Flashcards in 15CHAPTER 12: NERVOUS TISSUE Deck (38)
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1
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
2
What are the two major anatomical subdivisions of Nervous System?
Central nervous system (CNS)
Peripheral nervous system (PNS)
3
What is the Central nervous system (CNS)?
brain and spinal cord enclosed in bony coverings
4
What does the Peripheral nervous system (PNS) consist of?
Nerves and ganglion
5
What is a nerve?
bundle of axons (nerve fibers) wrapped in connective tissue
6
What is a ganglion?
swelling in a nerve where cell bodies of neurons are concentrated
7
What are the functional divisions of PNS?
Sensory (afferent = toward) divisions (receptors to CNS) and
Motor (efferent = away) division (CNS to effectors)
8
What are the universal properties of nerve cells (neurons)?
• Excitability
• Conductivity
• Secretion
9
What is excitability?
The response to changes in the body and external environment called stimuli, like muscle
10
What does conductivity produce?
traveling electrical signals, like muscle
11
What does nerve cells secrete?
secrete chemical neurotransmitter (NTr), unlike muscle
12
How many types of neuroglia are there and where can you find them?
6 kinds: 4 in the CNS and 2 in the PNS
13
What are the 4 types of neuroglia of the CNS?
1. Oligodendrocytes
2. Ependymal Cells
3. Microglia
4. Astrocytes
14
What is the function of oligodendroctyes?
Makes myelin sheath in CNS
15
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
16
What are microglia composed of?
Small macrophages, phagocytize pathogens, dead nervous tissue
17
What are the neuroglia of the PNS?
1. Schwann cells
2. Satellite cells
18
Where do you find satellite cells?
Surround somas of neurons in ganglia (collection of somas) of the PNS
19
What do schwann cells do?
Make myelin sheath around nerve fibers (axons) in PNS
20
What is the electrical insulation around axons?
Myelin
21
What is myelin composed of?
80% lipid, 20% protein
22
What is the function of astrocytes?
-Supportive framework
-Secrete nerve growth factors
-Regulate chemical composition of ECF i.e. absorb neurotransmitters and K+ ions
23
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
24
What axons can regenerate?
Only PNS axons
25
What is denervation atrophy?
shrinkage due to lack of nerve supply
26
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
27
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
28
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.
29
What is the refractory period?
Period of resistance to stimulation
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