Neurophysiology Flashcards
What are the general functions of the nervous system?
- Sensory (internal - e.g. BP & external - e.g. ppl. touch you)
- Communicative (within body system)
- Integrative (integrates info - e.g. you see wild boar = inc HR)
- Motor (movement)
What does the central nervous system consist of?
Brain
Spinal cord
What does the peripheral nervous system consist of?
Nerve fibers (made of axons of neurons)
neurons = nerve cells
The nervous system is organised into:
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
How many pairs of cranial nerves are there?
12 pairs !!
What are cranial nerves?
Nerves…
Can be a motor nerve or a sensory nerve OR both
Each nerve is responsible for a function (e.g. vagus nerve - main nerve for parasympathetic NS)
How many pairs of spinal nerves are there?
31 pairs !!
Where does the spinal cord end and what follows after?
Spinal cord ends around L1
After spinal cord ends, there is the Cauda equina (from L1 to Co)
Where does cervical nerve 8 lie?
Since there are only 7 cervical vertebrae, cervical nerve 8 lies BELOW C7
Where do the nerves lie before C7?
Where do the nerves lie after C7?
Before C7, the nerves lie BEFORE vertebrae
After C7, the nerves lie AFTER vertebrae
What is the PNS divided into?
- Afferent division (“A” for advance)
- Efferent division (“E” for exit)
What does the afferent division of the PNS do?
- Carries info to CNS (“A” for advance = advance into CNS (enters))
- Sensory & visceral (from internal organs) stimuli
Basically the input
What does the efferent division of the PNS do?
Transmit information from the CNS to effector organs (“E” for exit = exits CNS to go to organs)
Basically the output
What is the efferent nervous system divided into?
- Somatic nervous system
- Autonomic nervous system
What is the somatic nervous system?
- Fibers of motor neurons that supply skeletal muscles
- Subjected to VOLUNTARY control
What is the autonomic nervous system (ANS)?
- Fibers that innervate smooth muscle, cardiac muscle, & glands
- INVOLUNTARY
- Sympathetic & parasympathetic
What does an autonomic nerve pathway consist of?
two-neuron chain (in general!)
- Preganglionic neuron
- Postganglionic neuron
What does the preganglionic neuron do?
It synapses with the cell body of the postganglionic fiber in a ganglion outside the CNS
What is a synapse?
Connection b/w two neurons
What does the postganglionic neuron do?
Sends axons that end on the effector organ
What is a ganglion?
Cluster of neuronal cell body
What is dual innervation?
Innervation of a single organ by both branches of the autonomic nervous system
Sympathetic & parasympathetic dually innervate most visceral organs
Sympathetic
Parasympathetic
Sympathetic: “fight-or-flight”
Parasympathetic: “rest-and-digest”
Where are preganglionic neurons located in the sympathetic NS?
Located between segments T1 and L2 of the spinal cord
Where are the ganglion located in the sympathetic NS?
Closer to the spinal cord = can trigger action potential to a lot of neurons that lead to many different effectors
Small signal send down 1 path can trigger many effectors at once (bc one ganglion = many postganglionic fibers)
Why are post ganglionic fibers longer in the sympathetic NS?
Post ganglionic fibers are longer to ensure rapid & widespread responses
Which are longer in sympathetic innervation:
- Preganglionic fibers
- Post ganglionic fibers
Post ganglionic fibers are longer
Where do the sympathetic fibers originate from?
Thoracolumbar region = T1 to L2
Where do parasympathetic fibers originate from?
