CHAPTER 1 - NERVE CELLS AND NERVE IMPULSES Flashcards
TWO KINDS OF NERVOUS SYSTEM CELLS
NEURONS AND GLIAL CELLS
NEURONS IN ADULT BRAIN
86 BILLION NEURONS CEREBRAL CORTEX > 16 BILLION REST OF BRAIN > LESS THAN 1 BILLION SPINAL CORD > 1 BILLION CEREBELLUM > 69 BILLION
PIONEER OF NEUROSCIENCE
Santiago Ramón y Cajal
In the late 1800s, Santiago Ramón y Cajal used newly
discovered staining techniques to establish that the nervous
system is composed of separate cells, now known as
neurons.
STUCTURE OF ANIMAL CELL
*Neurons contain the same internal structures as other
animal cells.
*The surface of a cell is its
membrane (or plasma membrane)
* Most chemicals cannot cross the membrane > protein channels permit controlled flow of water, oxygen, sodium, potassium, calcium, chloride & others
* Mitochondria > performs metabolic activities, providing the energy that the cell
uses for all activities
* Ribosomes > Ribosomes are the sites within a cell that synthesize new protein molecules. Some ribosomes
float freely within the cell, but others are attached to the endoplasmic reticulum, a network of thin tubes that transport newly synthesized proteins to other locations.
NEURON STRUCTURE
*The most distinctive feature of neurons is their shape, which varies enormously from one neuron to another
*All neurons include a soma (cell body), and most also
have dendrites, an axon, and presynaptic terminals
*Dendrites are branching fibers that get narrower near
their ends.
*The cell body, or soma (Greek for “body”; plural: somata),contains the nucleus, ribosomes, and mitochondria.
* The axon is a thin fiber of constant diameter
CELL BODY
AKA SOMA > Most of a neuron’s metabolic work occurs here
Cell bodies of neurons range in diameter from 0.005 millimeter (mm) to 0.1 mm in mammals and up to a millimeter in certain invertebrates.
AXON
The axon conveys
an impulse toward other neurons, an organ, or a muscle.
Axons can be more than a meter in length
The length of an axon is enormous in comparison to its width,
Many vertebrate axons are covered with an insulating
material called a myelin sheath with interruptions known asnodes of Ranvier (RAHN-vee-ay).
An afferent axon brings information into
a structure; (REMEMBER WITH A > A FOR ADMIT)
An efferent axon carries information away from a
structure. (REMEMBER WITH E > E FOR EXIT)
*If a cell’s dendrites
and axon are entirely contained within a single structure, the cell is an interneuron or intrinsic neuron of that structure.
NEURONS VARIATIONS
Neurons vary enormously in size, shape, and function (they can look very different) pg 22 of text book
Some can receive input 200,000 other neurons and others receive input from just 2!
TRIPARTITE SYNAPSE HYPOTHESIS
- the tip of an axon releases chemicals that cause the neighboring astrocyte to release chemicals of its own, thus magnifying or modifying the message to the next neuron
ASTROCYTES (GLIAL CELLS)
*Astrocytes dilate the blood vessels to bring more nutrients into brain areas that have heightened activity
*In some brain areas, astrocytes
also respond to hormones and thereby influence neurons
*astrocytes are active partners of neurons in many ways.
MICROGLIA (TYPE OF GLIA CELLS)
Tiny cells called microglia act as part of the immune
system, removing viruses and fungi from the brain. They
proliferate after brain damage, removing dead or damaged
neurons (Brown & Neher, 2014). They also contribute to learning by removing the weakest synapses
OLIGODENDROCYTES (GLIA CELL)
*supply an axon with nutrients necessary for proper functioning
*build the myelin sheaths that surround and
insulate certain vertebrate axons
* Schwann cells have a similar function in the periphery
RADIAL GLIA
Radial glia guide the migration of neurons and
their axons and dendrites during embryonic development.
BLOOD BRAIN BARRIER
WHY WE NEED IT > Keeps out most viruses, bacteria and chemicals
* Depends on endothelial cells, joined so tightly that they block viruses, bacteria, and other harmful chemicals from passage
*the barrier keeps out useful
chemicals as well as harmful ones.
*No special mechanism is required for small, uncharged
molecules such as oxygen and carbon dioxide that cross
through cell walls freely. Also, molecules that dissolve in thefats of the membrane cross easily. Examples include vitamins
A and D and all the drugs that affect the brain—from antidepressantsand other psychiatric drugs to illegal drugs such as heroin
*Chemicals that are actively transported into the brain include glucose (the brain’s main fuel), amino acids (the building blocks of proteins), purines, choline, a few vitamins, and iron
* Essential to health
Nourishment of Vertebrate Neurons
Most cells use a variety of carbohydrates and fats for nutrition, but vertebrate neurons depend almost entirely on glucose
*glucose is the only nutrient that crosses the
blood–brain barrier in large quantities.
