Sensorimotor Flashcards
Initiating a motor sequence (PFC, Premotor, and PMC)
Prefrontal cortex - big picture decisions (when to take up, where to go, right/wrong behaviour)
Premotor - coordinates movements from many body parts (organizes movement sequences)
Primary motor cortex - produces skilled/specific movements
What does homunculus man represent?
Represents the brain’s sensory and motor cortices distribution
What do longer duration electrical stimulation suggest?
That M1 stores movement categories (monkeys)
Human motor cortex thought to be organized the same way
Initial thought (based on shorter duration signals) was that each part of homunculus controls muscles of corresponding part of the body
Coritcobulbar tracts
Facial movements
Corticospinal tracts
(Pyramidal)
Lateral corticospinal tracts are crossed (limbs)
Anterior corticospinal tracts are uncrossed (trunk)
What is basal ganglia comprised of?
Caudate nucleus
Putamen
Globus pallidus
Striatum
(Caudate and putamen)
Striatum receives most inputs
- extensive connections with the cortex via the substantia nigra
Globus pallidus
Outputs of the basal ganglia, primarily to the motor cortex
What does basal ganglia do?
Regulate movement force
Volume control theory (globus pallidus inhibits: turn it down and movement occurs, turn it up and movement is blocked)
Hyperkinetic vs hypokinetic
Hyperkinetic = too much movement
Hypokinetic = too little movement
Huntington’s disease
Hyperkinetic
- jerky, coordinated yet involuntary movements
- changes in the brain: degeneration of GABAergic neurons in the striatum, widespread damage in later stages
Parkinson’s disease
Hypokinetic
- tremor at rest, involuntary movements
- loss of locomotive disorders, postural disorders, akinesia
- dopamine reduced by 90%, substantia nigra disorders, ‘dark substance’ is no longer dark
What does accuracy/efficiency/correctness of movements require?
Cerebellum and basal ganglia
What has happened by the time that (any) information has reached the thalamus?
It has decussated (info. from left side of the body is being processed in the right side and vice versa)
What is associated with the dorsal (posterior) spinothalamic somatosensory pathway?
Proprioception, hapsis (touch, pressure, vibration first detected by the skin)
What is associated with the ventral (anterior) spinothalamic somatosensory pathway?
Nociception (painful stimuli)
In the four homunculus (sensory homunculus) model, where do cells from areas 3a, 3b, and 1 project to?
3a and 3b project to area 1
1 projects to area 2
Area 2 contains multimodal neurons responsive to force, orientation, and direction of movement
Association cortex - Posterior parietal cortex
Spatial processing (parietal lobes)
Position of body and objects around the body
Integrates sensory information: propriception, hapsis, hearing, and vision
Unilateral damage
Importance of where the decussation occurs
Nociception crosses immediately
Hapsis/proprioception cross later (at the medulla)
Unilateral damage causes loss of fine touch and pressure on same side of body below the cut …
and temperature and pain sensation on the opposite side of the body
Motor sequence
Movements are performed with the next sequence held in readiness while the ongoing one is underway
How do the prefrontal cortex, premotor cortex, and motor cortex act?
Hierarchically and in parallel
- brain circuits process info. hierarchically and in parallel
How does the frontal lobe display hierarchical and parallel control?
Hierarchical = illustrated when the prefrontal cortex formulates a plan of action and and then instructs premotor cortex to organize the appropriate sequence, which the motor cortex executes
Parallel = illustrated by the fact that we can make a variety of plans and make whole-body or discrete movements independently of each other
Position point theory
States that the motor cortex has a map of where parts of the body can be in space so that when a part of the cortex is stimulated, the associated part of the body moves to the appropriate spatial position, regardless of its starting position
What is an important feature of the motor cortex (M1)
Flexibility (plasticity)
What are the main efferent pathways from the motor cortex to the brainstem to the spinal cord?
Corticospinal tracts (pyramidal tracts)
- axons from these tracts originate mainly in motor cortex layer V pyramidal cells
- pyramidal tracts name comes from bumps (pyramids) formed on the brainstems ventral surface
What happens at the pyramidal protrusions (pyramids)?
The corticospinal axons cross
Three main basal ganglia connections
1) All areas of the neocortex project to the basal ganglia
2) Basal ganglia project to the motor cortex via relays in the thalamus
3) Basal ganglia receives connections from dopamine cells of midbrain substantia nigra over the nifrostriatal pathway and also projects to the substantia nigra
What does the basal ganglia form through its connections?
Reciprocal circuits, or loops, connecting all cortical regions to the motor cortex
What is the globus pallidus controlled by?
Two basal ganglia pathways (direct and indirect)
- if globus pallidus is excited, it inhibits the thalamus and blocks movement
- turned up = blocked movement
- turned down = allow movement
What is cerebellum critical for?
Acquiring and maintaining motor skills
What does the flocculus do?
Receives projections from the middle ear vestibular system, helps control balance
Describe homunculi (topographic organization) of cerebellum
Lateral parts of cerebellar hemispheres - movement of body appendages
Medial parts of cerebellar hemispheres - movement of body midline
What phenomenon would playing darts with drunk goggles show?
Many movements we make depend on moment-to-moment learning and adjustments made by the cerebellum
How is somatic sensation unique among sensory systems?
It is distributed throughout the body, not localized in the head
Glabrous skin
(Non-hairy skin) such as that on lips, tongue, and palms
Exquisitely sensitive to a wide range of stimuli
Covers body parts we use to explore objects
Three types of somatosensory receptors
Nociception (irritation - pain, temperature, itch)
Hapsis (pressure & fine touch)
Proprioception (movement - body awareness)
