Nervous System Flashcards
What are the three main components of the nervous system?
- CNS: inside vertebrae and cranial bones
- PNS: outside the skull and spine— directly connected to the CNS
- ENS: associated with the digestive tract— indirectly connected to the CNS
What are the two classes of cells that nervous tissue consists of? What are their function?
Neurons: transmit information
Neuralgia: which play supporting roles— protect and maintain neurons
What are the three functional classifications fo neurons?
- Sensory neurons
- Interneurons
- Motor/effector neurons
What do sensory neurons do?
Take information from the environment or non-neurons and transmit it to neurons
What do interneurons do?
Receive and transmit signals between other neurons
What do Motor/effector neurons do?
Receive information from other neurons and transmit it to non-neuronal cells (i.e.muscles)
What are the four types of glial cells in the nervous system?
- ependymal cells
- microfilm
- myelinating cells
- Astrocytes and satellite cells
What are ependymal cells? What is their function?
- Simple cuboidal epithelium that lines cavities in the CNS called ventricles
- secrete CSF
What are Microglia? What is their function?
Descendants of WBC’s, perform immune functions and also help modify connection between neurons
What are Schwann cells (PNS)/Oligodendrocytes (CNS)?
Wrap around axons and produce a myelin sheath (electrical insulation)
What are satellite cells (PNS) and astrocytes (CNS)?
- Cells that provide physiological support for neurons, helping maintain their extracellular environment
- attach to dendrites
Can axons in the PNS regrow?
Yes
Can axons in the CNS regrow?
No— glia prevent the axon from regrowing through physical and chemical barriers
What is the advantage that the CNS could get by not allowing new neurons to grow?
— neurons are very specialized and need specific chemicals to regrow
How are Na+ and K+ gradients maintained?
Primary active transport, Na-K-ATPase pump
How is the Cl- gradient is maintained?
Secondary active transport (co-transport with K+)
What do leak channels do?
- allow for ionic permeability at rest
- always open, even at rest
What allows ions to move through ion channels
their electrochemical gradient
What chemical has the most leak channels?
Potassium
What is the equilibrium potential?
A transmembrane potential where electrical forces are exactly the right size to balance out the force from that ion’s concentration gradient
What is the equilibrium potential for K+?
-90
What is the equilibrium potential for Na+?
+70
What is the equilibrium potential for Cl-?
-70
What determines how much an ion will contribute to the potential?
How permeable it is
How can a membrane channel change?
Shifts according to which ions are most permeable at a given time
A sensory neuron has an RMP of -70mV, and a myofibre at rest has an RMP of -90mV. What leak channels are present in each cell?
- Sensory neuron: Cl-
2. Myofibre neuron: K+
If a stimulus from the environment triggers the sensory neuron to open ion channels in its dendrites that are equally permeable to both Na+ and K+, what will happen to the membrane potential?
It will stay at about -70mV
What are the three kinds of gated ion channels?
- Voltage
- Ligand
- Mechanical
Where are ligand and voltage gated channels found in a neuron? What kind of potential do they produce?
- ligand gated Na+ channel on dendrites— graded potential
- voltage gated Na+ and K+ channels on the axon
- voltage gated Ca2+ channels at the axon terminals
What is a (post)synaptic potential?
A change in membrane potential that comes from the neurotransmitter released by another neuron
What an example of hyperpolarization?
An NT opens ion channels that are only permeable to K+
What affects the size of a graded potential?
- how many open channels there are
- the concentration of neurotransmitter released
Why is there only a small change in the membrane potential when ligand gated Cl- channels open?
The equilibrium channel of Cl is very close to the the RMP
What do mechanically gated ion channels do?
- produce a graded potential called a receptor potential
How are graded potentials generated?
- different ion channels
- generated locally by the stimulation that triggers the channel to open
Where is the threshold potential?
-55mV
How many gates do voltage gated sodium channels have?
2:
1) activation gate: opens rapidly in response to the depolarization
2) inactivation gate: starts open, then closes (and stays closed until the membrane gets back near to RMP or even more negative)
When does a voltage gated K channel open? How quickly does it open?
Right when the neuron crosses threshold; very slowly (K starts moving out of the cell and repolarizing around the time that sodium channels are closing)
Why does the potential go BELOW threshold when it is repolarizing?
- the K channels stay open for a short amount of time after repolarization
- there are more voltage gated channels than leak channels so K keeps moving out of the cell
What kind of feedback contributes to action potential?
Both positive and negative:
- positive: sodium channels depolarize the membrane and make more channels open
- negative: k channels repolarize/hyperpolarize and makes more channels close
What is the AP absolute and relative refractory period?
Absolute: cannot get another action potential once the membrane reaches threshold
Relative: Hyperpolarization causes a period of time where the cell is too polarizated to get to threshold
Depolarization spreads both directions, but the AP is only generated distally— why?
The sodium inactivation gates are still closed
What is myelin made out of?
Fat and protein
What is a node? What do they do?
- The 1-2mm long section between internodes that has no myelin wrapping
- section where VG channels and leak channels are
Why is myelin insulating?
It prevents ions form escaping through leak channels and therefor enhances the spread of potentials
What is conduction speed?
The time it takes an action potential to travel a given distance along an axon
Why do myelinated axons use less ATP?
pumps use ATP, unmyelinated axons need more action potentials
