biol 3410 11/14 lec

Signal Integration

  • Introduction to signal integration in the nervous system.

  • Examining presynaptic neuron activity effects on postsynaptic neuron membrane potential.

Case Study of Presynaptic Neurons

  • 3 presynaptic neurons; simultaneous firing leads to combined effects.

  • Example calculation based on EPSPs and IPSPs contributions to postsynaptic potential:

    • 2 EPSPs: +10 mV and +12 mV, summing to +22 mV

    • 1 IPSP: -5 mV, resulting in +17 mV overall.

    • Starting from -70 mV:

      • Final postsynaptic potential = -70 + 17 = -53 mV.

Action Potential Generation

  • If the resulting membrane potential is more positive than the threshold potential, an action potential is generated.

  • Clarification that -53 mV is above the threshold, thus an action potential will occur.

Types of Integration

  • Spatial Summation: Defined by simultaneous inputs from multiple neurons on a single postsynaptic neuron.

  • Temporal Summation: Involves rapid firing of a single presynaptic neuron, stimulating the postsynaptic neuron.

  • Often, signal integration in biological systems is a combination of both methods.

Spinal Cord Anatomy

  • Gray Matter:

    • Forms a butterfly shape in spinal cord; contains unmyelinated fibers and cell bodies.

  • White Matter:

    • Contains myelinated fibers, allowing for faster signal transmission.

Myelination Significance

  • Myelinated fibers found in spinal cord areas appearing white.

  • Gray matter consists of cell bodies and unmyelinated fibers, commonly linked to gray matter functions in reflex action.

Dorsal and Ventral Roots

  • Dorsal Roots: Carry sensory information; associated with sensory neurons.

  • Ventral Roots: Carry motor information; associated with motor neurons.

  • Spinal Nerves: Comprised of both dorsal and ventral roots merging.

Meninges

  • Protective coverings of spinal cord and brain include:

    • Dura mater (superficial)

    • Arachnoid mater

    • Pia mater (deep)

Reflex Arcs

  • Basic Components:

    • Receptor, sensory neuron (afferent), integrating center (spinal cord), motor neuron (efferent), and effector.

  • Responses can be either innate reflexes (like suckling) or learned reflexes (like driving).

Types of Reflexes

  • Monosynaptic Reflex Arc: Involves a single synapse (e.g., patellar reflex).

  • Polysynaptic Reflex Arc: Involves multiple synapses (e.g., withdrawal reflex when stepping on a nail).

    • Typically includes an interneuron that integrates the signal.

Example of Reflex Action

  • Patellar Reflex:

    • Triggered by tapping patellar tendon, stretching the associated muscle (quadriceps).

    • Action Potential travels through sensory neuron to spinal cord, activating motor neuron to cause muscle contraction.

    • Monosynaptic, Ipsilateral Reflex: Single pathway, same side of the body.

Neurological Mechanism in Reflex Action

  • The process involves the sensory neuron detecting stretch, synapsing with a motor neuron that causes muscle contraction while also suppressing the opposing muscle (hamstrings).

  • Neurotransmitters:

    • Peripheral muscle responses typically involve acetylcholine, while interneurons may utilize GABA for inhibition.

Summary

  • Signal integration through combined excitatory and inhibitory inputs is essential for neural function.

  • Reflex arcs facilitate rapid responses to stimuli through organized pathways, and the architecture of spinal components supports these processes efficiently.