MCAT Biology Chapter 4: Nervous System and Neural Signaling

What are the main signaling units of the nervous system?

Neurons

What type of cells support neurons and maintain their environment?

Glial cells

What is the primary function of neurons?

To transmit electrical impulses and translate them into chemical signals.

What is the central part of a neuron called?

The cell body or soma.

What role do dendrites play in a neuron?

Dendrites receive signals from other neurons and carry those signals toward the soma.

What is the axon hillock's function?

It acts as a gatekeeper, initiating an action potential if the signal reaches a certain threshold.

What does the axon do?

Carries the action potential away from the soma.

What is the myelin sheath?

A fatty insulating layer that surrounds the axon, allowing electrical impulses to travel faster.

What cells produce myelin in the central nervous system?

Oligodendrocytes.

What cells produce myelin in the peripheral nervous system?

Schwann cells.

What is saltatory conduction?

A process where the electrical signal jumps from one node of Ranvier to another, speeding up transmission.

What is the synaptic cleft?

The tiny space between neurons where neurotransmitters are released.

What happens at the nerve terminal?

The electrical signal is converted into a chemical message through the release of neurotransmitters.

What is an action potential?

The electrical signal that travels down the axon when a neuron reaches a certain threshold.

What is a synapse?

The communication point between two neurons, consisting of the axon terminal, synaptic cleft, and receiving neuron membrane.

How are nerves organized in the peripheral nervous system?

Multiple neurons are bundled together to form a nerve.

What are ganglia?

Clusters of cell bodies of neurons of the same type in the peripheral nervous system.

What are tracts in the central nervous system?

Bundles of axons that carry one type of information, either sensory or motor.

What are nuclei in the central nervous system?

Groups of cell bodies of neurons in the same tract.

What are astrocytes?

Star-shaped glial cells that help form the blood-brain barrier and provide support to neurons.

What is the blood-brain barrier?

A selective filter that controls what substances can pass from the bloodstream into the brain's nervous tissue.

What is the role of glial cells?

To nourish neurons, provide physical support, maintain chemical stability, and produce myelin.

What triggers the release of neurotransmitters?

The arrival of an action potential at the axon terminal.

What are nodes of Ranvier?

Exposed segments of the axon between myelin sheaths critical for speeding up transmission.

What happens when a neuron receives enough input?

It generates an action potential that travels down the axon.

What is the main function of neurotransmitters?

To carry messages across the synaptic cleft to the next cell.

What is the role of the axon in a neuron?

To conduct electrical signals away from the soma toward the target cell.

What role do astrocytes play in the nervous system?

Astrocytes provide nutrients to neurons and help regulate the extracellular environment, including ion and neurotransmitter concentrations.

What is the function of ependymal cells?

Ependymal cells line the ventricles of the brain and produce cerebrospinal fluid, which cushions the brain and helps transport nutrients and waste.

What is the role of microglia?

Microglia act as the immune defense of the central nervous system, engulfing waste products, cellular debris, and invading pathogens.

What is the function of oligodendrocytes?

Oligodendrocytes are found in the central nervous system and wrap multiple axons in myelin to increase conduction speed.

What do Schwann cells do?

Schwann cells are found in the peripheral nervous system and wrap around a single axon to form the myelin sheath segment by segment.

What does the all-or-nothing principle refer to in neural communication?

The all-or-nothing principle means that an action potential either fires completely or does not fire at all.

What is the resting membrane potential?

The resting membrane potential is the voltage difference across a neuron's membrane when the cell is at rest, typically around -70 millivolts.

What ions primarily contribute to the resting membrane potential?

Potassium ions (K⁺) and sodium ions (Na⁺) contribute to the resting membrane potential.

How do potassium ions affect the resting membrane potential?

Potassium ions exit the cell through potassium leak channels, making the inside of the cell more negative.

What effect do sodium ions have on the resting membrane potential?

Sodium ions enter the cell through sodium leak channels, making the inside of the cell less negative.

What is the function of the sodium-potassium ATPase pump?

The sodium-potassium ATPase pump maintains the resting membrane potential by pumping three sodium ions out and two potassium ions into the cell.

What is the role of the axon hillock in neuron firing?

The axon hillock integrates incoming signals and determines if the membrane potential is sufficient to trigger an action potential.

What are excitatory signals?

Excitatory signals make the neuron more likely to fire by causing depolarization, which makes the membrane potential less negative.

What are inhibitory signals?

Inhibitory signals decrease the likelihood of firing by causing hyperpolarization, making the membrane potential more negative.

What is summation in the context of neural signals?

Summation is the process by which multiple signals combine their effects to determine if the threshold for firing an action potential is reached.

What is temporal summation?

Temporal summation occurs when multiple signals come from the same neuron in rapid succession, increasing the chance of reaching threshold.

What is spatial summation?

Spatial summation occurs when signals arrive simultaneously from multiple different neurons at various locations on the dendritic tree.

What is the threshold for firing an action potential?

The threshold for firing an action potential is typically between -55 and -40 millivolts.

What happens if the threshold is not reached at the axon hillock?

If the threshold is not reached, no action potential is triggered, and the neuron does not fire.

What is the significance of the resting state of a neuron?

The resting state is critical for setting the stage for action potentials and allowing the neuron to respond to stimuli.

What is the role of neurotransmitters in neural communication?

Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another.

How does the movement of ions contribute to the action potential?

