Task 1 Flashcards
High level of motor system
cortex (SMA,PMA->6), parietal association cortex, PFC, basal ganglia
- goal of movement
- > concerned with movement strategy that best achieves the goal
middle level of motor system
basal ganglia, cerebellum, Brain stem, M1
- concerned with tactics
- > sequences of muscle contractions arranged in space and time
low level of motor system
spinal cord, brain stem, muscles
- activation of motor neurons and interneuron pool
- > generate goal directed movement
- > make necessary adjustments to posture
Lateral Pathways (2)
1) Corticospinal
2) Rubrospinal
- > voluntary movement of distal muscles under direct cortical control
Corticospinal tract
- cortex
- > internal capsule
- > cerebral peduncle
- > Pons
- > forms pyramidal tract in medulla
- > decussates at ventral horn of Spinal cord (location of motor neurons controlling distal muscles)
Rubrospinal tract
- red nucleus in midbrain
- decussates at Pons
- medulla
- ventral horn of Spinal cord
- no major role in humans
- can compensate by gaining larger role when corticospinal tract is lesioned
ventromedial pathways (4)
- Vestibulospinal tract
- Tectospinal tract
- Pontine reticulospinal tract
- medullary reticulospinal tract
- control of posture and locomotion
- under brainstem control
Vestibulospinal tract
- vestibular nuclei of medulla (gets info from inner ear via cranial nerve)
then: - bilaterally to SC -> control of neck and back muscles
- ipsilateral to SC -> to lumbar spinal cord -> maintain upright, balance, posture
Tectospinal cord
- visual cortex, somatosensory, auditory info
- > superior colliculus
- > creates map of world around us
- > ventral spinal cord
- > leads to orientation response
- directs head and eyes
Pontine reticulospinal tract
- starts in pontine reticular formation in brainstem
- > through medulla
- > to ventral spinal cord
- enhances antigravity reflexes of spinal cord
- helps maintaining standing posture by resisting effects of gravity
Medullary reticulospinal tract
- opposite function of pontine reticulospinal tract
- frees muscles from reflex control
role reticular formation
-maintaining behavioral arousal and consciousness
Area 4
- M1/primary motor cortex
- anterior to central sulcus
- input from area 6
- only active when movement
- not only cortical area that contributes to corticospinal tract or movement
- > lowest threshold for elicitation of movement by electrical stimulation
-Control of body parts is contralateral (75% decussate in pyramids, 15% in the spinal cord and only 10% do not decussate and are ipsilateral -> responsible for proximal forelimb muscles in shoulder)
Input M1
- from other cortical areas (1,2,3,6)
- cerebellum to thalamus to M1
Output M1
- pathway originates in cortical layer 5
- > layer 5 has pyramidal neurons, largest cells = Betz cells
- directly to spinal cord
- also brain stem areas involved in sensorimotor processing
Experiment monkeys and joystick
- M1 cells fired most vigorously during movement in one direction but also during movements that varied (plus minus 45 degree) from preferred direction
- > made sure that activation is due to direction and not just arm muscles moving
M1 , votes and voluntary movement
- much of motor cortex is active for every movement
- activity of each cell represents a single vote for a particular direction of movement
- direction of movement is determined by an average of votes from the population
-> more votes -> more cells -> more precise movement possible
- > seems that cells in M1 can switch from preferring one kind of movement to another as skills are learned
- > indeed it has been found that the motor cortex is plastic.
