C4 - Nervous System Flashcards
The nucleus is located in the cell body also called the…
Soma
What do dendrites do?
Receive incoming messages from other cells
What does the axon hillock play an important role in?
Integrating incoming signals and transmission of electrical impulses down the axon
Signals arriving from the dendrites can be what 2 overarching types?
Excitatory or inhibitory
What happens at the axon hillock if it receives an excitatory signal?
It will initiate an action potential, sending it down the axon
Most mammalian nerve fibers are insulated by what?
Myelin, which is a fatty membrane
What does the myelin sheath do?
It prevents signal loss, or crossing of signals. It also increases the speed of conduction in the axon
In the CNS and PNS, what makes the myelin sheath?
In the CNS the oligodendrocytes make it while in the PNS it is the Schwann cells
At certain intervals along the axon, there are small breaks in the myelin sheath with exposed areas of axon membrane called…
The nodes of ranvier
Nodes of ranvier are critical for what?
The rapid signal conduction along the axon
What is the place at the end of the axon called? What is released at this area?
The nerve terminal or synaptic bouton (knob) and it releases neurotransmitters
Neurons are not physically connected to one another, instead they have small spaces between the two neurons called…
The synaptic cleft
Together the nerve terminal, synaptic cleft, and postsynaptic membrane are known as the…
Synpase
Where do neurotransmitters released form the axon terminal go to?
They go through the synaptic cleft and bind to receptors on the postsynaptic neuron
In the PNS cell bodies of neurons of the same type are clustered together into what?
Ganglia
In the CNS axons may be bundled together to form what? How are they different from nerves?
It forms tracts, unlike nerves, tracts only carry one type of information (motor, or sensory, not both)
The cell bodies of neurons in the same tract are grouped together into what?
Nuclei
What cells in the nervous system support neurons? Also structural roles
Glial cells, or neuroglia
What are Astrocytes function?
They nourish neurons and form the BBB which controls the transmission of solutes from the bloodstream into nervous tissue
What are ependymal cells function?
They line the ventricles of the brain and produce CSF which physically supports the brain and serves as a shock absorber
What are microglial cells functions?
They are phagocytic cells that ingest and break down waste products and pathogens in the CNS
What is a cells resting membrane potential at? What does this term mean?
It is a cells net electrical potential difference that exists across the cell membrane. It is at about -70mV
What are the 2 most important ions involved in generating and maintaining the resting potential? What ion is higher concentrated intracellular vs extracellular
Potassium and sodium. Potassium has a way higher concentration inside the cell while sodium has a higher concentration outside
The constant facilitated movement of sodium into the cell and potassium out of the cell is made by what?
Potassium leak channels and sodium leaks channels for each.
What is the equilibrium potential of potassium and equilibrium potential of sodium at? And what again is the resting membrane potential at? Why is it so close to one vs the other?
The sodium equilibrium potential is about 60mV
The potassium equilibrium potential is about -90 mV
The resting membrane potential is at -70mV, much closer to that of the potassium equilibrium potential. This is due to the cell being much more permeable to potassium
There is also a means of moving both sodium and potassium back against their gradients, this is done through what? And what direction does it go?
The Na+/K+ ATPase continually pumps potassium into the cell and sodium out of the cell
- more ATP is spent by this process than any other single purpose in the body
In terms of polarization what do inhibitory and excitatory inputs cause?
Inhibitory inputs cause a drop in membrane potential hyperpolarizing the cell while excitatory causes a increase depolarizing the cell
What needs to happen for a cell to depolarize
It needs to reach a certain threshold (it is an all or nothing mechanism) usually falls in the range of -55mV to -40mV
The additive effect of multiple signals on a postsynaptic neuron is known as what?
Summation
There are two types of summation, describe each one
Temporal and spatial
In Temporal summation it is multiple signals that are integrated during a relatively short period of time
In spatial summation, the additive effects are based on the number and location of the incoming signals
If the cell is brought toward threshold, what channels open?
Voltage-gated sodium channels open in the membrane
When the cell reached +35mV what happens?
The sodium channels are inactivated and and voltage-gates potassium channels open
What are the three states that sodium channels exist in? When does each happen
Closed - before the cell reaches threshold
Open - from threshold to approximately +35
Inactivate - from approximately +35 to the resting potential
The restoration of negative membrane potential is called what? In fact it is often overshot by the rush of K+ into the cell causing…
Restoration of negative potential is called repolarization but when overshot it’s called hyperpolarization
What are the 2 types of refractory periods? Describe each
Absolute and relative
Absolute refractory period - no amount of stimulation can cause another action potential to occur
Relative refractory period - there must be a greater than normal stimulation to cause and action potential
What gradients does the action potentials rely on to occur?
Both the electrical and chemical gradients
Briefly sum up what happens in the polarization process of a cell
Action potentials rely on chemical and electrical gradients, neuron starts at -70mV resting potential (potassium high inside and sodium high outside of cell). Once cell reaches threshold. Sodium voltage gated channels open up and sodium floods the cell, making more positive (depolarization). Sodium channels become inactivated and potassium voltage gated channels open up and potassium flows out of cell repolarization the cell. Along with it, it gets overshot and hyperpolarization occurs. Then the Na+/K+ ATPase works to restore the resting potential and sodium and potassium gradients.
