Week 3 - cerebral cortex

• primary motor cortex develops the motor programme which is then sent to our muscles
• planning areas decide which actions you want to execute
• basal ganglia initiates motor movements
• cerebellum important for fine motor control
• the main output of the motor regions is the PMC sending out the most commands to the muscles
• cerebral cortex forms the outer layer of the brain
• the cerebrum is the front of the brain where the cerebral cortex lies and contains grey matter
• 6 distinct layers of the cerebral cortex are known as laminae
• cortex covers the other "sub-cortical" forebrain structures
• broadman found 52 areas of the cerebral cortex based on the profile of the lamineas
• M1 contains betz cells in layer 5
• betz cells are large pyramidal cells projecting from motor cortex to spinal tract
• Only 5% of betz cells project to motor neurons with the rest reaching spinal interneurons
• Betz cells can also project to brain stem
• there is a direct connection between the PMC and the spinal cord
• through the spinal cord there is a connection to the muscles of your whole body
• Betz cells from the motor cortex initiate, regulate and control voluntary skilled movements by innervating alpha and gamma motor neurons in the spinal cord.
• Betz cells provide conscious voluntary control of skeletal muscles.
• The corticospinal tract crosses at the medulla, hence limbs movements are controlled by the contralateral motor cortex.
• Right motor cortex controls the left side and vice versa.
• Betz cells form the corticospinal tract.
• Different parts of the Primary Motor Cortex send motor signals to different parts of the body.
• Fritsch and Hitzig mapped the somatotopic motor representation in the Primary Motor Cortex of a dog in 1870 through electrical stimulation.
• Penfield stimulated epileptic patients during surgery in 1940.
• Penfield discovered that electrical stimulation causes simple movements.
• The map of the somatotopic motor representation in the Primary Motor Cortex was established and cartooned ever after by Penfield.
• The mapping of the somatotopic motor representation in the Primary Motor Cortex can also be seen in humans.
• PMC and sensory MC have a strong relationship and are separated by the central sulcus
• Central sulcus also separates the parietal and frontal lobe
• even though there is separation of the mapping of different body parts there is a large overlap meaning some areas stimulate the same muscle
• it was initially thought that it was just muscles represented in the motor cortex however prolonged stimulation of 500ms + showed complex goal directed movements could be seen
• motor lesions result in loss of individuated use of fingers however the muscle activity measured is very similar
• Changes in activity are only seen in the precision grip and not power showing that it is the precision which requires PMC activity and it is less significant for power.
• If an animal has a motor lesion of the PMC they can perform gross motor control but not precision due to issues with the PMC
• frontal eye fields is important for volitional control of eye movements and heavily connected to the occipital cortex meaning bottom up signalling
• Frontal eye fields are also connected to frontal regions important for decision making
• Once an eye movement is decided a signal is sent to the superior colliculus triggering the movement
• frontal eye field is somatotopic (spatial)
• secondary motor areas involves supplementary, pre motor and posterior parietal cortex
• supplementary motor area is the medial part of the brain whereas pre motor is more lateral involving the the dorsal and ventral streams and the posterior parietal being at the back of the brain