Session 5 - Diencephalon and Basal Ganglia

What does diencephalon mean?

“in-between” brain

What brain structures are found in the diencephalon?

Thalamus, epithalamus, hypothalamus, subthalamus

What is the basal ganglia?

Group of subcortical nuclei involved with movement

Describe the epithalamus

Single midline structure, contains the pineal gland which secretes melatonin

Describe the thalamus

Large, bilaterally symmetrical, egg-shaped structure that acts as a relay and association nuclei

Describe the hypothalamus

Small structure that mediates complex functions

Describe the subthalamus 

Wedge-shaped transition between thalamus and midbrain

Ventral Anterior nucleus

Input: Basal ganglia

Output: Premotor cortex

Function: Motor planning

Ventral Lateral nucleus

Input: Cerebellum, basal ganglia

Output: Primary motor cortex

Function: Motor execution and coordination

Ventral Posterolateral nucleus

Input: Spinothalamic & DC-ML tracts

Output: Primary somatosensory cortex

Function: Body sensation (touch, proprioception, pain, temperature)

Ventral Posteromedial nucleus

Input: Trigenimothalamic & gustatory pathways

Output: Primary somatosensory cortex

Function: Face sensation & taste

Medial Geniculate Body nucleus

Input: Inferior colliculus

Output: Primary auditory cortex

Function: Hearing

Lateral Geniculate Body

Input: Retina (optic tract)

Output: Primary visual cortex

Function: Vision

Why does the thalamus have regulatory inputs?

Regulatory inputs outnumber specific inputs to determine whether information will be forwarded from a thalamic nucleus to the cerebral cortex; don’t need constant sensation

What is the blood supply of the thalamus?

Primary blood supply is from branches of the posterior cerebral artery (PCA)

Describe thalamic syndrome

Typically caused by occlusion of the thalamogeniculate branches of the PCA supplying posterior thalamus; symptoms are contralateral to lesion (hemianesthesia, ataxia, excruciating neurogenic pain)

What is the functional role of the hypothalamus?

Influences viscera via autonomic nervous system (ANS) and regulates endocrine function

What artery supplies blood to the hypothalamus?

Anterior Cerebral Artery + anterior communicating arteries

Posterior Cerebral Artery + posterior communicating arteries

Functions of the hypothalamus

Endocrine functions

Body temperature regulation

Sleep-wakefulness cycles

Emotional and behavioral functions

What is hypothalamic syndrome?

Problems with regulation of thirst, hunger, and body temperature; menstrual and sleep-wakefulness cycles

Where is the subthalamus located?

Transition between thalamus and midbrain

Role of subthalamus

Contains subthalamic nuclei

What artery supplies blood to the subthalamus?

Penetrating branches of the posterior cerebral artery

What does occlusion of the posterior cerebral artery result in?

Hemiballismus (Involuntary, violent, flinging movements of a limb on one side of body)

Is the basal ganglia white or gray matter?

Gray matter

What are the 5 pairs of nuclei in the basal ganglia?

Caudate nucleus

Putamen nucleus

Globus Pallidus nucleus

Subthalamic nucleus

Substantia Nigra Pars Compacta

What nuclei make up the striatum?

Caudate nucleus and Putamen

What nuclei make up the lentiform?

Putamen and globus pallidus

Explain the concept of Disinhibition

The Thalamocortical (VA/VL) projections are excitatory but are tonically inhibited by output nuclei of the basal ganglia; in order for the thalamus to excite the cerebral cortex you must phasically disinhibit the motor nuclei of the thalamus

What does the direct pathway do?

Facilitates initiation of movement by disinhibition the VA/V; promotes movement

What does the indirect pathway do?

Increases inhibition of VA/VL, thus failing to facilitate movement

What nucleui inhibit the VA/VL thus inhibiting movement?

Globus pallidus internus and Substantia Nigra pars reticulata

Describe the Direct pathway

Cerebral cortex excites striatum → Striatum inhibits globus pallidus internus → VA/VL in the thalamus are disinhibited → Cortical activity facilitated to initiate movement

Describe the Indirect pathway

Inhibits movement

What structure produces and releases dopamine?

Substantia nigra

What happens if there is no dopamine production?

Direct and indirect pathways fail

What type of issue is Parkinson’s disease, Huntington’s disease, and Hemiballism?

Basal ganglia issue

What is the cause of Parkinson’s Disease?

Death of neurons primarily in the substantia nigra pars compacta leading to a loss of dopaminergic production

What are the cardinal signs of Parkinson’s Disease?

Resting tremors, bradykinesia, rigidity, postural instability

What non-motor impairments are seen in patient’s with Parkinson’s disease?

Cognitive decline, autonomic changes, pain and fatigue

What is Huntington’s Disease?

Inherited neurodegenerative disease caused by gross atrophy of the striatum leading to loss of GABAergic neurons and reduction of inhibition in the basal ganglia circuitry

What is Huntington’s Disease characterized by?

Motor changes (choreoathetosis: involuntary, irregular, and writhing movements)

Cognitive decline leading to dementia

Psychiatric disorders

What is Hemiballismus?

Severe and dramatic form of dyskinesia characterized by wild, un-patterned, flinging movements of an entire extremity

What causes Hemiballismus?

A discrete lesion of the subthalamic nucleus contralateral to the symptoms, commonly results from vascular disorder of penetrating branches of the posterior cerebral artery