Nervous System Flashcards
Nervous system
Coordinates all activities of animals
CNS
brain and spinal cord
PNS
nerves and ganglia
Neuron anatomy
Cell body contains the nucleus
Dendrites receive input
Axon sends output
2 types of axon?
Unmyelinated / Myelinate
Neuroglia
4 types
Support for nerve cells
Schwann cells, myelin in PNS
Oligodendrocytes, myelin in CNS
Astrocytes, Microglia
3 types of neurons
Sensory - afferent neurons connect to receptors
Motor - efferent neurons connect to effectors
Interneurons - connect other neurons together
Simplest neural circuit
A reflex arc
Receptors detect stimuli ->
Sensory neurons transmit info from receptors to CNS ->
Interneurons in CNS integrate sensory signals and coordinate motor response ->
Motor neurons carry signals from the CNS to specific effectors->
Effectors (muscles or glands) respond to signal transmitted by nerves
Reflex def’n
A quick reaction that occurs in response to something before you even realize that you are reacting
A local motor response to a local sensation, same body region responds to the stimulus
Effectors
Muscles or glands, Communicated with by an efferent neuron
Reflex arcs involve at least…
Two neurons
Interneurons
Connect neurons in the brain with neurons in the spinal cord
Neuron vs Axon
Neuron is a cell, axon is a cellular process
BP regulation is monitored by what nerve?
Glossopharyngeal nerve -> vagus
Glossopharyngeal -> interneuron -> spinal nerves
Myelinated vs Unmyelinated neuron
Schwann cell has gaps vs Schwann cell is singular and wraps the entire axon
Nerves are composed of…
Nerve processes (usually axons) wrapped in connective tissue
Sensory neurons have cell bodies located…
Motor neurons have cell bodies located…
in the spinal ganglion
in the CNS
Cell bodies of neurons located either:
in CNS
in ganglia outside the CNS
Nerve impulse = …
Action potential = electrochemical message of neurons
All or none phenomenon
Nerve fiber can vary its signal by changing frequency of signal
Higher frequency = greater level of excitation
Four stages of nerve impulse conduction
At rest
depolarization
repolarization
Reestablishment of concentration gradients for Na and K
Axon hillock
This is where the action potential originates
4 channels in a cell
Potassium channel always open
Voltage-gated potassium channel
Voltage-gated Na+ channel
Na/K pump
Resting membrane potential of neuron
-70 mV
generated by difference in energy between Na and K
At rest…
Cells are polarized at -70 mV
High K concentration inside the cell relative
Low Na concentration inside the cell relative
Depolarization
Na+ voltage gated channel pops open when neuron receives an Action Potential sufficient enough to engage it
Na+ rushes in down its concentration gradient, K+ rushes out down its concentration gradient
At local level of a depolarizing cell…
Brief reversal of polarity of the cell membrane results in a transition from -70 mV to a positive membrane potential
Repolarization
Na+ voltage gated channel snaps shut
K+ voltage gated channel opens and K+ enters down its concentration gradient
Na/K pump re-establishes resting membrane potential of -70 mV using active transport of K+ in and Na+ out at a rate of 2 in, 3 out
As a result of depolarization…
The action potential is propogated along the length of the axon, starting at the axon hillock and moving towards the synapse
Synapse
Nervous impulses must…
A small gap between neurons
Cross the synapse in order to be transmitted
Electrical synapse
Relative concentration?
Utilize what?
Relative rate of transmission?
Very few and they are found in all nervous systems, including the human brain
-gap junctions - a type of intercellular complex between adjacent neurons. This allows ions and therefore electrical current to flow directly through the synapse
-Passive current flow is virtually instant, so it can communicate without delay
The end of the axon consists of…
Axon knobs which connect to dendrites of other neurons
Presynaptic neuron vs. Postsynaptic neuron
Pre- brings impulse to synapse, post- receives impulse
Gap between axon knob and dendrite is …
describe it
Synaptic cleft, a 20 nm fluid-filled gap
Axon knobs contain vesicles that house…
and are released by…
Neurotransmitters (acetylcholine)
AP stimulates the release of acetylcholine (neurotransmitter) into the synaptic cleft
How does acetylcholine act after its activated by an action potential?
What generates the AP in the next neuron?
_ -> __ ->
Its vesicle attaches to the presynaptic neuron’s membrane and Ach is exocytosed from the pre-synaptic neuron.
It attaches to postsynaptic neuron, causing ion channels to open.
Sodium rushes into the postsynaptic neuron along its concentration gradient and generates an action potential in the postsynaptic neuron
Electrical signal, Chemical signal, Electrical signal
What breaks down acetylcholine?
Acetylcholinesterase inactivates Ach and recycles Ach into choline and acetate.
Choline is reabsorbed and Ach is resynthesized and stored in vesicles in the pre-synaptic neuron.
Nerve agents
Inhibit Acetylcholinesterase, so its effects are never diminished as long as its effects are active.
What is a reflex arc and how does it work? Be sure to use and explain the following terms in your answer: receptors, sensory neurons, interneurons, motor neurons, effectors. Also, describe an example of a reflex arc.
Sensory receptors detect some sensory input, sensory neurons send afferent signals to the CNS, an interneuron communicates this information to a nerve, that nerve sends an efferent message to an effector muscle. An example of a reflex arc is detecting heat on your hand, your sensory neurons sending an afferent message to the CNS, the CNS sending an output through an interneuron to a spinal nerve, that nerve sending out an efferent neural message to the effector muscles of your hand to retract your hand.
What is the difference between a neuron and a nerve?
A nerve is a bundle of neurons wrapped in a connective tissue. Individual neurons can be plentiful whereas nerves are not as plentiful. A grouping of neurons form a nerve pathway.
What is the role of potassium ions in nerve impulse conduction? Be specific.
Potassium ions form a relative negative membrane potential across the plasma membrane in a neuron at rest. Potassium pumps out as voltage-gated potassium channels open and cause it to rush out down its concentration gradient. This causes the membrane to repolarize. The Na/K pump restores membrane potential with high potassium-low sodium inside the neuron.
What is the role of sodium ions in nerve impulse conduction? Be specific.
Sodium ions work in conjunction with potassium to form a relatively electronegative membrane potential. As the neuron depolarizes, sodium ion channels open and allow sodium to rush in down its concentration gradient. The negative membrane potential restored by the Na/K pump during repolarization.
What is the role of the sodium-potassium pump with regard to nerve impulse conduction?
The Na/K pump restores high K concentration in the axon and high concentration of sodium outside of the neuron. This is accomplished by active transport, and it moves potassium and sodium across the membrane at a ratio of 2 potassium, 3 sodium respectively - generating an electronegative membrane potential.
What changes in permeability occur in the neuron cell membrane over time? Why are these important for nerve impulse conduction?
Na+ voltage gate opens during depolarization -
Na+ voltage gate closes during repolarization - K+ voltage gate opens during repolarization
Na/K Pump restores electronegative membrane potential
After an action potential has been generated in a particular region of an axon, why is there a bit of a time lag before another action potential can been generated in the same place?
The cell must repolarize and re-generate that relatively electronegative membrane potential by creating high potassium in the axon with high sodium outside of the axon.
