Lecture II. The Nervous System and Its Cells Bio 3411 Friday August 28, 2009.

Lecture II. The Nervous System and Its Cells

Bio 3411 Friday

August 28, 2009

• T. Woolsey

• 3802 North Building

• 362-3601

• [email protected]

2Lecture II. The Nervous System and Its Cells

Readings

NEUROSCIENCE: 3rd ed, pp 1-22THE BRAIN ATLAS: 3rd ed, pp 4-17†

References:Jellison et al (2004). Diffusion tensor imaging of cerebral white matter: a pictorial review of physics, fiber tract anatomy, and tumor imaging

patterns. AJNR Am J Neuroradiol, 25:356-369†

Ludwig, E., & Klingler, J. (1956). Atlas cerebri humani. Der innere Bau des Gehirns dargestellt auf Grund makroskopischer Praparate. The inner structure of the brain demonstrated on the basis of macroscopical preparations . Boston,: Little, Brown.

Ramón y Cajal, S. (1988). Recollections of my life. New York: Garland.______________________

†(pdfs on course website: [http://artsci.wustl.edu/~sdanker/index.html])


Movie - vmjr-brain.mov


Overview

• A Few Facts

• Main Features of Nervous System

• Cells of Nervous System

• Importance in Health and in Disease


Facts


Organ

Weight 2-3% of body

O2 Consumption20% of total

Brain Energy (Glucose) Utilization20% of total

Brain Blood Flow20% of heart output at rest


Elements

Neurons (=nerve cells) ≈ 100 Billion

Glia (= glue; “supporting” cells) ≈ 1 Trillion

Synapses (=clasp) 1/1,000,000th of all stars &

planets in the universe/person [less than the total of human synapses of people living in the St.L area!!]

Genes 50% of ≈ 20,000-25,000 genes in the

human genome are expressed only in Brain[70% of the balance are also expressed in the nervous system; the total is

85% of the genome]10Lecture II. The Nervous System

and Its Cells

Features

Brain, Spinal Cord, Other


THE BRAIN ATLAS 3rded, p. 8

Mid-line (sagittal) section

through central nervous

system (CNS). Note the

relationship between

vertebrae (BLACK),

segments of the spinal

cord (RED) and spinal

nerves (YELLOW).


Magnetic

Resonance

Image (MRI) of

head and neck at

the midline.

THE BRAIN ATLAS 3rd ed, p. 111


Peripheral (PNS - outside the skeleton)

Sensory (sensation)

Motor (movement)Autonomic (“involuntary”)Enteric (gut)

Central (CNS -inside the skeleton)

Spinal Cord (Spine)

Brain (Skull)


Views of the human

spinal cord and lower

brain stem.

LEFT - Left lateral (side)

showing segments and

spinal nerves.

MIDDLE - Anterior (front)

view of spinal cord

without showing

enlargements.

RIGHT - Posterior (back)

view of spinal cord with

roots, ganglia and

nerves.



Spinal Cord Segment



Left Lateral

(side) view

of the

human

Brain



The different regions of the brain from the lateral (side) and median section (middle) human brain. These brain regions are discernable in in all vertebrates and in early embryos.

(cerebral cortex = gold; thalamus = blue/purple; midbrain = orange; pons = purple, cerebellum = blue; medulla = red/orange; spinal cord = green)


Gray Matter

Cortex, Nuclei or Ganglia (groups of nerve cell bodies and neuropil) generally of similar function

Neuropil - neuronal processes, synapses and glia

Components



23

White Matter

Bundles (groups of myelinated axons [see below] that course in the same direction)

Tracts (also groups of axons (myelinated and un-myelinated but indicates origin, destination and therefore function)

Components



25

Jellison et al (2004)

Ludwig, E., & Klingler, J. (1956)

The brain and spinal cord

are bathed in a colorless

fluid called cerebrospinal

fluid (CSF). The fluid is

made in chambers in the

brain called ventricles (blue).

It circulates between all the

cells and their processes

and in the space between a

membrane on the brain

surface (called the pia

mater) and a membrane that

is next to the skull or spine

(arachnoid mater) called the

subarachnoid space (gold).

Cerebrospinal Fluid (CSF)


– Other Blood Vessels (arteries, capillaries, veins and

venous sinuses) Coverings - meninges (dura mater (tough

mother), arachnoid (spider web like), pia (tender/affectionate))

Cerebrospinal fluid (CSF - ventricles, canals, intercellular space, subarachnoid space)

Components


Cells of Nervous System

Neurons, Contacts, Support


Santiago Ramón y Cajal

(1851-1932)

ca. 1892

Cajal (say kaahaal) shared the

1906 Nobel Prize for discoveries

indicating that the nervous

system was made up of

individual contiguous elements -

the neurons.


Cells of Nervous System

Neurons

Parts: cell body (soma), dendrites (input processes), axon (output process)

Types: local circuit (90%), projection (10%) Variations: stellate (star like); pyramidal

(conical/triangular); famous guys - Purkinje, Betz, Cajal, Retzius, Mauthner…

All variations are correlated to particular functions.


