Autonomic Nervous System Flashcards
Devision of the nervous system
Structure of neuron
ganglion
collection of cell body bundled together
Describe:
Efferent
-from brain to effector
Describe:
Afferent
-from effector to brain
Innervates definition
- supply an organ with nerves
- To stimulate a nerve (or other part of the body) into action
Overview:
Autonomic Nervous System
- conveys information from the CNS to the rest of the body (except the skeletal muscles–> somatic afferent system)
- innervates internal (visceral) organs- basic processes needed for normal bodily functions
- not under voluntary control
What does ANS regulates?
ANS regulates:
- contraction and relaxation of smooth muscle
- all exocrine glands eg. sweat gland
- some endocrine glands eg, pancreas, adrenal gland
- heartbeat
- certain intermediary metabolism
Autonomic Nervous System neuron structure
2 neuron system, serially connected -preganglionic neuron and postganglionic neuron connected by autonomic ganglion (synaptic cleft)
Autonomic Nervous System division
- sympathetic nervous system (fight or flight)
- parasympathetic nervous system (rest and digest)
- enteric nervous system (gut)–>sometimes considered part of the autonomic nervous system and sometimes considered an independent system.
Parasympathetic Nervous System
- rest & digest response
- branches off the cranial and sacral section of spinal cord
- both preganglionic and postganglionic neurons releases acetylcholine (Ach) as neurotransmitter
structure of parasympathetic neuron
- Preganglionic fibers of the parasympathetic branch are longer than those of the sympathetic branch.
- The ganglia of the parasympathetic system are generally situated close to, or within the tissue to be affected.
Sympathetic Nervous System
- flight or fight response
- branches off thoracic and lumbar section of spinal cord.
- preganglionic neurons releases acetylcholine (Ach) as neurotransmitter
- postganglinic neurons releases noradrenaline (NA) as neurotransmitter, -except postganglionic neurons of sweat gland –> Ach
structure of sympathetic neuron
- Sympathetic ganglia are usually situated near the central nervous system.
- The postganglionic fibers then extend a longer distance to the intended organ.
Other exception in sympathetic nervous system: Adrenal gland system
- branch off sympathetic nervous system
- preganglionic neurons do not synapse in the paraverterbral sympathetic ganglion (no postganglionic neurons
- Preganglionic neurons synapse directly on the adrenal gland in the adrenal medulla, release acetylcholine
How do drugs influence ANS?
Direct acting:
- parasympathomimetic
- sympathomimetic
- parasympatholytic
- sympatholytic
Parasympathomimetic
- drugs that mimics Ach (agonist)
- therfore, it’s cholingenic
- acts primarily on muscarinic receptor (M)
- limited clinical use
Sympathomimetic
- drugs that mimics NA & A (agonist)
- therefore, it’s adrenergic
- acts on adrenergic receptors alpha & beta receptor
Parasympatholytic
-drugs that inhibits/antagonise the action of Ach (antagonist)
Sympatholytic
-drugs that inhibits/antagonise the action of NA & A (antagonist)
Parasympathetic and Sympathetic branches
comparison of motor route of somatic nervous system and autonomic nervous system
Anatomy of the spinal cord and the relex arc
- The spinal cord consists of highly organized regions of gray matter and white matter.
- Gray matter contains the cell bodies of a variety of association and motor neurons -
- the white matter consists of tracts of myelinated nerve fibers.
Travelling of nerve impulse/action potential
- Incomming sensory fibers connect through the dorsal roots of spinal nerves.
- Outgoing motor fibers leave through the ventral roots of spinal nerves.
Preganglionic aka.
Presynaptic
Postganglionic aka.
Postsynaptic
Ganglion aka.
synaptic cleft
What happens when Na+enters cell?
- It causes the membrane to depolarize slightly (becomes more positive)
- Raising the membrane potential from -70mV closer to the action potential threshold
What happens when Cl- enters cell?
- makes the membrane potential slightly more negative than -70mV, known as hyperpolarization.
- the membrane potential is now even further away from the threshold potential, making it harderr for an action potential to be initiated
Neurotransmitter removal
-After neurotransmitter have been released during synaptic transmission, there must be a fast mechanism in place to remove the neurotransmitter ready for the next signal.
What happen to acetycholine in synapse
- acetycholine is enzymically degraded by acetylcholinesterase into acetate and choline
- therse products may be uptakes into the presynaptic nerve terminal and resynthesized into new acetylcholine for reuse.
Ways of halting neurotransmitter action
- Fast enzymic degradation
- Uptake into presynaptic cells or neighbouring cells
- Diffusion out of the synapse before further uptake or enzymatic degradation
Why do we need to remove neurotransmitter from the synapse after an action potential is generated
- Neurotransmitter must act to transmit each action potential separately.
- The delay between action potentials may be very short in rapidly firing nerves, ie motor neurons
- The neurotransmitter must be removed quickly before the next action potential reached the nerve terminal
If not, depolarizing block may occur.
Acetylcholine
- formed in presynaptic terminal by choline O-acetyltransferase
- this enzyme removes an acetyl group from acetyl coenzyme A and links it to choline
- released via exocytosis in response to an increased in Ca2+concentration
Formation of Acetycholine diagram
The neuron is presynaptic
At postsynaptic cell,
- if it’s a nerve cell, can cause action potential
- if it’s a muscle cell, can cause a response
Terminatin of ACh action
- unused ACh rapidly remoced
- results in BRIEF and LOCALISED action of neurotransmitter
Two ways of ACh removal in the synapse
- acetycholine is enzymically degraded by acetylcholinesterase into acetate and choline
- therse products may be uptakes (via ion gated membrane channel) into the presynaptic nerve terminal and resynthesized into new acetylcholine for reuse.
Noradrenaline (NA)
- synthesised at the postganglionic sympathetic nerve endings
- in adrenal medulla, NA & A is secreted as hormone
Termination of NA/A action
- Enzymatic degradation free NA/A–>slow
- -Monoamine oxidase (MAO)*-associated with mitochondria
- Catechol-o-methyl transferase(COMT)-present in cardiac and smooth muscle
- Reuptake by surrounding cells
- uptake 1-high affinity/low rate
- uptake 2-low affinigy/high rate
Autonomic Receptors
Types of neuron system
Cholingernic receptors and its endogenous agonist
Adrenergic receptors and its engodenous agonist
