7. Cognitive/Motor Flashcards
state of consciousness
level of arousal
how is state of consciousness measured?
by behaviour and brain activity
conscious experience
capacity to experience one’s existence
what does ElectoEncephaloGraph (EEG) measure?
mainly measures activity of neurons located near the scalp in grey matter of cortex
EEG components
frequency and amplitude
what does frequency refer to in EEG
levels of responsiveness
what does amplitude refer to in EEG
synchronous neural activity
relaxed EEG characteristics
slow frequency with big amplitude
alert EEG characteristics
high frequency with small amplitude: less synchrony
stage 1 NREM sleep characteristics
low amplitude
stage 4 NREM sleep characteristics
high amplitude, low frequency, more synchrony
what happens to amplitude and frequency from NREM stage 1 to 4?
amplitudes become bigger and frequencies smaller
REM sleep
- Rapid Eye Movement
- deepest sleep
- dreaming phases
characteristics of REM sleep
- increased eye movement
- increased skeletal muscle inhibition = low muscle tone
- increased heart rate and respiration
how does REM sleep appear on EEG?
low amplitude, high frequencies: resembles awake state
sleep apnea
sudden reduction in respiration in REM sleep due to high muscle relaxation: tongue falls back, blocking respiration and wakes person up
sleep cycle
- spend 30-45 min cycling through NREM stages of sleep
- go into REM sleep
- cycle again
the amount of REM sleep we get decreases with…
age
what regulates the state of consciousness?
the circadian rhythm
Circadian rhythm is mediated by…
hypothalamus and Reticular Activating System
awake state regulations from hypothalamus and reticular activating system
- reticular activating system activates aminergic neurons: norepinephrine and serotonin
- acetylcholine production deactivated
- hypothalamus increases histamine production
Asleep state regulations from hypothalamus and reticular activating system
- reticular activating system activates cholinergic neurons: acetylcholine
- norepinephrine and serotonin production deactivated
- hypothalamus inhibits histamine production
what mediates behaviour?
motivation and emotions
what is the mesolimbic pathway?
reward pathway, motivation
what is the limbic system?
controls our emotions
what does the mesolimbic pathway involve?
- dopamine as primary neurotransmitter
- anatomically: locus ceruleus in reticular activating system + midbrain + prefrontal cortex
anatomy involved in limbic system
- olfactory bulb
- amygdala = emotional response
- hippocampus = memory
declarative memory
conscious experiences that can be put into words
knowing faces, names and facts is an example of what memory?
declarative memory
where is short-term declarative memory located?
hippocampus + other temporal lobe structures
where is long-term declarative memory located?
cerebral cortex
procedural memory
skilled behavior
learning how to juggle or ride a bike are examples of which memory?
procedural memory
where is short-term procedural memory located?
widely distributed
where is long-term procedural memory located?
basal nuclei + cerebellum + premotor cortex
which hemisphere is language most located on?
left hemisphere
brain areas involved in language
- Broca’s area
- Wernicke’s area
Broca’s area is responsible for language…
production, articulation
Wernicke’s area is responsible for language…
comprehension (written + spoken)
aphasia
language deficit
parietal damage can lead to
sensory neglect of contralateral side of the world
sensory neglect
sensory information processed normally but is ignored/doesn’t exist in their visual field
limb extension..
increases the angle around the joint
extensor and flexor muscles during extension
- extensor muscle contracts (agonist)
- flexor muscle relaxes (antagonist)
limb flexion…
decreases the angle around the joint
extensor and flexor muscles during flexion
- flexor muscle contracts (agonist)
- extensor muscle relaxes (antagonist)
antagonist
relaxing muscle
agonist
contracting muscle
how is limb position maintained so there is no movement?
there’s a balance between flexor and extensor muscle tension
motor neurons key points
- excitatory only
- release acetylcholine
- receive inputs mostly from interneurons in grey matter of spinal cord
2 types of motor neurons
- alpha
- gamma
what do alpha motor neurons innervate?
skeletal/extrafusal muscle
what do gamma motor neurons innervate?
