Outcome 5 - Nervous System Flashcards
What are the 3 primary functions of the nervous system?
1) sensory
2) integrative
3) motor
What is the integrative function?
It is the procession, analyzing and decision part of the nervous system
Sensory neurons can also be called _______.
afferent
Motor neurone can also be called ________.
efferent
What are the 2 main divisions that make up the nervous system?
1) CNS
2) PNS
The PNS division will divide into 2 different additional divisions. What are they?
1) Autonomic
2) Somatic
What branch is called the “brain of your gut”?
Enteric
Which PNS division is involuntary? Voluntary?
Involuntary - Autonomic
Voluntary - Somatic
What are the three branches of the autonomic division of the nervous system?
1) Sympathetic
2) Parasympathetic
3) Enteric
Which division of the autonomic nervous system is activated during stress?
Sympathetic
Which division of the autonomic nervous system is activated to “stop and digest”?
Parasympathetic
Which type of muscles do motor neurons of the somatic system conduct impulses to?
Skeletal
What are the 2 principle cells of the nervous system?
Neurons and neuroglia
What characteristic does a neuron share with a muscle cell?
excitability/able to respond to stimulus
What are the four types of neuroglia found in the CNS?
1) astrocytes
2) oligodendrocytes
3) microglia
4) ependymal
What are the 2 types of neuroglia found in the PNS?
1) Schwann cells
2) satellite cells
What is the astrocyte responsible for?
- most abundant
- wrap processes around capillaries, neurons and Pia matter; structural support
- responsible for maintaining chemical balance in environment (mainly brain blood barrier)
- regulate environment for APs
What is the ependymal cells responsible for?
- type of epithelial cell
- lines the central canal is where the spinal cord is situated and ventricles of the brain
- responsible for the CSF blood barrier; produces CSF
What is the name of the structural feature where the cell body and axon meet?
Axon hillock
Which portion of the neuron is the receiver or “input”?
Dendrites
What type of neuron is found mostly in the brain and spinal cord?
Multipolar
A bundle of axons located in the CNS is called a _____.
tract
A bundle of axons located in the PNS is called a _______.
nerve
Why is white matter white?
Myelinated axons
White matter contains cell bodies. T/F
False
What component of the myelin sheath allows for some regeneration of axons in the PNS?
Schwann cells
What is the cell responsible for myelination of the CNS axons?
Oligodendrocytes
What type of electrical signal is used for short distance communication in the dendrite and cell body?
Graded potentials
What type of electrical signal is used for long distance communication in the axon?
action potentials
What is a resting membrane potential?
It is more negative inside the cell and more positive along the outside of the cell. (difference in voltage across the membrane when the neurone is at rest)
What are the four types of ion channels found in a neuron?
1) leakage channels
2) voltage gated
3) mechanically gated
4) ligand gated
What are leakage channels responsible for?
the resting membrane potential (Na+ and K+ leak channels)
What are the voltage gated channels responsible for?
depolarization and repolarization (APs)
What is the important characteristic of the mechanically gated channels?
They’re responsive to sensory receptors
What are ligand gated channels for?
chemical synapses
What cation is found in high concentration on the inside of the cell?
potassium
What active transport pump is said to be electrogenic?
Sodium-Potassium ATPase pump
What are the two phases of an action potential?
depolarization and repolarization
What is the absolute refractory period?
Period of time after an AP begun where a second AP can’t be created regardless of the strength (Na+ channels have to be back to resting state for another AP to occur)
What does saltatory conduction entail?
Myelinated axons + nodes of Ranvier – AP at a node to stimulate the myeline sheath to have a conduction current to carry the AP to the next node
What type of synapse is fastest?
Electrical
The influx of which cation causes exocytosis of the synaptic vesicles?
Calcium (Ca2+)
What anatomical structures are included in the CNS?
brain and spinal cord
What are neurons made up of?
axon, dendrites, and cell body
What is a ganglion?
it is a collection of neuronal cell bodies in the PNS
What is the nucleus in terms of the nervous system?
a collection of neuronal cell bodies in the CNS
The nervous system makes up ____ of your total body weight.
3%
What is the function of the sensory receptors?
To detect stimuli
Sensory neurons carry the nerve impulses away from the brain. T/F
False.
carries impulses TO the brain
Integration/processing is performed by _______.
Interneurons
What are some characteristics of the interneurons?
- they have short axons that contact nearby neurons in the BRAIN and SPINAL CORD
Motor neurons carry info ____ (to/from) the brain
from the brain
What makes up the PNS division?
cranial nerves, spinal nerves, ganglia, enteric plexuses, sensory receptors
How is the spinal cord connected to the brain?
