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125 Cards in this Set
- Front
- Back
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What two body systems provide the regulation and control of all other body systems that is necessary for homeostasis? What is the basic mechanism of action used by each?
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Nervous system - nerve impulses/action potentials, rapid response to stimuli
Endocrine system - hormones (chem messengers); slower + longer response; generally travel through the blood |
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What are the major functions of the nervous system?
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Sensory - detect change in internal/external environment; provide sensory input
Integrative - Process/analyze sensory input, store input and use memory to make descisions about behavior (trigger responses) Motor - activate effector organs (muscle contraction/gland secretion); |
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Identify the two major divisions of the nervous system.
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Central Nervous System - brain and spinal cord; (process and integrate sensory input, generate thoughts, emotions, memories, trigger motor responses)
Peripheral Nervous System - sensory input to CNS, motor output away from CNS to effectors |
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What are the anatomical components of each of the major divisions of the nervous system.
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CNS - brain + spinal cord
PNS - Nerves (bundle of nerve fibers), Ganglia, sensory receptors |
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Distinguish between cranial nerves and spinal nerves.
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Cranial - carry impulses to and from brain
Spinal - carry impulses to and from spinal cord |
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Distinguish between the afferent and efferent functions of the PNS.
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Afferent - sensory input to CNS
Efferent - Motor output away from CNS to effectors |
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What is the function of the somatic sensory neurons?
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Somatic nervous system (SNS) - voluntary nervous system; skeletal muscles
Sensory nerves carry input from somatosensory receptors Motor nerves supply skeletal muscles Pain receptors in skin, proprioceptors in joints and skeletal muscles, taste, vision, ballance |
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Ganglia
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Clusters of neuron cell bodies in PNS
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Why is the motor portion of the somatic nervous system called the voluntary nervous system?
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It controls the skeletal muscles
Somatic motor neurons = alpha motor neurons |
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Identify the divisions of the ANS.
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Sympathetic - fight or flight responses
Parasympathetic division - rest and digest; normal ongoing homeostasis Some organs (like cardiac muscle) are innervated by both divisions which act antagonistically |
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What division of the PNS is sometimes called the involuntary nervous system?
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The autonomic nervous system (ANS)
Afferent fiberst send CNS info about internal organs Efferent fibers carry impulses from CNS to smooth muscle, cardiac muscle, glands Monitor chem changes (pH), stretch etc. |
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Where is the enteric nervous system located?
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Gastrointestinal tract - located in the walls
Huge - more neurons than spinal cord |
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What is the general function of the enteric division of the PNS?
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Receptors to sense chem, mech, temp changes in gut
Intrinsic activity + sending input to CNS - input/output by nerves of ANS = extrinsic regulation Receptors sensitive to stretch and chem. composition of food passing by |
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Identify the three parts of a neuron.
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Cell body (soma)/perikaryon
Dendrites - afferent process Axon - efferent process |
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What organelles are typically present in the neuron cell body? Are any noticeably absent?
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Centrally located nucleus, large, dark staining = lots of RNA made
Lots of mitochondria Extensive Golgi apparatus around nucleus (involved with NT secretion) Lots of Lysosomes and RER No centrioles = no mitosis |
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What is the function of the neurofibrils?
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Intermediate fibers/filament bundles
Provide support and shape to neuron Network |
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What are Nissl bodies?
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Specialized RER
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Which neuron procces conducts impulses toward the cell body?
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Dendrites - afferent
Short, tapering, highly branched; high surfaced area; lots of chem gated ion channels in membrane to conduct gradients towards soma Similar cytoplasm, unlike axons |
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Which neuron proccess conducts impulses away from the cell body?
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Axon - efferent process
Starts at axon hillock; plasma mem. = axolemma; cytoplasm =axoplasm Branches = axon collaterals, at right angles and intermediate points along axon Distal end - telodendria (axon terminals); synaptic terminals/knobs on ends; form synapses at swellings (hold NTs) along axon called varicosities |
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What is the axon hillock?
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Conical region
Forms initial segment of axon Varies in length where the energy potential is generated/arises |
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Where are the synaptic vesicles located?
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In synaptic knobs/terminals @ end of telodendria (axon terminals)
Store NTs |
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What is axonal transport?
