Behavior and Biology for the MCAT: Everything You Need to Know
/Learn key MCAT concepts about behavior and biology, plus practice questions and answers
(Note: This guide is part of our MCAT Psychology and Sociology series .)
Part 1: Introduction to biology and behavior
Part 2: Anatomy of the nervous system
a) Divisions of the nervous system
b) Neurotransmitters
c) Regions of the brain
Part 3: Reflexes and innate behavior
Part 4: Methods used to study the brain
Part 5: High-yield terms
Part 6: Passage-based questions and answers
Part 7: Standalone questions and answers
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Part 1: Introduction to biology and behavior
Behavior refers to any and all of the actions our bodies perform: whether they are intentional, such as solving a mathematical equation, or unintentional, such as a knee-jerk reflex. Behavior can also include personality, cognition, and decision-making.
Our behavior is influenced by a complex interplay between our environment, our genes, and a variety of biological systems. Of these biological systems, perhaps the most important is the nervous system. In this guide, we’ll begin to introduce the role of the nervous and endocrine systems in shaping our behavior and interactions with the environment. What are the specific structures and pathways that are important to our behavior? And what happens to our behavior when these biological systems are disrupted or damaged?
The information presented in this guide will describe key aspects of the nervous system that are relevant to behavior. To better understand the nervous system in its entirety, be sure to refer to our guide on the nervous system.
Throughout this guide, several important keywords will be given in bold. You are encouraged to try creating your own definitions and examples to better aid your understanding. Similarly, we encourage you to sketch diagrams and annotate them with your own knowledge to deepen your understanding of different concepts. At the end of this guide, there are also MCAT-style practice questions that will test your knowledge of this material.
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Part 2: Anatomy of the nervous system
a) Divisions of the nervous system
The nervous system can be divided into the central nervous system (the brain and spinal cord) and the peripheral nervous system. The names of these divisions of the nervous system are intuitive; they match their location and function. After all, the brain and spinal cord are responsible for processing information and coordinating tasks with the peripheral nervous system, which includes all sensory neurons and nerves that move the muscles.
Figure: Divisions of the nervous system.
The peripheral nervous system and central nervous system communicate with each other through the peripheral nervous system’s efferent and afferent nerves. Afferent nerves are sensory nerves that ascend the spinal cord and carry sensory information from the environment into the brain. Efferent nerves are motor nerves that exit the brain and descend the spinal cord, relaying commands from the brain to our muscles. (It may be helpful to use this mnemonic: afferent nerves arrive at the brain, while efferent nerves exit.)
Afferent and efferent fibers are organized in the spinal cord and generally occupy different regions. The dorsal roots (back-facing side) of the spinal cord contain bundles of afferent (sensory) fibers. The ventral roots (belly-facing side) of the spinal cord contain bundles of efferent (motor) fibers.
The peripheral nervous system can be further divided into the somatic and autonomic nervous systems. The somatic nervous system governs voluntary movements and thus innervates the skeletal muscle. In contrast, the autonomic nervous system governs automatic or involuntary movements. This includes nervous system control of the digestive system, various glands, and smooth muscle.
The autonomic nervous system is further divided into the sympathetic (“fight-or-flight”) and parasympathetic (“rest-and-digest”) nervous systems. The sympathetic nervous system is designed to respond to stressors in the environment, and the parasympathetic nervous system is designed to help us rest. The sympathetic nervous system expends energy, while the parasympathetic nervous system conserves energy.
In response to a stressor, the sympathetic nervous system will cause:
inhibition of saliva production
dilation of the pupils: to take in as much light as possible to better assess the dangerous situation
accelerated heart rate: to transport oxygen to the muscles
slowed digestion: so blood can be diverted to the muscles
airway dilation: to provide more oxygen with each inhalation
increased glycogenolysis in the liver and increased blood glucose levels: to provide energy
Activation of the parasympathetic nervous system would cause the opposite effects. This includes the diversion of blood to the digestive tract so nutrients may be absorbed and glycogenesis in the liver is increased. (For more information on glycogenolysis and glycogenesis, refer to our guide on carbohydrate metabolism.)
When presented with a stressor or dangerous situation, the sympathetic nervous system is activated. The adrenal cortex releases cortisol while the adrenal medulla releases epinephrine: an important hormone and neurotransmitter, respectively, implicated in the stress response. Additionally, a cognitive appraisal of the situation is performed. During this appraisal, the ability to resolve the stressor or situation is assessed and likely outcomes are determined.
b) Neurotransmitters
Neurotransmitters are chemical messengers that transmit messages from a neuron cell to a target cell. They can be classified based on function (e.g., mood regulation), effect on the cell membrane potential (e.g., inhibitory, excitatory, or both), or locus of action (e.g., central or peripheral nervous system). For example, acetylcholine is the key excitatory neurotransmitter of the skeletal system and regulates movement.
| Name | Function | Main Functions | Location | Disorders associated with deficit |
|---|---|---|---|---|
You should remember how neurotransmitters function in relation to membrane potential. Neurotransmitters exit via exocytosis from the presynaptic terminal, travel across the synaptic cleft, and then bind to receptors on the target cell where they induce changes in the neuronal membrane's permeability to ions.
As noted, deficits in any of these neurotransmitters may cause disorder or illness. To learn more about this, be sure to refer to our guide on psychological disorders.
c) Regions of the brain
The brain is roughly composed of three main areas: 1) the hindbrain, 2) midbrain, and 3) forebrain. In humans, the brainstem is composed of regions from the midbrain and hindbrain. The functions carried out by these areas of the brain correspond with their evolutionary age: the ancient hindbrain governs basic survival mechanisms (including breathing), while the younger forebrain governs complex functions (such as interpreting language). As a result, while individuals can generally live without a forebrain, they would die without a midbrain or hindbrain.
| Substructure | Derived from | Main Functions |
|---|---|---|
The outermost part of the cerebrum is the cerebral cortex. This layer merits special attention because it is responsible for many of our higher cognitive functions. The cerebral cortex is rich with the cell bodies, or soma, of neurons. These neurons have long axons that extend through the brain and into the spinal cord.
The cerebral cortex can itself be divided into four major lobes, each with loosely specialized functions.
The frontal lobe governs executive function, initiates voluntary motor movement, and is responsible for producing speech.
The parietal lobe governs spatial processing, proprioception, and somatosensation.
The occipital lobe governs visual processing.
The temporal lobe governs learning, memory, speech perception, and auditory perception. An important language center known as Wernicke’s area is located here.
Figure: The four major lobes of the cerebral cortex.
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