Introduction to peripheral nervous system Flashcards
What are the two types of principle cells in the nervous system?
neurones
neuroglia
What are the two basic functions of neuroglia?
- Support, nurture and protect neurones
- Maintain the homeostasis (balance) of the fluid that bathes neurones
what are the 3 basic functions of neurones?
- Receive signals (or information).
- Integrate incoming signals (to determine whether or not the information should be passed along).
- Communicate signals to target cells (other neurons or muscles or glands).
Are neuroglia excitable? what does this mean?
they are non-excitable as they do not transmit impulses
why do neurones vary in size, shape and characteristics?
because they have different features depending on their role
What does the cell body of a neurone look like?
star shaped with nucleus in the centre
The cell body is the neurones _____
core
what are the three functions of the neurone’s cell body?
- to hold genetic information
- maintain structure
- provide energy to drive activity
What does the cell body contain? (3)
- the nucleus
- the cytoplasm
- organelles within the cytoplasm
where are the dendrites located on a neutron?
they are the root like shapes on the ends of the points of the cell body
What is the functions of dendrites?
- to receive incoming information
What are the two types of signals that dendrites can receive?
excitatory or inhibitory
what do excitatory impulses do to the neuron?
they make the neurone fire and generate an electrical impulse
what do inhibitory impulses do to the neuron?
they keep the neuron from firing
Most neurones receive ______ input signals through the ________, receiving thousands of input signals.
many
dendrites
whether or not a neurone is exited into firing an impulse depends on what?
the amount of excitatory and inhibitory signals it receives
If a neurone does end up firing, Where does the nerve impulse (or action potential) go?
the nerve impulse, or action potential, is conducted down the axon.
What shape and size is the axon?
it is the same diameter for most of its length and doesn’t have any spines
its size is dependent on its function
does a larger diameter axon has the ability to send signals faster or slower than a smaller axon?
much faster
what is the name of the special fatty insulating substance that covers many axons? what does this form?
myelin which forms the myelin sheath
What secrets myelin in the fibres of the peripheral nervous system?
Schwann cells
what secrets myelin in the fibres of the central nervous system?
oligodendrocytes
what is the function of the myelin sheath?
it helps to contain the nerve impulse, allowing it to move rapidly along the axon
What are the gaps along the myelin sheath? are they myelinated?
nodes of ranvier, they are non-myelinated
What is the function of the nodes of ranvier?
they expose the axon at various points to allow for regeneration of the impulse which supports the speed at which the nerve impulse passes along the axon
Where do axons arise from the cell body?
at a cone-shaped elevation called the axon hillock
what is the first portion of the axon called and what arises here? what name does this also give it?
the initial segment
the nerve impulse
the trigger zone
along the length of the axon there may be side branches called ____ ________ which are typically at ______ angles to the axon.
axon collaterals
right
What is at the end of the axon?
fine processes called the axon terminals
What does the tip of the axon terminal bulge out to form?
the synaptic bulb
what does the synaptic bulb contain?
neuro-transmitting chemicals
What is the small gap between one neurone and the next or the target cell called?
the synapse/synaptic cleft
what moves across the synapse? what do they do?
neuro-transmitting chemicals pass across the synapse to send the impulse either into the next neurone or effector cell
what are the 5 differences of a non-myelinated neurone to a mylienated neurone?
non-myelinated neurones have:
1. no myelin sheath
2. no nodes of ranvier
3. lower speeds of transmission
4. shorter axons
5. can lose nerve impulse during conduction
In what kind of environment are unmyelinated neurones found? give an example in the body.
found in areas where a short axon is appropriate – for example within the brain where the signal has to travel very short distances.
How does MS affect neurones?
Oligodendrocytes are damaged, and myelin is damaged and stripped away from the axon
What symptoms in MS demonstrate the disruption of messages along the axon? (3)
muscle weakness
poor coordination of movement
changes in senstation
what are the three types of neurones?
motor neurones
interneurones
sensory neurones
what are three characteristics of motor neurones?
- typically multipolar
- efferent
- take signals away from the CNS
What does multipolar mean?
that they have two or more dendrites and one axon
What does efferent mean?
they carry signals away from the CNS and towards the effector eg muscle cell
where are interneurones found? (2)
between motor and sensory pathways
within the CNS
how do interneurones communicate?
to communicate between the motor and sensory pathways and can also communicate with each other to form small circuits
What are three characteristics of sensory neurones?
