Chapter 12 Nervous Tissue Flashcards
(125 cards)
1
Q
Central nervous system (CNS)
A
consists of the brain and the spinal cord
2
Q
General functions of the nervous system
A
1- collect information
2-processes and evaluates information
3-initiate response to information
3
Q
Peripheral nervous system (PNS)
A
consists of the nerves and ganglia
4
Q
Types of nerves
A
Structural classification:
-caranial nerves
-spinal nerves
Functional classification:
-sensory nerves
-motor nerves
-mixed nerves (both sensory and motor)
5
Q
Sensory nervous system
A
detects stimuli and transmits information from receptors to the CNS
6
Q
Motor nervous system
A
initiates and transmits information from the CNS to effectors
7
Q
The 2 components of the sensory nervous system
A
somatic sensory and visceral sensory
8
Q
Somatic sensory
A
sensory input from the receptors of the five senses and proprioceptors; senses we consciously perceive
9
Q
Visceral sensory
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sensory input from receptors of internal organs and blood vessels; senses we are unaware of
10
Q
The 2 components of the motor nervous system
A
somatic motor and autonomic motor
11
Q
Somatic motor
A
motor output to skeletal muscle; voluntary
12
Q
Autonomic motor
A
motor output to cardiac muscle, smooth muscle, and glands; involuntary
13
Q
What is a nerve composed of?
A
cable like bundle of axons, connective tissue layers, and blood vessels, and it is a component of the PNS
14
Q
Epineurium
A
a thick layer of dense irregular connective tissue that encloses the nerve
15
Q
Perineurium
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a layer of dense irregular connective tissue that wraps each fascicle
16
Q
Endoneurium
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a delicate layer of areolar connective tissue that surrounds each axon
17
Q
Know the structure of a nerve and ganglion
A
18
Q
Are nerves vascularized?
A
yes
18
Q
Neurotransmitters
A
are molecules stored in vesicles and when released, bind to an excitable cell to cause either an excitatory or inhibitory effect on these target cells
19
Q
Know the structures in a typical neuron
A
19
Q
General characteristics of a neuron
A
- excitability
- conductivity
- secretion
- extreme longevity
- amitotic
20
Q
Ganglion
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a cluster of neuron cell bodies within the PNS
21
Q
Anterograde transport
A
the movement of materials from the cell body toward synaptic knobs
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Retrograde transport
A
the movement of materials from synaptic knobs toward the cell body
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Fast axonal transport
occurs at approximately 400 millimeters per day; involves movement along microtubules towards either direction (anterograde or retrograde)
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Slow axonal transport
occurs at approximately 0.1 to 3 millimeters per day; results from the flow of axoplasm; only allows movement to the synaptic knob (anterograde)
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Multipolar neurons
have many dendrites and a single axon that extends from the cell body; these are the most common types of neurons in the human body
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Bipolar neuron
have two processes that extend from the cell body- one dendrite and one axon; the location of these neurons is relatively limited to humans
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Unipolar neurons
have a single, short neuron process that emerges from the cell body and branches like a T
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Anaxonic neurons
have only dendrites and no axons; they produce graded potentials, but not action potentials
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Sensory neurons
responsible for conducting sensory input from both somatic sensory and visceral sensory receptors TOWARD the CNS; most are unipolar but some somatic sensory neurons are bipolar
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Motor neurons
conducting motor output AWAY FROM the CNS to both somatic effectors and autonomic effectors; all motor neurons are multipolar
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Interneurons
lie entirely within the CNS; receive, process, and store information and "decide" how the body responds to stimuli
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Synapse
the specific location where a neuron is functionally connected to either another neuron or an effector
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Chemical synapse
between two neurons; is composed of a presynaptic neuron and a postsynaptic neuron with a narrow fluid-filled gap
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Presynaptic neuron
the signal producer
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Postsynaptic neuron
the signal receiver
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Synaptic cleft
an extremely narrow, fluid-filled gap between two neurons
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Transmission
occurs between a presynaptic and postsynaptic neuron when neurotransmitter molecules stored in synaptic vesicles are released from the synaptic knob of a presynaptic neuron into the synaptic cleft
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Synaptic delay
the time between the neurotransmitter release from the presynaptic cell, its diffusion across the synaptic cleft, and neurotransmitter binding to receptors in the postsynaptic neuron plasma membrane
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Electrical synapse
composed of a presynaptic neuron and a postsynaptic neuron physically bound together
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Glial cells
found both in the CNS and PNS; have mitotic ability; smaller than neurons; they do not transmit electrical signals, but they do assist neurons with their functions
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4 types of glial cells found in the CNS
1- astrocytes
2- ependymal cells
3- microglia
4- oligodendrocytes
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Astrocytes
exhibit a starlike shape due to projections from their surface; most abundant glial cells in the CNS
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Astrocyte functions
- help form the blood-brain barrier (BBB)
- regulate interstitial fluid composition
- form structural support
- assist neuronal development
- alter synaptic activity
- occupy the space of dying neurons
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The blood-brain barrier (BBB)
