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central nervous system
brain and spinal cord
CNS
can not repair itself
peripheral nervous system
nerves
Sensory-somatic nervous system
12 pairs of cranial nerves (eyes, ears, etc) and 31 pairs of spinal nerves
Sensory-somatic nervous system
Consciously controlled (skeletal muscles)
Autonomic nervous system
sensory neurons and motor neurons that run between the CNS
Autonomic nervous system
Heart, lungs, smooth muscles, glands
Autonomic nervous system
Two subdivisions
1. Sympathetic nervous system
- Fight or Flight
2. Parasympathetic nervous system
- “normal conditions”
Neurons (Nerve cells)
structural and functional units of the nervous system
Neurons (Nerve cells)
Specialized to react to physical and chemical changes
Neurons (Nerve cells)
The brain is made up of about 200-100 billion nerve cells
Nerve Impulse
The electrochemical process of transmitting information from one neuron to another to cells outside the nervous system
Cell Body (soma)
contains cytoplasm, cell membrane, organelles (mitochondria, lysosomes, Golgi apparatus, nucleus, chromatophilic substance, and neurofibrils)
Dendrites
Numerous extensions from the neuron cell body that takes information to the cell body
Dendrites
Receives electrochemical messages (into cell)
Axon
The extension from the neuron cell body that takes information away from the cell body
Axon Terminal
End part of an axon that makes a synaptic contact with another cell
Neuroglial cells
Fill space, provide structural framework, produce myelin, and carry on phagocytosis
Neuroglial cells
Greatly out number neurons in the CNS (50x)
Neuroglial cells
They are cells- not nerve cells
CNS- Microglial cells
Support neurons and phagocytize (engulf bacteria debris)
CNS- Oligodendrocytes
Occur in rows along nerve fibers and they provide insulating layers of myelin around axons within the CNS
CNS- Astrocytes
Provide shape, support and structure
CNS- Astrocytes
Regulates nutrient and ion concentration
CNS- Astrocytes
Forms scar tissue to fill space following injury to CNS
CNS- Ependymal cells
Lines interior cavity of CNS
Ependymal cells make sure
nothing harmful gets in
PNS- Schwann cells
form a covering called myelin sheath
Myelin (CNS- Oligodendrocytes vs. PNS- Schwann cells)
Lipid-protein membrane layer
Myelin Sheath
Wraps around the axon and is necessary in order for the impulse to travel down the axon
Neurilemma
surrounds myelin sheath
Nodes of Ranvier
Narrow gaps in the myelin sheath between the Schwann cells
White Matter
Myelinated axons in the CNS
Gray Matter
Unmyelinated axon in the CNS
Afferent (sensory)
Travels towards the CNS
(Afferent) Sensory:
from outside body
(Afferent) Visceral:
Inside the body
Efferent (motor)
Travels away or out of the CNS
(Efferent) Somatic:
going to skeletal muscles
(Efferent) Autonomic:
smooth & cardiac muscles, glands
Interneurons
Within the CNS
Interneurons
Direct incoming impulses, process, interpret and re-direct
Bipolar Neurons
Has only 2 processes, one from each end
Bipolar Neurons
Found in eyes, nose and ear
Unipolar Neurons
Single process from cell body that divides into 2 branches (CNS + PNS)
Ganglia:
Unipolar neurons that are specialized masses of nervous tissue located outside the brain and spinal cord
Multipolar Neurons
Many processes (dendrites) arising from the cell body
Multipolar Neurons
One axon
Multipolar Neurons
Found mostly in the brain and spinal cord
10,000
specific types of neurons in the human brain
Active Transport
Movement of particles through the membrane from a region of low concentration to high concentration
Active Transport
ATP (energy) is required
Ex: Na+/K+ pump
Polarization =
electrically charged
Polarization
is important to the conduction of nerve impulses (& muscle contraction)
Polarization
is caused by the unequal distribution of positive and negative ions on either side of the cell membrane
Resting (membrane) potential
The difference between the electrical charges inside and outside the cell membrane
Na+ :
high concentration outside the cell and low inside (wants to go in)
K+ :
high concentration inside the cell and low outside (wants to go out)
Negatively charged particles inside cell
want to leave the cell but can’t get through the membrane
Threshold Potential
Stimulation level that must be exceeded to elicit a nerve impulse or a muscle contraction
Action Potential
The sequence of electrical changes when a nerve cell membrane is exposed to a stimulus that exceeds its threshold
Depolarization
When a cell responds to a stimulus causing the cell membrane’s resting potential to decrease
Depolarization
Inside the membrane becomes less negative compared to outside the cell
Depolarization
*Na+ channels open and rush into the cell
Repolarization
Membrane becomes negative again when membrane channels open up and K+ leaves the cell
Repolarization
*K+ channels open up and rush out of the cell
Na+/K+ pump- Pumps Na+ back outside and K+ back inside the cell
3 Na+ for every 2 K+
Threshold
The minimal amount of stimulus needed to produce an action potential
All or None Response
If a nerve fiber responds at all to a stimulus, it responds completely (like muscles)
All or None Response
Greater intensity of stimulation triggers more impulses per second, not a stronger impulse
Saltatory Conduction
Produced in myelinated neurons where the nerve impulse travels down the axon jumping from Node of Ranvier to Node of Ranvier
Reflexes
Rapid, automatic, subconscious response to a stimulus
Simple pathway including only a few neurons
Causes involuntary reaction
“Built in” or learned
