Chapter 8 Neurons Flashcards
What are the 4 CNS Glial supporting cells?
- Astrocytes
Blood-brain barrier - Oligodendrocytes
Myelin sheaths - Ependymal cells
Line ventricles - Microglia
Phagocytize
What are the two PNS Glial supporting cells?
- Schwann cells
Also called neurolemmocytes
Myelin sheaths - Satellite cells
Support cell bodies
What are neurons?
- Neuron is Functional unit of Nervous System
Carries out primary function of NS - Classified functionally 3 types
-Sensory Afferent neurons
-Interneurons
-Motor Efferent neurons - Amitotic neurons do not rgenerate
What is the axonal transport?
- Slow axonal transport
Moves material by cytoplasmic flow 0.2–2.5 mm/day
- Fast axonal transport
Moves organelles at rates of up to 400 mm/day
Forward transport: from cell body to axon terminal
Retrograde transport: axon terminal to cell body
What are myelin sheats and how are they formed?
- Myelinated axons conduct impulses more rapidly
-Myelin gives tissues white color = white matter
-Cell bodies and axons = grey matter
-Node of Ranvier is left open - In PNS, Schwann cells wrap around axons to form the myelin sheath
- In CNS, oligodendrocytes myelinate several axons
- Grey matter is unmyelinated while white matter is myelinated
Can neurons regenerate?
- When an axon in PNS is cut, the severed part degenerates, and a regeneration tube forms
- CNS axons are not as able to regenerate
What is memebrane potential?
- Neurons have a resting potential of −70mV
Na+/K+ pumps
Negative molecules inside the cell
Permeability of the membrane to ions
- At rest, there is a high concentration of K+ inside the cell and Na+ outside the cell
What is it called when membrane potential changes?
- Neurons and muscle cells can change their membrane potentials
- Called excitability
- Caused by changes in permeability to certain ions
- Ions follow electrochemical gradient = concentration gradient and attraction to opposite charges
- Flow of ions is called ion current
What is the name of neurons at rest? What are the three other membrane potential phases?
- At rest, a neuron is considered polarized when the inside is more negative than the outside
- When the membrane potential inside the cell increases = depolarization
Occurs when positive ions enter the cell, is excitatory - A return to resting potential = repolarization
- When the membrane potential inside the cell decreases = hyperpolarization
Occurs when positive ions leave the cell, is inhibitory. -85mV
What are the two types of electrical signals?
Graded and action potential
What is graded potential?
- Graded potentials
- Variable strength
- Decreases with distance
- Can sum to cause an AP
- Short distance communication
What is action potential?
- Action potentials
-Constant strength
-All or none
-Generated at axon hillock
-Long distance rapid communication
IDK
What are the three thresholds of graded potential?
-
Threshold
-Minimum depolarization
needed to cause an AP
-55mV -
Subthreshold
-Graded potential
below threshold
-55mV so no action potential sent -
Suprathreshold
-Graded potential
above threshold so action potential is sent
What are Excitory postsynaptic potential and inhibitory postsynaptic potential?
Membrane potential changes depending on which ion channels open
- Na+ or Ca2+ channels - graded depolarization
Excitatory postsynaptic potential (EPSP) - K+ or Cl− channels – graded hyperpolarization
Inhibitory postsynaptic potential (IPSP)
What is spatial summation?
Spatial summation occurs when excitatory potentials from many different presynaptic neurons cause the postsynaptic neuron to reach its threshold and fire.
How does temporal summation work?
- Two stimuli that follow one another in succession
- Graded potentials that arrive at trigger zone overlapping in time may sum to threshold and trigger AP
How do gated channels regulate ion movement?
- Changes in membrane potential are due to the flow of ions through ion channels
Closed at rest but open when ____
3 Types gated ion channels:
- Mechanically gated
Open in response to physical force - Chemically gated
Neurotransmitters - Voltage-gated
Respond to electrical signals
How do voltage gate Na+ channels work?
- Na+ channels open if membrane potential depolarizes to -55mV
- This is called threshold
Sodium rushes in due to electrochemical gradient
Membrane potential increases until channels become inactivated +30mV
How does action potential work?
- Occurs at threshold (−55mV)
- Voltage-gated Na+ channels open, Na+ rushes in
- As cell depolarizes more Na+ channels open, Na+ enters cell
- At +30mV repolarization as Na+ channels close and K+ channels now fully open
- Actually overshoots resting potential to -85mV which is hyperpolarization
- Na+/K+ pumps reestablish resting potential of -70mV
What is the all or nothing law?
Once threshold is reached, an action potential will happen
Size of stimulus will not affect the size of AP
Size of stimulus will not affect AP duration
How does stimulus intsnsit effect action potential?
A stronger stimulus will make action potentials occur more frequently
A stronger stimulus may also activate more neurons – called recruitment
How conduction work for unmyelinated sheaths?
- When an AP occurs on a neuron membrane, voltage- gated Na+ channels open as a wave down the entire axon
- The conduction rate is slow because so many APs are generated
How does conduction work for myelinated sheaths?
- Myelin provides insulation, increasing speed
Nodes of Ranvier allow Na+ and K+ across membrane every 1−2 mm
Action potentials “leap” from node to node - In demyelinating diseases, ions leak slowing conduction
What influences the speed of action potential?
- Myelination
Myelinated axons faster
Less ion leakage out of cell - Diameter of axon
Larger diameter faster
Reduces resistance
What is a synapse?
Communication point between a neuron and the cell it is signaling
In the CNS, this second cell will be another neuron
In the PNS, the second cell will be a muscle or gland
If two neurons in pathway
Presynaptic neuron is before synapse; postsynaptic neuron is after synapse
What is an electrical synapse?
- Electrical synapses occur in smooth muscle, cardiac muscle, and some neurons in brain
- Cells are joined by gap junctions
What are chemical synapses?
What is ACh or Acetylcholine?
- ACh is a neurotransmitter that opens ion channels when it binds to its receptor
- Can be excitatory or inhibitory, depending on the receptor and which ion channel it opens
-Excitatory in all somatic motor neurons
-Excitatory or Inhibitory in autonomic motor neurons
Know this table!