strictly controls the movement of substances from exiting the blood and entering the nervous tissue in the brain
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Ependymal cells
ciliated simple cuboidal or simple columnar epithelial cells that line the internal cavities of the brain and the central canal of the spinal cord
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Choroid plexus
helps produce cerebrospinal fluid, a clear liquid that bathes the external surfaces of the CNS and fills its internal cavities
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Microglia
typically small cells that have slender branches extending from the main portion of the cell; they represent the smallest portion of CNS glial cells; classified as phagocytotic cells of the immune system
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Oligodendrocytes
are large cells with a bulbous body and slender cytoplasmic extensions or processes; insulate axons within the CNS to form a myelin sheath through a process called myelination
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2 types of glial cells in the PNS
1- satellite cells
2- neurolemmocytes
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Satellite cells
are flattened cells arranged around neuronal cell bodies in a ganglion; physically separating cell bodies from their surrounding interstitial fluid; they electrically insulate the cell body and regulate the continuous exchange of nutrients and waste products between neuron cell bodies and their environment
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Neurolemmocytes
elongated and flattened cells wrap around and insulate axons within the PNS to form a myelin sheath through myelination
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Myelination
the process by which part of an axon is wrapped with myelin
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Myelin
the insulating covering around the axon that consists of repeating concentric layers of plasma membrane of glial cells
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Neurilemma
the periphery of the neurolemmocyte contains the cytoplasm and nucleus
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Neurofibril nodes (nodes of Ranvier)
gaps in between the neurolemmocytes
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Unmyelinated axons
no myelin covers them; in the PNS are also associated with neurolemmocytes, which help to protect and support the axon
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Axon regeneration process
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Pumps
maintain specific concentration gradients by moving substances against a concentration gradient, a process that requires cellular energy
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Channels
provide the means for a substance to move with a concentration gradient
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Major types of channels
- leak channels
- chemically-gated channels
- voltage-gated channels
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Leak channels
always open, allowing continuous diffusion of a specific type of ion from a region of high concentration to a region of low concentration
EXAMPLES:
- Na+ leak channels
- K+ leak channels
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Chemically gated channels
normally closed; they temporarily open in response to the binding of a neurotransmitter; when open, they allow a specific type of ion to diffuse across the plasma membrane
EXAMPLES:
- Chemically gated K+ channels
- Chemically gated Cl- channels
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Voltage-gated channels
normally closed, but they temporarily open in response to changes in electrical charge across the plasma membrane; when open, they allow a specific type of ion to diffuse across the membrane
EXAMPLES:
- Voltage-gated Na+ channels
- Voltage-gated K+ channels
- Voltage-gated Ca2+ channels
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Voltage-gated Na+ gates
1- activation gate
2- inactivation gate
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The 3 stages of voltage-gated Na+ channels
1- resting state
2- activation state
3- inactivation state
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Stages of voltage-gated Na+ channels
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Modality-gated channel
normally closed, but open in response to specific type of sensory stimulus
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Know the distribution of pumps and channels in the plasma membrane of a neuron
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Electrical energy
the movement of charged particles, and that all usable forms of energy are available to do work
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Voltage
amount of difference in electrical charge
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Current
movement of charged particles across plasma membrane through open channels
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Resistance
opposition to movement of charged particles
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Ohm's Law
current= voltage/resistance
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Know neurons and Ohm's law
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Neuron at rest
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Neurons at rest characteristics
-ion concentration gradients exist for K+, Na+, and Cl- across the plasma membrane along the entire neuron
- a Ca2+ concentration gradient exists at the synaptic knob
- gated channels are CLOSED
- there is an electrical charge difference across the plasma membrane
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Resting Membrane Potential (RMP)
the neuron is at rest, the membrane potential is at RMP; -70 mV
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Role of Na+/K+ pumps
push 3 Na+ out and pulls K+ in; maintains the concentration gradients for these ions
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Graded potentials
are relatively small, short-lived changes in the resting membrane potential that are caused by the movement of small amounts of ions across the plasma membrane
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Characteristics of graded potentials
- established in the receptive segment by the opening of chemically gated channels
- local currents associated with the graded potentials are short-lived because the flow or current of ions along the plasma membrane experiences resistance
- they vary in both the degree of change and the direction of change of the RMP
