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Anatomy Chapter 12
Terms in this set (49)
Regulation by the nervous system provides
Swift, but brief, responses to stimuli
The afferent division of the PNS
brings sensory information to the CNS
The part of the nervous system that controls voluntary contractiosn of skeletal muscles is the
somatic nervous system
Smooth muscle, cardiac muscle and glands are among the targets of the
Autonomic nervous system
In the CNS, a neuron typically receives information from other neurons at its
Neuroglia responsible for maintaining the blood-brain barrier are the
Phagocytic cells in neural tissue of the CNS are
Substances transported from an axon terminal to the cell body of the same neuron are delivered by
All the motor neurons that control the skeletal muscles are
The neural cells responsible for the analysis of sensory inputs and coordination of motor outputs are
Depolarization of a neuron cell membrane will shift the membrane potential toward
The primary determinant of the resting membrane potential is
the membrane permeability to potassium
Receptors that bind acetylcholine at the postsynaptic membrane are
Chemically regulated channels
Gated channels that open or close in response to a change in the transmembrane potential are
Action potentials vary in strength, depending on the intensity of the initial stimulus (T/F)
Changes in the transmembrane potential that are not restricted to the area surrounding the site of the stimulation are
Neuromodulators are compounds that influence the
Postsynaptic cell's response to a neurotransmitter, synaptic vesicles in the synaptic knob, release of calcium inion into the axoplasm
A transient hyperpolarization of the postsynaptic membrane is
A neuron that is brought closer to the threshold is considered to be
What are the major components of the central nervous system and the peripheral nervous system?
Central: brain and spinal cord. Peripheral: all other nerve fibers, divided between the efferent division (which consists of the somatic nervous system and the autonomic nervous system) and the afferent division (which consists of receptors and sensory neurons)
What two major cell populations are found in the nervous system? What is primary function of each type of cell?
1) neurons, transmit nerve impulses and 2) neuroglia, act as supporting cells
Which two types of neuroglia insulate neuron cell bodies and axons in the PNS from their surroundings?
Satellite cells and Schwann cells
What three functional groups of neurons are found in the nervous system? What is the function of each type of neuron?
Sensory neurons transmit impulses from the PNS to the CNS. Motor neurons transmit impulses from the CNS to peripheral effectors. Interneurons analyze sensory inputs and coordination of motor outputs
If the resting membrane potential is -70mV and the threshold is -55 mV, a membrane potential of -60 mV will
make it easier to produce an action potential
A graded potential
Decreases with distance from the point of stimulation, spreads passively because of local currents, may involve either depolarization or hyperpolarization
For an action potential to begin, an area of excitable membrane must
be depolarized to threshold level
During an absolute refractory period, the membrane
cannot respond to further stimulation
A neuron exhibiting facilitation requires a ______ additional stimulus to trigger an action potential
The loss of positive ions from the interior of a neuron produces
The continuous propagation of an action potential cannot occur in
Why can't most neurons in the CNS be replaced when they are lost to injury or disease?
Neurons lack centrioles and therefore cannot divide and replace themselves
What purpose do collateral serve in the nervous system?
Collaterals enable a single neuron to innervate several other cells.
What is the difference between axoplasmic transport and retrograde flow?
Axoplasmic transport is the movement of products that are synthesized in the cell body out to the synaptic knobs. Retrograde flow is the movement of materials toward the cell body.
How does a neuron become hyperpolarized?
The loss of positive ions is referred to as hyperpolarization. This increases the negativity of the resting membrane potential
What is the functional difference bewteen voltage, chemically, and mechanically regulated channels?
Voltage regulated channels open or close in response to changes in the transmembrane potential. Chemically regulated channels open or close when they bind specific extracellular chemicals. Mechanically regulated channels open or close in response to physical distortion of the membrane surface.
What four basic characteristics are associated with graded potentials?
1) The change in the transmembrane potential decreases with distance. 2) The graded potential spreads passively due to local currents. 3) The graded potential may involve either depolarization or hyperpolarization. 4) The stronger the stimulus, the greather the change in the transmembrane potential and the larger the area affected.