Craniosacral division = cranial, trunk, pelvic (above & below where the sympathetic fibers originate)
Parasympathetic innervation distribution
Long preganglionic & short postganglionic (more specific signals)
Effects of sympathetic stimulation on organs
Just read through –> can think of it on the spot (slide 16 of neuro1)
Sympathetic –> physical, stressful
- Heart: Inc HR & inc force of contraction of heart
- Most innervated blood vessels: constricts
- Lungs: dilates bronchioles, inhibits mucus secretion
- Digestive tract: dec motility, inhibits digestive secretions, contracts sphincters (prevent forward movement of food)
- Urinary bladder: relaxes
- Eye: dilates pupil, adjusts eye for far vision
- Liver: glycogenolysis (glucose released)
- Adipose cells: lipolysis (fatty acids released)
- Exocrine glands: inhibits pancreatic exocrine secretion, stim secretion of sweat glands, stim small vol. of thick saliva rich in mucus
- Endocrine glands: stim epinephrine & norepinephrine secretion, inhibit insulin secretion, stim glucagon secretion,
- Genitals: controls ejaculation & orgasmic contractions
- Brain activity: inc. alertness
Sympathetic NS vs Parasympathetic NS
Origin of preganglionic fibe:
- Sym: thoracic & lumbar region of spinal cord
- Para: brain & sacral region of spinal cord
Origin of postganglionic fiber:
- Sym: ganglion chain (near spinal cord) OR collateral ganglia (in b/w spinal cord & effector organs)
- Para: terminal ganglia (in/near effector organs
Fiber length:
- Symp: Short preganglionic fibers, long postganglionic fibers
- Para: Long preganglionic fibers, short postganglionic fibers
What is grey mattetr?
Generic term for collection of cell bodies (soma) in CNS
(DIFFERENT from ganglion = collection of cell bodies OUTSIDE CNS)
What is white matter?
Generic term for collection of CNS axons
How is the CNS protected from injury?
- Cranium & vertebral column
- Meninges (covers brain & spinal cord)
- Cerebrospinal fluid
- Blood-brain barrier
What is meninges?
- Three meningeal mbns
- Wrap, protect & nourish CNS
- Continuous with spinal meninges
What are the three meningeal membranes?
- Dura mater (most superficial; tough & inelastic )
- Arachnoid matar
- Pia mater (most inside - closely adhered to brain surface
What is located between the Arachnoid matar and the Pia matar?
Subarachnoid space
- Spiderweb-like structure
- Spaces b/w the spiderweb-like structure (lines) = Cerebrospinal fluid
How does the cerebrospinal fluid (CSF) protect the CNS?
- Shock absorbing fluid
- Brain floats in CSF, so surrounded by CSF and it cushions brain & spinal cord
- Cushions delicate neural structures
- Supports brain
- Transports nutrients, chemical messengers, wastes products
Where is cerebrospinal fluid formed?
Produced by ependymal cells of the choroid plexuses in ventricles (fluid-filled cavities) in brain
What are the ventricles of the brain?
Fluid filled cavities (filled with CSF)
Connected to e/o so CSF can flow from 1 ventricle to another
Production of CSF
- Produced by ependymal cells of choroid plexuses (in one of the ventricles)
- Circulates throughout the ventricles
- Exits 4th ventricle
- Flow into subarachnoid space
- Reabsorb into venous blood
How does the blood-brain barrier protect the CNS?
- Isolates CNS neural tissue from general circulation
- Highly selective BBB regulates Xchanges b/w blood & brain
- Allows chemical composition of bld. & CSF to differ
- Selectively isolates brain from chemicals in blood that might disrupt neural function
- Limits use of drugs for treatment of CNS
What is the BBB formed by?
Formed by network of tight junctions (formed by capillaries)
How is the CNS nourished?
Brain depends on constant delivery of oxygen & glucose by blood
bc. brain only utilizes glucose but X store it & X produce ATP w/o O2
What happens if brain is deprived of O2?
brain damage
- bc X anaerobic respiration
What % of body weight is the brain?
About 2% of body weight
BUT requires 13-15% of cardiac output
General functions of the central nervous system (CNS)?
- Subconsciously regulate homeostatic responses
- Experience emotions
- Voluntary control movements
- Perception of body & surroundings (inc. proprioception)
- Engage in other higher cognitive processes
What are the components of the brain?
