Autonomic Nervous System and Neurotransmitters in Nursing

Autonomic Nervous System (ANS) and Neurotransmitters

• The autonomic nervous system (ANS) is a branch of the peripheral nervous system (PNS) that controls involuntary actions, such as heart rate, digestion, and respiration.

Divisions of the ANS

• The ANS consists of two divisions: sympathetic and parasympathetic nervous systems.
• The sympathetic nervous system prepares the body for flight-or-fight responses, while the parasympathetic nervous system promotes relaxation and digestion.

Sympathetic Nervous System

• The sympathetic nervous system:
  • Prepares the body for heightened activity (e.g., exercise, excitement, emergency).
  • Increases heart rate and blood pressure.
  • Dilates airways and increases respiratory rate.
  • Decreases digestion and increases glucose release from the liver.
  • Stimulates sweat glands and salivary glands.

Parasympathetic Nervous System

• The parasympathetic nervous system:
  • Promotes relaxation and digestion.
  • Decreases heart rate and blood pressure.
  • Constricts airways and decreases respiratory rate.
  • Increases digestion and glucose uptake in the liver.
  • Stimulates salivary glands and promotes urination.

Comparison of Somatic and Autonomic Nervous Systems

• Both somatic and autonomic nervous systems are efferent divisions that distribute motor commands.
• Differences between the two systems include:
  • Neural pathways (afferent and efferent nerves).
  • Effectors (target organs).
  • Organ response.
  • Neurotransmitters (acetylcholine and noradrenalin).

Neurotransmitters and Receptors

• Acetylcholine (ACh) is released by preganglionic neurons in both somatic and autonomic nervous systems.
• Postganglionic neurons in the autonomic nervous system release ACh or noradrenalin (NA).
• Receptors bind ACh or NA, mediating the effects of the neurotransmitters.

Clinical Significance

• Understanding the autonomic nervous system is essential for informed clinical practice.
• Many drugs target ANS neurotransmitters and receptors, stimulating or inhibiting selected organs or body areas.
• It is crucial to understand how these drugs affect the ANS and their potential side effects.### Autonomic Nervous System (ANS)
• Divided into two divisions: Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS)

Sympathetic Nervous System (SNS)

• Also known as the Thoracolumbar Division
• Preganglionic neurons arise from T1-L2 spinal cord segments
• Cell bodies located in motor nuclei of lateral gray horns
• Axons exit spinal cord via spinal nerves (ventral root)
• Ganglia located close to spinal cord
• Preganglionic axon = short, Postganglionic axon = long
• Innervates:
  • Head and thorax (T1-T6)
  • Abdominopelvic organs (T5-L2)
  • Adrenal medulla

Parasympathetic Nervous System (PNS)

• Also known as the Craniosacral Division
• Preganglionic neurons arise from brainstem and sacral region of spinal cord (S2-S4)
• Cell bodies located in motor nuclei of brainstem and lateral gray matter of sacral spinal cord
• Axons exit CNS via cranial nerves (III, VII, IX, X) and spinal nerves (ventral root)
• Ganglia located close to or within target organs
• Preganglionic axon = long, Postganglionic axon = short
• Innervates:
  • Eye, lacrimal gland, nasal mucosa, salivary glands, and heart
  • Pelvic organs, stomach, small intestine, large intestine, and urinary bladder

Neurotransmitters

• Sympathetic postganglionic neurons release Noradrenaline (NA)
• Parasympathetic postganglionic neurons release Acetylcholine (ACh)
• ACh binds to cholinergic receptors, NA binds to adrenergic receptors

Receptors

• Cholinergic receptors:
  • Nicotinic: always excitatory, binds ACh
  • Muscarinic: excitatory or inhibitory, binds ACh
• Adrenergic receptors:
  • Alpha (a): excitatory or inhibitory, binds NA and Adrenaline (A)
  • Beta (b): excitatory or inhibitory, binds NA and A

Neurotransmitter-Receptor Binding

• Binding of NT to different receptors determines the response of the target organ

• NT binding mediates the differential effects of sympathetic and parasympathetic stimulation### Postsynaptic Potentials

• Graded potential = postsynaptic potential

• Excitatory postsynaptic potential (EPSP):

• NT binds receptors on postsynaptic membrane

• Opens gated ion channels, allowing Na+ ions to enter the cell

• Graded depolarization, making the postsynaptic cell more likely to fire

• Overall effect: increased target activity

• Inhibitory postsynaptic potential (IPSP):

• NT binds receptors on postsynaptic membrane

• Opens gated ion channels, allowing K+ ions to exit the cell

• Graded hyperpolarization, making the postsynaptic cell less likely to fire

• Overall effect: decreased target activity

Autonomic Nervous System (ANS)

• Sympathetic nervous system:
• Preganglionic neuron releases ACh, which binds to nicotinic cholinergic receptors, always excitatory
• Postganglionic neuron releases NA, which binds to adrenergic receptors
• Parasympathetic nervous system:
• Preganglionic neuron releases ACh, which binds to nicotinic cholinergic receptors, always excitatory
• Postganglionic neuron releases ACh, which binds to muscarinic receptors

Neurotransmitters

• Neurotransmitters (NTs) and electrical signals are the language of the nervous system
• 50+ NTs identified, some neurons make only 1 NT, most make 2 or more NTs
• NTs induce excitatory or inhibitory responses in postsynaptic membranes
• NT imbalances traditionally thought to cause neuropsychological disorders, but this theory is now questionable

Acetylcholine

• Motor control outside the CNS
• Involved in cognition, memory, and consciousness within the CNS
• Low levels found in Alzheimer's patients

Biogenic Amines

• Broadly distributed in the brain, involved in emotional behavior and regulating biological clock
• Imbalances associated with mental illness, but no consistent evidence to support this
• Drugs that enhance NT release or block reuptake associated with relief of symptoms of anxiety and depression in some people
• Includes noradrenaline, dopamine, and serotonin
• Noradrenaline: stimulates brain reward and pleasure centers, involved in reducing stress and enhancing attention
• Dopamine: stimulates brain reward and pleasure centers, high levels noted in schizophrenia, deficient in Parkinson's disease
• Serotonin: involved in mood regulation, sleep, appetite, nausea, and migraine headaches

Amino Acids

• GABA (γ-aminobutyric acid): main inhibitory NT in the brain, helps regulate sleep/wakefulness, involved in motor control
• Glutamate: involved in learning and memory, excessive release can lead to excitotoxicity and cell death

Neuropeptides

• Substance P: produced by damaged tissue, stimulates peripheral nociceptors, mediates pain transmission to the CNS
• Endorphins: includes endorphins and enkephalins, inhibits perception of pain in the CNS, natural opiates