State the all-or-none principle of action potentials.
The all-or-none principle of action potentials states that if a depolarization event is sufficient to reach threshold, it will cause an action potential in the cells. This action potential will be of the same strength regardless of the degree of stimulation above threshold.
Describe the steps involved in the generation of an action potential.
The membrane depolarizes to threshold. Next, voltage-regulated sodium channels are activated, and the membrane rapidly depolarizes. These sodium channels are then inactivated, and potassium channels are activated. Finally, normal permeability returns. The voltage-regulated sodium channels become activated once the repolarization is complete. The voltage regulated potassium channels begin closing as the transmembrane potential reaches the normal resting potential.
What is meant by saltatory propagation? How does it differ from continuous propagation?
In continuous conduction, which occurs in unmyelinated axons, an action potential appears to move acoss the membrane surface in a series of tiny steps. In saltatory conduction, which occurs in myelinated axons, only the nodes along the axon can respond to a depolarizing stimulus.
What is the relationship between axon diameter and propagation speed?
The larger the diameter of the neuron, the more quickly the action potential propogates.
What are the functional differences amount type A, B and C fibers?
Type A fibers are myelinated and carry action potentials very quickly (140 m/sec). Type B are also myelinated, but carry action potentials more slowly due to their smaller diameter. Type C fibers are extremely slow due to small diameter and lack of myelination.
How does an action potential in a skeletal muscle fiber differ from that in a neuron?
Action potentials last longer in muscle fibers than in nerve fibers. Muscle fibers conduct action potentials at a slower speed.
Why is an electrical synapse a more efficient carrier of nerve impulses from cell to cell that in a chemical synapse?
Electrical synapses occur between neighboring cells that are connected by gap junctions. Gap junctions allow for the direct passage of electrical current from one cell to the next, so activity in electrically coupled cells is nearly simulaneous. Chemical synapses involve the release, diffusion, and binding of a neurotransmitter in response to an action potential in the presynaptic cell, before electrical activity can be generate in the postsynaptic cell. Chemical synaptic transmission thus takes longer than electrical synaptic transmission.
Describe the steps that take place at a typical cholinergic synapse.
1) The action potential arrives at the synaptic knob, depolarizing it. 2) Extracellular calcium enters the synaptic knob triggering the exocytosis of ACh. 3) ACh binds to the postsynaptic membrane and depolarizes the next neuron in the chain. 4) ACh is removed by AChE
How does the action of a neurotransmitter differ from that of a neuromodulator?
Neurotransmitters are chimicals that are often classified as excitatory or inhibitory on the basis of their effects on postsynaptic membranes. Neuromodulators are compounds that influence neurotransmitter release or the postsynaptic cell's response to the neurotransmitter
What is the difference between temporal summation and spatial summation?
Temporal summation is the addition of stimuli that arrive in rapid succession. It occurs at a single synapse and is active repeatedly. Spatial summation occurs when simultaneous stimuli have a cumulative effect on the transmembrane potential. It involves multiple synapses that are active simultaneously.
What functions of neurons necessitate the support of energy from ATP?
The synthesis, release and recycling of neurotransmitter molecules; the movement of materials to and from the cell body via axoplasmic transport; and the recovery from action potentials
When a runner experiences "runner's high", why is the suppression of pain common?
During long-term strenuous physical activity, endorphins are released in the brain. Endorphins are structurally similar to morphine and relieve pain by suppressing the release of the neurotransmitter Substance P from pain neurons
Multiple sclerosis (MS) is a demyelination disorder. How does this condition produce musclular paralysis and sensory losses?
In MS, the myelin sheath is destroyed. Action potentials travel slower in unmyelinated fibers than in myelinated fibers. The destruction of myelin slows the time it takes for motor neurons to communicate with their effector muscles. This delay results in varying degrees of uncoordinated muscle activity and paralysis. Cumulative sensory and motor losses may eventually lead to generalized sensory deficiencies and muscular paralysis.
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