Nervous System: Structure, Function, and Neuron Types

What are the main functions of the nervous system?

Collect information, process and evaluate information, and initiate response.

What does the central nervous system consist of?

The brain and spinal cord.

What does the peripheral nervous system consist of?

Nerves and ganglia.

What is a ganglion?

A cluster of neuron cell bodies in the PNS.

What are the characteristics of neurons?

Excitability, conductivity, secretion, extreme longevity, and amitosis.

What is the role of dendrites in a neuron?

Dendrites receive input and transfer it to the cell body.

What is the function of the axon?

To conduct action potentials and release neurotransmitters at synaptic knobs.

What is retrograde transport?

Transport to the cell body, moving used materials for breakdown and recycling.

What are the two types of axonal transport mechanisms?

Fast axonal transport and slow axonal transport.

What is fast axonal transport?

Transport occurring at about 400 mm per day, involving movement along microtubules powered by motor proteins.

What is slow axonal transport?

Transport occurring at about 0.1 to 3 mm per day, resulting from the flow of axoplasm.

What is the role of Ca2+ in neurotransmitter release?

Calcium ions facilitate the release of neurotransmitters from synaptic vesicles.

How are neurotransmitters classified?

Based on chemical structure or function.

What is the function of acetylcholine as a neurotransmitter?

To transmit signals across synapses; it is removed from the synaptic cleft by enzymatic breakdown.

What is neuromodulation?

The process by which neurotransmitters influence the facilitation and inhibition of neuronal activity.

What is the resting membrane potential?

The electrical potential difference across the neuronal membrane when the neuron is not actively transmitting signals.

What is the difference between electrical and chemical synapses?

Electrical synapses allow direct ion flow between neurons, while chemical synapses use neurotransmitters to transmit signals.

What is an excitatory postsynaptic potential (EPSP)?

A depolarizing potential that makes a neuron more likely to fire an action potential.

What is an inhibitory postsynaptic potential (IPSP)?

A hyperpolarizing potential that makes a neuron less likely to fire an action potential.

What are the primary factors influencing the velocity of action potential propagation?

Axon diameter and the presence of myelin sheath.

What is the role of neurotransmitters in the nervous system?

To transmit signals between neurons and influence various physiological processes.

What are the four types of structural classifications of neurons?

Multipolar, bipolar, unipolar (pseudounipolar), and anaxonic neurons.

What type of neuron is most common and has many dendrites?

Multipolar neurons.

Where are bipolar neurons typically found?

In the retina of the eye.

What is the function of sensory neurons?

They conduct input from somatic and visceral receptors to the CNS.

What type of neurons are motor neurons?

Efferent neurons that conduct output from the CNS to effectors.

What is the primary function of interneurons?

To receive, process, and integrate information from other neurons.

What is a synapse?

The place where a neuron connects to another neuron or an effector.

What are the two types of synapses?

Chemical synapses and electrical synapses.

What is the role of astrocytes in the CNS?

They help form the blood-brain barrier and regulate the chemical environment around neurons.

What do ependymal cells do?

They line cavities in the brain and spinal cord and produce cerebrospinal fluid (CSF).

What is the function of microglia?

They act as immune cells in the CNS, engulfing infectious agents and debris.

What are the two primary factors that determine the effectiveness of PNS axon regeneration?

The integrity of the neuron cell body and the amount of remaining neurilemma.

What is the function of the myelin sheath?

To insulate axons and facilitate faster action potential propagation.

What is a glioma?

A tumor originating from glial cells in the CNS.

What happens during multiple sclerosis?

There is progressive demyelination of neurons in the CNS due to an autoimmune response.

What is Guillain-Barré syndrome?

A condition characterized by loss of myelin from peripheral nerves due to inflammation.

What is the role of neurofibril nodes (nodes of Ranvier)?

They are gaps between myelinated segments that facilitate rapid signal conduction.

What is the significance of the neurilemma?

It is essential for the regeneration of PNS axons after injury.

What is the primary function of dendrites?

To receive signals from other neurons.

What is the role of axons in neurons?

To transmit action potentials away from the neuron cell body.

What are synaptic vesicles?

They store neurotransmitters that are released during synaptic transmission.

What is the process of axon regeneration in the PNS?

Involves sealing off the axon, degeneration of distal parts, formation of a regeneration tube, and regrowth guided by neurolemmocytes.

What are pumps in the context of neurons?

Membrane proteins that maintain a concentration gradient by moving substances against their concentration gradient, requiring cellular energy.

What types of pumps are present in neurons?

Na+-K+ pumps and Ca2+ pumps.

