Brain 3: midbrain and Cerebellum Flashcards Preview

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Flashcards in Brain 3: midbrain and Cerebellum Deck (26):

What does midbrain contain

Cerebral peduncles
Tectum (superior colliculi and inferior colliculi)
substantia nigra
red nuclei


what is cerebral peduncles

anterior of midbrain
paired bundles of axons
axons from
corticospinal tracts - motor area in cerebral cortex to the SC
corticobulbar tracts - motor area in cerebral cortex to medulla
corticopontine tracts - motor area in cerebral cortex to pons


What is tectum

posteior to midbrain
contains 4 rounded elevations:
Superior colliculi: coordinates movements of head, eyes, trunk in response to visual stimuli (tracking movement)
Inferior colliculi: coordinates movements of head, eyes, trunk in response to auditory stimuli
Startle reflex - sudden movements of head, eyes, trunk that occur when surprised by a loud noise


Substantia nigra

in Midbrain
Neurons release dopamine and help control subconscious muscle activities
loss of these neurons is associated with Parkinson's disease


Red nuclei

in Midbrain
Invovled in voluntary muscle movements
rich blood supply
iron-containing pigment


Nuclei associated with cranial nerves in midbrain

CN III oculomoter nerves
CNIV trochlear nerves


what is Reticular formation

Found throughout brain stem
Net like arrangement of grey and white matter
Grey matter - cluster of cell bodies
White matter - small bundles of myelinated axons


Reticular activating system (RAS)

consists of sensory axons that project to the cerebral cortex
can be activated by visual, auditory, mental, pain, touch pressure, proprioceptive stimuli
BUT no smell.
involved in consciousness
active during arousal
helps maintain attention and alertness
prevents sensory overload by filtering out insignificant information so that it does not reach consciousness


inactivation of RAS produces

Sleep. A state of partial consciousness from which an individual can be aroused.


damage to the RAS results in

Coma: a state of unconsciousness from which an individual cannot be aroused
In the lightest state of coma, people still have brain stem and spinal cord reflexes
in deepest states, those reflexes are lost


which drug can affect RAS?

Melatonin by induce sleep
Anesthetics turn off consciousness via the RAS


what does RAS do to muscle

Consists of motor axons that connect to the cerebellum and spinal cord to help regulate muscle tone. )the slight degree of involuntary contraction in normal resting skeletal muscle.
Invovled in regulation of heart rate, BP, respiratory rate.



Highly folded surface, increasing the surface area of its outer grey matter, allowing for a greater number of neurons


how many % of brain mass is the cerebellum

a tenth of brain mass but contains half of the neurons


what separates the cerebellum from the cerebrum

Tentorium cerebelli
Transverse fissure


3 cerebellar hemispheres

consists of lobes separated by deep and distinct fissures
Anterior lobe and posterior lobe: govern subconscious movement of skeletal muscles
Flocculonodular lobe: Invovled in equibillum


cerebellar cortex

superficial layer of cortex
Folia: consists of grey matter in a series of folia
Arbor vitae: deep to the folia (grey matter) are tracts of white matter called arbor vitae


Cerebellar nuclei

Nuclei in white matter


3 cerebellar peduncles

superior, middle and inferior cerebellar peduncles


cerebellum to red nuclei (midbrain) and thalamus

superior cerebellar peduncles


largest and axons carry impulses for voluntary movements from pontine nucleus to cerebellum

middle cerebellar peduncles


what does inferior cerebellar preduncles do?

1. axons of spinocerebellar tracts that carry sensory information from proprioceptors in trunk and limbs
2. axons from vestibular apparatus of inner ear + from vestibular nuclei of medulla and pons
3. axons from the inferior olivary nucleus of meddula that enter cerebellum and regulate cerebellar neurons
4. axons that extend from the cerebellum to the vestibular nuclei of medulla and pons
5. axons that extend from cerebellum to reticular formation


Function of cerebellum

Primary: to evaluate how well movements initiated by the cerebrum are actually carried out
- if not carried out correctly, the cerebellum detects the discrepancy and sends feed back signals to the cerebral cortex
- the feedback signals help correct the errors, smooth the movements and coordinate complex sequences of skeletal muscle contractions
- also regulates balance and posture



Loss of ability to coordinate muscle movements
can't touch the tip of nose, can't coordinate moments with the proprioceptive info
changed speech pattern due to uncoordinated speech muscles
staggering or abnormal walking gait
alcohol inhibits activity of cerebellum so drunks show signs of ataxia
ataxia can also occur from degenerative disease (MS, Parkinson's) trauma brain tumors, genetic factors, meds side effects



problem with speech



difficulty to find a word trying to say