Chapter 11 Flashcards
What are the functions of the nervous system?
- sensory input
- Integration
- Motor output
What is the organization of the nervous system?
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
The CNS contains the
Brain and spinal cord
The PNS contains the
Paired spinal and cranial nerves
The PNS has two functional divisions, what are they?
Sensory (afferent) division
Motor (efferent) division
What fibers are in the sensory division?
Sensory afferent (Somatic afferent) fibers Visceral afferent fibers
Sensory afferent fibers carry
Impulses from the skin, skeletal muscles, and joints to the brain (CNS)
Visceral afferent fibers transmit
Impulses from visceral organs to the brain (CNS)
The motor division transmits
Impulses from the CNS to effector organs, muscles, and glands
What are the two main parts of the motor division?
Somatic and autonomic
Is the somatic nervous system voluntary or involuntary?
Voluntary
Is the autonomic nervous system voluntary or involuntary?
Involuntary
The autonomic nervous system regulates
Smooth muscle and cardiac muscle
What are the divisions of the autonomic nervous system?
Sympathetic and Parasympathetic
The two principal cell types of the nervous system are
Neurons and supporting cells
Supporting cells are
Cells that surround and wrap neurons
Nerugoglia (glia cells) are ______ cells that
Supporting cells that
Provide a supportive scaffolding for neurons
What are the most abundant, versatile, and highly branched glial cells?
Astrocytes (in CNS)
Astrocytes in CNS cling to
Neurons and their synaptic endings
Astrocytes in CNS cover
Capillaries
Astrocytes in CNS are the barrier between what?
Neurons and capillaries
What are small, ovoid cells with spiny processes?
Microglia in CNS
Microglia in CNS are phagocytes that
Monitor the health of neurons
Microglia in CNS are a type of (1) that (2)
(1) Macrophage
(2) Engulfs foreign particles
Ependymal cells in CNS range in shape from
Squamous to columnar
Ependymal cells in CNS line the
Cavities of the CNS (brain and spinal cord)
In ependymal cells in CNS, cilia circulate
Cerebrospinal fluid
Oligodendrocytes in CNS are (1) that (2)
(1) Branched cells
(2) Wrap CNS nerve fibers
What forms the myelin sheaths?
Oligodendrocytes in CNS and Shwann cells
Shwann cells surround
Fibers of the PNS
Schwann cells are involved in
Regeneration in the PNS
Schwann cells form the
Tube and encourage axon growth
Satellite cells surround
Neuron cell bodies with ganglia in the PNS
Nerve cells are
Neurons
Neurons are composed of
A body, axon, and dendrites
Amitotic is the
Simple division of nucleus with replication of chromosomes
Are neurons mitotic or amitotic?
Amitotic
The plasma membrane of neurons function in
Electrical signaling
The nerve cell body is called
Perikaryon or Soma
The nerve cell body contains
The nucleus and a nuceolus
The nerve cell body is the major
Biosynthetic Center
The nerve cell body is the focal point for the
Outgrowth of neuronal processes
The nerve cell body has no (1) hence its (2) nature
(1) No centrioles (2) Amitotic nature
An Axon hillock is a
Cone-shaped area from which axons arise
The cluster of cell bodies in the CNS are
Nuclei
The cluster of cell bodies in the PNS are
Ganglia
Processes are
Arm-like extensions from the soma (body)
Processes are called what in the PNS and CNS?
PNS - Nerves
CNS - Tracts
What are the two types of processes?
Axons and dendrites
Dendrites of motor neurons are short or long?
Short
Dendrites of motor neurons are what kind of processes?
Diffusely branched processes
Dendrites of motor neurons are the _______ regions of the neuron
Receptive or input
Dendrites of motor neurons create enormous
Surface area for receptions of signal from other neurons
Dendrites of motor neurons conduct impulse
Toward cell body
Axons arise from
The hillock
Axons are fat or thin?
Thin
T/F Axons can be short or very long
True
Long axons are called
Nerve fibers
How many unbranched axon per neuron?
Usually only one
Larger diameter of axons cause
Faster conduction
What are the functions of axons?
- Generate and transmit ACTION POTENTIALS
- Carries IMPULSES AWAY from cell body
- Secrete NEUROTRANSMITTERS from axonal terminals
Myelin sheath is the
Whitish, fatty, segmented sheath around most long axons
The myelin sheath functions are
- PROTECT the axon
- Electrically INSULATE fibers from one another
- INCREASE THE SPEED of nerve impulse transmission
Nodes of Ranvier are
Gaps in the myelin sheath between adjacent Shwann cells
Nodes of Ranvier are the sites where
Axon collaterals can emerge
In axons of the CNS both
Myelinated and unmyelinated fibers are present
In axons of the CNS myelin sheaths are formed by
Oligodendrocytes
The regions of the brain and spinal cord are
White matter and gray matter
White matter is a
Dense collection of myelinated fibers
White matter have (1) in regions of (2)
(1) Myelinated fibers
(2) Brain and spinal cord
Where is gray matter found?
