KIN 101 Midterm 2 Flashcards
CNS
CNS: Central Nervous System
- Consists of
○ Brain
○ Spinal cord
PNS
PNS: Peripheral Nervous System
- Consists of
○ Sensory division (afferents)
○ Efferent division (motor neurons)
PNS (Efferent division - Parasympathetic)
Parasympathetic: Rest
Controls: Cardiac muscle, smooth muscle,
exocrine glands/cells, some endocrine
glands/cells, some adipose tissue
Triggers tissue responses
PNS (Efferent division - Sympathetic)
Sympathetic: “Fight or Flight”
Controls: Cardiac muscle, smooth muscle,
exocrine glands/cells, some endocrine
glands/cells, some adipose tissue
Triggers tissue responses
Enteric Nervous System:
Enteric Nervous System:
network of neurons in the walls of the digestive
tract that controls gastrointestinal behavior
(Controlled by the autonomic nervous system but
is also able to function autonomously)
Neurons/Glial cells (two types of cells in the nervous system)
Nervous system is made up of two cells
- Neurons: the basic signaling units of the
nervous system
○ Neurons carry electrical signals
○ Known as functional units
- Glial cells/glia/neuroglia: support cells.
Nerves
Nerves: axons bundled with connective tissue
- There are sensory, motor and mixed nerves.
Neuron Classes (Myelinated Somatic)
Myelinated with a central nucleus
For somatic senses
Pseudounipolar:
Have a single process called the
axon, during development the
dendrite is fused with the axon
Neuron Classes (Unmyelinated Somatic)
Unmyelinated with a central nucleus
For vision and smell
Bipolar:
Have two relatively equal fibers
extending off the central cells of the
body
Neuron Classes (Interneurons)
- Have one central nucleus and dendrites branch out
in all directions
□ Anaxonic:
Interneurons have no apparent
axon
□ Multipolar:
Interneurons are highly branched but
lack long extensions
Neuron Classes (Motor neurons)
- Regular (to me) neurons
□ Multipolar:- Efferent neurons have 5 to 7 dendrites that
each branch 4 to 6 times. - A single long axon may branch several times
and end at enlarged axon terminals
- Efferent neurons have 5 to 7 dendrites that
Axon hillock (Neuron Anatomy)
Axon hillock: where axon begins and where action potential is produced
Dendrites (Neuron Anatomy)
Dendrites: input signal
Cell body (Neuron Anatomy)
Cell body: the control center and is the site for integration of electrical signals and protein synthesis
- (where summation occurs)
Presynaptic axon terminal (Neuron Anatomy)
Presynaptic axon terminal: output signal
Axonal transport (Definition)
Axonal transport: the process of moving proteins synthesized by the cell body in vesicles down the axon.
Axonal transport (Fast axonal transport)
Fast axonal transport:
- Moves organelles at a rate of up to 400 mm/day
- Fast is protein mediated
- Anterograde transport: from cell body to axon
terminal
- Retrograde transport: from axon terminal to cell
body
Axonal transport (Slow axonal transport)
Slow axonal transport:
- Moves material by axoplasmic (cytoplasmic)
flow at a rate of 0.2-2.5 mm/day
Establishing synapses (Growth cones)
Growth cones: allow developing neurons to find their targets.
- Growth factors, molecules in the extracellular
matrix, membrane proteins all help growth
cones work to help the neuron grow
Establishing synapses (Neurotrophic factors)
Neurotrophic factors: allow developing neurons to survive.
Establishing synapses (Are synapses fixed?)
Synapses are also not fixed to one place for life as they can be rearranged
- Synapse formation must be followed by
electrical and chemical activity, or the synapse
will disappear
- Neuroplasticity: Variations in activity can cause
the rearrangement of synaptic connections, this
occurs through life.
