Nervous System: Nervous Tissue Anatomy & Physiology Practice Flashcards

Comprehensive vocabulary flashcards covering PNS and CNS axon regeneration, membrane pumps and channels, Ohm's law, and the physiologic segments and potentials of neurons.

Wallerian degeneration

The process occurring during axon regeneration where the portion of the axon and myelin sheath distal to the cut disintegrate, while the neurilemma survives.

Regeneration tube

A structure formed by the neurilemma and endoneurium that guides the regeneration of a severed PNS axon.

Pumps

Membrane proteins that maintain a concentration gradient by moving substances up (against) their concentration gradient using cellular energy.

Leak (passive) channels

Protein pores in the membrane that are always open, allowing for the continuous diffusion of ions down their concentration gradients.

Chemically gated channels

Channels that are normally closed but open in response to a neurotransmitter binding to them.

Voltage-gated channels

Channels that are normally closed but open in response to changes in the membrane charge.

Modality-gated channels

Channels found in sensory receptors that open in response to specific sensory stimuli, such as changes in temperature, pressure, or light.

Resting state (Voltage-gated $Na^+$ channel)

The state where the activation gate is closed and the inactivation gate is open, preventing the entry of $Na^+$.

Activation state (Voltage-gated $Na^+$ channel)

The state where both the activation and inactivation gates are open, allowing $Na^+$ to move through the channel.

Inactivation state (Voltage-gated $Na^+$ channel)

The state where the activation gate is open but the inactivation gate is closed, preventing the entry of $Na^+$.

Receptive segment

The functional segment of a neuron comprising the dendrites and cell body, which contains chemically gated channels.

Initial segment

The functional segment located at the axon hillock, containing voltage-gated $Na^+$ and $K^+$ channels.

Conductive segment

The functional segment consisting of the axon and its branches, containing voltage-gated $Na^+$ and $K^+$ channels.

Transmissive segment

The functional segment at the synaptic knobs, containing voltage-gated $Ca^{2+}$ channels and $Ca^{2+}$ pumps.

Voltage ($V$)

The amount of difference in electrical charge between two places, representing potential energy, measured in volts or millivolts.

Current ($I$)

The movement of charged particles, such as ions, across a barrier separating them.

Resistance ($R$)

The opposition to the movement of charged particles, such as the barrier represented by the phospholipid bilayer.

Ohm’s law

An electrical principle stating that current is equal to voltage divided by resistance: $I = V / R$.

Resting membrane potential (RMP)

The electrical charge difference across the membrane of a resting neuron, typically $-70\,mV$.

Graded potentials

Small, short-lived changes in the resting membrane potential established in the receptive segment by the opening of chemically gated ion channels.

Excitatory postsynaptic potential (EPSP)

A graded potential resulting in depolarization, typically caused by the entry of $Na^+$.

Inhibitory postsynaptic potential (IPSP)

A graded potential resulting in hyperpolarization, caused by $K^+$ exit or $Cl^-$ entry.

Threshold

The minimum voltage change required to initiate an action potential, typically about $-55\,mV$.

Spatial summation

The process where multiple locations on a cell’s receptive regions receive neurotransmitters simultaneously, and their resulting postsynaptic potentials are added.

Temporal summation

The process where a single presynaptic neuron repeatedly releases neurotransmitters within a very short period, producing multiple EPSPs that are added.