Mostly in the Soma (nerve cell body)
T/F Gray matter is myelinated
False; Unmyelinated
What are the types of neuron classification?
Structural and Functional
Structural neuron classification is divided into
Multipolar
Bipolar
Unipolar
Functional neuron classification is divided into
Sensory (afferent)
Motor (efferent)
Interneurons (association neurons)
Action potentials are also known as
Nerve Impulses
Action potentials are
Electrical impulses carried along the length of axons
Action potentials are always (1) regardless of (2)
(1) The same
(2) Stimulus
What is the underlying functional feature of the nervous system?
Action Potentials
Voltage is the
Measure of potential energy generated by separated charges
There is a potential on either side of membranes when
- The # of ions is different across the membrane
2. The membrane provides a resistance to ion flow
Types of plasma membrane ion channels
- Passive/Leakage channels
- Chemically gated channels
- Voltage-gated channels
- Mechanically gated channels
Chemically gated channels open with
Binding of a specific neurotransmitter
Voltage-gated channels open and close
In response to membrane potential
A chemically gated channel is closed when
A neurotransmitter is not bound to the extracellular receptor
A chemically gated channel is open when
A neurotransmitter is attached to the receptor
Example of a chemically gated channel is
Na+ -K gated channel
In a Na+ -K gated channel, when it is closed (1) and when it is open (2)
(1) Na+ cannot enter the cell and K+ cannot exit the cell
(2) Na+ enters the cell and K+ exits the cell
A voltage-gated channel is closed when
The intracellular environment is negative
A voltage-gated channel is open when
The intracellular environment is positive
An example of a voltage-gated channel is
Na+ channel
In a Na+ channel, when it is closed (1) and when it is open (2)
(1) Na+ cannot enter the cell
(2) Na+ can enter the cell
Resting Membrane Potential is the
Potential difference (-70 mV) across the membrane of a resting neuron
Voltage across the membrane is
-70 mV
Resting Membrane Potential is more
Negative on the inside
The resting membrane potential is established by
Na/K pump
The resting membrane potential is generated by
Different concentrations of Na+, K+, Cl- and proteins anions (A-)
Ionic differences are the consequences of
- Differential permeability of the neurilemma to Na+ and K+
2. Operation of the sodium-potassium pump
Membrane potentials are used to
Integrate, send, and receive information
Membrane potential changes are produced by
- Changes in membrane permeability to ions
2. Alterations of ion concentrations across the membrane
Changes in membrane potential are caused by
- Depolarization
- Repolarization
- Hyperpolarization
In depolarization the inside of the membrane
Becomes less negative
In repolarization the membrane
Returns to it’s resting membrane potential
In hyperpolarization the inside of the membrane
Becomes more negative than the resting potential
Graded potentials are short lived or long lived?
Short lived
Graded potentials decrease
In intensity with distance
With graded potentials, magnitude
Varies directly with the strength of the stimulus
Sufficiently strong graded potentials can
Initiate action potentials
In graded potentials, voltage changes
Are decremental (or gradually decreasing)
In graded potentials, the current is
Quickly dissipated
Why is the current quickly dissipated in graded potentials?
Due to the leaky plasma membrane
Graded potentials only travel
Over short distances
Action potential is a
Brief reversal of membrane potential with a total amplitude (change in voltage) of 100 mV
Action potentials are only generated
By muscle cells and neurons
T/F Action potentials decrease in strength over distance
False, they do not decrease
When an action potential is in resting state Na+ and K+ channels
Are closed
What accounts for small movements of Na+ and K+ when an action potential is in resting state?
Leakage
When an action potential is in resting state, each Na+ channel
Has two voltage-regulated gates
What are the two Na+ voltage-regulated gates?
Activation gates
Inactivation gates
Are activation gates open or closed in resting state?
Closed
Are inactivation gates open or closed in resting state?
Open
When an action potential is in depolarization phase, Na+ permeability (1); membrane potential (2)
(1) Increases
(2) Reverses
When an action potential is in depolarization phase, Na+ (activation) gates are (1); K+ gates are (2)
(1) Opened
(2) Closed
Threshold is
A critical level of depolarization (-55 to -50 mV)
When an action potential is in repolarization phase, Na+ inactivation gates
Close
When an action potential is in depolarization phase, membrane permeability to Na+
Declines to resting levels
When an action potential is in depolarization phase, when Na+ gates close,
Voltage-sensitive K+ gates open
When an action potential is in depolarization phase, K+ (1) and internal negativity of (2) is (3)
(1) Exits the cell
(2) The resting neuron
(3) Restored
When an action potential is in Hyperpolarization phase, K+ gates
Remain open
When the K+ gates remain open during hyperpolarization phase, this causes
An excessive efflux (flowing out) of K+
What causes hyperpolarization of the membrane?