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Know the events in each neuron segment
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Postsynaptic potentials
graded potentials that occur in postsynaptic neurons
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Excitatory postsynaptic potentials (EPSP)
postsynaptic potentials that result in the neuron becoming more positive
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Inhibitory postsynaptic potentials (IPSP)
postsynaptic potentials resulting in the neuron becoming more negative
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Generation of an EPSP
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Generation of an IPSP
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Summation
the changes in the membrane potential associated with these graded postsynaptic potentials are "added" in the initial segment to determine if an action potential is initiated
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Threshold membrane potential
the minimum voltage change
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Spatial summation
multiple locations on the cell's receptive regions receive neurotransmitter simultaneously and generate postsynaptic potentials
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Temporal summation
a single presynaptic neuron repeatedly releases neurotransmitter and produces multiple EPSPs within a very short period of time
91
All-or-none law
if threshold is reached, action potential generated and propagated down the axon without any loss in intensity; if threshold not reached, voltage-gated channels stay closed, no action potential
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Action potential
involves depolarization and repolarization
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Depolarization
gain of positive charge as Na+ enters through voltage gated Na+ channels
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Repolarization
return to negative potential as K+ exits through voltage gated K+ channels
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Nerve signal
propagation of of an action potential
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Generation of an Action Potential: Depolarization and its Activation
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Generation of an Action Potential: Repolarization and its Propagation
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Refractory period
period of time after start of action potential when it is impossible or difficult to fire another action potential
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Absolute refractory period
no stimulus can initiate another action potential
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Relative refractory period
another action potential is possible but the minimum stimulus strength is now greater; some K+ channels are still open and cell is slightly hyperpolarized and further from threshold
101
Continuous conduction
occurs in unmyelinated axons and involves the sequential opening of voltage-gated Na+ channels and voltage-gated K+ channels located within the axon plasma membrane along the entire length of the axon
102
Saltatory conduction
occurs in myelinated axons; action potential only occurs ate neurofibril nodes ; much faster than continuous conduction and myelinated cells use less ATP to maintain resting membrane potential
103
Propagation of an action potential (continuous and saltatory conduction)
104
Steps involved when a nerve signal reaches the transmissive segment
105
Know the difference between a graded potential and an action potential
Shown on table 12.2
106
Velocity of action potential propagation is influenced by what two factors
1- diameter of the axon
2- myelination of the axon
107
Nerve fiber
an axon and its myelin sheath
108
Neurotransmitters
small, organic molecules that are:
- synthesized by neurons and stored within vesicles in synaptic knobs
- released from the vesicles when action potential triggers calcium entry into the synaptic knob
- bind to a specific receptor in a target cell
- trigger a physiologic response in the target cell
109
4 categories of neurotransmitters based on chemical structure
1- acetylcholine (ACh)
2- biogenic amines
3- amino acids
4- neuropeptides
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Acetylcholine
structure differs substantially from other transmitters
111
Biogenic amines
an amino acid is slightly modified to synthesize the transmitter
Catecholamines (dopamine)- are made from tyrosine
Indoleamines (serotonin)- are made from histidine or tryptophan
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Amino acids
include common transmitters glutamate, glycine, GABA
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Neuropeptides
chains of amino acids including endorphins, substance P, enkephalin, somatostatin
114
Neurotransmitters are also classified by function:
1) excitatory- transmitters cause EPSPs
2) inhibitory- transmitters cause IPSPs
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Neurotransmitters are also classified by action:
1) direct- transmitters bind to receptors that are chemically gated channels
2) indirect- transmitters bind to receptors that involve G-proteins and second messengers
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Acetylcholine release, removal from synaptic cleft, and action
117
Acetylcholinesterase
an enzyme that resides in the synaptic cleft
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Neuromodulators
chemicals that alter responses of local neurons; modify neurotransmitters
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Facilitation
modulation that causes greater response in postsynaptic neurons; may increase the amount of neurotransmitter in cleft or number of postsynaptic receptors
120
Inhibitation
modulation that causes weaker response; may decrease the amount of neurotransmitter in cleft or number of postsynaptic receptors
121
Nitric oxide
might be a neurotransmitter or a modulator; a short-lived, nonpolar gas; made and released by postsynaptic neurons in the brain where it is believed to strengthen memory by affecting presynaptic cells; effects in the PNS include blood vessel dilation
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Endocannabinoids
influence same receptors; small, nonpolar molecules; made and released by postsynaptic neurons; have effects on presynaptic neurotransmitter release; influence memory and appetite
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Subthreshold
any change in voltage below the threshold value is not sufficient to open voltage-gated channels
