Biological Perspective Notes (Exam Prep)

Neurons and Nerves: Building the Network

• Nervous system: extensive network of specialized cells that carry information to and from all body parts.

• Neuroscience: study of structure and function of neurons, nerves, and nervous tissue; links to behavior and learning.

Structure of the Neuron: The Nervous System’s Building Block

• Neuron: basic cell of the nervous system that receives and sends messages.

• Neuron parts:

  • Dendrites: receive messages from other neurons.

  • Soma (cell body): maintains life of the cell.

  • Axon: long tube that carries neural message to other cells.

  • Axon terminals: communicate with other nerve cells.

• Glial Cells: provide support, deliver nutrients, produce myelin, clean up waste.

• Myelin: fatty coating around some axons (insulated, speeds neural impulses).

Generating the Message Within the Neuron: The Neural Impulse

• Ions: charge particles; inside neuron is negatively charged, outside is positively charged.

• Resting potential: neuron is not firing.

• Action potential: reversal of electrical charge along the axon; allows positive ions to enter.

• All-or-none: a neuron fires completely or not at all.

• Sodium ions enter during the action potential: ext{Na}^+ ext{ ions enter the cell}

• Typical timing in monitoring the impulse: about 20-30\ \mathrm{ms} (milliseconds).

Neurotransmission: Communication Between Neurons

• Synapse: gap between neurons where communication occurs.

• Synaptic vesicles: contain neurotransmitters inside the axon terminal.

• Neurotransmitter: chemical released into synapse to affect next cell.

• Receptor sites: surface holes shaped to fit specific neurotransmitters.

• Neurons must be turned ON/OFF:

  • Excitatory neurotransmitter: increases likelihood receiving cell fires.

  • Inhibitory neurotransmitter: decreases likelihood receiving cell fires.

• Neurotransmitters as messengers:

  • Agonists: mimic/enhance neurotransmitter effects.

  • Antagonists: block/reduce neurotransmitter effects.

Neurotransmitters and Their Functions

• Acetylcholine (ACh): excitatory or inhibitory; arousal, attention, memory; controls muscle contractions.

• Norepinephrine (NE): mainly excitatory; arousal and mood.

• Dopamine (DA): excitatory or inhibitory; movement control and pleasure.

• Serotonin (5-HT): excitatory or inhibitory; sleep, mood, anxiety, appetite.

• GABA: major inhibitory neurotransmitter; regulates sleep and movement inhibition.

• Glutamate: major excitatory neurotransmitter; learning, memory, development, plasticity.

• Endorphins: inhibitory regulators; pain relief.

Neurotransmission: Cleanup and Regulation

• Reuptake: neurotransmitters are taken back into the presynaptic vesicles.

• Enzyme: breaks down neurotransmitters in the synapse.

The Nervous System: Central and Peripheral

• Central nervous system (CNS): brain and spinal cord; brain interprets/stores information and sends orders; spinal cord handles fast reflexes.

• Peripheral nervous system (PNS): nerves not in CNS; transmits info to/from CNS.

• Afferent (sensory) vs Efferent (motor) pathways.

• Autonomic nervous system (ANS): involuntary muscles/organs/glands; sympathetic (fight/flight) and parasympathetic (rest/digest).

• Somatic nervous system: nerves to/from senses and voluntary muscles.

• Parasympathetic vs Sympathetic divisions: opposite roles to maintain energy balance and response to stress.

The Central Nervous System (CNS)

• Sensory neuron (afferent): carries data from senses to CNS.

• Motor neuron (efferent): carries commands from CNS to muscles.

• Interneurons: connect sensory and motor neurons within the spinal cord; major part of brain.

• Neuroplasticity: brain’s ability to change structure/function with experience or trauma.

• Neurogenesis: formation of new neurons.

The Peripheral Nervous System (PNS)

• Somatic: sensory input to CNS; motor output to skeletal muscles.

• Autonomic: regulates glands, organs, and involuntary functions; includes sympathetic and parasympathetic branches.

Endocrine System and Hormones

• Endocrine glands secrete hormones directly into bloodstream.

• Hormones: chemical messengers in the bloodstream.

• Pituitary gland: master gland; influences all other hormone-secreting glands.

• Pineal gland: melatonin secretor.

• Thyroid gland: regulates metabolism.

• Pancreas: regulates blood sugar.

• Gonads (ovaries, testes): regulate sexual development/behavior and reproduction.

