Peripheral nervous system

Electrical and Chemical Signals in Neurons

  • Conversion in Signaling

    • Electrical signal in one nerve cell converted into a chemical signal.

    • The chemical signal crosses the synapse to initiate electrical signal in another nerve cell.

Neurotransmitters and Their Functions

  • Single Neurotransmitter Production

    • Generally, a neurotransmitter from a nerve cell is single-type specific.

    • Example: A cell producing dopamine is referred to as an adrenergic neuron.

  • Unreleased Factors and Neuropeptides

    • Neuropeptides can be released in conjunction with neurotransmitters based on action potential frequency.

    • Frequency effects: Low frequency may release neurotransmitter; high frequency may release additional neuropeptides.

    • Neuropeptides may enhance or antagonize the effects of the primary neurotransmitter.

Receptors in the Downstream Neuron

  • Diversity of Receptors

    • A downstream neuron can have multiple receptors for various neurotransmitters.

    • Neurons can be stimulated (depolarization) or inhibited (hyperpolarization) by different neurotransmitters, impacting action potential production.

Types of Neurotransmitters

  • Classes of Neurotransmitters

    • Peptides, Amino Acids, Amines, Glucuronates.

    • Examples include:

      • Peptides: Neuropeptides

      • Amino Acids: GABA (Gamma-Aminobutyric Acid)

      • Amines: Dopamine, Serotonin

      • Glucuronates: ATP

  • Acetylcholine

    • Vital neurotransmitter with widespread roles in neural controls (skeletal muscles, autonomic nervous system, brain).

    • Always excitatory, stimulates action potentials.

    • Types of Acetylcholine Receptors:

      • Nicotinic receptors (ionotropic).

      • Muscarinic receptors (metabotropic, activates signaling pathways).

  • Adrenaline/Noradrenaline

    • Primarily excitatory neurotransmitter present in both central and peripheral nervous systems.

    • Types of Adrenergic Receptors:

      • Alpha and beta receptors (metabotropic G protein-coupled receptors).

  • Dopamine

    • Central nervous system specific, lacks receptors in peripheral.

    • Primarily inhibitory; insufficient dopamine links to Parkinson's disease.

    • Includes several receptor types (D1, D2, etc.).

  • Serotonin

    • Primarily central nervous system neurotransmitter involved in mood regulation.

    • Various receptor types adjust its effect on action potentials.

  • GABA (Gamma-Aminobutyric Acid)

    • Exclusive to the central nervous system, acts as an inhibitory neurotransmitter causing hyperpolarization.

    • Types of GABA Receptors: GABA A and GABA B.

Nervous System Overview

  • Peripheral Nervous System Structure

    • Composed of two main branches: Somatic Nervous System and Autonomic Nervous System.

    • The Somatic Nervous System involves conscious control over skeletal muscles.

    • The Autonomic Nervous System regulates internal bodily functions without conscious control, further branching into:

      • Sympathetic Nervous System

      • Parasympathetic Nervous System

      • Enteric Nervous System

  • Cranial and Spinal Nerves

    • Comprises 31 pairs of spinal nerves and 12 pairs of cranial nerves.

Autonomic Nervous System Functions

  • Sympathetic Pathways

    • Two neurons relay information:

      • First neuron from spinal cord to paravertebral ganglion.

      • Second neuron to target tissue, usually far-reaching effects.

    • Controls responses related to fight-or-flight (dilation of pupils, heart rate increase, etc.).

  • Parasympathetic Pathways

    • Focused on rest and digest functions.

    • Utilizes cranial and sacral nerves, particularly the Vagus Nerve (Cranial Nerve X).

    • Regulates heart rate reduction, bronchial constriction, and digestive activity enhancement.

Reflex Actions and Neural Processing

  • Reflex Functions

    • Spinal cord performs reflex actions without requiring brain processing beforehand (e.g., pulling away from a painful stimulus).

    • Reflexes can be monosynaptic (simple, two-neuron) or polysynaptic (involving multiple neurons).

  • Polysynaptic Reflex Example

    • Touching a harmful object triggers sensory input to spinal cord, activating interneurons leading to motor neuron stimulation (e.g., moving hand away from pain).

  • Tendon Reflex and Reflex Testing

    • The patellar tendon reflex tests spinal cord functionality through involuntary leg action upon knee tap.

    • Through muscle spindles, reflex responses to overstretched tendons inhibit muscle contraction to protect from injury.

Conclusion

  • Understanding these core concepts about neurotransmitters, nervous system structures, and reflexes is fundamental for advanced neurological studies.