Midbrain And Diencephalon Flashcards
What do the alar plates give rise to ?
They migrate downwards to form the red nucleus, inferior and superior colliculus and substantia migrants
Alar plates migrate further down than basal plates and they give rise to more
What is the midbrain important for and what reduces in size during the development of the midbrain ?
Midbrain is important for processing sensory information and providing an output
The cerebral aqueduct reduces in size as development occurs
What do the basal plates give rise to ?
They give rise to the edinger-Westphal nucleus and he oculomotor nucleus
What is the overall function of the oculomotor nucleus ?
The oculomotor nucleus is a general somatic efferent nucleus
What is the overall function of the edinger-Westphal nucleus ?
It is a general visceral efferent nucleus
Where does the tectum lie ?
It lies posterior to the cerebral aqueduct
Where does the tegmentum lie ?
It is positions I between the base of the tectum and the substantia nigra
Where are the basis pedunculi and what do they contain ?
It is the anterolateral sections of the midbrain, made up of the substantia nigra and crus cerebri
It contains mainly descending pathways
On the ventral surface what are the limits of the midbrain ?
The rostral limit is the exit of the crura cerebri from the cerebral hemispheres and the caudal limit is the mammillary bodies
What are the main cranial nerves in the midbrain?
Cranial nerves 3,4 and 6
Which surface of the brain is the midbrain more clear on ?
The dorsal surface
What are the limits of the midbrain on the dorsal surface ?
The rostral limit is the superior colliculus and the caudal limit is the inferior colliculus
What inputs does the superior colliculus receive ?
Visual, auditory and somatosensory
What nucleus does the superior colliculus feed info out to and what is the motor response produced ?
It feeds info out to the oculomotor nucleus
It produces a motor response which orientates the head and eyes towards a stimulus
What happens if you have a lesion through the superior colliculus ?
It doesn’t cause the loss of visual sight but it makes the movements of the eye slower and they are not as accurate
Where does the inferior colliculus receive auditory information from and where does it send auditory info to ?
It receives auditory info from hindbrain structures and sends out the info to the superior colliculus and thalamus
What is the inferior colliculus important for ?
It is important in sound localisation and auditory processing
Why is the red nucleus highly pigmented ?
It has a high iron content and it is very vascular
The red nucleus is a motor nucleus associated with which structure ?
Cerebellum
Which tract originates in the red nucleus and what s it involved in ?
The rubrospinal tract which is important in fine motor control - more important in other animals and during development.
What are the 2 outputs of the red nucleus and where do they project to ?
The magnocellular output is to the spinal cord and ten parvocellular output is to the cerebellum
How is cerebellum ataxia caused ?
Caused by lesions to the parvocellular part of the nucleus
Which main structure of the midbrain is present on the anterior midbrain and which is present on the posterior midbrain ?
Anterior midbrain = red nucleus
Posterior midbrain = midbrain locomotor area
What does the midbrain locomotor area do ?
It stimulates generator patterns in the spinal cord to initiate movement
In doing this it can control pattern and speed of locomotion
What is the PAG important for ?
It is important for modulating pain in descending pathways
It contains opioids to help modulate the pain felt
What are the 2 components of the oculomotor nerve ?
It’s somatic motor output is to your eyes to control them and the visceral motor output is the parasympathetic control of the sileon muscles in the sphincter
What does the medial longitudinal fasiculus do ?
It provides vestibular inputs to cranial nerves 3,4 and 6 which helps to adjust the eyes to look at something and it is also needed for balance
What does the trochlear nerve do ?
It travels quite far down and crosses to innervate the superior oblique muscles of the eye
It is the only cranial nerve which exits on the dorsal surface
What happens to the eyes of a lesion or damage occurs to the trochlear nerve ?
It can lead to pathetic palsy in which you suffer from double vision because one eye is able to maintain a gaze however the other eye drifts
Which region of the brain is the abducens nerve present in ?
Hindbrain
What muscle does the abducens nerve control ?
It controls the lateral rectus muscle of the eye
Cranial nerves 3,4 and 6 completely control the eye. Which nerves control which muscles ?
