HOW THE BRAIN CONTROL MOVEMENT

HOW THE BRAIN CONTROL MOVEMENT

The brain controls movement through a complex, hierarchical system involving multiple regions that The brain controls voluntary movement through a precisely organized, hierarchical system that begins with intent and ends with the contraction of specific muscles. This is primarily executed via the motor pathways (descending tracts) involving several key brain regions.

---

🧠 Key Brain Regions for Movement

Movement is not controlled by a single area, but by a network of structures that coordinate planning, initiation, execution, and correction.

1. Cerebral Cortex (The Planner and Initiator):

   • Premotor Cortex and Supplementary Motor Area: These areas in the frontal lobe are involved in the planning and sequencing of complex movements (e.g., deciding the steps to pick up a cup).

   • Primary Motor Cortex (M1): Located in the frontal lobe's precentral gyrus, this is where the final, specific commands to initiate a voluntary movement are generated. It operates a motor homunculus, a map where different parts of the cortex control specific body parts (the hands and face take up the most space).

2. Cerebellum (The Coordinator and Corrector):

   • The cerebellum is essential for coordination, balance, and fine-tuning movement. It constantly compares the intended movement from the cortex with the actual movement reported by the body's sensory feedback, correcting any errors in real-time.

3. Basal Ganglia (The Regulator):

   • A group of deep structures that act as a gate, regulating the initiation and suppression of movements. They select the appropriate motor program and inhibit unwanted movements, which is why damage here (as in Parkinson's disease) leads to tremors and difficulty initiating movement.

---

⚡ The Motor Pathway (The Command Line)

The signal to move travels from the cortex down the primary descending pathway, the Corticospinal Tract, using two main types of neurons:

1. Upper Motor Neuron (UMN)

• Origin: The cell body of the UMN is located in the Primary Motor Cortex.

• Decussation (The Crossover): The axon of the UMN travels down through the brainstem. In the medulla oblongata, the majority of the fibers cross over (decussate) to the opposite side of the central nervous system.

• Descent: The pathway continues down the spinal cord on the side opposite to its origin (the contralateral side). This is why the left side of your brain controls the right side of your body, and vice-versa.

2. Lower Motor Neuron (LMN)

• Synapse: The UMN axon synapses with the LMN cell body in the ventral horn of the spinal cord (or in the brainstem for face/neck movements).

• Action: The LMN axon then leaves the spinal cord and travels through peripheral nerves to the skeletal muscle, where it releases neurotransmitters (acetylcholine) at the neuromuscular junction, causing the muscle to contract.

Diagram of Brain

The area of the brain that controls movement is in a very narrow strip that goes from near the top of the head right down along where your ear is located. 

It's called the motor strip. If I injure that area, I'll have problems controlling half of my body. If I have a stroke in the left hemisphere of my brain, the right side of the body will stop working. 

If I have an injury to my right hemisphere in this area, the left side of my body stops working (remember, we have two brains). This is why one half of the face may droop when a person has had a stroke. Diagram of Brain

MOVEMENT VIDEO :

GETTING INFORMATION IN AND OUT OF THE BRAIN

GETTING INFORMATION IN AND OUT OF THE BRAIN

Getting information into and out of the brain relies on the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) working together via specialized neural pathways.

The flow of information is categorized into two main directions:

1. Input (Afferent/Sensory): Information coming into the CNS (brain and spinal cord).

2. Output (Efferent/Motor): Information going out of the CNS to the body's effectors (muscles and glands).

---

👂 Input: Sensory (Afferent) Pathways

Sensory information from the environment (e.g., sight, touch, pain) travels toward the brain via sensory neurons.

• Peripheral Receptors: Specialized sensory receptors in the skin, eyes, ears, and internal organs detect stimuli (e.g., pressure, light, chemical signals).

• Transmission: This detection generates an electrical impulse (action potential) in a sensory neuron.

• Ascending Tracts: The impulse travels along the nerve fibers (axons) through peripheral nerves and then enters the spinal cord or brainstem. Once inside the spinal cord, it travels toward the brain in organized bundles called ascending tracts.

  • Body Below the Neck: Information ascends through the spinal cord. Major pathways, like the Spinothalamic Tract (for pain and temperature) and the Dorsal Column System (for fine touch and proprioception), carry the signal.

  • Head and Neck: Information is carried directly to the brainstem via the Cranial Nerves (e.g., the Optic Nerve for vision, the Vestibulocochlear Nerve for hearing/balance).

• Processing Centers: The sensory signal is typically relayed in the thalamus (the brain's major relay center) before reaching its final destination in the cerebral cortex (e.g., the Somatosensory Cortex in the parietal lobe for touch, the Visual Cortex in the occipital lobe for sight).

---

💪 Output: Motor (Efferent) Pathways

Instructions for movement and gland function travel away from the brain to the body's muscles and glands via motor neurons.

• Initiation: Voluntary movement instructions are typically initiated in the cerebral cortex, mainly the Primary Motor Cortex in the frontal lobe.

• Descending Tracts: The instructions travel down from the cortex as electrical impulses along upper motor neurons through the brainstem and into the spinal cord in bundles called descending tracts. The most famous of these is the Corticospinal Tract, which controls voluntary, skilled movements of the limbs.

