Module 1 - The Autonomic Nervous System Notes PDF

lOMoARcPSD|39895786 Module 1 - The Autonomic Nervous System - notes Systems Physiology (University of Queensland) Scan to open on Studocu Studocu is not sponsored or endorsed by any college or university Downloaded by Omena Ibe...

lOMoARcPSD|39895786 Module 1 - The Autonomic Nervous System - notes Systems Physiology (University of Queensland) Scan to open on Studocu Studocu is not sponsored or endorsed by any college or university Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 MODULE 1 : The Autonomic Nervous System (ANS) 1.1 Fight or Flight: The ANS Learning Objectives understand the structural and functional differences between the parasympathetic and the sympathetic nervous systems be able to explain how organs respond to the fight or flight response The Nervous System human body can be organised into two divisions: central nervous system (CNS) and the peripheral nervous system (PNS) PNS comprises of nerves and ganglia (cluster of nerve cell bodies) outside the brain and spinal cord ○ two types of neurons make up the PNS: afferent and efferent afferent = carry sensory information TO the brain / spinal cord efferent or motor = carry motor commands FROM brain / spinal cord PNS can be divided into somatic and autonomic NS ANS => functions unconsciously (involuntary control); controls intrinsic processes such as breathing and digestion Sympathetic and parasympathetic NS both systems have very different anatomical circuitry parasympathetic NS sympathetic NS calms you down activates your fight or flight response motor neurons in the brainstem and sacral motor neurons in thoracic and lumbar region of the spinal cord region of the spinal cord ganglia are close to the innervated organ ganglia are close to the spinal cord ∴ pre-ganglionic axons > post-ganglionic ∴ pre-ganglionic axons < post-ganglionic axons axons post-ganglionic axons pre-ganglionic axons Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 effect of these systems on organ activity: -> exceptions: most blood vessels, most sweat glands, salivary glands parasympathetic NS sympathetic NS brain activity ↑ -> increased alertness, improves memory and problem solving pupil constriction -> allows better focus pupils dilate -> ↑ field of vision ↓ cardiac output* -> ↓ heart rate, ↓ force of ↑ cardiac output* (↑ heart rate, ↑ force of contraction contraction) -> delivers more blood to highly active organs (e.g. brain, heart, skeletal muscle) bronchoconstriction (constriction of airways) bronchodilation (dilation of airways) -> ↑ air -> ↓ air intake intake GI tract activity ↑ -> ↑ motility (movement of GI tract activity ↓ -> ↓ motility and food through the digestive system and out contraction of sphincters of the body), relaxation of sphincters, ↑ secretion of digestive enzymes urinary bladder activity ↑ -> contraction urinary bladder activity ↓ -> relaxation (emptying) genital activity ↓ (except during orgasm) facilitates erection of penis and clitoris due to dilation of blood vessels to these organs blood vessels to GI tract, bladder and genitals constrict -> ↓ blood flow blood flow to skeletal muscles, brain and heart ↑ gallbladder contraction ↑ (aids emptying) gallbladder relaxes exocrine glands** => pancreas ↑ secretion, exocrine glands** => pancreas ↓ secretion, sweat glands ↑ secretion, salivary glands sweat glands ↑ secretion, salivary glands produce large volume of watery saliva produce small volume of thick saliva endocrine glands*** => pancreas ↑ endocrine glands*** => adrenal medulla secretion of insulin and glucagon secretes adrenaline and noradrenaline, pancreas ↓ insulin secretion inhibition of immune system * cardiac output = stroke volume x heart rate ** maintain contact with the body surface by a duct (epithelial tube that directs secretions to the surface), e.g. tear glands, sweat glands and mammary glands *** secrete hormones directly into the blood, have no contact with the body surface or cavities which lead to the “outside” ⭒ liver, gonads (reproductive organs) and pancreas have dual (exocrine AND endocrine) functions Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 1.2 ANS Circuitry Learning Objectives describe ANS circuitry using a simple diagram of the general circuitry between the sensory receptors and effector receptors understand the difference between pre- and post-ganglionic axons in the ANS define a ganglia explain the difference between boutons and varicosities Autonomic Ganglia ganglia = cluster of nerve cell bodies autonomic ganglia connect the central motor neurons to the effector organs ○ contains circuits that integrate and regulate neural signals before they reach the neuroeffector junction Ganglion Transmission signals from the pre-ganglionic axons are processed in the ganglia before being transmitted along the post-ganglionic axons ○ processing can include amplification, inhibition, divergence (separation) or convergence (combining) of pre-ganglionic information pre-ganglionic fibres: CNS (spinal cord) → Autonomic Ganglia Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 post-ganglionic fibres: Autonomic Ganglia → Effector Organs * receptors in viscera are activated by mechanical strain or chemical changes