PSYCH 100 Lecture - 9/11/25
CNS Tour: Brain Structures and Functions
Focus of today: the CNS with a tour of the brain; review of autonomic vs somatic divisions and sympathetic/parasympathetic balance; core idea: many target organs are innervated by both divisions.
Brainstem and Cerebellum (hindbrain components)
Foramen magnum: the opening through which the spinal cord enters the skull.
Medulla oblongata (medulla): continuous with the spinal cord; controls life-sustaining autonomic functions such as:
Breathing, heart rate, salivation, vomiting, etc.
Even a small injury to the medulla can be fatal; this area is well protected deep within the brainstem.
Pons: anterior to the medulla; a major expansion as you move up the brainstem; called a “bridge” (Latin: pons).
Reticular formation: a diffuse cluster of neurons running along the length of the brainstem from the medulla to the pons; involved in:
Movement, attention, arousal, and sleep regulation.
Lesions in parts of the reticular formation can produce permanent insomnia or, in other areas, a permanent coma; highlight the sensitivity of these regions.
Cerebellum (little brain): dorsal to brainstem; has left and right hemispheres and a highly folded outer cortex.
Roles: coordinated movement and balance/equilibrium; essential for smooth, precise motor control.
Despite ~20% of total brain volume, it contains >50% of neurons in the brain.
A Purkinje cell in the cerebellum has an enormous dendritic tree and can have up to 100{,}000 synaptic connections.
The cerebellum is one of the first brain areas affected by alcohol; a field sobriety test largely assesses cerebellar function (coordination, balance, gait).
Vestibular nucleus is located near the cerebellum and may participate in other cognitive functions.
Dentate gyrus is an area found primarily in primates, important in some memory-related processes.
Base-of-brain summary: the medulla, pons, and cerebellum form the brainstem/hindbrain region, critical for life support and motor coordination.
Chickens head-truncated story (from the lecture): a historical anecdote about a chicken that lived ~18 months after its head was mostly removed but retained brainstem activity that allowed breathing and feeding via a retained brainstem and a feeding tube. Important takeaway: basic autonomic functions can persist with brainstem tissue, though most of the brain is essential for life. This underscores the primacy of the brainstem for basic life functions.
Midbrain
The midbrain is a compact region above the hindbrain and contains two major regions:
Tectum (upper part) and Tegmentum (lower part).
Tectum:
Superior colliculi (top bumps): involved in vision; visually guided actions and reflexive responses to visual stimuli.
Inferior colliculi (bottom bumps): involved in auditory processing and sound localization.
Tegmentum:
Contains the substantia nigra, a darkly pigmented cluster of dopamine-containing neurons; degeneration here is a hallmark of Parkinson’s disease.
Thalamus
Thalamus is perched above the brainstem with a central role as a relay station.
All sensory information (except olfaction) is routed through the thalamus before reaching the cortex:
Vision: retinal input → LGN (lateral geniculate nucleus) → occipital cortex.
Hearing: auditory input → auditory thalamic nuclei → temporal cortex.
Olfaction (smell) largely bypasses the thalamus initially for olfactory processing; however, olfactory information can still interact with thalamic circuits later.
The thalamus ultimately projects to cortical areas across the sensory modalities.
Hypothalamus and Pituitary
Hypothalamus location: below the thalamus (hypo = below).
Key roles:
Regulates the pituitary gland and many motivational drives.
Involved in aggressive behaviors and general motivational states; part of the classic “four F’s” of motivated behavior:
Fighting, Feeding, Fleeing, and Sexual behavior.
Controls the sympathetic nervous system influencing fight/flight responses.
Feeding regulation: hypothalamic inputs influence hunger and satiety; damage to specific hypothalamic regions can alter eating and body size (e.g., ventromedial hypothalamus lesions can lead to obesity in animals).
Pituitary gland: an endocrine gland that communicates with the brain via releasing hormones from the hypothalamus; divided into anterior (adenohypophysis) and posterior (neurohypophysis) portions.
Posterior pituitary releases two hormones:
Vasopressin (antidiuretic hormone, ADH)
Oxytocin
Oxytocin: involved in milk letdown, lactation, and social bonding; linked to pair bonding and social affiliative behaviors; oxytocin release can be stimulated by social contact and even pet interaction (pet therapy).
Anterior pituitary releases releasing hormones from the hypothalamus (e.g., gonadotropin-releasing hormone, GnRH) which stimulate release of tropic hormones such as:
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
These hormones affect the gonads (ovaries and testes) and downstream reproductive function.
Note on the pituitary in lectures: there is a popular historical nickname for the pituitary, and some lay explanations about its “snot gland” origin are misguided; the gland is an endocrine gland, not a mucus-producing organ.
Hormones vs neurotransmitters (key distinction):
Neurotransmitters: typically have localized, synapse-to-neuron effects; cross the synaptic gap to a neighboring neuron.
