10-10b Organization of Peripheral Nervous System Flashcards
What is a neuron?
The fundamental functional unit of the nervous system
What are the major structures of a nerve?
axon
cell body
dendrites: receive info from multiple sources, integrates it, then transmits it through other n. via the axon
What are the major functional regions of a nerve?
Input
Integrative: Integrates all the inputs coming into the n./cell body
Conductive: transmitted to a distant region
Output
What are the different types of neurons/distinguishing characteristics of each?
motor n.: cell body, dendrites, and long axons that innervate the m.
Sensory n.: bipolar neuron, receives info from sensory receptors then transmits to cell body (integrates the info there), then transmits to central n.
separates in the center and sends an axon out on each side
Where is a motor n. located in the peripheral NS?
spinal cord
Where is the cell body for a peripheral sensory neuron?
dorsal root ganglion (outside S.C.)
What is the cell body/soma?
main integrative unit of the neuron supports basic metabolism multiple dendrites (receive input) > integrated in soma > AP sent down axon
What does the nucleus do in the soma?
stores DNA
What does the rough ER have? What is the ER responsible for?
mRNA
responsible for synthesis of lipids and proteins and synthesis of synaptic vesicles that carry the NT to the output region
What do lysosomes do?
digest compounds (glycogen > glucose) part of axoplasmic transport system
What do mitochondria do?
produce ATP
What does the golgi apparatus do?
stores the lipids and proteins that the ER creates
What are microtubules?
Freeways of the neuron that are apart of the axonal transport system
What are the two purposes of axons?
- transmit information to different neurons via AP via ions
- transportation system where NT vesicles (produced in cell body) are transported to the output region and presynaptic terminal (axonal transport system)
(also retrograde axonal transport system: vesicles taken from presynaptic terminal back to the neuron)
physical vesicles transported
How does tetanus enter the neuron?
microbacteria enter the peripheral part of the neuron and ride the retrograde transport system
How is myelin formed in myelinated axons? How do they form the myelin sheath?
Schwann cells
wrap around the axon in concentric circles to form myelin sheath
How is myelin formed in unmyelinated axons?
Schwann cells do not wrap around the n.
What is the function of a Schwann cell?
Protection and insulate the axon
How do neurons transmit information within the neuron and between neurons?
Resting membrane potential, Post synaptic potential, and Action potentials
synaptic mechanisms: convergence and divergence
What is RMP? What is the RMP (+ or -)? What does a pathology of RMP cause?
potential difference in the charges across a membrane
inside: negative at rest; baseline is important
pathology: epilepsy; if not stable, the n. will fire randomly and cause strange brain activity
What are the physical principles behind the neuronal membrane? construction?
ions are separated by the neuronal membrane via its semi-permeable phospholipid bilayer (lipids inside)
partially permeable to some ions and blocks the movement of other ions
What are the two forces acting on the phospholipid bilayer?
electrostatic and diffusion forces
How do electrostatic forces work?
like charges repel each other
How do diffusion forces work? What does it rely on?
Relies on the concentration of ions (more Na outside makes the ions want to move down the conc. gradient inside the cell)
Plays greater role in generation of AP
At RMP, what are the concentrations of ions intracellulary and extracellularly?
Intracellular:
high concentrations of proteins and K+ ions
Extracellular:
high concentrations of Na+ and Cl- ions
At RMP, what are the concentrations of ions intracellulary and extracellularly?
Intracellular:
high concentrations of proteins and K+ ions (more negative)
Extracellular:
high concentrations of Na+ and Cl- ions (more positive)
How do electrostatic and diffusion forces act on the ions intra/extracellularly during RMP?
Na+ wants to go into the cell (due to electrostatic and diffusion forces)
K+ diffusion force tries to push it outside, while electrostatic forces try to keep it inside
Cl- diffusion forces try to pull inside
What are the two mechanisms for ion transport?
Ion channels
Active mechanisms
How do ion channels work? What are the two different types?
Allow movement of ions intracellular to extracellular and back
Very specified for specific ions
Gated and leakage
How do ion channels work? What are the two different types?
