Movement - 3

Question 1

What brain region is at the top of the hierarchy?

Answer 1

Hypothalamus

Question 2

Name examples of involuntary movements.

Answer 2

• Pupil dilation
• Blood vessel dilation
• GI track peristalsis
• Stress response
• Milk let-down
• Vomiting.

Question 3

Feedback is central for movement control. What brain region can act as a comparator?

Answer 3

Hypothalamus

Question 4

How do we organize a stress response to resolve a stressful situation?

Answer 4

Sympathetic ANS activates → HPA-axis activates

Both run by the hypothalamus

Question 5

Describe characteristics of the sympathetic ANS that is activated under stress.

Answer 5

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).

Question 6

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?

Answer 6

Besides noradrenergic innervation of tissues, the sweat glands and the medulla of the adrenal gland are innervated by acetylcholine (cholinergic innervation).

Question 7

Where are the preganglionic cell bodies of the sympathetic nervous system located?

Answer 7

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.

Question 8

Where do the projections of the preganglionic neurons of the sympathetic nervous system go?

Answer 8

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.

Question 9

Describe the characteristics of the parasympathetic nervous system.

Answer 9

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.

Question 10

Where are the cell bodies of the preganglionic parasympathetic neurons located and where do they exit?

Answer 10

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.

Question 11

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.

Answer 11

• 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)

Question 12

Summary of what has been discussed so far.

Answer 12

Ok

Question 13

A revision is being made from cranio-sacral division to cranial division of the parasympathetic nervous system. Why?

Answer 13

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.

Question 14

Where is the enteric nervous system located and what does it do?

Answer 14

In the wall lining of the gut. It controls gut peristalsis.

Question 15

Where are the enteric nervous system neurons located within the wall lining of the gut?

Answer 15

The ENS neurons are located in the myenteric and submucous plexus.

Question 16

What do the myenteric and submucous plexus control?

Answer 16

• Myenteric → controls smooth muscle
• Submucous → controls secretory glands (secretion of digestive enzymes) and senses mechanical and chemical contents.

Question 17

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?

Answer 17

• 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.

Question 18

Describe characteristics of the vagus nerve.

Answer 18

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.

Question 19

Cranial nerve mnemonic

Answer 19

Ok

Question 20

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.

Answer 20

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).

Question 21

What is referred pain?

Answer 21

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).

Question 22

What happens when high blood pressure is sensed by the baroreceptors in the aorta?

Answer 22

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.

Question 23

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?

Answer 23

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).

Question 24

Besides blood pressure, also the chemical composition of the blood is sensed. How is this done?

Answer 24

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.

Question 25

How is the ANS controlled by the brain (same question in different words: what controls the preganglionic neurons)?

Answer 25

The paraventricular nucleus (PVN) of the hypothalamus is important for the control of the ANS.

The PVN is important for the outflow of information into the ANS. It has projections to the motor nucleus of the vagus nerve and projections to the preganglionic neurons in the sympathetic system of the spinal cord.

Question 26

How can the hypothalamus be divided?

Answer 26

The hypothalamus can be divided into a anterior, tuberal and posterior region.

Question 27

What nucleus of the hypothalamus resides in the anterior part and what is the function of this nuclei?

Answer 27

Suprachiasmatic nucleus, which receives innervation from the retina and controls circadian wakefulness.

Question 28

What nuclei of the hypothalamus reside in the tuberal part and what are their functions?

Answer 28

It contains the paraventricular nucleus and the supraoptic nucleus. Both nuclei have neurons projecting to the posterior pituitary and release oxytocin and vasopressin into the bloodstream.

These hormones have a motor effect on the body that the hypothalamus can initiate directly.

Question 29

What nuclei of the hypothalamus reside in the posterior part of the tuberal region?

Answer 29

Ventromedial nucleus that initiates attacks and the arcuate nucleus that initiates feeding.

Note: these two things are both discovered through optogenetics.

Question 30

Hypothalamus is in charge of the pituitary gland. It has a direct and indirect effect on the pituitary.