Glial Cells (glue)
Glial cells (glue): are said to be the unsung hero’s of the nervous system. They are also supportive
○ They outnumber neurons by 10-50 to 1
Glial cells (PNS - Satellite Cells)
Satellite cells (PNS): are non myelinating Schwann
cells that form capsules around
nerve cell bodies that are
located in the ganglia
Ganglion
Ganglion: collection of nerve cell bodies outside of the
CNS
Glial cells (CNS - Ependymal cells)
○ Ependymal cells
§ Create barriers between compartments
§ Form the ependyma which separates parts of
the nervous system
§ Are a source of neural stem cells
Glial cells (CNS - Astrocytes)
○ Astrocytes (CNS):
§ Take up K+, water and neurotransmitters
§ Secrete neurotrophic factors
§ Help form the blood and brain barrier
§ Provide substrates for ATP production
§ Source of neural stem cells
Glial cells (CNS - Microglia)
○ Microglia (modified immune cells)
§ Act as scavengers
Glial cells (CNS - Oligodendrocytes)
○ Oligodendrocytes
§ Form myelin sheaths (form one long one)
Glial cells (PNS - Schwann cells)
○ Schwann cells
§ Form myelin sheaths (multiple along the axon)
§ Secrete neurotrophic factors
§ Wrapping motion on the axon (nucleus within)
Steps of Repair of an Axon (step 1-3)
- If the cell body dies the cell dies
- In the axon, Axoplasm leaks out triggering
events to seal the damaged end - Schwann cells release chemical signals alerting
of tissue damage
- In the axon, Axoplasm leaks out triggering
Steps of Repair of an Axon (step 4-6)
- In the distal axon the myelin sheath unravels and the
axon degenerates
○ The debris from this is removed by
microglia and phagocytes in about one month - These axons in the PNS can regenerate and re-
establish synaptic connections
(this is unlikely in the CNS) - Schwann cells secrete neurotrophic factors to keep
the body alive and encourage axon regeneration, the
axon then behaves again like a growth cone and
navigates its way back together
Steps of Repair of an Axon (step 7)
- Sometimes loss is permanent and the pathway
is destroyed
○ If this is a motor neuron it may result in
permanent paralysis
○ If this occurs in a sensory neuron there is
a loss of sensation from the innervated area
RMP
RMP: the resting membrane potential and this causes
selectively permeable ion channels which
permit specific ions through
Nernst Equation
Nernst equation: predicts the membrane potential of a
typical cell if the membrane were
permeable only to one ion
(The number represents the equilibrium potential)
(Permeability does not matter in this equation)
Equilibrium potentials (Sodium/Potassium)
Equilibrium potential for Na+ is +60mV (most outside)
Equilibrium potential for K+ is -90mV (mostly inside)
Goldman-Hodgkin-Katz Equation
- Takes into account permeability of an ion channel
- Is negative at rest
- Is positive when action potential occurs
Ion concentrations (In action potential)
- Resting state = large potassium within (-70mV)
- Depolarization = sodium enters within (-55mV)
- Repolarization = Na+ leaves K+ enters (-70mV)
- Hyperpolarization = Too much K+ enters (-90mV)
Gated Channels (Mechanically gated channels)
- Mechanically gated
○ Respond to physical force such as pressure or
stretch
Gated Channels (Chemically gated channels)
- Chemically gated channels (most in nervous system)
○ Respond to a variety of neurotransmitters and
neuromodulators or intracellular signals
Gated Channels (Voltage-gated Channels)
- Voltage-gated channels (most in nervous system)
○ Respond to changes in the cells membrane
potential.