Foramen magnum
What do sensory neurons provide information about?
the somatic senses, and special senses
What are somatic senses?
tactile, thermal, pain and proprioceptive sensations
What are special senses?
smell, taste, vision, hearing and equilibrium
Where do motor neurons convey output to?
somatic and autonomic nervous system
What is the enteric plexus?
networks of neurons located in the walls of the GI to help regulate digestion
What causes the propagation of AP?
when AP is initiated, it travels along the membrane of a neuron due to the movement of ions through interstitial spaces or ion channels
What is an example of a long, long neuron?
sensory neurons
Where are the shorter neurons found?
within the CNS
What are characteristics of neuroglia?
- comprise 1/2 the volume of CNS
- smaller than neurons
- 5-25x more abundant than neurons
- they don’t generate or propagate APs
- they can multiply and divide in mature nervous tissue
What are neuroglia?
specialized connective tissue that helps with nourishment, protection, and maintaining chemical environment
What are oligodendrocytes responsible for?
form and maintain myelin sheath around CNS axons
what are microglia responsible for?
phagocytosis in development and repair
What are Schwann cells responsible for?
it forms myelin sheath around PNS axons
what are satellite cells responsible for?
surrounds ganglia and provides support and regulate exchange of material
What are the axolemma?
- the plasma membrane of the axon
What is the axon hillock?
- point in which the cell body connects to the axon
Where is the trigger zone where APs can start?
between the initial segment and the axon hillock
What are the 5 types of neurons?
1) multipolar
2) bipolar
3) unipolar
4) purkinje
5) pyramidal
What type of neurons make up the majority of interneurons?
- multipolar
Describe multipolar neurons.
- have more than two branches/nerve fibres coming off of the cell body
Describe bipolar neurons.
- two nerve fibers/dendrites/axons coming off the body
Describe unipolar neurons.
- one nerve fibre coming directly off the cell body
- aka pseudounipolar
What type of neurons make up the sensory receptors?
mostly unipolar neurons and are quite long!
What are myelin sheath?
multilayered lipid and protein covering that surrounds an axon
What is the purpose of the myelin sheath?
electrically insulate neurons, and increase the conduction speed of APs
Schwann cells cover _____ of an axon, and wrap itself around the axon about _____ times.
1mm, 100x
What is the neurolemma?
the outer layer that contains the cell organelles and the nucleus
What does the neurolemma do?
it aids in the repair of damaged axons and guides regeneration of axons
What is one difference between myelinated CNS and PNS axons?
CNS - few nodes of ranvier present
PNS - has neurolemma
Amount of myelination decreases from birth to maturity. T/F
False.
It increases
Increasing presence of myelin = _____ in nerve impulse conduction
INCREASE in nerve impulses
What gives grey matter its color?
Nissl bodies
How is the white and grey matter situated in the spinal cord?
white matter surrounds an inner core of grey matter
How is the white and grey matter situated in the brain?
thin shell of grey matter covers cerebrum and cerebellum
Which matter has more blood flow? And by how much?
Grey matter by 4x.
What are the two types of electrical signals?
1) graded potentials
2) action potentials
What is the difference between graded and action potentials?
graded - short distances
action - communication over long distances
____ potentials trigger axons to form nerve ______ potentials.
graded, action
How do graded potentials trigger APs?
in dendrite and cell bodies trigger graded potentials
then the graded potentials will trigger the axon to form the action potential
What is the purpose of graded potentials?
graded potentials drive the axon hillock to threshold membrane potential to generate AP
Graded potentials can be _______ (inhibitory) or ________ (excitatory).
hyper polarizing, depolarizing
At resting state, which side of the cell is more negative? positive?
negative - inside (cytoplasm)
positive - outside (interstitial space)
What is the resting membrane potential of neurons?
between -40 mV and -90 mV
typically ~-70 mV
What does the (-) indicate when describing the resting membrane potential?
it indicates that the INSIDE of the cell membrane is negative relative to the OUTSIDE
What plays a role in insulating and keeping out specific ions?
the lipid bilayer
What causes the _____ to open and close.
- leakage channels
- voltage gated channels
- ligand-gated channels
- mechanically-gated channels
- leakage = randomly open
- voltage-gated = change in membrane potential (voltage)
- ligand-gated = chemical stimulus
- mechanically-gated = mechanical stimulus
What factors generate resting action potential?
1) unequal distribution of ions in the ECF and cytosol
2) inability of most anions to leave the cell
3) electrogenic nature of the Na+/K+ ATPases
What is concentration gradient?
moving from an area of high concentration to low concentration
Extracellular: high ____ and _____
[Na+] and [Cl-]
Intracellular: high ____, _____, and _____.
ATP, protein and [K+]
The plasma membrane has more ____ leak channels. Which causes _____ diffusion of K+ to ______ of cell.
