NERVOUS SYSTEM (part 1) Neurons and Electrophysiology

PNS

Myelinated Axons:: Schwann cells in the ________ or oligodendrocyte extensions in the CNS repeatedly wrap around a segment of an axon to form a series of tightly wrapped membranes rich in phospholipids, with little cytoplasm sandwiched between the membrane layers.

Spatial Summation

________ uses multiple synapses acting simultaneously.

higher concentration of Cl

Negatively charged Cl-:: this exits the cell due to it being repelled by the negatively charged proteins and other negatively charged ions inside the cell, causing a(n) ________- outside than inside.

additional K+

When the negative charge inside the cell is great enough to prevent ________ from diffusing out, an equilibrium is established.

Voltage

________- gated ion channels:: open and close in response to a specific, small voltage change across the plasma membrane.

small electric currents

When stimulated, dendrites generate ________, which are conducted toward the neuron cell body.

potassium ions

The ________ leak out of the cell faster than positive sodium ions enter the cell and therefore create a slightly negative charge inside of the cell.

depolarization

In ________, resting membrane potential moves towards zero.

hyperpolarization

In ________, resting membrane potential moves farther away from zero.

Neurotransmitters

________ diffuse across the synaptic cleft toward the postsynaptic membrane.

Depolarization

________ only occurs for a brief moment of time.

Neurotransmitters

________ bind to specific receptor molecules of the postsynaptic membrane.

Neuron

the electrically excitable cells of the nervous system

Neuron cell body

performs the typical functions of any cell, such as protein synthesis and packaging of proteins into vesicles

Axon hillock

a single axon arising from a cone-shaped area of the neuron cell body

Initial segment

The axon hillock transitions to this as it narrows and is the actual beginning of the axon

Trigger zone

This is the combination of the axon hillock and the initial segment where action potentials are generated

Synapse

Point of contact between the axon ending and its effector

Synaptic vesicles

They store the signal molecules produced by the neuron

Neurotransmitters

these signal molecules control the effectors

Dendrites

are extensions of the cell body and receive information from other neurons or the environment portion of the neuron

Dendritic spines

they are small extensions on dendrite surfaces where axons of other neurons form connections with the dendrites

Sensory neurons (afferent neurons)

conduct action potentials toward the CNS

Motor neurons (efferent neurons)

conduct action potentials away from the CNS toward muscles or glands

Interneurons

conduct action potentials within the CNS from one neuron to another

Myelinated Axons

Schwann cells in the PNS or oligodendrocyte extensions in the CNS repeatedly wrap around a segment of an axon to form a series of tightly wrapped membranes rich in phospholipids, with little cytoplasm sandwiched between the membrane layers

Nodes of Ranvier

These are gaps in the myelin sheath

Unmyelinated Axons

The axons rest in invaginations of the Schwann cells or oligodendrocytes

Saltatory conduction

describes the way an electrical impulse skips from node to node down the full length of an axon, speeding the arrival of the impulse at the nerve terminal

Diffusion Tensor Imaging (DTI)

Visualizes white matter connectivity in the brain and it also measures movement of water at microstructural level

Glial Cells

Important in the nervous system and a major support cell for neurons

Action potential

electrical signals produced by the nervous system

Membrane potential

a measure of the electrical properties of the cell membrane

Diffusion

the characteristics of electrically excitable cells and the generation of action potentials are due to this principle

Sodium-potassium pumps

All along the neuron axon, they actively pump K+ against its concentration gradient into the cell, while at the same time, they pump Na+ against its concentration gradient out of the cell

Negatively charged proteins

are regularly synthesized inside the cell; because they are large and relatively insoluble, they cannot easily diffuse across the plasma membrane and stay inside the cell

Ion channels

Ions must pass through the plasma membrane through these channels

Leak ion channels or Non-gated ion channels

are always open and are responsible for the permeability of the plasma membrane to ions when the plasma membrane is unstimulated or at rest

