BIO NMDCAT

Withdrawal from painful stimuli is a spinal reflex that produces a rapid response before the brain becomes consciously aware of the stimulus. The cerebrum interprets pain after the reflex has occurred.

The pons serves as a bridge between different parts of the brain, especially the cerebrum and cerebellum. It also contains respiratory centers that help regulate breathing rhythm.

The medulla oblongata contains vital autonomic centers controlling respiration, cardiac activity, and vasomotor functions. The cerebrum is involved in higher mental functions, the cerebellum coordinates movement, and the hypothalamus regulates homeostasis but does not directly control these vital reflexes.

The cerebellum coordinates voluntary muscle movements and maintains posture and balance. Damage produces ataxia, characterized by uncoordinated movements without causing paralysis.

The thalamus receives and relays almost all sensory information to the cerebral cortex. The hypothalamus regulates homeostasis, while the pons and medulla mainly conduct impulses and control autonomic functions.

The hypothalamus acts as the body's thermostat. It detects changes in temperature and initiates sweating and vasodilation to lower body temperature.

The cerebrum is the largest part of the brain and controls intelligence, memory, learning, reasoning, speech, emotions, and voluntary activities. The remaining options are functions of lower brain centers.

The cerebellum compares intended movement with actual movement and makes continuous corrections to maintain posture and balance. This function is essential during walking on uneven ground.

Hyperkalemia reduces the concentration gradient for K⁺. As a result, less K⁺ leaves the cell through leak channels, leaving more positive charge inside and shifting the resting membrane potential toward depolarization.

Irritability (excitability) is the physiological ability of a neuron or muscle cell to respond to a stimulus by generating an electrical signal. Conductivity refers to its ability to transmit that signal.

Ependymal cells are ciliated, cuboidal-to-columnar glial cells that line the fluid-filled cavities of the CNS (ventricles and central canal) and help secrete and circulate cerebrospinal fluid.

Group A fibers (like somatic motor fibers and large sensory fibers for touch and position) are the thickest, most heavily myelinated fibers in the body, providing the fastest nerve conduction velocities.

Axoaxonic synapses occur when one axon terminal synapses onto another axon terminal. They regulate (facilitate or inhibit) the amount of calcium that enters the second terminal, modulating neurotransmitter release.

Endorphins and enkephalins are endogenous opioids that bind to opioid receptors in the brain and spinal cord, powerfully blocking the transmission and perception of pain signals.

In the PNS, a bundle of axons is called a nerve. In contrast, a bundle of axons in the CNS is called a tract. A ganglion is a cluster of cell bodies in the PNS.

Neuromuscular junctions (motor end plates) are the highly specialized synapses where motor neurons release acetylcholine to trigger skeletal muscle contraction.

Electrical synapses do not use neurotransmitters; instead, they utilize gap junctions (connexons) that physically connect the cytoplasm of adjacent cells, allowing instantaneous, bidirectional current flow.

Because a neuron cannot fire another action potential during the absolute refractory period regardless of stimulus strength, this period sets a strict upper limit on how frequently the neuron can fire.

Following peak depolarization, voltage-gated K⁺ channels open and K⁺ rushes out of the cell down its electrochemical gradient, restoring the negative internal charge during repolarization.