ch 12 neural tissue
Terms
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- nerves
- bundles of axons thhat carry sesnroy and motor nfo in the PNS with associated blood vessels and connecive tissues
- afferent division
- division of the PNSthat brings sensory info to the CNS from receptors in peripheral tissues and organs
- components of the Efferent division of the PNS
- somatic nervous system and autonomic nervous system
- somatic nervous system
- division of the effferent division of the PNS controls skeletal muscle contractions
- autonomic nervous system
- (visceral motor system) division of the efferent division of the PNS- provides automatic regulation of smooth muscle, cardiac muscle, and glandular secretions at the subconscious level- divided intoo the sympathetic and parasympathetic divisions
- parasympathetic activity _____ the heart rate
- slows
- sympathetic activity _____ the heart rate
- speeds up
- perikaryon
- the cytoplasm surrounding the nucleus of a neuron
- Nissl bodies
- areas of he perikaryon conaining clusters of RER and free ribosomes- accoun for the the gray color of areas containing cell bodies- the gray matter
- collaterals
- side branches on axons that enable a neuron to communicate w/ several other cells
- synaptic know
- structure of the synaptic terminal that occurs where the postsynaptic cell is another neuron- contains mitochondria, portions of the ER and thousands of vesicles filled w/ neurotransmitter molecules
- axoplasmic transport
- the movement of materials b/t the cell body and synaptic knobs
- retrograde flow
- axoplasmic transport in which substances are transported toward the cell body- if debris appear in the synaptic know it will go to the cell body and could alter the activity of the cell ex. rabies, heavy metals, viruses, pathogens
- structural classifications of neurons
- anaxonic, bipolar, unipolar, multipolar
- anaxonic neurons
- small- not anatomical features that distinguish dendrites from axons; located in brain and special sense organs; poorly understood
- bipolar neurons
- a dendritic process and an axon and a soma b/t the 2; rare; in sight, smell , and hearing organs
- unipolar neurons
- dendrites and axons are continuos- cell body off to the side; usually sensory PNS; can be very long
- Multipolar Neurons
- 2+ dendrites and 1 axon; most common type in the CNS; all motor neurons that control skeletal muscles
- Functional classification of neurons
- sensory, motor, interneurons
- sensory neurons
- form afferent division of the PNS; cell bodies located in peripheral sensory ganglia; unipolar w/ afferent fibers
- ganglion
- collection of cell bodies in the PNS
- somatic sensory neurons
- monitor outside world and our position w/in it
- visceral sensory neurons
- monitor internal conditions and the status of other organ systems
- Interoceptors
- sensory receptors that monitor the digestive, respiratory, cardio, urinary, and reprod. systems and provide sensations of taste, deep pressure, and pain
- exteroceptors
- provide info about the external environment in the form of touch, temp, or pressure sensations and the more complex senses of sight, smell, and hearing
- proprioceptors
- monitor the position and movement of skeletal muscles and joints
- sensory receptors
- either the processes of specialized sensory neurons or cell monitored by sensory organs
- Motor Neurons
- form efferent division of the PNS; can be somatic motor neurons or visceral (autonomic) motor neurons
- somatic motor neurons
- innervate skeletal muscle- conscious control- cell bodies in the CNS
- Visceral Motor Neurons
- unconscious control; innervate smooth and cardiac muscle, glands and adipose tissue; axons of visceral motor neurons in the CNS activate a 2nd set of visc. motor neurons in the peripheral autonomic ganglia
- preganglionic fibers
- the axons extending from the CNS to an autonomic ganglion
- postganglionic fibers
- axons connecting the ganglion cells with the peripheral effectors
- interneurons
- most prevalent; most are in the CNS but some are in the autonomic ganglia; involved in both sensory and motor unctions; involved w/ all higher functions ex. memory, planning, learning
- autonomic ganglion
- a collection of visceral motor neurons outside the central nervous system
- Ependymal cells
- line the ventricles and the central canal; help to circulate the CSF In some areas
- Astrocytes
- largest and most numerous neuroglia; help maintain blood-brain barrier; create a 3-D framework for the CNS; Repair damaged neural tissue; guide neuron development; control the interstitial environment
- oligodendrocytes
- responsible for myelination
- white matter of the CNS
- regions dominated by myelinated axons
- gray matter of the CNS