Gated ion channels

are closed until opened by specific signals which can change the permeability of the plasma membrane

Ligand-gated ion channels

stimulated to open by the binding of a specific molecule to the receptor site of the ion channel

Voltage-gated ion channels

open and close in response to a specific, small voltage change across the plasma membrane

Other gated ion channels

respond to stimuli other than ligands or voltage changes; they are present in specialized electrically excitable tissues

Potential difference

it is the electrical charge difference across the plasma membrane

Resting membrane potential

it is the potential difference in an unstimulated, or resting cell

Difference in potential

the charge difference across the plasma membrane at equilibrium which is measured in millivolts (mV)

Equilibrium

very little movement of K+ or other ions takes place across the plasma membrane

Nernst Equation

E ion = 58mv/z (log(extracellular/intracellular)), where z = ion valence (charge)

Depolarization

is the process or act by which polarity is eliminated

Hyperpolarization

is a process or act resulting in the membrane potential of a cell more negative than it typically is

Graded potential

is a relatively small change in the membrane potential localized to one area of the plasma membrane

Summation

combination of graded potentials, which, if sufficiently large, will result in action potential

Temporal Summation

occurs when a series of subthreshold EPSPs in one excitatory fiber produce an action potential in the postsynaptic cell

Spatial Summation

occurs when stimuli are applied at the same time, but in different areas, with a cumulative effect upon membrane potential

Threshold

the membrane potential at which an action potential is generated

Action potential

the means by which neurons communicate with their effectors

All-or-none principle

if a stimulus produces a depolarizing graded potential that is large enough to reach threshold, all the permeability changes responsible for an action potential proceed without stopping and are constant in magnitude

Refractory period

the time period where an area is less sensitive to further stimulation

Absolute refractory period

the first part of the refractory period, during which complete insensitivity exists to another stimulus no matter how strong

Relative refractory period

the time period where a stronger-than-threshold stimulus can produce an action potential

Electrical synapses

occur between cells connected by gap junctions

Gap junctions

a 2 nm gap between adjacent cell membranes where cytoplasm is shared through tunnel-like protein structures called connexons

Chemical synapse

occurs where a chemical messenger , called a neurotransmitter, is used to communicate a message to an effector

Presynaptic terminal

consists of the end of an axon of the presynaptic cell

Synaptic cleft

The space separating the axon ending and the cell with which it synapses

Postsynaptic membrane

the membrane of the postsynaptic cell associated with the presynaptic terminal

Neurotransmitters

act as the chemical signals and are stored in synaptic vesicles in the presynaptic terminal

Ionotropic receptor

also known as ligand-gated receptors

Metabotropic receptor

also known as G-protein coupled receptors, it is a type of membrane receptor that initiates a number of metabolic steps to modulate cell activity

Acetylcholine (ACh)

a neurotransmitter released from CNS synapses which has an excitatory effect, ANS synapses which has an inhibitory effect, and a neuromuscular junction which has an excitatory effect; its mechanism of action is ionotropic

Serotonin

a neurotransmitter released from CNS synapses which mostly has inhibitory effects; its mechanism of action is metabotropic and ionotropic

Dopamine

a neurotransmitter released from selected CNS synapses and some ANS synapses which has excitatory or inhibitory effects; its mechanism of action is metabotropic

Norepinephrine

a neurotransmitter released from selected CNS synapses and some ANS synapses on most sympathetic targets which has excitatory effects; its mechanism of action is metabotropic

Depression and Anxiety

Serotonin is important for emotional states such as these

Epilepsy

Characterized by excessive neuron function, Lock of GABA induces convulsions

ADHD

Characterized by an inability to focus

Parkinson Disease

Loss of muscular contraction control

Stroke

damage in the brain that results in a disruption in or lock of blood flow to the brain

K+

________ is higher inside the cell than outside while Na+ is higher outside the cell than inside.