What are channels in the context of neurons?

Protein pores in the membrane that allow ions to move down their concentration gradients when open.

What are leak channels?

Passive channels that are always open for continuous diffusion of ions.

What are chemically gated channels?

Channels that are normally closed and open when a neurotransmitter binds.

What are voltage-gated channels?

Channels that are normally closed but open when the membrane charge changes.

What are the three states of voltage-gated Na+ channels?

1. Resting state: activation gate closed, inactivation gate open. 2. Activation state: activation gate open, inactivation gate open. 3. Inactivation state: activation gate open, inactivation gate closed.

What are modality gated channels?

Channels that are normally closed but open in response to specific sensory stimuli, such as changes in temperature or pressure.

What is the role of Na+/K+ pumps in neurons?

They maintain resting membrane potential and contribute about -3 mV to the total resting membrane potential.

What is resting membrane potential (RMP)?

The charge difference across the membrane, typically -70 mV, measured with microelectrodes.

What is the significance of K+ diffusion in RMP?

K+ diffusion out of the cell is the most important factor in setting RMP, as it is influenced by both concentration and electrical gradients.

How does Na+ leakage affect RMP?

Na+ diffuses in due to its concentration gradient, making RMP less negative than it would be if only K+ were leaking.

What is Ohm's Law as it applies to neurons?

Current (I) = Voltage (V) / Resistance (R); current increases with larger voltage and smaller resistance.

What is the relationship between ion movement and electrical current in neurons?

Charged particles (ions) generate current when they diffuse through channels, creating voltage across the membrane.

What is the distribution of pumps and channels in the plasma membrane of a neuron?

Includes leak channels, Na+/K+ pumps, and various gated channels in different functional segments.

What functional segment of a neuron contains chemically gated channels?

The receptive segment (dendrite and cell body).

Which functional segments of a neuron contain voltage-gated channels?

The initial segment (axon hillock), conductive segment (axon and branches), and transmissive segment (synaptic knobs).

What is the effect of resistance on ion flow in neurons?

Resistance opposes the movement of charged particles; an increase in resistance lowers current.

What creates the membrane potential in neurons?

The uneven distribution of ions across the plasma membrane, primarily K+ and Na+.

What happens to voltage-gated Na+ channels during an action potential?

They transition from resting to activation state, allowing Na+ to flow into the cell.

What is the resting membrane potential (RMP)?

The electrical potential difference across the neuronal membrane when the neuron is not actively transmitting signals.

How is RMP established in neurons?

RMP is established by the differential distribution of ions across the neuronal membrane, primarily through the action of the sodium-potassium pump.

What role do chemically gated ion channels play in neurons?

They open in response to neurotransmitter binding, allowing ions to flow and generating graded potentials.

What are graded potentials?

Small, short-lived changes in the RMP that can cause depolarization or hyperpolarization.

Where does the summation of EPSPs and IPSPs occur?

At the axon hillock.

What is the threshold membrane potential required to initiate an action potential (AP)?

Typically around -55 mV.

What happens if the threshold is reached at the axon hillock?

Voltage-gated channels open, and an action potential is generated.

What is spatial summation?

The process where multiple locations on a neuron's receptive regions receive neurotransmitters simultaneously, generating postsynaptic potentials.

What is temporal summation?

The process where a single presynaptic neuron releases neurotransmitters repeatedly in a short time, generating multiple EPSPs.

What is the all-or-none law in action potentials?

If the threshold is reached, an action potential is generated and propagated without loss of intensity; if not reached, no action potential occurs.

What occurs during the depolarization phase of an action potential?

Na+ enters the neuron through voltage-gated Na+ channels, causing a gain of positive charge.

What occurs during the repolarization phase of an action potential?

K+ exits the neuron through voltage-gated K+ channels, returning the membrane potential to a negative value.

What is the refractory period?

The time after an action potential during which it is difficult or impossible to initiate another action potential.

What is the absolute refractory period?

A period during which no stimulus can initiate another action potential because Na+ channels are open and then inactivated.

What is the relative refractory period?

A period just after the absolute refractory period when another action potential is possible but requires a stronger stimulus.

How does hyperpolarization occur during repolarization?

K+ channels remain open longer, causing the membrane potential to become more negative than the resting membrane potential.

What is the role of the axolemma in neurons?

The axolemma conducts action potentials along the axon.

What triggers the opening of voltage-gated channels during an action potential?

The depolarization of the membrane to the threshold level.

What is the significance of local anesthetics in relation to action potentials?

Local anesthetics block the function of voltage-gated Na+ channels, preventing action potentials from being generated.