K+
MORE, INSIDE
What is the ratio of Na+ to K+ that gets move in Na+/K+ ATPase channels?
3 Na+ out to 2 K+ in
Where do graded potentials occur?
dendrites and cell bodies
What is a summative effect?
when several graded potentials “add up” to lead to an action potential in the trigger zone of the axon
Where do you find the two types of voltage-gated channels?
1) in axon plasma membrane (axolemma)
2) in the axon terminals (telodendria)
What happens when during depolarization?
voltage-gated NA+ channels OPEN causing Na+ ions rush IN to make the inside more positive inside
What happens during repolarization?
voltage-gated K+ channels open causing K+ ions to rush OUT to make the cell more negative
Describe the action potential events.
1) at resting membrane potential: voltage-gated Na+ channels are in resting state and voltage-gated K+ channels are closed
2) stimulus causes depolarization to threshold
3) voltage-gated Na+ channel activation gates are opens
4) voltage-gated K+ are open and Na+ inactivation gate opens
5) voltage-gated K+ channels are still open: Na+ channels are in the resting state
What is hyperpolarization?
when the membrane is temporarily more -ve than resting level
What causes hyperpolarization?
due to K+ voltage gated channels remaining open after repolarization
What are key points to remember about AP?
- all or nothing.
- same results every time
- AP can travel short or long distances
- each neuron will have its own threshold level; threshold is usually constant in cell
What is the absolute refractory period?
period of time after an AP has begun that 2nd AP can’t be created; allows for the movement of AP in one direction
What is the relative refractory period?
the period of time after an AP has begun that a 2nd AP CAN be created but only if the stimulus is greater than normal
- occurs when Na+ channels are back to their resting state and K+ channels aren’t.
What is the mode of conduction for action potentials?
propagation
How long does a single AP take?
0.5-2 msec
AP travels faster in ______ diameter axons.
larger; because it has less resistance for ions to flow
What are saltatory conductions?
special mode of nerve impulses that occurs along myelinated axons; occurs because of uneven distribution of voltage-gated channels
What are the two kinds of synapses?
1) electrical synapse
2) chemical synapse
What are the presynaptic neurons?
nerve cells that carries a nerve impulse toward a synapse; cell that sends the signals
What are the postsynaptic cell/postsynaptic neuron?
cell that receives a signal; carries nerve impulses away from a synapse or an effector cell that responds to the impulse at the synapse
What are the three types of synapses?
1) Axondendritic
2) axosomatic
3) axoaxonic
Describe axodendritic synapses.
they are between axons and dendrites and most common
Describe axosomatic synapses.
they are between axons to cell body; takes a weaker stimulus to create a graded potential
Describe axoaxonic synapses.
they are between axon to axon
What are gap junctions?
AP conductions that are directly between plasma membranes of adjacent neurons
What are connexons?
tunnels to connect 2 cells’ cytosol, it aids in the flow of ions to allow for AP to spread
What are characteristics of electrical synapses?
1) it allows for faster communication; AP directly from presynaptic to postsynaptic cell
2) synchronization to coordinate activity of a group of neurons or muscle fibres
What is the synaptic cleft?
it is the area that separates the pre and post synaptic neurons
- about 20-50 nm and filled with interstitial fluid
There IS conduction across the synaptic cleft. T/F
False.
No conduction.
How do chemical synapses work?
Presynaptic neurons releases neurotransmitters (NT) to bind to receptors on post synaptic neurons
How do chemical synapses work?
NTs bind to ligand gated channels to open and allow for ions to flow into the cell to cause postsynaptic potential (graded potentials)
Are electrical synapses faster than chemical synapses?
Yes because there is direct conduction.
What is the difference between electrical synapses and chemical synapses?
electrical synapses - APs conduct directly between plasma membranes of adjacent neurons through gap junctions/connexons (touch ish.)
chemical synapses - plasma membranes don’t touch and the use of NTs
What are some examples of small molecule NTs?
Acetylcholine, norepinephrine, epinephrine, serotonin, dopamine
What are some examples of neuropeptides?
endorphins, amphetamines, angiotensin II, CCK, hypothalamic-releasing & inhibiting hormones
Describe the sequence of events that occur at a chemical synapse during the transmission of a nerve impulse.
- Starts with pres. Nerve impulse travels down to the synaptic bulbs
- AP reaches synaptic bulbs
- That causes Ca2+ gated channels to open at the synaptic bulbs causing an influx of Ca2+
- Which causes exocytosis (release) of the synaptic vesicles full of neurotransmitters
- Neurotransmitters to bind to the ligand gated channels to open and let in a flow of ions in
- Causes postsynaptic potential (graded potential) if enough, it’ll cause a nerve impulse
*one-way information transfer
