Autonomic Nervous System and Brain Structures (Video)

Autonomic Nervous System (ANS)

• ANS is involuntary and largely unconscious; it manages internal organs and glands.
• It monitors and subtly adjusts:
  • internal body temperature, blood pressure, and blood glucose levels; fluctuations occur over the day.
  • You cannot consciously control these variables by will alone; they auto-regulate.
• ANS divisions:
  • Sympathetic nervous system (gas pedal): arousal and mobilization for action.
  • Example: being startled on a walk; initial sympathetic activation readies you to respond.
  • Physiological effects during arousal: increased heart rate, bronchi dilation, glucose release into bloodstream to fuel activity.
  • Parasympathetic nervous system (calm down): returns the body to baseline after threat assessment.
  • After assessing threat and resolving danger, parasympathetic activity calms and returns digestive and other systems toward baseline.
• How they work together in a threat scenario:
  • When a potential threat is perceived, sympathetic systems ramp up to prepare for action (fight/flight).
  • If the threat is deemed non-dangerous (e.g., a squirrel), parasympathetic systems calm the body and restore normal function.
  • In the interim, systems required for immediate action are upregulated, while housekeeping/digestion are downregulated to prioritize survival.
• Immune system interaction:
  • One system that gets inhibited during sympathetic activation is the immune system.
  • Immune function can be depressed for the next 60 ext{ s} (approximately) during short-term stress.
• Acute vs chronic stressors:
  • Acute stressors: occur and resolve quickly (e.g., squirrel or bear in the brush).
  • Chronic stressors: persistent and ongoing (e.g., ongoing financial worries, rent, or ongoing caregiving burdens).
  • Chronic stress keeps the sympathetic network turned up longer, which can suppress immune function over time and contribute to health problems.
• Nervous system organization recap:
  • Central nervous system (CNS): brain and spinal cord.
  • Peripheral nervous system (PNS): everything outside the CNS; divides into
  • Somatic: sensory and motor nerves; largely voluntary.
  • Autonomic: internal regulation (sympathetic and parasympathetic).

Neurons and Glial Cells

• Two broad cell types:
  • Neurons: information processing and communication between cells.
  • Glial cells: support cells; provide structure, insulation, nourishment (oxygen, glucose), and waste removal; do not primarily process information.
• Brain energy usage:
  • The brain is roughly a couple of pounds but consumes a large share of resources; about 20 ext{%} of the body's oxygen and calories is used by the brain.
• Neuron structure (simplified):
  • Cell body (soma) with nucleus.
  • Dendrites: branch-like projections that receive signals from other neurons.
  • Axon: elongated tail-like projection that transmits electrical signals away from the cell body.
  • Terminal buttons: end of the axon; contain neurotransmitters in vesicles.
  • Synapse/synaptic gap: the space between the terminal buttons of one neuron and the dendrites (or cell body) of the next neuron.
  • Myelin sheath: fatty insulation around many axons, produced by glial cells; protects against electrical shorts and increases transmission speed.
• Neurotransmission basics:
  • An electrical impulse travels along the axon to the terminal button.
  • Neurotransmitters are released from vesicles into the synaptic gap and bind to receptors on the receiving neuron’s dendrites.
  • When enough neurotransmitter molecules bind, the postsynaptic neuron fires an electrical signal of its own.
• Neurotransmitters and diversity:
  • There are 40+ neurotransmitters known; examples include dopamine, serotonin, oxytocin.
  • Different neurotransmitters are associated with different functions; some have excitatory effects, some inhibitory, and some can be both depending on context.
• Glial support details:
  • Glial cells insulate neurons with myelin, provide structural support, supply nourishment (oxygen, glucose), and help remove debris.
  • The brain’s high metabolic demand makes glial support critical.
• Why the synapse matters (practical application):
  • Understanding neurotransmitters helps explain how medications influence mood and behavior (see SSRIs, below).

