Transcript THE NERVOUS SYSTEM CH 48 AND 49

THE NERVOUS SYSTEM
CH 48 AND 49
• Designed to sense an animal’s
external environment, initiate a
response, and return the animal to
HOMEOSTASIS
• Involves a series of cell-cell
interactions
I. Nervous systems consist of circuits
of neurons and supporting cells
• Single celled organisms can respond to
environment
• Most multicelled animals need neurons
• Simplest nervous system is in cnidarians,
radially symmetrical animals with nerve net
• All bilaterally symmetrical animals have
centralized nervous system
What is the trend here? Importance?
II. The vertebrate nervous system
A. Organization of the nervous system
• Central nervous system (CNS)
– Brain and spine
– Where integration takes place
• Peripheral nervous system (PNS)
– Neurons that send info to CNS and receive info
from CNS
– Sensory neurons: send info to CNS
– Motor neurons: receive info from CNS
B. Neurons
• Sensory (afferent) neurons
– carry nerve impulses from the sensory receptors to
the CNS
– sensory receptors are located in:
– skin, eyes, ears, mouth, nose
• Motor (efferent) neurons
– Carry the nerve impulse from the CNS to effectors
– Effectors are muscles and glands
• interneurons
– Located in the CNS
– link sensory and motor neurons
Sense receptors send info to sense neurons which
send info to interneurons which send info to motor
neurons which send info to muscles or glands
1. Neuron structure and function
• Cell body: contains organelles
• Dendrites: short extensions off cell body that
receive signals
• Axon: Long extension off of the cell body that
relays the stimulus
• synaptic terminal: sends info from one cell to
another thru neurotransmitters
• synapse: space between two cells
• presynaptic cell sends info to postsynaptic cell
C. How information is sent thru the
nervous system
• all cells have a difference in charge on either
side of plasma membrane called a membrane
potential
• Rest membrane potential: Membrane
potential of unstimulated neuron
• Change in resting membrane potential results
in transmission of nerve impulse
What do you notice about the resting membrane potential?
1. Forming the resting membrane
potential
• Uses energy in active transport
• [ K+] is highest in cell, [Na+] is highest out
• Na+/K+ pumps use NRG of ATP to maintain
these K+ and Na+ gradients across the plasma
membrane (active transport: low to high
concentration using NRG)
• These concentration gradients represent
chemical potential energy
2. Generating the action potential
• Stimulus from the environment causes the
membrane of the nerve cell to depolarize:
– Na+ diffuses into the nerve cell
– K+ diffuses out
• As soon as this happens, the Na+/K+ pump
restores the membrane potential
3. Propagating the action potential
• The action potential travels down the nerve
cell from dendrites to axon in a wave of
depolarization and restoration of the
membrane potential
http://highered.mcgrawhill.com/sites/0072943696/student_view0/chapter8/animation__the_nerve_im
pulse.html
http://www.blackwellpublishing.com/matthews/actionp.html
http://wps.aw.com/bc_campbell_biology_8ap/
D. How the nerve impulse moves
from one cell to another
• The space between two nerve cells is called a
synapse
• Two nerves communicate with each other by
synaptic signaling
• How:
– When the action potential reaches the end of the
axon, it stimulates the release of neurotransmitters
into the synapse
– The neurotransmitters bind to receptors on the
postsynaptic cell to transmit the nerve impulse
http://highered.mcgrawhill.com/sites/0072943696/student_view0/chapter8/animation__chemical_synap
se__quiz_2_.html
E. What are neurotransmitters?
• Small molecules stored in vesicles in the
presynaptic neuron
• Most are made in RER and golgi
• Types:
– Dopamine: the “reward” neurotransmitter, cocaine
and meth increase dopamine release
– Serotonin: the “feel good” neurotransmitter. MDMA
either increases or prevents degradation of
serotonin. Low serotonin is associated with
depression
– Acetylcholine: involved in muscle contraction.
Broken down by acetylcholinesterase to control
muscle contraction
• http://www.youtube.com/watch?v=UabDiuTtU0
M&list=PLFCE4D99C4124A27A&index=50