Study Guide: Exam 3 – Spring 2026

Sensory Systems & Pain Processing

Sensation vs. Perception

  • Sensation: The process of detecting physical stimuli from the environment through sensory receptors.
  • Perception: The interpretation of sensory information by the brain, allowing it to make sense of incoming data.
  • Transduction: The conversion of physical energy (e.g., light, sound) into neural signals, allowing sensory information to be interpreted by the nervous system.

Somatosensory Processing

  • Sensory Receptors:

    • Different types of somatosensory receptors include:
    • Pacinian Corpuscles: Detect deep pressure and vibration.
    • Merkel's Discs: Sensitive to light touch and texture.
    • Differences in terms of:
    • Location in the skin.
    • Receptive fields: The area of skin that a specific receptor can detect stimuli from.
    • Type of sensory information encoded: Varies by receptor type.

  • Somatosensory Pathways:

    • Dorsal Column:
    • Responsible for transmitting fine touch and proprioception information to the brain.
    • Pathway: Information travels from the receptor in the skin through the dorsal column pathways to the Primary Somatosensory Cortex (S1).
    • Synapses occur in the medulla, and the information crosses to the contralateral side at this level.
    • Somatosensory Cortex: Located in the postcentral gyrus, responsible for processing sensory information.
    • Receptive Fields: Defined areas detected by individual receptors.
    • Sensory Adaptation: The gradual decrease in response to a stimulus over time.
    • Includes Tonic Activation (constant response) vs Phasic Activation (adaptation to constant stimulus).
    • Labeled Lines: Refers to distinct pathways for different sensory modalities, allowing the brain to interpret various types of sensory information.
    • Sensory Mapping: Illustrated by the sensory homunculus that represents body regions in the cortex, showing the relative size of sensory areas dedicated to them.
Example Test Question
  • When mechanically gated sodium (Na⁺) channels open in a sensory receptor cell, what is the immediate effect?
    • a. The receptor’s membrane potential becomes more negative (hyperpolarized)
    • b. The receptor’s membrane potential becomes less negative (depolarized)
    • c. Sodium ions are pumped out of the receptor cell
    • d. Neurotransmitters are immediately broken down in the synaptic cleft

Pain

  • Pain Perception: Involves specialized receptors and pathways that process and modulate painful stimuli.
  • TRPV1: A receptor sensitive to heat and pain, activated by high temperatures and substances like capsaicin found in spicy foods.
  • Afferent Fibers:
    • Aδ Fibers: Myelinated, fast-conducting fibers responsible for sharp, localized pain signals.
    • C Fibers: Unmyelinated, slow-conducting fibers associated with dull and burning pain.
  • Periaqueductal Gray (PAG): A midbrain structure involved in the descending control of pain; releases endorphins to inhibit pain transmission.
  • Spinothalamic Projections: Pain pathways from the spinal cord to the brain; synapses occur at various levels, with crossing occurring at the spinal cord level.
  • Placebo Effect: The phenomenon where a placebo treatment produces a physiological response.
Example Test Question
  • Which of the following fibers transmits sharp (fast), localized pain?
    • a. C fibers
    • b. Aδ fibers
    • c. B fibers
    • d. Type II fibers
Guiding Questions
  1. What is the difference between sensation and perception?
  2. How do mechanoreceptors differ from nociceptors?
  3. What is the function of the dorsal column pathway?
  4. How do Aδ and C fibers differ?
  5. How does the PAG contribute to pain modulation?
  6. What is sensory adaptation and why is it important?
  7. What is a homunculus?

Vision

  • Visual System: Converts light into neural signals to form visual perception.

Anatomy of the Eye

  • Cornea & Lens: Structures that help focus light onto the retina.
  • Pupil: The opening in the iris that regulates light entry.

Retina

  • Contains Photoreceptors that convert light into neural signals.
  • Fovea: Region of the retina with the highest visual acuity due to a high concentration of cones.
  • Optic Disc: The blind spot where the optic nerve exits the retina.

Photoreceptors

  • Rods: Function in low-light (scotopic) conditions; highly sensitive to dim light but do not detect color.
  • Cones: Function in bright light (photopic) conditions; responsible for color perception and visual acuity.
  • Photopigments:
    • Rhodopsin (in rods) and the roles of opsin in light absorption.
    • Changes in membrane potential due to light exposure vs. darkness, leading to neurotransmitter release.