Photograph of neurons stained by Golgi’s method which fills processes of some cells with black precipitates of heavy metals and Nissl which stains all nuclei and neuronal cytoplasm blue.


Pyramidal neuron (conical cell body) stained by Golgi’s method. There are multiple processes that resemble branches of trees (dendrites) and one that resembles a wire (axon; arrow). Inputs to the cell are mainly on dendrites and the cell body (soma) while outputs are mainly via the axon. This the principal long axon (output) cell in the cerebral cortex.


Photograph of a Purkinje cell in the cerebellum stained by Golgi’s method. The neuron has one complex dendrite that resembles a sea fan (arrow). Synapses on this cell type are estimated to be about 0.5 Million.


Cells of Nervous SystemContacts (Synapses)

• Types: asymmetrical = Type I (postsynaptic membrane is thicker than presynaptic membrane; spherical clear vesicles) these are excitatory synapses - on; symmetrical = Type II (postsynaptic membrane same as presynaptic membrane; flattened clear vesicles) these are inhibitory synapses - off

• Parts: bouton or ending (contains vesicles (transmitters, modulators) and mitochondia), presynaptic membrane (dense in electron microscope); synaptic cleft; postynaptic membrane (dense in electron microscope)

• Variations: large like to muscle, “chalice” in brain stem, “climbing” in the cerebellum; intermediate; small; in passing or as a terminal. All variations relate to specific functions (like variations in hammers - sledge vs. jeweler’s).


Photograph of the giant

neuron in the brainstem

of the gold fish

(Mauthner) stained by

Bodian’s method.

Synapses on this cell

type are particularly easy

to see. Much work on

this cell type contributed

to understanding the

structure of the synapse

before the electron

microscope was

perfected.


The main components of a synapse: synaptic cleft (space between the terminal and target process), membrane thickenings on the terminal (pre) and process (post), mitochondria and synaptic vseicles (contain transmitter(s)).

Electron micrograph of a synapse in the brain stained with the heavy metal element osmium (Os) which is lipophylic (stains lipids/fats). This synapse is only about 2 micrometers across.


Most brain synapses (type I) have a wider cleft (space between the terminal and target process), thicker membrane densities on the terminal (pre) and process (post) and rounder vesicles. Such synapses are excitatory (on).

About 10 - 20% brain synapses (type II) have a narrower cleft, thinner membrane densities on the terminal (pre) and process (post) and flat vesicles. Such synapses are inhibitory (off).


A neuron (red) grown in tissue-culture. Green shows proteins in processes from pre-synaptic neurons. The green/yellow dots on the red neuron indicate synapses. The inset shows a “cartoon” of blue synaptic terminals contacting a neuron. The picture gives a sense of the enormous numbers, distribution and density of synapses on a nerve cell. Neurons “integrate” information from thousands of synapses from many different sources.


Cells of Nervous SystemGlia (glue) or Supporting Cells

Parts: cell body (soma) and "short" processes

Types: astrocytes (star like); oligodendorcytes

(fewer (oligo) branches (dendrites); microglia

(small ones)

Variations: fleshy, fibrous (stringy), myelinating,

non-myelinating

All variations relate to specific functions.


Cajal’s drawing of “glia” in the spinal cord.

A

B

C

C

D

D Astrocytes - Fibrous

C Astrocytes - Protoplasmic (fleshy)in gray matter

B Oligodendrocytes which myelinate axons in fiber tracts

A Ependyma (lining of the central canal of the spinal cord)


Astrocyte Oligodendrocyte Microglial Cell

NEUROSCIENCE (3rd ed, p.8, fig 1.5)


THE BRAIN ATLAS 3rd ed, pp. 5, 7


Please vote on the following proposition:

I think that the TA can run up the stairs to the back row

of this auditorium in less than 10 seconds.

How Does This Work?

Yes ____ No ____

(Estimated elapsed time: )


Importance

Biology, Disease


Biology• Understanding the brain is THE major question

in biology and science.

• Is it possible for the brain to understand itself?

• The brain like any organ has functions: input,

output, “thought”, communication.


Brain Diseases• Interfere with brain functions as heart disease

interferes with the circulation.

• Many diseases have a strong genetic component.

• Prevalence is high: ≈ 15 - 30% of the population.

• Cost is high: >> $2+ Trillion/year in care, lost income,

social services, etc., in the US.

• Impact (personal, family, societal) is persistent,

pervasive, enormous, incalculable.


What this lecture was about

• A Few Facts(genes, size, energy)

• Main Features of Nervous System (brain, spinal cord, periphery)

• Cells of Nervous System (neurons, glia, contacts)

• Importance in Health and in Disease (bases, prevalence, impact)


Lecture II. The Nervous System and Its Cells Bio 3411 Friday August 28, 2009.

Documents

Transcript of Lecture II. The Nervous System and Its Cells Bio 3411 Friday August 28, 2009.