Chapter 4: The Nervous System Flashcards
What is contained in the soma of a neuron?
Endoplasmic reticulum and ribosomes
What appendages emanate from the soma? What is their role?
Dendrites; receive incoming messages from other cells
The info received by dendrites is transmitted through the ________ before it reaches the ________ ____________, which integrates the incoming signals.
soma; axon hillock
Signals arriving from the dendrites can be excitatory or inhibitory; the axon hillock sums up these signals, and if the result is excitatory enough, it will initiate what?
An action potential
What does myelin do?
It forms a sheath around the axon, allowing transmission to proceed without signal loss and crossing of signals. It also increases the speed of conduction.
What produces myelin in the CNS? PNS?
oligodendrocytes; Schwann cells
At certain intervals, there are small breaks in the myelin sheath with exposed areas of axon membrane called what?
What are these important for?
nodes of Ranvier; critical for rapid signal conduction
What structure is at the end of the axon?
two names
nerve terminal OR synaptic bouton (knob)
The nerve terminal is enlarged and flattened to maximize signal transmission and ensure proper release of what?
Neurotransmitters
Neurons are not physically connected to each other, rather there is a space into which the terminal portion of the axon releases neurotransmitters, which bind to the dendrites of the adjacent neuron. What is this space called?
synaptic cleft
What comprises a “synapse”?
Presynaptic nerve terminal, synaptic cleft, postsynaptic membrane
Multiple neurons may be bundled together to form a ________ in the PNS. What are the three types?
nerve;
1. sensory
2. motor
3. mixed
The cell bodies of neurons of the same type are clustered together into __________.
Ganglia
In the CNS, axons may be bundled together to form tracts, which only carry 1 type of information, unlike nerves. The cell bodies of neurons in the same tract are grouped into __________.
nuclei
Neurons are supported and myelinated by other cells called what?
glial cells (neuroglia)
What are the 5 types of glial cells?
- Astrocytes
- Ependymal cells
- Microglia
- Oligodendroycytes
- Schwann cells
____________ nourish neurons and form the blood-brain barrier (BBB), which controls the transmission of solutes from the bloodstream into nervous tissue.
Astrocytes
____________ cells line the ventricles of the brain and produce cerebrospinal fluid (CSF), which physically supports the brain and acts as a shock absorber.
Ependymal
____________ are phagocytic cells that ingest and breakdown waste products and pathogens in the CNS.
Microglia
____________ (CNS) and ____________ cells (PNS) produce myelin around axons.
oligodendrocytes; Schwann
Neurons use all-or-nothing messages called ________ ____________ to relay electrical impulses down the axon to the synaptic bouton.
action potentials
A cell’s ________ ____________ ____________ is the net electrical potential difference that exists across the cell membrane, created by movement of charged molecules across that membrane. About how much is it for neurons?
resting membrane potential; -70 mV
What is the resting membrane potential for neurons?
-70 mV, with the inside of the neuron being negative relative to the outside
What are the 2 most important ions involved in generating and maintaining the resting potential?
potassium and sodium
The potassium concentration inside is (>, <, =?) than the concentration outside of the cell. This causes potassium to favor flowing which direction?
greater than; move outside of the cell
To facilitate the outward movement of potassium, the cell membrane has transmembrane _______________ ______ ___________.
Potassium leak channels
When potassium ions equalize according to the electrochemical gradient, the potential difference that represents this potassium equilibrium is called?
About what level is it at?
equilibrium potential of potassium; -90 mV
negative because potassium leaves the cell
Sodium’s concentration gradient is the reverse of potassium’s, i.e. the inside concentration is (>, <, =?) the outside concentration.
less than
The equilibrium potential of sodium is around what level?
60 mV
it’s positive because sodium moves into the cell
The balance of potassium and sodium’s electrochemical gradients causes the nerve cell to average at about what resting membrane potential?
-70 mV
Since the ions leak at the membrane, there has to be a way to move both of the Na+ and K+ ions back against their gradients in order to maintain the resting potential. What pumps them back?
Na+/K+ ATPase
Which direction does Na+/K+ ATPase pump sodium and potassium?
K+ into the cell
Na+ out of the cell
Neurons can receive both excitatory and inhibitory input.
