http://www.youtube.com/watch?v=Q4uh2r1djWw

The Nervous System

The Nervous System

- General organization

- The basic units- the cells

- Neurophysiology

- Neural interactions

Brain, Spinal cord, Neuronal pathways, Special senses

The Central Nervous System

(CNS)

The Peripheral Nervous System

(PNS)

The Human Nervous System

The Nervous SystemMonitors changesProcesses and interpretsCauses a response

PNS CNS

Peripheral Nervous system

Central Nervous system

sensory motor

AutonomicSmooth and cardiac

muscles; Glands

Somatic

Skeletal muscles

Motor (Efferent)Sensory (Afferent)

Somatic (skin, skeletal muscle and joints)

Visceral (internal organs)

“As the entomologist chasing butterflies of bright colors, my attention was seeking in the garden of gray matter, those cells of delicate and elegant forms, the mysterious butterflies of the soul, whose fluttering wings would someday—who knows?—enlighten the secret of mental life”

Santiago Ramón y Cajal (1852-1934)

Neurons“The Mysterious Butterflies of the Soul”

Neurons“The Mysterious Butterflies of the Soul”

Santiago Ramón y Cajal

Nobel prize in physiology and medicine 1906

The neuron

Axon

Cell bodyDendrites

Telodendria

Nissl bodies

Most of our wiring is insulated

Myelin sheath

• Whitish, fatty (protein-lipoid), segmented sheath around most long (NOT ALL) axons

• It functions to:- Protect the axon- Electrically insulate fibers from one another- Increase the speed of nerve impulse transmission

Myelin sheath

• Formed by Schwann cells in the PNS

• A Schwann cell:- Envelopes an axon in a trough- Has concentric layers of membrane that make up the myelin sheath

Myelin sheath

Axons are bundled together to form fascicles

CNS: axon bundles form tracts PNS: axon bundles form nerves

Neurons are not alone

Neurons are Not Alone:The supporting neuroglia

CNS

Astrocytes

- Support and brace neurons- Anchor neurons to their nutrient supplies- Guide migration of young neurons- Control the chemical environment

MicrogliaThe “Immune System” of the CNS

- Small, ovoid cells with spiny processes- Turn into phagocytes upon inflammation

(monitor the health of neurons, in the absence of macrophages, due to the BBB)

Ependymal cells

- Ciliated epithelial cells lining the central cavities of the brain and spinal column

- Forming a permeable barrier between the CSF and nervous tissue

- Beating cilia helps circulating the CSF

CSF(cerebrospinal fluid)

Banizs et al. Development (2005)

What could happen in B?

B A

-Beating cilia helps circulating the CSF

Neurons are Not Alone:The supporting neuroglia

CNS

Oligodendrocytes

- Insulators of the thick neurons of the CNS

- A single oligodendrocyte can form myelin sheaths around several axons

The supporting neuroglia in the CNS

The supporting neuroglia in the PNS

- Schwann cellssurround and insulate axons (the “oligodendrocytes” of the PNS)- Satellite cellsSupport an nourish cell bodies (“astrocytes”

of the PNS)

Summary

Peripheral Nervous system

Central Nervous system

sensory motor

Autonomic

Smooth and cardiac muscles; Glands

Somatic

Skeletal muscles

Motor (Efferent)Sensory (Afferent)

Somatic (skin, skeletal muscle and joints)

Visceral (internal organs)

Summary

Not all neurons look like that

Neurophysiology

Opposite electrical charges attract each other

In case negative and positive charges are separated from each other, their coming together liberates energy

Thus, separated opposing electrical charges carry a potential energy

-- - - - ---

+ +++ +++

inside

outside

• Voltage (V)measure of differences in electrical potential energy

generated by separated charges• Current (I)the flow of electrical charge between two points• Resistance (R) hindrance to charge flow

Neurophysiology

-- - - - ---

+ +++ +++

inside

outside

Ohm’s law

--- - ----

+ ++

+ +++

inside

outside+++

-Current: ions

Resistance: membrane permeability

Voltage: potential across the membrane

--- - ----

+ ++

+ +++

inside

outside+++

-

Resistance: membrane permeability

How can ions move across the membrane?