Autonomic Nervous System Flashcards
What is the ANS?
Communication System
Part of the PNS
2 pathways
Afferent Pathway
Carries nerve impulses from the periphery to the CNS
Efferent Pathway
Carries nerve impulses from the CNS to the various targets
- sympathetic nervous system
- parasympathetic nervous system
- enteric nervous system
Functions of the ANS
Maintains homeostasis
Response to stress
Regulates day to day functions in the body
What is innervated? - Somatic vs ANS
Somatic = skeletal muscle Autonomic = smooth muscle, cardiac muscle, glands
What is the response? - Somatic vs ANS
Somatic = always excitatory (contraction) Autonomic = excitatory or inhibitory (contraction or relaxation, increased or decreased secretion)
Efferent (motor) Path? - Somatic vs ANS
Somatic = one neuron link Autonomic = two neuron link
Which transmitters? - Somatic vs ANS
Somatic = acetylcholine (ACh) Autonomic = ACh, norepinephrine, epinephrine
Overall Control? - Somatic vs ANS
Somatic = voluntary Autonomic = involuntary
Location of Cell Bodies of Preganglionic Fibers in the Parasympathetic System
Cranial and sacral nerves
Location of Cell Bodies of Preganglionic Fibers in the Sympathetic System
Thoracic and lumbar nerves
Parasympathetic Division
Cell bodies of the preganglionic fibres are found in the lateral region of the grey matter.
Axons of preganglionic fibres pass through the ventral roots and then join the spinal nerve and then branch off into ganglion
Ganglia are close to the target organs (terminal ganglia)
-long preganglionic fibre and short postganglionic fibre
Divergent Ganglion
One preganglionic fibre connects with several postganglionic fibres
Convergent Ganglion
Several preganglionic fibres converge onto a single postganglionic fibre
Sympathetic Division
Preganglionic sympathetic fibre has its cell body in the lateral region of the grey matter.
Axon of preganglionic fibre leaves the spinal cord by the ventral roots
3 Pathways a Sympathetic Preganglionic Fibre Can Take When it Leaves the Spinal Cord
- Synapse immediately with a postganglionic neuron in sympathetic ganglion at the same level
- Travel up or down the chain and synapse in ganglia at other levels
- Pass through chain without synapsing, continue to collateral ganglion as splanchnic nerve
Communicating Rami
Branches, or connections, between the spinal nerve and the ganglia
White Ramus Communicans
The branch that leads into the ganglion from the spinal nerve
Myelinated preganglionic fibre
Grey Ramus Communicans
The branch that goes back into the spinal nerve
Unmyelinated postganglionic fibre
2 Main Locations and Types of Ganglia in Sympathetic Division
- Sympathetic chain ganglia or sympathetic trunk
-parallel to the vertebral column - Collateral ganglia
-found in front of the vertebrae column
the preganglionic fibres are short and the postganglionic fibres are long
Varicosity
Chains of swellings along the branches of a POSTGANGLIONIC fibre.
Contain synaptic vesicles which release neurotransmitters
Adrenal Glands
Hormone producing glands above kidneys
Sympatho-Adrenal System
Innervated by sympathetic preganglionic fibres (NO PARASYMPATHETIC)
Acts as a modified sympathetic postganglionic fibre
ACh as a Transmitter
The major transmitter for all ANS ganglia - acts on postganglionic fibre
In the parasympathetic system = ACh is released and acts on the target tissue
NE/E as a Transmitter
NE/E are released from postganglionic sympathetic fibres and acts on most target tissues in the sympathetic system
Chromaffin Cells
releases NE/E into the blood from the adrenal medulla
Events at a Cholinergic Nerve Terminal
- Acetyl CoA combines with choline to form ACh
- Choline is brought into the nerve terminal by a choline carrier - ACh is packaged into vesicles and stored in the terminal until a stimulus comes
- Stimulus for the release of ACh from vesicles
- action potential opens voltage-gated calcium channels
- calcium rushes in and causes the vesicles containing ACh to move to the membrane and fuse
- ACh is released by exocytosis into the synapse - ACh acts on cholinergic receptors on the membrane of the postganglionic fibre
- Once released from the receptor, ACh is broken down by acetylcholinesterase into choline and acetate
Events at an Adrenergic Varicosity
- NE is synthesized from tyrosine which is taken up into the terminal
- tyrosine -> DOPA -> dopamine - Dopamine is packaged into a vesicle where it is converted to NE
- Release of NE occurs when an action potential comes down the sympathetic postganglionic fibre and causes the opening of calcium channels
- Increased calcium concentration causes the vesicles to fuse with the membrane and release via exocytosis
- NE binds to adrenergic receptors on the target tissue
How is the action of NE Terminated?
