Part 1
Biology 12


Neurons

Gathers & transmits electro-chemical signals
DID YOU KNOW????

Neurons cannot be repaired

Some last a life time

Approximately 1000 die each day!!!

 http://outreach.mcb.harvard.edu/animation s/actionpotential.swf
 http://people.eku.edu/ritchisong/301notes2
.htm


A nerve is a bundle of neurons attached by connective tissue


Average number of neurons in the human brain = 100 billion

Nerve “highway” in the human body contains
100 billion neurons

1000 impluses/sec

Longest is about 1 meter (Where?) – human

Length of giraffe primary afferent axon (from neck to toe) = 15 feet

Average number of neurons in the octopus brain = 300 million


SENSORY



Carries signals FROM periphery (outside) TO central nervous system for processing
Information FROM environment
NOTE: detect external stimuli (light, sound, touch, heat, smell, & taste) or internal conditions (blood pressure, CO
2 level & muscle tension)


MOTOR



Carries signals FROM central nervous system TO body part (e.g. muscles, skin, glands)
Response to sensory
Movement


INTERNEURONS



Connects sensory or motor neurons to central nervous system
Carries messages in-between neurons
Majority of neurons in the brain are interneurons


The three interconnected functions of the nervous system are carried out by three types of neurons
Sensory input
Sensory neuron
Integration
Sensory receptor
Motor neuron
Motor output
Interneuron
Effector
Peripheral nervous system (PNS)
Brain and spinal cord
Central nervous system (CNS)
Figure 27.2


Cell Body

Contains all organelles, including a nucleus

Dendrites


Projections off cell bodies
Make connections with other cells

Nucleus
Dendrites
Cell body
Cell body
Figure 27.3


Axon


Long cable like projection off cell body
Sends messages (nerve impulses)

Myelin Sheath



Fatty protein that covers/insulates most nerves
Increases speed of transmission
Formed by Schwann cells

Nodes of Ranvier

Exposed axon between myelin sheath

Dendrites
Cell body
Nucleus
Axon
Myelin sheath
Nodes of
Ranvier
Cell body
Figure 27.3


Synaptic knob



End of axon branches
Comes near dendrites of adjacent neurons
Passes messages across synapse (the space between neurons)

Signal direction Dendrites
Cell body
Nucleus
Axon
Supporting cell
Signal pathway
Nodes of
Ranvier
Myelin sheath
Cell body
Synaptic knobs
Figure 27.3


Moves in only one direction

From dendrite to cell body, axon, then synaptic knob

Signal direction Dendrites
Cell body
Nucleus
Axon
Supporting cell
Signal pathway
Nodes of
Ranvier
Myelin sheath
Cell body
Synaptic knobs
Figure 27.3







Cell body
Nucleus
Dendrites axon




Myelin sheath
Schwann cells
Node of Ranvier
Synaptic knob

Synaptic knob