Week 6 - Nervous System Flashcards
What are the three fundamental functions of the nervous system
Sensory Functions, Integrative Functions, and Motor Functions
What are the two major anatomical subdivisions of the nervous system
Central Nervous System (CNS) and Peripheral Nervous System (PNS)
What are the three functional categories
of neurons
Sensory (afferent), Interneurons, and Motor (efferent) Neurons
What are the common variations on neuron structures
Multipolar, Bipolar, and Unipolar Neurons
Describe the structure of a generalised neuron and the
List the neuronal supporting cells (neuroglia) with their primary functions
Discuss the myelin sheath that envelops many nerve fibres, including its function and how it is produced
Explain the difference between gray and white matter
Define resting membrane potential
List the steps involved in generating and propagating an action potential in neurons
Define saltatory conduction
Explain how signals are passed from neuron to neuron at the synaptic cleft
What are the two organ systems that coordinate body activies
Endocrine System (Hormones) and Nervous System (electrical and chemical signals)
What do Sensory Functions do
Respond to stimuli and generate signals about the stimuli and carry them to the spinal cord or brain
What do Integrative Functions do
Receive, process, store and retrieve information and make decisions how to respond
What do Motor Functions do
Issue outgoing signals to muscle cells and glands to produce an effective response
What is in the Central Nervous System
Brain and Spinal cord
What is the central nervous system responsible for
Carrying out Integrative Functions
What does CNS and PNS stand for
Central Nervous System and Peripheral Nervous System
What is the Peripheral Nervous System responsible for
Carrying out the Sensory and Motor Functions. Providing pathways of signal input and output. Connecting Central Nervous System to the body’s sense organs, muscles and glands
What are Dendrites
A part of a neuron, that consists of thick arms arising from the SOMA that divide like branches and act as stimuli for receiving signals from other neurons
What is the Axon Hillock
The leading branch from the Soma that leads into the Axon
What is an Axon
Nerve fibres that are long roughly cylindrical shape that act as an output pathway for signals to other cells. At the distal end of the Axon line their is usually Axon terminal branches
What is an Axon Terminal also called
Synaptic Terminal
Do all neurons have Axons
No, but most have one (never more than one)
What does a multipolar neuron consist of
One axon and Multiple Dendrites
What is the most common neuron
Multipolar Neuron
What is the main Neuron structure in the CNS
Multipolar Neuron
What does a bipolar neuron consist of
One axon and One Dendrite
What is the main Neuron structure for sensory
Bipolar Neuron
How many processes lead from the Soma
Two, (One Axon and One Dendrite)
What does a unipolar neuron consist of
Only one Process leading from the Soma (Looks like a T)
What are Sensory (afferent) Neurons
A classification of neuron that is mostly Unipolar or Bipolar and that transmits signals towards the CNS. specialises to detect stimuli from eyes, ears, skins, joints, internal organs and other sources
What are Interneurons
A classification of neuron that is mostly Multipolar and performs integrative functions, with arms that store and retrieve information. They make the decisions about the body’s response.
Where can you find Interneurons
CNS
What is the most abundant Neuron Type
Interneurons
What are Motor (efferent) Neurons
A classification of neuron that are mostly Multipolar and carry outgoing signals away from the CNS to muscle and gland cells that
carry out commands
How many Neuroglia are found per Neuron
10 - 1 Ratio
What do Neuroglia do
Perform protective and “Housekeeping” functions and aid neurons in their functioning
What are the two types of neuroglial cells in the PNS
Schwann cells and satellite cells
What are the four types of neuroglial cells in the CNS
oligodendrocytes, ependymal cells, microglia, and astrocytes
What are Schwann cells
Cells (Multiple) that wrap around nerve fibres of PNS, enclosing each in a sleeve called Neurilemma
How do Schwann cells insulate neurons
spiral repeatedly around a nerve fibre, depositing membrane, which constitutes a myelin sheath
Is regeneration of the CNS possible
no because it does not have Schwann cells in CNS
What are Satellite cells
They surround the cell bodies of peripheral neurons and electrically insulate Neurons.
What is the main function of Satellite cells
Regulate the chemical environment of neurons
What are Oligodendrocytes
large bulbous cells in CNS with multiple armlike processes, each reaching out to a nearby nerve fibre
How do Oligodendrocytes insulate neurons
the processes spiral around the nerve fibre, forming a myelin sheath
What Neuroglia in the CNS acts the same as another kind in the PNS
Oligodendrocytes (CNS) and Schwann Cells (PNS)
What are Ependymal Cells
cuboidal cells with Cilia that produce and circulate Cerebrospinal Fluid and line internal cavities of the brain and spinal cord. The fluid produces bathes the CNS surfaces
What is Microglia
Small phagocytic cells that wander through the CNS
What is the function of Microglia
To destroy tissue debris, microorganisms, and foreign matter. Also become concentrated in areas damaged by infection, trauma, or stroke
What are Astrocytes
the most abundant glial cells (hold nerve cells in place) in CNS that form the supportive framework
What are the functions of Astrocytes
They have perivascular feet that help form the blood-brain barrier. They secrete chemicals that control local blood flow and also nerve growth factors that promote neuron growth. form scar tissue in damaged regions of CNS
How do Astrocytes maintain a stable extracellular environment
by regulating amount of potassium ions (K+)
What is the Myelin Sheath
Layers of oligodendrocyte or Schwann Cells (Depending on if in CNS or PNS) plasma membranes wrapped around a fibre that insulates nerve fibre
What is Myelination
The insulation of Nerve fibres (like electrical tape around a wire)
Can 1 cell Myelinate one nerve
no, multiple cells are needed
What are Nodes of Ranvier
Small gaps in between each Myelinated axon that serves to facilitate the rapid conduction of nerve impulses
What is the name of Myelin-Covered segments
internodes
What is Multiple Sclerosis
An autoimmune disease against oligodendrocytes and myelin sheaths in CNS, and a degenerative disorder of the myelin sheath
What replaces the myelin sheaths in Multiple Sclerosis patients
nonfunctional, hardened scar tissue
What are the two types of Nervous Tissue
White and Gray Matter
What is White Matter
It is made of bundles of nerve fibres called TRACTS. The colour comes from Myelination.
