Chapter 5B Flashcards
The Peripheral Nervous System (PNS): Efferent division
-part of the nervous system that lies outside the brain and spinal cord
-sends commands away from brain to the periphery
-Efferent division consists of 2 subdivisions: autonomic and somatic
Autonomic Innervations
-cardiac muscle
-smooth muscle
-most exocrine glands
-some endocrine glands
-adipose tissue
Autonomic Nervous System (ANS)
-involuntary
-maintain dynamic equilibrium: homeostasis
-stress response
-reproduction
-thermoregulation
-extends from CNS to an innervated organ
Enteric Nervous System
-part of the ANS
-within the GI tract
-influences pancreas, liver, gallbladder (secretion, motility, blood flow)
Hub of the ANS
-hypothalamus
-brainstem
-spinal cord
Sympathetic Nervous System
-division of the autonomic NS
-flight or flight response
-heart rate increases
-blood pressure increases
-rate and depth of respiration increase
-energy stores are mobilized by working tissues ie. skeletal muscles
-digestion decreases
-redistribution of resources ie. blood flow and O2 delivery to digestive tract restricted
-O2 delivery increased to skeletal muscles, heart, lungs, skin
-glycogen breakdown
-hypothalamus
-secretion of epinephrine, norepinephrine, other hormones are increased
Parasympathetic Nervous System
-division of the autonomic NS
-rest and digest response
-heart rate decreases
-muscle use decreases
-digestion increases
-nutrients begin to be stored again
Two Neuron Chain (ANS)
-cell body of first neuron is located in the CNS, its axon is the preganglionic fibre which synapses with the cell body of the second neuron
-cell body of second neuron lies in a ganglion, its axon, the postganglionic fibre innervates the effector organ ie. smooth muscle or heart
Ganglion
cluster of neuronal cell bodies that lies outside the CNS
Sympathetic Innervation
-innervate thoracic and lumbar regions of the spinal cord
-“thoracolumbar”
Sympathetic Preganglionic Neurons
-short
-ganglions are paravertebral (para = adjacent to) meaning they lie on either side of the spinal cord
-secrete Acetylcholine (ACh) in the ganglion
Collateral Ganglia
-when some preganglionic fibres don’t synapse through the sympathetic ganglion chain
-they end here: between the CNS and innervated organs
-postganglionic fibres travel the rest of the distance
Sympathetic Preganglionic Receptors
-cholinergic nicotinic receptors
-in the ganglion
Parasympathetic Innervation
-preganglionic fibres arise from the cranial (brain) and sacral (lower spinal cord) areas of the CNS
-“craniosacral”
Parasympathetic Preganglionic Neurons
-longer than sympathetic preganglionuc fibres because they don’t end until reaching terminal ganglia (lie in or near effector organ)
-secretes Acetylcholine into the ganglion
Parasympathetic Preganglionic Receptors
-cholinergic nitcotinic
Sympathetic Postganglionic Neuron
-longer
-goes to target/effector organ
-secretes norepinephrine (20%) or epinephrine (80%) or dopamine (1%)
Sympathetic Postganglionic Receptors
-located on the target
-adrenergic; release noradrenaline aka norepinephrine
-alpha (a1 or a2) or beta (b1 b2 or b3)
Parasympathetic Postganglionic Neuron
-shorter
-secretes Acetylchloine
Parasympathetic Postganglionic Receptors
-on the target
-cholinergic just like all the autonomic preganglionic fibres
-muscanaric; fiver subtypes: _____
Nicotinic
-activated by tobacco plant derivative: nicotine
-found on all postganglionic cell bodies in autonomic ganglia
-respond to Ach from preganglionic fibres; open cation channels in postganglionic cell = depolarization and an action potential
Muscanaric
-activated by mushroom poison: muscarine
-found on effector cell membranes
-bind with Ach from parasympathetic post ganglionic fibres
-5 subtypes that are linked to G proteins which activate second messenger systems leading to target cell responses
Varicosities
-swellings in the terminal branches of postganglionic autonomic fibres
-opposed to single terminal swelling like a synaptic knob
Cholinergic Receptors
-bind to acetylcholine
-all preganglionic
-only symp. postganglionic
Adrenergic Receptors
-bind to norepinephrine and epinephrine
-sympathetic postganglionic neuron
Alpha Receptors
-both have higher affinity for norepinephrine over epinephrine
Beta Receptors
Alpha 1 (a1) Receptors
-use calcium second messenger system
-most tissues
-usually an excitatory response in effector organ
-present in most sympathetic target tissues
-ie. salivary glands, ejaculation, bladder
Alpha 2 (a2) Receptors
-uses cAMP
-inhibitory
-found in smooth muscles of the GI tract
-relaxation
-insulin decreases
-binding of a NT to a2 blocks cAMP production in target cell
-break down fat molecules
Secondary Messengers
-transfer the signal from the cell surface into the cytoplasm
-influences metabolic processes and thus cellular function
cAMP
cyclic adenosine mono phosphate
Beta 1 (b1) Receptors
-equal affinity for norepinephrine and epinephrine
-cAMP second messenger system
-excitatory
-usually increased heart rate
Beta 2 (b2) Receptors
-greater affinity for epinephrine over norepinephrine
-cAMP second messenger system
-generally inhibitory response
-flattening of ocular lens for far vision
-smooth muscles of respiratory tract
-vasodilation
-liver; make glucose available for breakdown
Beta 3 (b3) Receptors
-higher affinity for norepinephrine
-cAMP
-excitatory
-less common compared to b1 and b2
-break down adipose tissue for energy (brown fat)
comparison charts of sympathetic and parasympathetic ns….
