The Central Nervous System
- Brain
- Spinal Cord
4 Regions of the Brain
- Cerebrum
- Diencephalon
- Brainstem
- Cerebellum
Ventricles of the Brain
Internal cavities that produce and contain cerebrospinal fluid (CSF)
Cerebrospinal Fluid
- Bathes the brain (and spinal cord) externally and internally
- Very similar to blood plasma in composition
- Contains nutrients, O2, electrolytes
- Carries away wastes and CO2
- Reduces the weight of the brain by making it buoyant in the skull
CSF Locations
- Ventricles of Brain (Internal)
- Central Canal of Spinal Cord (Internal)
- Subarachnoid Space around the brain and spinal cord (External)
Production of CSF
- Produced from blood plasma in specialized capillaries called choroid plexuses
- Fluid leaked from choroid plexuses is taken up by ependymal cells
- Ependymal cells process the fluid and secrete it as CSF into ventricles
- Ependymal cells use cilia to circulate the CSF
- CSF is returned to venous sinuses that drain blood from the brain
Cerebrum
- Largest, most superior portion of brain
- Two Halves: Right & Left Hemisphere
- Site of the most complex information processing:
- Personality, Learning, Language
- Conscious interpretation of sensory info
- Conscious planning of movement
- Highly Folded
- Gyri: Folds
- Sulci: Shallow grooves between gyri
- Fissures: Deeper grooves at specific locations
- Longitudinal Fissure: Separates the two hemisperes.
Lobes of the Cerebrum
- Frontal
- Parietal
- Temporal
- Occipital
- Insula (Not visible externally)
Cerebral Cortex
- Thin, outer layer (about 2mm)
- Gray matter: contains cell bodies and unmyelinated axons
Corpus Callosum
- Thick white matter tract connecting the two hemispheres
- Contains myelinated axons
Nuclei of Cerebrum
Deeper areas of gray matter in cerebrum (ex. Basal nuclei)
Diencephalon
- Completely surrounded by the cerebrum
- 3 main parts:
- Thalamus
- Hypothalamus
- Epithalamus
Thalamus
Acts as a “filter” of incoming sensory information
Hypothalamus
- Helps regulate the endocrine system
- Note that the pituitary gland is connected to the hypothalamus
- Monitors the sleep-wake cycle
- Controls hunger, thirst, & body temperature
Epithalamus
- Contains pineal gland which secretes hormone melatonin
- Melatonin levels establish a normal sleep-wake cycle
Brainstem
- Important for autonomic functions (not under conscious control)
- 3 Portions (Listed superior to inferior)
- Midbrain
- Pon
- Medulla Oblongata
Midbrain
Contains important centers for auditory and visual reflexes
Pon
Sends signals to muscles of breathing (ex. Diapragm)
Medulla Oblongata
- Regulates heart rate and blood pressure
- Passes through foramen magnum; continuous with the spinal cord
Cerebellum
- Located inferior to the occipital lobe of the cerebrum
- Helps coordinate body movements and reduce movement errors
- Cerebellar Cortex: outer gray matter
- Arbor Vitae (“Tree of Life”): inner white matter
Meninges
- Connective tissue coverings of the brain (and Spinal Cord)
- Protect the CNS and create spaces for CSF
- 3 layers of meninges (Listed superficial to deep)
- Dura Mater
- Arachnoid Mater
- Pia Mater
Dura Mater
- Tough, thick outer layer
- Splits into two layer in specific locations to create venous sinuses
- Sudural Space
- Space between dura mater and arachnoid mater
Arachnoid Mater
- Thinner layer with web-like fibers extending towards pia mater
- Subarachnoid space contains CSF
Pia Mater
Thinnest, delicate layer, adhering directly to surface of brain
Cranial Nerves
- 12 pairs of cranial nerves emerge from the brain
- Each has a number (Roman Numeral) and a name
- Some are sensory, some are motor, and some are mixed (both sensory and motor)
- Cranial nerve function is often tested clinically by a neurologists
- Be aware of the Vagus Nerve (X)
Vagus Nerve (X)
- A major nerve of the parasympathetic nervous system
- Ex. Vagus nerve slows heart rate, reduces blod pressure
- Innervates many viscera in the thoracic and abdominopelvic cavities
Spinal Cord
- Extends from medulla oblongata (brain) to vertebral level L1/L2
- Contained within the vertebral canal of the vertebral column
- Spinal meninges
- Same as the brain
Spinal Dura Mater
- Epidural space contains fat the cushions the spinal cord against bone
- There is no epidural space around the brain
Spinal Arachnoid Mater
Subarachnoid space contains CSF
Spinal Pia Mater
Delicate innermost layer that clings to surface of spinal cord
Cervical Enlargement
Larger diameter area containing neurons serving upper limbs
Lumbar Enlargement
Larger diameter area containing neurons serving the lower limbs
Conus Medullaris
Inferior ending of spinal cord at L1/L2
Cauda Equina (“Horse’s tail”)
Large bundle of spinal nerves that descend from conus medullaris
Spinal Nerves
- 31 pairs of spinal nerves emerge from the spinal cord along its length
- All spinal nerves are mixed (carry both sensory amd motor info)
Spinal Gray Matter
- Butterfly-shaped; contains cell bodies and unmyelinated axons
- Divided into horns: Posterior horn, Lateral Horn, Anterior Horn
Spinal White Matter
- Surrounds the gray matter
- Divided into columns (funiculi): posterior column, lateral column, anterior column
- Columns contain myelinated axons
- Axons are grouped into ascending tracts & descending tracts
- Ascending tracts carry info superiorly
- Descending tracts carry info inferiorly