Excitatory input causes (depolarization/hyperpolarization?) and inhibitory input causes (depolarization/hyperpolarization?)
depolarization; hyperpolarization
What occurs in depolarization?
Is the neuron (less/more?) likely to fire an action potential?
Membrane potential goes up from resting potential; more likely to fire an action potential
Becomes more positive
What occurs in hyperpolarization?
Is the neuron (less/more?) likely to fire an action potential?
The membrane potential is lowered from resting potential; less likely to fire an action potential
If the axon hillock receives enough excitatory input to be depolarized to the ________________ value, an action potential will be triggered.
Threshold
A postsynaptic neuron may receive info from several different presynaptic neurons, which may be excitatory and/or inhibitory. The additive effect of multiple signals is known as ________________.
Summation
What are the 2 types of summation? What characterizes them?
- temporal - signals are integrated during a short period of time
- spatial - based on # and location of incoming signals
If the cell is brought to threshold, what channels open in the membrane?
voltage-gated Na+ channels
Why does sodium migrate into the cell during depolarization?
(from an electrical and chemical standpoint)
Electrical - cell interior is more negative than cell exterior
Chemical - cell exterior has higher concentration than cell interior
When the membrane potential reaches +35 mV after depolarization, the sodium channels will be (activated/inactivated?). They will remain this way until resting potential is re-achieved.
inactivated
After depolarization, the positive potential not only causes the voltage-gated sodium channels to inactivate, but also triggers what channels to open?
voltage-gated potassium channels
Once sodium has depolarized the cell, potassium cations are driven out of the cell, restoring the negative membrane potential, which is a process called ________________.
Repolarization
The efflux of K+ ions causes an overshoot of the resting membrane potential, which (depolarizes/hyperpolarizes?) the neuron.
Hyperpolarizes
Hyperpolarization makes the neuron ____________ to further action potentials.
refractory
What are the 2 types of refractory periods?
- Absolute
- Relative
What happens during the absolute refractory period?
no amount of stimulation can cause another action potential to occur
What happens during the relative refractory period?
There must be a greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value
How does impulse propagation work?
- Sodium rushes into a segment of the axon
- This causes depolarization
- Depolarization brings subsequent axon segments to threshold
- Threshold causes sodium channels to open
- Each of these segments then continues through the rest of the action potential in a wave-like fashion until the action potential reaches the nerve terminal
Since axon segments experience a refractory period, what does this mean?
Information can only flow in 1 direction
The longer the axon, the (more/less) resistance and the (faster/slower) conduction.
more; slower
The greater the axonal diameter, the (more/less) resistance and the (faster/slower) conduction.
less; faster
The effect of cross-sectional area is (more/less) significant than the effect of length.
More
Ion movement only occurs at nodes of Ranvier in a hopping fashion called ___________ _______________.
Saltatory conduction
If a neuron signals to a gland or muscle, rather than another neuron, the postsynaptic cell is termed an ___________.
Effector
Prior to release, neurotransmitters are stored in membrane-bound ____________ in the nerve terminal.
Vesicles
When an action potential reaches the nerve terminal, voltage-gated ____________ channels open, allowing this ion to flow into the cell.
calcium
After voltage-gated calcium channels open, the sudden increase in intracellular calcium triggers the ____________ of the membrane-bound vesicles with the cell membrane at the synapse, causing ____________ of the neurotransmitter.
fusion; exocytosis
Neurons can be either excitatory or inhibitory. What determines this?
The neurotransmitter receptor type: ligand-gated ion channel vs. G protein-coupled receptor (GPCR)
If the receptor is a ________-________ ion channel, the postsynaptic cell will either be depolarized or hyperpolarized.
ligand-gated
If it is __ ___________-_________ receptor, it will cause either changes in the levels of cyclic AMP (cAMP) or an influx of calcium.
G protein-coupled
What are the 3 main mechanisms by which the neurotransmitters are regulated?
- Breakdown by enzymatic reaction, e.g. acetylcholine by acetylcholinesterase
- Reuptake carriers (back to presynaptic neuron), e.g. serotonin (5-HT reputake)
- Diffusion out of synaptic cleft, e.g. nitric oxide
Sensory neurons are also known as ____________ neurons. Motor neurons are also known as ____________ neurons.
