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BMSC 207 > Neurons > Flashcards

Neurons Flashcards

1
Q

What is the central nervous system?

A

-Acts as the integrating center
-Consists of the brain and spinal chord

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2
Q

What is the peripheral nervous system?

A

-Nerve tissue completely or partially outside the CNS: cranial nerves and branches, spinal nerves and branches, ganglia, plexuses and sensory receptors

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3
Q

What are the three types of neurons?

A

Afferent: Sensory (Input signal, carry info TOWARDS CNS)
-Carry information about temperature, pressure, light and other stimuli to the CNS
-Specialized receptor converts stimulus to electrical energy

Interneurons:
-Complex branching neurons that facilitate communication between neurons

Efferent: Somatic motor and autonomic (Output signal, carry info AWAY from CNS)
-Motor: control skeletal muscles
-Autonomic: influences many internal organs (sympathetic and parasympathetic)
-Usually have axon terminals or varicosities

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4
Q

What are the 3 subdivisions of the peripheral nervous system?

A

-Afferent: Sensory
-Efferent: Somatic and autonomic
-Enteric (digestive tract): can act autonomously or controlled by the CNS through the autonomic division of the PNS

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5
Q

Describe the parts of a neuron

A

Dendrites: Input signal
-Receive incoming signals from neighboring cells

Cell body (soma): Integration
-Considered the control center, with processes that extend outward
-Includes nuclues, other organelles and axon hillock

Axon: Output signal
-Initial segment stemming from axon hillock
-Covered in myelin sheath
-Carries outgoing signals from the integrating center to target cells through presynaptic terminals containing transmitting elements

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6
Q

What are the various structural categories of neurons?

A
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7
Q

Describe axonal transport

A
  1. Peptides are synthesized on rough ER and packaged by golgi apparatus
  2. Fast axonal transport walk vesicles and mitochondria along microtubule network (Down axon = Anterograde)
  3. Synaptic vesicle contents are released by exocytosis
  4. Synaptic vesicles are recycled
  5. Retrograde (back to soma) fast axonal transport
  6. Old membrane components digested in lysosomes
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8
Q

Fast axonal vs. Slow axonal transport

A

Fast:
-Membrane bound proteins and organelles (vesicles or mitochondria)
-Anterograde: Cell body to axon terminal, up to 400mm/day
-Retrograde: Axon terminal to cell body, 200mm/day

Slow:
-Cytoplasmic proteins (enzymes) and cytoskeleton proteins
-Anterograde, up to 8mm/day, some evidence for retro
-Not well characterized, may be slower due to frequent periods of pausing movements

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9
Q

What are the functions of motor proteins in axonal transport?

A

Kinesis: Anterograde transport toward positive, distal end of the axon

Dyneins: Retrograde transport towards negative, proximal soma

ATP hydrolysis drives movement of proteins to “walk” along filaments

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10
Q

Describe synapses

A

-Chemical (majority) and electrical
-Presynaptic cells axon terminals communicates with a target cells postsynaptic dendrites at the synaptic cleft
-This space contains extracellular matrix (proteins and carbohydrates) that hold cells in close proximity

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11
Q

What are glial cells and where are they found?

A

-Communicate with neurons and provide important biochemical support

CNS:
-Ependymal cells
-Astrocytes
-Microglia (modified immune cells)
-Oligodendrocytes

PNS:
-Schwann cells
-Satellite cells

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12
Q

What is myelin and the two glia that form it?

A

-A substance composed of mutliple concentric layers of phospholipid membrane wrapped around an axon
-Provide structural stability, acts as insulation around the axon to speed up electrical signals (saltatory conduction), supply trophic facters

CNS: Oligodendrocytes
-Wraps the axons of multiple neurons

PNS: Schwann cells
-Myelate a small segment of one axon

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13
Q

What is a sattelite glial cell?

A

-Exists within ganglia (bundles of cell bodies) in the PNS
-Form a supportive capsule around the cells bodies (somas) of neurons (sensory and autonomic)
-Supply nutrients
-Structural support, provide a protective cushion

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14
Q

What are astrocytes and their function?

A

-Highly branched glial cells in CNS believed to make up half of all cells in the brain
-Several subtypes, form a functional network

Functions:
-Take up and release chemicals at synapses
-Provide neurons with substrates for ATP production
-Help maintain homeostasis in the extracellular fluid (take up K+ and H2O)
-Surround vessels
-Part of blood brain barrier
-Influence vascular dynamics

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15
Q

What are microglia?

A

-Specialized immune cells that reside in the CNS
-Serve to protect and preserve neuronal cells from pathogens and facilitate recovery from metabolic insults
-If the signals that activate microglia pass a threshold with respect to intensity, or microglia remain activated past a certain time period, these cells start to display detrimental properties (Alzheimers, ALS, neuropathic pain)

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16
Q

What are ependymal cells?

A

-Line fluid filled cavities in the brain and spinal cord
-Help to circulate cerebrospinal fluid that fills these cavities and surrounds the brain and spinal cord (protection, chemical stability, clearing waste)

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17
Q

What is the difference between the Nernst equation and the Goldman-Hodgkin-Katz equation?

