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Homeostasis 3 Cheat Sheet by

Nervous System

How It Works
Sensory input - detection of stimulus
 
Integr­ation - processing in the brain
 
Motor Output - response in other body part
Central Nervous System
brain and spinal cord
Peripheral Nervous System
Afferent System (sensory) - receives input from body receptors and transmits signals to CNS
 
Efferent System (motor) - carries signal from CNS to body

Efferent (Motor) Division

Somatic System
responds to external and internal stimuli by sending signals to skeletal muscles (volun­tary)
Autonomic System
involu­ntary. signals to smooth muscle, cardiac, and organs
 
1) Sympat­hetic Nervous System - prepares body for stress, affected by epinep­hrine
 
2) Parasy­mpa­thetic Nervous System - restores body back to normal

Reflex Arc

Simplest type of neural circuit
regulates reflexes
rapid involu­ntary response to stimuli
integr­ation occurs in spinal cord rather than brain
 

Neve Signals

Neurons Each Have
enlarged cell body, axon, dendrites
 
body- nucleus and organelles
 
axon- conducts signals from one neutron to next
 
dendrites- receives signals and sends to cell body
*Glial Cells
not neurons, help provide and support nerve cells.
1) Schwann Cells
wrap around axon of a neuron to provide insulation (high lipid content)
 
form myelin sheath
 
gaps between them are called Node of Ranvier

Na+ / K+ Pump

ATP drives active transport
3 Na+ pumped out - 2 K+ pumped in

...

Membrane Potential
V= V(inside) - V(outside)
 
resting potential of neuron is -70mV
Action Potential
depola­riz­ation followed by reploa­riz­ation.
 
increase in membrane potential followed by a decrease
 

Phases

Phase 1: RESTING STATE
before neuron receives stimulus (-70mv)
 
Na+ channels closed
 
K+ channels closed
Phase 2: THRESHOLD
depolr­ization stimulus opens Na+ channels
 
reaches threshold (-50mV)
Phase 3: DEPOLA­RIZ­ATION
depola­riz­ation opens all Na+ channels, positive feedback
Phase 4: REPOLA­RIZING
after peak action potential (+30mV)
 
K+ channels begin to open (flow of K+ depola­rizes cell)
 
Na+ channels begin to close
Phase 5: UNDERSHOOT
K+ channels close very slowly (-80+)

Synapse

Synapse
cell junction that controls commun­ication between neuron and other body cells
Electrical Synapse
rapid transm­ission. Current from presyn­aptic cell flows through postsy­naptic cell
 
channels between adjacent cells
Chemical Synapse
synaptic cleft - gap separating cells
 
synaptic vesicles - sacs at synaptic terminal containing neurot­ran­smi­tters
 
presyn­aptic membrane depola­rized. Ca2+ channels open. Stimulates exocytosis of synaptic vesicle
Neurot­ran­smi­tters
excitation or inhibition effect
 
Acetyl­choline - triggers muscle contra­ctions, hormones, wakefu­lness, memory. Most common
 
Endorphins - released during pleasure or stress
 

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