Lecture 9: Efferent Pathways

What does the somatic nervous system control?

voluntary skeletal movements

What does the autonomic nervous system do?

Controls involuntary actions

What makes up the autonomic system?

sympathetic, parasympathetic and enteric systems

What is the enteric nervous system?

the nervous system of the digestive tract

What is homeostasis?

A dynamic balance between the autonomic brances

When resting which activity dominates?

Parasympathetic

When in fight or flight which activity dominates?

Sympathetic

What controls respiration, heart rate, blood pressure, and consciousness?

The brainstem

Where do parasympathetic nerves originate?

At the base of the brain or the base of the spinal cord.

Where do sympathetic nerves originate?

spinal cord

What is the sympathetic chain?

A sympathetic chain consists of sympathetic ganglion and rami communicantes.

What nerve makes up (75%) the majority of the parasympathetic tract?

Vagus nerve

What do the sympathetic nerves travel between?

Paravertebral ganglia in the sympathetic chain

What permits coordination between the vertebral ganglia?

The traveling of sympathetic nerves

If neurons skip past the sympathetic chain, where do they connect instead?

At the prevertebral ganglia

Which nerves supply the GI tract?

Those that connect at the prevertebral ganglia

what is the effernt tract

A 2 neuron system

What do autonomic pathways consist of?

two neurons that synapse in an autonomic ganglion

What is the autonomic ganglion?

A group of neurons were all cells bodies lie outside the CNS

How does the preganglionic neuron travel?

It leaves the CNS to go to the autonomic ganglion

How does the postganglionic neuron travel?

They leave the autonomic ganglion so that the synapse goes straight to the target

Which neurotransmitter is used in both the sympathetic and parasympathetic pathways?

Acetylcholine

Which neurotransmitters are used in sympathetic pathways?

Acetylcholine and norepinephrine

Which neurotransmitter is used in parasympathetic pathways?

Acetylcholine

What does acetylcholine do?

Opens channels such as ionotropic receptors

What type of receptor are nicotinic receptors?

ionotropic- fairly quick

What type of neuron is an ionotropic receptor

Pregaglionic

What type of neuron has metabotropic receptors?

Postganglionic

What is the receptor on target tissues in sympathetic pathways?

Adrenergic receptor

What is the receptor on target tissues in parasympathetic pathways?

Muscarinic receptors

What does the adrenal gland serve as?

A modified sympathetic ganglion that is capable of releasing epinephrine

In which pathway is activation much more targeted/organized?

Parasypathetic

Why is activation in parasympathetic pathways closer to the target organ?

The ganglion is NOT near the spine or brain

What is Horner's syndrome?

A condition that results from damage to sympathetic facial nerves that causes pupil constriction in the eye and dry skin

How do sympathetic nerves stimulate pupil dilation?

Norepiniphrine

How are sweat glands stimulated?

Acetylcholine

When looking at Horner's syndrome, the stimulation of the adrenal gland can cause the pupil to dilate, but why does it not help the dry skin?

The adrenal gland produces epinephrine, which is similar to norepinephrine; however, the adrenal gland cannot substitute Ach to produce sweat to help with the dry skin.

How is memory in the amygdala enhanced by the adrenal gland?

Fear-induced stimulation of the adrenal medulla leads to norepinephrine release that promotes GABA inhibition and promotes LTP.

What is the neuromuscular junction?

point of contact between a motor neuron and a skeletal muscle cell

What does the neuromuscular junction produce?

Fast, onset, short-duration, and supra-threshold EPP in skeletal muscle.

Why is the autonomic postganglionic synapse slow?

Receptors are so spread out so the neuron has to diffuse, so the transmitter affects a larger area and has to work for a longer time.

What can autonomic neurons do?

Summ because of the varying number of synapses

How can you regulate contraction during reciprocal inhibition?

You have to control the muscles to retract by controlling the level of muscle excitation by inhibiting the motor neuron not the muscle

What is reciprocal innervation?

The direct excitation and inhibition of smooth and cardiac muscle

What does ACh do in reciprocal innervation?

It opens K channels which inhibits the SA node

What does parasympathetic stimulation do to smooth cardiac muscle?

It decreases the heart rate

What does norepinephrine do in reciprocal innervation?

It opens Na/Ca channels that excites the SA node

What does sympathetic stimulation do to smooth cardiac muscle?

It increases the heart rate

What does parasympathetic stimulation do to control pupil size?

Constriction

What does sympathetic stimulation do to control pupil size?

Dilation

What inhibits parasympathetic ACh and dilates the pupil?

Atropine

What does the enteric nervous system do?

Controls the gastrointestinal system

What is the myenteric plexus?

The nerve fibers that control the circular and longitudinal muscles to control contraction or relaxation

What does the myenteric plexus control?

motility

Which neurotransmitter is excitatory in the Myenteric plexus?

ACh

Which neurotransmitter is inhibitory in the Myenteric plexus?

NO

What does the submucosal plexus control?

secretions and the contraction of muscular muscosa

What does the myenteric plexus repond to?

Stretch and tnesion

What does the submucous plexus contain?

Chemical receptors that are sensitive to lumenal content such as acids, glucose, fats, and amino acids

What role does the sympathetic system play in the enteric citcuitry?

A very small role- it acts as an override to slow motility and decrease secretion

How does the parasympathetic system control the enteric circuitry?

Vagus nerve is dominant and prevents blood from entering the GI tract. It also activates nicotinic receptors as the ENS acts as a postganglionic nerve

What are inhibitory neurotransmitters in the enteric circuits?

NO

What are excitatory neurotransmitters in the enteric circuits?

ACh and substance P

How does contraction work in circular muscles?

The area behind the movement relaxes while the area in front contracts.

What does the vagus nerve do?

It regulates the vago-vagal reflex

What types of neurons does the vagus nerve have?

Sensory and motor neurons

What is esophageal peristalsis?

The tract in which the food moves into the stomach

When the esophageal contracts, what happens?

ACh releases from the ENS

When the esophageal relaxes, what happens?

NO releases from the myenteric ENS

Why is the relaxation of the lower sphincter important?

It contracts to stop food from going back up into the esophagus but relaxes to let food back in

What is achlasia?

Failure to relax the lower esophageal sphincter.

What causes achalasia?

The degeneration of inhibitory NO and VIP releasing neurons

Which nerve releases norephinephrine?

Sympathetic postganglionic nerve

What are the characterisitcs of the autonomic nervous system?

1) 2 neurons in the efferent pathway
2) The control contraction in SMOOTH muscles ONLY
3) Release at varicosities
4) The sympathetic and parasympathetic nerves innervate the same organ
5) It can be excitatory or inhibitory
6) Reach receptors over a very small postsynaptic area

What does achalasia NOT do?

Block esophageal ionotropic receptors

What do postganglionic synapses NOT do?

Activate ionotropic receptors

What is the prevetebral ganglia?

Sympathetic neurons that supply the gut