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What are the main components of the central nervous system (CNS)?
Brain and spinal cord, both containing neurons and glia.
What are the main components of the peripheral nervous system (PNS)?
Peripheral nerves and ganglia, containing neurons and glia.
What is the primary function of neurons?
Specialized cells for the transmission of information using a binary code.
What are the four morphological types of neurons?
Multipolar, Bipolar, Unipolar, and Anaxonic.
What is the function of dendrites in a neuron?
Receive input and send information to the cell body.
What is the function of the cell body (soma) in a neuron?
Contains the nucleus and organelles; sums input.
What is the function of the axon in a neuron?
Carries electrical impulses and information and may or may not be myelinated.
What are axon terminals?
End of the axon where neurotransmitters are released.
In the CNS, what is a group of cell bodies called?
Nucleus (if it's a named, distinct group) or gray matter (in cerebral cortex or spinal cord).
In the CNS, what is a bundle of axons called?
Tract (if it's a named, distinct bundle) or white matter (in cerebral cortex or spinal cord).
In the PNS, what is a group of cell bodies called?
Ganglion.
In the PNS, what is a bundle of axons called?
Nerve.
Where are the soma/cell bodies of neurons found?
Grey matter.
Where are axons found?
White matter.
What is the INPUT ZONE of a neuron?
Dendrites and cell body, where chemical signals from other neurons are received.
What is the SUMMATION ZONE of a neuron?
Axon hillock, where inputs are summed. If the threshold is reached, a signal is propagated.
What is the CONDUCTION ZONE of a neuron?
Axon, which carries electrical signals between brain areas, to and from the spinal cord, or from peripheral sensory receptors to effector cells.
What is the OUTPUT ZONE of a neuron?
Axon terminals, which contact the input zone of other neurons or effectors and release neurotransmitters.
Describe a multipolar neuron.
Multiple processes emanate from the cell body.
Describe a bipolar neuron.
Two processes emanate from the cell body.
Describe a unipolar neuron.
One process emanates from the cell body and branches into a dendrite and an axon.
Describe an anaxonic neuron.
No distinct axon; all processes look alike.
What is the general function of glia?
Support for neurons.
Name the four types of glial cells found in the CNS.
Astrocytes, microglia, ependymal cells, and oligodendrocytes.
Name the one type of glial cell found in the PNS.
Schwann cells.
What are the functions of astrocytes? (4)
Supply nutrients to neurons,
cover blood capillaries,
participate in injury response,
make up the blood-brain barrier.
What are the functions of microglia? (2)
Immune cells of the CNS
engulf microorganisms and debris.
What are the functions of ependymal cells? (2)
Line fluid-filled spaces of the brain and spinal cord (ventricles)
have cilia to circulate cerebrospinal fluid (CSF).
What are the functions of oligodendrocytes? (3)
Support nerve fibers,
feed nutrients to neurons,
ensheath them with myelin to maintain good signal strength.
What are the functions of Schwann cells?
Support peripheral nerve fibers and ensheath them with myelin.
What is myelin sheath?
Lipid wrapped around axon.
What cells produces myelin in the PNS and CNS?
Schwann cells in the PNS and oligodendrocytes in the CNS.
What are the Nodes of Ranvier?
Gaps between myelin sheaths which increase conduction velocity by propagating action potentials.
What is a synapse?
Communication between neurons occurs through a junction.
What key events occur at the presynaptic neuron in relation to the synapse?
Neurotransmitter (electrical → chemical) is released from the axon terminal, which contains synaptic vesicles filled with packets of neurotransmitters.
What key events occur at the postsynaptic neuron?
Neurotransmitters are received (chemical → electrical).
Briefly define afferent flow of information in the nervous system.
Information goes into the brain (ascending).
Briefly define efferent flow of information in the nervous system.
Response comes out of the brain (descending).
What is somatic information?
What we are aware of, have control over: somatic efferent & somatic afferent
What is autonomic information?
what we are not aware of, have no control over: autonomic efferent & autonomic afferent
How many neurons are between the brain and effector in the somatic efferent division?
