6. Thalamus and hypothalamus

Question 1

What is the diencephalon made up of?

Answer 1

The thalamus, the hypothalamus and the subthalamus

Question 2

What structures sit below the thalamus?

Answer 2

Thalamus sits above the pituitary gland, the brainstem and the hypothalamus

Question 3

What sits in between the two halves of the thalamus?

Answer 3

The third ventricle

Question 4

What lies directly on top of the thalamus?

Answer 4

Lateral ventricles

Question 5

What is the thalamus made up of?

Answer 5

Many nuclei each with a different function

Question 6

How is the thalamus connected to the forebrain?

Answer 6

Ipsilateral connections with forebrain - the part of the thalamus on the right will connect with the right hemisphere

Question 7

What is the function of the thalamus?

Answer 7

• It is a relay centre between the cerebral cortex and the rest of the CNS
  
  • The connection is two way, it is reciprocal
  • There is also integration and modification of information as it goes through the thalamus
  • Enhances or restricts signals so in some cases you don’t get massive sensory overloads

Question 8

What is the only function that is not represented but the thalamus?

Answer 8

There is a nucleus within the thalamus for virtually every functional system within the nervous system APART FROM OLFAFTION

Question 9

Outline the route of the somatosensory pathway

Answer 9

• One of the pathways that goes through the thalamus
• First some sort of sensory input (in this case touch)
• Enters the spinal cord through the dorsal root ganglia
• Travels to medulla and synapses
Secondary sensory neurone goes to thalamus. This is where the signal gets integrated and sent to the somatosensory cortex. This is where the process of proprioception is carried out

Question 10

How are thalamus nuclei classified?

Answer 10

Classified based on the connection of the nuclei with the cortex

Question 11

What are the different types of thalamic nuclei and what part of the cortex are they connected to?

Answer 11

• SPECIFIC
		○ Connected to primary cortical areas
	• ASSOCIATION
		○ Connected to association cortex
	• RETICULAR
		○ NOT connected to the cortex
	• INTRALAMINAR
		○ Connected to ALL cortical areas

Question 12

Where do intralaminar nuclei project to?

Answer 12

•Project to various medial temporal lobe structures (e.g. amygdala, hippocampus and basal ganglia)
–Amygdala = emotions, fear, anxiety
–Hippocampus = memory
–Basal ganglia = movement

Question 13

What type of neurones are intralaminar nuclei made of? What would happen if there was a loss of neurones from this area?

Answer 13

• Mostly glutamatergic neurons (i.e. excitatory)
• Loss of neurons in this region associated with progressive supranuclear palsy (rare brain disorder causing problems with walking and balance) and Parkinson’s disease

Question 14

Where is the reticular nucleus found and what types of neurones is it made up of?

Answer 14

• Forms the outer covering of the thalamus

* Majority of neurons are GABAergic (γ-aminobutyric acid) (i.e. inhibitory)

Question 15

What is the function of the reticular nucleus?

Answer 15

• Unlike other thalamic nuclei, they don’t connect with other parts of the cortex, but with other thalamic nuclei
• Receive inputs from collaterals of their axons from thalamic nuclei. Main axon will target areas of the brain such as the somatosensory cortex.
• Therefore, reticular nucleus acts to modulate thalamic activity (negative feedback). So controls flow of information to sensory parts of the brain that controls consciousness

Question 16

What is a reticular formation?

Answer 16

Set of interconnected pathways in the brainstem. Made up of many nuclei (about 20). All interconnected

Question 17

What is the function of the reticular formation? What would damage to this cause?

Answer 17

Send ascending projections to forebrain nuclei. Ascending reticular activating system (ARAS). Damage to this can cause coma/death
Involved in consciousness and arousal
Degrees of wakefulness depend on ARAS activity (increased activity = increased wakefulness)
Both intralaminar and reticular nucleus receive inputs from ARAS

Question 18

Outline the location of the hypothalamus

Answer 18

• Hypothalamus sits just below the thalamus
  
  • Very small nuclei – can be found if you go back through the eyes and temples. Is roughly the size of an acorn
  • The optic chiasm and pituitary stalk are seen just at the front of the hypothalamus
  • It is divided into two by the third ventricle

Question 19

How is the hypothalamus connected to the forebrain?

