ch 5b Flashcards
Name the 5 nuclei that the basal ganglia consist of
- Striatum: caudate nucleus and
putamen - Globus pallidus
- Substantia nigra
- Subthalamic nuclei
Name 4 neural circuits that involve basal ganglia
- Motor loop
- Oculomotor loop
- Prefrontal loop
- Limbic loop
Motor loop
related to movement
–> linked to primary motor cortex and premotor cortex
Oculomotor loop
related to eye movements
–> linked to frontal eye fields
Prefrontal loop
related to decision making
–> linked to dorsolateral prefrontal cortex
Limbic loop
related to emotions
How do the basal ganglia contribute to movement?
- Motor learning: selecting actions based on cost/reward
–> which limb trajectory is more cost efficient?, rewards favoured, motor planning w/ PPC and PM - Initiation of movement
- Movement vigor: controlling muscle force, speed/size of movement
Brainstem
-modulates action of spinal motor circuits
- Medial and Lateral brainstem pathways
Medial brainstem pathways
the basic postural control system controlling predominantly axial and proximal limb muscles
* Axial muscles = core/trunk muscles
* Proximal limb muscles = closer to the body (e.g., shoulder muscles)
* Includes: vestibulospinal, reticulospinal, and tectospinal tracts
Lateral brainstem pathways
goal-directed limb movements and control muscles of the limbs
* Includes: rubrospinal tract
Major descending brainstem pathways
-origin in the brain
-function
- Reticulospinal pathway (reticular formation)
-maintains posture and muscle tone - Vestibulospinal pathway (vestibular nuclei)
-posture, balance, location of head and body in space - Tectospinal pathway (superior colliculus)
-coordinates head and eye movements - Rubrospinal pathway (red nucleus)
-excite motor neurons innervating proximal upper limb flexors
Area in the brainstem that controls the initiation of walking
Mesencephalic locomotor region (MesLR)
3 functional zones of the cerebellum
- Vestibulocerebellum
- Spinocerebellum
- Cerebrocerebellum
functions of cerebellum related to movement
-smooth movements
-acts as a comparator (compares actual vs. expected sensory feedback)
-coordinates muscle groups by shaping commands
-gait patterns
-eye movement regulation: helps VO reflex work
-learning a new skill
Cerebellar related disorders:
Dysmetria
problem w/ limb trajectory or placement of a body part during active movement
–> reach up to touch dot, bring arm down to touch nose; might poke themselves in the face etc.
Cerebellar related disorders:
Dysdiadochokinesis
abnormalities w/ rapid alternating movements
Cerebellar related disorders:
Gait axia
coordination problem
-walk as if drunk
PPC
posterior parietal cortex
PMC
premotor cortex
SMA
supplementary motor area
PPC divisions/sub-regions (and their specific functions and inputs)
-Parietal Eye Field (PEF)= neurons respond to visual and auditory stimuli; gaze shift planning of eye movements
-Parietal Arm Fields (PAF)= vis. and som. input; guiding arm movements (planning reach)
-Parietal Grasp Field (PGF)= grasping actions; planning forearm orientation and finger movements based on vis. info
-Parietal Face Field (PFF)= vis. and tactile input (from face); planning facial expressions
-Parietal Foot Region (PFR)= planning foot/lower limb movements
PPC Functions
- Planning control of movement (recieves sensory info)
- Sensorimotor integration
- Spacial maps (where are you in space) and spatial working memory
How to know if a region of the brain is involved in motor planning?
look for changes in brain activity during the foreperiod prior to movement
SMA functions
-selection of movement sequences from memory “INTERNAL CUES”/memory
-bimanual movements (e.g playing piano)
-possible role in learning sequences (e.g. playing the piano)
Premotor Cortex functions
-selection of movement to EXTERNAL CUES
–> works w/ basal ganglia and DLPFC
-planning reaching movements based on target location
-planning grasping movements based on object details
-decision making
Primary motor cortex (M1):
Functions
- Neurons in M1 connect to alpha motor neurons in spinal cord to activate muscles
- Adapts movements to new conditions
- Neurons are related to muscle force
- Direction of movement is determined by the net action of M1 neurons
- Influenced by cortical and subcortical inputs
(exact contribution of M1 is still debated)
How is activity in individual neurons of M1 related to muscle force? (Experiment w PTN/pyramidal tract neuron and monkeys)
Main results=?