- Brain stem
- Cerebellum
- Forebrain
- Diencephalon: Hypothalamus & Thalamus
- Cerebrum: Basal nuclei (basal ganglia)
- Cerebral cortex
Which 3 structures in the brain ensure proper control of movement?
- Cerebral cortex
- Basal nuclei
- Cerebellum
What are the functions of the cerebral cortex?
- Sensory perception
- Voluntary control of movement
- Language
- Personality traits
- Cognitive processes = thinking, memory, decision making, self-consciousness, creativity
What are the functions of the basal nuclei?
- Inhibition of muscle tone
- Coordination of slow, sustained movements
- Suppression of useless patterns of movement
What are the functions of the thalamus?
- Relay station for all synaptic input EXCEPT olfactory input
- Crude awareness of sensation
- Some degree of consciousness
What are the functions of the Hypothalamus?
- Regulation of many homeostatic functions
- Important link b/w nervous & endocrine systems
- Extensive involvement with emotion & basic behavioural patterns
- Role in sleep-wake cycle
What are the functions of the cerebellum?
- Maintenance of balance
- Enhancement of muscle tone
- Coordination & planning of skilled voluntary muscle activity
What are the functions of the brainstem?
- Origin of majority of peripheral cranial nerves
- Cardiovascular, respiratory & digestive control centers
- Regulation of muscle reflexes involved with equilibrium & posture
- Reception & integration of all synaptic input from spinal cord; arousal & activation of cerebral cortex
- Role in sleep-wake cycle
What are the four lobes of the cerebral cortex?
- Frontal lobe
- Parietal lobe
- Occipital lobe
- Temporal lobe
What is the main function of temporal lobe?
Memory formation
What is the main function of the frontal lobe?
Prefrontal - complex cognitive, decision making, personality, social behaviour
What is the main function of the parietal lobe?
Somatosensory processing
What is the main function of the occipital lobe?
Visual
What is the sensory & motor homunculus?
Somatotopic map
- Proportion of somatosensory cortex devoted to reception of sensory input from each area
- Dist. of motor output from primary motor cortex to diff parts of the body
- Precise dist. is unique for each individual
- Use-dependent modification (can change with activity –> plasticity)
What is the spinal cord?
Long, slender cylinder of nerve tissue that extends from brain stem through vertebral canal & is connected to spinal nerves
- enclosed by protective vertebral column
What resides in the dorsal root ganglion?
Cell bodies of sensory afferent system
What are dermatomes?
Area of skin is supplied by a single spinal cord level (or a single spinal nerve on one side)
- Localise lesions to a specific spinal nerve/spinal level
What are myotomes?
Portion of skeletal muscle innervated by a single spinal cord level, (or a single spinal nerve on one side)
- Each skeletal muscle usually innervated by nerves from MORE THAN ONE spinal cord level
What information does the posterior root carry?
Posterior/dorsal root
Carries sensory information
What information does the ventral root carry?
Carries motor information
What does the ramus carry?
Sensory & motor information
Anterior ramus - go to the anterior side (skin & muscle on anterior side of trunk)
Posterior ramus - go to posterior side (skin & skeletal muscles of the back)
Dorsal & Ventral horn
Dorsal horn –> sensory information
Ventral horn –> motor information
The grey matter split in half
What are nerve plexuses?
Network of nerves that come together & then redistribute themselves out with a different distribution of nerves into the limbs
Either somatic or visceral
What happens in nerve plexuses?
- Fibers combine from different sources/level –> form new nerves with specific targets/destinations
- Each nerve exiting the plexus may contain fibers from diff spinal nerves
Advantage of nerve plexuses
When a muscle is innervated by nerves from a nerve plexus, damage to a single spinal nerve is less likely to result in total paralysis of that muscle
Do plexuses affect dermatome?