Where are Tracts found
CNS; white matter in the PNS are called nerves
Are there Tracts in the PNS
No, white matter in the PNS are called nerves
What is Gray matter made up of
Neurosomas, Dendrites
and Synapses
Why is Gray matter not white
little myelin, so duller colour
What is Gray Matters function
information-processing part of the
CNS
How is white and gray matter distributed in the Spinal Cord
white matter forms surface tissue
gray matter forms the inner core
How is white and gray matter distributed in the Brain
white matter forms most of the deep tissue
gray matter forms the surface layer and a few deep masses
What are membrane transport channels
Concentration Gradients, both active and passive, ligand and voltage-gated
protein channels; sodium/potassium pump
What is Resting Membrane Potential (RMP)
A charge difference between the inner and outer surfaces of a neuron’s plasma membrane when the neuron is at rest
What charge is the ECF-side of the Neuron when it is at rest
Positive
What charge is the ICF-side of the Neuron when it is at rest
Negative
How is RMP created
It is created by differences in ion concentrations
What is the charge of RMP
RMP is usually ~-70mV (millivolts)
How is the RMP maintained
The Na+ / K+ pump continually ejects 3 Na+ and pumps in K+ which maintains internal negative charge
How is the RMP threatened to be abolished
protein channels in the plasma membrane provide slow, constant leakage of Na+ and K+ which threatens to abolish the RMP
What is needed on the cell for Nerve Signaling
ligand-gated and voltage-gated channels
What is a Ligand-Gated Channel
A Channel that opens or closes when a ligand binds to it
What is a ligand
any chemical that binds to a protein
What is a voltage gated channel
A Channel that opens or closes in response to changes in the membrane potential Charge
What is the first step in nerve signaling
Initial Neuronal Excitation (usually occurs on a dendrite)
What is the Initial Neuronal Excitation
Na+ enters neuron, the local potential spreads toward the axon hillock, the axon hillock has lots of Na+ and K+ voltage-gated channels that open when the threshold potential is reached; this produces an action potential that will propagate down
the axon
What are the 4 steps of an action potential
- Stimulation of the Neuron which creates a gradually rising Local Potential
- Na+ rushes into cell and causes a rapidly rising membrane voltage towards 0 called Depolarisation
- Na+ channels begin to close at 0mV, but the voltage typically reaches about +35mV by the time all of them close
- K+ outflow causes the voltage to drop back (more slowly) into the negative range called repolarisation, slightly overshooting the original resting membrane potential (RMP); called hyperpolarization
What is Action Potential also written as
AP
What is Action Potential
voltage spike over a limited area of plasma membrane
What happens after Action Potential completes its process
Each AP triggers another one in the membrane ahead
Action Potential causes a chain reaction creating…
Nerve Signals
What is Continuous conduction
AP Chain that occurs on unmyelinated axons
What is Saltatory conduction
AP Chain that occurs on myelinated axons
With Continuous conduction, what parts of the axon does AP occur at
Each point
With Saltatory conduction, what parts of the axon does AP occur at
Only at the nodes of Ranvier
What is the Refractory Period
A period of time immediately after an action potential where the membrane cannot conduct another action potential
Why is the main function of the Refractory Period
To prevent an action potential from spreading down the axon backwards as it can only move forward
Do nerve signals travel faster down Myelinated or Unmyelinated fibres
myelinated fibres are 120m/s vs 2 m/s in
unmyelinated fibres
What is the Synapse
The point where Two Cells meet
What is a presynaptic neuron
Neuron that sends Signal
What is a postsynaptic neuron
Neuron that receives Signal
What is the Synaptic Cleft
gap between two neurons
What is an Axon Terminal
The arms at the end of the axon that contains Synaptic Vesicles that contain chemicals called neurotransmitters
What happens when an Axon Terminal receives a nerve signal
undergo exocytosis, and then release neurotransmitters into the
synaptic cleft where neurotransmitters bind to receptors on the membrane of the postsynaptic neuron
What is Acetylcholine
A Neurotransmitter that binds to Protein Receptors that are Ligand-Gated Channels on Postsynaptic cell which allows Na+ and K+ to flow through, producing a
local potential in the postsynaptic cell
What happens if cell depolarise to threshold in the Acetylcholine proccess
An action potential is triggered
How long does the Neurotransmitter stimulation of the postsynaptic cell last
Very Brief
What happens after the Neurotransmitter binds in the cleft
it needs to be removed and may be broken down by enzymes, may be reabsorbed by presynaptic neuron or could be diffused into surrounding tissue.
What happens if the Neurotransmitter is not removed
A disturbance may occur