- unipolar
- afferent
- carry signals toward the CNS
What does unipolar mean?
they only have one nerve process extending from the cell body
What does afferent mean?
they carry the signal towards the CNS.
what is at the end of the axon in a sensory neuron?
receptor endings
What is a bundle of axons in the peripheral nervous system called?
a nerve
What is a bundle of axons found In the central nervous system called?
a tract
What is the longest nerve in the body?
the sciatic nerve
What are the 4 types of neuroglia cells (glial cells) in the CNS?
oligodendrocytes, astrocytes, microglia, and ependymal cells in the CNS
What are the two types of neuroglial cells in the PNS?
schwann cells, satellite cells
What do neuroglia have the ability to do that neurones do not?
they have the ability to divide and multiply
Neuroglia act like the _____ that holds the __________ tissue together.
glue
nervous
In the case of traumatic injury, what are neuroglia able to do?
fill the space that neurones once held
Which of the glial cells act as the regulator for the CNS?
Astrocytes
Which of the glial cells act as the regulator for the PNS?
satellite cells
Astrocyes form the main ____________ _______ of the nervous system.
supporting tissue
What do astrocytes attach together? what do they form?
the attach neurones to blood vessels
the blood brain barrier
What do satellite cells support?
neurones in the PNS
What do satellite cells regulate?
the external chemical environment
What are satellite cells sensitive to? what can this do?
injury - exacerbate the pain response
What produces the myelin in the central nervous system?
Oligodendrocytes
What creates the myelin in the PNS?
Schwann cells
Schwann cells participate in ____ _____ regeneration.
PNS axon
satellite cells regulate ___________ of __________ between _________ and ___________ fluid.
exchange
materials
neurons
interstitial
What is interstitial fluid?
fluid in spaces between tissues
What is white matter formed by?
clusters of myelinated processes from the neurones found deep in the brain or periphery of the spinal cord
How do neurones pass messages?
electrical signals pass along the axon, this comes to the synaptic bulb which triggers the release of neurotransmitters to neurotransmitter receptors on the post synaptic neurone
When a neurone passes a message, electrical signals pass along the _____ to the ________. This then goes to the _________ _____ where the signal is transferred from __________ to ________ so it can cross the __________ ______. At the other side there is a ____________ _____, which has __________________ ________ that receive the ________________ molecules.
axon
synapse
synaptic bulb
electrical
chemical
synaptic cleft
postsynaptic neuron
neurotransmitter receptors
neurotransmitter
_____ triggers synaptic vesicle __________, thereby releasing the _________________ contained in the vesicles and initiating __________ _____________
Ca2+ triggers synaptic vesicle exocytosis, thereby releasing the neurotransmitters contained in the vesicles and initiating synaptic transmission
The natural state of a neurone is a ___________ concentration, meaning that there are more ___________ charged ions ________ than ______ the cell. This neurone is in a state of rest and described as the _________ __________ ___________.
negative
positively
outside
inside
resting membrane potential.
During the resting membrane potential, there are more __________ ions outside the __________ and more ____________ ions inside. The concentration of ions isn’t _____ though – ions are flowing in and out of the neurone constantly as the ions try to __________ their concentrations.
sodium
neurone
potassium
static
equalise
How is the neurone able to maintain a negative concentration gradient because of the cell membrane?
- the cell membrane is super permeable to potassium ions so lots of potassium leaks out of the neurone through the potassium leakage channels (holes in the cell wall)
- The cell membrane is semi-permeable to sodium ions so they slowly leak into the neurone through sodium leakage channels
The cell is also able to maintain a negative resting membrane potential because it ______ to. It has a pump that pumps __________ back into the ____ and pumps _______ out at the same time.
wants
potassium
cell
sodium
What happens during depolarisation of the neuron?
the opening of voltage gated sodium channels
What happens during depolarisation of the neuron?
closure of the voltage gated sodium channels and opening of the potassium voltage gated channels to restore the resting membrane potential
What are the three stages of action potentials?
depolarisation
repolarisation
hyperpolarisation
what happens during hyper polarisation?
potassium channels remain open which temporarily further action potentials (refractory period)
What is temporal summation?
stimuli in different places in the synapse at the same time
What is spatial summation?
stimuli in the same place in the synapse at different times