• Relay in Spinal Cord: In the spinal cord, the upper motor neuron synapses (communicates) with a lower motor neuron.

• Final Destination: The lower motor neuron's axon exits the spinal cord and travels through peripheral nerves to connect directly with the muscle fiber or gland, causing it to contract or secrete.

This constant, rapid flow of input (sensory) and output (motor) allows the brain to perceive the environment, process the information, and execute appropriate and timely responses.

How does information come into the brain? 

A lot of information comes in through the spinal cord at the base of the brain. Think of a spinal cord as a thick phone cable with thousands of phone lines. If you cut that spinal cord, you won't be able to move or feel anything in your body. Information goes OUT from the brain to make body parts (arms and legs) do their job. 

There is also a great deal of INCOMING information (hot, cold, pain, joint sensation, etc.). Vision and hearing do not go through the spinal cord but go directly into the brain. That’s why people can be completely paralyzed (unable to move their arms and legs) but still see and hear with no problems.

Information enters from the spinal cord and comes up the middle of the brain. It branches out like a tree and goes to the surface of the brain. The surface of the brain is gray due to the color of the cell bodies (that's why it's called the gray matter). The wires or axons have a coating on them that's colored white (called white matter).

GETTING INFORMATION IN AND OUT OF THE BRAIN VIDEO :

IS THE BRAIN ONE BIG COMPUTER?

IS THE BRAIN ONE BIG COMPUTER?

The brain functions as an incredibly sophisticated electrical and chemical machine, using a seamless two-step process to transmit and process information via its fundamental unit, the neuron (nerve cell).¹

The communication within the brain relies on the following cycle:

---

⚡ 1. The Electrical Signal (Action Potential)²

Information travels rapidly within a single neuron as an electrical signal called an action potential (or nerve impulse).³

• Basis: The neuron maintains an electrical charge difference, or resting membrane potential, across its cell membrane, established by an unequal distribution of positively and negatively charged ions (primarily Sodium (⁴$Na^+$), Potassium (⁵$K^+$), and Chloride (⁶$Cl^-$)) inside versus outside the cell.⁷

• Firing: When a neuron receives enough stimulation from its neighbors to reach a specific voltage threshold, voltage-gated ion channels rapidly open.⁸

  • This causes a sudden, massive influx of positive ions (⁹$Na^+$) into the cell, which momentarily reverses the electrical charge from negative to positive—this is the action potential.¹⁰

• Propagation: This electrical spike then travels quickly and in an all-or-nothing fashion down the length of the neuron's transmitting fiber, the axon, until it reaches the end terminal.¹¹

---

🧪 2. The Chemical Signal (Neurotransmitters)¹²

Once the electrical signal reaches the end of the axon, it must cross a tiny gap, the synapse, to communicate with the next neuron.¹³ This is where the signal converts from electrical to chemical.¹⁴

• Conversion and Release: When the action potential arrives at the axon terminal, it triggers the release of specialized chemical messengers called neurotransmitters into the synaptic cleft (the gap).¹⁵

• Crossing the Synapse: The neurotransmitters quickly diffuse across this gap and bind to receptors on the receiving neuron's dendrites.¹⁶ This binding is specific, like a key fitting a specific lock.¹⁷

• Effect: The action of the neurotransmitter on the receptor determines the next step for the receiving neuron:¹⁸

  • Excitatory Neurotransmitters (e.g., Glutamate) push the receiving neuron's voltage toward its firing threshold, making it more likely to generate its own action potential.¹⁹

  • Inhibitory Neurotransmitters (e.g., GABA) push the voltage away from the firing threshold, making it less likely to fire.²⁰

By constantly integrating thousands of these excitatory and inhibitory chemical inputs, the receiving neuron determines whether to generate its own electrical signal, thereby perpetuating the communication throughout the brain's vast neural circuits.²¹

Key Chemical Messengers

Neurotransmitter	Primary Role(s)
Glutamate	Major Excitatory neurotransmitter; learning and memory.
GABA (Gamma-Aminobutyric Acid)	Major Inhibitory neurotransmitter; calming, anxiety regulation.
Dopamine	Reward, motivation, motor control.
Serotonin	Mood, sleep, appetite.
Acetylcholine	Muscle contraction (PNS), attention, memory (CNS).

Diagram of Brain

Is the brain like a big phone system or is it one big computer with ON or OFF states ? Neither of the above is correct.

Let's look at the brain as an orchestra. In an orchestra, you have different musical sections. There is a percussion section, a string section, a woodwind section, and so on. Each has its own job to do and must work closely with the other sections. When playing music, each section waits for the conductor. The conductor raises a baton and all the members of the orchestra begin playing at the same time playing on the same note. If the drum section hasn't been practicing, they don't play as well as the rest of the orchestra. The overall sound of the music seems "off" or plays poorly at certain times. This is a better model of how the brain works. We used to think of the brain as a big computer, but it's really like millions of little computers all working together. Diagram of Brain

IS THE BRAIN ONE BIG COMPUTER? VIDEO