Antagonistic Effect
Complementary Effect
Co-operative Effect
Somatic Nervous System
-motor neurons innervate skeletal muscle
-1 neuron system; continuous from CNS to ending on skeletal muscle
-cell bodies within ventral horn of spinal cord (except for those that supply head are in brain stem)
-mostly voluntary control
-posture, balance, stereotypical movements are subconsciously controlled
Motor Neurons
-axon terminals release Ach
-brings about excitation and contraction
-can only stimulate, not inhibit
Higher centres involved in somatic control
-spinal cord
-motor cortex
-cerebellum
-basal nuclei
-brain stem
Neuromuscular Junction (NMJ)
-linkage of motor neurons and skeletal muscle fibres
-aka motor end plate
Synapse
-nerve and muscle cell don’t directly meet
-chemical messenger carries signal across synapse
-chemical messenger is a neurotransmitter: acetylcholine
Release of Ach
-action potential propogation triggers opening of voltage gated Ca2+ channels in terminal button
-diffusion of Ca2+ triggers release of Ach by exocytosis from vesicles
Motor End Plate
-where the receiving channels are
-produces a small graded potential called “endplate potential”
-this will trigger a full blown action potential
why is an EPP larger than an EPSP
- more NTs released from terminal button than presynaptic knob
- motor end plate has a larger surface area (more receptor sites)
- more ion channels are opened = larger depolarization
Removal of Ach from the synapse
-done by acetylcholinesterase enzyme (inactivates Ach)
-Ach removal ends the EPP, relaxing the muscle cell
Sustained muscle contraction
-another motor neuron action potential leads to the release of more Ach, keeping the contractile process going
Reuptake of Ach to the terminal
-Acetylcholine is broken down into
a)choline: reusable
b)acetic acid: not reusable, removed from the muscle
Vulnerability of the NMJ
-several chemical agents and diseases affect the NMJ
-can alter Ach release
Black Widow Spider Venom
-triggers explosive release of Ach from the vesicles at all cholinergic sites (not just NMJ)
-keeps depolarizing NMJ
-leads to respiratory failure and person dies
Botulinum Toxin
-poison produced by bacterial pathogen: clostredium botulinum
-blocks release of Ach to motor end plate
-prevents muscles from responding to nerve impulses
-flacid paralysis:muscles can’t be excited
-death due to respiratory failure due to inability to contract the diaphragm
Curare
-blocks action of Ach at receptor sites
-binds to Ach receptor sites
-doesn’t alter membrane permeability, not inactivated by AChE
-paralysis ensues
-deadly arrowhead poison
-person dies from respiratory failure
Organophosphates
-chemicals that inhibit AChE so it can’t remove ACh
-respiratory failure cause diaphragm can’t repolarize
Myasthenia Gravis
-inactivates ACh receptor sites on motor end plate
-immune system attacks receptor sites
-autoimmune disorder: body attacks itself
-drooping eyelids
-difficulty chewing/walking
-not genetic
Polio
-caused by poliovirus
-starts with contaminated food or H2O
-attacks somatic NS
-grows in cell body of motor neuron which leads to cell death
-results in paralysis
ALS/Lou Gehrig’s Disease
-neurofilaments block axonal transport of crucial materials
-extracellular accumulation of toxic levels of excitatory NT glutamate
-aggregation of misfolded intracellular proteins
-mitochondrial dysfunction leading to reduced energy productiion
