Nervous System 1, 2, & 3 (WS 7, 8, & 9)
Organization/Structure of Nervous System
Electrical signals in neurons
Cell-to-cell
communication
Integration of neural information transfer
Central Nervous System
CNS
Afferent- Things moving toward
Efferent- Things moving away
Nerves that are firing towards (afferent) or away (efferent)
from the CNS
Includes the brain and spinal cord
FUNCTIONS: Receives,
processes, and transfers information
Efferent Neurons
PNS
Includes:
Autonomic neurons
Automatic
Sympathetic and parasympathetic
Somatic motor neurons
Control of skeletal muscles
Nervous System Components and Functions
1. Central Nervous System
2. Peripheral Nervous System
Functions:
Rapid communication for homeostatic
balance
Properties of intelligence, consciousness & emotion,
and memory
Peripheral Nervous System
PNS
The nerves and Ganglia outside of CNS
Includes:
Sensory neurons- carry info toward CNS
Motor
neurons- carry info away from CNS
Nerves- Bundles of
axons
Ganglia- Collections of nerve cell bodies; create swelling
in nerves
Neurons
Basic functional unit of nervous system
Cell body site of energy
generation and synthesis
For communication in the
NS
Includes a:
Cell
body
Dendrites
Axon
Terminal
Myelin Sheath
Cell Types
Neurons- Transmit communication signals
Communication
Glial Cells- Support neurons
Support,
protection, myelin formation
* the cells that become TUMORS
Glial Cells
Found in CNS and PNS
Support neuron bodies, form myelin
sheaths
Involved in cleaning up dead cells and fixing cell
connections
barriers between compartments
Scavenger/defense
and metabolic assistance
FIG 8.5 IN BOOK
Node of Ranvier
A section of unmyelinated axon membrane between two schwann cells
Glial Cells (continued)
Outnumber neurons 10-50X
do NOT conduct signals
provide
physical support for neurons (direct growth and repair)
Form
myelin sheaths
Acts as insulator
Increases speed
Glial cells in PNS
1. Schwan cells- Myelin production
Areas of non-insulated Nodes
of Ranvier
2. satellite cells- Supporting cells around
ganglia
no myelin
Glial cells in CNS
1. Oligodendrocytes- wrap around neurons, support, and insulate with
myelin
2. Astrocytes- Contact neurons and blood vessels, transfer
nutrients
3. Microglia- Specialized macrophages remove damaged cells
Electric Signals in Neurons
Ionic concentrations and potentials
For an ion to move it needs incentive and opportunity
EX: I want to leave and go to lunch during class (incentive), but I can't leave in the middle of class (no opportunity)
Information Transfer in Neurons
1. Gated Channels
2. Graded Potentials
3. Action Potentials
Gated Channels
Channel opens in response to stimuli
Keeps things that aren't
lipophillic away from fats
Controls
permeability
Types:
1. Mechanically Gated- Physical factors
stimulate opening, pressure, and stretch
2. Chemically Gated-
Ligand stimulates (neurotransmitters, neuromodulators)
3. Voltage
Gated- Membrane potential changes stimulate opening
Graded Potentials
Localized, variable in size, dissipates
Dissipates due
to:
1. Positive charge leakage
2. Cytoplasmic resistance
Incoming (input) signals
vary in strength
decreased
strength over distance
slower moving than action potentials
(AP)
travel to trigger zone and integration occurs
Sub-threshold: too weak, no AP
Supra-threshold: Generation of AP
Action Potentials
All or none
Spontaneous or graded potential initiates
START
at trigger zone
Signal does NOT diminish with distance
Action Potential Components
Initiation
Depolarization
Signal Peak
Repolarization
Hyperpolarization
Refractory Period
Compromised ability to stimulate AP's
Two Types:
1.
Absolute Refractory Period
1/1000th of a second you are in this
period
2. Relative RP
this period is larger
Regulating RP
Na+ inactivation channel limits Na+ entry, K+ channel returns polarity to normal
Coding information in AP's
Control of Speed
Can change the frequency with which we see
the AP's
Firing rate- "wave of AP's"
Proportional
neurotransmitter (NT) release
Stronger Graded Potential
(GP)
aka stimulus= more AP's and more NT
Speed of AP Conduction
Change the speed by diameter of the axon
larger is faster
axon myelination increases speed(creates saltatory conduction)
Voltage gated channels only in nodes of Ranvier