Nervous System

• Anatomical Divisions

– CNS

• Brain

• Spinal Cord

– PNS

• Spinal Nerves & Plexi

• Cranial Nerves

• Peripheral Nerves

• Functional Divisions

– Afferent

– Efferent

• Somatic

• Autonomic

– Sympathetic

– Parasympathetic

The Brain

• Principle Parts of the Brain

– Cerebrum (Telencephalon)

– Diencephalon

• Thalamus

• Hypothalamus

• Pineal Gland

• Principle Parts of the Brain

– Brain Stem

• Midbrain (Mesencephalon)

• Pons (Metencephalon)

• Medulla Oblongata (Myelencephalon)

– Cerebellum

• Protection of the Brain

– Skull

– Meninges

– CSF

• Ventricles of the Brain

– Lateral Ventricles

– 3^rd Ventricle

– 4^th Ventricle

• The cerebral aqueduct links the 3^rd and 4^th ventricles

• CSF Circulation

• If the cerebral aqueduct were blocked…..

• Blood-Brain Barrier

– Only lipid soluble substances can diffuse across capillary endothelium

– Water soluble substances cross only by active or passive transport

• selective

• directional

• Brain regions without a blood-brain barrier

– portions of hypothalamus

– pineal gland

– choroid plexus

• Organization of Neural Tissue

– gray matter

• Arranged as nuclei, often around ventricles and cerebral aqueduct OR

• Thin outer layer of cerebrum and cerebellum (cortex)

– White matter

• arranged as “tracts”

• Found everywhere gray matter isn’t

Structure and Functions of Selected Brain Regions

• Medulla oblongata

• Pons

• Midbrain

• Diencephalon

• Cerebellum

• Cerebrum

– sulci and gyri

– lobes

– cerebral gray matter

• cerebral cortex

– motor and sensory cortex

• cerebral nuclei

– corpus striatum

– amygdala

– hippocampus

– cerebral white matter

• association fibers

• commissural fibers

• projection fibers

• Limbic System

– Functions: memory, emotions, and survival behaviors

– Examples of components

• parts of thalamus and hypothalamus

• hippocampus and fornix

• septal nuclei

• reticular formation

• Lateralization of Cerebral Function

Cranial Nerves

I - Olfactory

II - Optic

III - Oculomotor
IV - Trochlear
VI - Abducens

V - Trigeminal

VII - Facial

VIII - Vestibulocochlear

IX - Glossopharyngeal

X - Vagus

XI - Spinal Accessory
XII – Hypoglossal

• Blood Supply to the Brain

Spinal Cord

• Length: 18 inches

– terminates between L1 and L2 (at waist level)

• Diameter

– ½ inch (at cervical and lumbar enlargements)

– ¼ inch (thoracic region)

• Other Features

– Conus medullaris

– Cauda equina

• Protection of Spinal Cord

– Vertebrae

– Spinal Meninges

– CSF

• Cross-sectional organization

– Grey matter: organized into “horns”

– White matter: organized into “columns”

– Columns composed of

• ascending tracts

• descending tracts

• 31 spinal cord segments

– each segment is associated with a pair of spinal nerves

• Anatomy of Nerves

• Ventral rami of:

Ø C1-C5 form the cervical plexus

Ø C5-T1 form the brachial plexus

Ø T2-T12 form the intercostal nerves

Ø T12-S4 form the lumbosacral plexus

• Examples of Peripheral Nerves

– Phrenic nerve

• Emerges from the cervical plexus composed of axons from C3-C5

– Median nerve

• From brachial plexus; axons from C6-T1

– Femoral and Obturator nerves

• From lumbar plexus; axons from L2-L4

– Pudendal nerve

• From sacral plexus; axons from S2-S4

– Sciatic nerve

• From sacral plexus; axons from L4-S3

• Dermatomes

– Regions of skin served by the sensory axons of a specific spinal nerve

• Neural Pathways

– Sensory

• Some examples of ascending (sensory) spinal cord tracts

– lateral spinothalamic

– fasciculus gracilis

–Motor

• Pyramidal Pathways

– conscious control of skeletal muscles

– pyramidal tracts:

» corticobulbar tract

» corticospinal tracts

• Extrapyramidal Pathways

– unconscious control of skeletal muscles

– example of extrapyramidal pathways in spinal cord

» rubrospinal tract

· Spinal Reflex Arc

Autonomic Nervous System

• Sympathetic (thoracolumbar)

– “fight or flight”

• Parasympathetic (craniosacral)

– “rest and repose”

• Sympathetic system features

– Preganglionic fibers

• in ventral roots of T1-L2

• short

• go to sympathetic ganglia or adrenal medulla

• release ACh

–Ganglia

• collateral ganglia (prevertebral)

• sympathetic chain (paravertebral)

• adrenal medulla

– Postganglionic fibers

• long

• extensive divergence from sympathetic ganglia

• release E or NE (sometimes ACh)

• Parasympathetic system features

– Preganglionic fibers

• in cranial nerves III, VII, IX, X and pelvic nerves from S2-S4

• long, go straight to ganglia very close to the target organs

• release ACh

– Ganglia

• near target organs (e.g. ciliary ganglion near eye)

• in wall of target organ (intramural ganglia)

– Postganglionic fibers

• very short

• little divergence

• release ACh

Comparison of Somatic and Autonomic Divisions: