Introduction to the Neuron

Question 1

Central nervous system

Answer 1

Brain and spinal nerves

Question 2

Peripheral nervous system

Answer 2

Nerves outside of cranial and spinal

Question 3

Autonomic nervous system

Answer 3

Responsible for many reflexes such as salivary flow. Divided into Parasympathetic and sympathetic

Question 4

Synapses in a neuron

Answer 4

Each neuron has between 1,000 - 10,000 synapses

Question 5

Diameter of a neuron

Answer 5

4 to 100 microns (one micron is 1/1000 of mm)

Question 6

Velocity of neuron signal

Answer 6

1.2-250 mi/hr. The signal travels through neural networks via synapses

Question 7

Definition of neuron

Answer 7

Electrically excitable cell that processes and transmits information by electrical and chemical signaling
Three tasks: 1. receive, 2. conduct, 3. transmit signals

Question 8

Structure of the neuron

Answer 8

Cell body - contains organelles such as nucleus
Dendrites - transmit electrical impulses to the cell body
Axon hillock - located near the cell body nerve. Impulses originate there.
Axon - transmits impulse away from cell body
Myelin sheath - Myelin wrapped around the axon of neurons
Node of Ranvier - Permeable gaps in between myelin sheath to allow for exchange of ions
Pre-synaptic Terminal - end of the axon
Synaptic cleft - gap between pre and post synaptic terminal
Post-synaptic terminal - receiving portion of the adjacent neuron

Question 9

Glia

Answer 9

Glia - non-neuronal cells. Astrocytes: star shaped glial cells that perform many functions such as support the blood-brain barrier, provide nutrients to the nervous tissue, maintain extracellular ion balance, and repair the brain and spinal cord after traumatic injuries

Question 10

Action Potential

Answer 10

The electrical signal that is conducted along neuronal axons. Generated by special types of voltage-gated ion channels embedded in a cell’s plasma membrane.

Question 11

Two kinds of action potentials

Answer 11

1. generated by voltage-gated sodium channels in the axon (faster)
2. generated by voltage-gated calcium channels in the pre-synaptic terminal (slower)

Question 12

Resting membrane potential in neurons

Answer 12

-70 mV. There are largely negatively charged ions inside the cell. Neurons are excitable and can change their membrane potential if stimulated

Question 13

What happens to transmit an action potential

Answer 13

1. the ion channels open if the membrane potential is no longer near the resting potential of the cell, but increases to a precisely defined threshold value.
2. channels open, allowing an inward flow of sodium ions, which changes the electrochemical gradient, which produces a further rise in membrane potential, which causes more channels to open. Process continues until all available ion channels are open; membrane potential is much higher
3. inactivation of the ion channels when the polarity of the plasma membrane reverses. As the sodium channels close, sodium is actively transported out of the plasma membrane via na+/k+ pump (3 for 2)
4. after the action potential, there is a transient negative shift called the afterhyperpolarization

Question 14

Nodes of Ranvier

Answer 14

Areas where there is permeability to ion changes; only in a small area of the membrane

Question 15

Polarization

Answer 15

Depolarization - potential difference approaches zero as membrane becomes permeable to Na
Repolarization - back to the resting potential
After-hyperpolarization - potential difference increases as positive charges leave cell and negative ones enter

Question 16

The refractory period

Answer 16

Assures that impulse conduction happens only one way/unidirectional. Absolute refractory period is the interval which a second action potential simply isn’t going to happen, no matter the stimulus. The relative refractory period is the interval during which initiation of a second action potential is inhibited but not impossible

Question 17

Saltatory conduction

Answer 17

Action potential moves along myelinated axons from one node of Ranvier to the next. Only unmyelinated regions of the axon depolarize; thus, the impulse moves 50x faster.

Question 18

Myelin Sheath

Answer 18

in the central nervous system, myelinated axons form “white matter” (cell bodies and dendrites are gray). Demyelinating disorder - multiple sclerosis

Question 19

Na+/K+ pump

Answer 19

the pump is an enzyme located in the plasma membrane. When an action potential is completed, the sodium potassium pumps three sodium ions out for every two pumped it. It takes 1 ATP for every translation

Question 20

Calcium action potential

Answer 20

Transmitter is synthesized and stored in vesicles, and when terminal is depolarized, voltage-gated Ca channels open; this ion causes vesicles to fuse with presynaptic membrane and release neurotransmitters. Post-synapptic receives; a current there causes either an excitatory or inhibitory postsynaptic potential

Question 21

Reuptake

Answer 21

Reabsorption of neurotransmitter by a neurotransmitter transporter of a pre-synaptic neuron - efficiency - not going to waste

Question 22

Excitatory postsynaptic potential

Answer 22

Depolarize the postsynaptic neuron in order to continue transmitting the signal. Can summate or cancel out IPSP

Question 23

Inhibitory postsynaptic potental

Answer 23

Hyperpolarizes the postsynaptic neuron so that nothing happens. Can summate or cancel out EPSP

Question 24

Saltatory Conduction Overview

Answer 24

(1) Equilibrium = negative “resting” state (-70mv)
(2) Action potential transiently abolish the “resting” potential.
(3) Results in Na+ being able to enter the axon (along axon at Nodes of Ranvier)
(4) This rapid rise in Na+ renders the transmembrane positive (depolarization)
(5) This is followed by rise in K+ ions, which in turn close the Na+
(6) Na+/K+ pump remove NA+
(7) This occurs along each Node of Ranvier until the end of the axon

Question 25

Calcium voltage-gated Review

Answer 25

(8) Action potential invades the presynaptic terminal
(9) Increases influx of Ca+
(10) Causes vesicles to fuse with presynaptic membrane (11) Transmitter is released into the synaptic cleft (12) Post-synaptic terminal receives neurotransmitter (13) Causes IPSP or EPSP
(14) Reuptake of neurotransmitter

Question 26

Dopamine (DA)

Answer 26

A neurotransmitter that is produced in several areas in the brain, including the substantial nigra and the ventral tegmental area (both in the Midbrain). Problems with transmission of DA can lead to schizophrenia and parkinson’s disease. Plays major role in reward-driven learning - every reward increases dopamine transmission in the brain.

Question 27

Serotonin (5-HT)

Answer 27

Neurotransmitter. Regulation of mood, appetite, sleep, cognitive functions. Antidepressants modulate serotonin at synapses, preventing reuptake, so more goes to the post-synaptic terminal. Influences moral judgment, behavior, aggression (inhibits)