muscle spindle/intrafusal muscle
spinal interneurons
receive information from many neurons to be transmitted to motor neurons in dorsal root
information received at spinal interneuron (6)
- tension monitoring
- pain
- proprioceptive feedback
- voluntary movements
- coordinate complex movements
- length monitoring
sensory afferent pathway
proprioception pathway: up the ipsilateral dorsal columns, branching at interneuron for inhibition
motor efferent pathway
- descending motor commands (from brain) reach interneuron
- then passed to motor neuron in ventral horn
- motor efferent exits through ventral root
purpose of withdrawal reflex
to protect limbs from injury
2 parts of the withdrawal reflex
- flexion withdrawal
- cross extensor reflex
Withdrawal reflex
Flexion withdrawal
1. painful stimulus: nociceptors activated
2. nociceptors go through pain pathway, branching before the midline
3. ipsilateral extensor inhibited, ipsilateral flexor excited
cross extensor reflex
4. nociceptors at branching cross the midline
5. contralateral extensor excited, contralateral extensor inhibited
withdrawal reflex: ipsilateral extensor…
is inhibited: extensor muscle relaxes
withdrawal reflex: ipsilateral flexor…
is excited: flexor muscle contracts
withdrawal reflex: contralateral extensor…
is excited: extensor muscle contracts
withdrawal reflex: contralateral flexor…
is inhibited: flexor muscle relaxes1
irradiation
increase in rate and magnitude of withdrawal response with increased stimulus strength due to recruitment of interneurons
afterdischarge
difficulty to re-extend limb even after pain stimulus removed due to feedback loops in spinal cord maintaining withdrawal
withdrawal reflex is polysynaptic or monosynaptic?
polysynaptic: interneurons present between sensory input and motor output
is withdrawal reflex contralateral or ipsilateral?
both: ipsilateral on withdrawal reflex (same side as nociceptive input) and contralateral on cross extensor reflex
purpose of stretch reflex
to control muscle length
stretch reflex steps
- tap below knee cap gently
- activation of stretch receptor
- stretch receptor pulls on patella, pulling on stretch extensor muscle
- muscle length reported through proprioception pathway: ipsilateral dorsal columns
- monosynaptic and polysynaptic branching in grey cortex:
- excitatory synapse on motor neurons innervating ipsilateral extensor
- inhibitory synapse through interneuron inhibiting ipsilateral flexor - leg kicks
how is muscle length reported?
- muscle spindle is in parallel with extrafusal muscle fiber so both are always the same length
- muscle lengthens = muscle spindle lengthens = increase in muscle spindle afferent activity
- reported to CNS
extrafusal muscle fibers are activated by…
alpha motor neurons
intrafusal muscle fibers are activated by…
gamma motor neurons
what do extrafusal muscle fiber produce?
force creating movement
Ia primary afferents
signal dynamic changes in muscle length due to stimulus changes
–> rapidly adapting
II secondary afferents
signal static muscle length (position)
–> non-adapating
which afferent (Ia or II) mediates the stretch reflex?
Ia primary afferents
how is muscle flexion generated?
- alpha motor neuron activity commands muscles to shorten
- muscle spindle also shortens
- muscle spindle collapses: sensitivity reduced so receptor stops working
how is spindle sensitivity maintained?
by alpha-gamma coactivation: gamma motor neurons cause intrafusal fibers to contract, stretching the muscle spindle
properties of stretch reflex
- resists changes in muscle length: sets muscle tone
- mono and polysynaptic
- feedback from muscle spindles
properties of muscle spindles
- report muscle length
- in parallel with extrafusal muscle fibers
- intrafusal muscle fibers maintain muscle spindle sensitivity
- alpha-gamma coactivation
- Ia and II afferents
purpose of inverse stretch reflex
to control muscle tension (voluntarily)
organ involved in inverse stretch reflex
golgi tendon organ
organ that responds to tension
golgi tendon organ
properties of golgi tendon organ
- in series with extrafusal muscle fibers
- reports muscle tension
- Ib afferents
- underlines inverse stretch reflex
how does golgi tendon organ control muscle tension?
when tension increases, collagen fibers looping around the free nerve endings pinch the free nerve endings, activating mechanically-gated ion channels
inverse stretch reflex steps
- muscle contracts, increasing tension in extensor muscle
- activation of golgi tendon organ
- causes increased Ib afferent activity sending AP through dorsal root/column
- branching in grey matter:
- excitation of motor neurons innervating ipsilateral flexor
- inhibition of motor neurons innervating ipsilateral extensor
inverse stretch reflex is polysnaptic or monosynaptic?
polysynaptic
stretch reflex is polysnaptic or monosynaptic?
both
inverse stretch reflex: ipsilateral flexor
contracts
inverse stretch reflex: ipsilateral extensor
relaxes
motor control hierarchy
- higher centres consciously initiate movement
- 2 main pathways down brainstem and spinal cord
- motor neurons innervate muscle fibres or cranial muscles in brainstem
sensorimotor cortex =
primary motor cortex + somatosensory cortex
middle level composed of:
- sensorimotor cortex
- basal nuclei
- thalamus
- brainstem
- cerebellum
local level
brainstem and spinal cord
why is there an involuntary component to voluntary movements?
