What is the Brain Billions of nerve cells

What is the Brain? • Billions of nerve cells

What is the Brain? • Thousands of connections where one neuron may interact (communicate) with other neurons. As many as 10, 000 connections 40+ neurochemicals ( neurotransmitters)

Overarching Principles of Brain function • • Hierarchically organized Redundant control Inhibition Automaticity • Conscious vs Unconscious processes

NUTS AND BOLTS to get started

Planes of orientation

Confusing terms (Particularly where the CNS makes its’ 90 degree bend) • Anterior-Posterior/Rostral-Caudal • Dorsal-ventral/ Superior-inferior

Dorsal fins

The basic unit of the nervous system

Myelin gives a whitish appearance because its adipose content Shwann cells myelinate the PNS

Oligodendrocytes myelinate the CNS

White matter and gray matter reflect organization

Staining for myelin in the brain coronal section

Myelin Staining in the Spinal cord Horizontal plane Dorsal ventral

Organizational schemes always have shortcomings: The PNS can not be truly separated from the CNS

To consider the PNS we first must consider the spinal cord The vertebral column

Each vertebra houses a spinal cord segment Midsaggital view

Each segment is similar: Central gray and surrounding white matter

Central gray: Dorsal = sensory Ventral = motor

Each segment gives rise to nerve pairs: i. e. The PNS

31 peripheral nerve pairs

Each nerve pair contains thousands of incoming and outgoing axons

The PNS: All neural tissue outside of the cranium and vertebral column ( with one exception)

Major divisions of the PNS

motor output to skeletal muscles

And somatosensory input

The somatic division of the PNS gives rise to segmental organiztion: Dermatomes and myotomes

The autonomic division

The other subdivision of the PNSthe ANS

The sympathetic chain

Sympathetic activation may be magnified by adrenal gland

Some functional differences between the somatic branch and the ANS

THE CNS

Exception- The cranial nerves