Exam 1 Flashcards
Reticular Theory
It was postulated by Joseph von Gerlach in 1871. Said the nervous system was one continuous network. (popularized by Camillo Golgi.)
Cell Theory
All living organisms are composed of one or more cells. The cell is the most basic unit of life. All cells arise from pre-existing, living cells. So, the nervous system (described by the Reticular Theory) was considered an exception to the cell theory.
Early Neuron Doctrine
The nervous system is made up of discrete individual cells (neurons). These units are in close proximity, but separate from one another. Proposed by Santiago Ramon y Cajal. Discovered this when using Golgi staining on bird’s brains.
What was evidence of the Neuron Doctrine?
Individual neurons in the central nervous system. There were gaps in between neuron synapses.
Current Neuron Doctrine
Neural Units (the NS is made of discrete units called neurons), Neurons are cells (discrete units are cells), and Specialization (neurons differ in size, shape, and structure according to their location of functional specialization.)
How many neurons are there?
100 billion neurons
What are the cells of the Nervous system?
Neurons and Glia
What are the 3 types of neurons?
sensory, motor, and interneurons
What are the types of glia cells (5)?
astrocytes, ependymal cells, microglia, oligodendrocytes, schwann cells
Neuron
They carry our major brain functions. They are specialized for reception, conduction, and transmission of electrochemical cells. Convert electrical signals to chemical signals, then back to electrical signals.
What mechanisms do neurons use to communicate?
Chemical neurotranmission (between a neuron and its target) and electrical impulses (within neurons)
What does neurotransmission require?
Requires 2 neurons minimum- one presynaptic neuron (cell sending the singal) and one postsynaptic neuron (cell receiving the signal)
What are the specialized neuronal parts?
Dendrites, soma/cell body, axon, presynaptic terminals
Motor neuron (efferent)
Has its soma in the spinal cord and receives excitation from other neurons and conducts impulses along its axon to a muscle.
Sensory Neuron (afferent)
Is specialized at one end to be highly sensitive to a particular type of stimulation (touch, light, sound).
Interneurons (intrinsice neurons)
Are those whose dendrites and axons are completely contained within a single strucutre. (most within the brain)
Glia cells
Aid and modulate neurons’ activities, approximately 1-5 trillion, and have five major types
Astrocytes
Star shaped, most abundant type of glia, involved in the Blood Brain Barrier (BBB), absorb excess neurotransmitter and release NT, provides nutrients to neurons (glucose, lactate), ionic balance, repair injury (form scar tissue), and in develop they help neurons migrate (radial glia)
Brain Protection?
Brain and spinal cord are the most protected organs in the body. There is physical (skull, membranes, ventricles) and chemical (BBB) protection.
Blood Brain Barrier (BBB)
Involves the selective nature of brain capillaries, small molecules like O2 and CO2 pass with ease, and big molecules have to be fat soluble or have a transporter.
The cellular basis of the BBB
There are tight junctions of blood vessel epithelial cells. There are astrocyte endfeet (endfoot processes). Both of these prevent leaks of cells of molecules from the blood into the brain.
Ependymal cells
Epithelium-like lining of the ventricular system, have cilia which circulate Cerebral Spinal Fluid (CSF) around the CNS, covered with microvilli which absorb CSF, choroid plexus
choroid plexus
a population of modified ependymal cells and capillaries to make CSF
Microglia
Immune defense (macrophage) and scavenge dead neurons, plaques, and pathogens. They eat problematic cells and monitor environment.
Oligodendrocytes
They provide support and insulate the axons through myelination.
Schwann Cells
Myelinate peripheral nervous system neurons
What is the difference between Oligodendrocytes and schwann cells?
One oligodendrocyte can extend its processes to 50 axons, wrapping approximately 1 micron of myelin sheath around each axon. Schwann cells can wrap around only 1 axon.
What does proper neuronal function depend on?
Neurons and glia cells
What are examples of organelles?
nucleus, mitochondria, microtubules, neurofilaments, lysosomes, endoplasmic reticulum (smooth and rough), golgi apparatus, and plasma membrane
Nucleus
stores DNA which is transcribed (through transcription) to RNA then translated (through translation) to a protein
Mitochondria
cellular power plants, consume oxygen and glucose to make ATP, stores and releases Ca++, has its own separate DNA, and has other roles (including membrane potential maintenance, signaling, cellular differentiation, cell death, controls cell cycle and cell growth)
Microtubule
Polymers of a protein called tubulin, involved in maintaining structure of the cell, make up the internal structure of cilia and flagella, cell division (mitosis and meiosis), and provide platforms for intracellular transport (movement of secretory vesicles, organelles, intracellular substances
Neurofilaments
They are the major component of the neural cytoskeleton. They provide structural support for the axon and to regulate axon diameter.
