Chapter 12 - Nervous Tissue Flashcards
brain
Connected to spinal cord through foramen magnum of occipital bone
spinal cord
100mil neurons, encircled by bones of the vertebral column
peripheral nervous system
all nervous tissue outside the CNS
nerve
bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels.
cranial nerves
12 pairs
spinal nerves
31 pairs
ganglion
small masses of nervous tissue, located outside of the brain and spina cord, consisting of neuron cell bodies.
enteric plexus
extensive networks of neurons within walls of organs of the GI tracts
sensory receptor
structure of the nervous system that monitors changes in external or internal environment
somatic nervous system
consists of sensory neurons CNS to receptors for special senses. & motor neurons that conduct impulses from CNS to skeletal muscles. voluntary.
autonomic nervous system
1) sensory neurons from autonomic sensory receptors, in visceral organs 2) motor neurons to smooth muscle, cardiac muscle, glands. involuntary.
sympathetic
exercise / emergency actions
parasympathetic
rest and digest activities
enteric nervous system
brain of the gut. secretions and activities of GI tract.
sensory functions
detect stimuli
integrative functions
processes sensory information
motor functions
activates effectors
effector
muscles and glands for contraction / secretion
electrical excitability
possessed by neurons, respond to stimulus and convert to action potential
action potentials
nerve impulse, electrical signal that propagates along the surface of the membrane of a neuron.
cell body
contains a nucleus surrounded by cytoplasm, includes typical cellular organelles.
nissl bodies
prominent clusters of rough ER
dendrites
the receiving or input portions of a neuron, bind chemical messengers from other cells.
axon
propogates nerve impulses toward another neuron.
axon hillock
cone-shaped elevation joining the cell body to axon
initial segment
part of axon closest to the hillock
trigger zone
where nerve impulses arise, junction of hillock and initial segment
axon collateral
side branches
axon terminal
ending, fine processes
synpase
site of communication between two neurons or between a neuron and an effector
synaptic end bulb
tips of axon terminals swell into bulb-shaped structures
varicosities
string of swollen bumps at tips of axon terminals
synaptic vesicle
tiny membrane-enclosed sacs, storing neurotransmitters
neurotransmitter
Molecule released from a synaptic vesicle that excites or inhibits another neuron, muscle fiber or gland cell.
fast axonal transport
Carries materials from cell body to axon terminals and back, 200-400mm per day, uses proteins that function as motor to move materials along surfaces of microtubules
(forward) direction moves organelles and synaptic vesicles from the cell body to the axon terminals.
(backward) direction moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled.
slow axonal transport
.1-5mm per day, conveys axoplasm in one direction from body to terminal.
structural classification
according to the number of processes extending from the cell body
multipolar neuron
several dendrites, one axon, most neurons in brain and spinal cord are this type
bipolar neuron
one main dendrite, one axon. retina, inner ear, olfactory area.
unipolar neuron
dendrites and one axon that are fused together, forming continuous process that emerges from the cell body.
sensory functional classification
afferent, either contain sensory receptors at their dendrites, or are located just after sensory receptors. AP conveyed into CNS. generally unipolar.
motor functional classification
efferent, AP away from CNS to effectors, periphery, multipolar.
interneurons
association neurons, within CNS between sensory and motor neurons. Process and elicit motor response.
astrocytes
largest and most numerous neuroglia. Protoplasmic astrocytes in gray. Fibrous astrocytes in white.
Contain microfilaments for strength. Isolate neurons of CNS from harmful substance
Secrete chemicals in embryo.
Maintain appropriate chemical environment for generation of nerve impulses.
