Week 4 Flashcards
Where is the thalamus
The thalamus composes about four fifths of the diencephalon and forms most of the walls of the third ventricle. Consists of paired masses of gray matter, each positioned immediately below the lateral ventricle of its respective cerebral hemisphere
What is the function of the thalamus*
Primarily as a relay center through which all sensory information (except smell!) passes on the way to the cerebrum. Sensory nuclei lead to the thalamus and project to areas of the cerebral cortex. This is part of the system that promotes alertness and causes arousal from sleep in response to strong sensory stimuli
Where is the epithalamus and what does it do?
The epithalamus is the dorsal segment of the diencephalon and contains a choroid plexus over the third ventricle where cerebrospinal fluid is formed. It also contains the Pineal Gland which secretes the hormone melatonin that regulates circadian rythms
Where is the hypothalamus and what does it do
the most inferior portion of the diencephalon, located below the thalamus and forming part of the lateral walls of the third ventricle.
Contains neural centers for hunger and thirst, regulation of body temperature, and hormone secretion from the pituitary gland. Also contributes to regulation of sleep, wakefulness, sexual arousal and performance, and emotions such as anger, fear, pain, pleasure. It connects with the medulla oblongata and limbic system to evoke visceral response to emotion.
*Describe the different areas of the hypothalamus and what they do
Lateral hypothalamus: stimulates eating
Medial hypothalamus: inhibits eating
Preoptic area: causes shivering in response to cold and hyperventilation, vasodilation, salivation, and sweat secretion in response to heat. Also causes fever when sick
Other areas (not specific) have osmoreceptors to stimulate thirst and release of Antidiuretic Hormone from the posterior pituitary
Supraoptic and Paraventricual Nuclei: produce two hormones. Antidiuretic Hormone (vasopressin) stimulates kidneys to reabsorb water and excrete less urine. Oxytocin is the “love” hormone and stimulates contraction of the uterus in labor. These transport via the hypothalamic hypophyseal tract to the neurohypophysis (posterior pituitary) for release.
*Where is the pituitary gland and what does it do? Specific regions!
Located immediately inferior to the hypothalamus, only connected to diencephalon by a stalk
The neurohypophysis (posterior pituitary) stores and releases ADH and oxytocin (NOT made here, they are made in the hypothalamus and transported via the hypothalamic hypophyseal tract. remember that NEURAL tracts go the the NEUROhypophysis.)
The adenohypophysis (anterior pituitary) receives releasing and inhibiting hormones from the hypothalamus that regulate the ability of the anterior pituitary to produce and secrete its hormones (TSH, LH, FSH, ACTH, GH, and more), which then regulate other endocrine glands.
Describe the suprachiasmatic nuclei (SCN)
Bilaterally located within the anterior hypothalamus. Neurons function as “clock cells” with electrical activity that oscillates in a 24-hour pattern. The SCN is the master regulator of the body’s circadian rhythms: the 24-hour interval of physiological processes including metabolism, sleep, temperature, blood pressure, hormone secretion.
How does the suprachiasmatic nuclei detect light/dark cycles
By tracts from the retina (neural layer of the eyes) to the hypothalamus called retinohypothalamic tracts. These are activated by retinal ganglion cells (NOT rods/cones) that contain a light sensitive pigment melanopsin. The photosensitive retinal ganglion cells in the retina act via retinohypothalamic tracts to “entrain” the circadian clocks of the SCN to daily light/dark.
They are also responsible for the pupillary reflex constriction in response to light!
Describe the molecular mechanism for the circadian clock
There are certain genes found in the suprachiasmatic nuclei whose expression control the circadian clock. The genes have been found in other areas of the brain and peripheral organs and appear to work in complex negative feedback loops that suppress clock gene transcription after a delay, causing circadian oscillations. Although the peripheral “clock” cells have daily cycles of activity, they would not be synchronized without the suprachiasmatic nuclei.
Describe some of the outputs of the suprachiasmatic nuclei
connects to other hypothalamus nuclei, thalamus, arcuate nucleus, amygdaloid body, and more to influence circadian rhythms of temperature, feeding, movements, autonomic nervous system, and endocrine secretions. One important example is the SCN’s regulation (via sympathetic nerves) of the pineal gland and melatonin secretion, which is highest at night. Melatonin then influences other processes such as insulin secretion and blood pressure
list important areas are located in the midbrain
Nigrostriatal dopamine system
Mesolimbic dopamine system
Ventral tegmental area
Nucleus accumbens
Explain the two dopamine systems located in the midbrain
Nigrostriatal: projects from substantia nigra to the corpus striatum of basal nuclei. Required for motor coordination. Degeneration produces Parkinson’s disease
Mesolimbic: Projects dopaminergic input to the limbic system (forebrain) via the substantia nigra and ventral tegmental area. Involved in behavioral reward and implicated in addiction.
describe the nucleus accumbens
Located by head of caudate nucleus and anterior putamen as a part of the ventral striatum (although considered part of limbic system due to emotional reward function).
