IB Bio Nervous System Part I

neuron

nerve cell

nervous system

made of neurons

three parts of neuron

1. cell body
2. dendrites
3. axons

cell body function

does normal cellular functions

dendrites function

receive nerve impulses

axons function

deliver impulses to other neurons

sensory neurons

receive initial stimulus

are sensory neurons afferent, efferent, or interneurons?

afferent (carry messages toward central nervous system)

motor neurons

stimulate target cells (effectors) that produce some kind of response

are motor neurons afferent, efferent, or interneurons?

efferent (carry messages away from central nervous system)

associated neurons

receive impulses from sensory neurons or send impulses to motor neurons

are associated neurons afferent, efferent, or interneurons?

interneurons

associated neurons location

in spinal cord or brain

ion

single atom or group of atoms w/ positive or negative charge

two ions in nervous system

Na+ & K+

nerve impulses are a…

result of chemical changes across membrane

neuron membrane is…

polarized/non-firing b/c positive & negative charges = separated from each other

**ion** outside of neuron

Na+

**ion** inside of neuron

K+

**charge** outside of neuron

positive b/c only Na+

**charge** inside of neuron

negative b/c large negatively charged ions move in & contribute to overall level of charge (ex: Cl-, proteins-)

neuron membrane maintained by…

Na+/K+ pump

polarization

* outside: (+) charge, high Na+, low K+
* inside: (-) charge, high K+, low Na+, protein-

depolarization

* Na+ channels open & Na+ rushes inside of membrane from outside
* outside: no charge, Na+ =, low K+
* inside: no charge, Na+ =, high K+, protein-

repolarization

* K+ channels open & K+ ions sent out of neuron from inside → polarized membrane is restored
* outside: (+) charge, Na+ =, K+ =
* inside: (-) charge, Na+ =, K+ =, protein-

channel proteins

allow ions to flow thru them from one side to the other of plasma membrane; allow neuron to be depolarized

nerve impulses are simply…

waves of depolarization

where do nerve impulses originate?

wherever plasma membrane is “disturbed” by stimulation

two causes of nerve impulses

external stimuli or neurotransmitters

what reverses membrane polarity?

Na+/K+ pumps stop; Na+ channels allow inflow of Na+ ions

the flow of Na+ ions through Na+ channels begins…

wave of depolarization (neighboring channels open & depolarize)

how long does it take for membrane to repolarize itself & be ready for another impulse?

1 msec

action potential graph

resting state is at ___ mV

\-70 mV

no polarization will occur & not spread to its neighbors at ___ mV

less than -55 mV

resting potential

unstimulated, polarized state of neuron

what happens if stimulus is strong enough?

neuron is above threshold level & causes action potential (complete depolarization)

threshold

* amount of depolarization that will cause a neuron to fire (@ -55 mV)
* prevents neurons from accidentally firing

refractory period

* membrane cannot be stimulated (explains why nerve impulse only moves in one direction)
* neuron will not respond to new stimulus
* reestablishes original position of ions
* hyperpolarization

what does hyperpolarization prevent?

prevents nerve impulses moving in both directions

what does hyperpolarization allow?

allows nerve impulses to move in one direction

all-or-nothing principle

once threshold stimulus is achieved for neuron, impulse will begin & travel to end(s) of neuron

under the all-or-nothing principle, each neuron has its own ___ requirement

threshold

for both Na+ & K+…

there is no channel protein

pumps/transport proteins

active transport

channel protein

facilitated diffusion

how does a repolarized neuron go back to being polarized?

* by Na+/K+ pump (transport protein)
* out: 3Na+
* in: 2K+

neuron diagram

corpus callosum

communication btwn both brain hemispheres

pituitary gland

“master gland”, regulation of other glands & flow of hormones

cerebral cortex

controls high-level processes (ex: language, memory, reasoning, thought, learning, emotion)

thalamus

relays sensory & motor signals; sleep-wake regulation

hypothalamus

controls autonomic functions, body temperature, emotions, hunger, thirst, appetite, digestion, sleep

cerebellum

controls balance, equilibrium, posture, coordination, movement, fine motor skills

pons

“relay center”, transmits signals, controls unconscious movements, breathing, sleep & wake cycles

medulla oblongata

transmits signals, controls vital processes (heartbeat, breathing, blood pressure)

brain stem

controls automatic body functions (heart rate, breathing, sleep and wake cycles, swallowing)