A&P CH12 Flashcards
What is the difference in signals that are carried by the afferent vs efferent divisions of the Peripheral Nervous system (PNS)
Afferent- brings sensory info. to the CNS from receptors in peripheral tissues and organs
Efferent- carries motor commands from the CNS to muscles, glands and adipose
Name three groups of receptors and describe what they monitor
- special sensory receptors- monitor smell, taste, vision, balance and hearing
- Visceral sensory receptors- monitor internal organs
- somatic sensory receptors- monitor skeletal muscle, muscles, joints and skin surface
Name the effectors of the Somatic Nervous system (SNS) and of the Autonomic Nervous system (ANS)
SNS- skeletal muscle
ANS- smooth muscle, cardiac muscle, glands and adipose
There are three main anatomical divisions of the nervous system, but we will focus on the CNS and PNS. What nervous system organs are associated with each? (ie: What structures are part of the CNS? What structures are part of the PNS?)
CNS- brain and spinal cord
PNS- all nervous tissue outside of the CNS and ENS
Describe the following neuron structures, and state their functions: soma (cell body), perikaryon, Nissl bodies, dendrites, axon, axolemma, axoplasm, telodendria, and axon terminals
soma (cell body)- large and round nucleus with a prominent nucleolus
perikaryon- cytoplasm surrounding the nucleus: contains organelles that provide energy and synthesize organic material
Nissl bodies- clusters of free ribosomes and RER in the perikaryon: give a gray color to areas containing neuron cell bodies
dendrites- extensions that extend and branch out from the cell body: (intercellular communication)receive electrical signals from other neurons and transmit them toward the some
axon- long cytoplasmic process capable of propagating an action potential
axolemma- plasma membrane of the axon surrounding the axoplasm
axoplasm- cytoplasm of the axon: contains neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria and enzymes
telodendria- (terminal branches) terminal axonal branches that end in axon terminals
axon terminals- synaptic terminal: key role in communicating with another cell
What is the significance of neurons not having centrioles
centrioles help to organize the cytoskeleton and microtubules that move chromosomes during mitosis- without them CNS neurons cannot divide
What is the difference between anterograde and retrograde axoplasmic transport
anterograde- the flow of materials from the cell body to the axon terminal: via kinesin
retrograde- the flow of materials from the axon terminal to the cell body: via dynein
What type of axoplasmic transport is associated with the virus that causes rabies. What is the outcome of rabies?
retrograde flow, virus enters axon terminals and is carried to the soma with fatal results
Name four structural classifications of neurons; describe what they look like, where are they located, and state their function?
1, Anaxonic - small with numerous dendrites and no visible axons, located in the brain and special sense organs, don’t know functions
2. Bipolar- 2 distinct processes; one dendrite and one axon, special sense organs, relay info from receptor cells to other neurons
3. Unipolar- (psuedounipolar) dendrites and axon are continuous and the cell body lies off to one side, sensory neurons of the PNS, carries sensations
4. Multipolar- two or more dendrites and a single axon, most common neuron in CNS, motor neurons that control skeletal muscles
Name three functional classifications of neurons and state what they monitor
- Sensory neurons (afferent)- unipolar neurons that deliver info to the spinal cord or brain. collect info. about the external or internal environment
somatic- monitor the outside world and our position in it
visceral- monitor internal conditions and statuses of organs - Motor neurons (efferent)- carry commands from CNS to effectors
somatic-innervate skeletal muscle
visceral- innervate all peripheral effectors other than skeletal muscles (smooth/cardiac muscle, glands and adipose)
3, Interneurons - outnumber all other types of neurons combined, distribute sensory info, and coordinate motor activity
What is the function of interneurons and where are they mainly found
Located between sensory and motor neurons-located within the brain and spinal cord with some in autonomic ganglia
main unction- integration: distribute sensory info, and coordinate motor activity
List the neuroglia located in the CNS and state their function
- Astrocytes- maintain BBB, provide structural support, regulate ion, nutrient and dissolved gas concentrations, absorb and recycle neurotransmitters, form scar tissue after injury
- Ependymal cells- line ventricles (brain) and central canal (spine), assist in producing, circulating and monitoring CSF
- Oligodendrocytes- myelinate CNS axons, provide structural framework
- Mircoglia- remove cell debris, waste and pathogens by phagocytosis
List the neuroglia located in the PNS and state their function
- Satellite cells- surround neuron cell bodies in ganglia, regulate O2 and CO2, nutrient and neurotransmitter levels around neurons in ganglia
- Schwann cells- surround all axons in the PNS; myelinate peripheral axons, participate in repair after injury
What is the function of myelin? Knowing this, what would a demyelination disease do to the speed of action potential transmission?
serves as an electrical insulation and increases the speed at which an action potential travels along the axon; slow it down
What are internodes, and nodes of Ranvier?
large areas of axon wrapped in myelin, small gaps that separate adjacent internodes
What neuron structures are primarily located in white matter? Gray matter? Why is white matter whitish in color?
