CNS 5 Flashcards
Cerebellum (“Little Brain”)
Inputs:
1) sensory input form spinal cord
2) motor commands from cerebral cortex
Functional divisions:
Cerebellum
- Vermis : posture, neck and axial (Trunk) musculature
- Intermediate zone: locomotion
- Lateral zone: coordinating complex, skilled movements of arms, hands & fingers
- Flocculonodular lobe: balance
Ba sal Ganglia (Extrapyramidal System)
• Anatomy:
- Large, deep cerebral nuclei
1. Involved in initiating movement
2. Involved in suppressing activity of muscles that would resist the intended movement
Basal Ganglia (Extrapyramidal System)
Dysfunction:
either:
- poverty of movement (bradykinesia (slow movement) and rigidity and tremor)
Parkinson’s disease (PD) - Involuntary movement:
eg. Chorea, Tourette’s syndrome, hemiballismus
Brainstem
Function:
- Control of respiratory & cardiovascular musculature
- Control of transmission in sensory, motor, reflex & pain pathways
- Initiation of locomotion (Midbrain locomotor area (MLA))
Sleepy states
- alert wakefulness
- relaxed wakefulness
- relaxed drowsiness
NREM (slow wave) sleep
- stage N1
- stage N2
- stage N3
REM (periodoxical) sleep
El ectroencephalogram (EEG)
• Vo l t a g e f l u c t u a t i o n s r e c o r d e d b e t w e e n p a i r s o f e l e c t r o d e s o n t h e s c a l p
• Made up of summed, synchronous, post-synaptic potentials of many
neurons
• Waveforms vary with behavioural states: attention, arousal, sleep,
dreaming
- Abnormal in epilepsy and over brain tumours
- Used to verify brain death ie. To allow organs to be removed
Brainstem Control of Sleep,
Wakefulness, Arousal
• Controlled by the reticular activating system (RAS):
nuclei in brainstem and hypothalamus
Br ainstem Control of Sleep,
Wakefulness, Arousal
• Controlled by the reticular activating system (RAS): nuclei in brainstem and hypothalamus
- Visual and other sensory inputs activate RAS neurons
- Brainstem RAS supplies the monoamines norepinephrine (Noradrenaline), serotonin and histamine to hypothalamus and other brain areas
- Hypothalamus supplies orexins (Neuropeptide hormones) to thalamus and cortex, maintaining wakefulness
- Suprachiasmatic nucleus activates orexin-producing neurons at first light in the morning, promoting wakefulness. It also secretes melatonin at dusk. These mechanisms set the “circadian rhythm”.
- “Sleep centre” in pre-optic nucleus of hypothalamus delivers GABA-ergic inhibition of RAS, reducing orexin levels
- RAS is inhibited by GABA agonist sedatives like Valium and Xanax, by anti-histamines like Benadryl, by barbiturates like Nembutal and other anaesthetics
- Small lesions in RAS can produce coma
Conscious Experiences
• Awar enes s of pas s age of time, exter nal s ens or y inputs and internal states such as fatigue, thirst, happiness, memories, reasoning, ideas
Two main aspect of conscious experiences
Selective attention and conscious perception
Selective Attention
- Attention shifts from one focus or attractor to another
- Coincident attractors ( eg. Visual and auditory inputs coming from the same direction) are more likely to trigger a shift than separate attractors
- CNS areas implicated in triggering shifts: Thalamus and locus ceruleus in brainstem RAS
Conscious Perception
• Theory:
there isn’t a single cluster of
“consciousness neurons”. Rather, specific sets of neurons in widely separated brain areas temporarily function together:
“Temporary Sets”.
Destruction of specific brain areas can
abolish selective parts of
consciously perceived inputs ie. Hemi-neglect after a stroke affecting the parietal lobe: the person is unaware of half of their visual field.
Primary motivated behavior:
directly related to homeostasis eg.
Maintaining water balance, nutrition, body temperature.
Secondary motivated behavior:
that which results in pleasure. Can be
disadvantageous eg. Over-eating, taking recreational drugs.
Emotion
- Internal attitudes toward events and the environment ( eg. Being happy, sad, fearful)
- External responses (emotional behaviour)
Emotion: Neuroanatomical Mechanisms
• Theory:
there is no single cluster of neurons that generate all emotions.
Electrical stimulation in lateral hypothalamus elicits
Rage
Lesions of amygdala results in an absence of
Fear
Serotonin re-uptake inhibitors counteract
Depression by main ting levels of serotonin and norepinephrine at
synapses. They may thereby enhance
neurogenesis eg. In the hypothalamus
Working Memory (Shortterm Memory)
– Episodic: recent events, places
– Visuo-spatial: recent sights, locations – Phonological: recent words, sounds
Long-term Memory
Declarative (Involves consciousness)
- Semantic (Facts: ice is cold, fire is hot)
- Episodic (Personal experiences)
Procedural (Motor, mainly sub-conscious)
- Stimulus-response behaviours
- Motor skills: playing piano, skiing…
Transfer from s.t.m. to l.t.m. (Laying down, or consolidation of the memory trace) probably occurs in
temporal lobes
“Reward” system involving _________ is also implicated
hypothalamus
The caudate nucleus is implicated in consolidating stimulus-response
associations taught during
operant conditioning and in solving sequence tasks
Amnesia: retrograde & anterograde loss of s.t.m.
– Concussion: measured by type and duration of amnesia
– Retrograde → loss of memory of events prior to the injury
– Anterograde → loss of memory of event after the injury
Korsakoff’s Syndrome
(Damage to hippocampus) complete
anterograde amnesia
Alzheimer’s disease:
degeneration of memory-holding neurons, perhaps due to amyloid precursor proteins causing “excitotoxicity”
ie. Neurons are damaged by over-excitation
