Unit 4 Flashcards
What does the Diencephalon consist of?
Structures that are crucial for processing sensory information (thalamus)
Structures that are crucial for regulating ANS (hypothalamus)
Structures important for motor control (subthalamus)
Structures important for regulation of biological cycles and resistance against nicotine (epithalamus)
How can the brain be divided according to the prenatal development of the CNS?
Begins as neural tube (hollow tube)
-> develops 3 swellings which become forebrain, midbrain and hindbrain
How can the regions of the brain be further divided in the adult brain?
Prosencephalon: Telencephalon and Diencephalon
Mesencephalon
Rhombencephalon: Metencephalon and Myelencephalon
What does the thalamus consist of, where is it located and what is its role?
Consists of a pair of egg-shaped structures in centre of forebrain (one on each side of third ventricle)
Plays crucial role in processing sensory information detected throughout the body
Where does most of the input from the cortex come from?
The thalamus
What is the only sensory input which bypasses the thalamus?
Olfactory sensory information
What can thalamic nuclei be grouped into anatomically?
Anterior, medial and lateral groups
-> separated by internal medullary lamina (y-shaped thin lamina of white matter)
What does the internal medullary lamina consist of?
Afferent and efferent axons of thalamic nuclei
Where do thalamic nuclei lie?
Some within internal medullary lamina (important for maintaining cortical arousal)
Some in the reticular nucleus
What is the reticular nucleus?
A thin strip of nuclei slightly lateral to the main body of thalamic nuclei
Plays a role in sleep-wake cycles
What are the different types of nuclei present in the thalamus?
Specific nuclei
Non-specific nuclei
Association nuclei
Where are specific nuclei located and what do they do?
In the ventral part of the of lateral group
Receive specific sensory information
Project to specific sensory and motor areas of cortex
The ventral posterior nucleus as a specific nucleus example
Receives somatosensory information from trunk, limbs and head
Sends signal to corresponding parts of primary somatosensory cortex
-> brings information to conscious level
Where do non-specific nuclei lie and what is their task?
Lie in dorsal part of lateral group, as well as all of the anterior and medial groups
Project axons to broadly dispersed areas of cortex (e.g. association areas and limbic system)
What are association nuclei?
Some non-specific nuclei considered association nuclei
Don‘t receive sensory signals, but input from other brain areas
-> sent to different areas of cortex
Thought to have integrative function: bring information of different brain areas together
Whats an example of an association nucleus?
Anterior nuclear group
Receive signals from hypothalamus and projects to the cingulate gyrus (both components from limbic system)
-> involved in control of instinctive drives and emotional aspects of behaviour and memory
What is the limbic system responsible for?
Control and production of emotions
Memory storage
What is retrograde thalamic degeneration?
Lesions in sensory areas of cortex cause corresponding thalamic nuclei to degenerate and lose functionality
What purpose does the hypothalamus serve?
Main controller of ANS
-> capable of influencing behaviours under control of ANS (e.g. feeding, drinking, sleep, wakefulness, temperature regulation and aggression )
Receives information regarding internal state of body
(Can also renew olfactory and gustatory neurones in some cases)
Which are the 2 main sources the hypothalamus receives information about the internal states of the body from?
Neural connections
Signals from circulatory system (e.g. bloodstream)
What types of signals does the hypothalamus receive and process?
Physiological signals (e.g. temperature)
Chemical signals (e.g. blood glucose)
Hormonal signals (e.g. hunger hormones)
=> signals regarding internal state of the body
How does the hypothalamus produce effects on the internal state of the body?
Neural connections
Releasing hormones into bloodstream
The hypothalamus and homeostasis
Hypothalamus performs physiological adjustments to changes in internal and external environments
Example for the influence of the hypothalamus
Temperature receptors in skin and organs detect change in temperature
-> sent to hypothalamus
-> communicates with raphe nucleus in brainstem (controls temperature regulation behaviours
What is the name of the gland that allows the hypothalamus to influence internal states of thee body via hormonal communication?
Pituitary gland (endocrine gland attached to hypothalamus)
Why does the pituitary gland have the „master gland“ status?
Most hormones released from pituitary gland control other endocrine glands in body
What is an endocrine gland?
Hormonal gland
Given the fact that the hypothalamus controls the pituitary gland. What does the hypothalamus effectively control in the body?
The body‘s endocrine system
Which zones can nuclei in the hypothalamus be divided into?
Lateral zone
Medial zone
Periventricular zone
(Many nuclei still not well understood, but those that are: serve specific autonomic functions)
What tasks do the nuclei of the lateral zone of the hypothalamus do?
Control of food and water intake
What does damage to the lateral zone of the hypothalamus cause?
Aphagia ( abnormal lack of eating due to inability to detect hunger)
Adipsia (abnormal lack of drinking due to inability to detect thirst)
What is the periventricular zone
Thin layer of nuclei beside wall of third ventricle
Important role in regulating release of hormones from pituitary gland
What does the medial zone of the hypothalamus contain?
