Peripheral Nerves and the Autonomic Nervous System Flashcards
Afferent
-Sensory neurons -to CNS -travel through spinal cord and cranial nerves to the medulla
Efferent
-Motor neurons -away from CNS
Somatic (Efferent)
-Innervates skeletal muscle
Autonomic (Efferent)
-involuntary -innervates smooth muscle, cardiac muscle, GI, etc.
Nociceptors
Respond to chemicals and can also be referred to as chemoreceptors
Mechanoreceptors (Stretch receptors)
-Pressure, stretch -Action postentials from pulmonary mechano-stretch receptor sensory neurons
Proprioceptors
Change in muscle or tendon length/tension, an example would be the patellar tendon reflex
Nociceptors/chemoreceptors
Example would be vagal afferent nerves responding to endogenous agents
What does tetrodotoxin (puffer fish) inhibit at the NM junction? What symptoms would that cause?
Blocks voltage gated Na+ channels. It would block sympathetic and parasympathetic pathways so paralysis, respiratory failure, blurred vision, vertigo, numbness, paresthesia, nausea and ataxia.
What does conotoxin (cone snails) inhibit?
Voltage gated Ca++ channel blocker that doesn’t allow the release of NT in the synaptic cleft. If no NT is released, the signal is terminated so you lose response of the postganglionic effect. Ex. muscle paralysis of the diaphragm that causes respiratory arrest.
What does dendotoxin (mamba snakes) inhibit?
They block voltage gated K+ channels therefore enhancing the release of Ach at NMJ. Initially results in muscle hyper excitability and convulsions,
What is the mechanism of action of botulinum toxin?
Block Ach release from the nerve terminal by inhibiting the SNARE complex, thus no Ach release and no effect.
How does nerve gas work, and what effects does it have?
They block the effects of acetylcholinesterase activity which increases the duration of Ach in the synaptic cleft. So symptoms would include salvation, excretions, constricted pupils
What is a motor unit?
Motor neuron and all the skeletal muscle fibers that it innervates
Can be one neuron to multiple muscle fibers (back muscles) or one neuron to only a few fibers (hands and face)
Where do efferent autonomic nerves typically originate?
Medulla
How is heart rate affected during inspiration?
- Decreases in parasympathetic output from ANS
- Increases cardiac pacemaker
- Increases HR
How is heart rate affected during expiration?
- Decreases HR
- Increase in parasympathetic (vagus nerve) output from ANS
- Slows cardiac pacemaker
How does the pathways differ from sympathetic and parasympathetic when talking about the length of preganglionic/postganglionic axons and origination of nerves?
Sympathetic -> Shorter preganglionic nerves and longer postganglionic nerves, nerves usually originate in the spinal cord at a location near to the effector organ.
Parasympathetic -> Very long preganglionic neuron and originates in the medulla of brainstem and some in the sacral region
How can the sympathetic pathway affect organs without innervation (such as a heart transplant)?
Sympathetic preganglionic neurons also stimulate the adrenal medulla to release epinephrine into the blood stream that can lead to sympathetic affects in the heart
Overview Neurotransmitters and Receptors used by the ANS:
What are the two Ach receptors used by the ANS? Agonists and antagonists of each?
What are the main adrenergic receptors used by the ANS?
alpha and beta
How to alpha 1,2 receptors respond to Epi and NE?
They both have variable affinities:
a1: NE > E (Ex. blood vessel constriction/BP)
a2: E => NE (Ex. presynaptic neuron)
Where are the locations of B1 and B2 receptors? How does Epi and NE differ in thier responses at each receptor?
B1: Epi > NE (ex. Inc. Heart Rate and cardiac contractility)
B2: Epi >> NE (ex. Bronchodilation, some vasodilation)
What are ganglia?
Collection of cell bodies
What are the acetylcholine receptors on organs?
Muscarinic (M1-5)
What are possible symptons of hypercholinergic (excessive Ach release)?
What are some symptoms that an overdose of anticholinergics (anti-muscarinic)?
What is it meant by organs/vessels having autonomic tone?
Neural stimulation by both sympathetic and parasympathetic to most organs (balance) Notable Exceptions:
– Blood vessels- more sympathetic tone/innervation
– Gut- more parasympathetic tone/innervation
– Sweat glands- sympathetic innervation (Ach)
Drug X blocks N2 receptors. What would this do to blood pressure?
It would decrease blood pressure because there is more sympathetic innervation in blood vessels so there would be less constriction -> decrease BP
What are autonomic reflexes?
Automatic reflexes that do not require cerebral processing such as cardiovascular reflexes and gut reflexes
Explain the Vago-vagal reflex
Stretch receptors in your upper stomach send afferent signal to medulla that sends efferent parasympathetic signal to relax stomach, increase secretions, ect.
Explain the baroreceptor reflex
When BP is high, reflex reduces HR and BP
When BP is low, reflex raises HR and BP
Stretch receptors located in carotid sinus and aortic arch stretch and cause a reflexive signal to be sent to the medulla
Explain the coronary chemoreflex
Parasympathetic reflex of the autonomic nervous system to lower heart rate during heart damage. Chemicals (thromboxame A2/inflammatory mediators) are released and cause a afferent signal to be send to the medulla, response is to decrease HR and contractility
What are some ways to therapeutically manipulate the ANS?
- Receptor agonists/antagonists
- Block the breakdown of NT
Dopamine and NE are broken down in the nerve terminal by?
Monoamine oxidase
Catecholomethyl transferase
What does reserpine do to BP, and why?
Inhibits vesicular monoamine transporter so NE release from the sympathetic neuron would be inhibited -> less vessel contraction -> decrease in BP
What are other brain regions involved in the ANS?
Emotion-induced vasovagal syncope
Vasovagal syncope occurs when the nucleus of the solitary tract is activated by brain regions like the amygdala that can cause a parasympathetic response so strong that it drops HR and BP and causes the person to faint.
Triggers: pain, emotional reaction, visual stimuli
