CBNS116: Lecture 12-13

Basal ganglia+ HPA

What are the accessory systems of the motor pathway?

Basal ganglia and cerebellum

What basal ganglia nuclei is the striatum composed of?

Caudate nucleus, nucleus accumbens, putamen

What basal ganglia nuclei is the lenticular nucleus composed of?

Globus pallidus and putamen

What are the independent nuclei of the basal ganglia?

Subthalamic nucleus and the substantia nigra

What is the primary input center of the basal ganglia?

The striatum

This structure links the caudate and the putamen.

Nucleus accumbens

The globus palladus is divided into what segments?

External(GPe) and internal(GPi)

What parts is the substantia nigra split into?

Compact and reticular

A lens shaped structure enveloped in white matter

Subthalamic nucleus(STN)

Contains densely packed, pigmented dopaminergic neurons.

Compact substantia nigra

Contains loosely packed, nonpigmented dopaminergic neurons. Major output center.

Reticular substantia nigra

What areas of the basal ganglia collect inputs from the cortex?

Striatum and subthalamic nucleus

What areas of the basal ganglia do outputs leave from?

Globus pallidus, reticular substantia nigra

Describe the pathway outputs from the basal ganglia take.

Outputs—>thalamus—>cortex(continuous loop back to basal ganglia)

Fill in the blanks about the direct pathway of the motor loop: The cortex _______(excites/inhibits) the striatum(putamen), which then _______(excites/inhibits) the GPi and SNr. This removes constant GPi inhibition of the _______.

Excites; inhibits; thalamus

What is the overall effect of the direct pathway?

The thalamus is free to facilitate desired cortical output and movement

What is the function of the motor loop?

Facilitates the initiation of willed movements

In regards to the motor loop, when will movement be initiated?

Activation of the supplementary motor area(SMA) passes a threshold by the activity flowing through the basal ganglia pathway.

Fill in the blanks about the indirect pathway of the motor loop: The cortex excites the striatum, which inhibits the _____, which stops inhibiting the ________. As a result, the GPi/SNr is ________(excited/inhibited).

GPe, subthalamic nucleus; excited

What is the result of the indirect pathway?

Inhibits the thalamus, which suppresses unwanted output and movement

Where does dopaminergic modulation originate?

Compact substantia nigra.

Dopaminergic modulation works by ______(exciting/inhibiting) the direct pathway while ______(exciting/inhibiting) the indirect pathway. What is its effect on movement?

exciting; inhibiting. Facilitates smooth, voluntary movement.

What can damage to the caudate nucleus cause?

Extreme personality change, vulgarity, impulsiveness, indifference.

Identify the 3 parallel loops.

Motor, cognition, reward/emotion

Stimulants enhance dopamine signaling in what areas?

VTA, PFC, Nucleus accumbens

What is the effect of nicotine on dopaminergic VTA neurons?

Enhances excitatory signaling

How do opioids, cannabinoids, and benzodiazepines increase VTA dopamine?

Inhibit neurons that inhibit dopaminergic neurons

What arteries supply blood to the basal ganglia?

LSA, anterior cerebral arteries(ACA), and anterior choroidal artery(AChA)

A patient with a lesion in the subthalamic nucleus(STN), called hemiballismus, will present with what symptoms?

Wild, flailing, involuntary movement of the limbs.

What is the mechanism behind hemiballismus?

Damage to STN—>no stimulation of GPi—>no inhibition of thalamus. The indirect pathway is damaged.

What is the cause of Parkinson’s?

Loss of dopaminergic neurons in substantia nigra.

What are some symptoms of Parkinson’s?

Reduced, slowed movement, resting tremors

What is the mechanism behind Parkinson’s?

Loss of dopamine impairs direct pathway and disinhibits indirect pathway

A hereditary degeneration of striatum neurons(usually in the caudate nucleus).

Huntington’s

What are some symptoms of Huntington’s?

Involuntary dancelike movements, rapid mood changes.

What is the primary function of the hypothalamus?

Maintains homeostasis by linking the nervous system to the endocrine system.