No!! Even with nerve plexuses, you can still have dermatome –> does not affect outcome)
Note: Dermatomes can overlap!
What are neurons?
- Basic functional units of the nervous system
- Conducting cells of the nervous system –> processes & transmit info (electrical & chemical)
Structure of neurons
- Cell body (aka soma) –> contains organelles essential for survival (nucleus, mitochondria, etc)
- Short, branched dendrites –> highly branched, receives info from other neurons
- Long, single axon –> carries electrical signal (action potential) to target
What kinds of neurons are there?
- Bipolar neuron
- Unipolar neuron
- Multipolar neuron
Bipolar neuron
Rare –> found in organs for sight/sound/smell
Has two processes separated by the cell body
Basically: dendrite –> cell body –> axon
(cell body sandwiched b/w dendrite & axon)
Unipolar neuron
Common for sensory afferents
Has a single elongated process, with cell body located off to the side
Basically: axon & dendrite are continuous
Multipolar neuron
Common in CNS
Have more than two processes –> single axon & multiple dendrites
What are neuroglia?
Non-conducting cells –> support neuronal function
~50% of total cell population in nervous system
Types of neuroglia
- Astrocytes
- Myelinating glia
- Microglia
- Ependymal cells
What do astrocytes do?
Regulate chemical content of the extracellular space
What are some myelinating glia?
Oligodendrocytes (CNS) & Schwann cells (PNS)
What do microglia do?
Phagocytic role –> engulf cells, remove cell debris/wastes
Immunity
What do ependymal cells do?
Produce CSF
Located in choroid plexuses in ventricles
Definitions of membrane potentials (?)
- Polarization
- Depolarization
- Repolarization
- Hyperpolarization
- Polarization: mbn potential is not 0 mv
- Depolarization: potential becomes less polarized than resting potential (moves towards 0)
- Repolarization: potential returns to resting potential after being depolarized (moving back towards -70mv)
- Hyperpolarization: potential becomes more polarized than resting potential (moves past -70mv)
What do nerves use to communicate?
Neurons use electrical signals to receive, process, initiate, transmit messages –> sends to muscle cells
Electrical signals initiate contraction in muscle cells
Why is the resting membrane potential -70 mv?
Equilibrium potential of K+ is -90mv
Equilibrium potential of Na+ is +60mv
K+ exerts the dominant effect on resting mbn potential bc mbn is more permeable to K+
(small net diffusion of Na+ neutralizes some of the potential created by K+)
So, resting potential closer to equilibrium of K+ instead of Na+
What does the Na+-K+ pump do?
Actively transports Na+ out of the cell & K+ into the cell
–> keeps conc of Na+ high in ECF & keeps conc of K+ high in ICF
How are electrical signals produced?
Produced by changes in ion movement across the plasma mbn
- event triggers a change in mbn potential
- alters mbn permeability –> alters ion flow across mbn
What kind of gated channels are there?
- Voltage gated (changes in mbn potential)
- Chemically gated (e.g. neurotransmitters: acetylcholine –> open/close in response)
- Mechanically gated (e.g. can be pulled open)
- Thermally gated (in response to temp)
How do voltage gated channels work?
When there is a voltage threshold –> there is a voltage gated channel (detect changes in mbn potential/threshold values)
When certain voltage (threshold voltage) is reached (e.g. depolarizing event) –> gate opens
What are graded potentials?
- Local changes in mbn potential
- Occurs in varying grades/degrees of magnitude/strength
(stronger triggering event = larger resultant graded potential)
Action potential vs graded potential
Action potential:
- No size –> either HAVE or DON’T HAVE
- Can travel across axon
Graded potential:
- Can be varying degrees of magnitude/strength
- Cannot travel over axon, spread locally only
How are graded potentials spread?
Spread by passive current flow
- Current: any flow of electrical charges
- Resistance: hindrance to electrical charge movement
Locallly!!
