Neuroscience and Brain Basics - Study Notes

Neuron Structure and Basic Function

  • Neuron: cells in the nervous system that communicate with one another to perform information-processing tasks
    • Cell body (soma): coordinates information-processing tasks and keeps the cell alive
    • Dendrites: receive information from other neurons and relay it to the cell body
    • Axon: transmits information to other neurons, muscles, or glands
    • Myelin sheath: insulating layer of fatty material
    • Nodes of Ranvier: increase efficiency of signal transmission
    • Synapse: the junction between the axon of one neuron and the dendrites or cell body of another

Components and Basic Anatomy of a Neuron

  • Cell body, Axon, Nucleus, Dendrites, Terminal branches of axon, Myelin sheath, Neural impulse
  • Dendrites and terminal branches of axon facilitate input and output of neural signals

Myelin and Nodes of Ranvier

  • Axon insulated by myelin
  • Nodes of Ranvier critical for saltatory conduction, increasing signal speed

Types of Neurons

  • Sensory neurons: TO BRAIN – receive information from the external world, travel through spinal cord, convey to brain
  • Motor neurons: TO BODY – spinal cord to muscles to induce movement
  • Interneurons: connect sensory neurons, motor neurons, or other interneurons

Visualizing Neurons

  • Typical diagrams show sensory receptors, interneurons, sensory neuron, motor neuron, spinal cord, and interneuron connections

Quick Challenge and In-Class Activities (contextual, not core content)

  • 3 Minute Challenge: build a neuron conceptually using room items; no drawing; photograph and upload
  • In-Class Activity: 5 volunteers create a sweet neuron; photograph 5 neurons; class votes; winner creates first quiz question

Electrical Signaling Within a Neuron

  • Resting potential
    • At rest, positively charged potassium ions (K⁺) flow out
    • Cell is negatively charged: Vextrest≈−70 mVV_{ ext{rest}} \approx -70\,\text{mV}
    • Na⁺/K⁺ pump maintains/restores resting potential: 3Na+ out,2K+ in{3\text{Na}^+ \text{ out}}, {2\text{K}^+ \text{ in}}
  • Action potential: electric signal conducted along an axon to a synapse
    • Occurs only when threshold for stimulation is reached; all-or-none
    • Threshold: Vextth≈−55 mVV_{ ext{th}} \approx -55\,\text{mV}
    • Peak: membrane becomes positively charged: Vextpeak≈+40 mVV_{ ext{peak}} \approx +40\,\text{mV}
  • Refractory period: time after an action potential during which a new action potential cannot be initiated

The Synapse and Synaptic Transmission

  • The synapse (synaptic gap) is the junction between neurons where signaling occurs
  • Key components:
    • Sending neuron: contains terminal buttons
    • Terminal buttons: knoblike structures at axon end
    • Vesicles: contain neurotransmitters
    • Neurotransmitters: chemicals that transmit information across the synapse
    • Receptor sites: on the receiving neuron’s membrane to initiate a new signal
    • Receiving neuron: collects neurotransmitters via receptors
    • Dendrites and cell body of the postsynaptic neuron connect here

Chemical Signaling and Transmission Across the Synapse

  • An action potential reaching the axon terminal triggers neurotransmitter release into the synapse
  • Neurotransmitters bind to receptor sites on the postsynaptic neuron, initiating a new electric signal
  • Mechanisms for clearing neurotransmitters from the synapse:
    • Reuptake: neurotransmitters are reabsorbed by the presynaptic neuron
    • Enzyme deactivation: enzymes break down neurotransmitters in the synapse
    • Autoreceptors: receptors on presynaptic neuron regulate neurotransmitter release
  • Postsynaptic and presynaptic interactions enable precise signaling

