CNS: Anatomy and Physiology

Dr. Milind KothariProfessor of Neurology

Assoc Dean Student Affairs

Two Anatomical Divisions – Central nervous system (CNS)

• Brain• Spinal cord

– Peripheral nervous system (PNS)• All the neural tissue outside CNS• Afferent division (sensory input)• Efferent division (motor output)

– Somatic nervous system– Autonomic nervous system

General Organization of the nervous system

General Organization of the nervous system

Brain & spinal cord

Why is this so hard?

• Multiple anatomies• Embryological• Lobes• Vascular anatomy• Neurochemical anatomy

• 3 dimensional• Structures with multiple names • Sometimes left is right and sometimes left is

left

Principal CNS regions

Telencephalon

Diencephalon

Brainstem• Midbrain• Pons• Medulla

Spinal cord

Cerebellum

31 spinal levels: 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal

The bones of the skull & vertebrae dictate the name of the underlying CNS

Principal CNS regions

Frontal Parietal

Temporal

Occipital

Principal CNS regions

These named structures provide critical reference points for learning region-specific function as well as localizing a diagnosis…

…they also permit a significant expansion of the cortical surface area.

The paired cerebral cortices are covered by named sulci and gyri.

Telencephalon

• Midbrain• Pons• Medulla

Brainstem

Diencephalon, Brainstem & Cerebellum

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CNS Structures

• Lobes• Cortex• Ventricles• Subcortical structures• Brainstem• Spinal Cord

Central Nervous System– CNS: brain and spinal cord– Necessary for the maintenance of homeostasis– Contains 1011 neurons– Contains 1014 synapses– Responsible for everything we perceive, do, feel,

and think

Histology of neural tissue

Two types of neural cells in the nervous system:

Neurons - For processing, transfer, and storage of information

Neuroglia – For support, regulation & protection of neurons

Glial Cells– 90% of CNS composed of glia– Five types of glial cells

• Astrocyte—numerous functions• Ependymal cells—line cavities• Microglia—phagocytes• Oligodendrocytes—form myelin• Schwann cells (located in PNS)—form myelin

Glial Cells

Astrocytes– Development of neural connections– Possibly modulate synaptic activity– Remove neurotransmitter from synaptic cleft– Communicate to neurons through chemical

messengers– Protect neurons against toxic substances

and oxidative stress

Microglia– Protect CNS from foreign matter through

phagocytosis• Bacteria• Dead or injured cells

– Protect CNS from oxidative stress

CNS: Physical Support

Cerebrospinal Fluid (CSF)– Extracellular fluid of the CNS– Secreted by ependymal cells of the

choroid plexus• Circulates to subarachnoid space and ventricles• Reabsorbed by arachnoid villi

– Functions• Cushions brain • Maintains stable interstitial fluid environment

Cerebral Spinal Fluid

CSF Production– Total volume of CSF = 125–150 mL– Choroid plexus produces 400–500 mL/day– Recycled three times a day

Blood Supply to the CNS– CNS comprises 2% of body weight (3–4 pounds)

• Receives 15% of blood supply

– High metabolic rate• Brain uses 20% of oxygen consumed by body

at rest• Brain uses 50% of glucose consumed by body

at rest

– Depends on blood flow for energy

CNS: Gray and White Matter

White Matter in Brain

– Projection fibers• Cerebral cortex with lower levels of brain or spinal cord

– Association fibers • Connect two areas of cerebral cortex on same

side of brain

– Commissural fibers • Connect same cortical regions on two sides of brain

– Corpus callosum • Primary location of commissural fibers

CNS: Gray and White Matter

Brain

Midbrain

Spinal cordPons

Medulla oblongata

Forebrain

Cerebrum

Thalamus

Hypothalamus

Pituitary gland

Brainstem

Diencephalon

Cerebellum

Corpus callosum

(c) Midsagittal section

Brain: Midsagittal View

Premotor cortex(coordinatesvoluntarymovements)

Primary somatosensorycortex (somesthetic sensationsand proprioception)

Sensory associationareas (integration ofsensory information)

Primary motor cortex(voluntary movement)

Central sulcus

Prefrontalassociationareas (idea andplan for voluntarymovement, thoughts,personality)

Broca’s area(speech formation)

Limbic associationcortex (emotions,learning, and memory)

Olfactory cortex(smell)

Visual associationareas (higher visionprocessing)

Wernicke’s area(languagecomprehension)

Auditoryassociationareas

Primary auditorycortex (hearing)

Primary visual cortex(vision)

Functional Areas of Cerebrum

Topographical Organization: Motor

Topographical Organization: Sensory

Imaging

• CT• MRI

Advantages of CT

• cost• availability• decreased scan time• decreased sensitivity to patient motion• better visualization of acute blood• better visualization of bony abnormalities

Computerized Tomography

Brain window

Bone window

Advantages of MRI

• no ionizing radiation (peds & pregnant) • direct coronal, sagittal and transverse images• excellent contrast resolution• no interference from bony structures

Axial view

Coronal View

Sagittal view

Questions?