Introduction to Behavioral Neuroscience · Structure and Function of the Nervous System: Cells and Anatomy

The Brain: Structure and Function

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In 30 seconds
Why this matters
The college version
Eli explains
Worked example
Key takeaway
Check yourself
Study tools
Sources & references

In 30 seconds

The brain is the organ of behavior: the ~1.4 kg organ that perceives, plans, remembers, feels, and moves the body. Anatomically it is organized into three major regions. The (medulla, pons, cerebellum) handles vital functions and coordination. The is a compact relay and reflex center. The — the largest region in humans — includes the , the , the , and the thalamus and hypothalamus, and is responsible for the higher functions we associate with being human: language, reasoning, emotion, and complex movement.

A few organizing principles make the brain navigable. First, the brain is roughly symmetrical, with two cerebral hemispheres connected by the . Second, the outer cerebral cortex is gray matter folded into ridges (gyri) and grooves (sulci), which dramatically increases surface area. Third, the cortex is divided into four lobes on each hemisphere — frontal, parietal, temporal, and occipital — each associated with characteristic functions. Fourth, many functions are lateralized: the left hemisphere usually dominates language in right-handed people, while the right hemisphere is more involved in spatial attention.

Why this matters

Behavioral neuroscience is, at bottom, the study of what the brain does. Every symptom a clinician encounters — a stroke that destroys speech, a tremor that betrays basal ganglia disease, a memory loss that points to the hippocampus — is a lesson in brain geography. Knowing which region does what lets you predict what a person with damage in a given area can and cannot do, which is the core skill of clinical neurology and the key to understanding how behavior arises from tissue. This topic is also the map for every later chapter: vision lives in the , hearing in the , movement in the and basal ganglia, emotion in the limbic system.

The college version

Core Concepts

The hindbrain: survival and coordination

Medulla oblongata: the lowest part of the brainstem, continuous with the spinal cord. It contains centers for breathing, heart rate, and blood pressure, and it is where many sensory and motor pathways cross sides (decussate).
Pons: sits above the medulla; relays information between the cerebrum and cerebellum, and participates in sleep, arousal, and facial sensation/movement.
Cerebellum: the "little brain" at the back. It receives information about body position and ongoing movement and fine-tunes motor commands, producing smooth, coordinated, well-timed motion. It is also involved in some forms of motor learning and, increasingly, in non-motor cognitive tasks. Damage produces ataxia — clumsy, uncoordinated movement.

The midbrain: relay and reflex center

The midbrain is the smallest major region. It contains the superior colliculi (involved in visual reflexes and orienting) and inferior colliculi (auditory reflexes), the substantia nigra (dopamine-producing cells critical for initiating movement; degeneration here is central to Parkinson's disease), and the ventral tegmental area (a dopamine center implicated in reward and motivation). The midbrain also contains the cerebral aqueduct, connecting the third and fourth ventricles.

The forebrain: the human brain's headquarters

Cerebral cortex: the folded outer layer of gray matter. It is divided into four lobes per hemisphere:
- Frontal lobe: planning, decision-making, working memory, personality, and voluntary movement. The primary motor cortex (in the precentral gyrus) sends the main voluntary movement commands to the body. Broca's area, usually in the left frontal lobe, is critical for producing fluent speech.
- : processes touch, temperature, pain, and body awareness. The primary somatosensory cortex (in the postcentral gyrus) receives tactile information. The parietal lobe also integrates spatial information.
- Temporal lobe: hearing, language comprehension, and object/face recognition. Wernicke's area, usually in the left temporal lobe, is critical for understanding language. The temporal lobe also contains the hippocampus (memory) and amygdala (emotion) on its inner surface.
- Occipital lobe: the visual processing center at the back of the brain; the primary visual cortex receives signals from the eyes.
Basal ganglia: a set of deep forebrain structures (including the caudate, putamen, and globus pallidus) that regulate the initiation and smoothness of voluntary movement. They work with the cortex and thalamus in loops; dysfunction causes movement disorders such as Parkinson's disease (slowness, tremor, rigidity) and Huntington's disease (involuntary chorea).
Limbic system: a set of interconnected structures including the hippocampus (formation of new memories), amygdala (emotion, especially fear and threat detection), hypothalamus (homeostasis: hunger, thirst, temperature, sleep, and hormone control via the pituitary), and parts of the cortex and thalamus.
Thalamus: the brain's main sensory relay station; nearly all sensory information (except smell) passes through it en route to the cortex. It also participates in arousal and attention.
Corpus callosum: the massive band of white matter connecting the two hemispheres, allowing them to share information.

Hemispheres and lateralization

The two hemispheres are not identical in function. In most people, the left hemisphere is dominant for language (Broca's and Wernicke's areas) and analytic processing, while the right hemisphere is more involved in spatial attention, face processing, and the emotional tone of speech. The corpus callosum lets the hemispheres exchange information, so each half has access to what the other is doing. Lateralization is a matter of degree — both hemispheres participate in most tasks.

How It Works / Step-by-Step Process

Locate the region: ask which lobe or deep structure is involved in the behavior in question.
Identify the pathway: sensory info → receptors → (midbrain/thalamus relay) → primary sensory cortex → association areas.
For a movement, trace: motor planning in frontal association areas → primary motor cortex → descending tracts → spinal cord → muscle, with the basal ganglia and cerebellum modulating the plan.
For memory or emotion, identify limbic structures: hippocampus (encoding new memories), amygdala (emotional significance), hypothalamus (visceral response).
For clinical cases, connect symptoms to geography: language trouble → left frontal/temporal; vision trouble → occipital; coordination trouble → cerebellum; unsteady movement → basal ganglia.