Electrical signals (Graded potentials)
- Graded potentials: (work off summation)
○ Variable strength signals that travel over short
distances in the dendrites and cell body and
lose strength (aptitude) over time
- use voltage and chemically gated channels
- can be excitatory or inhibitory
- the results of are what cause action potential
- if they are more negative K+ leaves (inhibitory)
- if they are more positive Na+ enter (excitatory)
Electrical signals (action potentials)
- Action potentials (essentially what happens in the
axon hillock)
○ Brief large depolarizations that travel for long
distances (such as brain too toe) without losing
strength
○ Regenerate as they travel down the axon
- only use voltage gated channels
Graded potential (Two types - Subthreshold)
- Subthreshold graded potentials
○ A graded potential starts above the threshold at
its initiation point but decreases in strength as it
goes along. At the trigger zone it is below
threshold and therefore does not initiate an
action potential
Graded potential (Two types - Suprathreshold)
- Suprathreshold graded potentials
○ A stronger stimulus at the same point on the
cell body creates a graded potential that is still
above the threshold so by the time it reaches
the trigger zone it triggers the action potential
Axonal Na+ channels
Activation gates (the plate)
- Open rapidly
- Initiate the action potential
Inactivation gates (the ball)
- Close more slowly
- This terminates the action potential
- Causes the absolute refractory period
- Prevents action potentials from travelling
backwards
Refractory periods (Absolute - happens first)
Absolute refractory period: (Make hard to produce)
starts at the point the threshold is reached and
lasts until hyperpolarization reaches its low
Refractory periods (Relative - happens second)
Relative refractory period: (Don’t fire during)
starts when hyperpolarization begins to head back
towards resting membrane potential
Soma
Soma: main body of the cell
Factors to Conduction Speed (Two factors)
Two factors that influence conduction velocity
- Axon diameter
○ The larger the diameter of the axon the faster it will move
- The resistance of the membrane to ion leakage
○ The less leakage the faster it travels
(Speed is also influenced by myelin sheathes by increasing resistance - reduces ion leakage)
Saltatory Conduction
Saltatory conduction: when action potentials only occur at the nodes of Ranvier as they jump past large patches of membrane
Neurocrines (Two types)
Neurocrines
- Neurotransmitters and neuromodulators act as
paracrine with their target cells located close to
the neuron that secretes them
- Neurohormones are secreted into the blood and
distributed throughout the body
Neurocrine receptors (Two types - Ionotropic)
- Ionotropic receptors: open when a ligand
(neurocrine) binds to them (ligand gated-
chemical gated) then ions move across the
membrane. This mediates rapid responses
Neurocrine receptors (Two types - Metabolic)
- Metabotropic receptors: signal is transduced
through a G protein coupled second messenger
system. (these responses are slower)
Neurocrines cause
Responses possible:
- Excitatory post-synaptic potential (ECSP)
depolarization
- Inhibitory post-synaptic potential (IPSP)
hyperpolarization
- Other intracellular events like protein synthesis
can also occur.
Common Neurotransmitters
- Acetylcholine (ACh): neurons that secrete ACh and
receptors that bind ACh are cholinergic. - Glutamate: the main excitatory neurotransmitter of
the CNS they depolarize their target cells usually by
opening ion channels that allow the flow of positive
ion in - Gamma-aminobutyric acid: works by opening
chloride ions
Reserve pool
Neurotransmitters stored in vesicles that are farther from the synaptic cleft
Neurotransmitter release (What causes it?)
Ca2+ ions, action potentials.
Neurotransmitter termination (What removes them?)
blood vessels, glial cells
Acetylcholine (what happens to it after?)
- Acetophenone is synthesized in the presynaptic
vesicle - Once it reaches the post synaptic vesicle it becomes
acetylcholinesterase
Divergent pathway
Divergent pathway: one presynaptic neuron branches to affect a larger amount of postsynaptic neurons
- One response leads to multiple others that go
further
Convergent pathway
Convergent pathway: one presynaptic neuron branches to affect a larger amount of postsynaptic neurons
- Multiple signals can amplify the affects and
bring a neuron to threshold that otherwise
wouldn’t fire
Synaptic responses (Speed)
Fast synaptic responses:
ionotropic channels = ligand binds to receptor
and things flow
Slow synaptic potentials:
metabotropic channels = use Gproteins
Summation
When one or more signals add together
Summation occurs
- When the first one doesn’t have time to decay
- When they reach each other close enough in
time
- Called integration
- Temporal summation (adding together in time)
- Spatial summation (adding together from
different spaces)
Inhibitions (Two places they occur)
Global inhibition: the inhibition is happening at the top of the cell body
- Affects all targets
- No effects occur
- Nonselective
Presynaptic inhibition: when it occurs only at the presynaptic cleft
- Only on one terminal
- Effects still occur
- Selective