Trochlear controls superior oblique
Oculomotor controls superior and inferior rectus, inferior oblique and medial rectus
Abducens controls the lateral rectus
Which nerve controls the construction of the pupil ?
Oculomotor nerve
What is the direct light reflex ?
It’s the constriction of the pupil due to illumination of the retina
Contraction of the sphincter pupillae muscle of the iris constricts the pupil so less light hits the retina
What is the consensual light reflex ?
The consensual light reflex is when the pupil of an eye constricts to let less light in even though the retina of that eye has not be illuminated
This occurs because the afferent limb of the light reflex has a small group of optic tract fibres which project to the pretext all area instead of the lateral geniculate nucleus of the thalamus
This projection to the pretectal area is important because neurons in this area project bilaterally to the edinger- Westphal nucleus where efferent fibres leave the oculomotor nerve which controls the constriction of the pupil
Why is the substantia nigra dark in colour ?
Because it is rich in melanin
Where does the substantia nigra project to ?
It projects to the caudate and putamen nuclei in the striatum
Where does the ventral tegmental area project to ?
Projects to the ventral striatum in the Mesolimbic pathway from the substantia nigra
- important in reward and addiction
Projects to the frontal cortex in the mesocortical pathways
- important in arousal and memory
What is Benedict’s syndrome ?
It is damage to the tegmentum
Damage to the oculomotor and red nucleus causes cerebellar ataxia which leads to inappropriate movements of your eye
If dopaminergic systems are damaged different disorders occur, what happens between the substantia nigra and striatum, VTA and striatum and the VTA and the frontal cortex ?
Substantia nigra to striatum - Parkinson's disease VTA to striatum - drug addiction - OCD - attention deficit hyperactive disorder VTA to frontal cortex - schizophrenia
What is part of the diencephalon ?
The thalamus, hypothalamus and epithalamus
What is the diencephalon important for ?
Critical in transmitting and processing sensory info
Describe the anterior nuclear group of the thalamus nuclei ?
It is part of the limbic system
Receives info from mammillary bodies of hypothalamus and projects to cingulate gyrus
Describe the ventral posterior nucleus of the thalamic nuclei ?
It is the termination site for all ascending pathways from the spinal cord and BRAINSTEM which carry sensory info from the contra lateral half of the body
- spinothalamic tract
- medial lemniscus tract
- Trigeminothalamic tract
Describe the lateral geniculate nucleus of the thalamic nuclei ?
It is the termination nucleus for the visual system with the optic tracts of the retinal ganglion cells terminating here
Describe the medial geniculate nucleus of the thalamic nuclei ?
It is part of the auditory system
Receives ascending fibres from the inferior colliculus
Describe the ventral anterior nucleus of the thalamic nuclei ?
It contains 2 parts, a larger principal part and smaller magnocellular part
What are the 3 subdivisions of the ventral lateral nucleus ?
Pars oralis
Pars medialis
Pars caudalis
What is the epithalamus important for ?
It is involved in circadian rhythm
What is the reticular nucleus important for ?
It provides GABAergic inputs to the thalamus
What is the subthalamic nucleus important for ?
It is involved in control of movement
- this is the part of the brain which receives deep brain stimulation to control Parkinson’s disease
What are the functions of the medial hypothalamus?
Homeostasis
Endocrine function
Autonomic function
Survival behaviours, thirst, hunger, defence and parental care
What are the functions of the lateral hypothalamus ?
Important in sleep/wakefulness
What hormone does the paraventricular nucleus release ?
Oxytocin
What hormone does the supra optic nucleus release ?
Vasopressin
Where is the diencephalon situated ?
Between the telencephalon and BRAINSTEM
Which ascending pathway is the diencephalon not involved with ?
Olfaction system
The thalamus receives lots of sensory info, where do the nuclei receive it from and then send it ?
Nuclei receive info from somatosensory, visual and auditory fibres and they pass the info onto appropriate areas in the cortex
Some nuclei receive info from subcortical motor areas and they send out info to the overlying cortex to execute these moto actions
Other nuclei receive a diffuse network of inputs and Hesse are sent out to more wide spread areas
