Cerebral Cortex

  • cerebral cortex refers to the outer edge of the largest part of the brain, the cerebrum

  • longitudinal fissure separates the cerebrum into left and right hemispheres

  • corpus collosum: thick group of neurons that connect the hemispheres for quick communication

  • unlike the spinal cord, the outer part of cerebral cortex is grey matter, while the inside is white matter and basal nuclei

  • controls higher functions such as speech, emotions, behaviour, learning

  • the cortex has six different layers that arrange themselves into columns based on cell types

    • stellate cell: primary processing of sensory input

    • pyramidal cell: motor neuron that is part of a pathway which eventually terminates on skeletal muscle

  • gyri are the folds of the brain, sulci are the grooves

    • the central and lateral sulcus divide the cerebral cortex into lobes

Primary Motor Cortex (Precentral Gyrus)

  • found in the frontal lobe

  • executes fine motor movements along with the premotor cortex

    • premotor cortex plans the movement

  • Betz cells: specialized type of pyramidal neuron

    • axons descend into the spinal cord

    • secrets neurotransmitter called glutamate, which is excitatory

    • glutamate synapses with alpha-motor neurons of skeletal muscles

Corticospinal Tract

  • controls voluntary motor movements

  • has both lateral and ventral tracts

    • lateral: bigger portion, controls muscles of the extremities

      • crosses at medulla, point of decussation

    • ventral: smaller portion, controls trunk muscles

      • crosses within spinal cord, point of decussation

  • both tracts start in the primary motor cortex within cell bodies of Betz cells

  • Upper motor neurons (Betz cells)

    • cell bodies found in motor cortex

    • decussates

  • Lower motor neuron (alpha-motor neuron)

    • found in spinal cord

    • somatic efferent

    • terminate on skeletal muscle

Motor Homunculus

  • primary motor cortex somatotopic map

    • location and relative amount of the motor cortex that is devoted to output to the muscles of each body part

Other Brain Regions Involved

  • motor program: essentially a list of instructions for movement to occur

  • carried out by:

    • Cerebellum: proprioception and timing of movements, communicates to

    • Posterior parietal cortex: gathers and processes afferent/sensory information, communicates with

    • Pre-motor cortex: plans out movement, transmits to primary motor cortex

    • Supplemental motor area: prepares and plans for complex motor movements that require more the 1 muscle, coordinates muscle contractions

  • Readiness potential: electrical potential that is required to get the primary motor cortex ready to work

Primary Somatosensory Cortex/ Post-Central Gyrus

  • located in the parietal lobe, where sensory input and awareness is

  • crude sensory information is broken down to be able to tell the level and location of the signal on the body

  • initial cortical processing and perception of:

    • somaesthetic sensations

      • touch, pressure, heat, cold, pain

    • mild proprioception, main role is in sensory refinement

Fasiculus Cuneatus

  • sensory ascending pathway to detect fine touch, fine pressure, and mild proprioception

  • 1st order neuron is a sensory afferent neuron, a receptor

    • 1st neuron synapses with 2nd neuron at the medulla

    • 2nd neuron synapses with the 3rd in the thalamus

    • 3rd terminates on the somatosensory cortex

Sensory Homunculus

  • somatosensory cortex somatotopic map

    • cortical representation of body parts are larger for those that have higher sensitivity and use

    • use-dependent competition: the more a body part is used, the bigger its corresponding spot will be on the somatosensory cortex

Electroencephalogram (EEG)

  • recording of the electrical activity of the cerebral cortex

  • the collective postsynaptic potential activity in the cell bodies and dendrites (EPSPs + IPSPs)

  • variable waveforms are based on the degree of activity within the cerebral cortex

  • uses:

    • diagnostic tool (ex. for epilepsy)

    • legal determination of brain death

    • distinguishing stages of sleep