Neurotransmitters, Excitatory vs Inhibitory, and Pharmacology

• Excitatory vs inhibitory transmitters:
  • Excitatory neurotransmitters increase the likelihood that the next neuron will fire.
  • Inhibitory neurotransmitters decrease the likelihood of the next neuron firing.
  • Some neurotransmitters can be excitatory in some circuits and inhibitory in others (context-dependent).
• Key pharmacology concept: reuptake
  • After a neurotransmitter binds to the postsynaptic receptor, it is often cleared by reuptake into the presynaptic neuron for reuse.
  • Reuptake is the process of pulling neurotransmitters back into the sending neuron.
• Prozac and SSRIs (Selective Serotonin Reuptake Inhibitors):
  • Prozac is an SSRI; it specifically targets serotonin (5-HT).
  • Mechanism: slows down reuptake of serotonin, increasing serotonin availability in the synapse.
  • Visual analogy: a bathtub with a drain and a spigot. If the drain is slowed, the water level rises even if the input rate stays the same.
  • In SSRI terms: input rate (serotonin release) stays similar, but reuptake (drain rate) decreases, so more serotonin remains in the synapse.
  • Expectation vs time: antidepressants often take about 4 ext{ to } 6 ext{ weeks} to exert noticeable effects because the brain gradually adapts to the new serotonin levels.
• Other strategies to modulate neurotransmission:
  • Use molecules that mimic a neurotransmitter to block receptor sites, reducing the effective signaling.
  • This is a form of competitive inhibition that reduces receptor activation by the natural neurotransmitter.
• Why antidepressants aren’t a universal fix:
  • Not everyone’s depression is strictly due to a chemical imbalance; life events and psychosocial factors contribute significantly.
  • Medications are most effective when combined with therapy to address life circumstances and coping strategies.
• Takeaway about treatment context:
  • Medication can help, but psychological therapies (like therapy/counseling) are essential for a comprehensive approach.

Brain Imaging, History, and Methods

• Early lesion studies: Phineas Gage (mid-1800s)
  • A railroad work accident damaged his left frontal region; despite surviving, he showed dramatic personality and behavioral changes, highlighting the role of the prefrontal cortex in emotion and behavior regulation.
  • Lesson: brain areas contribute to complex functions like personality and social behavior; damage can reveal functional roles.
• Brain imaging technologies (evolution of tools):
  • X-ray: good for bone; limited for soft tissue like the brain.
  • CT scan (computed tomography): uses X-rays; better for structural detail than plain X-ray.
  • PET scan (positron emission tomography): shows brain activity by mapping metabolic processes.
  • MRI (magnetic resonance imaging): high-resolution structural detail.
  • fMRI (functional MRI): measures brain activity by detecting changes associated with blood flow.
• Brain structure overview (hindbrain, midbrain, forebrain):
  • Hindbrain: basic, automatic functions; includes brainstem components and cerebellum.
  • Midbrain: connects hindbrain and forebrain; relays and modulates signals.
  • Forebrain: higher-level processing; includes limbic system and cerebral cortex.
• Key subcortical structures and their functions:
  • Thalamus: sensory relay station; routes information between lower and upper brain systems.
  • Hypothalamus: regulates eating, drinking, sex; mediates stress responses and body temperature regulation.
  • Reticular formation: arousal and stereotyped (automatic/habitual) patterns of behavior.
  • Medulla: breathing and reflexes (life-sustaining functions).
  • Cerebellum: motor coordination and balance.
  • Hippocampus: memory encoding and retrieval; not the sole storage site but critical for memory formation.
  • Amygdala: threat detection, fear, and emotional processing.
• Cerebral cortex and hemispheres:
  • The cortex is a wrinkled outer layer; two hemispheres (left and right) connected by the corpus callosum.
  • Four lobes per hemisphere:
  • Frontal lobe: personality, intelligence, voluntary motor control, behavioral inhibition, planning and imagination (ability to simulate scenarios mentally).
  • Parietal lobe: spatial location, attention, motor control.
  • Occipital lobe: vision processing.
  • Temporal lobe: hearing, language processing, memory; divisions for producing speech vs understanding speech.
  • Corpus callosum: a bundle of neural fibers that connects the two hemispheres and allows communication between them.