What are the 3 functional regions of the hypothalamus?

Anterior, tuberal, and posterior

Function of the anterior hypothalamus:

Circadian rhythm, temperature and water balance, secretes ADH and oxytocin.

Function of the tuberal hypothalamus :

Satiety center

Function of the posterior hypothalamus:

Memory, wakefulness, heat conservation

What are the 3 major input pathways to the hypothalamus?

1. forebrain

2. retina

3. brainstem/spinal cord

Emotional inputs from the forebrain come from what sources?

Septal nuclei, hippocampus, amygdala

Visceral and somatosensory inputs from the brainstem/spinal cord come from what sources?

Nucleus of the solitary tract(NST), parabrachial nuclei

Where are temperature sensitive neurons of the hypothalamus located?

Medial preoptic nucleus

Where are osmolality(blood concentration) sensitive neurons of the hypothalamus located?

Circumventricular organs

Where neurons of the hypothalamus are sensitive to glucose/satiety levels.

Arcuate neurons

What are the 3 major output pathways from the hypothalamus?

1. Brainstem/spinal cord—>visceral motor activation

2. Thalamus/cortex

3. Limbic system: amygdala and septal nuclei

What tract projects from the hypothalamus to the anterior thalamus?

Mammillothalamic tract

Identify the 2 mechanisms of pituitary control and the lobe they coorespond to.

Magnocellular—>posterior lobe. Parvocellular—>anterior lobe

What hormones are used in each system of pituitary control

Magnocellular: ADH and oxytocin

Parvocellular: Adenohypophysis secretion

Describe the mechanism behind the magnocellular system.

Hormones travel down axons directly into the pituitary

Describe the mechanism behind the parvocellular system.

Secretes releasing/inhibiting factors into the hypophyseal portal vascular system.

The neural route is for the _____ lobe while the vascular route is for the ______ lobe.

Posterior; anterior

The _________ nucleus detects rising osmolality(too little water) of the blood. The ____________ nuclei will release _____ to increase kidney water absorption. This signals to the cortex to make the person thirsty.

Medial preoptic; paraventricular/supraoptic; ADH

How does ghrelin make you hungry?

Binds to arcuate neurons to stimulate the lateral hypothalamus, signaling feeding behavior

How does leptin make you feel full?

Binds to arcuate neurons to inhibit feeding behavior

Decreased temperature activates the ________ nuclei which activates the ________ nervous system to trigger shivering and skin vasodilation. It also stimulates the anterior pituitary to release ____. Finally, it projects to the ________ to cause voluntary responses like curling up into a ball.

Medial preoptic; sympathetic; TSH; cerebral cortex

Describe the mechanism that translates emotion into physical responses.

Amygdala—>hypothalamus(via stria terminalis and ventral amydalofugal pathway)—>leads to physical responses like pupil dilation and adrenaline release.

Which part of the endocrine system is responsible for stress and fight/flight response?

Adrenal

What does the adrenal medulla produce?

Epinephrine/norepinephrine

What does the zona reticularis of the adrenal cortex produce?

Adrenal androgens

What does the zona fasciculata of the adrenal cortex produce?

Cortisol

What does the zona glomeruosa of the adrenal cortex produce?

Aldosterone

The hypothalamus induces the release of cortisol by releasing what hormone?

corticotropin-releasing hormone (CRH)

What is the effect of corticotropin-releasing hormone (CRH)?

Causes pituitary to release adrenocorticotropic-releasing hormone (ACTH)

What is the function of adrenocorticotropic-releasing hormone (ACTH) in the HPA axis.

Induces cortisol release from adrenal cortex

What is the role of cortisol in the sleep wake cycle?

Cortisol levels rise within the first 30 min of waking to induce wakefulness, then steadily drops until it reaches its lowest point at midnight.

What are some side effects of elevated cortisol/HPA axis?

Weight gain, sex hormone imbalances, suppressed immune system

What is the effect of chronic high cortisol on BDNF expression?

Reduces it, leading to quicker brain degeneration