Chapter 4 Flashcards
cerebellum divided into three imperfectly delineated lobes
anterior lobe, posterior lobe, floccular lobe
sign of increased intracranial pressure
the tonsils (T) may herniate through formen magnum— pressure on medulla
- life threatening
function cerebellum
modulates and refines motor control; participates in acquiring and maintaining motor skills, from playing a musical instrument to pitching a baseball to texting
3 parts of the brain involved in movement
1) motor cortex –> sends signals
2) basal ganglia –> initiates and stops movement
3) cerebellum –> ensures movement is smooth; fine tuning
amount of neurons in the cerebellum vs. neocortex
despite its small size relative to the neocortex, the cerebellum contains about four times more neurons than the neocortex
- 69 billion neurons compared to 16 billion neurons
somatotopy
body regions correspond to specific areas of the brain that control them
somatotopy in the anterior lobe
body appears inverted; hindlimbs are on top (rostral) and forelimbs are next (more caudal), and the face at the very bottom
somatotopy in the posterior lobe
the body appears straight, but dually represented (i.e., has one representation on each side of the midline); trunk is towards the midline; extremities are more lateral
significance of somatotopy
disorders of one region of the brain will affect one region of the body
- disorders affecting the midline cerebellum = affect primarily trunk musculature and cause problems in balance and equilibrium
different parts of the cerebellar hemispheres subserve different movements
- lateral –> associated with movements of the limbs, hands, feet, and digits
- medial areas –> associated with the face and the body’s midline
pathways from the cerebellar hemispheres
project to cerebellar nuclei in its base, which in turn project to other brain regions, including the motor cortex
lateral hemispheres of the cerebellum
- function: participates in the planning and programming of voluntary movements, particularly learned, skillful movements that become more rapid, precise, and automatic with practice
- dentate nucleus
- dentate neurons rate of firing tend to change during movement
- clinical observation: disrupts arm, hand, and finger movements; deficits in learned, skillful movements (e.g., piano playing) may be permanent
lesions of lateral hemispheres of the cerebellum
problems in movement of extremities; affect muscles of extremities
manifestations:
- ataxia
- hypotonia
- asynergia/adiodockokinesia
- nystagmus
- dysmetria/dysarthria
- tremor
hypotonia
decrease in resistance to passive stretching of muscle, and pendular tendon reflex
asynergia/adiodockokinesia
asynergy between agonist/antagonist muscles (jerky movement) / inability to perform quick alternating movements
dysmetria
e.g., miss touching nose with tip of finger
medial (vermis) hemisphere of the cerebellum
- function: involved in posture and balance/equilibrium
- these areas are heavily connected to the vestibular nuclei and hence their role in the regulation of posture, maintenance of equilibrium, and coordination of eye movement
- clinical observation: tumors or damage in midline areas of the cerebellum disrupt balance, eye movements, upright posture, and walking; when lying down, a person with damage to the medial cerebellum may show few symptoms
lesions of the medial cerebellum
manifestations:
- unsteadiness of gait and nystagmus
- very similar to vestibular signs
- potential problems with control of eye movement
floccular lobe of the cerebellum
- receives projections from the vestibular system and so takes part in controlling balance
- many of its projections go to the spinal cord and to the motor nuclei that control eye movements
complete loss of cerebellum
those experiencing this can walk, but with difficulty, and retain most cognitive function, but with impairments
attempts to understand how the cerebellum controls movements center on two major ideas
1) role in movement timing
2) helps maintain movement accuracy
motor test of timing in role in movement timing as an attempt to understand how the cerebellum controls movements
- patients with cerebellar damage and control participants were asked to tap a finger in rhythm with a metronome
- after many taps, the metronome was turned off, and both groups attempted to continue tapping to the same beat
- those with damage to the cerebellum, especially the lateral cerebellum, performed poorly
perceptual test of timing in role in movement timing as an attempt to understand how the cerebellum controls movements
- patients and controls were presented with two pairs of tones
- silent period between the first two tones was always the same length
- silent period between the second two tones changed from trial to trial
- both groups were required to report whether the second silent period was longer or shorter than the first
- those with damage to the cerebellum performed poorly
- shows that the cerebellum acts like a clock or pacemaker to ensure that both movements and perceptions are appropriately timed
helps maintain movement accuracy attempt to understand how the cerebellum controls movements
- patients and control participants throw darts at a target
- after a number of throws, both groups donned glasses containing wedge-shaped prisms
- both groups showed initial distortion in aim
- control participants saw the dart miss the mark, they adjusted each successive throw until reasonable accuracy was restored
- patients with damage to the cerebellum did not correct for this error
cerebellum improves motor skills by making required adjustments to movements
1st attempt:
- aim at the bullseye, throw the dart, and find that it misses the board completely
2nd attempt:
- aim to correct for the original error
- notice that there are actually two versions of each throw: 1) the movement that you intended to make and 2) the actual movement
- sensory receptors in your arm and shoulder and by those in your eyes record 1) and 2); if the throw is successful, no correction is needed on your next try; but if you miss, an adjustment is called for (all by way of spinocerebellar tracts)
how the brain corrects for the aim in the dart experiment
- cortex sends instructions to the spinal cord to throw a dart at the target
- cortex also sends a copy of the same instructions to the cerebellum through the inferior olivary nucleus
- cerebellum acts as servomechanism, which in engineering is a device that uses error-sensing negative feedback to correct an action (feedback via spinocerebellar tract)
other functional considerations of the cerebellum
- involved in motor learning
- conditioned blink response
- possible that similar changes in the cerebellum may underlie the acquisition of skilled, voluntary movements in general
conditioned blink response experiment
- a puff of air directed at a rabbit’s cornea elicits a reflex blink
- if the puff of air is regularly preceded by a sound, after a while the sound itself elicits the same blink
- various specific lesions in the pathways that lead from the ear (conditioned stimulus) or the eye (unconditioned stimulus) to the cerebellum interfere with learning of this conditioned response
cerebellum involved in cognitive functions
- parts of the cerebellar cortex that deal with inputs from association cortex— the lateral hemispheres (or cerebroceebellum)— are greatly expanded in humans, and especially the association cortex fibers that come from the prefrontal cortex
cerebellar damage or malformation can be associated with a variety of cognitive or behavioral disturbances
- impairments in executive function (planning, set shifting, verbal fluency, abstract reasoning, working memory)
- impairments and spatial cognition (visual spatial organization and memory)
- impairments in spatial cognition (visual spatial organization and memory)
- impairments in linguistic processing (agrammatism and dysprosodia)
- mainly when the lesions involve the lateral hemispheric regions
cerebellum involved in emotion
- connections between more medial parts of the cerebellum and limbic cortex (amygdala) (as well as cerebellum-hypothalamus interconnections) seem to play a role in affective and autonomic functions
- clinical observations: patients with the cerebellar lesions experience dysregulation of affect when their lesions encroach upon the more medial parts (towards the vermis); example is coupling cognition-emtion to proper motor and facial gestures
pseudobulbar affect (PBA)
- pathologic (forced, spasmodic) laughing and crying
- involves inappropriate outbursts of laughter and crying: the slightest provocation or sometimes for no apparent reason, the patient is thrown into hilarious laughter or crying that may last for many minutes to the point of exhaustion
- the patients report that they don’t have the feeling accompanying the emotion they are expressing, i.e., they cry, but they are not feeling sad; they laugh, but they are not feeling happy