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Materials moved up and down axon from cell body
Slow axonal transport - away from stoma (enterograde), proteins walk vesicles down microtubules Fast axonal transport - bidirectional, can move mitochondria, tetanus toxin (towards CNS), Herpes, polio; difft carrying proteins |
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Enterograde
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Away from stoma of neuron
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Retrograde
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Towards stoma of neuron
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Axon terminals
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Telodendria - tiny processes at distal end of axon
Terminate in bulb shaped ends (synaptic terminals/knobs) |
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Which type of axonal transport is bi-directional?
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Fast axonal transport
Enterograde and retrograde |
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What is myelin?
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Schwann cells form myelin sheath by wrapping around axon many times, tightening and squeezing cytoplasm out;
coil of wrapped membranes Neurilema - outer exposed plasma membrane of schwann cell (only in PNS) |
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What is the function of myelin?
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Protect and insulate axon
Increases speed of impulse conduction (white fatty segmented sheath) Neurilema can help with nerve regeneration |
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Describe the process of myelination in the PNS.
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Schwann cells indent, wrap around short length of axon, spiral around
Loose coil of wrapped membranes tightens, squeezing cytoplasm out Unmyelinated = surrounded by schwann cells, but not wrapped in them; small diameter nerve fibers generally |
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Describe the process of myelination in the CNS.
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Formed bye oligodendrocytes; each has multiple flat processes that can associate w/segment of difft. nerve fiber
Nodes of Renvier widely spread No neurilemma formed Thin fibers generally unmyelinated |
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What are the nodes of Renvier?
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Gaps b/w adjacent schwann bundle/myelin units
Widely spaced in CNS AP jumps from node to node |
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What is the neurilemma? Do all myelinated nerve fibers have a neurilemma?
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Outer, exposed plasma membrane of Schwann cell; nucleus, organelles, cytoplasm
Only in PNS; helps w/nerve regeneration |
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Describe the association b/w Schwann cells and unmyelinated fibers of the PNS.
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Surrounded/partially enclosed by indents in Schwann cells, not fully wrapped
Usu. small diameter nerve fibers |
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What is the composition of gray matter?
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Unmyelinated axons and cell bodies
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What is the composition of white matter?
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Tissue w/only myelinated fibers
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Describe the process of nerve fiber regeneration in the PNS.
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If neuron cell body and schwann cells are undamaged
Damaged fiber end seal off Wallerian degeneration happens distally from break (cleans up where new axon will form) Macrophate infiltration - clean up tissue debris Shwann cells and neurolema release growth factors, form regeneration tube to guide axon as it regrows - back to original connection |
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What factors inhibit the process of nerve fiber regeneration in the CNS?
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Miroglia + astrocytes very slow at clean up
Astrocytes good at forming scar tissue/glial scarring Secondary demyelination - oligodendrocytes die, so no neurolema/channel for sprouting axon CNS neuroglial cells secrete factsrs to inhibit axonal growth (impt during fetal growth) |
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Tract
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a bundle of nerve fibers in CNS
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Describe the structure of bipolar, unipolar and multipolar neurons (structural classifications).
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Bipolar - 2 processes; extend from opposite sides of cell body (1 axon, 1 dendrite)
Unipolar - One short process w/2 branches; central process = proximal branch near to CNS that ends in axonal terminals (NT release and communicate w/other neurons); peripheral process = distal branch that terminates in dendrites/associated w/sensory receptors Multipolar - numerous processes (3+), one axon, the rest dendrites |
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Describe the function of bipolar, unipolar and multipolar neurons (structural classifications).
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Bipolar - Always sensory; only found in sight, smell and hearing
Unipolar - always sensory; almost always in neural ganglia of PNS Multipolar - either sensory or motor; nost common type of neuron (99%) |
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Which structural type of neuron is most prevalent in the nervous system as a whole?
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Multipolar neurons make up 99%
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What is the function of afferent, efferent and association neurons?
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Afferent (sensory) - from receptors to CNS; cell bodies in sensory ganglia of PNS, mosly unipolar
Efferent (motor) - from CNS to effector organs (muscles and glands); multipolar Association (interneurons) - b/w sensory and motor neurons in CNS; mostly multipolar; most common functional group (99%) |
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What is meant by the term "transmembrane potential"?
