Nervous Tissue- Topic 10
Terms in this set (48)
Whats the function of the nervous system?
The main control and regulatory system of the body that communicates electrically (with action potentials) and chemically (with neurotransmitters) to send messages very quickly from the Central Nervous System (the brain and spinal cord) to the periphery of the body and from the periphery of the body to
Specialized structures that detect changes=sensory input (temperature, pressure, touch, etc.).
Nerve pathway through which sensory input is transmitted to CNS and is formed by axons of sensory neurons.
Structure (CNS) that analyzes the sensory input and makes a decision to respond to thechange; Decision is made by interneurons, also called association neurons.
The nerve pathway through which motor output is sent away from CNS and is carried by axons of motor neurons.
carry out the decision (motor output).
Examples of Sensory Receptors:
Examples would include the eyes, Merkel/tactile cells, ears, temperature and pain receptors (nociceptors).
This division manily controls skeletal muscles of the body and is voluntary.
This division is also called visceral division; it carries signals to internal organs (viscera) like glands, cardic muscles, and smooth muscles. It is involuntary.
Enclosed and protected by the cranium and spinal cord.
Terves (spinal and cranial nerves) and ganglia (like dorsal root ganglion) has sensory and motor. It also has somatic and visceral division.
This neuron has an extention coming off the soma that divides into a dendrite and an axon; seen in sensory neurons of dorsal root ganglion.
Has one dendrite and one axon. Rare form. Found in sensory organs (like olfactory receptor/smell).
This is the most common neuron. Multipolar neurons have many more branches of dendrites than the other two neuron types but only one axon.; Found mostly in CNS.
Are receiving regions of neurons. Local potentials are usually created on dendrites and then travel to axon hillock.
This part of the neuron contains the nucleus and other organelles.
Are conducting regions of neurons. Can have a myelin sheath (myelinated axons/fibers) or lack a myelin sheath (unmyelinated axons/fibers).
Describe the location of the cell bodies of each neuron within the nervous system:
Somas of neurons and dendrites are located in the gray matter of the brain and spinal cord. If somas are located outside CNS, those places are called ganglia.
List four types of CNS glial cells and their functions:
• Ependymal cells
Form the myelin sheath in the brain and the spinal cord.
Line the cavities of the brain (ventricles) and spinal cord(central canal).
Phagocytize and destroy microorganisms, foreign matter, and dead nervous tissue.
Have the most functions and participate in forming the BBB.
Describe how the anatomy of each CNS glial cell supports its fucntion:
• Oligodendrocytes - these glial cells have as many as 15 armlike projections. These projections reach out to
surrounding nerve fibers and form the myelin sheath around different axons.
• Ependymal cells - these cuboidal epithelial cells are great for lining the internal cavities of the brain and
spinal cord. These cells produce the cerebrospinal fluid (CSF) that bathes the CNS and its cavities with the
nutrient rich fluid.
• Microglia - these cells have a soma with many fingerlike projections. These projections allow the microgliato probe, attach, and destroy cellular debris or foreign material that they come across.
• Astrocytes - the most abundant glial cells that have a star-shaped appearance with armlike projections to connect to capillaries in the brain. Form a tight seal called the blood-brain barrier.
List the two types of PNS glial cells:
• Schwann cells
These glial cells form the neurilemma and the myelin sheath around all PNS nerve
Provide electrical insulation and regulate chemical environment of neurons.
Describe how the anatomy of the PNS glial cells supports its fucntion:
• Schwann cells - this cell wraps itself around individual nerve fibers forming the internodes. Portions not covered by the cell are called nodes of Ranvier.
• Satellite cells - these cells surround the somas. Their thick covering protects the soma much like the Schwann cells protect the nerve fiber by providing electrical and chemical regulation.
The abillty to trnasport/allow solvants through a membrane.
Explain how ion channels affect neuron selective permeabiltity:
When ion channels are open, permeability of plasma membrane is increasing. When ion channels are closed, solutes will not be able to pass through.
ECF concentration is high, ICF concentration is low.
ICF concentration is high, ECF concentration is low
ECF concentration is high, ICF concentration is low.
Unequal distribution of ions across the plasma membrane (see D3) due to its selective permeability. Normally permeable to Na and K (due to constantly open channels) and not permeable to cytoplasmic anions (PO4-, SO4-, organic acids, and proteins).
A voltage difference across the plasma membrane due to unequal distribution of ions, selective permeability of membrane and Na/K pump. has the "potential" to cause a flow of ions.
Constantly open ion channels
These channels are constantly open and allows ions to move in and out the cell as long as teh solute fits throught the channel opening.
Gated ion channels
These channels open in response to signals.
Explain how constantlly open ion channels cause the development of the resting membrane potential (Vm) in neurons:
Constantly open ion channels allow ions to pass through the plasma membrane along the concentration gradient. Na leaks into the cell and K leaks out of the cell. To maintain the concentration gradient, the Na/K
pump re-establishes the electrical conditions across the plasma membrane to maintain Vm.
Ligand ion channels
open in response to chemicals attaching to them (ex: ligand-gated Na channels on
junctional folds of NMJ)
Voltage gated ion channels
open in response to voltage change (ex: voltage gated Na channels on the axon
hillock, forming the trigger zone)
Identify the voltage ion channels that are essential for the development of the action potential:
• two types:
• voltage gated Na channels-open first and cause depolarization (Na rushes in and brings positive charge)
• voltage gated K channels are slower and cause the repolarization of the cell (K moves out of the cell and takes
away positive charge), as well as the hyperpolarization.
Discuss the sequence of events that occur for an action potential to be generated:
1. Chemicals (neurotransmitters) attach to ligand gated channels on dendrites of neurons and cause a local potential.
2. Local potential travels towards the axon hillock
3. If local potential is strong enough to reach threshold at axon hillock, voltage gated channels open.
4. Na rushes into the neuron and starts the depolarization wave.
5. When Na channels become inactivated, voltage gated K channels open fully and K exists the neuron initiating the repolarization. Steps 4 and 5 are an ACTION POTENTIAL (nerve signal).
6. Action Potential is conducted/propagated along the axon. In an unmyelinated axon, conduction is continuous (slower). In a myelinated axon, conduction is saltatory (faster).
Describe the role of the sodium- potassium pump in maintaining the Vm and making continued action poetntials possible:
The Na+/K+ pump allows for future action potentials by reestablishing the electrical conditions across the plasma membrane and maintaining the Vm. It pumps K ions back into the ICF and Na ions into ECF. As the cell re-establishes its electrical conditions, it can be excited (depolarized), which brings it closer to threshold when generation of action potential is possible.
A minimum change in voltage across the plasma membrane (around -55mV) that can open voltage gated Na and K channels and generate an action potential(nerve signal).
Absolute refractory period
Period of absolute resistance to stimulation: absolutely no stimulus will trigger an action potential.
Relative refractory period
Period of relative resistance to stimulation: only a strong stimulus will trigger an action potential.
Explain the physiological basis of the absolute refractory period:
Absolute refractory period happens during the the period when Na+ gates are open, but inactivated. As such, no action potential can be generated in that portion of the plasma membrane.
Explain the physiological basis of the relative refractory period:
Relative refractory period happens during the period when K+ gates are open and extra K leaving the cell hyper polarizes the plasma membrane. When the plasma membrane is hyper polarized, it is further away from the threshold and only a strong stimulus will excite the cell.