Learning and memory by influencing formation of neural synapses.
oligodendrocytes
forming and maintaining the myelin sheath around CNS axons.
myelin sheath
multilayered lipid and protein covering to insulate axons and increase speed of impulse conduction.
microglia
Small, slender, function as phagocytes.
ependymal cells
produce, monitor, assist in circulation of cerebrospinal fluid. form barrier.
schwann cells
encircle PNS axons, form myelin sheath 1:1.
satellite cells
surround the cell bodies of neurons of PNS ganglia. regulate exchanges, between cell bodies and it fluid, provide support.
neurolemma
outer nucleated cytoplasmic layer of the schwann cell, encloses the myelin sheath. only around axons in PNS.
nodes of ranvier
gaps in myelin sheath.
clusters of neuronal cell bodies - nucleus
neuronal cell bodies in PNS = ganglion. Neuronal cell bodies in CNS = nucleus
bundles of axons - tracts
bundle of axons located in PNS. tract= bundle of axons in CNS.
white matter
composed of myelinated axons.
gray matter
contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. Nissil bodies make it gray, little or no myelin.
graded/action/muscle/nerve potentials
electrical signals Short - long - muscle - neuron
membrane potential
electrical potential difference
resting membrane potential
voltage in excitable cells.
leak channel
randomly alternate. generally plasma membranes have more K+ leak channels.
ligand-gated ion channel
opens and closes in response to the binding of a ligand (chemical) stimulus.
voltage-gated ion channel
opens in response to a change in membrane potential (voltage)
resting membrane potential
small buildup of negative ions in the cytosol along the inside of the membrane, buildup of positive ions in the ECF. exhibits membrane potential = polarized.
factors that contribute to the resting membrane potential
1) unequal distribution of ions in the ECF and cytosol
2) Inability of most anions to leave the cell
3) Electrogenic nature of the Na+ - K+ ATPases
graded potential
small deviation from the resting membrane potential, makes membrane more or less polarized. A graded potential occurs when a stimulus causes mechanically-gated or ligand-gated channels to open or close in an excitable cell’s plasma membrane
decremental conduction
localized current gradually dies out as the charges are lost across the membrane through leak channels.
summation
becomes stronger and last longer by summating with other graded potentials.
action potential / impulse
sequence of rapidly occurring events that decrease and reverse the membrane potential, restoring to resting state.
threshold
depolarization reaches threshold to generate action potential.
subthreshold stimulus
weak depolarization that cannot bring the membrane potential to threshold.
threshold stimulus
stimulus just strong enough to depolarize the membrane to thrshold.
suprathreshold stimulus
Above threshold, Several action potentials will form.
depolarizing phase
membrane of axon depolarizes to threshold, sodium channels open rapidly.
repolarizing phase
Inactivation gates close. Because the voltage-gated K channels open more slowly, their opening occurs at about the same time the voltage-gated Na channels are closing. Sodium inflow slows, potassium outflow accelerates.
after hyperpolarizing phase
alternate between closed (resting) and open (activated) states.
refractory period
an excitable cell cannot generate another action potential in response to a normal threshold stimulus
absolute refractory period
even a very strong stimulus cannot initiate a second action potential. This period coincides with the period of Na+ channel activation and inactivation
relative refractory period
a second action potential can be initiated, but only by a larger than normal stimulus. It coincides with the period when the voltage-gated K channels are still open after inac- tivated Na channels have returned to their resting state
nerve impulse propagation
positive feedback, an action potential keeps its strength as it spreads along the membrane
continuous conduction
step-by- step depolarization and repolarization of each adjacent segment of the plasma membrane. ions flow through their voltage-gated channels in each adjacent segment of the membrane. Continuous conduction occurs in unmyelinated axons and in muscle fibers.
saltatory conduction
special mode of action potential propagation that occurs along myelinated axons, occurs because of the uneven distribution of voltage-gated channels.
factors that affect the speed of propagation
1) amount of myelination.
2) axon diameter
3) temperature
acodendritic
axon to dendrite
axoaxonic
axon to cell body
electrical synapse
action potentials (impulses) conduct directly between the plasma membranes of adjacent neurons through structures called gap junctions.
advantages of electrical synapses
faster communication and synchronization.
synaptic cleft
space filled with IT fluid separating plasma membranes of pre and post synaptic neurons in a chemical synapse.
postsynaptic potential
Nerve impulses cannot conduct across the synaptic cleft, so the pre-syn-neur releases a neurotransmitted that diffuses through the fluid and binds to receptors, post-syn-neur receives and produces post-syn potential.