The rapid influx of sodium ions followed by the efflux of potassium ions generates the action potential, allowing the signal to propagate along the axon.

What is the importance of myelin in neural conduction?

Myelin insulates axons, increasing the speed of electrical signal transmission along the neuron.

What is the function of dendrites?

Dendrites receive incoming signals from other neurons and transmit them to the cell body.

What is the significance of the action potential's all-or-nothing response?

The all-or-nothing response ensures that signals are transmitted reliably without partial responses.

What is the resting membrane potential of a neuron?

Typically around -70 millivolts.

What happens when a neuron reaches threshold potential?

Voltage-gated sodium channels open, allowing sodium ions (Na⁺) to flood into the cell.

What is the phase called when the membrane potential rises due to sodium influx?

Depolarization.

What is the peak membrane potential reached during depolarization?

Around +35 millivolts.

What occurs after the peak of depolarization?

Sodium channels inactivate and voltage-gated potassium channels open.

What is the phase called when potassium ions (K⁺) flow out of the cell?

Repolarization.

What is hyperpolarization?

A brief dip in membrane potential that makes the inside of the cell more negative than the resting potential.

What are the two types of refractory periods?

Absolute refractory period and relative refractory period.

What characterizes the absolute refractory period?

It is impossible for another action potential to occur, regardless of stimulus strength.

What characterizes the relative refractory period?

Another action potential can occur, but it requires a stronger-than-normal stimulus.

What role does the Na⁺/K⁺ ATPase pump play after an action potential?

It restores the ion gradients by pumping three sodium ions out and two potassium ions in.

What is impulse propagation?

The process by which the action potential moves from the cell body toward the axon terminal.

How does the action potential propagate in unmyelinated axons?

It propagates continuously, with each segment depolarizing and repolarizing in turn.

What are the nodes of Ranvier?

Small exposed regions of myelinated axons that contain dense clusters of voltage-gated ion channels.

What happens when an action potential reaches the axon terminal?

It triggers the release of neurotransmitters into the synapse.

What triggers the release of neurotransmitters from vesicles?

The opening of voltage-gated calcium channels when the action potential arrives at the axon terminal.

What happens to neurotransmitters after they bind to receptors on the postsynaptic cell?

They initiate a response, possibly triggering another action potential.

What are the three main ways neurotransmitters are removed from the synapse?

Enzymatic breakdown, reuptake by the presynaptic neuron, or diffusion away from the synaptic cleft.

What is the role of enzymes in neurotransmitter removal?

They chemically degrade neurotransmitters into inactive components.

What is the effect of a stronger stimulus on action potentials?

It increases the frequency of action potentials, not their size.

What is the significance of the refractory periods in neuronal signaling?

They ensure that signals travel in one direction and prevent immediate repeated firing.

What happens during the depolarization phase of an action potential?

Sodium ions enter the neuron, causing the membrane potential to become more positive.

Why do action potentials only move in one direction?

Due to the refractory state of the previously activated segment of the axon.

What is the primary ion responsible for depolarization during an action potential?

Sodium ions (Na⁺).

What is the primary ion responsible for repolarization during an action potential?

Potassium ions (K⁺).

What is the primary function of the nervous system?

To detect stimuli, process information, and coordinate appropriate responses.

What are the three main types of neurons?

Sensory neurons, motor neurons, and interneurons.

What do sensory neurons do?

They carry information into the central nervous system from sensory receptors.

What is the role of motor neurons?

They carry instructions from the central nervous system to muscles and glands.

What are interneurons responsible for?

They connect sensory and motor neurons and are crucial for reflexes and higher-order processing.

What are the two main branches of the nervous system?

The central nervous system (CNS) and the peripheral nervous system (PNS).

What does the central nervous system consist of?

The brain and spinal cord.

What is the function of the spinal cord?

It serves as the main communication highway between the brain and the body and handles certain reflexes.

What does the peripheral nervous system include?

All the nerves that branch off the CNS and reach the rest of the body.

What is the somatic nervous system responsible for?

Controlling voluntary movements and relaying sensory information to the CNS.

What does the autonomic nervous system govern?

Involuntary functions such as heart rate, digestion, and respiratory rate.

What are the two divisions of the autonomic nervous system?

The sympathetic and parasympathetic nervous systems.

What is the primary role of the parasympathetic nervous system?

To conserve energy and support functions during rest, often described as 'rest and digest.'

What effects does the parasympathetic nervous system have on the body?

It constricts pupils, slows heart rate, stimulates digestion, and promotes urinary function.

What is the sympathetic nervous system known for?

Preparing the body for rapid action during stress, often described as 'fight or flight.'

What effects does the sympathetic nervous system have on the body?

It dilates pupils, increases heart rate, dilates airways, and inhibits digestive activity.

What are reflexes?

Automatic, involuntary responses to specific stimuli that occur faster than conscious processing.

What is a reflex arc?

A simple neural circuit that coordinates reflex actions, often bypassing the brain.

What are the components of a reflex arc?

A sensory neuron, a motor neuron, and often one or more interneurons.

What is a monosynaptic reflex arc?

A reflex arc where the sensory neuron fires directly onto the motor neuron, creating a fast response.

What is a polysynaptic reflex arc?

A reflex arc where the sensory neuron synapses on interneurons before activating motor neurons.

What is an example of a monosynaptic reflex?

The knee-jerk reflex.

What happens in a withdrawal reflex?

Interneurons activate motor neurons to contract flexor muscles and inhibit opposing muscles.