W3 Flashcards
(17 cards)
What is the cerebral cortex?
The cerebral cortex is the brain’s outermost layer, responsible for higher-level cognitive functions like thinking, memory, and perception.
How is the cerebral cortex organised?
The cortex forms the outer surface of the forebrain known as Greymatter
The 6 distinct layers are known as Laminae
As you go down the laminae, you get deeper into the brain.
Lamina 5 is in the pyramidal layer, sending info to the brainstem and spinal cord
Lamine 6 is in the intergranular layer, sending information to thalamus.
What are the key takeaways from Brodmann’s work on the cerebral cortex organisation?
Brodmann divided the cortex into 52 distinct areas based on their laminae, asserting that these anatomical distinctions are functionally relevant
For example, Brodmann area 4 (primary motor cortex) contains Betz cells which are large fat cells known as pyramidal cells (Laminae layer 5) that project from motor cortex to spinal tract, only 5% project to motor neurons and the rest reach spinal interneurons.
What is the Corticospinal tract?
The corticospinal tract is a major pathway in the brain that allows you to consciously control your voluntary muscle movements.
Betz cells in your motor cortex send signals down your spinal cord, eventually connecting with alpha and gamma motor neurons.
These motor neurons then directly activate your skeletal muscles, allowing you to perform specific, skilled movements.
The tract crosses over in the medulla (part of your brainstem), meaning the left side of your brain controls the right side of your body, and vice versa.
How did researchers map the motor cortex?
ANIMALS Fritsch and Htizig (1870) → Electrical stimulation on dog brains, found stimulating different parts of motor cortex cause specific movements. This organized mapping of body parts on the brain is called ‘somatotopic representation.’
HUMANS Penfield (1940) → stimulated epileptic patients in for surgery and found a similar somatotopic representation was present
Essentially, directly stimulating specific points in the motor cortex triggers specific muscle movements.
How do cortical motor maps vary between species and within individuals?
Cortical motor maps, representing body parts in the brain, are not fixed.
In animals, they differ significantly across species (e.g., rabbits vs. monkeys) based on which body parts are used most.
For example, monkeys have large hand/foot representations, while rabbits prioritize face representation → developed through function
In humans, individuals who use their feet extensively (like those without arms) show enlarged foot representation in their motor cortex, demonstrating the brain’s adaptability.
Why do our cortical motor muscle maps overlap?
The brain’s muscle maps aren’t perfectly separated. They overlap so different muscles can work together smoothly.
Think of lifting your arm – it needs several muscles firing at once, and the overlap lets the brain coordinate that.
What happens when we electrically stimulate the brain’s motor areas?
The primary motor cortex doesn’t just map individual muscles; it also helps organize entire actions.
Brief micro-stimulation (50ms): Simple movements / contractions of contralateral muscles
Prolonged stimulation: Complex goal-directed actions.
What did a study on monkey hand grips and brain activity reveal about the motor cortex?
Scientists measured muscle activity (EMG) and brain cell (motor cortex) activity in monkeys performing “power grips” (strong, whole hand) and “precision grips” (delicate, finger-only). They found:
**Muscle Activity (EMG): **Power grips showed much higher muscle activity (more force).
**Brain Cell Activity (Motor Cortex): **Precision grips showed higher brain cell activity, regardless of how much force was used. This means the primary motor cortex is more involved in complex, fine motor movements (like precision grips) than simply generating large amounts of force (like power grips). Essentially, the brain works harder for finesse, not just brute strength.
What is the primary motor cortex (M1) and what does it do?
The primary motor cortex (M1) is a brain area in the frontal lobe that controls voluntary movements.
Contains Betz cells send signals directly to muscles via the spinal cord.
M1 is organized somatotopically, meaning body parts are mapped onto it, with areas controlling fine motor skills (like fingers) taking up more space than larger body parts.
While it’s not fully understood what M1 precisely codes, it essentially sends signals for movement, and damage (like a stroke) can cause permanent loss of fine motor control.
What are the main functions of the frontal cortex related to movement?
Primary Motor Cortex: Directly controls voluntary body movements.
Frontal Eye Fields: Specifically control voluntary eye movements.
How do the Frontal Eye Fields control eye movements, and what influences them?
The Frontal Eye Fields have a “somatotopic” (spatial) map, meaning specific areas correspond to specific eye movements in space.
Stimulating a particular area of the Frontal Eye Fields triggers an eye movement towards that corresponding spatial location.
In the frontal lobe so planning, cognition, and decision-making, allowing for purposeful and directed eye movements.
They also work with the superior colliculus which handles automatic/ eye movements
What are secondary motor areas and what do they do?
Secondary motor areas are brain regions that help plan and prepare movements before the primary motor cortex executes them.
They have strong connections with each other and the primary motor cortex. Think of them as the “planning committee” before the “action team” takes over.
What is the Supplementary Motor Area (SMA)?
The SMA is involved in planning and executing complex movement sequences, especially those initiated internally (like deciding to get up and walk).
It’s now divided into the
SMA proper: related to learning new sequences
Pre-SMA: more related to executing learned sequences
What is the Premotor Cortex (PMC)?
The PMC is crucial for preparing movements based on external cues and sensory information.
It’s divided into:
Dorsal PMC (PMd): Important for learning conditional actions (like reacting to traffic lights) and “getting ready” for movement.
Ventral PMC (PMv): Important for using sensory information (touch, sight, sound) to guide movements, like grasping an object. It also contains mirror neurons, which are active when you perform an action or see someone else perform it.
What is the Posterior Parietal Cortex and its role with the motor areas?
The posterior parietal cortex acts as a bridge between the frontal cortex (decision-making) and the premotor areas (planning)
It gathers sensory information about the environment and helps determine potential actions or goals (like deciding between picking up a coffee or a sandwich).
The frontal cortex then chooses the action, and the secondary motor areas plan how to execute it.
