6. Thalamus and Hypothalamus

Question 1

Name the structures that made the diancephalon.

Answer 1

• Thalamus
• Subthalamus
• Hypothalamus

Question 2

Label the diagram

Answer 2

Question 3

Name the locations of the:

• Thalamus
• Lateral ventricles
• 3rd ventricle

Answer 3

• Thalamus - right in the middle of the brain
• The thalamus sits ventral + underneath the lateral ventricles
• The thalamus is divided into 2 by the 3rd ventricle

Question 4

Explain the function of the thalamus.

Answer 4

• Relay site for numerous inputs/outputs - all pass through the thalamus
• Key relay centre to cortical sensory areas
• Involved in almost all sensory systems (except olfactory)
• Enhances or restricts signals – prevents sensory overload

Question 5

Describe the Somatosensory pathway.

Answer 5

1. Sensory input
2. Enters through the spinal cord through the dorsal root ganglion
3. Travels into the medulla
4. Synapses with a secondary sensory neurone
5. Goes to the ventral posterior lateral nucleus of the thalamus -controls signal
6. And finally the primary somatosensory cortex

Question 6

What is the function of the intralaminar nuclei? What would loss of neurones in this region cause?

Answer 6

• The intralaminar nuclei project to various medial temporal lobe structures:
  
  • Amygdala = emotions, fear, anxiety
  • Hippocampus = memory
  • Basal Ganglia = movement
• Most neurones are glutamatergic neurons (i.e. excitatory) - stimulation of the intralaminar nuclei leads to excitation
• Loss of neurones in this region is associated with progressive supranuclear palsy (PSP=rare brain disorder causing problem with walking and balance) and Parkinson’s disease

Question 7

What is the function of the reticular nucleus?

Answer 7

• Forms the outer covering of the thalamus
• Majority of the neurones are GABAergic (gamma-aminobutyric acid) i.e. inhibitory
• Unlike other thalamic nuclei, they don’t connect with distal regions but with other thalamic nuclei
• It receives inputs from collaterals of their axons from thalamic nuclei
• Therefore, the reticular nucleus acts to modulate thalamic activity (negative feedback)

Question 8

What is the reticular formation?

Answer 8

• Composed of about 20 nuclei
• Set of interconnected pathways in the brainstem
  
  • Send ascending projections to forebrain nuclei
    
    • Ascending Reticular Activating System (ARAS) - crucial for consciousness
• Involved in consciousness and arousal
  
  • Degree of wakefulness depends on ARAS activity
• Both intralaminar and reticular nucleus receive inputs from the ARAS

Question 9

Describe the position of the hypothalamus and its function.

Answer 9

• The hypothalamus sit underneath the thalamus and is just above the pituitary gland
• Divided into 2 bu the third ventricle
• Collection of individual nuclei with distinct functions
• Largely ipsilateral (connect to nuclei on the same side)
• Involved in 4 F’s
  
  • Fighting
  • Fleeing
  • Feeding
  • Mating

Question 10

What structures is the hypothalamus connected to and how does this relate to its function?

Answer 10

• The hypothalamus has direct connections with the autonomic nervous system
• Neurons in hypothalamic paraventricular nucleus with direct projections to pre-autonomic neurons in spinal cord
• Connections with endocrine systems e.g. the hypothalamic-pituitary axis
• Neurohypophysis receives neurones from both PVN and SON – secrete (do not make them) AVP and OXY
• Adenohypophysis receives input from lots of hypothalamic nuclei – releases ACTH, TSH, GH, LH, FSH and prolactin

Question 11

Explain the function of the Paraventricular nucleus

Answer 11

• Sends projections to autonomic nervous system and pituitary gland
• Also involved in feeding behaviour
  
  • PVN lesions cause hyperphagia and weight gain
  • PVN receives input from hypothalamic nuclei involved in feeding

Question 12

What are the types of projections from the hypothalamus?

Answer 12

• Magnocellular neurones - projections to the posterior pituitary –> release of vasopressin and oxytocin
• Parvocellular neurones- sympathetic neurones that go to the body before they synpase to a ganglion –> projects to the:
  
  • vessels
  • heart
  • kidney

Question 13

What is the location of the suprachiasmatic nucleus and what is its function?

Answer 13

• Sits at the base of the hypothalamus and sits above the optic chiasm
• Internal body clock – regulates sleep cycle
• Controlled by light – retinal ganglion cells (light sensitive) connected to suprachiasmatic nucleus (light activates this) this activates pineal gland and does not secrete melatonin (tired hormone).
• Lesion in SCN can lead to a fragmented sleeping pattern
• Schizophrenia
• Symptoms: Hallucinations, delusions, confused thoughts, loss of motivation, sleep disturbances, lack of concentration