Chemical Control

Question 1

What are diffuse modulatory systems?

Answer 1

Exist only in the central nervous system. Several related cell groups that differ with respect to the neurotransmitter that they use. All extend spatial reach with highly divergent axonal projections and prolong their action by using metabotropic postsynaptic receptors.

Believed to regulate, among other things, the level of arousal and mood.

Question 2

Where is the hypothalamus located? Where is the pituitary located in respect to the hypothalamus?

Answer 2

Forms the wall of the third ventricle and sits below the dorsal thalamus.

The pituitary is located ventral to the hypothalmus, and posterior to the optic chiasm.

Question 3

What is the main function of the hypothalamus?

Answer 3

Homeostasis

- Eg. temperature, glucose levels, blood pressure etc.

Question 4

What are the three functional zones of the hypothalamus?

Answer 4

Lateral
Medial
Periventricular

Question 5

What is the function of the periventricular zone of the hypothalamus?

Answer 5

• Contains suprachiasmatic nucleus (SCN) to receive direct retinal innervation (from neighbouring optic chiasm) and functions to synchronize the circadian rhythms
• Control of ANS, regulating sympathetic and parasympathetic innervation of visceral organs
• Neurosecretory neurons extend axons towrd the stalk of the pituitary gland. These are cells that command our attention.

Question 6

Where is the periventricular zone of the hypothalamus located?

Answer 6

It comprises the neurons that surround the third ventricle. The other two functional areas of the hypothalamus are further away from the third ventricle (in layers radiating outward)

Question 7

What type of neurosecretory cells does the hypothalamus project to the posterior parietal lobe?

Answer 7

Magnocellular neurosecretory cells

• Releases neurohormones into capillaries of posterior pituitary

Question 8

What type of neurosecretory cells does the hypothalamus project to the anterior parietal lobe?

Answer 8

Parvocellular neurosecretory cells from the periventricular zone of the hypothalamus. However these don’t descent staight into th anterior pituitary. They secrete hypophysiotropic hormones into a capillary bed at the floor of the third ventricle, these capillaries branch in the anterior lobe of the pituitary. This network of blood vessels is called hypothalamo-pituitary portal circulation. Hypophysiotropic hormones bind to specific receptors on the surface of pituitary cells. Activation causes secretion or stop of secretion into general circulation

Question 9

Of the posterior and anterior lobes of the pituitary, which one is part of the brain and which one is an actual gland?

Answer 9

Anterior pituitary is actual gland, posterior is part of brain

Question 10

What two neurohormones do magnocellular neurosecretory cells release?

Answer 10

• Oxytocin

- Vasopressin (antidiuretic hormone, ADH)

Question 11

How does the kidney control the brain to signal low blood volume and pressure?

Answer 11

• The kidney secretes the enzyme, renin
• Renin causes conversion of angiotensinogen from the liver to angiotensin I
• Angiotensin I breaks down to angiotensin II, which acts on kidney and blood vessels to increase blood pressure
• Subfornical organ in the brain (telencephaol, lacks blood brain barrier) also senses angiotensin II and projecting cells to hypothalamus activates vasopressin containing neurosecretory cells and signals lateral hypothalamus to produce thirst.

Question 12

What neurosecretory cells from the hypothalamus control the adrenal cortex? How?

Answer 12

Parvocellualr neurosecretory cells, they are from the periventricular zone of the hypothalamus, which reacts to stress to release corticotropin-releasing hormone (CRH) into blood of the portal circulation to anterior pituitary.

• Stimulates release of corticotropin or ACTH (adrenocorticotropic hormone).
• ACTH enters general circulation and travels to adrenal cortex, where cortisol release is stimulated

Question 13

What does the adrenal cortex produce?

Answer 13

Cortisol (steroid hormone)

Question 14

Why does cortisol easily cross the blood brin barrier? What effect does it have on the brain?

Answer 14

It is lipophilic (steroid derived from cholesterol). It inhibits corticotropin-releasing hormone (CRH) release from the periventricular zone of the hypothalamus (which would go on to stimulate ACTH release from anterior pituitary)

There are cortisol receptors throughout the brain, activation of these causes a variety of stress-coping mechanisms

Question 15

What organ does the adrenal cortex and adrenal medulla sit on?

Answer 15

The kidneys.

Question 16

What are autonomic ganglia?

Answer 16

Contains the cell bodies of all autonomic lower motor neurons, lie outside the CNS.

Question 17

What are postganglionic neurons? What drives them?

Answer 17

Neurons in autonomic ganglia, driven by preganglionic neurons, who’s cell bodies are in the spinal cord and brain stem.

Question 18

The somatic motor system drives peripheral targets via what type of pathway (monosynatpic or disynaptic)?

Answer 18

Monosynaptic

Question 19

The ANS uses a monosynaptic or disynaptic pathway?

Answer 19

Disynaptic, due to autonomic sympathetic and parasympathetic ganglion acting as connectors between CNS sympathetic/paraympathetic nervous system neurons and PNS autonomic neurons.

Question 20

Both sympathetic and parasympathetic controls of ANS are disynaptic, which one has a more proximal division to the brain?

Answer 20

The sympathetic nervous system has its autonomic ganglion located more proximally to the brain. Parasympathetic ganglia are typically located next o, on, or in their target organs.

Question 21

What does the nucleus of the solitary tract in the medulla do?

Answer 21

It connects the hypothalamus to preganglionic neurons of the ANS. It is so important for autonomic control, that if the everything above it were to be cut off, it would still modulate autonomic activity to a degree. It acts to coordinate sensory information from internal organs and coodinate output to the autonomic brain stem nuclei

Question 22

What do preganglionic neurons of the ANS secrete?

Answer 22

Acetylcholine, activating nicotinic ACh receptors on the postganglionic cell. Ganglionic ACh can also activated muscarinic receptors, which can be excitatory or inhibitory. These are slow events.

Question 23

What do postganglionic parasympathetic neurons secrete?

Answer 23

Acetylcholine. Has very local effects on target and uses muscarinic receptors with G-proteins.

Question 24

What do postganglionic sympathetic neurons secrete?

Answer 24

Often norepinephrine, often spreads by blood transport.

Question 25

What are sympathomimetic drugs? What is an example?

Answer 25

Drugs that either promote actions of norepinephrine of inhibit muscarinic actions of acetylcholine.

• Eg. Atropine

Question 26

What are parasympathomimetic drugs?

Answer 26

Promote the muscarinic actions of ACh or inhibit the actions of NE. For example, propranolol is an antagonist of NE receptor, it slows down the heart rate and lowers blood pressure, therefore is sometimes used to combat stage-fright.

Question 27

What is adrenalin (epinephrine) secreted from?

Answer 27

Adrenal medulla

Question 28

What are four principles in common of diffuse modulatory systems?

Answer 28

1. The core of each system has a small set of neurons (several thousand)
2. Neurons of the diffuse systems arise from the central core of the brain, most of them from the brain stem
3. Each neuron can influence many others, because each one has an axon that may contact more then 100,000 postsynaptic neurons spread widely across the brain.
4. The synapses made by many of these systems release transmitter molecules into the extracellular fluid, so they can diffuse to many neurons rather than be confined to the vicinity of the synaptic cleft