Ch. 9 Autonomic Nervous System (ANS) Flashcards
Somatic Motor Neurons
Have cell bodies in spinal cord and just one neuron traveling from spinal cord to effector (neuromuscular junction = effector)
Controls skeletal muscle
Somatic motor neurons release only ____ which is always ____.
Acetylcholine (ACh); excitatory
The ANS has what 2 divisions?
Sympathetic and Parasympathetic divisions
The Autonomic motor system has 2 neurons in the PNS. Describe them.
The First has cell bodies in the brain or spinal cord and synapses in an Autonomic Ganglion.
The Second has cell bodies in the ganglion and synapses on the effector.
Autonomic neurons release mainly ____ and ____ and may be ____ or ____.
Acetylcholine, Norepinephrine
Excitatory or Inhibitory
–e.g. raise HR, lower HR
Autonomic Neurons
Innervate organs not under voluntary control
Effects include:
- cardiac muscle
- smooth muscle of visceral organs and blood vessels
- glands
Part of PNS
Can stimulate or inhibit, depending on organ and receptors
Preganglionic Neurons
Originate in midbrain or hindbrain or from thoracic, lumbar, or sacral spinal cord
Autonomic Neurons
Postganglionic Neurons
Originate in ganglion
Where are Autonomic Ganglia located?
In head, neck, and abdomen as well as in chains on either side of the spinal cord
Sympathetic Division: Preganglionic Neurons
Come from thoracic and lumbar regions of spinal cord
–aka Thoracolumbar Division
Synapse in sympathetic ganglia that run parallel to spinal cord
- -aka Paravertebral ganglia
- -these ganglia are connected, forming a sympathetic chain of ganglia
Adrenal Glands
Adrenal medulla secretes Epinephrine (adrenaline) and norepinephrine (lesser extent) when stimulated by the Sympathetic Nervous System; the adrenal medulla is innervated directly by preganglionic sympathetic neurons
Parasympathetic Division
Preganglionic neurons come from the brain or sacral region of the spinal cord (Craniosacral Division)
Synapse on ganglia located near or in effector organs; called terminal ganglia
Preganglionic neurons do not travel w/ somatic neurons (as sympathetic postganglionic neurons do)
Terminal ganglia supply very short postganglionic neurons to effectors
What are the 2 parasympathetic cranial nerves we need to know?
Oculomotor nerve (III) and Vagus nerve (X)
Oculomotor Nerve (III)
Motor nerve
Preganglionic fibers exit midbrain and synapse on the ciliary ganglion
Postganglionic fibers innervate the ciliary muscle of the eye
–regulate ciliary muscles of eye (vision)
Vagus Nerve (X)
Sensory and motor nerve (mixed nerve)
Preganglionic fibers exit medulla, branch into several plexi and nerves, and travel to ganglia w/in effector organs (heart, lungs, esophagus, stomach, pancreas, liver, intestines)
Vagus controls basal HR (resting)
General Functions: Sympathetic
Activates body for “fight or flight” through release of Norepinephrine from Postganglionic neurons and secretion of Epinephrine (adrenaline) from Adrenal Medulla.
Prepares body for intense physical activity in emergencies by increasing HR and blood glucose levels and by diverting blood to skeletal muscles.
Regulates heart, blood vessels, and other organs.
General Functions: Parasympathetic
Antagonist to sympathetic divison
Allows body to “rest and digest” through release of ACh (acetylcholine) from Postganglionic neurons
Slows HR and increases digestive activities
The Sympathetic system is activated by what 2 receptors?
Alpha and Beta
The Parasympathetic system is activated by what receptor?
Muscarinic
Synaptic Transmission: Cholinergic
ACh is neurotransmitter used by ALL preganglionic neurons (sympathetic and parasympathetic)
It’s also the neurotransmitter released from MOST parasympathetic postganglionic neurons
SOME sympathetic postganglionic neurons (those that innervate sweat glands and skeletal muscle blood vessels) release ACh.
Synaptic Transmission: Adrenergic
Norepinephrine is the neurotransmitter released by MOST sympathetic postganglionic neurons
These synapses are called Adrenergic
*According to lecture, epinephrine can also be released in this transmission
Varicosities
Axons of postganglionic neurons have various swellings called Varicosities that release neurotransmitter along the length of the axon
Sympathetic and parasympathetic neurons innervate the same tissues but release different neurotransmitters
*Not a true/classic synapse where it ends at target
Adrenergic Stimulation
Can be epinephrine in blood or norepinephrine from sympathetic nerves
Can stimulate or inhibit, depending on receptors
Adrenergic Stimulation: Stimulation
Heart, dilatory muscles of iris, smooth muscles of many blood vessels (causes vessel constriction)
*pretty much everything but skeletal muscle
Adrenergic Stimulation: Inhibition
Bronchioles in lungs, other blood vessels; inhibits contraction and causes dilation of these structures
*inhibits particularly in skeletal muscle
Adrenergic Receptors are only found in what system?
Sympathetic
How many types of alpha receptors (Adrenergic) are there?
2 types:
Alpha 1
Alpha 2
How many types of beta receptors (Adrenergic) are there?
2 types:
Beta 1
Beta 2
Adrenergic Receptors: Alpha
More sensitive to norepinephrine
More sensitive to postganglionic neuron
Adrenergic Receptors: Beta
More sensitive to blood epinephrine
Epinephrine from Adrenal Medulla; sensitive to circulating neurotransmitter
Cholinergic Stimulation
ACh released from preganglionic neurons of both sympathetic and parasympathetic division is stimulatory
ACh from post ganglionic neurons of the parasympathetic division is usually stimulatory, but some are inhibitory, depending on receptors
*In general, sympathetic and parasympathetic effects are opposite
What are the 2 types of Cholinergic Receptors?
Nicotinic and Muscarinic
Cholinergic Receptors: Nicotinic
Found in autonomic ganglia
Stimulated by ACh from preganglionic neurons
Serves as ligand-gated ion channels for Na+ and K+
Cholinergic Receptors: Muscarinic
Found in visceral organs
Stimulated by release of ACh from postganglionic neurons
Five types identified; can be stimulatory or inhibitory (opening K+ or Ca2+ channels)
Organs w/ Dual Innervation
Most visceral organs are innervated by both sympathetic and parasympathetic neurons; the divisions most often oppose each other
- -HR - sym increases, para decreases
- -Digestive functions - sym decreases, para increases
- -Pupil diameter - sym dilates, para constricts
Complementary effects occur when both divisions produce similar effects on the same target
–ex: Salivary gland secretion: Parasympathetic division stimulates secretion of watery saliva; sympathetic constricts blood vessels so secretion is thicker
Organs w/o Dual Innervation
The following organs are innervated by the sympathetic division only:
- Adrenal medulla
- Arrector pili muscles in skin
- Sweat glands in skin
- Most blood vessels
Regulated by increase and decrease in sympathetic nerve activity
Important for body temperature regulation through blood vessels and sweat glands
