Nervous System Organization

• Key objectives are to understand the basic organization of the main structures that form the nervous system and to gain a 3D appreciation of the brain's parts and their relative positions.

Overview of the Nervous System (NS)

• Neurons and neuroglial cells are components of the NS.
• The brain and spinal cord constitute the Central Nervous System (CNS).
• The Peripheral Nervous System (PNS) include cranial nerves, spinal nerves, and ganglia.

Gray Matter vs. White Matter

• Gray matter and white matter differ in color and contents.
• In the PNS, cranial and spinal nerves conduct information to and from the CNS.
• The Autonomic Nervous System innervates the body's involuntary structures like the heart, smooth muscle, and glands.
• The Autonomic Nervous System is distributed throughout the CNS and PNS.
• The Autonomic Nervous System is divided into two parts: the Sympathetic division and the Parasympathetic division.

Organization of the NS

• The CNS includes the brain and spinal cord.
• The PNS contains sensory, somatic motor, and autonomic motor neurons.
• Direct sensory input is received by the CNS from eyes, nose, ears, and tongue.
• Somatic and visceral sensory neurons send information to the CNS.
• Autonomic motor neurons stimulate the heart and calm involuntary muscles and glands.
• Somatic motor neurons stimulate voluntary skeletal muscles.
• The Autonomic Nervous System modulates cardiovascular functions.
• Sympathetic activity stimulates organ function and increases heart rate.
• Parasympathetic activity inhibits organ function and decreases heart rate.

Embryological Development

• The neural plate forms from the ectoderm.
• The neural groove forms.
• The neural tube forms.
• The brain develops from three primary vesicles that turn into five secondary brain vesicles.

Divisions

• The Forebrain include the cerebrum and diencephalon.
• The Hindbrain include the medulla, pons, and cerebellum.
• The Brainstem include the medulla oblongata, pons, and midbrain.

Sectional Planes

• The different sectional planes are sagittal, coronal, and horizontal

Divisions - Forebrain: Cerebrum

• The cerebrum is the largest part of the brain.
• Two hemispheres are connected by the corpus callosum (white matter).
• The cerebrum extends from the frontal to occipital bones of the skull, superior to the anterior and middle cranial fossae.
• It is located superiorly to the tentorium cerebelli posteriorly.
• Hemispheres are separated by a deep longitudinal fissure.
• The Falx cerebri projects into the longitudinal fissure.

Divisions - Midbrain

• Anatomical structures: Tectum, Tegmentum, Cerebral aqueduct, Crus cerebri
• The Superior colliculus contains Cerebral gray matter
• Mesencephalic nucleus of trigeminal nerve and Lemnisci
• Temporo-pontine fibers and corticospinal fibers are present

Divisions - Hindbrain

• The Pons are located on the anterior surface of the brainstem, in front of the cerebellum and is 2.5 cm in length and forms the origin of the middle cerebellar peduncles
• The Medulla Oblongata the most inferior portion of the brainstem and 3cm in length and is Continuous with the spinal cord and extends superiorly from the foramen magnum.
• The Cerebellum lies in the posterior cranial fossa.
• It is located posterior to the pons and medulla oblongata.
• It has Two laterally placed hemispheres connected by the vermis.
• Midbrain connects to via superior cerebellar peduncles and Medulla oblongata connects via inferior cerebellar peduncles.
• Gray matter (Folia) is separated by closely set transverse fissures
• It Contains masses of gray matter (nuclei)
• The largest nuclei is the dentate nucleus.

Spinal Cord

• Embedding in the vertebral column and surrounded by 3 meninges
• Dura mater, Arachnoid mater, and Pia mater
• Is protected by CSF located within the subarachnoid space
• Bundles of nerve fibres supported by connective tissue.
• There are 12 pairs of cranial nerves that leave the brain and pass through foramina in the skull.
• There are 31 pairs of spinal nerves that leave the spinal cord and pass through the intervertebral foramina in the vertebral column.
• 8 cervical (but only 7 cervical vertebrae)
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
• 31 pairs of spinal nerves are attached by anterior (motor) roots and posterior (sensory) roots.
• Each root is attached to the cord by series of rootlets, which extend the whole length of the corresponding segment of the cord.
• Each posterior root possess a posterior (dorsal) root ganglion (DRG).
• Cells of DRG give rise to peripheral and central nerve fibers (i.e. axons).
• Ganglion = collection of nerve cell bodies located outside the CNS.

Cranial Nerves

• Olfactory nerve functions for smell.
• Oculomotor nerve functions in, eye movement and pupil reflex.
• Trigeminal nerve function for face sensation and chewing.
• Facial nerve movement and taste
• glossopharyngeal nerve functions in throat sensation, taste, and swallowing.
• Accessory movement, neck movement.
• Optic Nerve vision.
• Trochlear nerve for eye movement.
• Abducens eye movement.
• Vestibulocochlear functions in hearing and balance.
• Vagus movement, sensation, and abdominal organs.
• Hypoglossal movement, sensation, and abdominal organs.