Slide Set 4 Flashcards
The nervous system is composed of
- Central nervous system
- peripheral nervous system
CNS
= structural and functional center of entire nervous system
= brain + spinal cord
PNS
= cranial, spinal nerves
The nervous system is divided according to the types of organs they innervate :
- somatic nervous system
- autonomic nervous system
Which system do we have control over?
SNS
Which system has no voluntary control over?
ANS
somatic nervous system is composed of 2 divisions
afferent : sensory division, info carried to somatic integration center (CNS)
efferent : motor division, info carried to somatic effectors (skeletal muscles)
autonomic nervous system is composed of 2 divisions
afferent (incoming): from visceral receptors
efferent (outgoing) : to visceral effectors
Efferent (outgoing) division of ANS is divided into
- parasympathetic : “rest-and-repair”
- sympathetic : “fight-or-flight” response
Heart rate is controlled by
sympathetic system
Stomach is controlled by
parasympathetic system
Cells of nervous system
- neurons : conduct impulses
- glial cells : support function of neurons
Neurons
- dendrites : receive signals
- axons : carry outgoing info
5 types of glial cells
- astrocytes
- Microglia
- oligeodendrocytes
- ependymal cells
Astrocytes
Form tight sheets around the brain's capillaries Helps BBB (blood brain barrier)
What can and can’t cross BBB?
can : lipid soluble (ethanol, caffeine, oxygen, glucose)
can’t : water soluble (sodium, potassium) -> need carrier
What can cross BBB and is used to deliver drugs or genetic material into a cell?
Liposome A
What are the macrophages of the brain?
microglia
Which glial cells :
- are macrophages in the brain, usually stationary except in inflamed tissue
microglia
Which glial cells :
- resemble epithelial cells, have glia, allows circulation of fluid
ependymal cells
Which glial cells :
- hold nerve cells together and produce myelin sheath
oligodendrocytes
Which glial cells :
- form tight sheets around brain’s capillaries
- connect neurons to capillaries
- constitute BBB
astrocytes
which glial cells make myelin
oligodendrocytes (in CNS) schwann cells (in PNS)
What is a disorder of oligodendrocytes
multiple sclerosis
characterised by loss and destruction of myelin
Gaps in myelin sheath
= nodes of Ranvier
In PNS which glial cells are present
- schwann cells : support nerve fibres, form myelin sheaths
satellite cells are a type of schwann cell, don’t from myelin sheath
4 functional regions of neuron
- input zone : information received at dendrites and cell body
- summation zone : info summed up at axon hillock
- conduction zone : signal transmitted along axon via voltage gated channels
- output zone : signal given to next axon via synaptic knob
What are interneurons
- within central nervous system
- conduct impulses from sensory neurons (afferent) to motor neurons (efferent)
The reflex arc
- sensory receptor send message to CNS (AFFERENT)
- reaches interneuron
- interneurons elicits outgoing response from motor neuron (EFFERENT)
Bundles of nerve fibres within
- PNS =
- CNS=
- PNS = nerves
- CNS= tracts
What are mature neurons incapable of?
cell division
Can nerve fibres be repaired when damaged?
yes is damage is not extensive : cell body and neurilemma (cytoplasm of schwann cells) are intact
Nerve impulse = electrical signalling =
wave of electrical fluctuation that travels along the plasma membrane, is unidirectional
Resting membrane potential
= when a neuron is not conduction electrical signals
= -70mV
Slight positive ions on a membranes outer surface is produced by :
- ion transport mechanisms
- permeability characteristics of the membrane
Membrane potential
- slight excess of POSITIVE ions on the outside of the cell membrane
- inside is NEGATIVE
Na+/K+ pump :
3Na+ out (-> outside is +)
2K+ in (-> inside is -)
Depolarization
membrane potential becomes less negative
-40mV
Repolarization
return to RMP
hyperpolarization
more negative than -70mv (-80mv)
What determines the RMP
- K+ concentration gradient
- cell’s permeability (to K+, Na+, Cl-)
changes to cell permeability : can depolarise or hyperpolarize a cell
Types of gated channels that control ion permeability
mechanically gates (sensory neurons) chemical gated (response to ligand) voltage gated (changes in membrane potential)
What determines the permeability of the cell membrane?
1- specific membrane transport channels
(only positive ions can move across the cell membrane)
2- active transport mechanism: sodium-potassium ATPase
Action potential
Change in resting membrane potential
Because there is a potential difference across the cell membrane, the membrane is said to be __.
polarized
Stimulus/Excitation of a neuron:
NA+ channels open
- > flows into cell
- > causes depolarisation (inside is +)
- > decrease in membrane potential
Inhibition of a neuron:
K+ channels open
- > flows out of cell
- > causes hyperpolarisation (inside is more -)
- > increase in membrane potential
Treshold potential
usually -59mv
= minimum magnitude of a voltage fluctuation that will trigger the opening of a voltage gated channel
What activates opening of sodium gated channel?
depolarizing stimulus
What activates opening of sodium gated channel?
depolarizing stimulus
-> Na+ rushes in the cell
Na+ channels have 2 gates:
activation
inactivation
When the inactivation gate of sodium channel closes the gated channel, what remains open?
activation gate
Absolute refractory period
a local area of a neurones membrane resists restimulation
NO RESPONSE
=> Na+ open, then close and K+ channels open
Relative refractory period
After absolute RP, membrane will respond only to a VERY STRONG stimulus
=> K+ are still open
Relative refractory period
after absolute RP, membrane will respond only to a very strong stimulus
Consequence of refractory period
prevent restimulation therefore the action potential never goes backwards
What is a saltatory conduction?
Impulse regeneration leaps from node to node (node of Ranvier) and generates the action potential in myelinated axons
Synpases
= gaps where neurotransmitters are released
Where can an axon terminate
- muscle, gland, neuron
Chemical synapse structure
- synaptic knob
- synaptic cleft
neurotransmitters
means by which neurons communicate with one another and with muscle cells, can be inhibitory or stimulatory
neurotransmitters
means by which neurons communicate with one another and with muscle cells
Example of a neurotransmitter
acetylcholine
- excitatory at muscle cells
- inhibitory at cardiac muscle
Neurotransmittor action is terminated by
enzymes
glial cells
Neurotransmittor action is terminated by
enzymes
If 2 excitatory neurons fire and 1 inhibitory neuron fires, i there action potential ?
NO
- inhibitory neuron is stronger
-
- temporal (same stimulus within a critical time)
- spacial (from different sources)