The efflux of K+
When an action potential is in hyperpolarization phase, the neuron is insensitive to
Stimulus and depolarization
Repolarization restores
The resting electrical conditions of the neuron
Repolarization does not restore
The resting ionic conditions
After repolarization, the Na+ - K+ pump
Redistributes the ion back to resting conditions
What are the phases of the action potential?
- Resting state
- Depolarization phase
- Repolarization phase
- Hyperpolarization phase
Threshold is typically reached when
The membrane is depolarized by 15 - 20 mV
The threshold is established by
The total amount of current flowing through the membrane
Are weak (subthreshold) stimuli or strong (threshold) stimuli relayed into action potentials?
Strong stimuli are relayed into action potentials
The all-or-none phenomenon says that
Action potentials either happen completely or not at all
The absolute refractory period is the
Time from the opening of the Na+ activation gates until the closing of inactivation gates
The absolute refractory period prevents the neuron from
Generating an action potential
The absolute refractory period ensures that each action potential
Is Separate
The absolute refractory period enforces
One-way transmission of nerve impulses
The relative refractory period is
The interval following the absolute refractory period
What are the position of the Na+ and K+ gates during the relative refractory period?
Na+ gates are closed
K+ gates are open
What is occuring during the relative refractory period?
Repolarization
During the relative refractory period, the threshold level is
Elevated
An elevated threshold level during the relative refractory period allows
Strong stimuli to increase the frequency of action potential events
Rate of impulse propagation is determined by
- Axon diameter
2. Presence of a myelin sheath
A current can pass through a myelin sheath
ONLY at the nodes of Ranvier (myelin sheath gaps)
Action potentials are triggered (1) and (2)
(1) ONLY at the nodes
(2) Jump from one node to the next
Multiple sclerosis is
An autoimmune disease that mainly affects young adults
In MS the immune system
Attacks myelin proteins
In MS the axons
Are not damaged
The symptoms of MS are
Visual disturbances
Weakness
Loss of muscular control
Urinary incontinence
In MS the nerve fibers (1) and myelin sheaths in the CNS become (2)
(1) Are severed
(2) Nonfunctional scleroses
Nonfunctional scleroses is when
Sheaths are reduced to hard lesions
A synapse is
A junction that mediates information transfer from one neuron to
a) another neuron
b) an effector cell
A presynaptic neuron conducts
Impulses toward the synapse
A postsynaptic neuron transmits
Impulses away from the synapse
What are the two types of postsynaptic potentials?
(1) EPSP - Excitatory postsynaptic potentials
(2) IPSP - Inhibitory postsynaptic potentials
EPSPs are
Graded potentials that can initiate an action potential in an axon
EPSPS use only
Chemically gated channels
Postsynaptic membranes do not
Generate action potentials
Only ____ generate action potentials
Axons
The strength of an EPSP depends on
The amount of neurotransmitter bound to receptors
If EPSPs reach the axon hillock,
Action potential occurs down the axon
Can a single EPSP induce an action potential?
No
EPSPs must (1) to (2)
(1) Summate temporally or spatially
(2) Induce an action potential
Temporal summation occurs when
Presynaptic neurons transmit impulses in rapid-fire order
Spatial summation occurs when
The postsynaptic neuron is stimulated by a large number of terminals at the same time
IPSPs can also summate
With EPSPs
When IPSPs summate with EPSPs,
They cancel each other
Neurotransmitters are
Chemicals used for neuronal communication with the body and the brain
T/F Only a handful of neurotransmitters have been identified
False, 50 different neurotransmitters have been identified
How are neurotransmitters classified?
Chemically and functionally
GABA stands for
Gamma - aminobutyric acid
GABA is the most
Prevalent neurotransmitter in the brain
Is GABA excitatory or inhibitory?
Inhibitory
Huntington’s is the
Lack of CABA releasing neurons
Norepinephrine is a neurotransmitter that
Makes a person feel good
Norepinephrine reuptake is
Blocked by cocaine
Dopamine is a neurotrasmitter that
Makes a person feel good
Dopamine plays a part in
The regulation of skeletal muscle
Dopamine is deficient in
Parkinson’s disease
Serotonin is a neurotransmitter that
Regulates mood
Serotonin is excitatory or inhibitory?
Inhibitory
Serotonin reuptake is
Blocked by Prozac
Endorphins are neurotransmitters that
Inhibit pain
Effects of endorphins are mimicked by
Morphine and heroin
Acetylcholine was the
First neurotransmitter identified
Acetylcholine is the best
Understood neurotransmitter
Acetylcholine is released
At the neuromuscular junction
Acetylcholine is synthesized and enclosed in
Synaptic vesicles
Acetylcholine is degraded by
The enzyme acteylcholinesterase (AChE)
Acetylecholine is released by
- All neurons that stimulate skeletal muscle
2. Some neurons in the autonomic nervous system
The functional classification of neurotransmitters is divided into
Excitatory and inhibitory
Excitatory neurotransmitters cause
Depolarizations
Inhibitory neurotransmitters cause
Hyperpolarizations
T/F Some neurotransmitters have both excitatory and inhibitory effects
True