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