The Nervous System Flashcards
(87 cards)
1
Q
What two systems maintain internal coordination?
A
Endocrine and nervous systems
2
Q
Communicates by means of chemical, messengers (hormones) secreted into the blood
A
Endocrine system
3
Q
Employs electrical and chemical means to send messages from cell to cell
A
Nervous system
4
Q
What are the two major anatomical subdivisions of the Nervous System?
A
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
5
Q
- brain and spinal cord enclosed in bony coverings
- enclosed by cranium and vertebral column
A
Central nervous system (CNS)
6
Q
All the nervous system except the brain and spinal cord; composed of nerves and ganglia
A
Peripheral nervous system (PNS)
7
Q
A bundle of fibers (axons) wrapped in fibrous connective tissue
A
Nerve
8
Q
A knot like swelling in a nerve where neuron cell bodies are concentrated
A
Ganglion
9
Q
Carries sensory signals from various receptors to the CNS
- informs the CNS of stimuli within or around the body
A
Sensory (afferent) division
10
Q
Carries signals from receptors in the skin, muscles, bones, and joints
A
Somatic sensory division
11
Q
Carries signals from the viscera of the thoracic and abdominal cavities
- heart, lungs, stomach, and urinary bladder
A
Visceral sensory division
12
Q
Carries signals from the CNS to gland and muscle cells that carry out the body’s response
A
Motor (efferent) division
13
Q
Cells and organs that respond to commands from the CNS
A
Effectors
14
Q
Carries signals to skeletal muscles
- output produces muscular contraction as well as somatic reflexes- involuntary muscle contractions
A
Somatic motor division
15
Q
-Carries signals to glands, cardiac muscle, and smooth muscle
- involuntary, and responses of this system receptors are viscera, reflexes
A
Visceral motor division (autonomic nervous system)
16
Q
- tends to arouse body for action
- accelerating heart beat and respiration, while inhibiting digestive and urinary systems
A
Sympathetic division
17
Q
- tends to have calming effect
- slows heart rate and breathing
- stimulates digestive and urinary systems
A
Parasympathetic division
18
Q
Neurons respond to environmental changes called stimuli
A
Excitability (irritability)
19
Q
Neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations
A
Conductivity
20
Q
When electrical signal reaches end of nerve fiber, a chemical neurotransmitter is secreted that crosses the gap and stimulates the next cell
A
Secretion
21
Q
What are the three general classes of neurons based on function?
A
Sensory, interneuron, motor
22
Q
- specialized to detect stimuli
- transmit information about them to the CNS
- begin in almost every organ in the body and end in the CNS
A
Sensory (afferent) neurons
23
Q
Conducting signals toward CNS
A
Afferent
24
Q
-lie entirely within the CNS
- receive signals Demi many neurons and carry out the intergrative function (process, store, and retrieve information and “make decisions” that determine how the body will respond to stimuli)
- 90% of all neurons are these
- lie between and interconnect the incoming sensory pathways and the outgoing motor pathways of the CNS
A
Interneurons (associated neurons)
25
-
Send signals out to muscles and gland cells (the effectors)
- motor because most of them lead to muscles
- efferent neurons conduct signals away from the CNS
Motor (efferent) neuron
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The control center of the neuron
- also called neurosoma, cell body, or perikaryon
- has a single, centrally located nucleus with large nucleolus
- cytoplasm contains mitochondria, lysosomes, a Golgi complex, numerous inclusions, and extensive rough ER and cytoskeleton
- cytoskeleton consists of dense mesh of microtubules and neurofibrils (bundles of actin filaments)
Soma
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Vast number of branches coming from a few thick branches from the soma
- resemble bare branches of a tree in winter
- primary site for receiving signals from other neurons
- the more of these a neuron has, the more information it can receive and incorporate into decision making
- provide precise pathway for the reception and processing of neural information
Dendrites
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Originates from a mound on one side of the soma called the axon hillock
- cylindrical, relatively unbranched for most of its length
- branch extensively on distal end
- specialized for rapid conduction of nerve signals to points remote to the soma
Axon (nerve fiber)
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Branches of axon
Axon collaterals
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Cytoplasm of axon
Axoplasm
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Plasma membrane of axon
Axolemma
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What enclose and axon?