afferent neurons transmit sensory information along sensory fibres from receptors in the organs, through the dorsal side of the spinal cord either directly or via interneurons, to the autonomic motor neurons (neuron in red in the lateral horn of the spinal cord) autonomic motor (efferent) neurons transmit their signals along pre-ganglionic fibres, via the ventral side of the spinal cord to the ganglia forming synaptic boutons on the ganglia cells, to the autonomic ganglion ○ synaptic boutons = small swellings that are found at the terminal ends of axons autonomic ganglia, once activated, send their signals via post-ganglionic fibres to the visceral effector cells (small muscles or secretory cells) ⬤ stimulus → visceral receptor ---------(visceral sensory neuron)-----passes through dorsal く⬤ root of spinal cord-------- --------(autonomic motor/pre-ganglionic neuron)-----exits spinal cord via ventral root---------(in the autonomic ganglion)- く⬤ -----(post-ganglionic く neuron)-----exits autonomic ganglion--------- visceral effector → response Axon terminals: “boutons” axon terminals / synaptic or terminal “boutons” = small swellings found at the terminal ends of axons where synapses occur with other cells / neurons ○ often drawn in an exaggerated way in simple schematic diagrams of neurons Sympathetic Varicosities post-ganglionic axons terminate on the effector organ in these “strings of beads” known as varicosities two distinct kinds of smooth visceral muscles : single-unit smooth muscle cells and multi-unit smooth cells Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 single-unit smooth muscle cells are coupled by gap junctions, enabling electrical signals to be propagated to adjacent cells ○ e.g. those that line the walls of the gastrointestinal tract ○ not all cells are innervated by sympathetic varicosities, but those that are can rapidly spread the signal to adjacent cells, resulting in synchronised depolarisation and contraction as a single unit ○ these cells are found in the walls of hollow organs ○ contract synchronously because of gap junctions (connexins) between cells multi-unit smooth muscles are not linked together by gap junctions ○ thus, each smooth muscle cell must be individually innervated ○ e.g. those in your eyes ○ these cells are found in the airways to the lungs and large arteries Ganglion Cell Innervation ganglion cells are innervated by pre-ganglionic nerve endings, known as boutons these nerve endings (boutons) release acetylcholine, which activates the post-synaptic nicotinic receptors found on the ganglion cells once these receptors are activated, the ion channels open and result in a post-synaptic potential which activate the ganglia → ganglia then sends its signals along the post-ganglionic fibres to the effector organs signal is sent from activated ganglia cells via post-synaptic fibres to the smooth muscle cells smooth muscle cells are innervated by varicosities Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 varicosities contain packets of the neurotransmitter and mitochondria for the production of ATP same kind of varicosities that innervate sympathetic and parasympathetic nerve fibres parasympathetic nerves are cholinergic because they release acetylcholine (ACh) ○ cholinergic = relating to or denoting nerve cells in which acetylcholine acts as a neurotransmitter sympathetic nerves are adrenergic because they release noradrenaline (NAd) or adrenaline (Ad) ○ adrenergic = relating to or denoting nerve cells in which adrenaline, noradrenaline, or a similar substance acts as a neurotransmitter 1.3 Transmission & Receptors Learning Objectives understand the mechanisms involved in neurotransmitter release describe the sequence of events in parasympathetic AND sympathetic transmission, form transmitters to receptors explain how different cholinergic and adrenergic receptors give rise to specific physiological effects in different organs Cholinergic Transmission post-ganglionic nerve endings synapse onto the effector organ post-ganglionic nerve endings : choline is pumped into the nerve ending and is converted into ACh, which is then stored into vesicles the vesicles containing ACh are stored near the nerve endings when the nerve terminal is stimulated by an action potential, calcium channels open and the influx of calcium ions into the terminal results in the activation of the vesicles to move towards the pre-synaptic membrane and fuse with it, thus releasing the neurotransmitter ACh into the synaptic cleft ACh act on the post-synaptic ACh receptors, which produces a response in the effector organ ACh also acts on the pre-synaptic membrane to inhibit any further release of ACh ACh left in the synaptic cleft is broken down into choline and acetate, where the choline is recycled back into the nerve terminal to be converted and stored as ACh in vesicles Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 cholinergic receptors - two main types: ○ muscarinic receptors = G-Protein coupled receptors M1 - mainly found in the CNS M2 - cardiac muscle M3 - GIT smooth muscle ○ nicotinic receptors = ion channels N1 - skeletal muscle receptors - cholinergic signalling in the neuromuscular junction N2 - neuronal, e.g. ganglion cells - cholinergic signalling in the CNS Adrenergic Transmission post-ganglionic nerve endings synapse onto the effector organs tyrosine comes into the terminal and is converted into dopamine, which is then converted into noradrenaline NAd is stored in vesicles and when the nerve ending is activated (from an action potential), calcium ions enter the nerve ending via activated calcium channels → this causes the vesicles carrying the neurotransmitter to move towards the pre-synaptic membrane and fuse with it Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 NAd is released into the synaptic cleft, where it acts on two types of receptors: α- and β-receptors → triggers a response in the effector organ NAd also acts back on α2-receptors on the pre-synaptic membrane, which inhibit any further release of NAd from the post-ganglionic neuron (negative feedback) Adrenergic Receptors (GPCR) α - receptors (two types) ○ α1 receptors vasoconstriction in the GIT - reduce blood flow to the gut ○ α2 receptors found in the CNS auto-inhibition β - receptors (two types) ○ β1 receptors Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 increased cardiac muscle contractility ○ β2 receptors vasodilation (skeletal muscle vasculature) - increased blood flow bronchodilation ** NAd has varying effects depending on the adrenergic receptor on the surface of the effector organ NAd binds to α1 receptors on the surface of smooth muscle cells and this receptor is a G-coupled receptor → this binding causes an increase in calcium release from the ER which causes muscle contraction ○ no ionic change across the membrane ○ all calcium is released internally to produce an effect ATP binds to P2X receptors (found on smooth muscle cells) and since these receptors are channels, they open upon binding resulting in an influx of calcium ions → depolarisation of membrane and therefore, results in smooth muscle contraction ATP also acts on P2Y receptors on the pre-synaptic membrane → causes auto-inhibition which basically inhibits the release of vesicles containing ATP and NAd from the sympathetic nerve viscosities co-transmission of NAd and ATP, which are stored in the same vesicle and released together ○ produces a fast contraction due to depolarisation and a smaller contraction produced by the NAd effect Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 Pre / Post Ganglionic Systems recall: signals from the CNS are first propagated through pre-ganglionic fibres to the ganglion, where the signal is further propagated through the post-ganglionic fibres onto target organs Pre-ganglionic fibres (Parasympathetic and Sympathetic) all pre-ganglionic neurons - in both the parasympathetic and sympathetic divisions - release ACh which acts on nicotinic (N2) receptors located on post-ganglionic neurons at the ganglion Post-ganglionic fibres (Parasympathetic) post-ganglionic parasympathetic varicosities release ACh onto muscarinic receptors on the postsynaptic target organs ^ muscarinic (M2) receptors at the heart and blood vessels are activated by ACh release during parasympathetic activation Post-ganglionic fibres (Sympathetic) sympathetic post-ganglionic neurons primarily act by releasing noradrenaline (NA) and adrenaline (A) to act on adrenergic receptors ATP is also co-released with NA and acts faster in inducing contractions of the smooth muscle by activating post-synaptic voltage-gated calcium channels sympathetic post-ganglionic neurons also work through cholinergic pathways onto certain organs (e.g. sweat glands and vessels) and even through dopaminergic (D) pathways (in the renal system) ○ sweat glands (and other glandular structures) typically carry M3 receptors Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 sympathetic nervous system also has a neuroendocrine component, where sympathetic pre-ganglionic fibres directly innervate chromaffin cells within the adrenal medulla to promote the secretion of NA and A ○ these cells reside near blood vessels, where these hormones are released for systemic circulation → resulting in the global broadcasting of the sympathetic nervous system activation Summary Nicotinic Receptors (Cholinergic) ligand-gated ion channels stimulated by ACh (or Nicotine) when activated, these receptors are permeable to Na+ and K+, which facilitates rapid depolarisation of the cell 2 subtypes (N1, N2) ○ N1 or Nm subtype are found at the neuromuscular junction ○ N2 or Nn subtype are found at post-ganglionic neuron Muscarinic Receptors (Cholinergic) G-protein coupled receptors stimulation by ACh activation of these receptors can either stimulate or inhibit the function of the targeted cell 5 subtypes (M1 - M5) ** ○ ** only need to know M1, M2 and M3 for this course ○ M1 and M3 (and M5) preferentially couples with Gq, resulting in stimulatory signalling pathways ○ M2 (and M4) preferentially couples with Gi, resulting in inhibitory signalling pathways Adrenergic Receptors G-coupled protein receptors stimulated by NA and A 2 types: α and β, each with multiple subtypes ○ α receptors have a greater affinity for noradrenaline ○ β receptors have a greater affinity for adrenaline Downloaded by Omena Ibe ([email protected])  lOMoARcPSD|39895786 Downloaded by Omena Ibe ([email protected])