Allow movement of ions intracellular to extracellular and back
Very specified for specific ions
Gated (mostly) and leakage
What are the different gated ion channels
ligand-gated ion channels: Receptor on one end and when NT sits on the receptor, it opens the ion channel
mechanical-gaed ion channel: Mechanical stress applied at the level of the channels causes gate to open
voltage-gated ion channel: channel that only opens when there is a specific potential difference across the cell membrane, are sensitive to closing, and have a bandwidth of potential they stay open during
What are leakage channels? Which ion has more?
open for the most part and allow passage of ions
more K+ leakage channels than Na+
What are distinct about active mechanisms of ion transport? Which one is necessary for RMP? What does this one result in?
require ATP
Na+/K+ pump: Transports 3 Na+ ions from inside to outside and 2 K+ ions from outside to inside; it works against the diffusion forces; results in a negative charge inside the membrane
Where is K+ more concentrated? How many are transported with each pump of the Na/K pump?
inside
2 (to make the inside more negative)
Where is Na+ more concentrated? How many are transported with each pump of the Na/K pump?
outside
3 (to keep the outside more positive)
What are the four main mechanisms that control the negative intracellular RMP?
- many K+ leak channels cause K+’s strong diffusion forces to bring it outside the cell (overcomes electrostatic forces); this helps make the inside -
- Fewer Cl- leak channels cause Cl- to move into the cell via diffusion forces (override electrostatic forces); this helps make the inside -
- Very few Na+ leak channels cause Na+ to move inside the cell=slow diffusion (despite strong electrostatic and diffusion forces urging it inside); helps make the inside more -
- Na/K+ pump brings 3 Na+ outside and 2 K+ inside to help keep the inside negative
What describes the loss of negativity inside the cell?
depolarization (inside becomes less negative); loss of polarity
What describes the increase in negativity inside the cell?
hyperpolarization (inside becomes more negative); more polarity than normal polarity
What generates a post-synaptic potential? Describe the change and its length. What are the two kinds of PSP? Define
Change in the synapse causes a change in the potential for the n.
“graded” small change in the potential and then it gets back to resting MP
Can be excitatory synapse (EPSP): depolarization due to inside becoming more positive
Inhibitory synapse (IPSP): inside becomes more negative and hyperpolarization
List the sequence of an AP
- EPSP stimulus (synaptic input)/mechanical/ligand gated opens Na+ channels and it a little comes in and membrane becomes depolarized
- at threshold of AP, at -55mV voltage gated Na+ channels open and Na+ pours into the cell (inside of cell becomes more positive and depolarization amplifies)
- at +30, voltage gated Na+ channels close and slower voltage gated K+ channels open and it leaves the cell due to diffusion forces (makes inside cell more negative)
- repolarization triggers Na/K pump at RMP
- slow closing K+ channels cause more K+ to be pushed out and causes the membrane to become hyperpolarized (-90mV)
How do axons conduct information?
propagation of AP:
P is carried down the axon to the output region of the cell
Na starts diffusing to neighboring regions of the axon
Each neighboring region becomes positive and reaches threshold then voltage gated Na channels open and lead to more coming in and moves the AP to the next part of the axon
Cause depolarization in the surrounding axon to trigger AP
What is at the axon hillock?
high concentrations of voltage gated Na channels (IPSPs)
first opening of voltage gated Na channels
AP moves it down the axon
What are the three functions of the myelin sheath?
It acts as an electrical insulator for parts of the axons, thus preventing action potential from developing
2) It allows accumulation of charge at the nodes of Ranvier; threshold is reached quickly
3) Speeds up the conduction of action potential
What prevents the AP from moving backwards?
hyperpolarization
What happens in MS?
myelin is lost, so APs are slowed
What is the relationships between axon diameter and propagation speed?
wider diameter, faster the propagation
What are the different nerve fiber classifications?
motor (A alpha): highly myelinated, large, fastest, motor control
sensory (A alpha beta): myelinated, second largest, second fastest, touch, position perception
sensory (A gamma): thinly myelinated, medium, cold, perception, and pain
Sensory (C): unmyelinated, small, warm, perception, and pain
autonomic (C): unmyelinated, small, HR, BP, sweating, GIT, GUT function, slowest
What does the spinal cord do? How many pairs of spinal nerves are there? Are they sensory or motor nerves?
Vital two-way link between the brain and the periphery Connects to the periphery via 31 pairs of spinal nerves Spinal nerves: sensory or motor? mixed
Where does the spinal cord end?
L2/L3
What distinguishes the ventral part of the spinal segment?
broader grey matter
What distinguishes the dorsal part of the spinal segment?
has a Dorsal Root Ganglia
What is the collection of nerves coming out of the ventral end of the spinal segment?
ventral root
What information do the ventral roots carry?
motor information
info from spinal cord to m.
What information do the dorsal roots carry?
sensory
to spinal cord from periphery
