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F 18 BI-207 Intro to the Nervous System

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Jennifer Jezylo

on 31 October 2018

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Transcript of F 18 BI-207 Intro to the Nervous System

Introduction ...
Central nervous system (CNS)
Brain and spinal cord
Interprets sensory input (from afferent neurons) and coordinates a response
Helps maintain homeostasis
Peripheral nervous system (PNS)
Somatic nervous system
Autonomic nervous system
Nerves carrying sensory info to the CNS (sensory or afferent) and ...
Nerves carrying motor commands from the CNS to muscles or glands (motor or efferent)
Neuroglia (neuroglial cells) – "Helper" cells
Support and nourishment
Oligodendricytes -
- Support/connect
- Secrete myelin for CNS neurons
Ependymal cells (ciliated, cuboidal/columnar epithelial cells)
- Produce/circulate cerebral spinal fluid (CSF)
Microglial cells - phagocytic cells
Astrocytes
- Produce neurotransmitters
- Regulate K+ ion
- Bind blood vessels & neurons (support)
Schwann cells (PNS) - (Flattened, wrapping cells)
- Form myelin sheath for PNS
Parts -
- Neurolemma = Cell body with cytoplasm, organelles, etc.
- Myelin sheath
Satellite cells - Support cells in the PNS
Neurons –
Cells that transport nerve impulses (information) throughout the body
Three parts of a neuron:
Axon
- Conducts information (nerve impulses) away from the cell body, toward other neurons (or target cells)
Myelin sheath (Myelin - lipid)
Protective, insulating covering of some axons
Formed by lipid-like neuroglial cells called Schwann cells which wrap
themselves around the axon many times
Gaps in the myelin sheath are called nodes of Ranvier
Myelin sheath is important in ...
1. Nerve regeneration in the PNS
2. Protection
3. Increasing the SPEED of the action potential
Cell Body
- Contains the nucleus,
aka soma, cyton, or perikaryon
Houses the organelles - mitochondria, golgi bodies, Nissl body (or rough ER)
Dendrites
(many) - Extensions from the cell that receive information and send it towards the cell body
Described in relation to the central nervous system (CNS)
Sensory (afferent)
– Takes messages to the CNS from a sensory receptor
Motor (efferent)
– Conducts messages away from the CNS to an effector (muscle cell or gland)
Interneuron
– Conducts messages between neurons within the CNS
Receive input from sensory neurons and other interneurons
Combines and sums up input from all connected neurons before stimulating a motor neuron
Synaptic cleft (gap) –
A gap between the axon of one neuron and the dendrite (or cell body) of another neuron
Electrical activity in the neuron causes release of chemicals (neurotransmitters) into the gap
Neurotransmitters - Chemical messengers of the nervous system ... help "bridge the gap" between neurons or between neurons and their EFFECTORS
Nervous system activity -
1) Electrical activity (from ions) within neurons
2) Chemical (neurotransmitter) flow between neurons
The cell membrane is permeable to some ions and not to others -
Na+ ion concentration is greater outside the cell (There are many Cl- ions extracellularly, as well)
A neuron at rest usually has an accumulation of large, negatively-charged proteins and K+ inside the cell
This imbalance is mostly due to the Na+- K+ ATP-ase pump, which actively moves three Na+ out and two K+ in, but as this happens…
The cell membrane is permeable to K+ ions which pass freely through, and diffuse down their concentration gradient … back out of the cell (until they're pulled back in)
This eventually causes the inside to become negatively charged and the outside to be positively charged (relative to each other)
The
charge difference
is the resting potential of the cell membrane (Usually ~ -70 millivolts)
Resting potential
– The sodium (Na+) concentration is greater outside the axon and the charge is more positive extracellularly ... The potassium ion (K+) concentration is greater intracellularly (and the intracellular charge is more negative - due to large, negatively charged proteins)
MAINTAINED by the sodium-potassium pump
Action potential – A rapid change in polarity (sodium ions rush in =
depolarization
) across the axon membrane as the nerve impulse occurs. Immediately, potassium ions rush out (beginning of
repolarization
)
This is an "All-or-none" phenomenon