Two
Somatic efferent pathway
upper motor neuron (within CNS)
cell body: in brain
axon: in spinal cord, axon is myelinated
neurotransmitter: acetylcholine (Ach)
lower motor neuron
cell body: in spinal cord (CNS)
axon: in spinal nerve (PNS), axon is myelinated
neurotransmitter: acetylcholine (Ach)
How many neurons are between the brain and effector in the autonomic efferent division?
Three
What are the two divisions of the autonomic efferent system?
Sympathetic and Parasympathetic
Autonomic efferent pathway
neuron 1
cell body: in brain
axon: brain or spinal cord (CNS)
neuron 2
cell body: brain or spinal cord (CNS)
axon: in PNS, myelinated, synapse in autonomic ganglion
neurotransmitter: acetylcholine (Ach)
neuron 3
cell body: autonomic ganglion
axon: in PNS, unmyelinated, synapse on efferector organ
neurotransmitter: acetylcholine (Ach) / norepinephrine (NE)
What is a ganglion?
Group of cell bodies
Which neurotransmitter is associated with the sympathetic nervous system?
Norepinephrine (NE)
What is the main function of the sympathetic nervous system?
Prepares the body for acute/stress responses (fight or flight)
List 6 effects of the sympathetic nervous system.
Increases heart rate,
constricts blood vessels to the skin,
decreases gastric motility,
decreases salivation,
increases pupil size,
increases sweating
Which neurotransmitter is associated with the parasympathetic nervous system?
Acetylcholine (ACh)
What is the main function of the parasympathetic nervous system?
Prepares the body for restful situations (rest and digest)
List 4 effects of the parasympathetic nervous system.
Decreases heart rate,
increases gastric motility,
decreases pupil size,
increases salivation
Where are the cell bodies of sympathetic preganglionic neurons located?
Thoracolumbar levels of the spinal cord (T1 - L2)
Describe the location of sympathetic chain ganglia relative to the CNS
Close to the CNS on either side of the vertebral column
Describe the axon length of sympathetic preganglionic neurons.
Short Axon
Describe the axon length of sympathetic postganglionic neurons.
Long axon
Where are the cell bodies of parasympathetic preganglionic neurons located?
Craniosacral (brainstem and sacral spinal cord)
Describe the location of parasympathetic ganglia relative to the CNS and effector
Distant from CNS, close to the effector
Describe the axon length of parasympathetic preganglionic neurons.
Long Axon
Describe the axon length of parasympathetic postganglionic neurons.
Short axon
How does a chemical signal transform into an electrical signal in neurons?
Chemical signal (neurotransmitter) binds to and opens chemically-gated ion channels, ions flow in/out changing voltage; if membrane reaches -60mV at axon hillock, an action potential begins.
How do chemically-gated ion channels operate, and where are they located?
Chemical neurotransmitter binds to ion channel, channel shape changes, ions cross membrane driven by electrochemical gradient; neurotransmitter unbinds, channel closes.
located in dendrites & cell body
How do voltage-gated ion channels operate, and where are they located?
Membrane depolarized to threshold voltage, channel shape changes, ions cross membrane driven by electrochemical gradient; membrane potential changes causing channel to inactivate or close.
located in axon hillock, axon, & axon terminals
How do mechanically-gated ion channels operate, and where are they located?
Deformation of the membrane, channel shape changes, ions cross membrane driven by electrochemical gradient; when membrane returns to original shape the channel closes.
located in dendrites
What are local potentials (PSP)?
Excitatory or inhibitory voltage change in a small location of the dendrite/cell body of a POSTsynaptic cell
What happens during Excitatory local potentials (EPSPs)? (3)
A presynaptic neuron releases excitatory neurotransmitter.
When neurotransmitter binds, it opens chemical gated Na+ channels;
Na+ enters postsynaptic cell causing depolarization
What happens during Inhibitory local potentials (IPSPs)?
A presynaptic neuron releases inhibitory neurotransmitter. When neurotransmitter binds, it opens chemically gated K+ or Cl- channels; K+ exits or Cl- enters postsynaptic cell, causing hyperpolarization.
What is spatial summation?
Summed input from multiple PREsynaptic neurons
What is temporal summation?
Summed input from repeated firing of one PREsynaptic neuron.
