CNS and Action Potentials

Question 1

What are the two branches of the nervous system and what do they consist of?

Answer 1

Central: Brain and spinal cord

Peripheral: afferent and efferent neurons.

Question 2

What is the difference between afferent and efferent neurons?

Answer 2

Afferent: stimulated by external stimulus to send signal to CNS for integration

Efferent: sends information to CNS through motor neurons to target cells

Question 3

What is a neuron’s structure and function?

Answer 3

Structure: Soma (cell body) from which dendrites or axons protrude, high density of ion channels.

Function: Receive and send electrical signals and secrete signalling molecules (neurotransmitters and neurohormones)

Question 4

How do nerve cells develop?

Answer 4

1. Neurostem cells originating from the ectodermal layer mature into common progenitors.
2. Common progenitors are stimulated to differentiate into either neuronal progenitors or glial progenitors
3. Neuronal progenitors develop into neurons and glial progenitors develop into astrocytes or oligodendrocytes

Question 5

What is the difference between a dendrite and an axon?

Answer 5

Dendrite: receive incoming signals, branched for high surface area for reception

Axons: carry outgoing electrical signals starting originating at the axon hillock

Question 6

What are the type of neuron shapes?

Answer 6

Multipolar: many dendrites and branched axons

Pseudounipolar: Cell body located off one side of a long process due to fusion of dendrite with axon

Bipolar: single axon and dendrite coming off the cell body

Axonic: Lack identifiable axon but have numerous branched dendrites

Question 7

How do afferent neurons, interneurons, and efferent neurons differ in function and structure?

Answer 7

Afferent: carry info about stimuli from receptors to CNS; pseudounipolar with cell bodies close to CNS

Interneurons: Site of integration between sensory and motor neurons; axonic/multipolar with complex branching axons and dendrites

Efferent: Send signal from CNS to target cells to perform a response; Multipolar with long sheathed axon.

Question 8

What is found at the end of axons?

Answer 8

collateral: divisions of axon

Axon terminal: enlarged endings that store and release neurotransmitter

Varicosities: enlarged regions along axon of autonomic neurons that store and release neurotransmitter.

Question 9

What is the difference between sensory nerves, motor nerves, and mixed nerves?

Answer 9

Sensory: bundles of afferent axons

Motor: bundles of efferent axons

Mixed: bundles of both afferent and efferent axons

Question 10

What is axonal transport?

Answer 10

Motor protein (dynein) walking from soma ER along microtubule holding proteins in vesicles to transport the axon.

Question 11

What are glial cells and what kinds are there?

Answer 11

Communicate with neurons and provide biochemical and structural support.

CNS: ependymal cells, astrocytes, microglia, oligodendrocytes,

PNS: schwann cells, satellite cells

Question 12

What do schwann cells and oligodendrocytes do?

Answer 12

Support and insulate axons by forming myelin by squeezing out glial cytoplasm and wrapping around the axon. Gap junctions connect the membrane layers of myelin and allow the flow of nutrients and information from layer to layer.

Question 13

What is the difference between an oligodendrocyte and a schwann cell?

Answer 13

Schwann cell: singular cell makes a singular myelin sheath, found in PNS

Oligodendrocyte: singular cell makes many segments of myelin, found in CNS

Question 14

What is a satellite cell?

Answer 14

Nonmyelinating Schwann cell in PNS that form capsules around nerve cell bodies in ganglia.

Question 15

What is an astrocyte?

Answer 15

Highly branched CNS glial cells that have many functions:

• surround blood vessels and become part of blood brain barrier
• produce trophic factors
• take up excess water and K+
  -act as neural stem cells
• pass lactate to neurons

Question 16

What are microglia?

Answer 16

Specialized immune cells that reside in CNS that remove damaged cells and foreign invaders.

Question 17

What do ependymal cells do?

Answer 17

Specialized cells that create a selectively permeable epithelial layer that separates the fluid compartments (ventricles) of the CNS and make neural stem cells.

Question 18

What are trophic factors?

Answer 18

Chemicals for nourishment and promotion of growth and survival

Question 19

What are two factors that influence the membrane potential?

Answer 19

Uneven distribution of ions and differing membrane permeability of those ions

Question 20

What are the three categories of channels that act in response to stimuli and where do you find them?

Answer 20

Mechanically gated ion channels: found in sensory neurons and act in response to physical stimulus

Chemically gated ion channels: found in most neurons and bind to many ligands

Voltage gated ion channels: respond to changes in cell’s membrane potential

Question 21

What is a graded potential?

Answer 21

Depolarization/hyperpolarization that travel over short distances and lose strength as they travel. Used for short distance communication (postsynaptic potentials), can be summed and long lasting, and intensity reflects the size of the stimulus with

Question 22

What are action potentials?

Answer 22

Very fast and large depolarization that travel for long distances without losing strength and are used for their rapid signalling over long distances.

Question 23

What is the difference between subthreshold and suprathreshold graded potential?

