Download Nervous System Neuron: nerve cell, functional unit of nervous

Nervous System
Neuron: nerve cell, functional unit of nervous system.
1. PNS-Sensory: receives stimuli and sends signal to CNS-Inter
2. CNS-Inter: receives signals from sensory and sends them to the motor.
3. PNS Motor: receives signals from inter-neuron and responds to stimuli.
Two Forms of Neural Communication:
1. Intra-Neuron: Electrical (in the neuron)
2. Inter-Neuron: Chemical (between cells)
Reflex Arc: pathway of impulses occurring during reflex with the center of coordination being
the spinal cord.
1. Stimulus
2. Receptors: initiate the impulse
3. Sensory Neuron: carries impulse to the spinal cord.
4. Synapse: tiny gap between terminal branches of one neuron and the dendrites of the next.
5. Interneuron: small nerve cell between sensory and motor neuron.
6. Motor Neuron: carries impulse to effector from interneuron.
7. Effector: muscle of gland that reacts.
Parts of Brain
Brain: extension of spinal cord, 1000000000000000 neurons, interacts with PNS-sensory and
motor neurons.
Cerebrum Cortex relates to intelligence and the evolution of the brain.
● Folds may have to do with intelligence, the folding leads to an increased surface area and
thus more neurons.
● There is no correlation between the size of the brain and the level of intelligence it has to
do with how well neurons can “talk” to each other.
● “little brain” many neurons. Voluntary muscle movement, fine motor skills, controls the
skeletal muscles. . The left side of the cerebellum controls the body’s right side and the
right side controls the body’s left side.
Brain Stem/Medulla Oblongata: involuntary actions: breathing, cardiac, swallow, relay sensory
messages.
Hippocampus: memory
Thalymus: stimulus related to cerebrum such as pain.
Amygdala: related to emotion such as that associated with taste.
Spinal Chord: communicates with PNS and Brain.
1. Cervical: neck, arms, upper trunk
2. Thoracic: upper back, abdomen,
3,4. Lumbar, Sacral: legs, bladder, bowels, sex organs.
- Symmetrical motor disks, sensory tracts sending information to the brain.
-pairs sensory, motor neurons, per vertebrate
-bundles 1000000 neurons grouped into different tracts
-associate with different brain and body parts
100-1000 neurons can transfer one signal.
Parts of a Neuron:
1. Dendrites (where signals initiate)
● “”tree” branched network 1000 dendrites per neuron allow it to talk to multiple neurons.
● Receptor s bind neurotransmitters from many neurons
● Ion Channels trigger/suppress action potentials. When the NT binds with the receptor it
opens the ion channels which create an action potential.
2. Cell Body (Soma)
● Ion channels/resting potential, NT Ligand-gated, voltage gated.
3. Axon Hillock (action potential started)
● Processing of information
● Summation of “excitatory” and “inhibitory” signals
4. Axon (extended soma) AP Action Potential, electrical signal
● Myelin sheath
● Glial cells: non-neuronal, fatty, insulates/propagates AP
● Salutatory conductance: signal “jumps”
● Nodes of Ranvier unmyelinated ion channels
● Signal shot down axon 300 mph with the help of fatty cells which make sure the AP
doesn’t lose strength and they jump from node to node with help of insulated fat.
5. Axon Terminus
● Also multi-branched
● Releases neurotransmitter (NT)
● Calcium triggered exocytosis of synaptic vesicles
● Triggers little vesicles to come to end talks to them through the calcium ions, allows them
to enter, then axon releases neurotransmitter
● Calcium also tells muscle to contract.
6. Synapse
Pre-synaptic membrane:
● Axon terminus releases ligand/NT, NTase
Post-synaptic membrane:
● NT receptor, Ion channels.
The What? Yes that’s Right ACTION POTENTIAL.
1. Resting Potential=polarized=unstimulated
Outside of Cell: positive charged sodium and potassium
Inside cell: negatively charged
-unstimulated neuron (resting) -70 mV indicating the negative charge of the inside of the neuron
3 Channels That Regulate the Unstimulated Cell:
Na+channel: facilitates Na+ into the cell.