Signal Processing in Retina

  • Bipolar Cells: Transmit signals from photoreceptors to ganglion cells.
  • Ganglion Cells: Carry visual information from the retina to the brain via the optic nerve.
  • Amacrine & Horizontal Cells: Facilitate lateral inhibition to enhance contrast in visual perception.

Visual Pathways

  • Lateral Geniculate Nucleus (LGN): Thalamic relay center for visual processing.
  • Primary Visual Cortex (V1): Main area of the brain for processing visual stimuli.
  • Receptive Fields: Areas of the retina impacting neuronal activity at various visual processing levels. Bipolar cells have receptive fields distinct from ganglion cells.
  • Simple vs. Complex Cells: Different neuron types that detect specific visual features.

Ventral vs. Dorsal Pathway

  • What vs. Where: The ventral pathway (what) is involved in object recognition, while the dorsal pathway (where) is responsible for spatial awareness.
  • Visual Agnosia: The inability to recognize objects despite intact vision; various types exist.
Example Test Questions

  1. How do photoreceptors differ from most neurons?

    • a. They are hyperpolarized at rest
    • b. They are depolarized at rest and hyperpolarize when activated by light
    • c. They lack neurotransmitter release
    • d. They fire action potentials

  2. Why does a star appear dimmer when viewed directly at night?

    • a. The optic disc is the blind spot
    • b. Cones are more sensitive to low light
    • c. Cones in the periphery are more sensitive to low light
    • d. Rods in the peripheral retina are more sensitive to low light

  3. Which cells carry visual information to the brain?

    • a. Bipolar cells
    • b. Horizontal cells
    • c. Ganglion cells
    • d. Rod cells
Guiding Questions
  1. How do rods and cones differ in structure and function?
  2. What is the functional role of the fovea?
  3. Why is there a blind spot in vision?
  4. What happens to photoreceptors when light hits them?
  5. What is lateral inhibition and why is it important?
  6. How are the dorsal and ventral visual streams functionally distinct?
  7. Where do you find the brain region highly specialized in processing faces?
  8. How is the visual field projected on the retina? Which part of the brain processes each part of the visual field?

Hormones & Endocrine Regulation

  • Endocrine System: Regulates body functions through hormonal signaling.

Hypothalamic-Pituitary Axis

  • Controls hormone release via the anterior and posterior pituitary.
  • Releasing Hormones:
    • Example: Gonadotropin-Releasing Hormone (GnRH): Stimulates the release of FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone).

Major Hormones

  • Estrogen, Progesterone, Testosterone: Regulate reproductive and metabolic functions.
  • Oxytocin & Vasopressin: Involved in social bonding, labor, and fluid balance; released by the posterior pituitary.

Neuroendocrine Signaling

  • Hormones released by neurons that influence body processes.
  • Negative Feedback: Feedback loops maintain hormone levels within physiological ranges.
Example Test Questions
  1. Which hormone is released by neuroendocrine cells in the posterior pituitary?
    • a. Vasopressin
    • b. FSH
    • c. LH
    • d. Cortisol
Guiding Questions
  1. How do the hypothalamus and pituitary gland interact?
  2. What are the differences between anterior and posterior pituitary functions? Be specific!
  3. How does negative feedback maintain hormone balance?
  4. What roles do oxytocin and vasopressin play?
  5. How do gonadal hormones influence both body and brain function?

Homeostasis

Thermoregulation

  • Homeostasis: The body’s ability to maintain internal stability despite external changes.
Negative Feedback
  • A regulatory mechanism where deviations from a set point trigger corrective responses to maintain homeostasis.
  • Set Point & Set Zone: The optimal range for physiological functions, such as body temperature or hydration.
Thermoregulatory Responses
  • Include mechanisms such as vasoconstriction (heat retention) and behavioral vs. physiological thermoregulation (e.g., seeking shade vs. sweating).
  • Involves the Preoptic Area (POA) of the hypothalamus, which integrates sensory inputs to regulate body temperature.

Ectotherm vs. Endotherm

  • Ectotherms: Organisms that rely on external heat sources for temperature regulation.
  • Endotherms: Organisms that internally regulate body temperature.