Lysosomes
cell’s waste disposal system, autophagy, and repair the plasma membrane
Endoplasmic Reticulum (ER)
interconnected network of flattened, membrane enclosed sacs. Made of smooth and rough ER
Smooth ER
Lipid metabolism (membrane formation), metabolism of carbohydrates, drug detoxification, attachment of receptors on cell membrane proteins, steroid metabolism, Ca++ storage and release
Rough ER
Protein synthesis at ribosomes and synthesize (lysosomes enzymes, secreted proteins, membrane bound proteins)
golgi apparatus
packages proteins inside the cell before they are sent to their destination. They are important in the processing of proteins for secretion.
What affects what crosses a plasma membrane?
Size and charge affect the rate of diffusion across a membrane.
How do neurons store energy?
In the form of an electrochemical gradient. (which allows neurons to send and receive signals)
Resting Membrane potential
The imbalance in both concentration of ions and the sum of charges of compounds inside versus outside the neuron. At rest, the membrane maintains an electrical polarization (diff in electrical charge between two locations). The inside of the membrane is slightly negative with respect to the outside (-70mV). The resting potential refers to the state of the neuron prior to the sending of a nerve impulse.
What forces work to maintain the resting potential?
Diffusion (selective permeability), concentration gradient (certain ions are more conc. either inside or outside the cell), electrostatic force (charge difference), and Na/K pump
Selective permeability
Allows some chemicals to pass more freely than other molecules pass. It is due to the opening and closing of ina channels. The membrane is selectively permeable.
Chemical Gradients
Chemicals separate as far from one another as possible. Selective permeability of the membrane leads to the build up of ions either outside or inside the cell. This creates a chemical force to push chemicals DOWN a concentration gradient.
Electrical Driving Force
Opposite charges attract, while the same charges repel. A buildup of charged chemicals (ions) can lead to electrical force.
Sodium Potassium Exchange pump
The Na/K pump pumps 3 Na out of the cell and lets in two K ions. The pump needs ATP to work. This pump maintains the resting membrane potential.
What is necessary for neurons to be able to send the electrical signal down the axon?
The resting membrane potential
Synapse
Junctions where Neurons communicate by transmitting chemicals.
Charles Scott Sherrington
In 1906, he coined the term synapse to describe the specialized gap that existed between neurons. Our teacher said he was one of the fathers of neuroscience.
How do neurotransmitters work?
They bind to receptors, causing changes in ionic concentration in the post synaptic cell.
Receptor receiving neurotransmitter?
The receptors are proteins in the synapse/body of neurons that bind neurotransmitters. They can alter ion channels or even pass ions through the membrane. The can be presynaptic OR postsynaptic.
Two kinds of synapses
excitatory and inhibitory
Excitatory synapse
When opened, an ion channel opens and changes the charge (more +) inside the post synaptic neuron. This increases the change of an action potential. It is usually to the body or dendrite of a neuron. Creates DEPOLARIZATION and is known as the Excitatory Postsynaptic Potential (EPSP).
Inhibitory synapse
When opened, an ion channel opens and changes the charge (more -) inside the postsynaptic neuron. This decreases the change of an action potential. Often located on the cell body or also at terminals that are synapsing with other neurons. Creates HYPERPOLARIZATION and is known as the Inhibitory Postsynaptic Potential (IPSP).
Integration of EPSP and IPSP
They control whether a neuron will respond to the signals. The response could be an action potential.
When does an action potential occur?
An action potential occurs when a threshold voltage is reached The threshold voltage varies from neuron to neuron.
Two types of summation
Spatial and temporal
Spatial summation
multiple signals must be near the same site to help each other alter membrane potential
Temporal summation
The signals must occur within a specific time period to help each other affect membrane potential.
What happens when threshold is reached?
Voltage gated Na and K ion channels open.