- myelinated axons
- neuron cell bodies, dendrites and unmyelinated axons
-because of the lipids in myelin
What is Wallerian degeneration?
a process in which the axon distal to the injury site degenerates and macrophages migrate to clean up debris- Schwann cells proliferate and create a path for the axon to grow and the Schwann cell wraps around the axon
Why is repair of damaged PNS neurons more likely than repair of CNS neurons
In CNS;
1. many more axons are likely to be involved
2. astrocytes produce scar tissue that prevents axon growth
3. astrocytes release chemicals that block axon regrowth
State the difference between sodium (Na+) and potassium (K+) in respect to intercellular vs extracellular concentrations in a resting cell
Extracellular fluid contains high conc. of sodium and chloride ions
intracellular fluid (cytosol) contains high conc. of potassium ions and negatively charged proteins
What is a leak channel? Do they ever close? In respect to resting membrane potential and leak channels, what occurs with Na+ and K+ ions. Are leak channels active or passive?
membrane channels that are always open, no
intracellular conc. of potassium is high so they move out of the cell through leak channels; the extracellular conc. of sodium is high so they move into the cell through leak channels
-movement driven by electrochemical gradient
-passive
-electrical gradient of potassium opposes the movement of K out of the cell
What is the function of the sodium/potassium pump? Is it active or passive? Review page 97—how many of each Na+ and K+ ions are exchanged
exchanges 3 intracellular Na ions for 2 extracellular K ions
balances the passive forces of diffusion and resting potential stays stable as ionic conc. gradients are maintained
When a cell is at rest, what molecules cause the inner surface of the plasma membrane to be more negatively charged?
-Review Figure 12-9 Electrochemical Gradients for Potassium and Sodium Ions.
Note that K+ or Na+ chemical gradients move ions from high concentration to low concentration through leak channels
Note that K+ or Na+ electrical gradients move ions that attract one another—in other words cations will move toward anions (opposites attract)
Note Remember under normal conditions, a cell’s plasma membrane is selectively permeable- meaning that it allows certain ions/molecules in while excluding others
negatively charged proteins and the leak of potassium
What is the resting membrane potential of a neuron in millivolts?
-70
What are gated ion channels; are they active or passive?
active channels that open or close in response to specific stimuli
-active
What are the 3 types of gated ion channels? What makes each open and close?
- chemically gated/ ligand-gated ion channels; open or close when they bind a specific chemical or ligand
- voltage gated ion channels; open or close in response to changes in the membrane potential
- mechanically gated ion channels; open or close in response to physical distortion of the membrane surface
What is a graded potential?
(local potentials) changes in the membrane potential that cannot spread far from the site of simulation
Define depolarization. What initiates depolarization? What occurs ionically to cause depolarization
occurs when the plasma membrane of a resting cell is exposed to a chemical that opens chemically gated sodium ion channels
any shift in the membrane potential toward a less negative potential- towards 0mV
sodium ions enter the cell and are attracted to the negative charges along the inner surface of the plasma membrane
Define repolarization. What initiates repolarization? What occurs ionically to cause repolarization?
the process of restoring the membrane potential after depolarization
occurs when the chemical stimulus is removed and normal permeability is restored
Define hyperpolarization.
-Review Table 12-2 Graded Potentials
caused by the loss of positive ions, an increase in the negativity of the resting membrane potential
What is the difference between a graded potential and an action potential?
action potentials are propagated- they spread along the surface of an axon and do not diminish as it moves away from the source while graded potentials do not spread
Define threshold. What is the threshold in mV of an axon?
-Review Spotlight Figure 12-13 Generation of an Action Potential
the membrane potential at which an action potential begins
Know what occurs in steps 1-4 of Spotlight Figure 12-13
- Depolarization to threshold- graded potential is large enough to depolarize the membrane of the initial segment to threshold
2.Activation of sodium ion channels and rapid depolarization- sodium rushes in driven by its electrochemical gradient - inactivation of sodium ion channels and activation of potassium ion channels start repolarization- K ions move out of the cytosol
- temporary hyperpolarization- potassium channels are slow to close so additional potassium leaves the cytosol
What is the refractory period?
the time between the initiation of an action potential and the restoration of the normal resting membrane potential- membrane will not respond to stimuli
The presence of what substance on an axon determines whether continuous or saltatory propagation of an action potential occurs? What occurs in saltatory propagation?
myelin- the presence of myelin increases the resistance to the flow of ions across the membrane
-continuous propagation cannot occur along a myelinated axon
-saltatory propagation: the relatively rapid propagation of an action potential between successive nodes of a myelinated axon
What are two factors that affect action potential propagation speed?
myelination and axon diameter
axon diameter- ions must move through the cytosol in order to depolarize adjacent portions of the plasma membrane
When discussing Type A, B, and C fibers, which one propagates actions potentials the fastest? Which one is unmyelinated?
Type A is the fastest (120 m/sec) bc they are myelinated
Type C is the slowest (1 m/sec) since they are unmyelinated
What is released at a chemical synapse?
information passes from the presynaptic neuron to the postsynaptic neuron
What is a neuromuscular junction? What is a neuroglandular junction
- a synapse between a neuron and a skeletal muscle cell
-a cell junction at which a neuron controls or regulates the activity of a secretory (gland) cell
What neurotransmitter is released at cholinergic synapses?
ACh- acetylcholine
What ion enters the axon terminal triggering the release of ACh?
calcium ions
What enzyme breaks down ACh into choline and acetate?
AChE- acetylcholinesterase
Name 4 classes of neurotransmitters. Which type acts as neuromodulators?
- biogenic amines
- amino acids
- neuropeptides- neuromodulators : alters the rate of neurotransmitter release by the presynaptic neuron or change the postsynaptic cells response to neurotransmitters
4, dissolved gases
What is an excitatory postsynaptic potential (EPSP)? What is an inhibitory postsynaptic potential (IPSP)?
EPSP- a graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane
IPSP- a graded hyperpolarization of the postsynaptic membrane
What is the difference between temporal and spatial summation?
summation- the temporal or spatial addition of contractile force or neural stimuli
temporal- the addition of stimuli occurring in rapid succession at a single synapse that is active repeatedly
spatial- occurs when simultaneous stimuli applied at different locations have a cumulative effect on the membrane potential