• Adrenal glands: respond to stress; multiple hormones; contribute to secondary sex characteristics during adolescence.

Hormones and Stress

• General Adaptation Syndrome: Alarm -> Resistance -> Exhaustion.

• Immune system: psychoneuroimmunology studies brain–hormone–immune interactions; chronic stress can be detrimental.

• Allostasis: maintaining stability through change.

• Allostatic load: wear-and-tear from prolonged stress.

• Stress links to health outcomes (heart disease, liver function, cancer treatment effectiveness, Type 2 diabetes).

Methods for Studying Specific Regions of the Brain

• Lesioning studies: destroy brain cells to study function.

• Brain stimulation: ESB (electrical stimulation of the brain) induces neuron activity.

• Invasive techniques: deep brain stimulation (DBS).

• Noninvasive techniques: transcranial magnetic stimulation (TMS), repetitive TMS (rTMS), transcranial direct current stimulation (tDCS).

Neuroimaging Techniques

• Mapping brain structure: CT, MRI.

• Mapping brain function: EEG, MEG, PET, SPECT, fMRI.

• PET/SPECT involve radioactive tracers; fMRI tracks blood flow changes over time to create functional activity "movies".

The Hindbrain

• Medulla: life-sustaining functions (breathing, swallowing, heart rate).

• Pons: connects brain regions; involved in sleep, dreaming, arousal, left–right coordination.

• Reticular formation (RF): selective attention.

• Cerebellum: coordinates rapid, involuntary movements; balance.

The Limbic System: Structures Under the Cortex

• A group of structures under the cortex involved in learning, emotion, and motivation.

• Thalamus: relays sensory info to cortex; processes some sensory data.

• Hypothalamus: motivates behavior (sleep, hunger, thirst, sex); regulates fear, aggression.

• Amygdala: fear responses, emotional processing.

• Hippocampus: formation of long-term memories and memory storage relative to location.

• Cingulate cortex: emotional and cognitive processing.

The Cortex: Processing Senses and Movement

• Cortex: outermost brain layer; higher thought processes and sensory interpretation.

• Corticalization: wrinkling to fit more cortical cells in the skull.

• Cerebral hemispheres connected by the corpus callosum.

• Lobes and primary vs. association areas:

  • Occipital lobe: primary visual cortex; visual processing.

  • Parietal lobe: somatosensory cortex; touch, temperature, body position.

  • Temporal lobe: primary auditory cortex; language comprehension.

  • Frontal lobe: motor cortex; planning and execution; higher thought; language production.

• Association areas: coordinate/integrate information and support higher mental processing.

• Broca’s aphasia: damage to Broca’s area (usually left frontal lobe); speech is halting or nonfluent.

• Wernicke’s aphasia: damage to Wernicke’s area (usually left temporal lobe); comprehension is impaired.

• Spatial neglect: damage to right hemisphere association areas; neglect of left visual field.

The Cerebral Hemispheres and Lateralization

• Cerebrum: two hemispheres; methods like split-brain study show specialized functions.

• Left hemisphere: language, writing, logical thought, analysis, math; controls right hand.

• Right hemisphere: emotion, spatial skills, faces, patterns, melodies; controls left hand.

• Handedness often reflects hemispheric specialization, not a strict rule.

• Table-like specialization snapshot: left vs right (language vs spatial/emotional, etc.).

Attention-Deficit/Hyperactivity Disorder (ADHD): Possible Causes

• Likely multiple causes and brain routes to ADHD.

• Environmental factors (e.g., lead exposure).

• Genetic/heredity factors.

• Personality and other factors may contribute.

Quick Reference Concepts

• Neuron parts and primary functions: dendrites, soma, axon, axon terminals.

• Glial support and myelination accelerate signaling.

• Resting potential vs action potential; threshold event.

• Synapse transmission, neurotransmitter action, receptor specificity.

• Excitatory vs inhibitory signaling in neural circuits.

• Major neurotransmitters and their roles.

• CNS vs PNS; autonomic vs somatic; sympathetic vs parasympathetic branches.

• Endocrine system organization; master role of the pituitary.

• Stress responses, allostasis, and health implications.

• Techniques to study brain structure and function (lesions, stimulation, imaging).

• Hindbrain, limbic system, cortex, and hemispheric specialization.

• Language-related aphasias and spatial neglect as case examples.

• ADHD: multiple potential etiologies and contributing factors.