A PTN (pyramidal tract neuron) = a motor cortex neuron
-Money wrist flexor movement: Load, No load, and Extensor load groups
-movement is the same, but increased force: increase in PTN and muscle frequency
-This shows that PTN is related to muscle force
Do motor cortex cells have a preferred direction?
YES! activity is increased when moving to the preferred direction
Cortical motor commands descend in two tracts: (2 fibres)
- Corticobulbar fibres control the motor nuclei in the brainstem
- Corticospinal fibres control the spinal motor neurons that innervate the trunk and limb muscles
corticobulbar fibres are involved in controlling which muscles?
facial muscles
Corticospinal fibres control which muscles/movements?
control voluntary movement of the distal limb muscles
6 locations that corticospinal fibres can be found?
- M1 (30%)
- Premotor and SMA (29%)
- Pareital cortex: 4. somatosensory cortex and 5. PPC
- Cingulate gyrus
Walking is an interaction between these 3 factors
- Spinal cord circuitry
- Sensory feedback (from muscle spindles, GTOs, cutaneous receptors)
- Descending commands:
How does stretching your hip flexors trigger swing phase of walking?
muscle spindles detect change in length and send info to the CPG/central pattern generator circuitry (via the 1a afferents) which activates flexor/extensor motor neurons which causes the hip flexor muscles to swing the legs forward
How does the extensor load information help maintain stance phase of walking?
nervous system must maintain extensor leg muscle activity during stance phase to stop the body from collapsing under the force of gravity
-uses feedback from the GTOs in extensor muscles
-1b afferents signal weight-bearing load to spinal cord circuitry
Extensor load info: stance phase
Describe experiment (cat, treadmill extensor and flexor muscle activity, 1b afferents stimulated in extensor muscle)
-1b afferents stimulated in extensor muscle= prolonged extensor muscle activity and delayed flexor muscle activity
-RESULT= cat’s hindleg is dragged since the spinal cord thinks it has to maintain stance phase
Normally, the decrease in loading of the leg would correspond to decreased 1b activity, indicating that
it is “safe” to swing the leg because it is no longer holding the animal’s weight
Primary motor cortex neurons contribute to changes in gait
-when do they increase their activity?
-increase their activity just prior to and during a step over an obstacle
Posterior parietal cortex (PPC) neurons are related to motor planning of
gait modifiations
How are PPC neurons related to step-advanced neurons (function: example of cat stepping over object)
-step-advanced neurons may encode the relationship (or gap closure) between the obstacle and the cat that allows the animal to change paw position to properly step over the object
-the other PPC neurons may encode the same thing (in ‘working memory’) to facilitate trial limb movements over the obstacle
Neurons responsible for the execution of the step over an obstacle
Primary motor cortex neurons
Voluntary movements: the brain must do what to activate muscles
brain must integrate sensory info, form a motor plan, and coordinate networks of neurons to develop motor commands to activate muscles
(Sensorimotor integration)
Sensory systems and receptors encode input in different egocentric-based coordinate reference frames
(3)
Vision= eye or retina-centered
Vestibular= head-centered
Somatosensory= body-part-centered (ex. head, hand, foot)
Think of sensorimotor integration as
putting signals into common “language”
Sensorimotor integration is largely performed by neurons in the
PPC, Premotor cortex, and SMAs
Sensorimotor integration (example of reaching to a doorknob)
-hand and target position can each be defined with respect to different reference frames (eye-, hand-, or shoulder-/body- centered)
-brain must compute difference between the position of hand (H) and target (T); which= difference vector (M)
-this shapes the reaching movement to doorknob
