Organization of the PNS (10/10b) [Biomedical] Flashcards
Neuron
Fundamental functional unit of the nervous system
Has axons and dendrites
4 Main Functional Regions of Neurons
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
Types of Neurons
Sensory* Motor* Local interneuron Projection interneuron Neuroendocrine cell
Soma Structure - Soma
main integrative unit of neuron, supports basic metabolism of neuron
dendrites receive input from other neurons, soma integrates inputs, and signal is transmitted
Soma Structure - Endoplasmic Reticulum (ER)
lipid and protein synthesis, biosynthesis and recycling of vesicles
Soma Structure - Lysosomes
digest compounds, glycogen → glucose, part of axoplasmic transport system
Soma Structure - Mitochondria
creates energy (ATP) through oxidative phosphorylation
Soma Structure - Microtubules
axonal transport
Soma Structure - Golgi Apparatus (GA)
storage of lipids and proteins
Axon Functions
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)
Axonal Transport - Anterograde
from the center of the cell (soma) to the peripheral (axon tip)
Axonal Transport - Retrograde
from the periphery of the cell (axon tip) to the center (soma)
Schwann cells provide what?
protection and insulation
Myelinated axons
In the PNS, Schwann cells myelinate axons by investing them with up to 300 concentric layers to form myelin sheath
Unmyelinated axons
Do not have a myelin sheath, but are associated with and enveloped by Schwann cells, which provide trophic support
How Do Neurons Transmit Information?
Cellular Mechanisms
- resting membrane potential
- post synaptic potential
- action potential
Synaptic Mechanisms
- convergence
- divergence
Behavioral Mechanisms
- feedback
- feedforward
Neuronal Cell Membrane
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
Forces that Guide Ion Movement
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
Electrostatic forces want to hold the ions where they are, but the diffusion forces are stronger and want to push K+ ___ and Na+/Cl- ___
K+ out
Na+/Cl- in
Ion Channels - Overview
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
Ion Channels - Ligand Gated
receptor on one end, when a neurotransmitter comes in contact with receptor site, ion channel opens
Ion Channels - Mechanical Gated
stress applied to channel, opens the gate
Ion Channels - Voltage Gated
only opens when there is a specific membrane potential across the membrane
Ion Channels - Leakage
randomly opens and allows ions out
There are more potassium leakage channels than sodium leakage channels
Sodium Potassium Pump
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
Resting Membrane Potential (RMP)
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
Mechanisms of RMP
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
Change in RMP — Terminologies
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)
Excitatory Postsynaptic Potential (EPSP)
inside becomes more positive than resting,
membrane becomes depolarized
Inhibitory Postsynaptic Potential (IPSP)
inside becomes more negative than resting, the membrane becomes hyperpolarized
Action Potential - Generation
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
Action Potential - Propagation
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
Function of Myelin Sheath
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
Increased action potential conduction velocity due to
Myelination
Larger axon diameter
Nerve Fibers - Motor Axons
Myelinated, large diameter, muscle control
Nerve Fibers - Sensory Axons
Myelinated — large diameter, touch, vibration, position perception
Thinly Myelinated — medium diameter, cold perception, pain
Unmyelinated — small diameter, warmth perception, pain
Nerve Fibers - Autonomic Axons
Thinly Myelinated — smaller diameter, heart rate, blood pressure, sweating, GIT, GUT function
Unmyelinated — smallest diameter, heart rate, blood pressure, sweating, GIT, GUT function
Spinal Cord
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
Dorsal vs Ventral
Dorsal = posterior Ventral = anterior
Spinal cord - Transverse Organization
Spinal segment with grey matter in the middle, surrounded by white matter
Dorsal root = afferent, sensory
Ventral root = efferent, motor