$ of a dendrite or cell body causes a sudden change in the permeability of the cell membrane
At the point of $, the membrane becomes permeable to Na+ ions and they rush into the cell through voltage-gated channels
The rush of Na+ ions causes more voltage-gated channels in the cell membrane to open, causing more Na+ ions to rush in
Voltage-gated channels control the passage of ions through the cell membrane and exist along the entire length of the axon
The end result is that the interior of the nerve cell is now positively charged and the outside is negatively charged (relative to each other)
This reversal in polarity (depolarization) begins an action potential
The action potential begins at the point where the soma joins the axon (axon hillock)
The polarity reversal in the first part of the axon causes more voltage-gated channels to open along the axon
This continues like a wave down the axon membrane
Action potentials travel only in one direction … away from the soma, toward the axon terminal (bulb)
Soon after they open, Na+ gated channels close, and K+ gated channels open
K+ ions flow outward, and the outside again becomes positively charged (repolarization)
This signals the end of the action potential
Refractory period – No more action potentials can be generated by this axon until the resting membrane potential is restored
The Na+/K+ pump re-establishes the original concentrations of ions and the neuron is ready for the next action potential (repolarization)
Absolute refractory period
Relative refractory period
$ of an axon, dendrite, or soma causes the permeability of the post-synaptic membrane to change, and causes chemically-gated ion channels to open
Na+ ions rush in causing the inside of the next cell to become positively charged
Neurotransmitters - Chemical messengers of the nervous system
1. The basic tissue type that functions in communication is ...
a. Epithelial
b. Muscle tissue
c. Nervous tissue
d. Connective
e. All of the above
4. The SOMATIC nervous system refers to the ...
a. Voluntary nervous system
b. System innervating skeletal muscles
c. Has acetylcholine as its main neurotransmitter
d. Part of the peripheral nervous system
e. All of the above
Ependymal cells ...
a. Are phagocytes
b. Produce cerebral spinal fluid
c. Are connecting cells
d. Regulate ions
e. Are a neurotransmitter
1) The resting membrane potential of a neuron is maintained by ...
a. Permeability of the axon membrane
b. Sodium ion and potassium ion concentrations
c. Charge differences between the inside and outside of the cell
d. The sodium-potassium pump
e. All of the above
2. The main cell of this tissue type is a(n)...
a. Neuron
b. Epithelial
c. Neuroglial cell
d. Osteocyte
e. Myocyte
Nervous System - Chapter 7
Tissues of the Nervous System...
Neurons ...
Potential - A difference in electrical charge between two locations
Synapses ...
Nerve impulses – The way the nervous system conveys information...
5. What is a neurotransmitter?
a. A mineral stored in bone
b. Found in the sarcolemma
c. A chemical messenger
d. An ion
e. Seen only in the Central Nervous System
3. A specialized energy source found in skeletal muscle is ...
a. Creatine phosphate
b. Glycogen
c. Fat
d. Phosphate
e. Both a and b
7. The major ion required for muscle contraction is ...
a. Phosphate ion
b. Sodium ion
c. Potassium ion
d. Calcium ion
e. Acetylcholine
8. What is the serous membrane covering the organs of the abdominal cavity?
a. Visceral pleura
b. Parietal pleura
c. Visceral peritoneum
d. Parietal peritoneum
e. Meninges
9. Inflammation of the dorsal body cavity membranes is ...
a. Pleurisy
b. Peritonitis
c. Meningitis
d. Pericarditis
e. a, b, and d
11. What specific muscle type is found in the myocardium?
a. Skeletal
b. Connective
c. Cardiac
d. Smooth
e. nervous
12. What is the membrane that lines the walls of the abdominal cavity?
a. Visceral pleura
b. Mucous
c. Visceral peritoneum
d. Parietal peritoneum
e. Pleura
13. A specialized energy source found in muscle tissue is/are ...
a. Glycogen
b. Calcium
c. Creatine phosphate
d. All of the above
e. Both a and c
13. Aerobic cell respiration occurs in which organelle?
a. Bone
b. Mitochondria
c. Nucleus
d. Muscle
e. Calcium
14. A fracture of the right distal humerus would be ...
a. Closer to the hip
b. Closer to the elbow
c. Nearest to the ankle
d. Closer to the shoulder
e. In the pectoral girdle

