ANS Flashcards
Where is the ANS in the NS
part of the PNS
Place of the ANS in the structural organization of the nervous system
- Effectors:
- Cardiac muscle
- Smooth muscle
- Glands
What neuron chain does ANS use
2 neuron chain
Where is cell body of preganglionic neuron and where do they synapse
Brainstem or spinal cord and synapse in post-ganglionic cell body outside of the CNS
Primary neurotransmitters
acetylcholine (ACh) and norepinephrine (NE).
T or F: most effectors are influenced by both divisions simultaneously
T
Sympathetic and parasympathetic nervous systems are distinguished by
- their unique sites of origin.
- the relative length of their fibres.
- the location of their ganglia.
- Key anatomical differences between ANS divisions.
- Anatomical and Physiological Differences between the Parasympathetic and
Name sacral nerve roots of parasympathetic (craniosacral)
- Oculomotor nerve (III)
- Facial nerve (VII)
- Glossopharyngeal nerve (IX)
- Vagus nerve (X)
- Vagus nerves accounts for approximately 90% of all preganglionic parasympathetic fibres
- Sacral outflow: Located in the lateral gray matter of spinal cord segments S2-4.
- Parasympathetic nerves branch and form the splanchnic nerves.
- These innervate the distal half of the large intestine, urinary bladder, ureters, and reproductive organs.
in the sympathetic (thoracolumnar) where do the sympathetic fibers arise at
between T1-L2
* The cell bodies of these neurons are located in the lateral horns of the gray matter in spinal cord.
* The paravertebral chain ganglia flanks each side of the vertebral column.
How many chain ganglia are there
There are 23 chain ganglia (3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal).
What happens when a preganglionic nerve reaches a chain ganglion
1 of 3 things can happen:
* It can synapse at the same level it exits.
* It can ascend or descend to synapse at another level.
* It can bypass the chain ganglion and synapse at a distant collateral ganglion.
T or F: Upon stimulation, medullary cells secrete norepinephrine and epinephrine into blood
T
Describe Ach and Ne
- Acetylcholine (ACh) and norepinephrine (NE) are the major neurotransmitters within the ANS
- ACh releasing fibres are “cholinergic”
- NE releasing fibres are “adrenergic”
- The different types of receptors for ACh and NE determine whether they will be excitatory or inhibitory.
T or F: All ACh receptors are nicotinic
F, All ACh receptors are either nicotinic or muscarinic
Where are nicotinic and muscanaric receptors found
- Nicotinic (excitatory) receptors are found on:
- All post-ganglionic neurons (sympathetic and parasympathetic)
- The hormone producing cells of the adrenal medulla
- At the motor end plates of skeletal muscle.
- Muscarinic (inhibitory or excitatory) are found:
- On all parasympathetic target organs
- Some sympathetic targets (e.g. sweat glands, some blood vessels
Parasympathetic inhibition & excitation example:
- Inhibitory example: binding of ACh to muscarinic receptor on cardiac muscle slows heart rate
- Excitatory example: binding of ACh to muscarinic receptors of smooth muscle increase GI tract motility.
2 classes of adregenic recewptors
alpha and beta receptors
* Organs that respond to NE (or epinephrine – “E”) have A and B receptor
* B1 and B3 receptors are excitatory (e.g. increased heart rate)
- B2 receptors are mostly inhibitory (e.g. dilation of blood vessels and bronchioles).
what is *Sympathetic tone (vasomotor tone):
continual state of partial constriction of blood vessels
what is Parasympathetic tone:
- It is maintained in the heart and smooth muscles of digestive and urinary tracts
- This activity slows the heart and controls normal activity of the digestive and urinary tracts.
Roles for SNS
- Thermoregulation in response to temperature change on skin
- Release of renin from kidneys = increased blood pressure
- Metabolic effects (increased glucose and fats available for utilization via cortisol release)
- Adrenal medulla hormones causes stronger and faster skeletal muscle contractions
- Note: All of these play a role in survival.
ratio of pre to post ganglion in PNS
ratio of about 1:3 pre to post ganglionic fibres at most
* These fibres release ACh at their effector target that is quickly hydrolyzed by acetylcholinesterase
* Result: brief and local control over effectors.
ratio of pre to post ganglion in SNS
high ratio of pre to postganglionic receptors (approximately 1:10).
why do effects of SNS last longer than PNS
The effects of the sympathetic system last longer than the parasympathetic system for 3 reasons:
* NE is inactivated more slowly than ACh
* NE acts through second messengers while ACh acts directly via ligand gated ion channels
* NE and E are released in the blood where they are active until they are broken down by liver
What is main intergrator of ANS
Hypothalamus