Threshold
the change in potential necessary to initiate an action potential
Three stages of an actin potential
- Depolarization 2. Repolarization 3. Hyperpolarization (Refactory)
axon hillock
where EPSPs trigger an action potential
Ten steps of an action potential
- Threshold potential is reached. 2. Voltage gated Na2+ channels open. 3. Na enters neurons. 4. Voltage gated K+ channels open. 5. K+ leaves neurons. 6. Na+2 channels close. 7. Neuron membrane potential returns to below threshold. 8. K+ channels close. 9. Membrane potential return to resting state after a brief hyperpolarization. 10. The Na/K pump restores ion concentration.
Propagation (AP)
describes the transmission of the action potential down the axon. The action potential does not directly travel down the axon.
Action potential
A nerve signal that is an electrochemical message of neurons. An all or none phenomenon. The signal is varied by changing the frequency of signal conduction. It is an active process that requires ATP. It is non-decremental and it is short (<1msec).
Positive feedback loop in action potential
Positive feedback loop of activation of Na+ conductance explains the regenerative property of action potentials.
Myelin
an insulating material composed of fats and proteins.
Nodes of Ranvier
The gaps between sections of Myelin Sheath. This is also the location where the action potential is regenerated at each node of ranvier.
Saltatory conduction (high speed conduction)
When the action potential is only regenerated at each node of Ranvier. The action potentials depolarize the membrane only at the nodes. This action potential is faster than unmyelinated AP propagation.
Symptoms of Multiple Sclerosis
Weakness and clumsiness, stiffness and gait disturbances, visual disturbances, and mental disturbances (including lack of judgement, emotional liability, sudden weeping or laughter).
Epidemiology of Multiple Sclerosis
MS was first described in 1868. It affects mainly caucasians. It is the most common degenerative disease of young adults (1 per 400). The average age of onset is 28(female) and 30 (male). The female to male ratio is 2:1. It is a chronic illness with cumulative disability.
Etiology of MS
It’s unknown (maybe genes, environment, or combo). It is a autoimmune attack against oligodendrocytes (clonal expansion of B cells and T cells). It leads to inflammation of the central nervous system’s (brain and spinal cord) white matter (where the myelin is located).
Role of genetics in MS
Monozygotic (identical) twin concordance rate is 30% while dizygotic twin (fraternal) concordance rate is 5%. MS seems to be genuinely polygenic (chromosomes 1, 6, 10, 17, 19).
Cell and Axon Loss in MS
The loss of myelin causes neurons to be much more susceptible to apoptosis (cell death). There is also plaque formation (scar tissue). Demyelination also happens (induced axon loss is irreversible). The progressive disability is believed to result from cumulative axon damage and degeneration, along with neuron loss- brain atrophy.
The treatments of MS
Corticosteroids which reduce inflammation.
Immune system inhibitors (beta interferons, glatiramer acetate (copaxone), dimethyl fumarate (tecfidera), and fingolimod (gilenya). Other options include physical therapy and muscle relaxants.
Neurotransmission (between neurons)
The action potential release of neurotransmitter from a vesicle into the synapse.
How does an AP cause release of neurotransmitters?
When the AP reaches the terminal, voltage gated Ca2+ channels open, letting Ca2+ into the neuron terminals. This initiates neurotransmitter vesicle docking at the plasma membrane of the terminal. The neurotransmitter is released into the synapse.
Neurotransmitters
Chemical messengers that carry the message of the nerve impulse across the synapse (released into the synapse). They bind to receptors and cause changes in the ionic concentration in the post-synaptic cell.
What are the criteria for a neurotransmitter?
Chemical must be produced or found within a neuron. When neuron is stimulated (depolarized), a neuron must release the chemical.
When released, it must act on a receptor and cause a biological effect.
After released, it must be inactivated.
It applied exogenerously, it should have the same effect as when it is released by a neuron.
What is a structure with high maintenance?
a synapse
What determines if a neurotransmitter with be inhibitory versus excitatory?
Depends on the RECEPTOR, not the neurotransmitter. For example, acetylcholine is excitatory in the muscles, but inhibitory in the heart.
What can end neurotransmission?