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Separation/difference of electrical charge across a plasma membrane
Slight +ve on outside, slight -ve on inside Also called membrane potential |
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What is meant by the term "resting membrane potential"?
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The transmembrane potential in a resting neuron
arbitrarily outside charge designated as 0, so resting axon always has -ve value Greater diff. = greater potential energy = more negative value Cell is polarized; hyperpolarized = increase in RMP = more -ve; depolarized = decrease in RMP = more +ve |
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What causes the voltage difference across the plasma membrane
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Sodium and Chloride higher in extracellular fluid
Potassium and organic anions (phosphate and proteins) highers in intercellular fluid Variable permeability to Na, Cl, K, impermeable to organic ions |
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In the resting state, where (what region) is K+ in the highest concentration?
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Intracellular fluid
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In the resting state, where (what region) is Na+ in the highest concentration?
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Extracellular fluid
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What is meant by the term "equlibrium potential"?
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Membrane potential at which the electrical force of repulsion/attraction of an ion equals the chem force of conc. gradient for the ion
Each ion has it's own equlibrium potential Equilibrium potentials and variable permeability to ions determine RMP |
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In the resting state, is the membrane more premeable to Na or K?
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More permeable to K
K has -80 mV; Na has +50 mV RMP of neurons -70 - closer to that of K, because there are more K leakage channels |
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Name and describe the types of ion channels that create the property of excitability in nerve and muscle cells. Identify each type of channel as active or passive.
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Leakage - passive; always open, continuous leakage; k channels for leaking in, more prevalent than Na leakage channels leaking out
Chem/ligand gated ion channel - active; receptor region for ligand; opened by NT and hormones Voltage gated ion channel(active) - selective for ions; causes excitability; opening channel decreases resistance to flow of ion; ion flow down electrochem gradient = change in voltage across membrane |
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What type of ion channel is always open?
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Leakage channels
K channels more prevalent in neurons than Na |
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Describe the operation of the different types of gated channels.
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Chem gated - receptor region for ligand; opened by NT or hormones
Voltage gated - respond to voltage change; excitability; ion selective; opening channel = change in voltage across membrane |
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What prevents the cell from reaching equilibrium with respect to the diffusion of Na and K across the membrane?
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Na/K pump maintains RMP; 3 Na out, 2K in per turn
Otherwise they would reach equilibrium b/c of leakage, which would disrupt RMP |
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Describe the operation of the sodium-potassium pump.
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Maintains electrochem. gradient
3 Na out/2 K in ATP driven Prevent equilibrium |
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What three factors are at work to establish and maintain the resting membrane potential?
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Unequal distribution of ions across plasma membrane - unequal distribution of charge
Differential permeability of plasma membrane to K (moderate out of cell) and Na (much less permeable) Na/K pump |
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What is the term which describes a decrease in the membrane potential?
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Depolarization - associated with increased inflow of Na; inside becomes more +ve
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What is the term which describes a membrane potential which is greater (ie. more negative) than the resting membrane potential?
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Hyperpolarization - associated w/increased outflow of K; inside becomes more -ve
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Does an inflow of Na promote depolarization or hperpolarization?
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Depolarization
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Does an outflow of K promote depolarization or hyperpolarization?
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Hyperpolarization
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What is a graded potential?
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Membrane potential
Short lived, local changes in membrane potential; triggered by chem, mech or elec stimulus that opened gated ion channels Local currents die out w/ increasing distance from stimulus site, b/c of leakage channels Magnitude of potential varies based on size of stimulus Generator (receptor) potentials, postsynaptic potentials caused by NTs; on denrites and cell body of neurons |
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What is the functional significance of graded potentials?
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Required to start an action potential
Receptors responding to stimuli Communication b/w neurons across synapse - what NTs cause On dendrites and cell body |
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What is an action potential?
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Rapidly occuring events; brief large depolarization and subsequent repolarization of plasma membrane; propagated
On axons All or nothing events; constant and maximum strength |
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What is a threshold stimulus? What will be the result of threshold stimulus?
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Critical level - membrane must depolarize appx -55 or -50 mV for the depolarization to become self generating
Have opened enough Na channels to activate more Na channels; causes rapid depolarization Positive feedback cycle initiated Generates AP |
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At what membrane potential (ie voltage) does the action potential of a neuron become all or none?