What are these direct and indirect effects?

Answer 30

• Direct release of oxytocin and vasopressin from paraventricular and supraoptic nucleus neurons into posterior pituitary
• Indirect release of 7 hormones by hypothalamus in anterior part of pituitary gland. This is done by the hypothalamic release of releasing factor (RF) into a portal system in the anterior pituitary. RF is sensed by specialized glandular cells that secrete hormones into the bloodstream (see table for hormones).

Note: releasing factor hormone can be in all sorts of forms (see control of release in table).

Question 31

Adrenocorticotropic hormone (ACTH) is a hormone that is released from the anterior pituitary by the stimulation and release of corticotropin-releasing hormone (CRH). What is the function of ACTH?

Answer 31

It regulates the stress response by the adrenal cortex (by regulating the levels of cortisol and androgens produced by the adrenal cortex).

Question 32

What is the name for the release of CRH by the hypothalamus onto the anterior pituitary gland, which releases ACTH onto the adrenal cortex?

Answer 32

Hypothalamic-pituitary-adrenal cortical axis (HPA axis).

Note: there are also other axes with the same mechanism → see picture.

Question 33

The HPA axis has amplification through a cascade effect. Explain this.

Answer 33

• Parvocellular CRH neurons in the hypothalamus release about 0,1 ug of CRH onto the anterior pituitary gland.
• As a consequence, the glandular cells of the anterior pituitary gland release 1 ug of ACTH (10x more).
• ACTH goes into the bloodstream and into the adrenal gland cortex. The adrenal gland cortex then releases about 40 ug of cortisol. Cortisol regulates the release of glucose and adrenaline and is important for immune suppression.

Question 34

Describe the stress response when the sympathetic ANS is activated.

Answer 34

The paraventricular nucleus (PVN) of the hypothalamus is activated and innervates preganglionic sympathetic neurons (cholinergic). ACh is released onto postganglionic sympathetic neurons, which will mostly release noradrenaline. The effects of noradrenaline can be seen in many targets (bronchiole dilation in lungs, heart rate increases, etc…)

Question 35

At the same time as the sympathetic ANS is activated, the hypothalamo-pituitary-adrenal (HPA) axis is also activated. Describe the stress response of the HPA axis.

Answer 35

The paraventricular nucleus of the hypothalamus activates its parvocellular CRH neurons. CRH is released into the portal system of the anterior pituitary gland. ACTH is released into the bloodstream from the anterior pituitary gland, which results in the release of cortisol from the adrenal cortex. Effects of this can be seen by glucose mobilization, adrenaline release and immune suppression.

Question 36

What other function does the hypothalamus have?

Answer 36

Regulating motivation through neural mechanisms.

Question 37

How do they know that the hypothalamus is involved in the regulation of motivation?

Answer 37

• By classical studies with lesioning the lateral hypothalamus of animals. This resulted in animals becoming very lean and being not very active. This would indicate that the hypothalamus has a hunger center. But this classical study was difficult to interpret and the results became not true.
• Then optogenetic constructs were made from the lateral hypothalamus. They used a setting where the mouse would run away from a certain object under normal conditions. But when the light was activated in the lateral hypothalamus, the mouse would attack the object.

Question 38

Just know that many (optogenetic) experiments have been performed on the nuclei of the hypothalamus. By doing this, they found many functions of the nuclei of the hypothalamus. Many were motor functions like drinking, feeding, sex, aggression, fear and thermoregulation.

The hypothalamus is thus a master controller of motivational states.

Question 39

In the lateral hypothalamus, orexin neurons reside. They used optogenetics to research the function of these neurons.

What did they do and what did they find?

Answer 39

They used optogenetics (through the use of adenovirus as a vector) to target the orexin neurons for optogenetics. When the light was activated, animals started to run. So the orexin neurons seem to be important in initiating movement/overall activation of movement.

They did many more optogenetic tests with orexin neurons and found that the neurons were also important in wakefulness, arousal, metabolism and feeding.