Nervous System Organization, Neurons, Synapses, and CNS Function (Flashcards)

A comprehensive set of Q&A flashcards covering neuron structure, synapses, CNS organization, neurotransmitters, and electrical signaling.

What is the basic functional unit of the nervous system?

Neuron.

Approximately how many neurons are in the human nervous system?

More than 100 billion neurons.

How does the output signal travel from one neuron to the next?

By way of a single axon that branches to other parts, with signals typically passing from the axon to the dendrites of the next neuron across a synapse.

What is the soma and its role?

Cell body; the support center of the neuron.

What is the function of dendrites?

Receive messages from other cells.

What does the term synapse refer to?

The junction between two neurons where signals pass, usually in the forward direction from presynaptic axon to postsynaptic membrane.

What are the two parts of the CNS as described in the notes?

Sensory receptors and motor receptors.

What are nociceptors?

Pain receptors.

What are effectors in the nervous system?

Muscles and glands that perform functions dictated by nerve signals.

What does the autonomic nervous system control?

Smooth muscles, glands, and other internal bodily systems.

Name the CNS structures that can control skeletal muscles.

Spinal cord, reticular formation (medulla, pons, mesencephalon), basal ganglia, cerebellum, and motor cortex.

What does the motor axis of the nervous system refer to in terms of effectors and levels?

Effectors are skeletal muscle, smooth muscle, and glands; Levels include spinal cord, reticular form, basal ganglia, cerebellum, and motor cortex.

How should the spinal cord level be understood beyond just a conduit for signals?

It mediates walking, reflexes, automatic responses, and various autonomic functions; not merely a conduit.

What functions are controlled by the lower brain/subcortical level?

Subconscious activities, arterial pressure and respiration, equilibrium, feeding reflexes, and emotions.

What are the roles of the higher brain/cortical level?

Determinative and precise operations using cortical information; supports thought processes and memory; requires coordination with lower centers.

What is the integrative function of the nervous system?

Processing incoming information to produce appropriate mental and motor responses; over 99% of sensory information is discarded as irrelevant.

What is the role of the synapse in processing information?

It determines the direction of signal spread; can be facilitatory or inhibitory; signals can be amplified or redirected by neurotransmitters and receptors.

What is a chemical synapse?

A junction where most CNS transmission occurs via neurotransmitters.

What are the main components of a presynaptic terminal?

Terminal knobs/buttons/end-feet, synaptic cleft, synaptic vesicles with neurotransmitter, mitochondria, and voltage-gated Ca++ channels.

What are the two components of postsynaptic receptor proteins?

Binding components and ionophore components.

What are the two types of ionophore components?

Chemically activated ion channels (Na+, K+, Cl−) and enzymes that modulate receptor numbers and second messengers.

What is the mechanism that leads to transmitter release at the presynaptic terminal?

Depolarization causes Ca++ influx, Ca++ binds release sites, triggering exocytosis of neurotransmitter into the synaptic cleft.

What are the fates of transmitter substances after release?

Diffusion, enzymatic destruction (e.g., acetylcholine with cholinesterase), and reuptake into the presynaptic terminal.

What are the postsynaptic receptors for excitatory and inhibitory transmission?

Excitatory receptors open Na+ channels; inhibitory receptors open Cl− channels or increase K+ conductance; can alter intracellular metabolism.

Name the classes of neurotransmitters mentioned.

Small molecule transmitters (ACH, amines, amino acids) and neuropeptides (neuroactive peptides).

What is the Dale Principle?

Release of only a single type of transmitter by each neuron at all of its terminals.

What is the resting membrane potential (RMP) of a neuron?

Approximately -65 millivolts.

Which pumps/ion gradients contribute to the resting membrane potential?

Na+/K+ pump extrudes Na+ and brings in K+, creating a negative interior; Na+ approximately +61 mV, K+ approximately -86 mV, Cl− approximately -70 mV per Nernst potentials.

What maintains uniform potential inside the soma?

A highly conductive intracellular solution; changes in one part of the intra-somal fluid create nearly identical changes elsewhere; large soma diameter reduces resistance.

What is an EPSP and what does it cause?

Excitatory postsynaptic potential; increased Na+ and K+ permeability causing depolarization (e.g., from -65 mV to -45 mV).

Where does the action potential typically begin and why?

At the axon hillock due to a higher density of voltage-gated Na+ channels; EPSP at the axon hillock reaches threshold to trigger AP.

What is an IPSP and how does it occur?

Inhibitory postsynaptic potential; opening of K+ and Cl− channels causing hyperpolarization or decreased excitability.

What is presynaptic inhibition?

A presynaptic mechanism where transmitter release is reduced by a synapse altering Ca++ entry, leading to less excitation of the postsynaptic neuron.

What are spatial and temporal summation?

Spatial: multiple simultaneous postsynaptic potentials from different terminals; Temporal: rapid, repeated EPSPs from a single terminal.

What determines the rate of firing of a neuron?

The excitatory state, i.e., the balance of excitation vs. inhibition; firing occurs when excitation exceeds threshold.

What is synaptic fatigue and what causes it?

A decline in postsynaptic firing with rapid stimulation due to transmitter depletion, receptor desensitization, and ion concentration changes.

What is the effect of hypoxia on synaptic transmission?

Oxygen deprivation reduces neuronal excitability; severe hypoxia can render neurons inexitable and cause unconsciousness.

How do caffeine and related compounds affect neuronal excitability?

They increase excitability by lowering the threshold for excitation.

What effect does strychnine have on neurons?

Increases excitability by inhibiting inhibitory glycine in the spinal cord, causing tonic muscle spasms.

How do general anesthetics affect synaptic transmission?

They raise the threshold for excitation, reducing synaptic transmission, often by altering membrane properties.

How do acidosis and alkalosis affect neuronal activity?

Alkalosis increases excitability and can trigger seizures; acidosis depresses activity and can lead to coma.

What is the effect of hypocalcemia on transmitter release?

Decreases transmitter release by reducing Ca++ entry into the presynaptic terminal.