Various nuclei
-> some have well defined funtions
Whats an example for a nucleus in the medial zone of the hypothalamus? (Hint: sleep/wake cycle)
Suprachiasmatic nucleus
Receives sensory fibres directly from retina
-> communicates indirectly with pineal gland
-> control sleep/ wake cycle
What is one of the most important nuclei in the medial zone of the hypothalamus?
Mammillary nucleus
Lies within mammillary body
-> receives axons from hippocampus (via fornix)
-> projects axons to anterior nucleus of the thalamus (via mammillothalamic tract)
=> important link in limbic system
What is the subthalamus?
Small region ventral to thalamus + lateral to hypothalamus
Contains two nuclear groups:
- subthalamic nucleus
- zonal inserta
Where is the subthalamic nucleus located?
Ventral part of the subthalamus
Which purpose does the subthalamic nucleus serve?
Forms connections with basal ganglia (globus pallidus and substantia nigra)
Important for movement
What is the zona inserta?
Extension of the brainstem
Less well known
-> considered to play some role in movement control
Where is the epithalamus located?
Posterior part of diencephalon
Just above superior colliculus (mesencephalon)
What does the epithalamus consist of?
Pineal gland and habenula
What does the pineal gland do?
Synthesise and secrete melatonin
What is melatonin?
Hormone
Involved in regulating sleep/ wake cycle
How does our sleep/ wake cycle work?
Lasts one day
-> sleepy at night and more alert during day
How is the sleep/ wake cycle controlled?
At night: suprachiasmatic nucleus in hypothalamus stimulates pineal gland to secrete melatonin
-> produces sleepiness
During day: pineal gland doesn‘t receive stimulation
-> doesn‘t produce melatonin
What does the habenula consist of and do?
Nuclear groups
-> links structures in limbic system and brainstem
Important role in addiction
-> contains receptors that inhibit the reinforcing effects of nicotine
How do the receptors in the habenula correlate to nicotine addiction?
Less-sensitive nicotine receptors
->more likely to be susceptible to addictive effects of nicotine
Where is the basal ganglia and what does it consist of?
Beneath cortex
Caudate nucleus and putamen (striatum/neostratium)
Globus pallidus
What is the basal ganglia important for?
Controlling voluntary movements
-> influences primary motor cortex‘s control
Damage and degeneration produce movement deficits
What can the globus pallidus be divided into?
Medial part
Lateral part
How does the basal ganglia operate?(creation of loops)
Receives information from motor areas of cortex, primary somatosensory cortex and substantia nigra
Sends information to motor areas of cortex and some motor nuclei in brainstem
-> connection of incoming and outgoing information in form of loops
-> allows direct and indirect control of voluntary movement
The direct pathway to produce movement?
Motor cortex
-> excitatory input to striatum
-> striatum inhibits internal globus pallidus
-> internal globus pallidus does NOT inhibit thalamus
-> excitatory effect on thalamus
-> thalamus excites motor cortex
-> movement facilitated
The indirect pathway
Used to inhibit movement
Motor cortex excites striatum
-> inhibits external globus pallidus
-> external globus pallidus can‘t inhibit subthallamic nucleus
-> subthalamic nucleus can excite internal globus pallidus
-> internal globus pallidus inhibits thalamus
-> thalamus can‘t excite motor cortex
-> movement inhibited
The hyperdirect pathway
Bypasses striatum to inhibit movement faster
Can also stop movements already initiated
How does the hyperdirect pathway operate?
Begins in pre-supplementary motor area
-> directly excites subthalamic nucleus
-> excites internal globus pallidus
-> inhibits thalamus
-> movement inhibited
What could serve as an example for the different pathways of producing movement?
Out running, you stop for a light (slowly coming to a stop = indirect pathway)
Light turns green, movement initiated (direct pathway)
Car comes by fast, you stop the movement immediately (hyperdirect pathway)
What is the fourth important pathway?
Dopaminergic pathway
Uses nigrostriatal system
-> between substantia nigra and striatum
Important for influencing voluntary movement control, muscle tone and posture
What happens if the nigrostriatal system degenerates?
Development of Parkinson‘s disease
What is Parkinson’s disease?
neurodegenerative disease
Characterised by difficulties in initiating movements (especially previously automatic ones), muscle rigidity, slowness and tremors
Which effect does dopamine have?
Excitatory or inhibitory
What is Huntington‘s disease?
Neurodegenerative disease
Caused by degeneration of GABAergic and cholinergic neurones in striatum
What is the effect of Huntington‘s disease?
Neurones affected play important role in inhibitory control of external pallidus
-> crucial in stopping unwanted body movements
-> external globus pallidus can now inhibit subthalamic nucleus
-> subthalamus cant excite internal globus pallidus
-> reduced inhibitory control of thalamus and cortex
-> excessive, uncontrollable movements and inability to cease movements