The rewarding effect of addictive drugs are believed to be due to a rapid increase of dopamine released in the nucleus accumbens - the “dopamine hypothesis” of addiction. The nucleus accumbens receives emotional information from the limbic system and has output to the corpus striatum, this enables it to relate emotions to motivated actions. Continued exposure to addictive drugs (or smartphones) causes down regulation of dopamine receptors in the nucleus accumbens, requiring higher doses for the effect.
what is the effect of THC on the brain?
THC from marijuana stimulates mesolimbic dopamine release, but long term use appears to blunt activity of the mesolimbic system in a way that correlates with declines in working memory
What brain structures are involved in relapse?
Stopping the use of an addictive drug cause withdrawal symptoms including fear and anxiety caused by circuits with the nucleus accumbens and amygdaloid body. People relapse to avoid this state. Relapse may result from failure of the glutamate-releasing axons that project from the prefrontal cortex (controls drug seeking behavior) to the nucleus accumbens and other limbic systems.
structures in the metencephalon
Pons
Cerebellum
Describe the pons location and function. *name the specific areas of importance
Pons is on the underside of the brain between midbrain and medulla oblongata. It connects to the cerebellum and has fibers included in motor and sensory tracts that pass from medulla, through pons, to midbrain. Pons and medulla nuclei regulate breathing, the pons has two respiratory control centers: the apneustic and pneumotaxic centers. (medulla has one respiratory center)
What does damage to the pons cause
Locked-in syndrome is caused by damage to the Ventral Pons. There is paralysis of all voluntary muscles except eye blinks.
describe functions of cerebellum
Smooth, goal directed movements Maintaining posture and balance Learning new movement activities Autonomic function Cognitive skills Muscle memory The cerebellum receives sensory input from proprioceptors and works with motor areas of cerebral cortex to coordinate body movements. Purkinje cells carry the output of the cerebellum via inhibitory signals ONLY.
May also be involved in sensory data, memory, emotion, speech, schizophrenia, autism, (motivation and reward in mice)
Describe the function of the medullar oblongata and its important nuclei
The only structure of the myelencephalon, continuous with pons and spinal cord. All of the descending and ascending fiber tracts that provide communication between the spinal cord and brain pass through the medulla. Many cross over (decussation) to the contralateral side in elevated triangular structures called pyramids. Reason why brain controls opposite body side!
Vagus nuclei: give rise to important parasympathetic vagus nerve (X)
Vital centers:
-vasomotor center: controls autonomic innervation of blood vessels (vasoconstriction and vasodilation)
-cardiac control center: associated with vasomotor center and regulates autonomic nerve control of the heart
-rhythmicity (respiratory) center: acts with centers in the pons to control breathing
What does the reticular activating system do generally?
The normal cycles of sleep (and the ability to tune out stimuli/be awoken by stimuli) depend on activation and inhibition of neural pathways from the pons through midbrain reticular formation. This constitutes an ascending arousal system known as the Reticular Activating System (RAS).
How does the RAS work? where are the networks and what neurotransmitters do they use?
The RAS includes groups of cholinergic neurons in the brain stem that project to the thalamus, enhancing transmission of sensory information from thalamus to cerebral cortex. Also has neurons in hypothalamus and basal forebrain which release monoamines (dopamine, norepinephrine, histamine, serotonin) that project to cerebral cortex.
Other RAS neurons in the *lateral hypothalamic area release arousal neurotransmitters, like orexin (hypocretin-1) which promotes wakefulness.
What area inhibits RAS arousal pathways?
Neurons in the ventrolateral preoptic nucleus (VLPO) of the hypothalamus release GABA to increase the depth of sleep. The inhibitory VLPO neurons and the arousal neurons that release monoamines are believed to mutually inhibit each other, creating a switch that controls falling asleep and waking up.
Explain the brain region that is defective in Narcolepsy
Narcolepsy is caused by autoimmune destruction of orexin (hypocretin-1) neurons in the lateral hypothalamic area (LHA). Orexin stimulates wakefulness and suppresses REM sleep, as well as playing roles in craving food/drugs, physical activity, metabolic rate, and elevation of blood pressure and heart rate.
side note: An orexin antagonist drug has recently been made to help promote sleep called Lemborexant
What would damage to the RAS cause
Unconsciousness and coma
What are the roles of the gray and white matter in the spinal cord?
Gray: central matter, arranged in an “H” with two dorsal (posterior) horns and two ventral (anterior) horns
White: outside matter, composed of ascending and descending fiber tracts (myelinated!)
How are the fiber tracts within the white matter of the spinal cord named?
Ascending (sensory/afferent) start with the prefix spino- and end with the name of the brain region where spinal cord fibers first synapse. e.g. anterior spinothalamic tract
Descending (motor/efferent) begin with a prefix denoting the brain region that gives rise to the fibers and end with suffix -spinal. e.g. lateral corticospinal tract.
