Neurons

The efferent (motor) pathway carries signals away from the CNS to the target effectors (muscles or glands). The afferent (sensory) pathway carries signals toward the CNS.

The patellar reflex is a monosynaptic spinal stretch reflex mediated specifically by the femoral nerve and the lumbar spinal cord segments L2, L3, and L4.

The Na⁺/K⁺ pump is an active transport ATPase that hydrolyzes ATP to move sodium and potassium against their concentration gradients, consuming a massive portion of the neuron's metabolic energy.

Conduction velocity is positively correlated with both axon diameter (reducing internal electrical resistance) and the presence of myelination (allowing fast saltatory conduction).

Synaptic fatigue occurs when the rate of neurotransmitter release exceeds the rate of its synthesis and recycling, causing a temporary failure of synaptic transmission despite incoming action potentials.

Depolarization refers to any shift in membrane potential toward a less negative (or more positive) value, generally caused by the influx of positive ions like sodium.

Norepinephrine (and epinephrine from the adrenal medulla) acts on sympathetic target organs to mediate the 'fight or flight' stress responses, such as increased heart rate and bronchodilation.

Parkinson's disease is characterized by the selective death of dopaminergic neurons in the substantia nigra of the midbrain, leading to tremors, rigidity, and loss of motor control.

Nodes of Ranvier are the unmyelinated gaps between adjacent myelin segments (internodes) where action potentials are regenerated during saltatory conduction.

Because the membrane segment immediately behind the advancing action potential is in its refractory period (Na⁺ channels are inactivated), the impulse cannot spread backward, ensuring unidirectional propagation.

Multiple sclerosis is an autoimmune disorder characterized by the progressive demyelination of axons in the CNS, which disrupts saltatory conduction and leads to severe neurological deficits.

Temporal summation occurs when a single presynaptic neuron fires multiple times in rapid succession, allowing the resulting graded potentials to add together before the previous ones dissipate.

A nerve fiber consists of an axon (axis cylinder) along with its surrounding myelin sheath and neurilemma (Schwann cell sheath). The term does not typically include the cell body or dendrites.

Once the threshold voltage is reached, the action potential occurs with a constant, maximum amplitude independent of stimulus strength. Stronger stimuli increase the frequency of impulses, not their amplitude.

At rest, sodium leak channels are very rare compared to abundant potassium leak channels, making the resting membrane highly impermeable to Na+ and highly permeable to K+.

The arrival of an action potential at the synaptic knob opens voltage-gated Ca²⁺ channels. The resulting Ca²⁺ influx causes synaptic vesicles to fuse with the presynaptic membrane and release their contents.

Acetylcholine (ACh) is the primary neurotransmitter of the parasympathetic nervous system (both pre- and postganglionic), while the sympathetic system predominantly relies on norepinephrine for postganglionic signaling.

Neurotransmitters bind to specific ligand-gated receptors on the postsynaptic membrane, which undergo a conformational change to open ion channels and generate graded potentials.

An EPSP involves the opening of cation channels (usually Na⁺), leading to a localized, graded depolarization that makes the postsynaptic neuron more likely to fire an action potential.