Movement - 3 Flashcards
What brain region is at the top of the hierarchy?
Hypothalamus
Name examples of involuntary movements.
- Pupil dilation
- Blood vessel dilation
- GI track peristalsis
- Stress response
- Milk let-down
- Vomiting.
Feedback is central for movement control. What brain region can act as a comparator?
Hypothalamus
How do we organize a stress response to resolve a stressful situation?
Sympathetic ANS activates → HPA-axis activates
Both run by the hypothalamus
Describe characteristics of the sympathetic ANS that is activated under stress.
This system is also called the fight or flight system.
It is composed of a number of neurons in the spinal cords. Here cholinergic preganglionic neurons from the spinal cord synapse onto postganglionic neurons. These postganglionic neurons innervate tissues in the body, where (mostly) norepinephrine is released onto tissues (noradrenergic postganglionic neurons).
Norepinephrine is an important player in the sympathetic nervous system. It innervates most of the tissues that are needed during the fight or flight response.
There is an exception to this. What exception?
Besides noradrenergic innervation of tissues, the sweat glands and the medulla of the adrenal gland are innervated by acetylcholine (cholinergic innervation).
Where are the preganglionic cell bodies of the sympathetic nervous system located?
In the intermediolateral cell column of the lateral horn of the spinal cord. Important to remember is that the intermediolateral cell column of the lateral horn is only located at thoracic and lumbar level of the spinal cord.
Where do the projections of the preganglionic neurons of the sympathetic nervous system go?
From the lateral horn, the projections go to the ventral horn. From here they go into the white communicating ramus and synapse with postganglionic neurons in sympathetic chain ganglia. The projections can also go on to another ganglion e.g. to the prevertebral ganglion that project to the viscera or to the blood vessels and skin.
Describe the characteristics of the parasympathetic nervous system.
This system is also called the rest and digest system or the craniosacral system (nerves originate from cranial and sacral nerves).
In this system, there’s only cholinergic neurotransmission. Furthermore, the ganglia of this system are much closer located to the target tissue.
Where are the cell bodies of the preganglionic parasympathetic neurons located and where do they exit?
The preganglionic neurons are located in the intermediate gray zone in the spinal cord. They exit the spinal cord through the ventral root and go onto postganglionic neurons near the organs.
The parasympathetic nervous system is controlled in the brain stem nuclei that send out cranial nerves to the body. Name three brain stem nuclei and their cranial nerves that are important in the parasympathetic nervous system.
- Oculomotor nuclei → ocolomotor nerve (for pupil constriction)
- Salivatory nuclei → facial nerve and glossopharyngeal nerve (for salivation).
- Dorsal motor nucleus of vagus → vagus nerve (for rest and digest)
Summary of what has been discussed so far.
Ok
A revision is being made from cranio-sacral division to cranial division of the parasympathetic nervous system. Why?
Genetic markers of the parasympathetic sacral nerves have been found that are the same as the genetic markers for the nerves of the sympathetic nervous system. So now, the parasympathetic nervous system is only composed of the cranial nerves.
Where is the enteric nervous system located and what does it do?
In the wall lining of the gut. It controls gut peristalsis.
Where are the enteric nervous system neurons located within the wall lining of the gut?
The ENS neurons are located in the myenteric and submucous plexus.
What do the myenteric and submucous plexus control?
- Myenteric → controls smooth muscle
- Submucous → controls secretory glands (secretion of digestive enzymes) and senses mechanical and chemical contents.
The enteric nervous system (ENS) is controlled by the autonomic nervous system.
- How is parasympathetic innervation of the ENS achieved?
- How is sympathetic innervation of the ENS achieved?
- Parasympathetic innervation → dorsal motor nucleus of vagus → vagus nerve (and sacral cord) → into postganglionic parasympathetic neurons in the lining of the gut.
- Sympathetic innervation → preganglionic sympathetic axon → prevertebral ganglion → postganglionic sympathetic axon → innervates neurons in the lining of the gut.
Describe characteristics of the vagus nerve.
This nerve is important for innervating many tissues in the body (both motor and sensory). It is therefore also called the wanderer. It is mostly an important component of the parasympathetic autonomic nervous system.
Cranial nerve mnemonic
Ok
So the vagus nerve sends out inputs to many different tissues. But it also has the ability to receive output from tissues, such as the gut lining. Describe how the vagus nerve receives this output.
The vagus nerve receives information from the gut lining, for e.g. what’s inside the gut. These afferents terminate in the nucleus of the solitary tract (dorsal to RF).
What is referred pain?
It is pain perceived at a location other than the site of the painful stimulus, which is the result of a network of interconnecting sensory nerves (like the vagus nerve), that supplies many different tissues.
In other words:
Some second-order visceral afferents of the vagus nerve are the same as are used by external pain sensory (anterolateral system).
What happens when high blood pressure is sensed by the baroreceptors in the aorta?
A negative feedbackloop is initiated:
The high BP is received by the baroreceptor afferents, which project to the sensory fibers of the vagus nerve into the nucleus of the solitary tract (NTS) where the information is integrated. The information is then sent into the nucleus ambiguus (motor nucleus for vagus nerve). Here, the vagus nerve efferents are activated, which synapse onto postganglionic parasympathetic fibers in the cardiac plexus. These postganglionic fibers release ACh into the heart, to slow down the heart rate.
So when there’s high blood pressure the parasympathetic nervous system is activated. For this the sympathetic nervous system needs to be inactivated. How is this achieved?
At the same time the information of high blood pressure is integrated by other neurons in the NTS. The information is relayed here to inhibitory interneurons that impinge on the sympathetic nervous system. The interneurons cause the activity of the sympathetic neurons to go down. So there’s less activation of the preganglionic neurons, which then will innervate less sympathetic chain ganglia and thus releasing less noradrenaline into the bloodstream (preventing an increase in blood pressure).
Besides blood pressure, also the chemical composition of the blood is sensed. How is this done?
This is done by the peripheral senses at the carotid body located in the neck. This information is relayed to chemoreceptor afferents into the glossopharyngeal nerve, that can send information back to the vagus nerve.