Endocrine System and Hormones

• Glands and hormones (endocrine communication):
  • Glands produce hormones that travel via the bloodstream to target organs to regulate functions.
  • Pituitary gland: regulates growth; abnormalities can affect development in children.
  • Hypothalamus: controls body temperature among other homeostatic processes.
  • Adrenal glands: release adrenaline during arousal or stress.
  • Pancreas: regulates blood sugar via insulin and glucose processing; dysregulation can contribute to diabetes and related complications.
  • Thyroid problems can cause lethargy and fatigue; thyroid function is commonly checked when energy levels are off.
  • Calcium and muscle contraction: calcium is essential for muscle contraction, including cardiac muscle; calcium regulation is critical for heart function.
• Brain injury and recovery factors:
  • Recovery depends on age (younger brains recover more quickly), extent of damage, and speed/quality of intervention.
  • Early intervention after brain injury (e.g., stroke) improves recovery outcomes.
• Mechanisms of brain repair after injury:
  • Collateral sprouting: neighboring healthy neurons grow new branches to compensate for damaged axons.
  • Substitution of function: other brain regions take over functions of damaged areas, though this is not automatic or always complete.
  • Neurogenesis: neurogenesis (new neuron formation) has been observed in the hippocampus under certain conditions.
  • Rehabilitation is essential to promote functional recovery; you can’t simply “tell the brain to take over” without practice and therapy.

Putting It All Together: Structure, Function, and Clinical Relevance

• Structure-function relationships:
  • Basic organization (hindbrain → midbrain → forebrain) supports a spectrum from reflexive to complex cognitive functions.
  • The limbic system (amygdala, hippocampus) interfaces with the cortex to regulate emotion and memory.
• Practical implications for health and learning:
  • Understanding ANS helps explain stress responses, physical readiness, and the impact of chronic stress on health.
  • Knowledge of neurotransmission and pharmacology informs how antidepressants work and why efficacy may take weeks.
  • Recognizing the role of environment and life events in mental health emphasizes the value of therapy and social support alongside medication.
  • Early intervention and rehabilitation after brain injury can meaningfully affect recovery trajectories.

Quick Recap for Exam Prep

• Autonomic Nervous System: two branches (sympathetic = arousal; parasympathetic = calm) and their roles in preparing the body for action and recovery; stress type (acute vs chronic) matters for health.
• Neurons and Glia: basic neuron anatomy (dendrites, soma, axon, terminal buttons, synapse) and the role of glia; myelin; neurotransmitters (40+), and the concepts of excitatory vs inhibitory signaling.
• Neurotransmitter Modulation: reuptake and SSRIs (e.g., fluoxetine/Prozac); time course of clinical effects; competing strategies to modulate signaling (reuptake inhibition vs receptor antagonism).
• Brain Imaging and Lesions: Phineas Gage as classic lesion study; imaging modalities (X-ray, CT, PET, MRI, fMRI) and what they reveal about structure and function.
• Brain Organization: hindbrain, midbrain, forebrain; thalamus, hypothalamus, reticular formation, medulla, cerebellum, hippocampus, amygdala; cerebral cortex and four lobes; corpus callosum.
• Endocrine System: glands and hormones; pituitary, hypothalamus, adrenal, pancreas; calcium and muscle contraction; impact of thyroid function on energy.
• Brain Repair and Recovery: collateral sprouting, substitution of function, neurogenesis; importance of age, damage extent, and timely intervention.
• Integration of biology with psychology and daily life: stress, mental health, therapy, and healthcare systems.