Biological Bases of Behavior
The Biological domain asks how physiology produces behavior: how neurons signal, which transmitters carry which message, which structure does what, and how genes and hormones shape behavior. Expect lesion-to-symptom predictions, neurotransmitter-to-disorder matches, and items that force you to separate structure from function.
Neuron and synapse
- Resting potential is about −70 mV, maintained by the Na+/K+ pump. The action potential is an all-or-none depolarization (Na+ in) followed by repolarization (K+ out) and a refractory period.
- Dendrites receive graded potentials; the axon conducts all-or-none. At terminals, Ca2+ influx triggers vesicle release; transmission ends by reuptake, enzymatic breakdown (AChE), or diffusion.
- Agonists mimic or enhance a transmitter; antagonists block it. A drug that blocks reuptake is an agonist in effect.
Neuroanatomy
- Medulla: vital reflexes (breathing, heart rate). Pons: arousal and sleep relay. Cerebellum: coordination, balance, motor learning. Reticular formation: arousal.
- Thalamus: sensory relay except olfaction. Hypothalamus: homeostasis and the "four Fs." Amygdala: fear learning. Hippocampus: consolidation into long-term memory. Basal ganglia: movement initiation.
- Broca's area (left frontal) produces speech; Wernicke's area (left temporal) comprehends it. Wernicke's aphasia is fluent but meaningless speech with poor comprehension; Broca's aphasia is halting speech with intact comprehension.
- Roughly 95% of right-handers are left-hemisphere dominant for language; the right hemisphere handles spatial and prosodic processing.
Worked example
A stroke patient speaks in fluent, grammatical sentences that convey nothing, cannot follow simple commands, and seems unaware of the errors. Which lesion? Fluent output plus broken comprehension points to Wernicke's area. If output were sparse and effortful while comprehension stayed intact, Broca's area would fit. The fluency/comprehension double dissociation is the deciding evidence.
Traps that cost marks
- Swapping sympathetic (fight-or-flight: dilated pupils, inhibited digestion) with parasympathetic (rest-and-digest) effects.
- Treating structural and functional imaging as interchangeable: CT and MRI show structure; PET and fMRI show activity.
- Assuming "left hemisphere equals language" universally rather than as the typical pattern.