15. The epiphyseal plates ...
a. Are the areas of continued long bone growth
b. Can prevent growth if fused prematurely
c. Are only found on the axial articulations
d. Fused soon after birth
e. Both a and b

16. The articulation between the atlas and the axis ...
a. Allow head flexion/extension
b. Is a semi-movable joint
c. Is an appendicular articulation
d. Allow head rotation
e. Is important in breathing

10. What basic tissue type is found in the myocardium?
a. Connective
b. Cardiac
c. Muscle
d. Epithelial
e. Nervous

6. An impacted fracture of the distal tibial would be ...
a. Bone ends pushed together near the ankle
b. Bone in many pieces in the forearm
c. Incomplete fracture of the pectoral girdle
d. Bone ends pushed together near the hip
e. A fracture of the patellar bone

Classification of neurons:
a. Bipolar - Rare (retina, inner ear, olfactory)
b. Unipolar
Mostly in PNS
Most sensory (afferent) neurons
c. Multipolar (Most in the CNS)


Inhibitory synapses
decrease the likelihood of the firing action potential in a cell while
excitatory synapses
increase its likelihood ...
Excitatory synapses stimulate release of neurotransmitters while inhibitory synapses inhibit release.
Information transfer via chemical synapse:
Impulse traveling through (pre-synaptic) axon reaches axon terminal
- Ca++ channels (and Na+ channels) open
- NT released and Ca++ is removed
- NT diffuses across synaptic gap and binds (reversibly)
to receptor proteins on post-synaptic membrane
- Ion channels open in post-synaptic membrane
causing changes in the membrane potential
(excitatory or inhibitory)

Classifying NTs:
Based on three criteria: The chemical must ...
Be present in the presynaptic nerve terminal and packaged into synaptic vesicles
Be released from the nerve terminal by the arrival of an action potential in a
calcium-dependent manner (CALCIUM voltage-gated channels)
Specific receptors for the substance on the postsynaptic cell
- There are > 2 dozen compounds that have been accepted as NTs
and many others that are suspected.
- Based on their structure, biochemical characteristics,
pharmacological profile, evolutionary origin, and properties in
general, neurotransmitters are classified into different families.
- Each family may have one or more subfamilies.
Categories of neurotransmitters:
Amino acids
(primarily glutamic acid, GABA, aspartic acid and glycine)
Peptides
(vasopressin, somatostatin, neurotensin, etc.)
- Neuropeptides are responsible for mediating sensory and emotional responses
including hunger, thirst, sex drive, pleasure and pain
Acetylcholine (ACh) -
M
ost widely seen NT
- Neurons that synthesize and release ACh are termed cholinergic neurons (Cholinergic synapses)
- Possible connection between ACh ↓ and Alzheimer’s disease?
- Removed from the synaptic cleft by acetylcholinesterase (enzyme degradation)
Catacholamines
- Nor-epinephrine, epinephrine, serotonin and dopamine
- Two different classes of receptors:
Alpha-adrenergic and Beta-adrenergic (Catecholamines are also known
as adrenergic neurotransmitters)
Neurons that secrete them are adrenergic neurons (Nor-epinephrine-
secreting neurons are nor-adrenergic)
- Epinephrine and nor-epinephrine are usually catabolized to inactive compounds by
monoamine oxidase (MAO)
- Compounds that inhibit the action of MAO have beneficial effects in the treatment of
depression (tricyclic anti-depressants)

Serotonin (5-hydroxytryptamine, 5HT)
Greatest concentration (90%) is found in the gastrointestinal tract (Don't worry about till digestion)
The remainder found in platelets and the CNS
- Mainly inhibitory (in the CNS)
Neurons that secrete 5HT are termed
serotonergic neurons
Effects:
- Some 5HT receptors mediate platelet aggregation
- Other 5HT receptors are suspected in control of food intake (mice lacking this gene become
obese from increased food intake and are also subject to fatal seizures)
- A few 5HT receptors are present in the gastrointestinal tract and are related to vomiting (nausea)
- Specialized 5HT receptors are distributed throughout the limbic system of the brain and have high
affinity for antidepressant drugs
Prozac® blocks its re-uptake

