Navigation
Examines the functional anatomy of the brain and spinal cord as the primary processing centers.
Imagine your body is a high-speed fiber-optic network; while your 'cables' carry data, your brain and spinal cord act as a supercomputer making split-second decisions before you're even aware there's a problem.
The brain is organized into four main functional regions. The Cerebrum is the largest part, responsible for higher-level functions like logic, sensory processing, and voluntary movement. Beneath it lies the Diencephalon, containing the Thalamus (the brain's relay station) and the Hypothalamus (the master regulator of homeostasis). The Cerebellum, located posteriorly, fine-tunes motor activities and maintains balance. Finally, the Brainstem (midbrain, pons, and medulla oblongata) manages 'autopilot' functions like heart rate and breathing. These regions work in concert to process neurons worth of data simultaneously.
Quick Check
Which specific part of the brain is responsible for maintaining homeostasis, such as body temperature and thirst?
Answer
The Hypothalamus
The CNS is extremely fragile and requires a specialized environment. The Blood-Brain Barrier (BBB) is a highly selective filter formed by astrocytes and tight junctions in capillary walls. It prevents toxins from entering the brain while allowing , , and glucose to pass. Surrounding the brain and spinal cord is Cerebrospinal Fluid (CSF). Produced by the choroid plexus, CSF provides buoyancy—reducing the brain's effective weight from to —and acts as a hydraulic shock absorber to prevent mechanical injury.
To understand the protective role of CSF, consider the physics of buoyancy: 1. The brain has a mass of . 2. Without fluid, gravity exerts a force of on the base of the skull. 3. When submerged in CSF, the buoyant force counteracts gravity. 4. This reduces the 'effective weight' to nearly zero, preventing the brain from crushing its own blood vessels at the base of the skull.
Quick Check
What specialized glial cells help form the Blood-Brain Barrier?
Answer
Astrocytes
The spinal cord is an integration center for reflexes—rapid, involuntary responses to stimuli. In cross-section, it features an inner 'H' of gray matter (cell bodies) and outer white matter (myelinated axons). A reflex arc bypasses the conscious brain to save time. The pathway follows five steps: 1. Receptor (detects stimulus), 2. Sensory (afferent) neuron (transmits to CNS), 3. Integration center (interneuron in the spinal cord), 4. Motor (efferent) neuron (transmits to effector), and 5. Effector (muscle or gland). This allows for responses in milliseconds.
If you touch a hot stove, the signal must travel from your finger to your spinal cord and back to your arm muscle. 1. Distance (round trip). 2. Nerve conduction velocity . 3. Time . 4. Because the brain is bypassed, you move in , whereas conscious perception might take or more.
Which region of the brain is most likely damaged if a patient has trouble with balance and fine motor coordination?
In a reflex arc, which neuron carries the signal away from the spinal cord toward a muscle?
The Blood-Brain Barrier is permeable to all substances to ensure the brain receives maximum nutrients.
Review Tomorrow
In 24 hours, try to sketch the 5 steps of the reflex arc from memory and label the afferent and efferent pathways.
Practice Activity
Research the 'Patellar Reflex' and identify which specific spinal cord segments are involved in that involuntary kick.