Enzymatic breakdown, reuptake by neuron, uptake by glia
Main neurotransmitter groups
- small molecule neurotransmitters
2. large molecule neurotransmitters
Small molecule neurotransmitters
Acetylcholine, biogenic amines(NE, Epi, histamine), amino acids (glycine, GABA, glutamate), and others (adenosine, endocannabinoids, gases)
Large Molecule Neurotransmitters
opioid peptides, hypothalamic peptides, pituitary peptides, brain gut peptides, insulin
types of receptors
- Ionotropic (ion channels)
- metabotropic (activates G proteins which can directly or indirectly regulate an ion channel)
- both alter the flow of + or - ions into the neuron
Ionotropic receptor
Embedded membrane protein with two parts.
- A binding site for a NT
- A pore that regulates ion flow to directly and rapidly change membrane voltage.
Metabotropic Receptor
Embedded membrane protein with a binding site for a neurotransmitter but no pore. They are linked to a G-protein and they:
- alter ion flow in a membrane channel
- formation of new ion channels
- production of new proteins
Electrical synapses
They are directly connect and include a direct ion transfer through gap junctions. They dont have neurotransmitters.
four ways of imaging the brain
PET, SPECT, MRI, fMRI
PET (Positron emission tomography)
- radioactive isotopes (interact with NT)
- measure the activity and distribution of drugs
- measure the concentrations and locations of drug receptors (which let you know which are bound and not bound)
- Access competition for receptors
- measure energy needs or blood flow
SPECT (single photon emission computed tomography)
- longer half life radioactive isotopes
- lower resolution than PET
- subset of PET
MRI (magnetic resonance imaging)
- uses a magnet to align H atoms
- uses radiofrequency (RF) waves create in phase H atoms
- measure of relaxation of H atoms after RF is turned off
- great resolution
- primarily shows anatomical features of the brain
fMRI (functional magnetic resonance imaging)
- Inject a magnetic dye to increase contrast
- can measure blood flow (blood oxygen level dependent (BOLD))
Phrenology
It was pseudoscience described by Franz Joseph Gall (1758-1828). He said skull measurements can give an index of psychological aptitudes. (This ended up being false but different parts of the brain having different functions arose from this.)
Flourens (1825)
He studied brain ablations in animals. He was the first to prove the mind was located in the brain, not the heart. He observed the effects of brain damage on motility, sensibility, and behavior. He was the pioneer of the modern theory of brain function (diff parts of the brain have diff functions).
two divisions of the nervous system
Central NS and peripheral NS
Anatomical divisions of the CNS
Spinal Cord and Brain (hindbrain, midbrain, and forebrain)
-information passes up and down through these divisions in the hierarchical manner
Spinal Cord
Relays information to and from the body and the brain. Includes motor pathways and sensory pathways (positional, pain, touch). The spinal cord also serves as a mini brain for some reflexes (pain reflex arc).
Long Neurons in the Spinal Cord
They transverse large portions of the spinal cord. These neurons tracts make up the majority of the white matter (myelinated).
White matter vs gray matter
White matter is myelinated and gray matter is not myelinated.
Short Neurons in the Spinal cord
They relay information from the white matter tracts to other neurons. These neurons typically make up the gray matter.
Spinal Cord Cross Section (5 parts)
Dorsal Root ganglia, white matter, gray matter, dorsal horn, ventral horn
Dorsal Root Ganglia
cell bodies of the sensory neurons
Gray matter
Cell bodies and dendrites
Dorsal Horn
Grey matter that receives several types of sensory information from the body.
ventral horn
grey matter that contains motor neurons
What are the three major divisions of the brain?
Hindbrain, Midbrain, Forebrain
What does the Hindbrain consist of?
The medulla, pons, and cerebellum
Where is the hindbrain located?
at the posterior portion of the brain
What structures of the brain combine and make up the brain stem?
Hindbrain structures, the midbrain, and other central structures of the brain (cortical structures, including thalamus, hypothalamus, and pineal gland)
Medulla
It is responsible for vital reflexes, including breathing, heart rate, vomiting, salivation, and coughing/sneezing
Cranial Nerves
Control sensory and motor functions in the head and many parasympathetic outputs to the organs. (they are a way to exit the skull)
Pons
Along with the medulla, contains the reticular formation and raphe system. It increases arousal (wakefulness) and readiness of other parts of the brain.
Cerebellum
Helps regulate motor movement, balance, and coordination. It is also important for shifting attention between auditory and visual stimuli. It is involved in playing an instrument and is quickly affected by alcohol.
Midbrain
Includes the Tectum and Tegmentum
Tectum
- Sensory processing.