Dopamine

Mostly in CNS (secreted by cells in substantia nigra of the brain)
Can be excitatory or inhibitory
Cocaine works by blocking re-uptake of dopamine
Signs/symptoms of Parkinson’s disease caused by a deficiency of dopamine
Possibly involved in the patho-physiology of schizophrenia

The inside of an axon (intra-cellular fluid) has an electrical charge different from the extra-cellular fluid surrounding it ...
Neuron potential is produced by complex interaction of ions including the ...
The ability of the ion to move through the cell membrane (membrane permeability)
Concentration of ions (inside and outside of the cell)
Ionic charge (inside and outside of the cell)

If the change is great enough, a new action potential begins, continuing the electrical impulse.
If the positive change is not great enough, the membrane potential of the receiving neuron will not generate an action potential, and the signal will terminate.
NT is removed from cleft in a number of ways:
Can be repackaged by pre-synaptic vesicles (by astrocytes or other means)
Can be degraded by enzymes in the synaptic cleft
Can be removed from the synaptic cleft (diffusion)
Calcium ion is ...
a. Stored in the matrix of bone
b. Required for muscle contraction
c. Stored in the sarcolemma of a muscle fiber
d. All of the above
e. Both a and b

With respect to the nervous system, afferent neurons ...
a. Refer to motor neurons
b. Are the same as efferent neurons
c. Carry information towards effectors
d. Carry sensory information
e. Are found in the somatic NS
This prevents continuous stimulation of the post synaptic membrane
Several drugs and toxins affect the CNS by action here...
Interfere with (or potentiate) the action of neurotramsmitters
Enhance or block their release
Mimic the action of the neurotransmitter
Block receptors
Interfere with removal of the neurotransmitter
Which neuroglial cell helps form the myelin sheath in PNS neurons?
a. Ependymal cells
b. Oligodendricytes
c. Microglial cells
d. Schwann cells
e. Neurons
The rough endoplasmic reticulum of a neuron is called ...
a. Soma
b. Nodes of Ranvier
c. Nissl bodies
d. Sarcoplasmic reticulum
e. Chondrocyte
What's this?
a. Ependymal cell
b. Microglia
c. Oligodendricyte
d. Neuron
e. Schwann cell
What's this?
a. Ependymal cell
b. Microglia
c. Oligodendricyte
d. Neuron
e. Schwann cell
What's this?
a. Ependymal cell
b. Microglia
c. Oligodendricyte
d. Neuron
e. Schwann cell
What's this?
a. Ependymal cell
b. Microglia
c. Oligodendricyte
d. Neuron
e. Astrocyte
What's this?
a. Ependymal cell
b. Microglia
c. Oligodendricyte
d. Neuron
e. Schwann cell
Blood/Brain Barrier
The sodium-potassium pump ...
a. Is an active transport system
b. A passive protein pump
c. Requires ATP to function
d. Both a and c
e. Both a and b

There are two types of signals produced by this membrane change ...
Graded potentials - Short-lived very localized changes which vary in magnitude depending on signal strength
Action potentials - Long distance signals
(more later)
Depolarization = A decrease in membrane potential
Inside of the axon membrane becomes LESS negative
INCREASES the probability of generating an action potential
Hyperpolarization = An increase in membrane potential
Inside of the axon becomes MORE negative
DECREASES the probability of generating an action potential
Sodium ion ...
a. Is an anion
b. Has lost an electron
c. Has a negative charge
d. All of the above
e. Both a and c
When potassium is written as an ion it ...
a. Is K-
b. Has gained an electron
c. Is a cation
d. Both a and b
e. Both b and c
Calcium ion ...
a. Has gained two electrons
b. Is a cation
c. Has lost two electrons
d. Has lost one electron
e. Both b and c

Amino Acid NTs:

GABA (gamma-aminobutyric acid)