Afferent; efferent
Reflexes only require processing at the level of what?
The spinal cord
The brain consists of what 2 types of matter?
- White matter
- Grey matter
What does white matter consists of?
Axons encased in myelin sheaths
What does grey matter consist of?
Unmyelinated cell bodies and dendrites
In the brain, which type of matter lies deeper than the other?
White lies deeper than grey
What structure is at the base of the brain?
Brainstem
The spinal cord extends downward from the brainstem and is divided into what 4 regions?
- Cervical
- Thoracic
- Lumbar
- Sacral
Almost all of the structures below the neck receive sensory and motor innervation from ________________.
The spinal cord
The spinal cord is protected by the ____________ ________, which transmits nerves at the space between adjacent vertebrae.
vertebral column
Like the brain, the spinal cord also consists of white and grey matter. The white matter lies on the ____________ of the cord.
White
The grey matter is deep within it
The axons of motor and sensory neurons are (in/out?) of the spinal cord.
in
The sensory neurons bring info in from the periphery and enter on the (dorsal/ventral?) side of the spinal cord.
Dorsal
The cell bodies of these sensory neurons are found in the ____________ ______ ____________.
Dorsal root ganglia
Motor neurons exit the spinal cord (dorsally/ventrally?).
Ventrally
Label the diagram
Word bank: Dorsal root ganglion, white matter, grey matter, motor (ventral) root, sensory neurons, motor neurons, sensory (dorsal) root
Tue PNS is made up of nerve tissue and fibers outside the brain and spinal cord, including all 31 pairs of ____________ nerves and 10 of the 12 pairs of ____________ nerves.
spinal; cranial
What are the 2 subdivisions of the PNS?
Somatic and autonomic
Sensory neurons transmit info thru (afferent/efferent?) neurons; motor impulses travel along (afferent/efferent?) neurons.
afferent; efferent
The peripheral component of the autonomic nervous system contains how many neurons?
Two
In contrast to the somatic nervous system which connects directly
A motor neuron in the somatic nervous system goes directly from where to where without synpasing?
Spinal cord to muscle
In the autonomic nervous system, 2 neurons work in series to transmit messages from the spinal cord. The first neuron is known as the ____________________ neuron, whereas the second is the ____________________ neuron.
Preganglionic; postganglionic
The soma of the preganglionic neuron is in the ____, and its axon travels to a ganglion in the ____. Here it synapses on the soma of the postganglionic neuron, which then stimulates the target tissue.
CNS; PNS
What are the 2 subdivisions of the ANS?
sympathetic and parasympathetic nervous systems
What is the main role of the parasympathetic nervous system?
Conserve energy
Which neurotransmitter is responsible for managing parasympathetic responses?
In both preganglionic and postganglionic neurons
Acetylcholine
Which cranial nerve is responsible for parasympathetic innervation of the thoracic and abdominal cavity?
Vagus nerve
What activates the sympathetic nervous system?
Stress
Which neurotransmitters are responsible for managing sympathetic nervous system responses for the preganglionic and postganglionic neurotransmitters?
Preganglionic = acetylcholine
Postganglionic = norepinephrine
What types of neurons contribute to reflex arcs?
Interneurons in the spinal cord
What are the 2 types of reflex arcs?
Monosynaptic
Polysynaptic
In a monosynaptic reflex arc, there is (how many?) synapses between the sensory neuron that receives the stimulus and the motor neuron that responds to it?
One
What is an example of the monosynaptic reflex arc?
Knee-jerk reflex
Serves to protect the muscles
Patellar tendon is stretched > info goes up to spinal cord > interfaces with motor neuron > quadriceps muscle contracts > leg extends to lessen tension on patellar tendon
In a polysynaptic reflex arc, there is at least one ________________ between the sensory and motor neurons.
interneuron
What is an example of the polysynaptic reflex arc?
Withdrawal reflex
Someone steps on nail > extremity flexes (monosynaptic) but to maintain balance > other foot must be planted firmly > motor neuron that controls quad in opposite limb is stimulated and extended (interneurons provide the necessary connections for this)
