Neural Signaling and Regulation

Nerve Cells and Their Function

  • Nerve Cells (Neurons)

    • Composed of:

    • Dendrites

    • Cell body

    • Axon

    • Function: Receive signals at dendrites and transmit them along the axon for rapid communication.

Types of Nerve Signals

  • Afferent (Sensory) Nerves: Carry signals to the brain or Central Nervous System (CNS).

  • Efferent (Motor) Nerves: Carry signals away from the CNS.

Neuron Structure

  • Components of a Neuron:

    • Dendrites

    • Cell body

    • Axon

    • Electrical Properties:

    • Resting Membrane Potential:

      • Charge: -70 mV (negative inside, positive outside)

      • High Na+ outside, Low K+ inside

  • Permeability:

    • Membrane is permeable to K+ but not to Na+ or large negatively charged ions.

Action Potentials

  • Definition: An action potential is an electrical signal that moves along the axon. It is characterized as a wave of positive charge.

  • Triggering:

    • Stimulus at dendrites opens Na+ channels, leading to depolarization (influx of Na+) which flips the membrane potential.

  • Phases of Action Potential:

    1. Depolarization: Rush of Na+ into the neuron.

    2. Repolarization: K+ flows out to restore negative charge inside.

    3. Undershoot: Temporary hyperpolarization occurs.

  • Properties:

    • Action potential is an "all or nothing" response. Once triggered, it always reaches completion.

Synaptic Transmission

  • Synapses: Action potentials are transmitted between neurons across synapses. Transmission may be electrical or chemical (via neurotransmitters).

  • Ion Channel Opening:

    • When neurotransmitters bind to the receptors on the post-synaptic neuron, ion channels may open, leading to the depolarization if sufficient channels open.

Neurotoxins and Their Effects

  • Botulism:

    • Caused by Clostridium botulinum which releases a neurotoxin that blocks acetylcholine release, leading to flaccid paralysis.

  • Tetanus:

    • Caused by Clostridium tetani which blocks inhibitory neurotransmitters, causing spastic paralysis.

Speed of Nerve Signal Transmission

  • Factors:

    • Greater axon diameter and presence of myelin sheaths (from Schwann cells and oligodendrocytes) increase transmission speed.

    • Saltatory Conduction: Action potentials jump between nodes of Ranvier, speeding up transmission.

Peripheral and Central Nervous Systems

  • Structure:

    • Central Nervous System (CNS): Comprises the brain and spinal cord.

    • Peripheral Nervous System (PNS): Comprises cranial and spinal nerves.

Reflex Arcs

  • Definition: Reflex actions occur through a sensory and motor nerve circuit involving the CNS, allowing for quick responses to stimuli.

Autonomic Nervous System

  • Divisions:

    1. Sympathetic Division: "Fight or flight" responses, accelerating heart rate, dilating pupils.

    2. Parasympathetic Division: "Rest and digest" responses, slowing heart rate, stimulating digestion.

Sensory Pathways

  • Common Functions:

    1. Reception

    2. Transduction

    3. Transmission

    4. Perception

  • Types of Receptors:

    • Exteroceptors: Respond to external environment

    • Interoceptors: Respond to internal conditions (e.g., blood O2 levels)

Sensory Transduction

  • Definition: Process of converting stimulus energy into a change in the membrane potential (receptor potential).

  • Characteristics:

    • Graded potentials; magnitude varies with stimulus strength.

Perception of Stimuli

  • Definition: The brain's interpretation of sensory information based on action potentials received from various receptors.

  • Factors Influencing Perception:

    • Amplification and adaptation to stimuli.

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