Answer 23

Sub: Graded potential starts above threshold, and by the time it reaches axon hillock, it is below the threshold and does not initiate action potential.

Supra: Graded potential starts above threshold and by the time it reaches axon hillock, it is still above the threshold and will initiate action potential.

Question 24

What is local current flow? How does it relate to the loss of strength of graded potentials?

Answer 24

Local current flow is the wave of depolarization via entry of Na+. The depolarization dies out because of positive ion leakage channels as well as cytoplasmic resistance.

Question 25

What are the steps of an action potential?

Answer 25

1. Resting membrane potential
2. Cell is depolarized at axon by graded potential due to stimulus
3. Membrane depolarizes to threshold at axon hillock causing Voltage Na+ channels to open quickly and let Na+ in, and slowly opening K+ channels.
4. Rapid entry of Na+ depolarizes cell greatly
5. Na+ channels inactivate and K+ channels fully open due to positive voltage.
6. K+ shoots out of cell, repolarizing the membrane
7. remain open after repolarization, causing afrerhyperpolarization
8. K+ channels close due to negative voltage and Na+ channels begin to recover
9. Cell returns to resting ion permeability and resting membrane potential as Na_ channels fully recover.

Question 26

What is the difference between the two gates on a voltage gated sodium channel?

Answer 26

In response to depolarization, activation gate opens and allows sodium into the cell. Inactivation gate closes after a delay and prevent Na+ from entering

Question 27

What are the three patterns of action potentials and how are they formed?

Answer 27

Single AP: one action potential
Tonic AP: constant firing of action potential
Bursting AP: Few action potentials at once

Question 28

How are action potentials conducted?

Answer 28

1. From initial state of -70mV, Na+ from graded potential enters a trigger zone in axon hillock.
2. Depolarization opens voltage gated Na+ channels which enter the axon and the initial segment of axon depolarizes
3. Positive charge from depolarized trigger zone spreads via local current flow to adjacent sections of the membrane
4. Membrane distal to trigger zone depolarizes from local current flow, Na+ channels open and allows Na+ into cell
5. Refractory period prevents backwards conduction

Question 29

What is the difference between hyperkalemia and hypokalemia?

Answer 29

Hyperkalemia: increase in blood K+ concentration results in a less negative membrane potential, bringing it closer to threshold mV which makes it more reactive.

Hypokalemia: decrease in blood K+ concentration results in a more negative membrane potential, bringing it farther from threshold mV which makes it less reactive.

Question 30

Why is

Answer 30

unmyelinated: Na+ is attracted to nearby areas due to local flow and open more Na+ channels, but may leak. SLOWER.

myelinated: Na+ is released in one node of ranvier and must rush to another node of ranvier to open the Na+ gate. FASTER

Question 31

Why is conduction faster in myelinated axons?

Answer 31

Myelin prevents leakage of Na+, keeping the momentum of the charge as it travels via local current flow.

Question 32

What are two ways action potentials are conducted faster?

Answer 32

1. Saltatory Conduction: Insulation separating voltage gated channels into nodes of Ranvier allowing the jump of action potential from one node to another.
2. Larger diameter of axon allows no resistance form the membrane

Question 33

What is Multiple Sclerosis?

Answer 33

Autoimmune disease characterized by the demyelination of CNS axons, causing multiple patterns of progression including relapsing-remitting and progressive phases. Some things thought to cause MS is the environment, viruses, genetics, and cerebral blood flow.

Question 34

What are the symptoms and treatments of multiple sclerosis?

Answer 34

Symptoms: loss of balance, loss of speech, loss of vision, abnormal pupil reflexes, numbness, and pain.

Treatments: immunosuppressants, drugs to manage symptoms

Question 35

What is the Guillain Barre syndrome?

Answer 35

Autoimmune disease characterized by the demyelination of PNS axons, resulting in the slowing and or loss of AP conduction that may take months to years to recover form. Caused by GI/lung infection and may be associated with chronic illness like lupus and HIV.

Question 36

What are the symptoms and treatments of Guillain Barre syndrome?

Answer 36

Symptoms: tingling, weakness, pain in hands/feet, inability ot speak, paralysis, respiratory distress

Treatment: Plasmapheresis (removing antibodies from blood), immunoglobulin G (inactivate antibodies)

Question 37

What is fugu poison?

Answer 37

Tetrodotoxin is an antagonist of voltage gated Na+ channels with high affinity, high specificity, efficiacy, and potency. It prevents entry of Na+ into cells through voltage gated channels.

Question 38

What are the symptoms of fugu poison?

Answer 38

Intoxication 1: Numbness of lips and tongue, paraesthesia, headache, nausea, diarrhea, vomiting, reeling/walking issues.

Intoxication 2: increasing paralysis, respiratory distress, inability to speak, dyspnea, hypotension, convulsions, mental impairment, cardiac arrhythmia, death within 20min - 8 hours.