Neurons and Synapses

Flashcards covering key vocabulary related to neurons and synapses, aimed at aiding in the understanding of the nervous system.

Neuron

A cell that transmits electrical impulses.

Dendrite

short, branched nerve fibers.  Many are located in the brain, for example.

Thin processes from the cell body that receive stimuli.

Cell body or soma

contains the organelles to keep the neuron alive and functioning

Axon

A long extension of the neuron that transmits nerve impulses to other neurons or effectors over long distances.

Motor axons

may be very long and, in the peripheral nervous system, many are myelinated

Axon branches of motor neurons

have synaptic knobs at each end, which release neurotransmitters that are chemicals that transmit the impulse between neurons or between a neuron and a muscle cell

Myelin Sheath

A fatty layer that insulates the axon and increases the speed of impulse transmission.

Synapse

The junction between two neurons or between a neuron and an effector cell.

Synapses exist between:

•Neurons

•Neurons and receptor cells

•Involved in sensory reception

•Neurons and effector cells

•Respond to a stimulus: muscle cells, gland cells, etc.

Neurotransmitter

Chemicals that transmit impulses across the synapse.

Action Potential

A rapid change in membrane potential that occurs when a neuron generates an impulse.

two phases:

•Depolarization: change form negative to positive

•Repolarization: Change back from positive to negative

Resting Potential

The state of a neuron when it is not transmitting an impulse, typically around -70 mV.

•Inside of axon is negatively charged, with respect to the outside

Saltatory Conduction

The process by which nerve impulses jump from one node of Ranvier to the next along a myelinated axon.

•Impulses travel in one direction-never backwards

Node of Ranvier

Gaps in the myelin sheath where action potentials are generated.

Calcium Influx

The influx of calcium ions that triggers the release of neurotransmitters from synaptic vesicles.

Potassium Ion (K+)

An ion that flows out of the neuron during repolarization.

Sodium Ion (Na+)

An ion that flows into the neuron during depolarization.

Voltage-Gated Ion Channels

Channels that open or close in response to changes in membrane potential, allowing ions to enter or exit the neuron.

CNS

Central Nervous System, consisting of the brain and spinal cord.

PNS

Peripheral Nervous System, consisting of all neural elements outside the CNS.

Myelination

The process of forming a myelin sheath around a nerve fiber.

Myelination allows for

Saltatory conduction

Impulse Direction

The direction in which an electrical signal travels along a neuron.

post-synaptic cell

may be another neuron or an effector cells such as glands, muscles, etc.

nerve impulses are carried by-

temporary shifts in electrical charge

The charge is changed by moving ___ in and ___ out of the axon

SODIUM ions in

And

POTASSIUM ions out

Depolarization

Sodium ions (Na+) flow into the axon

Repolarization

Potassium ions (K+) flow out of the axon

Nerve fibers are

myelinated

Myelin

the membrane of Schwann cells, wrapped around a nerve fiber many times

Myelination insulates-

the axon, thereby increasing the speed of the impulse

Na⁺/K⁺ pumps

generate resting potential

*Reminder: 3 Na⁺ Out and 2 K⁺ in.  This maintains the concentration gradient for both ions

Oscilloscope traces

Nerve impulses work on an “all or none” principal. 

The impulse isonly initiatedif the threshold potential is reached.

The impulse is carried from node to node due to

action potentials being propagated along the axon

local currents

when ions migrate laterally

provide the threshold potential to open sodium and potassium voltage-gates

sodium and potassium channels are

voltage-gated

•Nerve impulses work on an “all or none” principal. 

•The impulse isonly initiated if-

the threshold potential is reached

pre-synaptic neurons

depolarized, they release a neurotransmitter into the synapse

Depolarization opens

voltage gated calcium channels

Calcium influx signals

synaptic vesicles to fuse with pre-synaptic membrane, releasing neurotransmitter (Acetylcholine in this case) by exocytosis

Acetylcholine (ACh) diffuses across

synaptic cleft and binds to receptor proteins on postsynaptic membrane

This binding of ACh opens

sodium ion channels and an action potential is initiated in the postsynaptic neuron

After ACh binds to receptor

it is rapidly broken down and reabsorbed by presynaptic neuron

This is called a cholinergic synapse

since acetylcholine is the active neurotransmitter