Area 6
- anterior to area 4
- 2 somatotopically organized motor maps in area 6
- lateral : premotor area (PMA)
- medial: supplementary motor area (SMA)
- active also when we only rehearse movement
Posterior Parietal cortex
- Association area
- mental body image
- directs behavior by providing spatial information
- Area 5: input from primary somatosensory cortical areas 1,2,3,
- Area 7: input from higher order visual areas
Damage to posterior parietal
-produces deficits in perception and memory of spatial relationships and accurate reaching
Dorsal premotor area (PMd)
- critical for implenting associations between arbitrary cues and motor responses
- crucial for selecting motor responses based on spatial cues (visual and auditory)
- guide movements based on sensory info -> receives combination of somatosensory and visual info for the visual guidance of movements
- caudal (strongly connected with M1) and rostral (strongly connected with PFC) PMd have unique functions
Ventral premotor areas (PMv)
- contributes to hand movements
- transforming visual representation of an objects geometric properties to motor commands acting on muscles of hand -> ‘pre shaping’
- firing of neurons increases (decreases) as function of amount of grip forces
- neurons active before and during object related hand movements execution and observation
-underlie cognitive-related functions like the understanding of actions (mirror neurons found in PMv)
nonprimary areas projecting to spinal cord
- hierarchical organization of the motor cortex (and CNS in general) was overruled by the finding that some neurons from the nonprimary areas (which are “under” the M1) also project directly to the spinal cord.
- > neurons only have a weak influence in the spinal motor-neurons
brain machine interface
- connecting motor neurons in the motor cortex to a computer and sending the planned action to a robot, that then acts on the plan
- > Helpful for people with spinal cord injuries, amputations and other diseases
effector
-part of body that can move
Alpha neurons
- provide point of translation between nervous system and muscular system
- originating in the spinal cord and terminating on muscle fibers
- > action potentials in alpha motor neurons cause muscle fibers to contract
extrapyramidal tracts
- neural pathways that project from subcortex to spinal cord
- rubrospinal
- tectospinal
- vestibulospinal
- reticulospinal
Hemiplegia
- loss of ability to produce voluntary movement
- results from damage to primary motor cortex or corticospinal tract
- > deficits are present in effectors contralateral to lesion
-reflexes are absent immediately after a lesion but may become hyperactive and even spastic after a couple of weeks
pyramidal tracts
-axons travel directly from cortex to spinal segments
Lesion of the secondary motor areas result in…
- Apraxia:
- problems performing purposeful and coordinated movements
- loss of ‘praxis’/skilled movement
- affects motor planning
- no motor or sensory impairment
- normal muscle strength/tone
- can produce simple gestures
- cannot link gestures into meaningful actions
contralateral neglect
….
CNS
- cerebellum
- cerebrum
- brain stem
- spinal cord
PNS
- somatic PNS: all spinal nerves that innervate skin, joints and muscles that are under voluntary control
- ANS/visceral PNS: neurons innervating internal organs, blood vessels, glands
Development embryo
- begins at flat disk with 3 layers
1) endoderm (becomes organs)
2) mesoderm (bones and muscles)
3) ectoderm: becomes NS
Neurolation
neural plate -> neural groove -> neural tube and neural crest
-entire CNS develops from walls of neural tube
- neurons with cell bodies in PNS derive from neural crest
Effects of lateral pathway lesions: in animals
- in monkeys:
- unable to make fractionated movements of the arms and hands
- could not move their shoulders, elbows, wrists, and fingers independently
- could grasp small objects with hands, but only by using all fingers at once
- voluntary movements were also slower and less accurate
-could sit upright and stand with normal posture
lesions in corticospinal tracts in humans
-movement deficit as severe as that observed after lesions in the lateral columns
- > many functions gradually reappeared over the months following surgery.
- > rubrospinal compensates
Parkinsons
…
ideomotor apraxia
- patient has rough sense of desired action
- problems executing it
example:
-if asked to pantomime how to comb his hair, patient might knock his fist against his head
ideational apraxia
- more severe
- knowledge about intent of an action is disrupted
- no longer comprehend appropriate use for a tool
example:
- patient uses comb t brush his teeth
parietal lobe (association area) lesions lead to…
-apraxia (even more often than damage to secondary . motor areas)
-disrupt ability to produce movement
-lead to impairments in recognition of actions produced by others
(even if sensory capabilities appear to be intact)
Lesions of primary motor cortex result in ..
- hemiplegia
- loss of voluntary movements on contralateral side of body
- affects most distal effectors (fingers, hand)
- results often from hemorrhage in middle cerebral artery -> unable to move affected limb
- reflexes are absent immediately after stroke produced hemiplegia
when does activity occur in M1?
- immediately before and during voluntary movement
- encodes for force and direction of movement
