Nervous System Flashcards
9.1 INTRO TO NERVOUS SYSTEM 9.2 ELECTRICAL IMPULSE 9.4 AUTONOMIC NERVOUS SYSTEM
NERVOUS SYSTEM
An elaborate communication system that contains more than 100 million nerve cells in the brain alone
Responses to changes in internal and external environments are made possible by
electrochemical messages relaid to and from the brain
There are 2 types of cells in the nervous system:
Glial Cells - non conducting cells important for structural support and metabolism of the nerve cells
Neurons - nerve cells that conduct nerve impulses; the functional units of the nervous system
Glial Cells -
non conducting cells important for structural support and metabolism of the nerve cells
Neurons -
nerve cells that conduct nerve impulses; the functional units of the nervous system
Sensory neurons
Aka afferent neurons
Sense and relay info from the environment to the CNS
Located in clusters called ganglia located outside the spinal cord
Interneurons
Link neurons within the body
Found mainly throughout brain & spinal cord
Integrate the sensory information and connect neurons to outgoing motor neurons
Motor neurons
Aka efferent neurons
Relay info to the effectors like muscles, organs, and glands
Dendrite
Receive information from other nerve cells
Conduct nerve impulses toward the cell body
Node of Ranvier
The areas b/w the sections of myelin sheath
Allows nerve impulse to jump from node to node, speeding up transmission
Axon
Projects nerve impulses away from the cell body
It carries the nerve impulse toward other neurons
Myelin Sheath
Formed by special cells called Schwann cells
It insulates by preventing the loss of charged ions from the nerve cell
Speeds the rate of nerve impulse transmission
Speed of nerve impulse is affected by
Diameter of the axon (small = faster)
Whether the axon is myelinated or not (if there is then its faster)
The Reflex Arc
Reflexes like reaching to touch a hot stove do not require information to travel to your brain and get processed
Reflex Arc -
5 essential components
simple connection of neurons that result in a reflex action in response to a stimulus
Involuntary and often unconscious
The receptor The sensory neuron The interneuron The motor neuron Effector
ELECTRICAL CURRENT
Current is the movement of electrons along a wire
NERVE IMPULSE
Is an electrochemical message created by the movement of ions through the nerve cell membrane
ELECTRICAL CURRENT
Electrical current diminishes as it moves through the wire
NERVE IMPULSE
Nerve impulses remain as strong at the end of a nerve as they were at the beginning
ELECTRICAL CURRENT
Electricity relies on external energy source to push electrons
NERVE IMPULSE
Nerves use cellular energy to generate current
ELECTRICAL CURRENT
Electricity moves faster
NERVE IMPULSE
Nerve impulse is slower than electrical current
The Giant Axon of the Squid
When a tiny electrode was placed inside the large nerve cell of the squid, the inside of the neuron is negative relative to the outside (at rest) … why?
Negatively charged protein molecules inside the cell are too large to leave the cell
Sodium-potassium pump located in the cell membrane actively pump out 3 Na+ out for every 2 K+ in
Nerve cell membrane is super permeable to K+ so K+ tends to leak out
Resting Potential
→ -70mV
→ polarized
Graded Potential
→ +ve
→ below threshold
Action Potential
→ +50mV
→ @threshold and over
→ depolarized
Resting Potential
When the difference in voltage b/w the inside and the outside of the neuron (at rest) is measured, it is charged and is called polarized membrane .
RESTING POTENTIAL = -70 mV
This separation of electrical charges by a membrane has the potential to work
Upon Excitation
Some stimulus cause the resting potential to move towards 0mV
Na+ channels open up, allowing Na+ to rush in
If enough Na+ rushes in causing the membrane potential to go from -70mV to -55mV
The voltage-gated Na+ gates open causing a rapid influx of Na+
Voltage-gated Na+ channels always closed until Na+ reaches threshold
This causes a charge reversal (aka depolarization)
Action Potential
The reversal of potential
A rapid change in the electrical potential difference across the membrane was detected every time the nerve became excited
Resting potential went from -70mV to +40mV when it was excited
Repolarization
Once the voltage inside the nerve cell becomes positive
The voltage-gated Na+ gates close (Na+ no longer enters)
K+ channels open (K+ leaves)
Repolarization Results in
an overall loss of positive charge from the neuron, making the charge move back towards the resting potential
K+ channels repolarization
stay open longer than needed, and allow more K+ to exit
Makes the cell more negative than resting potential (hyperpolarization)
repolarization pump
The Na+/K+ pump works to restore the potential back to -70mV known as
Refractory Period -
recovery time required before a neuron can produce another action potential
Movement of Action Potential
Similar to the wave
The action potential moves along the nerve cell membrane, creating a wave of depolarization and repolarization
Threshold Levels - All-or-None Response
A potential stimulus must be above the critical value to produce a response
Threshold level
min level of a stimulus required to produce a response
All-or-none response