What does saltatory conduction refer to?
The signal hopping from node to node (node of ranvier to node of ranvier) on an axon. This increases the conduction of the nerve impulse
Prior to release neurotransmitters are stored in what?
Membrane bound vesicles in the nerve terminal
What happens when the action potential reaches the nerve terminal? What is the resulting effect?
Voltage gated calcium channels open, this allows calcium to flow into the cell and sudden increase in intracellular calcium triggers fusion of the membrane bound vesicles with the cell membrane at the synapse, causing exocytosis of the neurotransmitter
If the receptor on the postsynaptic neuron is a ligand gated ion channel vs a G protein-coupled receptor what effects does each have?
If it’s a ligand gated ion channel, the postsynaptic cell will either be depolarized or hyperpolarized
If it’s a G protein-coupled receptor, it will cause either changes in the levels of cyclic AMP (cAMP) or an influx of calcium
What are the 3 ways neurotransmitters are removed from the synaptic cleft? Give common examples of each
1 - can be broken down by enzymatic degradation (common example is breakdown of ACH from ACHe
2 - neurotransmitters can be brought back into the presynaptic neuron using reuptake carriers (common examples being serotonin (5-HT) or Dopamine (DA) and norepinephrine (NE))
3 - they can simply diffuse out of the synaptic cleft (common example being nitric oxide)
What is the most numerous type of neuron of the 3? What behavior are they linked to?
Interneurons. They are often linked to reflexive behavior and are predominately located in the brain and spinal cord
What is white and grey matter? Where do they lie in the spinal cord and brain?
White mater consist of axons encased in myelin sheath, while grey matter consists of unmyelinated cell bodies and dendrites
In the brain white matter lies deeper than grey matter, but in the spinal cord the white matter lies on the outside of the cord while the grey is deeper within
What 4 segements can the spinal cord be divided into? What is the spinal cord protected by?
Cervical, thoracic, lumbar, sacral. All protected by the vertebral column
Where do sensory neurons enter and motor neurons leave the spinal cord?
Sensory neurons enter dorsally and motor neurons leave ventrally
The cell bodies of sensory neurons are found where?
In the dorsal root ganglia
The peripheral nervous system includes what nerves?
10 of the 12 cranial nerves (the olfactory, and optic nerves are technically outgrowths of the CNS) and 31 pairs of spinal nerves
What are all the divisions of the nervous system and their branches? Name them all
The nervous system breaks up into the PNS and CNS, CNS branches into the brain and spinal cord. The PNS splits up into the autonomic and somatic nervous system, then the autonomic nervous system further branches into the sympathetic and parasympathetic nervous system.
Main difference between the somatic and autonomic nervous system?
The somatic nervous system is under conscious control and consists of sensory and motor neurons distributed throughout the skin, joints, and muscles
The ANS manages the involuntary muscles associated with many internal organs and glands like respiration, HR, sweating, piloerection, body temp, etc…
What is different about the synapsing of neurons between the ANS and SNS?
A motor neuron in the SNS goes directly from the spinal cord to the muscle without synapsing
In the ANS two neurons work in series to transmit messages from the spinal cord, first neuron is known as the preganglionic neuron whereas the second is the postganglionic neuron
What is the main roles of the parasympathetic and sympathetic nervous systems?
Parasympathetic nervous systems is to conserve energy while the sympathetic nervous system is to respond to stress
What is the neurotransmitter responsible for parasympathetic responses in the body? Where is it released?
Acetylcholine, released in both preganglionic and postganglionic neurons
What nerve is the main one used in the parasympathetic nervous system and what regions does it innervate?
Cranial nerve 10 (Vagus nerve) it innervates the thoracic and abdominal cavity
List as many functions as you can that the parasympathetic nervous system does?
-Constructs pupils
-Stimulates saliva flow
-constricts bronchi
-slows heartbeat
-inhibits release of glucose
-stimulates bile release
-inhibits adrenaline production
-stimulates peristalsis and secretion
-contracts bladder
-promotes erection of genitals
List as many functions that you can that the sympathetic nervous system does?
-dilates pupils
-inhibits salvation
-relaxes bronchi
-accelerates heartbeat
-stimulates glucose production and release
-inhibits peristalsis and secretions
-secretion of adrenaline and noradrenaline
-inhibits bladder contractions
-stimulates orgasm
-stimulates sweating or piloerection
What are the two types of reflex arcs?
Monosynaptic and polysnaptic
What type of reflex arc is the knee jerk reflex and the withdraw reflex? Explain why? And what makes them different from one another
The knee jerk reflex is a monosynaptic reflex arc. This means there is a single synapse between the sensory neuron that revives the stimulus and the motor neuron that responds to it. When the reflex occurs the extension of the leg which lessens the tension on the patellar tendon protecting it from possible injury
The withdraw reflex is polysnaptic meaning there is at least one interneuron between the sensory and motor neurons. When pain is felt in one leg it contracts lifting the foot away from the source of pain but for the person to maintain balance it also needs to firmly plant the other foot on the ground. For this to happen Interneurons in the spinal cord provide the connections from the incoming sensory signal to the motor neurons in the support limb
