Transcript Neurons, Neurons, Neurons!

Neurons, Neurons, Neurons!
Mrs. Hartley
Anatomy and Physiology
Remember:Divisions of Nervous
System
Nervous System
Peripheral Nervous
System Autonomic
Cardiac and smooth muscle
And Glands
Parasympathetic
“rest and digest”
Sympathetic
“fight or flight”
Central Nervous System
Receives sensory input and
sends motor output
Brain and Spinal Cord
Peripheral Nervous
System Somatic
Sensory Input from
Face, ears, nose, eyes
Motor output from CNS
To skin and skeletal
muscle
Neurons
• Primary structural and
functional unit of nerve
tissue
• Responsive cells that
conduct impulses at great
speeds
• Cell body, axons,
dendrites, myelin
sheaths, synaptic
terminals
• Direction of impulse:
dendrites to cell body to
axon to axon terminal to
synaptic end bulb
Cell Body: cytoplasm enveloped by
plasma membrane
• Prominent nucleus/nucleolus
• Many functional organelles (mitochondria,
Golgi, etc.)
Axon
• Conducts impulses away from the cell
body
• Terminal end communicates with the next
cell
Dendrites
• Thin, branching extensions of cell body
• Receive impulses from adjacent neurons
• Uni-directional: only towards cell body
Myelin Sheath (pink)
• White, fatty insulating barrier
• Aids in nerve impulse conduction
What Goes Wrong in MS?
When myelin is damaged, dense, scar-like tissue forms around nerve fibers
throughout the brain and spinal cord. These scars, sometimes referred to
as sclerosis, plaques, or lesions, can slow down or completely prevent the
transmission of signals between nerve cells. Messages from the brain and
spinal cord cannot reach other parts of the body. Damage, or scarring,
occurs in many places throughout the central nervous system, hence the
term "Multiple Sclerosis."
Nodes of Ranvier
• Gaps in myelin sheath
• Aid in impulse conduction
Information from one neuron flows to another
neuron across a synapse. The synapse is a
small gap separating neurons. The synapse
consists of:
1. a presynaptic ending that contains
neurotransmitters, mitochondria and other
cell organelles,
2. a postsynaptic ending that contains
receptor sites for neurotransmitters and,
3. a synaptic cleft or space between the
presynaptic and postsynaptic endings.
http://www.blackwellpublishing.com/matthews/nmj.html
So…How Are Impulses Created?
• Excitability: neurons have the ability to
respond when a stimulus becomes great
enough to alter the resting membrane
potential of a particular region of a
membrane
– Uneven distribution of ions (electrically
charged particles) of sodium and potassium
causing an electrical gradient
Depolarization and Repolarization
• Rapid change in
membrane’s
permeability to
sodium ions causing
the electrical charge
inside the cell to
become more
+positive
• Soon after, resting
membrane potential is
restored
• Potassium flows out
of the cell and sodium
stops flowing in
http://www.blackwellpublishing.com/matthews/channel.html
Action Potential
• Depolarization + rapid repolarization
results in an action potential or nerve
impulse
• Rapid at 1/1000s and in rapid succession
Myelinated vs. Unmyelinated
• Unmyelinated:
impulse continues
along the length of
the neuron
unimpeded
• 10 m/s
• Myelinated
• Nodes of Ranvier
• Myelin disrupts
impulse…saltatory
conduction….impuls
e skips, quickening
the impulse
• 130 m/s
http://www.brainviews.com/abFiles/AniSalt.htm
http://www.blackwellpublishing.com/matthews/actionp.html
So Let’s Play a Game!
• “Saltatory Conduction”
• “All or None Game”
• All or None response: if stimulus is large
enough, impulse will be conducted along
the entire length of the neuron