Chapter 55 Guyton - Cortical And Brain Stem Control Of Motor Function Flashcards
Where is the motor cortex is located?
Anterior to the central cortical sulcus, occupying approximately the posterior one third of the frontal lobes
Where is the somatosensory cortex located?
Posterior to the central sulcus
It feeds the motor cortex many of the signals that initiate motor activities.
What sub areas are the motor cortex divided into?
- The primary motor cortex
- The premotor area
- The supplementary motor area
Where is the primary motor cortex located?
It lies in the first convolution of the frontal lobes anterior to the central sulcus. It begins laterally in the Sylvian fissure, spreads superiorly to the uppermost portion of the brain and then dips deep into the longitudinal fissure.
Where is the premotor area located?
Lies 1-3 centimetres anterior to the primary cortex extending inferiorly into the Sylvian fissure and superiorly into the longitudinal fissure where it abuts the supplementary motor area which has functions similar to those of the premotor area.
Where does the posterior part of the premotor cortex send its signals?
Either directly to the primary motor cortex to excite specific muscles or often by way of the basal ganglia and thalamus back to the primary motor cortex.
Where lies the supplementary motor area?
It lies mainly in the longitudinal fissure but extends a few centimetres onto the superior frontal cortex
Describe the transmission of signals from the motor cortex to the muscles.
Motor signals are transmitted directly from the cortex to the spinal cord through the corticospinal tract and indirectly through multiple accessory pathways that involve the basal ganglia, cerebellum and various nuclei of the brain stem.
Describe the pathway of the corticospinal (pyramidal) tract:
It’s the most important pathways from the motor cortex - passes through the posterior limb of the internal capsule (between the caudate nucleus and the putamen of the basal ganglia) and then downward through the brain stem forming the pyramids of medulla. The majority of the pyramidal fibres then cross in the lower medulla to the opposite side and descend into the lateral corticospinal tracts of the cord finally terminating principally on the interneurons in the intermediate regions of the cord gray matter. A few terminate on sensory relay neurons in the dorsal horn and a very few terminate directly on the anterior motor neurons that cause muscle contraction.
What are Betz cells and where are they located?
Only in the primary motor cortex. Their large myelinated fibres transmit nerve impulses to the spinal cord at 70 m/sec which is the most rapid rate of transmission of any signal from the brain to the cord.
Name 5 of the more important incoming pathways to the motor cortex.
- Subcortical fibres from adjacent regions of the cerebral cortex especially from the somatosensory areas of the parietal cortex, the adjacent areas of the frontal cortex anterior to motor cortex and the visual and auditory cortices.
- Subcortical fibres that arrive through the corpus callously from the opposite cerebra hemisphere. These fibres connect corresponding areas of the cortices in the two sides of the brain.
- Somatosensory fibres that arrive directly from the ventrobasal complex of the thalamus. These relay mainly cutaneous tactile signals and joint and muscle signals from the peripheral body.
- Tracts from the ventrolateral and ventroanterior nuclei of the thalamus which in turn receives signals from the cerebellum and basal ganglia. Provide signals that are necessary for coordination among the motor control functions of the motor cortex, basal ganglia and cerebellum.
- Fibres from the intalaminar nuclei of the thalamus. These fibres control the general level of excitability of the motor cortex in the same way that the control the general level of excitability of most other regions of the cerebral cortex.
Where is the red nucleus located and what does it do?
Located in mesencephalon and functions in close association with the corticospinal tract.
What does the corticorubrospinal pathway do?
Serves as an accessory route for transmission of relatively discrete signals from the motor cortex to the spinal cord.
What is the lateral motor system of the cord?
The name of the corticospinal and rubrospinal tracts together.
What are dynamic and static neurons?
The dynamic neurons are excited at a high rate for a short period at the beginning of a contraction causing the initial rapid development of force. Then the static neurons fire at a much slower rate but they continue firing at this slow rate to maintain the force of contraction as long as contraction is needed.