K+ channel: facilitates K+ out of the cell
Na+-K+ Pump: 3 Na+ out of the cell and 2K+ into the cell
● “-“ charged proteins cannot leave cell easily
● Endothermic reaction, only part that is exothermic is ATP-ADP phosphorylation which
is unstable to stable.
● This phosphate allow sthe pump to open and allows Na out and K in once the phosphate
leaves
2. Ligand Gated Channel is Activated by a Neurotransmitter
● Depolarizes the cell putting it at -55mV
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Na + voltage gated channel
Puts cell at +40mV and creates the long awaited ACTION POTENTIAL!!!
+40 mV goes to axon terminal and sets off neurotransmitter
Purpose of the refractory period is to make the stimulus reach the end because of the
potassium. Parts of axon not covered by myelin the action potential jumps Nodes of
Ranvier which have voltage gated channels.
This is known as the refractory period.
Cell begins to Reset
Once refectory, +40 mV is reached a 2nd AP is not fired, no more Na enters the cell, and
potassium channels remain open.
Repolarizing: Na voltage gated channels close, more K open (membrane potential returns
to resting)
By the time K channels close it becomes hyperpolarized (more than -70 mV) at -85mV
The cell returns to its original state and is ready for another stimulus.
REST=POLARIZED -70mV, reset Na and K channels, the neuron is reset to original
state so it can go through the process again.
NT/Neurotransmitter Receptor
-Excitatory NT: depolarizes neuron (-70mV to -55mV) YES AP!!!
Opens Na+ and Ca+2, closes K channels
- Inhibitory NT depolarizes neuron (-70mV to -85mV) Cl- channels open and K+ channels open.
NO AP
-Excitatory is needed to create an action potential
Neurotransmitters
Glutamate: Major neurotransmitter in the brain
● learning, memory, plasticity
● Open/allows entry (synaptic connects) Na+,Ca+2 channels into receiving or post-synaptic
neuron. This is an excitatory signal because it makes inside of cell positive and thus
excitatory.
● K+ channels may also close which creates an action potential
● There will be excess neurotransmitters which is bad because it will overstimulate.
Ways to clear NT:
1. NT hydrolyzing enzyme released by pre-synaptic neuron.
2. Reabsorb NT by pre-synaptic neuron so that AP will activate that NT.
GABA: Gamma Amino Butyric Acid
● Brain NT, derived from glutamate but does opposite of glutamate, inhibitory,
hyperpolarizes the cell and makes it more negative
● Opens K+ channels
● Opens and allows entrance of Cl● Both of these make the cell hyperpolarized.
Dopamine
● Excitatory: motivation, reward, pleasure
● Opens Ca+2 channels into the cell
● Recreational drug increases the life of dopamine
Senses:
Smell:
-strength of smell: number of NT, receptors, dendrites, ligand gated channels.
Smell=Olfaction
Olfactory Receptors: dendrites binddodor molecules and creates an AP convert into glumeri at
olfactory bulb which means the combination of odors stimuli converge and then send one signal
to olfactory cortex which tells the brain what you are smelling.
Taste:
The Five Tastes:
● Sweet, sour salty, bitter, and umani
● Sour/Salty are acidic
● Bittter/Sweet are Basic
● Umani is savory/meaty
The Tongue:
● Integrates smell (olfactory receptors), texture (mechanoreceptors) and temperature
(thermoreceptors) the taste are the receptors clustered into buds.
3 Parts of Brain Triggered While Eating:
1. Somatosensory and frontal cerebral cortex
● Perception of taste
2. Amygdala and Hypothalymus
● Emotional quality of the taste.
3. Hippocampus
● Memory of the taste
Hearing:
Sound waves enter the Outer Ear Canal.
In the Middle Ear or Eardrum the chains of auditory ossicles (small bones) vibrate.
The vibrations cause a disruption in the Inner Ear Cochlea (fluid) this makes the basilar
membrane move and makes hair cells vibrate that talk to neurons (mechanoreceptors). These
mechanoreceptors then release glutamate which talk’s to brain’s temporal lobe. At this point
your brain comprehends the sound that has entered your ear.