Water Balance & Hydration

  • Essential for maintaining blood pressure and cellular functions.
  • Hypovolemic Thirst: Triggered by loss of blood volume, prompting increased water and salt intake.
  • Osmotic Thirst: Triggered by high osmotic pressure (due to water loss); leads to pure water intake.
  • Baroreceptors: Detect changes in blood pressure and mediate compensatory responses.
  • Osmosensory Neurons/Osmoreceptors: Detect changes in extracellular solute concentration.
  • Vasopressin (ADH): Promotes water retention by reducing urine output; released by the posterior pituitary.
  • Atrial Natriuretic Peptide (ANP): Reduces blood pressure and inhibits water retention.
  • Angiotensin II: Stimulates thirst and induces vasoconstriction to restore blood volume.

Nutrient Balance & Appetite Regulation (Feeding)

  • Basal Metabolic Rate: The energy required for basic physiological functions.
  • Diabetes: Differentiating Type I (insulin deficiency) and Type II (insulin resistance); understand the role of insulin in each.
  • Energy Storage:
    • Glycogen: Short-term energy storage in the liver and muscles.
    • Fat Storage: Long-term energy storage in adipose tissue.
  • Hormones that regulate hunger, energy storage, and metabolism interact with specific neurons in the arcuate nucleus of the hypothalamus.
    • Ghrelin: Increases hunger, secreted by the stomach.
    • Insulin: Regulates blood glucose levels, promotes energy storage; acts as a satiety signal.
    • Leptin: Signals satiety and suppresses appetite; released by fat cells.
    • GLP-1: Reduces hunger.
    • PYY: Reduces hunger.
    • Ventromedial Hypothalamus (VMH) vs Lateral Hypothalamus (LH): Orexigenic neurons are found in the LH, influencing feeding behavior. Lesion studies reveal their distinct roles.
    • Arcuate Nucleus: Contains POMC vs NPY neurons, both critical in appetite regulation.
Example Questions

  1. Which hormone promotes water retention by reducing urine output?

    • a. ANP
    • b. Vasopressin (ADH)
    • c. Angiotensin II
    • d. Estrogen

  2. Insulin can act:

    • a. As a signal to store glucose as glycogen
    • b. As a signal to use glucose for energy
    • c. As a signal influencing hunger or fullness
    • d. All of the above
Guiding Questions
  1. How do feedback loops maintain homeostasis?
  2. What are the differences between osmotic and hypovolemic thirst?
  3. How do vasopressin and angiotensin II affect thirst and water retention?
  4. What is the function of leptin and ghrelin? What happens when leptin levels decrease? How is leptin produced? What hormones signal satiety to the brain?
  5. Which hypothalamic areas regulate feeding behavior?

Biological Rhythms

  • Sleep and Circadian Rhythms: Regulated by internal and external cues; important note: no questions on sleep phases and EEG in the exam.

Circadian Rhythms

  • 24-hour biological cycles regulated by the Suprachiasmatic Nucleus (SCN).
  • Other Rhythms: Include ultradian (less than 24 hours) and infradian (more than 24 hours) rhythms.
  • Zeitgeber: External cues (like light) that synchronize biological rhythms.

Molecular Clock

  • Molecular mechanisms involve the Clock and Cycle genes which regulate the body's internal timekeeping.
  • Retinal Ganglion Cells & Light Exposure: Blue light impacts melatonin production, influencing sleep cycles.
  • Pineal Gland & Melatonin: Produces melatonin, a hormone that promotes sleep.
  • Cortisol: A hormone with a daily rhythm that peaks in the morning.
Guiding Questions
  1. What is the role of the SCN in regulating circadian rhythms?
  2. How do Clock and Per genes regulate the circadian cycle?
  3. How does light affect melatonin secretion?
  4. What are examples of ultradian and infradian rhythms?
  5. How do hormones like melatonin and cortisol follow daily rhythms?
  6. Can you “read” and explain an “actigram” (graph showing the circadian activity of a lab mouse or rat)?
Example Test Questions
  • Which structure serves as the brain’s master circadian clock?
    • a. Pineal gland
    • b. Suprachiasmatic nucleus (SCN)
    • c. Hypothalamus
    • d. Pituitary gland