IB Bio Nervous System Part II

synapse

very small gap bwtn one neuron & the next

how large is a synaptic space?

\~ 20 nm

presynaptic cell aka…

axon

postsynaptic cell aka…

dendrite

how are electrical signals of an impulse transmitted?

by gap junctions (small tubes of cytoplasm)

how do impulses __normally__ travel across synapses?

by chemical signals thru diffusion

neurotransmitter

chemical that crosses synapse

what occurs when the nerve impulse reaches the end of the axon?

* membrane depolarizes
* gated channels open → Ca+2 enters cell by facilitated diffusion

influx of Ca+2 into terminal end of axon causes…

synaptic vesicles to merge with presynaptic membrane

where are neurotransmitters stored?

in vesicles

vesicle

small membrane-bound structure used to transport material w/i cell

exocytosis

merging of membrane & release of materials

after exocytosis…

neurotransmitters are released & forced into synapse

where do neurotransmitters bind to after being released into synapse?

postsynaptic receptors on dendrites

depending on kind of neurotransmitters & kind of membrane…

postsynaptic neuron is either excited or inhibited

when the postsynaptic neuron is excited…

Na+ enters

when the postsynaptic neuron is inhibited…

K+ enters (neuron tries not to have action potential; no stimulus)

what happens to neurotransmitters at end of chem impulse?

neurotransmitters are degraded & recycled

if there is a stimulus…

* gain Na+
* lose K+

if there is no stimulus…

* neuron less likely to depolarize
* lose Na+
* gain K+

what are the two colors of neuron matter?

white & gray

why do nerves look white in white matter?

b/c myelin sheath contains type of white fat

what does myelin sheath surround?

surrounds axon

white matter neurons transmit impulses ____

very fast (\~ 100 m/sec)

white matter neurons aka

long distance neurons (> 2 cm)

long distance neurons

longest nerves; single cells from base of spine to tips of toes (peripheral NS)

why do long distance neurons need myelin sheath?

b/c myelin sheath speeds impulses to travel long distances

gray matter neurons are ___

unmyelinated

gray matter neurons aka

short distance neurons

location of short distance neurons

brain & spinal cord (central NS)

gray matter neurons transmit impulses ____

moderately fast (\~ 30 m/sec)

nervous system divided into…

central & peripheral NS

central NS consists of…

brain & spinal cord

peripheral NS consists of…

all other neurons besides brain & spinal cord

in peripheral NS, nerve fibers carry info…

to (afferent division) & from (efferent division)

peripheral NS divided into…

somatic & autonomic NS

what does somatic NS control?

voluntary action

what does autonomic NS control?

involuntary action

autonomic NS divided into…

sympathetic & parasympathetic NS

neurotransmitter in sympathetic NS =

adrenalin aka epinephrine

when does sympathetic NS function?

functions when person is under stress & need to prep for fight or flight

where do sympathetic nerves exit?

exits spinal cord from central position (cervical, thoracic, & lumbar regions)

what does sympathetic NS tend to do?

tends to awaken body in morning

neurotransmitter in parasympathetic NS =

acetycholine

what does parasympathetic NS regulate?

regulates internal organ function when body is at rest (cranial & sacral regions)

what does parasympathetic NS tend to do?

tends to relax body to prep for sleep (every 90 min)

both sets of nerves (sympathetic & parasympathetic)

* enter each organ to accelerate or decelerate organ function
* final reaction depends on which signals are stronger
* work antagonistic (against) to each other