ANS- 2A Flashcards
motor (efferent) nervous system
-2 components:
-somatic and autonomic
-distinguished by the types of effector organs they innervate and the types of functions they control
somatic nervous system
-voluntary motor system
-conscious
-pathways consist of single motoneuron and skeletal muscle fibers it innervates
-cell body of motoneuron is located in CNS (brain or spinal cord)
-its axons synapse directly on skeletal muscles
-ACh released from presynaptic terminals of motoneurons -> activates nicotinic receptors on motor end plates of skeletal muscle
autonomic nervous system
-2 divisions: sympathetic + parasympathetic
-involuntary
-controls and modulates functions on visceral organs
-pathways have preganglionic and postganglionic
-preganglionic cell body- CNS
-postganglionic cell body- autonomic ganglia located outside CNS
-preganglion release ACh
-postganglion release ACh or norepinephrine or in some cases neuropeptides
sympathetic preganglion
-originate in nuclei of thoracolumbar spinal cord
-leave the spinal cord via ventral motor roots and white rami
-project either to prevertebral ganglia of sympathetic chain or to series of prevertebral ganglia
-T1-L3
-sympathetic division = thoracolumbar
-always cholinergic -> release ACh
-interact with nicotinic (N2) receptors on cell bodies of postganglia
parasympathetic preganglion
-originate the brain stem and sacral spinal cord
Adrenergic neurons
-release norepinephrine or epinephrine
-receptors for norepinephrine on effector organs are called adrenoreceptors
-either sympathetic or parasympathetic
-norepinephrine or epinephrine is secreted into circulation by adrenal medulla
-postganglion can be adrenergic or cholinergic
cholinergic neurons
-release acetylcholine (ACh)
-receptors for ACh -> cholinoreceptors
-either sympathetic or parasympathetic, ALL preganglionic neurons release ACh
-postganglion can be adrenergic or cholinergic
neuroeffector junctions
-junctions between postganglionic autonomic neurons and their effectors
-analogous to neuromuscular junctions of the somatic nervous system*
-postganglionic neurons innervate target tissues form DIFFUSE branching networks
-beads, or varicosities* line these branches and are sites of neurotransmitter synthesis, storage, and release
-varicosities are analogous to presynaptic nerve terminals of NMJ
-overlap in branching networks from different postganglionic neurons -> target tissues may be innervated by many postganglionic neurons
-postsynaptic receptors are widely distributed on target tissues
-there is no specialized region of receptors analogous to motor end plate of skeletal muscle
neuromuscular junction
-somatic nervous system
-effector (skeletal muscle fiber) is innervated by single motoneuron
sympathetic nervous system
-mobilize body for activity
-fight or flight
-increased arterial pressure, increased blood flow to active muscles, increased metabolic rate, increased blood glucose concentration, increased mental activity and alertness
paravertebral ganglia
-preganglionic neuron synapses on postganglionic neurons in paravertebral ganglia of sympathetic chain
-occur in ganglia at same segmental level of chain OR preganglion may turn in the cranial or caudal direction and innervate ganglia at higher or lower levels in the chain -> allow for synapse in multiple ganglia
prevertebral ganglia
-preganglion can pass through sympathetic chain without synapsing and continues on to synapse in prevertebral ganglia
-celiac, superior mesenteric, inferior mesenteric
-supply visceral organs, glands, and enteric nervous system of GI tract
-postganglion travel to periphery and innervate effector organs
sympathetic pathways
-preganglia originating in upper thoracic spinal cord-> thorax (heart)
-preganglia originating in lumbar spinal cord -> pelvic (colon, genitals)
-blood vessels, thermoregulatory sweat glands, pilomotor muscles of skin -> preganglionic neurons synapse on multiple postganglionic neurons up and down sympathetic chain -> broad distribution throughout body
-superior cervical ganglion -> head (eyes, salivary glands)
-celiac ganglion -> stomach and small intestine
