Final Exam 13

Stress Response During Exam Periods

  • During final exams, students often experience heightened stress levels.

    • Increased sympathetic activity leads to higher cortisol levels compared to relaxed periods, such as during Thanksgiving.

  • Sympathetic and parasympathetic nervous systems are in constant balance, a state referred to as sympathetic-parasympathetic tone.

    • Too much parasympathetic activity can lead to a lack of responsiveness in critical stressful situations.

    • Conversely, excessive sympathetic activation can lead to stress-related breakdowns, as evidenced by soldiers experiencing long-term combat stress in battlefield situations.

Physiological Responses to Stress

  • The response to stress includes activating the sympathetic nervous system, triggering the adrenal glands to release adrenaline.

    • Adrenaline (epinephrine) and norepinephrine are critical hormones involved in the fight-or-flight response.

  • Effects of sympathetic activation:

    • Increased heart rate, preparing the body for quick physical response.

    • Blood flow is redirected from the gastrointestinal tract to muscles and the central nervous system.

    • Smooth muscle in non-essential areas (like digestion) will loosen to redirect energy during emergencies.

  • Immediate physiological markers of stress response include a racing heart and increased adrenaline levels, making relaxation post-stress challenging.

  • Example scenario: Feeling of blood running cold due to blood flow distribution changes during a stressful encounter (e.g., encountering armed individuals in a swamp).

Neuronal Histology

Types of Neurons

  • Neurons are categorized based on their structure and function:

    1. Multipolar Neurons

      • The most common type; possess many dendrites and a single axon.

      • Receive thousands of inputs at dendritic ends, influencing action potentials.

    2. Bipolar Neurons

      • Have one dendritic pole and one axonal pole.

      • Critical for sensory functions in localization, such as in the retina (vision) and olfactory system (smell).

    3. Pseudounipolar Neurons

      • Single pole divided into two branches; one extends to a receptor and one to the spinal cord.

      • Transmit somatosensory information: touch, temperature, pain, pressure.

Neuron Activation and Action Potentials

  • Neurotransmitter reception at dendrites leads to excitatory or inhibitory signals influencing the neuron's action potential at the axon hillock.

  • Trigger Zone (Axon Hillock):

    • Decision-making area for firing action potentials based on summed inputs.

  • Overview of neuron communication:

    • Dendrites receive signals, and if summed input exceeds a threshold, an action potential is generated.

    • Action potentials propagate down axons either along myelinated or unmyelinated sections.

Glial Cells

Types and Functions

  • Astrocytes

    • Play a key role in supporting neurons structurally and functionally by maintaining the extracellular ion balance and assisting in nutrient transport.

    • Aid in establishing the blood-brain barrier, enhancing neuronal protection but also complicating drug delivery in therapeutic contexts.

  • Microglial Cells

    • Serve as the brain's immune response, removing debris and pathogens.

  • Oligodendrocytes and Schwann Cells

    • Both myelinate axons, enhancing the speed of action potential conduction.

    • Oligodendrocytes in the CNS myelinate multiple axons, while Schwann Cells in the PNS myelinate single axons.

  • Multiple Sclerosis

    • An autoimmune condition where the immune system attacks oligodendrocytes, leading to demyelination in the central nervous system, thereby slowing signal transmission.

Peripheral and Central Nervous Systems

  • Overview of sensory transmission:

    • Pseudounipolar neurons convert sensory stimuli into action potentials, traveling through dorsal roots into the CNS, with areas for potential reflex action.

  • Dorsal Root Ganglia

    • Grouping of pseudounipolar neuron cell bodies located just outside the spinal cord.

    • These ganglia function as relay stations for sensory input before reaching the spinal cord.

  • Reflex Arcs

    • Allow for quick, involuntary responses to stimuli without requiring immediate brain involvement (e.g., pulling back from a hot stove).

The Autonomic Nervous System

  • The autonomic system regulates smooth muscle, glandular, and involuntary bodily functions.

  • Comprised of sympathetic and parasympathetic systems, which generally serve opposing functions:

    • Sympathetic activation increases heart rate and inhibits digestive functions (fight or flight).

    • Parasympathetic promotes relaxation and restoration (rest and digest).

  • Preganglionic and Postganglionic Neurons

    • Preganglionic neurons from CNS synapse within ganglia to postganglionic neurons that directly affect target organs, utilizing neurotransmitters like acetylcholine and norepinephrine.