Inhibitory neurotransmitter
Widely distributed in the neurons of the cortex
Contributes to motor control, vision, olfaction, and many other cortical functions
Also regulates anxiety
Some medications that increase the level of GABA in the brain are used to treat epilepsy and to calm the trembling of people suffering from Huntington’s disease.
Glutamate
Excitatory neurotransmitter
Associated with learning and memory
Thought to be associated with Alzheimer’s disease, whose first symptoms include memory malfunctions.
Excessive glutamate release can overstimulate the brain and lead to excito-toxicity causing cell death resulting in seizures or strokes
Excito-toxicity has been implicated in certain chronic diseases including ischemic stroke, epilepsy, Amyotrophic lateral sclerosis (ALS), Alzheimer’s disease, Huntington’s disease, and Parkinson’s disease.
Amino Acids:
Acetylcholine (Ach):
Widely distributed excitatory neurotransmitter that triggers muscle contraction and stimulates the excretion of certain hormones
Neurons that synthesize and release ACh are termed
cholinergic neurons
Two main classes of ACh receptors:
-
Muscarinic receptors: Indirect action
-
Nicotinic receptors: Direct action
Further divided into neuromuscular junction receptors (found at all skeletal neuromuscular junctions) and
May either excite or inhibit internal organs in the autonomic system

- IN THE HEART, acetylcholine is INHIBITORY (slows down heart rate
and strength of contraction)
Neuronal synapse receptors … In the central nervous system
- Involved in wakefulness, attentiveness, anger, aggression,
sexuality, and thirst, among other things.
Removed from the synaptic cleft by ACETYLCHOLINESTERASE (enzyme)
and may either excite or inhibit internal organs in the autonomic system. It is distinguished as the transmitter at the neuromuscular junction connecting motor nerves to muscles. The paralytic arrow-poison curare acts by blocking transmission at these synapses
Catacholamines
Catacholamines
Catacholamines:
Nor-epinephrine
(AKA nor-adrenaline)
Mostly excitatory effects
Receptors are known as alpha and beta adrenergic receptors
- Some drugs block the effects of beta noradrenergic
receptors while having little or no effect on alpha receptors
- They are sometimes used to treat high blood pressure, atrial
fibrillation and congestive heart failure
Main neurotransmitter in the sympathetic branch (post-synaptic neuron) of the autonomic NS (fight or flight)
Epinephrine
(AKA adrenaline)
Mostly excitatory effects
Works at Alpha and beta receptors similar to nor-epinephrine.

2) The ion important in release of neurotransmitter from the pre-synaptic neuron is ...
a. Calcium
b. Sodium
c. An anion
d. Gained two electrons
e. a, c, and d
3. The main neurotransmitter of the somatic nervous system is ...
a. Acetylcholine
b. Epinephrine
c. Inhibitory in cardiac muscle
d. Nor-epinephrine
e. Both a and c
4) A neuroglial cell important in maintaining the blood brain barrier is called a(n)...
a. Ependymal cell
b. Microglial cells
c. Astrocyte
d. Schwann cell
e. Oligodendricyte
5) Dopamine receptors ...
a. Are mostly found in the substantia nigra of the brain
b. Are blocked by cocaine
c. Can be excitatory or inhibitory
d. All of the above
e. Both a and c
6) White matter ...
a. Is found in axon tracts
b. Consists of interneurons
c. Can be found superficially in the brain
d. Is mostly in the PNS
e. Both a and c
7) During depolarization ...
a. Potassium ion rushes into the axon
b. The sodium/potassium pump helps restore ion balance
c. The charge is more negative extracellularly
d. Sodium ion is concentrated extracellular
e. Calcium ion is pumped out of the cell

8) The membranes that line the dorsal body cavity are ...
a. Parietal pleura
b. Parietal peritoneum
c. Meninges
d. Visceral pleara
e. Both a and b
9) A complete fracture of the left distal tibia would be ...
a. Piercing the skin
b. Closer to the ankle on the medial aspect of the leg
c. Closer to the ankle on the lateral aspect of the leg
d. Not all the way through the bone
e. Both a and b
10) The hormone important in increasing blood calcium by stimulating osteoclasts is ...
a. Calcitriol
b. Parathyroid Hormone
c. Calcitonin
d. Thyroid Hormone
e. Both a and b

11) Calcitriol works by ...
a. Stimulating osteoblasts
b. Stimulating osteocytes
c. Increasing digestive calcium absorption
d. Decreasing calcium excretion in the urine
e. Stimulating osteoblasts
12) GABA is ...
a. Mostly an inhibitory neurotransmitter
b. Mostly an excitatory neurotransmitter
c. Found at neuromuscular junctions
d. Important in regulating digestive functions
e. All of the above, except a
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