- areas containing neuron cell bodies, dendrites, and unmyelinated axons
- microglia
- least numerous and smalles neurons; phagocytic cells
- satellite cells
- surround cell bodies in the ganglia and regulate the environment around the neurons
- schwann cells
- form a sheath around peripheral axons
- neurilemma
- wherever a schwann cell covers and axon, the outer surface of the schwann cell; participate in the repair of damaged nerves
- Wallerian Degeneration
- axon distal to the injury site degenerates and macrophages migrate into the area to phagocytize the debris- schwann cells proliferate and form a solid cell cord that ollows the parth of the original axon
- Why regeneration in the CNS is unlikely:
- many more axons are likely to be involved; astrocytes produce scar tissue that can prevent axon regrowth across the damaged area; astrocytes releases chems that block the regrowth of axons
- graded potenetial
- a temporary, localized change int the resting potential that decreases w/ distance from the stimulus; produces an action potential if it is large enough; any stimulus that opens a gated channel will produce a graded potential
- action potential
- an electrical impulse that is propagated across the surface of an axon and doesn\'t dimish as it moves away from its source
- The ECF contains high concentrations of ____ and ____ while the cytosol contains high concentrations of ___?
- Na and Cl; K
- It is easier for ____ to diffuse out of the cell than is is for ___ to enter the cell. As a result the inner surface has a ___ charge and the outer surface has a___ charge.
- K Na negative positive
- Resting potential
- the potential difference, measured across a cell membrane tha results from the uneven distribution of positive and negative ions across the cell membrane; usually about -70 mV
- current
- movement of charges to eliminate a potential difference
- gated channels
- open or close in response to certain stimuli; 3 classes: chemically regulated, voltage regulated, & mechanically regulated; the opening of gated channel alters the rate of ion movement & thus changes the transmembrane potential
- chemically regulated channels
- open or close when bind to certain chems; ex. receptors that bind ACh at the neuromuscular junctions; most abundant on dendrites and cell body of a neuron; where most synaptic comm. occurs
- voltage regulated channels
- characteristic of areaas of excitable membrane; open and close in response to changes in the transmembrane potential;
- excitable membrane
- a membane capable of generating and conducting an action potential
- Mechanically regulated channels
- open or close in response to physical distortion of the embrane surface; important in sensory receptors
- depolarization
- any shift from the resting potential toward O mV; occurs when Na channels open
- local current
- the movemnt of positive charges parallel to the inner and outer surfaces of a membrane
- repolarization
- occurs when a chemical stimulus is removed and norm membrane permeability is restored; typically involved a combo ofion movement thru membrane chnnels and the activities of ion pumps, esp the Na-K pump
- Hyperpolarization
- what happens when a gated K channel is opened and the rate of K outflow increases and the interior of the cell would become less positive
- graded potentials on the dendrites and cell body create a graded potential at synaptic terminals to trigger the release of neurotransmitter because
- graded potentials at opposite ends of the cell are linked by action potential
- action potentials
- propagated changes in he transmembrane potential that affect an entire exitable membrne
- threshold
- the stimulus that initiates an action potential is a depolarization large enough to open voltage regulated Na channels; that opening occurs at a transmembrane potential generally b/t -60 and -55 mV
- All-or-none principal
- the properties of the action potential are independt of the relative strength of the depolarizing stimulus- it either produces a an action potential or not
- Steps in generation of an action potential
- 1. depolarization to threshold 2.activation of sodium channels and rapid depolarization 3. Inactivation of Na channels and the activation of K Channels 4. Return to normal permeability
- refractory period
- from the time an action potential begins until the norm resting potential has stabilized when the membrane will not respond normally to stimuli
- absolute refractory period
- from the moment the oltae-regulate sodium channels open at threshold until na chnnel inactivation ends when the membrane can\'t respond to further stimulation b/c all the volt-regulated na channels are already open or incactivated
- relative refractory period
