Myelin Sheath-Properties of Synapses

Myelin Sheath

A layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next.

Myelinated Axons

found only in vertebrates, are covered with layers of fats and proteins

saltatory conduction

jumping of action potentials from node to node

After an action potential occurs at a node, ____________, pushing a chain of positive charge along the axon to the next node, where they regenerate the action potential

sodium ions enter the axon and diffuse

In myelinated axons, the action potential starts at the ___________

first node of Ranvier

In addition to providing rapid conduction of impulses, saltatory conduction _________.

conserves energy

Transmission in myelinated axons is ______ than in unmyelinated axons.

faster

A condition where the immune system attacks myelin sheaths.

Multiple Sclerosis

What prevents an action potential near the center of an axon from reinvading the areas that it has just passed?

the areas it just passed are still in their refractory period

1st part of refractory period where the membrane cannot produce another action potential, regardless of the stimulation.

Absolute Refractory Period

2nd part of refractory period where a stronger than-usual stimulus is necessary to initiate an action potential.

Relative Refractory Period

the absolute refractory period is _________, and the relative refractory period is _______.

about 1 millisecond (ms), 2 to 4 ms.

Refractory Period

period in which the cell resists the production of further action potentials

Neurons without an axon exchange information with only their closest neighbors.

Local Neurons

When a local neuron receives information from other neurons, it has a _______.

graded potential

What is a membrane potential that varies in magnitude in proportion to the intensity of the stimulus.

Graded Potential

Why is it difficult to study local neurons?

because it is almost impossible to insert an electrode into a tiny cell without damaging it.

What will happen if you could activate all your neurons at one time?

you would have an epileptic seizure

In a myelinated axon, how would the action potential be affected if the nodes were much farther apart?

If they were much farther apart, then it could success- if action potential would travel faster fully jump from one node to the next.

In a myelinated axon, how would the action potential be affected if the nodes were much closer together?

If the nodes were closer, the action potential would travel more slowly.

Reflex Arc

The circuit from sensory neuron to muscle response.

__________ anatomically demonstrated a narrow gap separating one neuron from another.

Ramón y Cajal

_________ physiologically demonstrated that communication between one neuron and the next differs from communication along a single axon.

Charles Scott Sherrington

It is an automatic muscular responses to stimuli.

Rreflexes

The _______ controlled the flexion and extension reflexes.

spinal cord

Reflexes are ______ than conduction along an axon.

slower

Several weak stimuli presented at nearby places or times produce a __________ than one stimulus alone does.

stronger reflex

When one set of muscles becomes ______, a different set becomes ______.

excited, relaxed

Speed of __________ varied but was never more than about 15 meters per second (m/s).

conduction through the reflex arc

When Sherrington pinched a dog's foot, the dog flexed that leg after a short delay. The delay occurs where one neuron _______ with another.

communicates

Temporal Summation

A phenomenon where repeated stimuli within a brief time have a cumulative effect..

Presynaptic Neuron

It is the neuron that delivers transmission.

Postsynaptic Neuron

It is the neuron that receives transmission.

Graded potentials may be either _______ (excitatory) or ________(inhibitory)

depolarizations, hyperpolarizations

A graded depolarization is known as an ______.

excitatory postsynaptic otential (EPSP)

It happens when the synaptic inputs from separate locations combine their effects on a neuron.

spatial summation

Sherrington concluded that pinching two points activated __________ , whose axons converged onto one neuron in the spinal cord.

separate sensory neurons

A combination of excitations exceeded the threshold and produced an _______.

action potential

______ summation and ______ summation ordinarily occur together.

Temporal, spatial

A pinch on the foot sends a message along a sensory neuron to an ______ that excites the ____ neurons connected to the flexor muscles of that leg and the extensor muscles of the other legs.

interneuron, motor

Inhibitory Postsynaptic Potential (IPSP)

The temporary hyperpolarization of a membrane.

An IPSP occurs when synaptic input selectively opens the gates for ________ to leave the cell (carrying a positive charge with them) or for _______ to enter the cell (carrying a negative charge).

potassium ions, chloride ions

What ion gates in the membrane open during an EPSP?

During an EPSP, sodium gates open.

What gates open during an IPSP?

During an IPSP, potassium or chloride gates open.

What is the difference between temporal summation and spatial summation?

Temporal summation is the combined effect of 2. quickly repeated stimulation at a single synapse. Spatial summation is the combined effect of several nearly simultaneous stimulations at several synapses onto one neuron.