Schwann cells and myelin sheath
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Little swelling that forms a junction (synapse) with the next cell
Synaptic knob
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- one axon and multiple dendrites
- most common
- most neurons in the brain and spinal cord
Multipolar neuron
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- one axon and one dendrite
- olfactory cells, retina, inner ear
Bipolar neuron
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- single process leading away from the soma
- sensory from skin and organs to spinal cord
Unipolar neuron
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- many dendrites but no axon
- help in visual processes
Anaxonic neuron
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two-way passage of proteins, organelles, and other material along an axon
axonal transport
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movement down the axon away from the soma
anterograde transport
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movement up the axon toward the soma
retrograde transport
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- support and protect the neurons
- bind neurons together and form framework for nervous tissue
- in fetus, guide migrating neurons to their destination
-If mature neuron is not in synaptic contact with another neuron it is covered by glial cells
neuroglia or glial cells
42
What are the four types of Neuroglia that only occur in CNS?
1. oligodendrocytes
2. ependymal cells
3. microglia
4. astrocytes
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- form myelin sheaths in CNS
- each arm like process wraps around a nerve fiber forming an insulating layer that speeds up signal conduction
oligodendrocytes
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- line internal cavities of the brain
- cuboidal epithelium with cilia on apical surface
- secretes and circulates cerebrospinal fluid (CSF) (clear liquid that bathes the CNS)
ependymal cells
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- small, wandering macrophages formed white blood cell called monocytes
- though to perform a complete checkup on the brain tissue several times a day
- wander in search of cellular debris to phagocytize
microglia
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- most abundant glial cell in CNS
- cover entire brain surface and most nonsynaptic regions of the neurons in the gray matter of the CNS
- diverse functions: form a supportive framework; have extensions that contact blood capillaries that stimulate them to form a tight seal called the blood-brain barrier; convert blood glucose to lactate and supply this to the neurons for nourishment
astrocytes
47
What two types of Neuroglia only occur in PNS?
1. Schwann cells
2. Satellite cells
48
- envelope nerve fibers in PNS
- wind repeatedly around a nerve fiber
- produce a myelin sheath similar to the ones produced by oligodendrocytes in CNS
- assist in the regeneration of damaged fibers
Schwann cells
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- surround the neurosomas in ganglia of the PNS
- provide electrical insulation around the soma
- regulate the chemical environment of the neurons
Satellite cells
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an insulating layer around a nerve fiber
- formed by oligodendrocytes in CNS and Schwann cells in PNS
- consists of the plasma membrane of glial cells (20% protein and 80% lipid)
myelin sheath
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production of the myelin sheath
- begins at week 14 of fetal development
- proceeds rapidly during infancy
- completed in late adolescence
- dietary fat is important to CNS development
myelination
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What are the segmented parts of the myelin sheath?