- to execute individual muscle contractions
- to make corrections based on sensory information while the movement is being executed
2 major pathways down the spinal cord
- corticospinal
- extrapyrimidal
Corticospinal pathway contols
skilled movements
Extrapyrimidal pathway controls
trunk and posture
voluntary control of movement steps
- consciously initiate a movement
- at premotor cortex: motion decomposed into individual muscle contractions required
- at primary motor cortex neurons send information down spinal cord
- somatosensory cortex regulates movement to sensory information received
central sulcus separates… from…
primary motor cortex from somatosensory cortex
somatotopic motor representation
size of body structures in primary motor cortex is proportional to the number of neurons dedicated to their motor control and to the degree of skill required to operate that area
corticospinal descending pathway
- originates in primary motor cortex
- compact, discrete fiber tract direct to spinal cord: directly involves alpha and gamma motor neurons and branching at interneuron
- crossed at medulla –> controls contralateral muscles
- extremities: mostly hands and feet
- controls skilled movements
corticospical descending pathway is mono or polysynaptic?
both
corticospinal controls ipsilateral or contralateral muscles?
contralateral
extrapyramidal descending pathway
- originates from neurons in brainstem
- diffused and indirect: several descending tracts via brainstem, only innervating interneurons in spinal cord
- crossed and uncrossed –> controls contralateral and ipsilateral muscles
- trunk + postural muscles
- controls upright posture, balance, and walking unconsciously
extrapyrimidal descending pathway is mono or polysynaptic?
polysynaptic
extrapyramidal controls ipsilateral or contralateral muscles?
both
muscle tone
resistance of skeletal muscle to stretch
how is normal muscle tone reflected on stretch reflex?
slight and uniform reflex
consequences of damage to motor descending pathways
- hypertonia
- spasticity
- rigidity
hypertonia
abnormally high muscle tone
spasticity
overactive motor reflexes
rigidity reflects
constant muscle contraction
why is stretch reflex much stronger when there is damage to descending pathways?
descending pathway branches into interneurons, which are mostly inhibitory
–> damage means no more inhibition of those interneurons
consequences of damage to motor neurons
- hypotonia
- atrophy
- decreased or missing reflexes
hypotonia
abnormally low muscle tone
atrophy
loss of muscle mass
basal nuclei
collection of cell bodies in CNS
basal nuclei function
helps determine specific movements needed to accomplish a desired action
2 basal nuclei movement disorders
- Parkinson disease
- Huntington disease
Parkinson disease
reduced dopamine input to basal nuclei
Parkinson’s symptoms
- akinesia
- bradykinesia
- muscular rigidity
- resting tremor
akinesia
reduced movements
bradykinesia
slow movements
resting tremor
tremor stops only when person makes a movement with that shaking limb
Parkinson disease treatment
increasing dopamine concentrations in the brain
-> no cure
Huntington disease
genetic mutation that causes widespread loss of neurons in the brain, mostly in the basal nuclei
Huntington’s symptoms
- hyperkinetic disorder
- choreiform movements
hyperkinetic disorder
excessive motor movements
choreiform movements
jerky, random involuntary movements of limbs and face
cerebellum functions
movement timing, planning and error correction + learning new motor slills
how is cerebellum linked to sensation?
it receives sensory information that goes through the brainstem (next to each other so information shared)
cerebellar deficits
- asynergia
- dysmetria
- ataxia
- intention tremor
asynergia
Smoot movements broken down into their individual components
dysmetria
unable to target movements correctly when trying to reach for something
ataxia
incoordination of muscle groups –> awkward gate
intention tremor
tremor only during voluntary movements
what is a symptom that isn’t seen in patients with cerebellar deficits?
paralysis or weakness
–> still independent but can’t learn skilled movements