Types of Neurotransmitters (NTs) and Their Roles

  • Acetylcholine (Ach): voluntary motor control, memory, learning — associated with Alzheimer’s Disease
  • Dopamine (DA): regulates motor behavior, pleasure, emotional arousal — associated with Parkinson’s Disease, schizophrenia, drug addiction
  • Norepinephrine (NE): influences mood & arousal — associated with depression
  • Serotonin (5-HT): regulates sleep, dreaming, mood, aggression, appetite, sexual behavior — associated with depression/anxiety/OCD
  • Endorphins: modulate pain and pleasure pathways and emotion centers; linked to runner’s high

How Drugs Mimic or Influence Neurotransmission

  • Many drugs affect the nervous system by increasing, interfering with, or mimicking neurotransmitter manufacture or function
  • Examples:
    • L-Dopa: precursor to dopamine; used in Parkinson’s Disease
    • Prozac: SSRI (selective serotonin reuptake inhibitor) used in depression

The Nervous System: Organization and Major Divisions

  • Nervous system: interacting network of neurons that conveys electrochemical information
  • Nerves: bundles of axons and glial cells that support neurons
  • CNS (Central Nervous System): brain and spinal cord
  • PNS (Peripheral Nervous System): connects CNS to body’s organs and muscles; includes Somatic and Autonomic divisions

Peripheral Nervous System: Divisions

  • Somatic nervous system: conveys information into and out of the CNS; communicates with sense organs (eyes) and voluntary muscles; consists of Sensory NS + Motor NS
  • Autonomic nervous system (ANS): carries involuntary commands that control blood vessels, organs, and glands; includes Sympathetic NS + Parasympathetic NS

Somatic vs Autonomic Divisions

  • Somatic NS
    • Sensory nervous system: transmits sensory input from body to brain
    • Motor nervous system: transmits motor output from brain to body
  • Autonomic NS
    • Sympathetic nervous system: prepares body for action in threatening situations
    • Parasympathetic nervous system: helps body return to a normal resting state

Organization Diagram (Nervous System Overview)

  • CNS: brain and spinal cord
  • PNS: somatic (sensory and motor) and autonomic (sympathetic and parasympathetic)
  • Autonomic: controls internal organs and glands
  • Sensory (afferent) nervous system: carries sensory input
  • Motor (efferent) nervous system: carries motor output

The Sympathetic vs Parasympathetic Systems in Action

  • Sympathetic: dilates pupil, relaxes bronchi, inhibits digestion, accelerates heartbeat, stimulates glucose release, stimulates epinephrine/norepinephrine secretion, relaxes bladder, stimulates gallbladder, contracts bladder, stimulates ejaculation in males, allows blood flow to sex organs
  • Parasympathetic: constricts pupil, stimulates digestion, slows heartbeat, conserves energy

The Central Nervous System (CNS) and Spinal Reflexes

  • CNS consists of brain and spinal cord; communicates and coordinates activity
  • Spinal reflexes: simple neural pathways that rapidly generate muscle contractions without brain involvement

The Pain Withdrawal Reflex (Example of a Reflex Arc)

  • Sensory receptors detect a painful stimulus
  • Sensory neuron transmits signal to spinal cord
  • Interneurons process the signal and activate motor neurons
  • Motor neuron triggers muscle withdrawal

The Human Brain: Major Divisions and Structure

  • Hindbrain (brain stem): coordinates information to/from spinal cord; basic life functions
    • Pons: relays information from cerebellum to the rest of the brain; involved in sleep and dreams
    • Cerebellum: fine motor skills, coordination, balance
    • Medulla: coordinates heart rate, circulation, respiration
    • Reticular formation: regulates sleep, wakefulness, and arousal level
  • Midbrain: orientation and movement; important for vision, hearing, and voluntary motor control
    • Tectum: orientation to environment
    • Tegmentum: movement and arousal
  • Forebrain: critical for complex cognitive, emotional, sensory, and motor functions
    • Cerebral cortex: outermost layer; divided into two hemispheres
    • Subcortical structures: under cortex near center of brain