Reuptake into the nerve terminal
- NE is removed from the synaptic space by a special transport system which takes NE back into the varicosity
- packaged and used again
Co-transmission
more than one transmitter type is usually released at one time from a given site
the composition of the mixture may vary under different circumstances
Cholinergic Receptors
Binds ACh
Nicotinic (2) = skeletal and nervous tissue
-Nm in somatic system
-Nn in the ganglion of ANS
Muscarinic (5) = smooth muscle, cardiac muscle, glands
Adrenergic Receptors
Binds NE/E
Alpha (2) + Beta (3) = in smooth muscle, cardiac muscle, glands
Serpentine shaped
Nicotinic Receptors
Ionotropic receptor = receptor that forms ion channels following the binding of a ligand; ligand-gated ion channels
Doughnut shaped
Muscarinic Receptors
Metabotropic receptor = membrane receptor that initiates the formation of second messengers following the binding of a ligand
Serpentine shaped
Mechanism of Nicotinic Receptors
- An AP arrives in the preganglionic fibre - opens calcium channels
- Increased calcium causes vesicles of ACh to release into the synapse
- ACh moves across to the postganglionic fibre and binds to Nn receptor (ligand-gated ion channel)
- Binding of ACh opens an ion channel in the receptor
- sodium entered the postganglionic fibre - Movement of sodium brings positive charge, EPSP
- EPSP causes the opening of voltage-gated sodium channels and the additional sodium causes an action potential as the threshold is reached
Mechanism of Muscrainic and Adrenergic receptors
The binding of neurotransmitters to receptors produces a response through G-protein coupled mechanism
Players in the Signal Transduction Story
- Transmitters/hormones
- ACh, NE/E - Receptors
- muscarinic, adrenergicc - G-proteins
- Gs, Gi
- transduce extracellular signals into an intracellular response - Enzymes
- Adenylyl cyclase
- catalyze the production of second messengers - Second messengers
- cAMP, calcium - Protein kinases
- Response
Summary of Signal Transduction Story
- a transmitter bings to a receptor
- the binding causes a conformational change, a cascade of events
- the complex causes a conformational change in the G-protein
- The G-protein may alter the activity of a membrane-bound enzyme
- the enzyme then alters the production of second messengers
- second messengers may alter enzyme activity inside of the cell
- may alter the phosphorylation state of proteins
- physiological changes
Dual Innervation
Most tissues receive innervations from both the parasympathetic and sympathetic divisions
EXCEPT: sweat glands (sympathetic innervation only) and most blood vessels
Parasympathetic System
Plays a role in housekeeping
Sympathetic System
Plays a role in fright, flight, or fight response
How are Eyes Affected by ANS?
Sympathetic = dilation of the pupil - adjustment for far vision Parasympathetic = constriction of the pupil - adjustment for near vision
How is the Cardiovascular System Affected by ANS?
Sympathetic = increase heart rate and force of contraction Parasympathetic = decrease heart rate
How are Blood Vessels Affected by ANS?
Sympathetic = constriction Parasympathetic = no innervation - no response
How are Sweat Glands Affected by ANS?
Sympathetic = general increase of temperature Parasympathetic = no innervation - no response
How are Salivary Glands Affected by ANS?
Sympathetic = small volume of thick saliva Parasympathetic = large volume of watery saliva
How is the Stomach/Pancreas Affected by ANS?
Sympathetic = decreased secretion Parasympathetic = increased secretion
How is the Digestive Tract Affected by ANS?
Sympathetic = decreased motility, contraction of sphincters Parasympathetic = increased motility, relaxation of sphincters
How are the Lungs Affected by ANS?
Sympathetic = airway dilation Parasympathetic = airway constriction
How is the Bladder Affected by ANS?
Sympathetic = prevent voiding Parasympathetic = voiding
How is Genitalia Affected by ANS?
Sympathetic = decreased blood flow, contracts smooth. muscle Parasympathetic = increased blood flow, no innervation of smooth muscle
Horner’s Syndrome
Damage to the sympathetic nerves innervating the face (unilateral) will cause:
- constriction of the pupil (myosis)
- drooping of the eyelid (ptosis)
- lack of sweating (anhidrosis)
- dilation of blood vessels (flushing)
General Scheme for Reflex Arc
Stimulus -> sensor -> integrator (brain/spinal cord) -> effector (smooth muscle, cardiac muscle, glands) -> response
Major Integrating Centers for Autonomic Reflexes
Hypothalamus
-head ganglion of ANS
-temperature regulation
Brainstem (Medulla)
-blood pressure regulation, salivation, swallowing, vomiting, respiration
Spinal Cord
-regulates urination, defecation, erection
Role of ANS in Micturition (Urination) Reflex
Low volume in the bladder
- low parasympathetic activity, the bladder does not contract
- tonic somatic activity, external sphincter contracts
High volume in the bladder
- high parasympathetic activity, the bladder contracts
- removal of tonic somatic activity, the external sphincter relaxes and urination occurs
Role of ANS in Temperature Regulation
Temperature receptors in the skin and hypothalamus Hypothalamus is the integrating center -changes in blood flow to the skin -changes in the amount of sweating -changes in metabolism
It’s Too Cold!
Increased sympathetic activity
- increased metabolism and heat production
- vasoconstriction of blood vessels
- piloerection (goosebumps)
Decreased sympathetic activity
-inhibition of sweating
It’s Too Hot!
Increased sympathetic activity
-increased sweating
Decreased sympathetic activity
- decreased metabolism and heat production
- reduce vasoconstriction
- no piloerection
How do Drugs Interfere with the ANS
Interferes with
- synthesis, storage, and release of transmitters
- inactivation of transmitter by uptake or breakdown
- react with receptors of transmitters causing activation (agonist drugs) or block (antagonist drugs)
Agonist Drugs
drugs that mimic the action of the normal transmitters when they react with receptors
Antagonist Drugs
drugs that block or inhibit the action of the physiological transmitter upon binding to a receptor
