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BIOL 3322 Midterm: brain and behavior exam 1

Course Code
BIOL 3322
qing lin
Study Guide

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Cells of the Nervous System 1/12/11
*Figure 3.6: structure of animal cell shares qualities with nervous cell:
-cell membrane separates inside/outside of cell
-semi permeable: has ion channels that allow for flow in and out, channels are specific
-mitochondria (energy center)
-microtubules (transport
Two Kinds of Cells in the Nervous System
-neurons: cells in nervous system that receive and convey info
-Golgi: Golgi stain
-Santiago Ramon and Cajal: “The Father of Neuroscience”
-discovered that neurons separate
-Basic Structure *Figure 3.5
-soma: cell body
-axon: sends info. Has a presynaptic terminal at end. Usually one per neuron. Sometimes
branches called axon collateral
-dendrites: where neurons receive info (many of them)
-dendritic spines: increase surface area of dendrites. Spines change in number and shape
-synapse: gap between adjacent neurons. Where info is transferred from one neuron to the next
-myelin sheath: fatty tissue that insulates axons. Increases rate of neurotransmission
-Efferent: carries info AWAY from the brain **motor neurons
-Afferent: carries info TO the brain **sensory neurons
-interneurons: cells dendrites and axons are totally within one structure
-variation in neurons shapes and sizes
-Glia Cells: do no transmit info. Synchronize activity of neurons, housekeeping/clean up after neurons,
provide structural support. There are more glia than neurons but they are smaller. *Figure 3.10
1. astrocytes: star shaped, provide supportive matrix
2. microglia: respond to injury or disease. Surround injured tissue and trigger an
inflammatory response
3. oligodendrocytes: build the myelin sheath in the central nervous system
4. Shwann cells: build the myelin sheath in the peripheral nervous system
-Blood-Brain Barrier
-to protect the brain, body has built a wall outside the brain's blood vessels
-chemicals can't get through
-fat soluble molecules can get through
-active transport lets most things through
Neural Conduction: flow of information within a neuron
I. Electricity
1. flow of electrons from a body that contains more electrons to a body that contains fewer
2. measured in volts
3. negative pole= body with HIGHER number of electrons, more negative pull
4. positive pole= body with FEWER number of electrons, less negative pull
5. electrical potential: the difference in the electrical charge in negative and positive poles.

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Electricity caused by movement of electrons.
II. Movement of Ions create electrical charges
-the directions of these ions are determined by passive forces:
1. concentration gradient: difference in distribution of various ions inside and outside of the
cell. Ions flow from high concentration to low
2. voltage/electrical gradient: difference in distribution of charges of ions inside the cell from
that outside the cell. Move from area of high charge to low charge
3. equilibrium: force of concentration gradient is equal
III. Methods for encoding activity of a neuron
**see handout
IV. Resting Potential of a neuron
**A. difference in electrical charge against an undisturbed neuron (-70 mV) is maintained by
1. selective permeability of the membrane
2. voltage gated ion channels (specific, triggered by charge of membrane)
3. relative concentration of intercellular and extracellular ions **Figure 4.1
-Na+ and Cl-: more outside of the cell
-K+ more inside the cell
-A- negatively charged ion stuck inside the cell
4. Passive Forces **Figure 4.2
-no energy required
-concentration gradient
1. Na+ into the cell
2. K+ out of the cell
3. Cl- into the cell
-electrical gradient
1. Na+ into the cell
2. K+ into the cell
3. Cl- out of the cell
5. Active Forces (sodium-potassium pump): uses energy, or ATP, to pump 3 Na+ out for
every 2 K+ pumped in
6. Status of ion channels at Resting Potential
**At resting potential, Na+ channels are CLOSED
**K+ channels are MOSTLY CLOSED
**Cl- channels MOSTLY OPEN
V. Graded Potentials
1. slight change in the voltage of an axon's membrane
2. Hyperpolarization: increased polarization (from -70 mV to -71 mV) makes charge more
3. depolarization: descreased polarization (from -70 to -68) makes charge more positive
VI. Action Potential
1. large, brief reversing charge in the voltage of a neuron. Briefly, inside the axon is POSITIVE relative
to the outside
2. Threshold potential: voltage level at which the action potential is triggered. Varies but is
usually around -65 mV
3. Axon Hillock: area of neuron where axon exits the cell body (action potential is
generated in area right next to this)
4. Status of ion channels at Action Potential
-Na+ channels FLY OPEN

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5. Flow of ions: massive flow of Na+ into the cells and a slow flow of K+ out of the cell
causes the charge of the ion to go all the way up to +50 mV
6. All or None Law: the size, shape, and intensity of action potential is independent of the
intensity that produced it. Just need enough to get to -65 mV and you either get an action
potential at -65 mV or you don't get one at all. No such thing as a strong/weak action
VIII. Repolarization
1. returning to resting potential
2. when you hit +50 mV:
-electrical gradient forces a massive flow of K+ OUT OF CELL (this is what drives repolarization)
3. As cell get scloser to resting potential, K+ closes slowly, so slowly that K+ continues to
leave cells
4. Too much leaves the cell resulting in a brief hyperpolarization
5. Sodium-potassium pump brings axon back to resting potential
-Na+ opens channels causing rising phase
-Na+ doors close at 50 mV
-K+ open channels cause repolarization and hyperpolarization
IX. Refractory Period: cell resists production of more action potentials
1. Absolute refractory: first part, Na+ channels closed and WILL NOT open regardless of the
2. Relative refractory: higher than normal level of stimulation is needed to elicit an action
3. Implications of Refractory period
a) action potential is normally unidirectional
b) RATE of action potential is related to intensity of stimulation
X. Propagation of Action Potential
1. action potential starts right when the axons leaves cell body
2. one action potential causes another and maintains strength all the way down (kind of like
the wave at a football game)
3. Determinant of Speed at which action potential travels
a) diameter of axon: greater the diameter the greater the speed of action potentials
b) presence of myelin sheath: results in faster conduction
-nodes of ranvier: gaps between the sheath, exposed pieces of axon
-saltatory conduction: action potential jumps from node to node
XI. Excitatory and Inhibitory Post-Synaptic Potentials (EPSPs and IPSPs)
1. brief depolarizing (EPSP) or hyperpolarizing (IPSP) graded potentials that do fade and don't
maintain strength
a) EPSP: increases likelihood of action potential occuring. Depolarization, makes more positive, closer
to action potential. Ex: something that opens some Na+ channels
b) IPSP: makes cell a little more negtive and less likely for an action potential to occur. Ex: something
opens the Cl- channels to make more negative or opening up of the K+ channels to flow out
2. Spatial Summation **Figure 4.4
a) when repeated stimuli produced simultaneously at DIFFERENT synapses will add together
3. Temporal Summation **Figure 4.5
a) when stimuli that are produced in rapid succession at the SAME synapse will add together
4. Relationship to Action Potential: any given moment a neuron has thousands of IPSP and
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