- begins when the na channels regain their norm resting condition and continues till the transmembrane potential stabilizes at resting levels
- the larger the axon diameter the _____ the resistance
- lower
- Axon classification according to relationships among the diameter, myelination, and propagation speed:
- Types A, B, and C
- Type A fibers
- larges axon- myelinated axons that carry action potentials at speed of up to 140 meters per second or more than 300 mph; carry info about position, balance, and delicate touch and pressure sensations from the skin surface
- Type B fibers
- smaller myellinated axons w/ diameters of 2-4 um. propagation speeds avg around 18 meters/second or 40 mph.; carry info to the CNS; deliver temperatur, pain, and genreral touch and pressure sensations and carry instructions to smoot and cardicac muscle, glands, and peripheral effectors
- Type C fibers
- unmyelinated, smallest (less tha 2 um) Propagation at 1 meter pers second or 2 mph.carry info to the CNS; deliver temperatur, pain, and genreral touch and pressure sensations and carry instructions to smoot and cardicac muscle, glands, and peripheral effectors
- nerve impulses
- an action potential in a neuron cell membrane
- electrical synapses
- occur in the CNS and PNS but are rare. pre and post- synaptic membranes are bound by interlocking membrane proteinat a gap junction; pores w/in these protein permit the passage of ocal currents and the 2 neurons act as if they share a common cell membrane
- chemical synapses
- an arriving action potential may or may not release enough neurotransmitter to bring the postsynaptic neuron to threshhold; most abundant type of synapse; involve neurotransmitters
- excitatory neurotransmitters
- cause depolarization and promot the generation of action potentials
- inhibitory neurotransmitters
- cause hyperpolarization and suppress the generation of action potentials
- The effecto of a neurotransmitter on the postsynaptic membrane depends on the properties of the ______ NOT on the nature of the _____
- The effect of a neurotransmitter on the postsynaptic membrane depends on the properties of the RECEPTOR NOT THE NEUROTRANSMITTER!!!
- cholinergic synapses
- synapses that release ACh
- ACh is released at:
- 1) neuromuscular junctions involving skeletal muscle fibers 2) at many synapses in the CNS 3) At all neuron-to-neuron synapses in the PNS 4) all neuromuscular and neuroglandular junctions w/int the parasympathetic division of the ANS
- Events at a cholinergic synapse
- 1) an arriving action potential depolarizes the synaptic knob 2) Ca ions enter the cytoplasm tof the synaptic knob and ACh is released thru exocytosis of neurotransmitter vesicles 3) ACh diffuses across the synaptic cleft and binds to receptor on the postsynaptic membrane and chemicaly regulated na channels on the postsynaptic surface are activated, producing a raed depolarization; and ACh release ceases b/c ca ions are removed from the cytoplasm of the synaptic knob 4. The depolarization ends as ACh is brokend down into acteate and choline by AChE and the synaptic knob reabsorbs choline from teh synaptic cleft and uses it to resynthesize ACh
- norepinephrine
- neurotransmitter tht is widely distributed in the brain and in portions of the ANS; has an excitatory depolarizing effect of the the postsynaptic membrane
- adrenergic synapses
- synapses that release NE
- Dopamine
- CNS neurotransmitter not enough- Parkinson\'s Too much excitatory effects
- Serotonin
- CNS neurotransmitter
- GABA
- inhibitory neurotransmitter; in CNS reduces anxiety
- neuromodulators
- compounds that alter the rate of neurotransmitter release by the presynaptic neuron or change the postsynaptic cells respnse to neurotransmitters
- opioids
- 4 classes in the CNS: endorphins, enkephalins, endomorphins, and dynorphins; they inhibit the release of substance P; Dynorphins VERY powerful;
- postsynaptic potentials
- graded potentials that develop in the postsynaptic membrane in respoonse to a neurotransmitter 2 major types develop at neuron-neuron synapses
- excitatory postsynaptic potentials
- a graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane; results from the opening of cehm regulated membran channels that lead to depolarization of the cell membrane
- Inhibitory Postsynaptic Potential
- graded hyperpolarization of the postsynaptic membrane
- summation
- the process in which EPSPs combine and through summation the effects of all the graded potentials that affect 1 portion of the ell membrane are integrated1
- temporal summation
- occurs at a single synaps when a second EPSP arrives before the effects of the first have disappeared
- spatial summation
- results from the cumulative effects of multiple synapses at various location