excitatory postsynaptic potential (EPSP)
neurotransmitter causes depolarization of the postsynaptic membrane is excitatory because it brings the membrane closer to the threshold.
inhibitory postsynaptic potential (IPSP)
neurotransmitter causes hyperpolarization of the postsynaptic membrane is inhibitory.
neurotransmitter receptors
in plasma membrane of a postsynaptic cell.
removal of neurotransmitter
- diffusion. 2. enzymatic degradation. 3. update by cells
spatial summation
is summation of post- synaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same. time.
temporal summation
sum- mation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times.
neurosecretory cells
Within the brain, certain neurons, called neurosecretory cells, also secrete hormones
neurotransmitters
The small-molecule neurotransmitters include acetylcholine, amino acids, biogenic amines, ATP and other purines, nitric ox- ide, and carbon monoxide.
acetylcholine
best-studied neurotransmitter, released by many PNS neurons and by some CNS neurons. ACh is an excitatory neurotransmitter at some syn- apses, such as the neuromuscular junction, where the binding of ACh to ionotropic receptors opens cation channels. It is also an inhibitory neurotransmitter at other syn- apses, where it binds to metabotropic receptors coupled to G pro- teins that open K channels
glutamate
neurotransmitter in CNS, powerful excitation. bind- ing of the neurotransmitter to ionotropic receptors opens cation channels. The consequent inflow of cations (mainly Na ions) produces an EPSP. Inactivation of glutamate occurs via reuptake. Glutamate transporters actively transport glutamate back into the synaptic end bulbs and neighboring neuroglia.
gamma-aminobutyric acid & glycine
inhibitory transmitter in CNS. At many synapses, the binding of GABA to ionotropic receptors opens Cl– channels
biogenic amines
Certain amino acids are modified and decarboxylated (carboxyl group removed) to produce biogenic amines. most bind to metabotropic receptors
norepinephrine & epinephrine.
Awakening from deep sleep, dreaming, regulating mood. Both epinephrine and norepinephrine also serve as hormones. Cells of the adrenal medulla, the inner portion of the adrenal gland, release them into the blood.
dopamine
are active during emotional responses, addictive behaviors, and pleasurable experiences. In addition, dopamine-releasing neurons help regulate skeletal muscle tone and some aspects of movement due to contraction of skeletal muscles.
seratonin
involved in sensory perception, temperature regulation, control of mood, appetite, and the induction of sleep.
nitric oxide
excitatory neuro- transmitter secreted in the brain, spinal cord, adrenal glands, and nerves to the penis and has widespread effects throughout the body.
neuropeptides
bind to metabotropic receptors and have excitatory or inhibitory actions, depending on the type of metabotropic receptor at the synapse. Neuropeptides are formed in the neuron cell body, packaged into vesicles, and transported to axon terminals. Besides their role as neurotransmitters, many neuropeptides serve as hormones that reg- ulate physiological responses elsewhere in the body.
neural circuits
The CNS contains billions of neurons organized into complicated networks called neural circuits, functional groups of neurons that process specific types of information.
simple series
a presynaptic neuron stimulates a single postsynaptic neuron. The second neuron then stimulates another, and so on.
diverging circuit
the nerve impulse from a single presynaptic neuron causes the stimulation of increasing numbers of cells along the circuit
converging circuit
the postsynaptic neuron receives nerve impulses from several different sources.
reverberating circuit
incoming impulse stimulates the first neuron, which stimulates the second, which stimulates the third, and so on. Branches from later neurons synapse with earlier ones. This arrangement sends impulses back through the circuit again and again.
parallel after discharge circuit
In this circuit, a single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell. A differing number of synapses between the first and last neurons imposes varying synaptic delays, so that the last neuron exhibits multiple EPSPs or IPSPs. If the input is excitatory, the postsynaptic neuron then can send out a stream of impulses in quick succession.
neurogenesis
the birth of new neurons from undifferentiated stem cells
plasticity
the capability to change based on experience. At the level of individual neurons, the changes that can occur include the sprouting of new dendrites, synthesis of new proteins, and changes in synaptic contacts with other neurons.