Answer 19

Ipsilateral connections with the forebrain

Question 20

What are the functions of the hypothalamus?

Answer 20

• It is involved in the four F’s: Fleeing, fighting, feeding and mating
  
  • Made up of many nuclei which all have distinct functions; regulating the CVS, feeding, connections to other limbic regions. Some are involved with endocrine control and have connections to the pituitary gland
  • It has lots of connections within itself between the different nuclei of the hypothalamus
  • Some neurones send really long projections down to the spinal cord, usually to the thoracic level. These neurones are usually involved in the CVS so activation of these results in changes of blood pressure and changes in activity of the renal nerves which can also alter renal function
  • It also has links with the endocrine system as the hypothalamus projects to both the anterior and posterior pituitary gland
  • The hypothalamus is also involved in controlling behaviour (e.g. feeding

Question 21

How does the hypothalamus control pituitary secretions?

Answer 21

○ Posterior pituitary gland receives inputs from both supraoptic and paraventricular nuclei. These nuclei send their axons down into the posterior pituitary gland where the hormones are secreted directly into the bloodstream. They usually secrete vasopressin and oxytocin
○ The anterior pituitary receives inputs from various hypothalamic nuclei but they do not synthesise the hormones themselves. Instead, the neurones stimulate cells in the adenohypophysis to release hormones. This is why a pituitary tumour is likely to be in the anterior pituitary gland as it contains its own cell bodies that can synthesise and secrete hormones

Question 22

How does they hypothalamus control feeding behaviour?

Answer 22

○ The hypothalamus has lots of receptors for hormones originating in your gut so has a direct GI link. Also has connections to other brain regions which receive input from GI regions.
○ This allows it to integrate this sensory information and make changes to feeding behaviour
○ The hypothalamus is often a target in the treatment of obesity and feeding disorders

Question 23

What neurones does the paraventricular nucleus contain?

Answer 23

Contains parvocellular and magnocellular neurones (parvo=small, magno=large)

Question 24

Where do parvocellular neurones project to and what is their function?

Answer 24

• It is parvocellular neurones that project all the way down to the spinal cord to a region called the intermediolateral cell column, which is an area of grey matter. It contains these sympathetic preganglionic neurones.
  
  • These parvocellular neurones will synapse in the sympathetic ganglia in the spinal cord and then go and synapse onto blood vessels which causes vasoconstriction and an increase in blood pressure. They project to the heart where it causes an increase in heart rate and CO and they also project to the kidneys where renal blood flow and the secretion of hormones from the kidneys is affected which all affects renal output and thus BP

Question 25

Where do magnocellular neurones project to and what is their effect?

Answer 25

The magnocellular neurones project into the neurohypophysis where they secrete oxytocin and vasopressin. Both have an effect on the CVS, VP has an effect on the kidneys, and oxytocin has effects in uterine contractions and emotions

Question 26

What is the function of the suprachiasmic nucleus and where is it found?

Answer 26

• Sits in the base of the hypothalamus, just above the optic chiasm
  
  • This is your internal body clock and what regulates the sleep wake cycle
  • Activity of the brain decreases during the day and increases during the day in response to light

Question 27

How does the suprachiasmic nucleus determine the sleep wake cycle?

Answer 27

• Rods and cones in the eye are involved in vision but there are also retinal ganglion cells that are light sensitive but are not involved in sight. They are connected via a retinohypothalamic tract to the suprachiasmatic nucleus. They are especially responsive to blue light which is emitted from screens
  
  • The suprachiasmatic nucleus then projects to various other regions including the PVN which all send their axons down to the spinal cord from which they are sent back up to the pineal gland. This secretes melatonin which makes you feel tired

Question 28

What does a lesion of the suprachiasmic nucleus result in? Why is this clinically important?

Answer 28

• Lesion of the SCN causes a disrupted sleeping cycle but the amount of sleep remains the same
  
  • This is important as the symptoms of schizophrenia include - Hallucinations, delusions, confused thoughts, loss of motivation, sleep disturbances, lack of concentration
  • There is evidence that disruptions in the SCN are what contributes to the sleep disturbances

Question 29

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Answer 29

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