Organization of the PNS (10/10b) [Biomedical]

Question 1

Neuron

Answer 1

Fundamental functional unit of the nervous system

Has axons and dendrites

Question 2

4 Main Functional Regions of Neurons

Answer 2

Input — area of neuron that receives input

Integrative — integrates all inputs coming into the cell body

Conductive — inputs are transmitted to a distant region of the neuron

Output — area of neuron that creates output

Question 3

Types of Neurons

Answer 3

Sensory*
Motor* 
Local interneuron
Projection interneuron
Neuroendocrine cell

Question 4

Soma Structure - Soma

Answer 4

main integrative unit of neuron, supports basic metabolism of neuron

dendrites receive input from other neurons, soma integrates inputs, and signal is transmitted

Question 5

Soma Structure - Endoplasmic Reticulum (ER)

Answer 5

lipid and protein synthesis, biosynthesis and recycling of vesicles

Question 6

Soma Structure - Lysosomes

Answer 6

digest compounds, glycogen → glucose, part of axoplasmic transport system

Question 7

Soma Structure - Mitochondria

Answer 7

creates energy (ATP) through oxidative phosphorylation

Question 8

Soma Structure - Microtubules

Answer 8

axonal transport

Question 9

Soma Structure - Golgi Apparatus (GA)

Answer 9

storage of lipids and proteins

Question 10

Axon Functions

Answer 10

Transmission of information: propagation of action potential (EX: electric potentials)

Transportation of metabolically important materials to and from the soma to the axonal end (axonal transport system)

Question 11

Axonal Transport - Anterograde

Answer 11

from the center of the cell (soma) to the peripheral (axon tip)

Question 12

Axonal Transport - Retrograde

Answer 12

from the periphery of the cell (axon tip) to the center (soma)

Question 13

Schwann cells provide what?

Answer 13

protection and insulation

Question 14

Myelinated axons

Answer 14

In the PNS, Schwann cells myelinate axons by investing them with up to 300 concentric layers to form myelin sheath

Question 15

Unmyelinated axons

Answer 15

Do not have a myelin sheath, but are associated with and enveloped by Schwann cells, which provide trophic support

Question 16

How Do Neurons Transmit Information?

Answer 16

Cellular Mechanisms

• resting membrane potential
• post synaptic potential
• action potential

Synaptic Mechanisms

• convergence
• divergence

Behavioral Mechanisms

• feedback
• feedforward

Question 17

Neuronal Cell Membrane

Answer 17

Barrier between inside/outside is semipermeable — blocks movement of some ions, allows some ions

Extracellular — more positive than inside, high Na+, high Cl-

Intracellular — more negative than outside, high K+, high proteins

Question 18

Forces that Guide Ion Movement

Answer 18

Electrostatic Force — like charges repel each other

Diffusion Force — ions tend to move from higher concentration to lower concentration
- more involved in generation of AP

Question 19

Electrostatic forces want to hold the ions where they are, but the diffusion forces are stronger and want to push K+ ___ and Na+/Cl- ___

Answer 19

K+ out

Na+/Cl- in

Question 20

Ion Channels - Overview

Answer 20

They are specific to certain ions (EX: potassium channels) and are usually gated

Not really active ion transport systems

Ligand gated, mechanical gated, voltage gated, or leakage

Question 21

Ion Channels - Ligand Gated

Answer 21

receptor on one end, when a neurotransmitter comes in contact with receptor site, ion channel opens

Question 22

Ion Channels - Mechanical Gated

Answer 22

stress applied to channel, opens the gate

Question 23

Ion Channels - Voltage Gated

Answer 23

only opens when there is a specific membrane potential across the membrane

Question 24

Ion Channels - Leakage

Answer 24

randomly opens and allows ions out

There are more potassium leakage channels than sodium leakage channels

Question 25

Sodium Potassium Pump

Answer 25

Active ion transport mechanism

Transports 3 Na+ ions out, and 2 K+ ions in

1 net negative charge inside the membrane

This transport is against the diffusion gradient of Na+ and K → requires ATP

Question 26

Resting Membrane Potential (RMP)

Answer 26

There is a difference in the charges across a membrane, and the inner part is negative

Important to maintain resting potential in order to control responses

Question 27

Mechanisms of RMP

Answer 27

PART 1 - POTASSIUM

• There are many K+ leak channels are more permeable than Na+ leak channels
• There is more K inside compared to outside.
• Concentration gradient is strong for K+ to go from in to out
• Lots of K+ leaves the cell making the inside of the neuron negative

PART 2 - SODIUM

• Concentration and electrostatic forces forces Na+ to the inside of the cell
• But the diffusion is slower because there are lesser Na+ channels open

PART 3
- Na+/K+ pumps are active mechanisms at resting membrane

Question 28

Change in RMP — Terminologies

Answer 28

RMP - the membrane is polarized carries negative charge on the inside

Depolarization — inside becomes less negative (aka normal polarity is being lost)

Hyperpolarization — inside becomes more negative (aka more polar than normal polarity)

Question 29

Excitatory Postsynaptic Potential (EPSP)

Answer 29

inside becomes more positive than resting,

membrane becomes depolarized

Question 30

Inhibitory Postsynaptic Potential (IPSP)

Answer 30

inside becomes more negative than resting, the membrane becomes hyperpolarized

Question 31

Action Potential - Generation

Answer 31

When EPSP reaches a threshold, it creates an action potential

Has depolarizing and repolarizing phases

Stimulus could be a signal from another neuron

Na+ channels open fast and close slow, K+ channels close and open slow

Question 32

Action Potential - Propagation

Answer 32

Action potential must be conducted down the axon

Sodium comes in, starts diffusion to neighboring regions of the axon and makes the regions depolarized

When it reaches the threshold, Na+/K+ channels open and more sodium enters

Further depolarizes down the axon and propagates the action potential

Question 33

Function of Myelin Sheath

Answer 33

It acts as an electrical insulator for parts of the axons, thus preventing action potential from developing

It allows accumulation of charge at the nodes of Ranvier (btwn 2 Schwann cells)
- the charge gets sucked in and jumps to the next node of Ranvier

Speeds up the conduction of action potential

Conduction in unmyelinated axon is much slower since you don’t get the accumulation of charge

Question 34

Increased action potential conduction velocity due to

Answer 34

Myelination

Larger axon diameter

Question 35

Nerve Fibers - Motor Axons

Answer 35

Myelinated, large diameter, muscle control

Question 36

Nerve Fibers - Sensory Axons

Answer 36

Myelinated — large diameter, touch, vibration, position perception

Thinly Myelinated — medium diameter, cold perception, pain

Unmyelinated — small diameter, warmth perception, pain

Question 37

Nerve Fibers - Autonomic Axons

Answer 37

Thinly Myelinated — smaller diameter, heart rate, blood pressure, sweating, GIT, GUT function

Unmyelinated — smallest diameter, heart rate, blood pressure, sweating, GIT, GUT function

Question 38

Spinal Cord

Answer 38

part of the CNS than profusely connects to the PNS

Vital two-way link between the brain and the periphery

Connects to the periphery via 31 pairs of spinal nerves

Spinal nerves are both sensory or motor

Cervical and lumbar enlargements

Longitudinal and Transverse Organization

Question 39

Dorsal vs Ventral

Answer 39

Dorsal = posterior
Ventral = anterior

Question 40

Spinal cord - Transverse Organization

Answer 40

Spinal segment with grey matter in the middle, surrounded by white matter

Dorsal root = afferent, sensory

Ventral root = efferent, motor