Nervous System Structure and Function

Ryan, a college student, experienced increasingly frequent seizures despite medication.
His neurologist recommended seizure surgery due to the medication's ineffectiveness and side effects.
Ryan had a focal-seizure disorder caused by scar tissue in the medial temporal lobe of his left brain hemisphere.
The surgery involved removing the seizure focus while preserving critical brain functions like speech comprehension.
Dr. L. stimulated parts of Ryan’s brain with a metal probe to determine which regions could be safely removed.
Ryan remained awake during the surgery to provide feedback to the surgeon.
The surgery was successful, reducing Ryan's seizure frequency and improving his concentration.

LO 3.1: Apply anatomical terms to the nervous system.
LO 3.2: Differentiate the locations of the three layers of the meninges.
LO 3.3: Describe the locations and functions of CSF within the ventricular system.
LO 3.4: Summarize the process of human brain development from ectoderm plate, to neural tube, to three interconnected chambers.
LO 3.5: Explain how prenatal development contributes to the development of complex human brains.
LO 3.6: Provide examples of how genetic change, personal experience, and neurogenesis can influence postnatal brain development.
LO 3.7: Identify the structures and functions of the forebrain, including the telencephalon and diencephalon.
LO 3.8: Identify the location and functions of the structures of the mesencephalon.
LO 3.9: Contrast the locations and functions of the structures of the metencephalon and myelencephalon.
LO 3.10: Describe the structure and functions of the spinal cord.
LO 3.11: Identify the functions of the cranial nerves.
LO 3.12: Differentiate between the functions of afferent and efferent axons of the spinal nerves.
LO 3.13: Compare the functions and locations of the sympathetic and parasympathetic divisions of the autonomic nervous system.

The nervous system comprises the brain, spinal cord (central nervous system - CNS), cranial nerves, spinal nerves, and peripheral ganglia (peripheral nervous system - PNS).
The CNS is protected by bone: the skull encases the brain, and the vertebral column houses the spinal cord.
The brain consists of neurons, glia, and supporting cells.
The brain is highly protected, encased in the skull, floating in cerebrospinal fluid (CSF), and guarded by the blood-brain barrier.
The brain receives approximately 20% of the heart's blood flow continuously to maintain constant function.
The brain has limited fuel storage (primarily glucose) and cannot function anaerobically, making a consistent blood supply essential.
A 1-second interruption of blood flow depletes much of the dissolved oxygen.
A 6-second interruption causes unconsciousness.
Permanent brain damage can occur within minutes of interrupted blood flow.

Anatomical terms are crucial for describing the nervous system.
Early anatomists named brain structures based on their resemblance to common objects (e.g., amygdala = "almond-shaped object," hippocampus = "sea horse," cortex = "tree bark").
Directions in the nervous system are described relative to the neuraxis, an imaginary line running the length of the CNS.
In animals with a straight neuraxis (e.g., alligator):
- Anterior: front end
- Posterior: tail end
- Rostral: toward the nose and mouth (especially for the brain)
- Caudal: toward the tail
- Dorsal: top of the head and back
- Ventral: front surface (belly)
In humans, the neuraxis bends due to our upright posture.
- Superior: above
- Inferior: below
Lateral: toward the side
Medial: toward the middle
Ipsilateral: structures on the same side of the body
Contralateral: structures on opposite sides of the body

Transverse (cross or frontal) sections: slicing like a loaf of bread, dividing the brain into front and back halves.
Horizontal sections: parallel to the ground, cutting off the upper half of the brain.
Sagittal sections: perpendicular to the ground and parallel to the neuraxis, dividing the brain into symmetrical right and left halves; the midsagittal plane divides the brain into two symmetrical halves.
Cross sections of the spinal cord are parallel to the ground due to our upright posture.

The meninges are protective sheaths of tough connective tissue covering the brain, spinal cord, cranial and spinal nerves, and peripheral ganglia.
Three layers of meninges:
- Dura mater: the outer layer; durable, thick, tough, flexible, and unstretchable.
- Arachnoid membrane: the middle layer; soft and spongy with a weblike appearance (arachnoid trabeculae).
- Pia mater: the inner layer; closely attached to the brain and spinal cord, containing smaller surface blood vessels.
Subarachnoid space: a gap between the pia mater and arachnoid membrane, filled with cerebrospinal fluid (CSF).
The peripheral nervous system is covered with two layers of meninges.
The middle layer (arachnoid membrane), with its associated pool of CSF, covers only the brain and spinal cord.
Outside the central nervous system, the outer and inner layers (dura mater and pia mater) fuse and form a sheath that covers the spinal and cranial nerves and the peripheral ganglia.

The ventricular system consists of interconnected, hollow chambers called ventricles, filled with CSF.
Lateral ventricles: the largest chambers, connected to the third ventricle.
Third ventricle: located at the midline of the brain, dividing the surrounding brain into symmetrical halves. The massa intermedia, a bridge of neural tissue, crosses through the middle of the third ventricle.
Cerebral aqueduct: a long tube connecting the third ventricle to the fourth ventricle.
The lateral ventricles are also known as the first and second ventricles.
Ventricles produce and contain CSF.
CSF is manufactured by special tissue with a rich blood supply called the choroid plexus.