A

-Nernst equation calculates the equilibrium potential for a single ion whereas the GHK equation is determined by the combined contribution of each ion (concentration x permeability)

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18
Q

What are the 5 major types of gated channels that control ion permeability in neurons?

A
  1. Na+ channels
  2. K+ channel
  3. Ca2+ channel
  4. Cl- channel
    (All allowed to flow through due to selectivity)
  5. Monovalent cation channels (allow Na+ and K+ to pass)
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19
Q

Explain gated channels in neurons

A

Mechanically gated channels
-Open in response to physcial forces (pressure or stretch), found in sensory neurons

Chemically gated ion channels
-In neurons, respong to ligands including extracellular neurotransmitter and neuromodulators or intracellular signaling molecules

Voltage-gated channels
-Respond to changes in the cells membrane potential

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20
Q

Describe channelopathies

A
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21
Q

What is Ohm’s Law?

A

-Current flow (I) (flow of electrical charge carried by an ion) is directy proportional to the electrical potential difference (in volts, V) between two points and inversely proportional to the resistance (R)
-I=V/R

22
Q

What are two sources of resistance in a cell?

A

-Membrane resistance (Rm): Resistance of phospholipid bilayer

-Internal resistance of the cytoplasm (Ri): cytoplasmic composition and size of the cell

-Resistance will determine how far current will flow in a cell before the energy is dissipated

23
Q

What are graded potentials?

A

-Variable strength signals that travel over short distances and lose strength as they travel due to current leak and cytoplasmic resistance
-Generated by chemically (ligand) gated ion channels or closure of leak channels (CNS and efferent neurons)
-Can be depolarizing (Excitatory Postsynaptic Potential - EPSP) or Hyperpolarizing (Inhibitory Postsynaptic Potential - IPSP)
-If strong enough (excitatory), graded potentials reach the trigger zone and fire an action potential

24
Q

Describe the trigger zone in the axon hillock

A
25
Q

What are action potentials?

A

Very brief, large depolarizations that travel for long distances through a neuron without losing strength. Rapid signals over long distances

26
Q

Describe the movements of Na+ and K+ across the membrane during action potentials

A

Rising phase (depolarization)
-Depolarizing stimuli open voltage gated Na+ channels (-55mV), allow Na+ to travel down electrochemical gradient
-At around +30mV Na+ channels inactivate

Falling phase (repolarization)
-Voltage gated K+ channels also open in response to depolarization, but do so more slowly than Na+ channels causing delayed efflux

After-hyperpolarization phase (undershoot)
-Voltage gated K+ do not immediately close when reaching -70mV causing membrane potential to dip below the resting membrane potential
-Leak channels bring membrane potential back to -70mV
-Na-K ATPase returns ions to original compartments (this does not need to happen before another AP can be triggered)

27
Q

How do voltage gated Na+ channels suddenly close at the peak of an action potential?

A
28
Q

What are refractory periods and their purpose?

A

-Ensure an AP travels in one direction
-Limits the rate at which signals can be transmitted down a neuron

29
Q

Explain how action potentials are conducted (propogated)

A
30
Q

What are the two phsical parameters that determine the velocity of action potentials?

A

The diameter of the axon
-a larger diameter axon will offer less internal resistance to current flow
-More ions will flow in a given time, bringing adjacent regions of the membrane to threshold faster

The resistance of the axon membrane to ion leakage
-Current will spread to adjacent sections more rapidly if it is not lost via leak channels (myelin)

31
Q

Explain how myelinated axons rapidly increase conduction velocity

A
32
Q

Explain how the concentration gradient for K+ is affected in normokalemia, hyperkalemia and hypokalemia

A
33
Q

Explain the secretion of chemicals in neurons

A
34
Q

Explain electrical synapses in cell-to-cell communication

A
35
Q

Explain chemical synapse in cell to cell communication

A
36
Q

Describe Ionotropic receptors

A
37
Q

Describe metabotropic receptors (G-protein coupled receptors)

A
38
Q

Describe phospholipase C signal transduction pathway when metabotropic receptors interact with a membrane bound enzyme

A
39
Q

How do metabotropic receptors interact directly with ion channels

A
40
Q

Describe Adenlyl cyclase signal transduction pathway when metabotropic receptros interact with a membrane bound enzyme

A
41
Q

Describe the process of neurotransmitter release

A
42
Q

Explain the process of neurotransmitter termination

A
43
Q

How does a stronger stimuli effect neurotransmitters

A
44
Q

What is convergence and divergence?

A

Convergence:
-many presynaptic neurons may converge on one or a small number of postsynaptic neurons

Divergence:
-neurons can have branching axons that contact many different postsynaptic neurons

45
Q

What is spatial summation in synaptic signaling?

A
46
Q

How can spatial summation create synaptic inhibition?

A
47
Q

What is temporal summation in synaptic signaling?

A
48
Q

What is presynaptic modulation?

A
49
Q

Describe global presynaptic inhibition

A
50
Q

Describe selective presynaptic inhibition

A
51
Q

What is postsynaptic modulation

A

BMSC 207 (14 decks)

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