Chapter 1 Flashcards
Nervous system consists of which two kinds of cells?
- Neurons
- Glia’s
What do neurons?
Receive information and transmit it to other cells
The adult human brain contains how many neurons on average?
86 billion. 16 billion in the cerebral cortex, 69 billion neurons in the cerebellum, 1 billion in the spinal cord and less than 1 billion in the rest of the brain
membrane (or plasma membrane)
A structure that separates the inside of the cell from the outside environment.
What is the surface of a cell?
The membrane
Which cells doesn’t have a nucleus?
Mammalian red blood cells
Protein channels in the membrane permit a controlled flow of…
Water, oxygen, sodium, potassium, calcium, chloride, and other important chemicals.
What is a nucleus?
The structure that contains the chromosomes
Mitochondrion
is the structure that performs metabolic activities, providing the energy that the cell uses for all activities
Ribosomes
are the sites within a cell that synthesize new protein molecules
Endoplasmic reticulum
a network of thin tubes that transport newly synthesized proteins to other locations. Some ribosomes might be attached.
All neurons have..
- A soma
- most also have dendrites, an axon and presynaptic terminals.
How does the motor neuron receives its actions
With its soma in the spinal cord, it receives excitation through its dendrites and conducts impulses along its axon to a muscle.
How does the sensory neuron receive
it is specialized at one end to be highly sensitive to a particular type of stimulation, such as light, sound, or touch. The sensory neurons conducts touch info from the skin to the spinal cord. Tiny branches lead directly from the receptors into the axon, and the cell’s soma is located on a little stalk off the main trunk.
What are dendrites?
- Are branching fibers with a surface lined with synaptic receptors responsible for receiving info and bringing it into the neuron
- Greater the surface area, more info it can receive
Dendritic spines
- These further branch out and increase the surface area of the dendrit
- The shape of dendrites vary and depend upon varying inputs
Cell body/Soma
a.Contains the nucleus, mitochondria, ribosomes, and other structures found in other cells
b. Responsible for the metabolic work of the neuron
c. Covered with synapses on its surface
Axon
a. Thin fiber of a neuron responsible for transmitting nerve impulses toward other neurons, organs, or muscles
b. Some neurons are covered with an insulating material called the myelin sheath with interruptions in the sheath known as nodes of Ranvier
c. Neuron can only have one axon
Presynaptic terminals
the end of an axon, releases chemicals that cross through the junction between that neuron and another cell
Afferent axon
Brings info into a structure
Efferent axon
carries information away from a structure
Interneurons/intrinsic neurons
Are those whose dendrites and axons are completely contained within a single
structure
Glia
Are the other major components of the nervous system that exchange chemicals with adjacent neurons and perform many functions
Astrocytes
- A kind of Glia
- Helps synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon
- Helps synchronize closely related neurons, enabling their axons to send messages in waves
- Important for generating rhythms, such as rhythm of breathing
- Dilate blood vessels to bring more nutrients into brain areas that have heightened activity
- Tripartite synapse– theory proposing that the tip of an axon releases chemicals that cause the neighboring astrocyte to release chemicals of its own, thus magnifying of modifying the message to the next neuron; possible contributor to learning and memory
- In some brain areas, they also respond to hormones and thereby influence neurons
Microglia
- Act as part of the immune system
- Remove waste material and other microorganisms (viruses and fungi) that could prove harmful to the neuron
- Proliferate after brain damage, removing dead or damaged neurons
Oligodendrocytes (in brain and spinal cord) & Schwann cells (in periphery of body
- Build the myelin sheath that surrounds the axon of some neurons
- Supply an axon with nutrients necessary for proper functioning
Radial glia
- Guide the migration of neurons and the growth of their axons and dendrites during embryonic development
- When embryonic development finishes, most of them differentiate into neurons and some differentiate into astrocytes and oligodendrocytes
What are the four major structures that compose a neuron
- Dendrites
- Soma
- Axon
- Presynaptic terminal
Which kind of glia cell wraps around the synaptic terminals of axons?
Astrocytes
The blood-brain barrier
a mechanism that surrounds the brain and blocks most chemicals from enterin
Why we need the blood-brain barrier?
- The immune system destroys damaged or infected cells throughout the body
- Certain viruses do cross the blood-brain barrier. When they do, can lead to long lasting, fatal consequences and even death
i. Examples– rabies, spirochete responsible for syphilis - Microglia are more effective against several other viruses that enter the brain, mounting an inflammatory response that fights the virus without killing the neuron; might control the virus without eliminating it
i. Ex– chicken pox (cells remain in spinal cord long after they’ve been eliminated from the body and may emerge decades later)
How does the blood-brain barrier works?
