Reticular formation and Cerebellum Flashcards
Reticular formation
It is composed of grey matter scattered throughout the midbrain, pons and medulla.
What is the role of reticular formation?
it covers the arousal of the brain via the thalamus.
it is involved in habituation - a process in which the brain learns to ignore repetitive, unimportant stimuli.
What inhibits the reticular formation?
it is inhibited by sleep centers in the hypothalamus and other brain regions.
it is depressed by alcohol, sleep-inducing drugs and tranquilisers
Where is the cerebellum located?
posterior to the cranial fossa, and underneath the tentorium cerebelli. it is also posterior to the superior and inferior medullary velum, brainstem, 4th ventricle, vela and cerebellar peduncles.
What does the cerebellum consist of?
cortex, white matter and deep nuclei.
Synergistic multijoint movement
frontal motor association areas via the corticopontine-cerebellar tract inform the cerebellum of intent to start voluntary muscle contraction.
at the same time, the cerebellum receives information from proprioceptors throughout the body, as well as visual and vestibular input. this information allows the cerebellum to evaluate body position and momentum.
the cerebellar cortex and deep cerebellar nuclei then evaluate the best way to coordinate the force of each muscle contraction to ensure successful movement.
this decision is sent back to the motor cortex for execution.
What happens to a patient with cerebellar lesions?
movement is executed with suboptimal coordination and precision
posterior cerebellar incisure
contains the falx cerebelli
vermis
connects the right and left cerebellar hemispheres
folia
parallel surface folds of grey matter
what are the two main inputs of cerebellar circuits?
climbing fibers and mossy fibers
climbing fibers
innervate Purkinje cells directly. there are mainly from the inferior olivary nucleus and detect proprioceptive input. they are very precise, as there is one ION neuron innervating one Purkinje cell
Mossy fibers
firstly innervate granulate cells, and then the granulate cells have parallel fibers (axons) which innervate the purkinje cells
Purkinje neurons
are the sole output of the cerebellar cortex. they are inhibitory. they work with input axons to regulate the firing frequency and amplitude of the neurons in the deep cerebellar nuclei and produce the blueprint which is sent to the motor cortex.
Purkinje cells have an oval-shaped cell body and an elaborate flattened, fan-like dendrite tree
primary fissure
divides the cerebellum into the inferior and posterior lobes
flocculonodular lobe
lies deep to the vermis, in the inferior surface. it communicates with the vestibular system.
What is the structure of the flocculonodular lobe?
it is made up of the flocculus and the modulus. inferiorly, lie the tonsils.
how does increased intracranial pressure affect the tonsils?
it can push the tonsils down, transferring the pressure onto the tonsils which then put pressure onto the medulla. This can cause the medulla nerves to get damaged and may cause death.
zones of the cerebellum
each zone projects to a specific deep cerebellum nucleus which corresponds to a distinctive functional subdivision in the sagittal plane
the median zone (vermis)
projects to the fastigial nucleus
the intermediate zone
projects to the interposed/interpositus nucleus
the lateral zone
projects to the dentate nucleus
the cerebrocerebellar circuits (function)
control multi-joint movement in the limbs.
the cerebrocerebellar circuits (pathway)
first, the cerebral cortex communicates with the cerebellum that it would like to initiate a movement. that information travels through the cerebropontine cerebellar tract from the premotor cortex. the information proceeds to the lateral zone. sensory information is sent via the spine-olivary tract, crosses over to the olive, and crosses over back again to the lateral zone. neurons in the cerebellum integrate the information and send it to the deep cerebellar nucleus (dentate nucleus), which relays the motion blueprint back to the motor cortex. if the blueprint is approved, information is sent down to the muscles via the lateral corticospinal tract.