-superior mesenteric ganglion -> small and large intestine
-inferior mesenteric ganglion -> lower large intestine, anus, bladder, and genitalia
adrenal medulla
-specialized sympathetic ganglion
-ANS
-preganglionic neurons originate thoracic spinal cord (T5-T9) -> pass through sympathetic chain and celiac ganglion without synapsing -> travel in greater splanchnic nerve to adrenal medulla
-synapse on chromaffin cells -> release ACh -> activates nicotinic receptors
-when activated chromaffin cells secrete catecholamines (epinephrine and norepinephrine) into circulation-> AS A HORMONE bc its systemic
sympathetic postganglionic neurons
-adrenergic in all effector organs EXCEPT thermoregulatory sweat glands (cholinergic)
-when stimulated -> norepinephrine and ATP are leased from small dense core vesicles
-these neurotransmitters at the neuroeffector junction -> bind to and activate their respective receptors on target tissue (vascular smooth muscle)
thermoregulatory sweat glands
-only sympathetic postganglia that are cholinergic (the rest are adrenergic)
-innervated by sympathetic cholinergic neurons have muscarinic cholinoreceptors
parasympathetic nervous system
-restorative, conserve energy
-preganglia cell bodies in either brain stem (midbrain, pons, medulla) or sacral spinal cord
-preganglia axons project to series of ganglia located near effector organs
-ganglia located near, on, or in effector organs
parasympathetic preganglionic neurons
-arise from nuclei of cranial nerves (3,7,9,10) or sacral spinal cord (S2-S4) -> craniosacral
-ganglia located near, on, or in effector organs
-long axons
-cholinergic and release ACh -> interacts with nicotinic (N2) receptors on cell bodies
parasympathetic postganglionic neurons
-parasympathetic postganglionic neurons are typically cholinergic as well
-when stimulated ACh is released from varicosities and bind to muscarinic receptors on target tissue
-high frequency stimulation (intense)- large dense core vesicles release their peptides -> bind to receptors on target tissue and augment the actions of ACh
micturition
-voluntary but sensation is autonomic
-emptying bladder is voluntary bc external sphincter is skeletal
-micturition reflex -> ANS
-detrusor muscle of bladder wall (body) and internal bladder sphincter are composed of smooth muscle -> innervated sympathetic and parasympathetically
-reflex occurs when bladder senses being full
-sympathetic -> bladder filling
-detrusor relaxed filling- beta 2
-sphincter contracted filling- alpha 1
-parasympathetic-> bladder emptying
-detrusor is contracted- M
-sphincter relaxed- M
-relaxed and contracted emptying- muscarinic
size of pupil
-controlled by 2 muscles of iris: pupillary dilator (radial) and pupillary constrictors (sphincter)
-pupillary dilator muscle- sympathetic innervation through alpha 1 receptors -> constrict radial muscle -> dilation (mydriasis)
-pupillary constrictor muscle- parasympathetic innervation through muscarinic receptors -> constriction sphincter muscle -> constriction of pupil (miosis)
pupillary light reflex
-light strikes retina and activates parasympathetic preganglionic nerves in Edinger-Westphal nucleus
-activation of parasympathetic fibers cause contraction of sphincter muscle and pupillary constriction
-accommodation response- blurred retinal image activates parasympathetic preganglionic neurons in Edinger-Westphal nuclei -> leads to contraction of sphincter muscle and pupillary constriction
-at same time, ciliary muscle contracts causing the lens to round up and its refractive power to increase
gastrointestinal tract
-contraction of wall of GI tract is accompanied by relaxation of sphincters (parasympathetic)
-allows the contents to propel forward
-relaxation of wall of GI is accompanied by contraction of sphincters (sympathetic)
-combined effect of these is to slow or stop movement of contents
sympathetic and parasympathetic innervation generalization
-parasympathetic- effector organs have muscarinic receptors
-sympathetic- multiple receptor types in effector organs -> 4 adrenoreceptors (alpha1, alpha2, beta1, beta2) + muscarinic receptors
-sympathetic adrenoreceptor- receptor type is related to function