- Depends on endothelial cells that form the walls of the capillaries– outside they’re separated by small gaps but in the brain they’re joined tightly to block viruses, bacteria, and other harmful chemicals from passing into the brain
- Why similar defenses aren’t around our other organs—the barrier blocks useful chemicals too, such as fuels and amino acids; for these to pass through blood-brain barrier, there are special mechanisms that aren’t found in the rest of the body
- No special mechanism needed for small, uncharged molecules (oxygen, CO2) that cross through cell walls freely- Same with molecules that dissolve in the fats of the membrane
Active transport
a protein-mediated process that expends energy to pump chemicals from the blood into the brain
What is brought into the brain true active transport?
Glucose,amino acids, purines, choline, vitamines and iron. Insulina and some hormones.
What is a major advantage of the bloon-brain barrier
Keeps out viruses
Glucose
GlucoseIs a simple sugar that is the primary source of nutrition for neurons, only neuron that crosses blood-brain barrier in large amounts. Is the brains main fuel.
Thiamine
Is a chemical that is necessary for the use of glucose
Electrical gradient/polarization
a difference in the electrical charge inside and outside of the cell.
Resting potential
The difference in voltage in a resting neuron
Selective permeability
allowing some chemicals to pass more freely than others true the membrane
What can pass freely through channels that are always open?
- Oxygen,
- carbon dioxide,
- urea
- water
What can pass through channels/gates in the membrane?
- Sodium
- potassium
- calcium
- chloride
What happens when the membrane is at rest
- Sodium channels are closed
- Potassium channels are partially closed allowing the slow passage of sodium
sodium–potassium pump
a protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it. The sodium–potassium pump is an active transport that requires energy.
sodium–potassium pump
a protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it. The sodium–potassium pump is an active transport that requires energy.
Concentration gradient
difference in distribution of ions across the membrane
Why a resting potential?
- The resting potential prepares the neuron to respond rapidly
- Excitation of the neuron opens channels that allow sodium to enter the cell rapidly
- Because the membrane did its works in advance by maintaining the concentration gradient for sodium, the cell is prepared to respond
Action potentials
- A rapid depolarization of the neuron
- Messages sent by axons
What happens when an axon’s membrane is at rest?
the recordings show a negative potential inside the axon
Hyperpolarization
increasing the polarization or the difference between the electrical charge of two places
Depolarize in the neuron
reduce its polarization toward zero
Threshold of excitation
a level above which any stimulation produces a massive depolarization
The all-or-none law
the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold
3 principles behind the action potential
- At the start, sodium ions are mostly outside the neuron, and potassium ions are mostly inside.
- When the membrane is depolarized, sodium and potassium channels in the membrane open.
- At the peak of the action potential, the sodium channels close.
3 principles behind the action potential
- At the start, sodium ions are mostly outside the neuron, and potassium ions are mostly inside.
- When the membrane is depolarized, sodium and potassium channels in the membrane open.
- At the peak of the action potential, the sodium channels close.
Voltage-gated channels
- Membrane channels whose permeability depends upon the voltage difference across the membrane
- Sodium channels are voltage activated channels
- When sodium channels are opened, positively charged sodium ions rush in and a subsequent nerve impulse occurs
Voltage-gated channels
- Membrane channels whose permeability depends upon the voltage difference across the membrane
- Sodium channels are voltage activated channels
- When sodium channels are opened, positively charged sodium ions rush in and a subsequent nerve impulse occurs
propagation of the action potential
describes the transmission of an action potential down an axon. The propagation of an animal species is the production of off- spring. In a sense, the action potential gives birth to a new action potential at each point along the axon.
Myelin
an insulating material composed of fats and proteins.
Myelinated axons
those covered with a myelin sheath. Myelinated axons, found only in vertebrates, are covered with layers of fats and proteins. The myelin sheath is interrupted periodically by short sections of axon called nodes of Ranvier, each one about 1 micrometer wide
Saltatory conduction
- The “jumping” of action potentials from node to node
- Provides rapid conduction of impulses
- Conserves energy for the cell
- Instead of admitting sodium ions at every point along the axon, and then having to pump them out via sodium-potassium pump, a myelinated axon admits sodium only at its nodes
Local Neurons
Neurons without an axon exchange information with only their closest neighbors.
Graded potential
When a local neuron receives information from other neurons, it has a graded potential, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus.
