bio first unit nervous system

main functions of the nervous system

1. recieve information and carry it to the Central nervous system

2. interpret impulses and make decisions about response

3. sort impulses and set priority for actions

   1. transmit impulses to motor units (muscles) which carry out said action

motor units

muscles

what does the CNS consist of

brain and spinal cord

what are the 2 types of nerve cells

glial cells and neurons

glial cells

support neurons (nourish, remove waste, and help fight infections)

(ex: shwann cells, oligodenchrocytes, microglia, and astrocyte)

only shwann cells are very important in this unit

neurons

transmit messages

what is a nerve

a nerve is a bundle of neurons

what is an axon

branches that carry impulses away from the cell body

myelin sheath

fatty sheaths that prevent the loss of charged ions

myelin sheath purpose

to prevent the loss of charged ions. this increases the speed of nerve impulse transmittions

schwann cells

schwann cells wrap around the axon to MAKE the myelin sheath

unmyelinated/myelinated neurons

unmyelinated — gray matter. is formed in the cell bodies yup!

myelinated — white matter. formed in the CNS and in the PNS

PNS

peripheral nervous system (nerves in your body other than spinal cord and brain. These are in charge of sending messages to your spinal cord)

most neurons in the PNS are…

myelinated

myelinated nerve fibers are covered by…

neurilemma. neurilemma helps the regeneration of nerves after trauma alongside myelin sheath

anaxonic neuron

no axons

found in CNS

unipolar neuron

cell body in the middle-ish

bipolar neuron

cell body in the middle, one side is one long dendrite, and the other side is a long axon

multipolar neuron

one long axon, many small tiny dendrites

action potential

(temporary) change in electrical voltage

electrical action potentials

1. depolarization

2. repolarization

3. refractory period

resting potential

-70mV

why is the inside of the neuron more neg. than the outside

1. sodium pumps

2. neg charged proteins

3. chloride ions in the cell (membrane is almost impermeable to Cl-

sodium potassium exchange pump ratio

3 Na out, 2 K in

relatively neg charge (plus all the other factors)

threshold potential

-55mV

what happens when a neuron reaches threshold potential

sodium gates open and reach equilibrium in the nerve which makes it up to +35mV and then the cell is no longer polarized. It becomes depolarized and the sodium gate closes

repolarization

after the action potential has peaked, sodium pumps close and potassium channels open

what does repolarzation do

makes the outsde more positive than the ousite

refractory period

recovery time in which the neuron cannot fire another electrical signal

what happens when it tries to reach -55mV but it fails

failed initiation

saltatory conduction

when action potential “jumps” through the nodes of ranvier.

what is an axon terminal

at the end of an axon whereit connects to a dendrite of another neuron

synapse

space between the presynaptic neuron’s axon terminal and the dendrites of the post synaptic neuron

what does the axon terminal have a lot of?

vesicles and mitochondria

what do the vesicles in the axon terminal hold?

neurotransmittors

step one for neuron transmission

action potential reaches the voltage gated calcium channels (activated by the action potential). This opens the calcim channels and lets calcium ions flow into the presynaptic neuron

step 2 for neuron transmission

the calcium ions induce the neurotransmitter vesicles to fuse with the presynaptic membrane

what process does the vesicles in the presynaptic membrane do

exocytosis after fusing with the membrane

all the things in the post synaptic membrane

neurotransmitter receptors and acetylcholinesterase

step 3 for neuron transmission

neurotransmitters are released and diffuse across the synaptic cleft (the gap) to the postsynaptic membrane

difference between synapse and synapse cleft

synaptic cleft - the space between the presynaptic axon terminal and the post synaptic dendrite

synapse - the whole thing (the presynaptic membrane and the post synaptic membrane)

step 4 for neuron transmission

neurotransmitters bnd to neurotransmiter repectors on post synaptic membrane and induces the action potential in the post synaptic neuron

why are neurotransmitters destroyed

because all they need to do is to bring the charge up and depolarize a neuron, and then it needs to be taken care off after

step 5 of neuron transmission

neurotransmitter receptors let go of the neurotransmittors and then are either broken down by acetylcholinesterase or are taken back up into the presynaptic meuron

2 types of neurotransmitters

exitatory and inhibitory

excitatory - triggers sodium ion channels to open, bringing the neuron CLOSER TO THRESHOLD (causes depolarization)

inhibitory - triggers potassium and chlorine channels to open letting them flow in or out of the post synaptic neuron which causes hyperpolarization, bring the neuron further from threshold potential

hyperpolarization

when the cell is more negative than resting position

2 examples excitatory

acetylcholine - (causes the sodium channels to open after reaching threshold potential). broken down by cholinesterse and reabsorbed by the presynaptic neuron. once the acytlcholine is removed the channels close

norepinephrine - also one aswell

inhibitory neurotransmitter

GABA — triggers the potassium ion channels to opne

dopamine

• affects brain synapses in the control of body movements

• is linked to sensations of pleasure

too much = schizophrenia

too little = parkinsons

seratonin

• regulates temperature and sensory perception

• involved in mood control

too little = depression

endorphins

• act as a natural painkiller

• affects emotional areas of the brain

too little = inc. risk of alchoholism

norepinephrine

• used by brain

• readies the body to respond to danger

too much = high blood pressure, anciety, and insomnia

too little = exhaustion

things that affect speed of nerve impulse

1. myelinated neurons have a faster transmission speed (saltatory conduction)

2. diameter of axon - larger the diameter, the faster the rate of conduction (unmyelinated neurons have a smaller diameter but still move slower)

how is intensity of stimulus detected

frequency of an impulse

all or none response

a stimulus must be ;arge enough for start an impulse