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Happens at threshold
-55 to -50 mV - closer to equilibrium potential for Na |
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How does depolarization influence membrane permeability to Na?
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Opening of voltage gated Na channels dramatically increases Na permeability
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Why is the depolarization phase an example of positive feedback?
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Depolarization self generating
As Na channels open, depolarization triggers even more Na channels (specifically, their activation gate opens w/ depolarization) to open |
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What happens to the membrane potential when Na rushes into the cell?
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Membrane potential ultimatly reverses; overshoots to about +30 mV, becoming more and more positive
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What stops the flow of Na into the cell?
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Depolarization opens activation gate allowing Na in
But also closes inactivation gate (happens more slowly) Once this gate is closed, no more Na can flow into the cell |
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Why is it impossible to immediatly fire a second action potential in a neuron immediatly after the voltage-gated Na channels close?
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The membrane is depolarized, so there is no electrochemical gradient to power the flow of Na into the cell
Channels are not reset yet |
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What causes the voltage -gated K channels to open?
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Depolarization activates it
Slow moving gate |
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What happens to the membrane potential when K rushes out of the cell?
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repolarization/hyperpolarization
Excess efflux of K from cell causes -80 mV potential (closer to equilibrium potential for K) |
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What causes the after-hperpolarization (ie the undershoot of the AP)?
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Voltage-gated K channel closes slowly
excess K efflux from cell = -80 mV membrane potential |
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What restores the resting membrane potential following an action potential?
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Na/K pumps work to restore and maintain ionic distributions of resting state (back to -70 mV)
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Describe the absolute refractory period and tell why it is important.
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Time when a second AP can't be generated, no matter how huge the stimulus; state of activation gates hasn't been reset; all or none event is already occuring
Ensures that every AP is a separate all or none event Ensures that AP flows in one direction down axon towards axon terminals |
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Describe the reletive refractory period and identify the phase of the action potential to which it corresponds.
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Second AP can be generated, but only by stimulus that is larger than threshold
When voltage gated Na channels are starting to close, K gate is mostly open (ie, we've started to reset the channels) |
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Explain why the generation of an action potential is said to be an all or none phenomenon.
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If depolarization reaches threshold (-55 to -50 mV), voltage gated channels open and AP occurs
Every time AP happens, it has constant and maximum strength |
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Describe the process of impulse propagation in unmyelinated fibers.
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Continuous propagation - generated at axon hillock (trigger zone)
Na coming into cell during AP moves laterally through axoplasm away from depolarized area, and mirror image action happens in ECF Causes local current which depolarizes adjacent patches of membrane - self-propagation Impulse travels in one direction - to axon terminals |
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Describe the process of impulse propagation in myelinated fibers.
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Saltatory propagation - much faster
APs only occur at nodes of Ranvier, where gates are concentrated AP jumps from node to node, not generated continuously b/c of myelin insulation |
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Why is propagation faster in myelinated fibers?
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AP jumps from node to node, not generated continuously
Myelin prevents leakage of almost all ions across membrane |
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What factors influence the speed of impulse conduction in nerve fibers?
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Diameter of fiber/axon - larger diameter = smaller resistance of current flow
Presence/absence of myelin sheath - continuous conduction is slower than saltatory conduction Propagation speed NOT related to stimulus strength!!! |
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Describe the three types of nerve fibers with respect to their relative diameters, degree of myelination, and speed of impulse conduction.
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A fibers - Largest diameter, heavily myelinated, very fast conduction (somatic sensory, motor fibers serving skin, skeletal muscles, joints)
B fibers - Intermediate diameter, lightly myelinated, medium conduction rate (afferent and efferent ANS fibers serving visceral organs) C fibers - smallest diameter, unmyelinated, slow impulses (poorly localized pain, touch, pressure and visceral/ANS efferent fibers) |
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What is the function of synaptic vesicles?
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Hold one type of NT, release it into synaptic cleft
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What is the function of neurotransmitters?
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Diffuse across synaptic cleft
Attatch to ligand gated ion channels to allow ions to flood in May be 2-3 difft neurotransmitters in presynaptic cell that have difft effects on postsynaptic cell |
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Axodendritic
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Synapse from axon to dendrite
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Axoaxonic
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Synapse from axon to soma of other cell
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Axoaxonic
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Synapse from axon to axon of other cell
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Describe the process of impulse trasmission across a synapse.