Common Confusions

Do not confuse	With	Difference
Broca's area and Wernicke's area	Production vs comprehension	Broca's (left frontal) = non-fluent speech production; Wernicke's (left temporal) = fluent but meaningless speech with comprehension problems.
Basal ganglia and cerebellum	Movement initiation vs coordination	Basal ganglia gate and initiate movement; cerebellum smooths and times it.
Hippocampus and amygdala	Memory vs emotion	Hippocampus encodes new memories; amygdala attaches emotional significance, especially fear.
Thalamus and hypothalamus	Relay vs homeostasis	Thalamus relays sensory/motor info to cortex; hypothalamus regulates internal state (hunger, temperature, hormones).
The four lobes have exclusive functions.	Overlapping roles	Lobes have primary associations, but most behaviors engage multiple regions.
The left brain does everything important.	Lateralization is relative	Language is left-dominant in most people, but both hemispheres cooperate in nearly every task.

Eli explains

The same idea, in plain words

Explain it like I’m 10

Your brain is like a control room with three floors. The bottom floor (hindbrain) keeps you breathing and balanced without you thinking about it. The middle floor (midbrain) handles quick look-and-listen reflexes and motivation. The top floor (forebrain) is the big thinking room: the folded surface plans, talks, remembers, and feels, with different walls of the room handling sight, sound, touch, and movement. The two sides of the room talk to each other through a big cable called the corpus callosum.

Worked example

Consider a person who has a stroke affecting the left hemisphere, in the territory that includes Broca's area. The person understands what others say and knows what they want to say, but produces halting, effortful, non-fluent speech. This pattern — intact comprehension with impaired speech production — is the classic signature of Broca's aphasia and illustrates the principle that language is localizable: different components (production vs comprehension) live in different regions.

Contrast this with damage to Wernicke's area in the left temporal lobe, which typically produces fluent but meaningless speech with impaired comprehension. The two cases are mirror images, and they are the single best demonstration in neurology that behavior maps onto brain geography. When later chapters discuss language, memory, or emotion, the same question applies: which structures are doing the work, and what happens when they are damaged?

Key takeaways

Three regions: hindbrain (medulla, pons, cerebellum — survival + coordination), midbrain (relays, reflexes, dopamine), forebrain (cortex, basal ganglia, limbic system, thalamus, hypothalamus — higher function).
Four lobes per hemisphere: frontal (planning, movement, speech production), parietal (touch, spatial), temporal (hearing, language comprehension, memory, emotion), occipital (vision).
Primary areas: primary motor cortex = precentral gyrus (frontal); primary somatosensory cortex = postcentral gyrus (parietal); primary visual cortex = occipital; primary auditory cortex = temporal.
Basal ganglia = movement gating: damage → Parkinson's (loss of dopamine in substantia nigra) or Huntington's (involuntary movements).
Limbic system = memory and emotion: hippocampus (new memories), amygdala (emotion/fear), hypothalamus (homeostasis).
Lateralization: left hemisphere usually does language (Broca's = production, Wernicke's = comprehension); right hemisphere does spatial attention. Corpus callosum connects them.

Check yourself

5 review questions from the chapter. Try each one, then open the answer.

Name the three major brain regions and one key function of each.
Show answer
Hindbrain (vital functions such as breathing and heart rate, plus coordination via the cerebellum); midbrain (visual/auditory reflexes, dopamine-based movement and reward systems); forebrain (higher cognition, emotion, memory, homeostasis).
Which lobe contains the primary motor cortex, and which contains the primary somatosensory cortex?
Show answer
Primary motor cortex is in the frontal lobe (precentral gyrus); primary somatosensory cortex is in the parietal lobe (postcentral gyrus).
What are the roles of the hippocampus, amygdala, and hypothalamus?
Show answer
Hippocampus: formation of new memories. Amygdala: emotion, especially fear and threat detection. Hypothalamus: homeostasis (hunger, thirst, temperature, sleep, hormone regulation).
What does the corpus callosum do?
Show answer
It is the large axon bundle that connects the two cerebral hemispheres, allowing them to share information.
A stroke produces fluent but meaningless speech with poor comprehension. Which area is most likely damaged, and in which hemisphere?
Show answer
Wernicke's area in the left temporal lobe (in most people), because comprehension is impaired while speech remains fluent.

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Study tools & related lessonsKey vocabulary · Related

Key vocabulary

hindbrain: Medulla, pons, and cerebellum.
midbrain: Small region above the pons containing colliculi, substantia nigra, and ventral tegmental area.
forebrain: Cortex, basal ganglia, limbic system, thalamus, hypothalamus.
cerebral cortex: The folded outer layer of gray matter.
gyrus / sulcus: A ridge / groove of the folded cortex.
frontal lobe: The most anterior lobe; motor cortex, planning, language production.
parietal lobe: The lobe behind the frontal lobe; somatosensory cortex.
temporal lobe: The lobe under the temples; auditory cortex, hippocampus, amygdala.
occipital lobe: The most posterior lobe; visual cortex.
basal ganglia: Deep forebrain structures regulating movement.
limbic system: Interconnected emotion/memory structures (hippocampus, amygdala, hypothalamus).
corpus callosum: The large axon bundle connecting the hemispheres.

Sources & references

openstax.org — Introduction Behavioral Neuroscience

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