Hormones: released into the bloodstream and can have broad, diffuse effects on many tissues with receptors for the hormone; same chemical can act as either a hormone or a neurotransmitter depending on context, mechanism, and target.
Analogy: neurotransmitters are like a direct whisper to a specific person; hormones are like posting a message to the whole class via bloodstream.
Limbic system (top of brainstem/cortical border area): amygdala and hippocampus (often included with limbic structures)
Amygdala: central role in emotion, especially fear and anxiety; electrical stimulation induces fear responses in animals; lesions can reduce fear (Klüver–Bucy syndrome when amygdala is removed in animals). In humans, calcifications of the amygdala (e.g., in Urbach–Wiethe disease) can markedly blunt fear responses.
Klüver–Bücy syndrome: classic description of reduced fear and altered emotional responses following amygdala removal.
Urbach–Wiethe disease (amygdala calcification): humans with amygdala damage show diminished fear and altered emotional processing; some cases discussed in popular culture and neuroscience.
Hippocampus: critical for forming new memories; deep within the temporal lobes; the hippocampus is highly involved in encoding memory and consolidation.
HM case (a famous memory patient): bilateral hippocampal damage due to surgical treatment for epilepsy; seizures stopped but he could not form new long-term memories; illustrates hippocampal role in memory formation.
The hippocampus is sensitive to stress hormones (cortisol) via cortisol receptors; cortisol can affect memory formation, especially under chronic or intense stress.
Stress and memory: Chronic or acute stress can impair memory and learning by acting on hippocampal receptors; cortex and amygdala can also be modulated by stress.
Cortex: The Cerebral Cortex (Cerebrum) and its Lobes
The cerebrum (cerebral cortex): the outer covering of the brain; highly folded (convoluted) to fit within the skull.
Two-thirds of the cortex lie hidden in the sulci and gyri; the visible surface is only part of the cortex.
Gray matter vs white matter:
Gray matter: neuronal cell bodies (darker regions on histology).
White matter: myelinated axons (lighter regions); connect cortex to other brain areas.
Cortical folding increases surface area, allowing more neurons within a limited skull volume; larger, more convoluted cortices are seen in more evolved mammals.
Cortical surface area comparisons (rough proportions):
In humans, cortex would flatten to about the size of several large sheets of paper; see analogy below.
In chimpanzees and other primates, surface area decreases accordingly; the idea is to illustrate relative cortical expansion.
Major lobes (four):
Occipital lobe (posterior): primary role in vision; visual processing; damage can cause visual field deficits or blind spots (scotomas).
Temporal lobe (lateral): primary auditory cortex; language comprehension areas (e.g., Wernicke’s area in the left temporal lobe); right temporal involvement in face recognition (prosopagnosia).
Parietal lobe (superior posterolateral): somatosensation and associative processing; somatosensory cortex (postcentral gyrus) with a somatotopic map that forms a homunculus; fingertips and lips occupy large areas due to high sensory density.
Frontal lobe (anterior): motor cortex (precentral gyrus) with a motor homunculus; executive functions in the prefrontal cortex (working memory, planning, abstract thinking, impulse control).
Somatosensory cortex and the homunculus:
The primary somatosensory cortex (postcentral gyrus) contains a spatial map of the body; highly sensitive regions (face, lips, fingertips) occupy larger cortical areas.
Plasticity: after digit amputation in monkeys, adjacent digits can take over nearby cortical areas, reflecting remapping.
Phantom limb syndrome: after an amputation, people can feel sensations (including pain) from the missing limb due to retained cortical maps; reorganization can contribute.
Prosopagnosia (face blindness): lesions in the right temporal lobe can impair facial recognition; a domain-specific deficit within the temporal lobe.
Temporal lobe and language:
Left temporal lobe often houses Wernicke’s area (speech comprehension); left frontal lobe houses Broca’s area (speech production).
Motor cortex and somatic mapping:
The motor cortex is organized so that areas controlling fine motor movements (e.g., face, hands) take up larger cortical territory than less precise movements (e.g., trunk).
Prefrontal cortex and human-specific traits:
In the anterior frontal lobe, higher-order functions emerge: working memory, planning ahead, abstract thinking, impulse control, and other executive functions.
Historically, the prefrontal cortex was a target for early psychosurgical procedures (lobotomies).
Lobotomies, Phineas Gage, and the Frontal Cortex
Lobotomy/lobectomy overview:
Lobotomy: surgical disconnection of prefrontal brain tissue; historically done in the mid-20th century for severe psychiatric disorders.
Transorbital lobotomy: a variation developed by Freeman (and Moniz in Europe) using a tool inserted above the eye, with manipulation to sever frontal connections; performed while the patient was awake.
The procedure was also carried out in other forms (e.g., drilling from the top). The aim was to reduce aggression or other symptoms, but outcomes were often poor and many patients ended up sedated, emotionally blunted, or otherwise impaired.
The rise of antipsychotic medications in the 1950s reduced the use of lobotomies.
