
To an effector cell
Presynaptic neuron
conducts impulses toward the synapse
Postsynaptic neuron
transmits impulses away from the synapse
Action potential (AP)
Brief reversal of membrane potential with a total amplitude of ~100 mV
Generation of an action potential
Resting state:
Only leakage channels for Na+ and K+ are open
All gated Na+ and K+ channels are closed
Phases of action potential
Resting state->depolarization->depolarization->hyperpolarization->restarts
Depolarizing Phase
Depolarizing local currents open voltage-gated Na+ channels Na+ influx causes more depolarization At threshold (–55 to –50 mV) positive feedback leads to opening of all Na+ channels, and a reversal of membrane polarity to +30mV (spike of action potential)
Repolarizing phase
Na+ channel slow inactivation gates close
Membrane permeability to Na+ declines to resting levels
Slow voltage-sensitive K+ gates open
K+ exits the cell and internal negativity is restored
Hyperpolarization
Some K+ channels remain open, allowing excessive K+ efflux
This causes after-hyperpolarization of the membrane (undershoot)
Absolute refractory period
Time from the opening of the Na+ channels until the resetting of the channels
Ensures that each AP is an all-or-none event
Enforces one-way transmission of nerve impulses
Relative refractory period
Follows the absolute refractory period
Most Na+ channels have returned to their resting state
Some K+ channels are still open
Repolarization is occurring
Threshold for AP generation is elevated
Exceptionally strong stimulus may generate an AP
Neurotransmitters
Biogenic Amines,Ach, purines, amino acids,peptides, gases and lipids
Graded potential vs. action potential
Graded potentials: Incoming short-distance signals
Action potentials: Long-distance signals of axons
Resting Membrane Potential (Vr)
Potential difference across the membrane of a resting cell
Approximately –70 mV in neurons (cytoplasmic side of membrane is negatively charged relative to outside)
Generated by:
Differences in ionic makeup of ICF and ECF
Differential permeability of the plasma membrane
Impulse conduction
Larger diameter fibers have less resistance to local current flow and have faster impulse conduction
Impulse conduction slows and eventually ceases
Weak vs strong stimuli
Strong stimuli can generate action potentials more often than weaker stimuli
Nerve fiber classification
Nerve fibers are classified according to:
Diameter
Degree of myelination
Speed of conduction
Multiple Sclerosis (MS)
An autoimmune disease that mainly affects young adults
Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence
Myelin sheaths in the CNS become nonfunctional scleroses
Shunting and short-circuiting of nerve impulses occurs
Impulse conduction slows and eventually ceases
