Organization of nervous tissue & Electrical signals Flashcards
Gray matter
Groups of neuron cell bodies and their dendrits, with very little myelin
Cortex
Gray matter on the surface of the brain
Nuclei
gray matter located deeper within the brain
ganglion
Clusters of neuron cell bodies that form gray matter in PNS
White matter
bundles of parallel myelinated axons
Nerve tracts
White matter of the CNS that propegate action potentials from one area of CNS to another
Action potentials
Electrical signals produced by specialized cells
Action potentials are how cells communicate with other cells
Electrical properties of cells (2)
- Ionic concentration differs across the plasma membrane
2. Permeability characteristics differ across the plasma membrane
What is the purpose of the sodium potassium pump in a neuron?
maintains high concentraion of K+ in the cytoplasm and high concentration of Na+ in the extracellular fluid.
Uses ATP to make the sodium-potassium pump work
Ion channels (4)
Leak ion channels (always open)
Ligand-gated - opened by binding a specific molecule to the recptor site of the ion channel
VOltage-gated - open and close in response to specific, small voltage change across plasma membrane
Other ion gated
Opposite charges between the inside of the cell and the extracellular fluid results in -
polarization
Potential difference
Electrical charge difference across the plasma membrane
Resting membrane potential
The potential difference in an unstimulated, resting cell
When is resting membrane potential equilibrium established
When tendancy for K+ to diffuce out o the cell is equal to tendency for K+ to move in to the cell
Which ions most influence resting potential?
K+
Which ions have minor influence on resting potential?
Na+, Cl-, and Ca2+
Depolarization
Occurs when teh membrane potential becomes more positive; membrane potential moves closer to zero
Hyperpolarization
occurs when teh membrane potential becomes more negative; membrane potential moves further away from zero
Hypokalemia
Lower-than-normal concentraion of K+ in teh blood or extracellular fluid > hyperpolarizes resting membrane potential
Causes excitable tissues to become less sensitive to stimulation > muscular weakness, abnormal electrocardiogram, sluggish reflexes
Caused by depletion of potassium during starvation, alkalosis, or certain kidney diseases
Hypocalcemia
lower-than-normal concentration of Ca2+ in the blood or extracellular fluid
Nervousness and uncontrolled contraction of skeletal muscles (tetany)
Caused by lack of dietary calcium or vitamin D
Graded potential
relatively small change in teh membrane potential that is localized to one area of the plasma membrane
Often leads to action potentials
Summation
effects of one graded potential combine with effects of a different grade potential elsewhere on plasma membrane
Threshold
The limite at which graded potentials must summat to trigger an action potential
It’s when voltage-gated Na+ channels open
Where do action potentials initiate?
Action potentials occur at the trigger zone because there is a higher proportion of voltage-gated channels there than other parts of the cell body
Phases of the action potential
Depolarization (becomes more positive)
Repolarization (become more negative)
Afterpotential (short period of hyperpolarization)
All or none principle
stimulus is large enough to reach the threshold, an action potential occurs. If a stimulus is too weak, for depolarizing graded potential to not meet the threshold, there is no action potential produced.
Refractory period
The time period when an action potential causes an area to become less sensitive to further stimulation
Absolute refractory period
the first part of the refractory period where complete insensitivity to another stimulus exists.
Relative refractory period
A very strong stimulus can initiate another action potential during the relative refractor period
Propagation of Action potentials
Like dominoes - each domino triggers the next domino to topple
Local current
movement of positively charged ions
Continuous conduction
Action potential that occurs in unmyelinated axons
The local current causes the membrane adjacent to the action potential to depolarize > depolarization reaches threshold > produces further action potential
Saltatory conduction
Action potential conducted in myelinated axons from one node of Ranvier to another
What determines the speed of an action potential? (2)
The thickness of the myeline sheath. Cells with more oligodendrocytes or Schwann cells conduct action potentially more rapidly.
Diameter of an axon > the larger, the more rapidly the action potential will be conducted
Types of nerve fibers (3)
Type A
Type B
Type C
Type A fibers
large diameter, myelinated axons that conduct rapid action potentials
Motor neurons supplying skeletal muscle and sensory neurons
Type B fibers
medium diameter, lightly myelinated axons
Part of ANS - signals internal organs and responses necessary to maintain homeostasis
Type C fibers
small diameter, unmyelinated axons
Part of ANS - signals internal organs and responses necessary to maintain homeostasis