- Superior and Inferior Colliculus (produces orienting movements to sight and sound)
Tegmentum
- Reticular formation (sleep/arousal/attention)
- Substantia Nigra (Motor control)
- VTA- Ventral Tegmentum Area (reward and addiction pathway induced by dopamine neurotransmitter)
What two parts make up the forebrain?
Subcortical regions and cerebral cortex
Subcoritcal regions
- limbic regions
- basal ganglia
- thalamus
- hypothalamus
What does the limbic system do? What does it include?
It is associated with motivation, emotion, drives, and aggression. It includes the amygdala, hippocampus, cingulate gyrus, olfactory bulb, and thalamus/hypothalamus.
amygdala
reward and fear
hippocampus
long term memory
cingulate gyrus
autonomic functions
olfactory bulb
smell
Patient H.M.
In 1953, HM underwent brain surgery to help reduce epileptic seizures. The hippocampus along with some surrounding neuronal tissue, was surgically removed (area in red). Because of HM, it is known that memory function originates in this region.
Thalamus
Relay station from the sensory organs. Also, main source of input to the cortex.
Hypothalamus
Signals the pituitary gland to alter the release of hormones. Affects sleeping and temperature regulation. Associated with motivated behaviors: emotional behavior, eating, drinking, sexual behavior.
Basal Ganglia
Collection of nuclei just below the cortex. (caudate, putamen, nucleus accumbens, globus palidus, substantia nigra, subthalamic nucleus)
Controls- voluntary motor movement and reward system.
Important for: attention, cognitive function, memory, emotional expression
Related disorders: Parkinsons, tourette’s syndrome, drug addiction
Forebrain (two parts)
subcortical and cerebral cortex
Subcortical
Limbic system, basal ganglia, thalamus, hypothalamus
Hemispheres of the brain
Each side receives sensory information and controls motor movement from the opposite (contralateral) side of the body. They are “virtually” identical.
corpus callosum
connects the two hemispheres of the brain
Lobes of the cerebral cortex
Frontal lobes, parietal lobes, temporal lobes, and occipital lobe (only 1 of these)
The occipital lobe
Posterior end of the cortex.
Known as the primary visual cortex.
Highly responsible for visual input.
Damage can result in cortical blindness (differs from retina induced blindess).
The parietal lobe
Contains the primary somatosensory cortex. (touch and proprioception)
The parietal lobe is essential for spatial information as well as the numerical information.
The temporal Lobe
Lateral portion of each hemisphere near the temples.
Auditory information and processing spoken language.
Complex aspects of vision (movement, emotional, and motivational behaviors)
Kluver-bucy syndrome
Kluver bucy syndrome
It causes individuals to put objects in their mouths and engage in inappropriate sexual behavior. Other symptoms may include: visual agnosia (inability to visually recognixe objects), loss of normal fear and anger responses, memory loss, distractibility, seizures, dementia
The frontal lobe
Prefrontal cortex (integration center), primary motor cortex, higher functions, working memory, judgement, behavior control, language
prefrontal cortex
Executive function:
- planning
- personality
- decision making
- social behavior
- orchestration of thoughts and actions
Phineas Gage (1823-1860)
American railroad construction foreman. Large iron rod was driven completely through the head. Destroyed much of his brain’s left frontal lobe. Affected his personality and behavior over the succeeding twelve years.
Features of the cerebral cortex
- Gyri (bumps)
2. Sulci (grooves)
Brain Size and intelligence
Research has not supported that a larger brain is directly correlated with higher intelligence. Brain to body ratio research has some limited validity. Moderate correlation exists between IQ and brain size (.3). Amount of grey and white matter may also play a role. IQ is correlated with amount of grey matter.
Organization of the cerebral cortex
Contains up to six distinct laminae (layers) that are parallel to the surface of the cortex. Cell of the cortex are also divided intro columns that lie perpendicular to the laminar.
Layers of the cortex
Different layers have different cells types. Density of cells in each layer varies. Difference in appearance relate to function.
physical protection of the brain
skull, meninges, ventricles
The ventricles
Central canal (fluid filled channel in the center of the spinal cord) Ventricles (four fluid filled cavities within the brain containing cerebrospinal fluid) Cerebrospinal fluid (CSF) (clear fluid found in the brain and spinal cord, provides "cushioning" for the brain, reservoir of hormones and nutrition for the brain and spinal cord)
