Neuroscience Exam 1
1) 100 billion neurons, 10,000 different neurons in the brain
2) Motor neurons = muscle cells. Sensory neurons = periphery nervous system
The nervous system has two different cases of cells.
1) Nerve cell = neurons -> excitable cells for communication
2) Glial cells = Glia or neura glia -> support cells -> non-excitable. Allow for the
nervous system to function better
muscle cells and neurons are the only excitable cells in the body
min CNS PNS Schwan cell
n Glial cell
Node of Ranvier
*Cell body is located in ventral horn in spinal cord
Axon Hillock is the trigger zone that generates the action potential
Glial cell -> support cell in CNS
Schwan cell -> support cell in the PNS
Soma=cell body=metabolic center of the neuron
A typical neuron has 4 morphologically defined regions
1) Cell body metabolic cell
Body only represents 10% of a cells total volume
2) Dendrite receptive portion
Diameter= .2-20 micrometers
Longer axons are up to 1 meter long
3) Presynaptic terminal
Innervates dendrites of another nerve
Neurons are not replicated
Mature neurons don’t undergo proliferation. Ramon y Cajal Neurobiologist responsible for:
1) Neuron Doctrine
2) Principle of dynamic polarization. -> info flows in a precise and specific direction
3) Principle of connection specificity
a) No cytoplasmic continuity
b) Nerve cells do not connect indiscriminately
c) Each nerve makes specific and precise connections at specific points
Neuronal differentiation: The feature that most dramatically distinguishes one neuron
from another is based on cell shape, number and form of neurons processes.
Neurons are classified into three main groups on the number of neuritis
a) Unipolar cells
b) Bipolar cells
c) Multipolar cells
Neurons can also be classified further by Functionality in 3 major groups:
a) Afferent: carry signal toward CNS (sensory)
b) Efferent: carry signal away from CNS (motor)
c) Interneurons: carry info to/from different parts of the CNS
3. Glial Cells: nerve cells are surrounded by glia (GLUE) cells. Glial cells are NON-
EXICTATORY Roles of glial cells= a) supporting element
b) form myelin
c) act as scavengers (clean up and removal of debris)
d) buffer ions and chemical transfers
e) provides a roll in migration of neurons in early life
f) contributes to the blood brain barrier
g) gives the cells nutrition
Glial cells in the vertebrate nervous system are divide in 2 major classes based on their
1) Microglia: Act as part of the immune system and remove debris in the system
a) Oligodendrocytes: provide myelin in the CNS
b) Schwann cells: provide myelin in the PNS
3) Astrocytes: everything else except for myelination
3. Axoplasmic (axonal) transport
There are 3 different ways to bring the newly found secretory products from the golgi
apparatus to the end of the axon
a) Fast anterograde transport (Forward)
b) Slow anterograde transport (Forward)
c) Fast retrograde transport
1) Fast Anterograde Axonal Transport: Material is enclosed into synaptic vesicles
and hen “walked down” the microtubules of the axon. This transport is based on
stable microtubules. The “legs” are provided by the protein called Kinesin.
Kinesin only moves the material from the soma to the axon terminal. At the nerve
terminals the vesicles are reused many times known as a process called
Exocytosis. Relies on Oxidative metabolism.
2) Slow Anterograde Transport: Cytosol (cytoskeletal and soluble proteins) are
transported down the axon by this. Slower component transport at a rate of 0.2-3
mm/day. Contains about 75% of total protein moved by slower component
3) Fast Retrograde Transport- from the nerve endings toward the cell body.
Particles move along in the microtubules and requires a oxidative
metabolism as well. The “legs” in returning the vesicles to the body is Dynein. HANDOUT 2
1. Biophysical Considerations (59-61)
a) Chemical motion: Area of high concentration Low concentration. Does not
require metabolic activity or external energy. Energy is only required when
moving against the concentration gradient.
b) Electrical motion:
i) Cations: positively charged ions. Attracted to the negative cathode
tube. (K+, Na, Ca++) are the cations in the nervous system.
ii) Anions: Negatively charged ions. Attracted to the positive anode
Semi-permeable membranes permit passage of substances. The ease of something
going through a membrane is called membrane permeability. The ease of a charged
molecule going through a membrane is conductance.
A. Membrane properties: current flow into and out of the cell is controlled by ion
channels in the membrane. Gated and Non-gated channels.
These channels have 3 important properties.
1) They conduct ins really fast. (100 million Ions/sec)
2) Very selective
3) They open and close in response to specific signals
i) Non-gated: Always open. Which gives rise to the resting membrane
ii) Gated: At rest they are closed. This is critical for producing action
3 major signals can gate ion channels:
1) Voltage: (voltage-gated channels)
2) Chemical transmitter (transmitter-gated channels)
3) Pressure or stretch channels (mechanically gated channels)
There are 3 phases a Gated channel can be in at a given time. (closed and activatable
(resting); open (active); closed and non-activatable (refractory).