Phineas Gage (classic brain-behavior case):
A railroad foreman who survived a traumatic rod injury through the prefrontal cortex (just below the eye) that dramatically altered his personality and behavior.
Before: mild-mannered, responsible; after: impulsive, emotionally changeable, socially inappropriate behavior.
This case helped establish links between frontal cortex function and personality/decision-making.
Ethical implications and scientific progress:
Early lobotomies reflected limited understanding and often caused harm; they were replaced by better pharmacological treatments and more precise neuroscience.
The field emphasizes caution in brain interventions and the importance of evidence-based practice.
Cortex and Brain Matter: Summary Points
The cortex is the outermost layer of the brain; gray matter (cell bodies) forms the cortex’s surface; white matter (myelinated axons) lies beneath and connects regions.
The convoluted cortex allows more surface area to fit in the skull; greater convolution is associated with higher cognitive processing in mammals.
The four lobes provide a simplified map for understanding functions:
Occipital lobe: vision
Temporal lobe: audition and language (left hemisphere language areas)
Parietal lobe: somatosensation and sensory integration
Frontal lobe: motor control and higher cognitive functions
An understanding of these regions and their connections underpins how brain injuries, disease, and pharmacological interventions affect behavior and cognition.
Quick Reference: Neural Communications and Hormonal Influences
Neurotransmitters: localized signaling across synapses; fast, targeted effects on specific neurons.
Hormones: signaling molecules released into the bloodstream; can affect many tissues and produce slower, diffuse effects; same chemicals can act as neurotransmitters or hormones depending on context.
Hormonal interactions with the brain (e.g., hypothalamic control over pituitary hormones) influence development, stress responses, reproduction, and metabolism.
Real-World Connections and Implications
The cerebellum’s role in movement and balance links to athletic performance and motor learning; alcohol’s early effects on balance reflect cerebellar sensitivity.
The amygdala’s involvement in fear has implications for anxiety disorders and certain personality profiles; Urbach–Wiethe disease illustrates how amygdala damage alters fear processing.
The hippocampus’ vulnerability to cortisol explains why chronic stress can impair memory and learning; HM’s case illustrates the necessity of the hippocampus for forming new memories.
The thalamus as a relay station highlights how sensory processing depends on proper thalamocortical communication; olfaction’s bypass of the thalamus explains unique olfactory pathways.
The prefrontal cortex’s role in executive function underscores why injuries or disorders affecting this region can disrupt planning, impulse control, and working memory; historical lobotomies demonstrate why careful, ethical considerations are essential in neurosurgical interventions.
Key Terms and Concepts (quick glossary)
Foramen magnum: opening at the base of the skull for spinal cord entry.
Medulla oblongata: brainstem region governing vital autonomic functions.
Pons: brainstem bridge between medulla and cerebellum.
Reticular formation: arousal, attention, sleep, and motor control along the brainstem.
Cerebellum: coordination, balance; high neuron density; Purkinje cells with extensive dendritic trees.
Superior colliculus: visual processing and visually guided actions.
Inferior colliculus: auditory localization.
Substantia nigra: dopamine-rich region implicated in Parkinson’s disease.
Thalamus: sensory relay station to cortex; olfaction bypasses initial thalamic relay.
Hypothalamus: drives motivated behaviors; controls the pituitary; four F’s.
Pituitary gland: anterior (releasing hormones) and posterior (vasopressin, oxytocin).
Ghrelin and CCK: hormones regulating hunger and satiety; ghrelin is hunger-promoting; CCK reduces hunger.
Amygdala: fear and anxiety; lesion effects; Klüver–Bücy syndrome; Urbach–Wiethe disease (amygdala calcification).
Hippocampus: memory formation and stress hormone sensitivity; HM case.
Cortisol: stress hormone that can affect memory and hippocampal health.
Prosopagnosia: face recognition deficit linked to right temporal lobe.
Wernicke’s area: language comprehension; Broca’s area: speech production.
Prefrontal cortex: working memory, planning, abstract thinking, impulse control; site of historical lobotomies.
Phineas Gage: classic case linking prefrontal cortex damage to personality changes.
Gray matter vs white matter: cell bodies vs myelinated axons.
Cortical folding: increases surface area to fit more neurons.
Homunculus: somatotopic map of the body on primary motor and somatosensory cortices.
Phantom limb: perception of a missing limb due to persistent cortical maps.
For exam readiness: occipital (vision), temporal (audition/language), parietal (somatosensation), frontal (motor/executive functions), thalamus (relay), hypothalamus/pituitary (hormonal control), limbic system (amygdala, hippocampus).
Note: This set of notes paraphrases and expands on the ideas presented in the transcript, including examples and anecdotes used by the lecturer (e.g., the ch
icken story, the lobotomy history, and discussions of real cases like HM and Urbach–Wiethe disease) to illustrate brain–behavior relationships and their broader implications.