Flashcards in 15CHAPTER 12: NERVOUS TISSUE Deck (38):
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Nervous system uses electrical and chemical means to send messages from cell to cell: what are the three basic steps?`
1. Sense organs receive information and send info to spinal cord and brain
2. Brain and spinal cord determine responses
3. Brain and spinal cord issue commands to glands and muscles
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What are the two major anatomical subdivisions of Nervous System?
Central nervous system (CNS)
Peripheral nervous system (PNS)
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What is the Central nervous system (CNS)?
brain and spinal cord enclosed in bony coverings
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What does the Peripheral nervous system (PNS) consist of?
Nerves and ganglion
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What is a nerve?
bundle of axons (nerve fibers) wrapped in connective tissue
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What is a ganglion?
swelling in a nerve where cell bodies of neurons are concentrated
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What are the functional divisions of PNS?
Sensory (afferent = toward) divisions (receptors to CNS) and
Motor (efferent = away) division (CNS to effectors)
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What are the universal properties of nerve cells (neurons)?
• Excitability
• Conductivity
• Secretion
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What is excitability?
The response to changes in the body and external environment called stimuli, like muscle
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What does conductivity produce?
traveling electrical signals, like muscle
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What does nerve cells secrete?
secrete chemical neurotransmitter (NTr), unlike muscle
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How many types of neuroglia are there and where can you find them?
6 kinds: 4 in the CNS and 2 in the PNS
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What are the 4 types of neuroglia of the CNS?
1. Oligodendrocytes
2. Ependymal Cells
3. Microglia
4. Astrocytes
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What is the function of oligodendroctyes?
Makes myelin sheath in CNS
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What is the function of ependymal cells and where are they found?
-Secrete and circulate cerebrospinal fluid
-Line internal cavities of brain and spinal cord
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What are microglia composed of?
Small macrophages, phagocytize pathogens, dead nervous tissue
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What are the neuroglia of the PNS?
1. Schwann cells
2. Satellite cells
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Where do you find satellite cells?
Surround somas of neurons in ganglia (collection of somas) of the PNS
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What do schwann cells do?
Make myelin sheath around nerve fibers (axons) in PNS
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What is the electrical insulation around axons?
Myelin
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What is myelin composed of?
80% lipid, 20% protein
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What is the function of astrocytes?
-Supportive framework
-Secrete nerve growth factors
-Regulate chemical composition of ECF i.e. absorb neurotransmitters and K+ ions
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What does conduction speed of nerve fibers depends on?
1.Diameter of the nerve fiber (axon):
2.Presence or absence of myelin: faster conduction with myelin
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What axons can regenerate?
Only PNS axons
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What is denervation atrophy?
shrinkage due to lack of nerve supply
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What is the Resting membrane potential (RMP)
– The charge difference across the plasma membrane
– Around -70 mV in resting neuron
– Changes in RMP allow signal conduction
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What are local potentials?
A short range change in the RMP; may or may not reach the trigger zone, often restricted to dendrite and soma, signal can fade, excitatory or inhibitory
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What are the 7 steps of an Action Potential?
1. A local potential arrives at the trigger zone from the cell soma.
2. Membrane potential depolarizes, and reaches threshold (-55 mV)
3. Voltage-regulated Na+ channels open and Na+ enters; potential rises quickly.
4. Na+ channels start to close
5. K+ channels open and K+ leaves -----This repolarizes and then
6. hyperpolarizes the membrane potential.
7. Pumps and diffusion return Na+/K+ balance.
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What is the refractory period?
Period of resistance to stimulation
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What are the 2 types of refractory periods?
Absolute refractory period
Relative refractory period
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What is a synapse?
A junction between two neurons or a neuron and a muscle cell
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What do presynaptic neuron (axons) release?
A neurotransmitter (chemical signal) which crossed the synaptic cleft and stimulates the postsynaptic neuron
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What are the steps of synaptic transmission?
1. AP arrives at the synaptic knob of the presynaptic neuron.
2. Calcium enters the presynaptic neuron
3. Calcium triggers exocytosis of neurotransmitter
4. Neurotransmitter diffuses across the synaptic cleft and binds to a receptor on the postsynaptic neuron and alters physiology of that cell.
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What are the 4 major categories of neurotransmitters based on chemical composition?
Acetylcholine (ACh), Monoamines, Amino acids and Neuropeptides.
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What are the 3 types of synapses with different modes of actions?
Excitatory cholinergic synapse
Inhibitory GABA-ergic (gamma aminobutyric acid) synapse
Excitatory adrenergic synapse
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What are considered neuromodulators?
Hormones, neuropeptides, other messengers that modify synaptic transmission
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What doe neuromodulators do?
-Raise or lower number of receptors in post synaptic neuron membrane
-Alter rate of neurotransmitter release, synthesis, or breakdown
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