biol 3410 11/21 lec

Synaptic Input to a Postsynaptic Neuron

  • Overview: In this scenario, 5 presynaptic neurons are involved in synapsing with a single postsynaptic neuron.

    • 2 presynaptic neurons produce Inhibitory Postsynaptic Potentials (IPSPs) of -6.

    • 2 presynaptic neurons produce Excitatory Postsynaptic Potentials (EPSPs) of +5.

    • 1 presynaptic neuron produces an EPSP of +10.

Resting and Threshold Membrane Potentials

  • Key Values:

    • Resting membrane potential: -70 mV

    • Threshold potential: -55 mV

Calculating Net Potential

  • If all 5 neurons fire at once:

    • Total IPSPs contribution: 2 neurons x -6 = -12 mV

    • Total EPSPs contribution:

      • 2 neurons x +5 = +10 mV

      • 1 neuron x +10 = +10 mV

    • Total EPSPs = +10 + +10 = +20 mV

    • Net change: +20 (EPSPs) - 12 (IPSPs) = +8 mV

    • Net membrane potential: -70 mV + 8 mV = -62 mV

Conclusion on Action Potential

  • Result: Since the net membrane potential (-62 mV) is still less than the threshold potential (-55 mV), no action potential will be produced.

Autonomic Nervous System Discussion

  • Importance: Understanding the autonomic nervous system (ANS) is critical, particularly in the context of health care and medication side effects.

Overview of the Nervous System

  • The nervous system is divided into several components:

    • Somatic nervous system: Controls skeletal muscles.

    • Autonomic nervous system: Regulates smooth muscle, glands, and cardiac muscle; divided into sympathetic and parasympathetic divisions.

Divisions of the Autonomic Nervous System

  • Sympathetic Division:

    • Nickname: Fight or flight.

    • Structure: Consists of a two-neuron chain (preganglionic and postganglionic neurons).

    • Preganglionic fibers originate from the thoracic and lumbar regions of the spinal cord.

  • Parasympathetic Division:

    • Nickname: Rest and digest.

    • Structure: Also consists of a two-neuron chain but with different origin locations, mainly from the brain stem and sacral spinal cord.

Differentiating Somatic and Autonomic Nervous Systems

  • Motor Output:

    • Somatic: One neuron directly stimulates the effector (skeletal muscle).

    • Autonomic: Two neurons with a synapse in between, often in ganglia.

  • Neurotransmitters:

    • Somatic uses acetylcholine.

    • Autonomic uses both acetylcholine and norepinephrine, depending on the type of neuron and effectors.

  • Effectors:

    • Somatic: Only skeletal muscle.

    • Autonomic: Smooth muscle, glands, and cardiac muscle.

Functionality of the Autonomic Nervous System

  • Dual Innervation: Many organs receive input from both sympathetic and parasympathetic divisions, allowing for opposed effects (e.g., heart rate regulation).

  • Responses: Sympathetic often promotes activity during stress, while parasympathetic promotes relaxation and recuperation.

Pathways of the Sympathetic Division

  • Preganglionic Neurons: Located in the lateral horns of the thoracolumbar spinal cord.

  • Postganglionic Neurons: Can have cell bodies in chain ganglia close to the spinal cord or in collateral/prevertebral ganglia further out (for below-diaphragm effectors).

Pathways of the Parasympathetic Division

  • Cell bodies located in the brain stem and sacral spinal cord, with ganglia typically found near or within effector organs.

    • Primarily uses acetylcholine.

  • Cranial nerve VI: Vagal nerve is significant as it innervates many organs from the heart to the intestines.

Neurotransmitters and Receptors

  • Cholinergic Neurons: Can be found in both autonomic divisions (preganglionic fibers release acetylcholine).

    • Types of receptors:

      • Nicotinic: Found in both sympathetic and parasympathetic systems, as well as in somatic neuromuscular junctions.

      • Muscarinic: Mostly in parasympathetic but can also appear in sympathetic pathways.

Summary

  • Understanding how the autonomic nervous system works is essential for comprehending various physiological responses and potential effects of medical treatments.