a nerve or muscle fibre responds completely or not at all to a stimulus
↑ in intensity of the stimulus above threshold ≠ increased response
Neurons either fire maximally or not at all
When the depolarization reaches about -55mV
a neuron will fire an action potential. (this is the threshold)
If the neuron does not reach this critical threshold level
then no action potential will fire
If the threshold level is reached,
an action potential of a fixed size will always fire (for any given neuron), the size of the action potential is always the same
∴ the neuron either does not reach the threshold or a full action potential is fired
“ALL OR NONE” principle
The more intense the stimulus
the greater the frequency of impulses
Every neuron may have a different threshold level
Ex. a glass rod at 40 oC may cause a single neuron to reach threshold level, but the same glass rod at 50 oC will cause 2 or more neurons to fire
(more neurons firing = more neurons telling the brain info = ↑ frequency = ↑ stimulus
Synapses
the junction b/w 2 neurons or b/w a neurons and an effector (muscle or gland) (the action potential that travels through synaptic cleft)
Neurotransmitters
chemicals released from vesicles into synapses
Once the nerve impulse reaches the end of the axon, small vesicles containing neurotransmitter fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft
These neurotransmitters diffuse across the synaptic cleft and bind to receptors in the post-synaptic membrane
depolarization
This triggers opening of the sodium channels causing influx of sodium into the post-synaptic neuron causing depolarization
With the sodium channels open, the postsynaptic neuron would remain in a constant state of depolarization
How can the nerve respond to the next impulse if it never recovers?
Reuptake of neurotransmitter from the presynaptic neuron and neighboring glial cells
Degradation by enzymes (ex. Cholinesterase)
The greater the number of synapses
the slower the speed of transmission
Neurotransmitters can be
EXCITATORY: causing depolarization of post-synaptic neuron
INHIBITORY: causing hyperpolarization of post-synaptic neuron
EXCITATORY:
causing depolarization of post-synaptic neuron
INHIBITORY:
causing hyperpolarization of post-synaptic neuron
Summation
Effect produced by the accumulation of neurotransmitters from 2 or more neurons
A and B does not create action potential, no charge reversal
But when fired at the same time, it can cause depolarization of the post-synaptic membrane
D becomes more negatively charged when C is activated
Neuron C is inhibitory and causes hyperpolarization (influx of potassium channels, release more negative ions)
Inhibitory & Excitatory Neurotransmitters
Throwing a ball
Contracting triceps (excitatory) Relaxing biceps (inhibitory)
Inhibitory & Excitatory Neurotransmitters
Prioritization (ex. Biology class)
Listening to teacher voice (excitatory)
Looking at diagram on blackboard (excitatory)
Hearing background noise (inhibitory)
Sensing a draft in the classroom (inhibitory)
Inhibitory & Excitatory Neurotransmitters
Pain senses shut off in intense situation to help survival (inhibitory)
Acetylcholine
a neurotransmitter found in the end plates of many nerve cells
Acetylcholine Can act as
an excitatory (inhibitory in some other synapses) neurotransmitter on many postsynaptic neurons by opening the sodium ion channels Sodium rushes in and reverses the charge in the post-synaptic neuron (depolarization) Then degraded by an enzyme (cholinesterase) after the nerve impulse has been transmitted
What happens if you block cholinesterase?
When cholinesterase is inhibited, acetylcholine is released and not destroyed
Nerve cannot respond to the next impulse
Neurotransmitters and Depression
There is a link b/w neurotransmitters and depression
Dopamine
Norepinephrine
Serotonin
This has given a rise to a class of drugs that targets synaptic transmission
Ex. SSRI’s (selective serotonin reuptake inhibitors)
They work to block the reuptake of neurotransmitters after the nerve impulse has been transmitted
This serves to prolong the effect of the neurotransmitter
SSRI works if the person has serotonin imbalance
It allows the synapses to reach threshold → fires one
does not work for everybody because some people don’t have serotonin imbalance or receptors for serotonin
if you didn’t have a problem before, you will after you take this drug because your body maintains homeostasis. If they repress reuptake of serotonin, homeostasis is maintained if there is less release of serotonin. If you get off this drug, your body is not releasing enough serotonin.
AUTONOMIC NERVOUS SYSTEM
It is part of the PNS
It works with the endocrine system in adjusting the body to changes in the external and internal environment
All autonomic nerves are motor nerves that regulate the organs of the body without conscious control
Autonomic Nerves
made up of the sympathetic nervous system and the parasympathetic nervous system
Autonomic Nerves Sympathetic:
Prepares the body for stress
The neurotransmitters released:
Acetylcholine
Norepinephrine
Autonomic Nerves Parasympathetic
Restores the body’s normal balance
Only releases acetylcholine
Sympathetic & Parasympathetic
These 2 (often opposing) systems have to balance each other constantly for a person to stay healthy