Subcortical Forebrain Structures

  • Thalamus: relays and filters sensory information; transmits to cortex
  • Hypothalamus: regulates body temperature, hunger, thirst, sexual behavior
  • Pituitary gland: the master gland; releases hormones that direct other glands
  • Hippocampus: critical for creating new memories
  • Amygdala: emotional processes, especially emotional memories

The Cerebral Cortex: Lobes and Functions

  • Four lobes per hemisphere (occipital, parietal, temporal, frontal)
    • Occipital lobe: visual information processing
    • Parietal lobe: processes information about touch; contains the Somatosensory Cortex
    • Temporal lobe: hearing and language
    • Frontal lobe: movement, abstract thinking, planning, memory, judgment; houses the Motor Cortex

The Cerebral Cortex and Lobes (Visual Overview)

  • Frontal lobe, Parietal lobe, Occipital lobe, Temporal lobe

Motor and Somatosensory Cortices (Topographic Mapping)

  • Motor cortex: controls voluntary movement; organized in a topographic map of the body
  • Somatosensory cortex: processes tactile information from the body; likewise organized topographically
  • Example mappings (from head to toe): facial regions, hands, arms, torso, legs, feet, etc.

Corpus Callosum and Hemispheric Specialization

  • Corpus callosum: thick band of nerve fibers connecting the two hemispheres; supports cross-hemisphere communication
  • Contralateral representation: right hemisphere controls left side of the body; left hemisphere controls right side

Left vs Right Hemispheres: Specialized Roles (Simplified)

  • Left hemisphere: language and analytic tasks
  • Right hemisphere: visual-spatial processing and holistic tasks
  • Important caveat: seizures can cross hemispheres in epilepsy; split-brain procedure can sever the corpus callosum

Split-Brain Studies and Implications

  • Split-brain experiments show distinct contributions of each hemisphere
  • Language is typically lateralized to the left hemisphere; visual-spatial processing tends to involve the right hemisphere
  • Contralateral representation remains a fundamental principle of brain organization

The Frontal Lobes and Emotional Regulation

  • Phineas Gage case: 1848, an accident to the frontal lobe resulted in drastic personality and behavior changes
  • Frontal lobe involvement: emotion regulation, planning, decision making
  • Video reference: (Phineas Gage case overview)

Key Takeaways on Brain Organization and Function

  • The brain consists of three major divisions: hindbrain, midbrain, forebrain
  • The CNS and PNS work together to process information and coordinate behavior
  • The cortex and subcortical structures collaborate to support cognition, memory, emotion, and motor control
  • The left and right hemispheres are interconnected and specialized, but both are essential for nearly all functions
  • Understanding neural signaling, neurotransmitters, and brain structures provides insight into behavior, disease, and therapeutic approaches

Quick Reference: Important Terms and Concepts

  • Resting potential: Vextrest≈−70 mVV_{ ext{rest}} \approx -70\,\text{mV}
  • Action potential threshold: Vextth≈−55 mVV_{ ext{th}} \approx -55\,\text{mV}
  • Action potential peak: Vextpeak≈+40 mVV_{ ext{peak}} \approx +40\,\text{mV}
  • Na⁺/K⁺ pump: 3 Na+ out, 2 K+ in3\,\text{Na}^+ \text{ out}, \ 2\,\text{K}^+ \text{ in}
  • Nodes of Ranvier: gaps in myelin that increase signal speed
  • Neurotransmitters: Ach, DA, NE, 5-HT, endorphins
  • Reuptake, enzyme deactivation, autoreceptors: mechanisms for clearing neurotransmitters
  • Corpus callosum: connects hemispheres; supports interhemispheric communication
  • Contralateral representation: right controls left side, left controls right side
  • Split-brain procedures: sever the corpus callosum to treat epilepsy; reveal lateralization in function
  • Phineas Gage: case illustrating frontal lobe role in emotion and behavior