What are the 6 steps of action potentials
voltage gated Na+ channel opens when the membrane depolarises to -60mV
influx of Na+ causes ‘rapid depolarisation phase’ of the action potential
at +30mV, the voltage gated Na+ channels get inactivated and Na+ entry stops
voltage gated K+ channels open and K+ exits causing ‘repolarisation phase’ of the action potential
voltage gated K+ channels begin to close slowly and K+ still exits causing the ‘hyperpolarisation phase’ of the action potential. membrane potential reaches -90mV
all voltage gated K+ channels close and the membrane returs to -70mV through the help of sodium-potassium pump
What happens during the depolarization phase of action potential propagation?
A flood of Na+ enters the axon hillock and diffuses from the points of entry down the axon towards the terminal.
What is the absolute refractory period?
A period when a second action potential cannot be generated because voltage-gated Na+ channels are either open or inactive.
What is the relative refractory period?
A period when a second action potential can only be generated if the stimulus is larger than normal because some voltage-gated Na+ channels are shifting from inactive to closed.
In an unmyelinated axon, how does the action potential propagate?
Na+ influx at the axon hillock causes diffusion into the initial segment, triggering depolarization. This process repeats down the axon.
Why can't an action potential move backwards down the axon?
The initial segment of the axon is in the absolute refractory period of repolarization.
How does myelination affect action potential conduction velocity?
Myelination increases action potential conduction velocity through saltatory conduction.
What is saltatory conduction?
The 'jumping' of action potentials from one node of Ranvier to the next in myelinated axons.
What is the role of voltage gated Ca2+ channels in the presynaptic axon terminal?
They open when an action potential arrives, allowing Ca2+ to enter and trigger neurotransmitter release.
What happens when Ca2+ enters the axon terminal?
It interacts with vesicles, causing them to fuse with the membrane and release neurotransmitter into the synaptic cleft via regulated exocytosis.
What is the role of neurotransmitters in synaptic transmission?
They diffuse across the synaptic cleft and bind to chemically-gated ion channels on the postsynaptic cell, leading to the formation of local potentials.
What is the effect of an excitatory neurotransmitter, such as ACh, on the postsynaptic cell?
It opens Na+ channels, causing EPSPs (excitatory postsynaptic potentials).
What is the effect of an inhibitory neurotransmitter, such as GABA, on the postsynaptic cell?
It opens Cl- or K+ channels, causing IPSPs (inhibitory postsynaptic potentials).
How is synaptic transmission terminated? (3)
Neurotransmitter unbinds from chemically-gated channels,
enzymes degrade the neurotransmitter in the synaptic cleft,
portions of the degraded neurotransmitter are recycled into the axon terminal.
Where does the spinal cord start and end?
Starts at foramen magnum and ends at inferior border of 1st lumbar vertebra (L1).
What encloses the spinal cord?
Meninges housed within the spinal cavity.
What is the dorsal side referring to?
Posterior.
What is the ventral side referring to?
Anterior.
What non-neural structure is associated with the meningeal sac, and what does it contain?
cerebrospinal fluid (CSF).
What is the tapered cone at the end of the spinal cord called, what is it made of, and where does it end?
Conus medullaris —> made of fibrous tissue, ends at L1/L2.
What is the function of the filum terminale?
Anchors the spinal cord.
How many spinal nerve segments are there, and what pairs correspond with each segment?
31 segments each with a pair of spinal nerves (one left and one right).
How many Cervical spinal nerves (pairs) are there?
8 pairs
How many Thoracic spinal nerves (pairs) are there?
12 pairs
How many Lumbar spinal nerves (pairs) are there?
5 pairs
How many Sacral spinal nerves (pairs) are there?
5 pairs
How many Coccygeal spinal nerves (pairs) are there?
1 pair
What is the exception to the rule of spinal nerves being named by the vertebra they exit below?
The first cervical spinal nerve exits between the skull and the first cervical vertebra.
What is the cauda equina?
Large collection of long nerves inferior to end of spinal cord.
How efferent information leaves the spinal cord?
Leaves through ventral roots.
What is the location and route of somatic motor neurons?
Ventral horn of spinal cord, axon exits via ventral nerve root to skeletal muscle.