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CHAPTER 15 : COORDINATION
NERVE CELLS
-the nervous system contains millions of nerve cells called neurons to transmit messages
from one part of the body to another
NEURON
-neuron is a specialized conductor cell that receives and transmits electrochemical nerve
impulses
-there are 3 parts : the cell body, dendrites, axon
1)CELL BODY (SOMA)
-body of the neuron
-contains nucleus where most protein synthesis occurs
2)DENDRITES
-cellular extensions with many branches
-fibres that carry information toward the cell body
3)AXON
-finer, cable-like projection of the cell body
-carries nerve signals away from the cell body
-axon terminal contains synapses where neurotransmitter chemicals are released to
communicate with target neurons
4)MYELIN SHEATH
-fatty substance that wraps around nerve fibers
-function : speeds up nerve impulses transmission
-produced by special cells called Schwann cells in the process called myelination
5)SCHWANN CELL
-supply myelin for the peripheral nervous system
-the small uncovered areas of axon between Schwann cells are called nodes of Ranvier and
this causes fast transmission of nerve impulses
,TYPES OF NEURONS
SENSORY NEURON MOTOR NEURON RELAY NEURON
-transmit nerve impulse -transmit nerve impulses -found in CNS that connects
from receptors to CNS from spinal cord to muscles sensory and motor neurons
-cell body is at dorsal root to produce movement
ganglion -cell body is at CNS/spinal
cord
REFLEX ARCS
-the pathway along which impulses are transmitted from a receptor to an effector without
involving ‘conscious’ regions of the brain
-the transmission of impulses via a reflex arc produces a reflex action which is a fast,
automatic response to a stimulus.
Describe the structure of a sensory neuron. [6]
The sensory neuron consists of a cell body that has a nucleus, many mitochondria and many
Rough endoplasmic reticulum. It has a long dendron and short axon. It has myelin sheath
produced by Schwann cells to speed up the rate of transmission. The gaps between the
myelin sheath are Nodes of Ranvier where depolarization takes place.
, Describe how a resting potential is set up and maintained in a myelinated neuron.
[9]
Resting potential is maintained by the sodium-potassium pump. There are 3 Na+
moving out of the cell and 2 K+ moves into the cell (2m) by active transport against
the concentration gradient. K+ then diffuses out of the cell and Na+ diffuses into the
cell by facilitated diffusion down its concentration through the ion channels. The
membrane is more permeable to K+. The inside of the cell becomes more negative
than outside.
-the differences between the electrical charge inside and outside of the neuron when a
neuron is not conducting an impulse
1)The resting potential is maintained by a sodium-potassium pump, pumping 3 Na+ out the
cell and 2 K+ in, by active transport.
2)This creates an electrochemical gradient and results in K+ out and Na+ in by facilitated
diffusion.
3)The membrane is more permeable to K+ so more K+ goes out than Na+. Resting potential
is -70mV.
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