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AP reaches synaptic knob
Depolarization causes opening of voltage gated Ca chanels, Excite synaptic knob, triggers exocytosis of NT from synaptic vessicles NT diffuses and binds to receptors in postsynaptic membrane, opens ligand-gated ion channels "Post synaptic potential" - change in current/membrane potential NT broken down |
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What ion trigger exocytosis of neurotransmitter from the synaptic vesicles?
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AP causes depolarization; opening of Ca channels
Ca increase inside synaptic knob releases NT |
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By what process does the neurotransmitter get across the synaptic cleft?
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Diffusion
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What effect does neurotransmitter have on the postsynaptic membrane?
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Binds to ligand-gated ion channels
Causes change in chrrent/membrane potential Post synaptic potential occurs |
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In what way is the postsynaptic membrane specialized to receive communication from presynaptic neurons?
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Receptors in postsynaptic memgrane - opening of ligand-gated ion channels
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What is synaptic delay?
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Time required for processes at chemical synapse
Slowest point of info flow; slower than impulse transmission down axon Reflexes - short pathways, quick, few synapses Complex reasoning - multiplse synapses = slower |
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What is a postsynaptic potential?
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Graded potential in postsynaptic membrane
Caused by NT-receptor binding Currents result in either excitation or inhibition of new cell |
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Describe and identify the functional importance of an excitatory postsynaptic potential.
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EPSP - excitation/depolarization; membrane potential closer to threshold; b/c of ligand gated Na/K channels; spreads towards axon hillock
Electrochem gradient so much bigger for Na that causes some depolarization |
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Describe and identify the functional importance of an inhibitory postsynaptic potential (IPSP).
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IPSP - inhibition/hyperpolarization
Increases membrane potential Ligand gated K or Cl channels open Inhibit firing of AP at hillock |
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When numerous EPSPs and IPSPs are occurring in a neuron at one time, what determines whether or not the neuron will fire an action potential?
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Summation of all presynaptic neuron signals, both inhibitory and facilitory
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Describe the difference between temporal and spatial summation.
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Temporal - accumulation of NT from 1 presynaptic neuron firing several impulses in rapid succession
Spatial - buildup of NT from several presynaptic knobs close to eachother on the dendrite/cell body of the postsynaptic neuron |
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Distinguish between synaptic potentiation and presynaptic inhibition.
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Synaptic potentiation - repeated/continuous use of synapse enhances presynaptic neuron's ability to excite the postynaptic neuron; EPSPs have greater effect; memory and learning
Presynaptic inhibition - Excitatory NT by neuron is inhibited by another neuron via axoaxonic synapse = smaller than anticipated EPSP |
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At what type of synapse does presynaptic inhibition or facilitation occur?
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Axoaxonic synapse - where the inhibitory/facilitory neuron connects directly to the presynaptic neuron before it connects to the cell body of third cell
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What are the two basic cell types found in nervous tissue? Which of these basic types is most numerous?
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Neuroglia (glial cells) - the supporting cells
Neurons - excitable nerve cells that transmit elec. signals Neuroglia outnumber neurons 10 to 1 |
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Name and describe the structure of the four types of supporting cells of the CNS .
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Astrocytes - star shaped with many processes; largest and most abundant
Oligodendrocytes - fewer processes and smaller than astrocytes Microglia - small phagocytic neuroglia; least numerous in CNS Ependymal cells - range in hight; squamous/columnar; ciliated |
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Name and describe the function of the four types of supporting cells of the CNS .
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Astrocytes - blood-brain barrier; structural support to neurons; regulate ion (K), nutrient and gas conc. in interstitial fluid; absorb and recycle NTs; form scar tissue; regulate cell migration during embryonic development
Oligodendrocytes - support neurons; form myelin sheaths by wrapping cytoplasmic extensions around axons Microglia - remove cell debris and wastes; remove pathogens by phagocytosis since immune system is denied access to CNS Ependymal cells - produce, circulate (using cillia) and monitor cerebrospinal fluid (CSF); form permeable barrer |
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Name and describe the structure of the two types of supporting cells of the PNS.