1. Nodes of Ranvier
2. Internodes
3. Initial segment
4. Trigger zone
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gap between segments
Nodes of Ranvier
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myelin-covered segments from one gap to the next
Internodes
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short section of nerve fiber between the axon hillock and the first glial cell
Initial segment
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the axon hillock and the initial segment
- play an important role in initiating a nerve signal
Trigger zone
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degenerative disorder of the myelin sheath
- oligodendrocytes and myelin sheaths in the CNS deteriorate
- myelin replaced by hardened scar tissue
- nerve conduction disrupted (double vision, tremors, numbness, speech defects)
- onset between 20 and 40 and fatal from 25 to 30 years after diagnosis
- cause may be autoimmune triggered by virus
multiple sclerosis
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formed by Schwann cells, basal lamina, and the neurilemma near the injury
- guides the growing sprout back to the original target cells and reestablishes synaptic contact
regeneration tube
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conduction speed of fibers: 0.5 to 2.0 m/s
small, unmyelinated fibers
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conduction speed of fibers: 3 to 15.0 m/s
small, myelinated fibers
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conduction speed of fibers: up to 120 m/s
large, myelinated fibers
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Living cells are ______
polarized
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charge difference across the plasma membrane
- about -70 mV in a resting, unstimulated neuron
- negative value means there are more negatively charged particles on the inside of the membrane than on the outside
resting membrane potential (RMP)
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a rapid up-and-down shift in the membrane voltage
- sodium ions arrive at the axon hillock
- depolarize the membrane at that point
- threshold
action potential
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critical voltage to which local potentials must rise to open the voltage-regulated gates (-55mV)
threshold
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polarity reversed from RMP
depolarization
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do not get weaker with distance
nondecremental
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once started goes to completion and cannot be stopped
irreversible
69
the period of resistance to stimulation
refractory period
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What are the two phases of the refractory period?
1. absolute refractory period
2. relative refractory period
71
- no stimulus of any strength will trigger AP
- as long as Na+ gates are open
- from action potential to RMP
absolute refractory period
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- only especially strong stimulus will trigger new AP
- K+ gates are still open and any effect of incoming Na+ is opposed by the outgoing K+
relative refractory period
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synapses: first neuron in the signal path
- releases neurotransmitter
presynaptic neuron
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synapses: second neuron
- responds to neurotransmitter
postsynaptic neuron
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synapses: may synapse with a dendrite, soma, or axon of postsynaptic neuron to form axodendritic, axosomatic, or axoaxonic synapses
presynaptic neuron
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____ ______ of presynaptic neuron contains synaptic vesicles containing neurotransmitter
synaptic knob
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_____ ______ membrane contains proteins that function as receptors and ligand-regulated ion gates
postsynaptic neuron
78
- synthesized by the presynaptic neuron
- released in response to stimulation
- bind to specific receptors on the postsynaptic cell
- alter the physiology of that cell
neurotransmitters
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employs acetylcholine (ACh) as its neurotransmitter
- ACh excites some postsynaptic cells (skeletal muscle)
- inhibits others
Cholinergic synapse
80
any voltage change in the direction of threshold that makes a neuron more likely to fire
- usually results from Na+ flowing into the cell cancelling some of the negative charge on the inside of the membrane
excitatory postsynaptic potential (EPSP)
81
excitatory brain neurotransmitters that produce EPSPs
glutamate and aspartate
82
any voltage change away from threshold that makes a neuron less likely to fire
- neurotransmitter hyperpolarizes the postsynaptic cell and makes it more negative than the RMP making it less likely to fire
- produced by neurotransmitters that open ligand-regulated chloride gates (causing inflow of Cl- making the cytosol more negative)
inhibitory postsynaptic potential (IPSP)
83
occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades
- allows EPSPs to add up over time to a threshold voltage that triggers an action potential
temporal summation
84
occurs when EPSPs from several different synapses add up to threshold at an axon hillock
- several synapses admit enough Na+ to reach threshold
- presynaptic neurons cooperate to induce the postsynaptic neuron to fire
spatial summation
85
a process in which one neuron enhances the effect of another one
- combined effort of several neurons facilitates firing of postsynaptic neuron
facilitation
86
process in which one presynaptic neuron suppresses another one
- opposite of facilitation
- reduces or halts unwanted synaptic transmission
- neuron 1 releases inhibitory GABA (prevents voltage-gated calcium channels from opening in synaptic knob and presynaptic neurons releases less or no neurotransmitter
presynaptic inhibitation
87
What are the two subdivisions of the peripheral nervous system (PNS)?
Sensory division & motor division