Ions Intercellular Extracellular Ratio Equilibrium
Concentration concentration potential
K+ 100 5 20:1 -80 Na+ 15 150 1:10 +60
Ca++ .0002 .2 1:1000 +123
Cl- 13 150 1:11.5 -65
A membranes selectivity for ions is determined by the various types of ion channels
i) Glial cells:
As K+ leaves the cell, the cell becomes more
5 Eventually the large negative charge will prevent
100 K+ from leaving the cell. At -80 mV he concentration
Gradient and the electrical charge are in equilibrium
Which prevents further K+ from leaving. Outside
Cell is determined to be 0 charge because it is
-80 mV A large area.
ii) The Nernst equation is used to determine Equilibrium Potential.
iii) Neurons: at rest a neuron have a resting membrane potential of -65 mV.
There are a lot more non-gated K+ channels then there are Non-gated Na+
channels which allows the cell to maintain a -65 resting potential.
iv) Sodium-potassium pump: K+ is more concentrated on the inside while Na+
and Ca++ are more Concentrated on the outside. This Ion pump is what gives
rise to this concentration gradient. The Sodium-potassium pump is an
enzyme that breaks down ATP with the presence of Na+ and this chemical
reaction is what drives the pump. This then exchanges the internal Na+ for an
external K+ This then assures a K+ concentrated inside and an Na+
concentrated outside. 3 Na+ for every 2 K+. This pump is responsible for 70%
of the total ATP utilized in the brain. Goldman’s equation is used to find
membrane potential with the relationship between the concentration inside
and outside the cell with more than one ion present.
Handout 3 A. Introduction: Membrane potential is the difference in electrical potential between
the inside and the outside of a cell. All neurons, axons and muscle fibers have
membrane potential. Resting potential=no activity. Excitable cell is
active=membrane potential varied.
These variations are:
i) Local potential
ii) Action potentials
Gated channels are critical in these.
B. Local Potentials: change in membrane potential in a localized area of the cell.
i) Synaptic potential- chemically ligand) gated channel
-closed at rest
-chemical agent acts against the membrane
ii) Generator potential: -Mechanical deformation of the membrane
-Mechanically gated channel
iii) Electronic potential: -Created by an electrical current
-working on voltage or electrically gated channels
1) Ionic basis of local potentials:
i) Synaptic potentials occur primarily via transmitter-gated channels by:
a) Open chemically gated K+ (hyperpolarize the cell) IPSP (Inhibitory Post
b) Open chemically gated Na+ channels (depolarize the cell) EPSP
(Excitatory post synaptic potential)
c) Open chemically gated Na+ and K+ channels (depolarize) EPSP
d) Open chemically gated Cl- channels, creates IPSP or stabilizes the
ii) Generator potential: Primarily Mechanical gated channels
a) Opening of mechanically gated Na+ and K+ channels, EPSP
b) Activate generator potentials
iii) Electronic potentials: occur in voltage gated channels
a) Opening of electrically gated Na+ channels in a response to a localized
b) Opening/closing of different electric gated channels to an external
2) Characteristics of local potentials
i) Graded response: amplitude is proportional to the strength of the stimulus
whether EPSP or IPSP.
a) Spatial summation: Same time but different locations b) Temporal summation: same location but at slightly different times.
C) Action Potentials: All or none-transfer info without loss over relatively long
1. Phase 1- Absolute refractory period
2. Phase 2- Relative refractory period
-2 AP possible but needs to be larger than
3. Phase 3- after hyperpolarization
About 5 milliseconds in time
*Threshold is a fixed value and doesn’t change
1) Ionic Basis of Action Potential: The ionic conductance change for Na+ and K+ result in
ionic shifts and flows that are associated with membrane potentials. gNa+=permeability or conductance to
gK+=permeability or conductance to K+
as K+ leaves the cell, the more negative
it becomes. –After hyperpolarization
The amounts of Na+ and K+ moving
across the membrane are small and DO
NOT CHANGE the concentration enough to result in a change of resting potential.
The Na+ moving into the cell is constantly being pumped out by the NaK pump during the long
intervals between AP.
2) Threshold- when the Electric gated Na+ channels open and the AP is generated. High
density of electric gated Na+ channels in the *axon hillock or trigger zone.
Density of voltage gated channels Location
Na+ Axon hillock
Nodes of Ranvier
K+ Diffuse along axon
Cl- Dendrite or soma
Ca++ Dendrite, soma, terminal axon
If the membrane potential remains depolarized above threshold, the membrane cannot
be make AP.
3) Conduction propagation of the AP- An AP generated anywhere of a neuron or muscle
cell spreads to all other regions of that cell.
4) Rate of conduction of the Action Potential
i) Effect of axon diameter: bigger axon diameter=faster velocity
Unmyelinated axons- CV (conduction velocity)=axon diameter x 0.5
Myelinated axons CV=axon diameter x 5.5
ii) Effect of myelination Complete myelination would not allow the AP to propagate. Which is why there is
gaps between each section of myelin.