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Satellite cells - surround neuron cell bodies in ganglia
Schwann cells (neurolemmocytes) - surround all axons in PNS |
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Name and describe the function of the two types of supporting cells of the PNS.
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Satellite cells - not well understood; monitor chem. composition of ECF around neurons; regulate exchange b/w ECF and soma
Schwann cells (neurolemmocytes) - myelination of peripheral axons; repair process after PNS injury |
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What cell produces myelin in the PNS? In the CNS?
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- Schwann cells
- Oligodendrocytes |
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What cell serves as a phagocyte in the CNS?
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Microglia
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What is the largest glial cell in the CNS? The most numerous?
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Largest - astrocyte
Most abundant - asrocyte |
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What glial cell forms the blood-brain barrier?
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Astrocytes
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Identify the special characteristics of neurons.
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1 - Extreme longevity (100+ years_
2 - Amniotic (loose ability to divide and reproduce) 3 - High metabolic rate (require continuous O2 and glucose or die within a few minutes) |
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Identify and distinguish between the main classes of neurotransmitters.
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acH - at Neuromuscular junction; released by neurons in CNS and a few in ANS
Biogenic amines - regulate mood, emotions, mental stability Amino Acids - so far just found in CNS; exitatory (glutamate + aspartate), inhibitory (GABA + glycine) Neuropeptides - amino acid chains with broad range of effects Soluble gases - CO and NO; not packaged in vesicles or stored in synaptic knobs; sent straight through membrane and bind w/receptor on inside of cell; retrograde messengers that increase synaptic strength Neuromodulators - not NT's, but released by neurons and modify neuronal inhibition (facilitory or inhibitory) |
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Identify the neurotransmitters derived from the amino acid tyrosine.
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Catecholamines (type of biolgenic amine) -
- norepinephrine - epinephrine - dopamine |
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What is the neurotransmitter at the neuromuscular junction?
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Acetylcholine (ACh) - synthesized from acetic acid
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Which neurotransmitters play a role in reducing pain and elevating mood?
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Types of Neuropeptides:
- Enkephalins - women in labor - endorphins - athletes |
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Identify the main inhibitory and excitatory amino acid NTs?
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Excitatory - glutamate + aspartate
Inhibitory - y-aminobutyric acid (GABA) + glycine |
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How does the number of neurons in a pathway influence the speed with which information can be transmitted?
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More neurons = more synapses = slower
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What are neuronal pools?
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Groups/organizations of neurons that process and integrate incoming information from other sources
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Describe each of the four types of neuronal circuits.
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Diverging (amplifying) - one incoming fiber conducts to many other neurons
Converging circuits - several presynaptic neurons synapse with a single postsynaptic neuron; more effective stimulation or inhibition b/c of concentrating info. Reverberating (oscillating) - signal travels through chain where later neurons synapse with neurons in previous part of pathway, so impulses go through over and over again; long lasting signal Parallel after-discharge circuits - single neuron stimulates parallel pathways with difft. numbers of synapses, so the common output cell receives the impulses at difft times |
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Give an example of each of the four types of neuronal circuits.
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Diverging (amplifying) - few motor neurons in brain activate more neurons in spinal cord
Converging - single motor neuron that synapses with skeletal muscle fibers gets input from difft. pathways that originate in brain Reverberating - breathing, waking up, short-term memory, wake/sleep cycles (sleep when reverberation stops), swinging arms while you walk Parallel after-discharge - complex,precise mental processing like math calculations |
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What type of circuit concentrates information from a variety of sources?
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Converging circuits
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What type of circuit is probably involved with rhythmic activities (breathing etc)?
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Reverberating (oscillating) circuits
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Which type of circuit produces bursts of impulses in the output cell over a period of 15+ msec?
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Parallel after-discharge circuits
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Describe and give an example of serial processing.
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- System works in predictable all or none manner; one neuron to next ending in predictable result
- The reflex arc; jerk away if you step on a nail |
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Describe and give an example of parallel processing.
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- Inputs segregated into many difft. pathways, processed separately and simultaneously by difft. parts of CNS
- How a smell evokes various thoughts, memories, etc |
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Axon Collateral
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Smaller branches of an axon that emanate from the main axon cylinder
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What is the function of the visceral sensory neurons?
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Transmit impulses from visceral organs (organs within the ventral body cavity)
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