DIE OUT over short distances
What are action potentials?
Brief, rapid, large changes in mbn potential
- Inside of excitable cell transiently becomes more +ve than the outside
What leads to action potentials?
Marked changes in mbn permeability & ion movement lead to an action potential
What are the ion channels involved in the generation of action potentials?
Voltage-gated sodium channel
Voltage-gated potassium channel
Which voltage-gated ion channel opens first?
Na+ opens first because rapid compared to K+
K+ is delayed in opening
BUT both are triggered at threshold
What are the three states of the voltage-gated sodium channel?
- Closed but capable of opening (inactivation gate is open)
- Open (activated)
- Closed & not capable of opening (inactivated)
Steps in generation of action potentials (8 steps)
- Resting potential: all voltage-gated channels closed
- At threshold, Na+ channel opens (activated) & permeability of Na+ inc.
- Na+ rush in –> causes explosive depolarization to +30 mv –> generates rising action potential
- At peak of AP, Na+ channel inactivated, permeability of Na+ dec. (net movement of Na+ ends), K+ channel opens & permeability of K+ inc.
- K+ leaves cell –> repolarization to resting potential –> generates falling phase of AP
- Return to resting potential –> Na+ channel resets to “closed but capable of opening” state –> ready to respond to another depolarising triggering event
- Further outward movement of K+ through still-open K+ briefly hyperpolarizes mbn –> generates after hyperpolarization
- K+ channel closes & mbn returns to resting potential
What happens when membrane potential has been restored to resting (at the completion of an action potential)?
Ion distribution has been altered slightly (only small amounts of Na+ rush in & K+ rush out)
Where are action potentials propagated from?
From the axon hillock to the axon terminals
Na+-K+ pumps
- Pump has:
- 3 high-affinity sites for Na+
- 2 low-affinity for K+
when exposed to ICF - When Na+ from ICF (conc. low) binds to pump –> splits ATP into ADP + phosphate group binds to pump
- Phosphorylation causes pump to change conformation = Na+ binding sites are exposed to opposite side of mbn & 3 Na+ are released ECF –> affinity of Na+ binding sites greatly dec.
- Change in shape also exposes pump’s binding sites for K+ to ECF & greatly inc. affinity of K+ sites
- When 2 K+ from ECF (conc low) bind to pump –> release phosphate group. Dephosphorylation causes pump to revert to its original conformation
- Two K+ are released to ICF (K+ conc. high) as affinity of K+ binding sites dec. during change in shape
At same time: affinity of Na+ binding sites inc.
How does action potential propagate along an axon?
- Input zone (dendrites) –> receives incoming signals from other neurons
- Trigger zone (axon hillock) –> initiates action potentials
- Conducting zone (axon) –> conducts action potentials in undiminishing fashion, often over long distances
- Output zone (axon terminals) –> releases NT that influences other cells
What does refractory period do?
- Ensures one-way propagation of AP & limits their frequency
- Prevents tetanic contraction
- Cannot be initiated in a region that has just undergone an AP (for a while)
BASICALLY,
during repolarization, cannot have another AP
What do the “backward” current and “forward” current do?
“Backward” current flow = X reexcite previously active area bc area is in refractory period
“Forward” current flow = excites new inactive area
What is absolute refractory period?
Membrane CANNOT respond to further stimulation
IMPOSSIBLE to send more AP
Inactivation of Na+ channels & activation of K+ channels to start repolarization
What is relative refractory period?
Membrane CAN respond only to a LARGER-than-normal stimulus
Time lag in closing all K+ channels leading to temporary hyperpolarization
Basically, Relative refractory period happens after absolute refractory period
Can weak stimuli initiate AP?
NO
Does not initiate AP bc it doesn’t cross threshold
AP allows discrimination of stimuli –> all or NONE
How does the strength of stimulus affect AP?
The stronger the stimulus, the higher the frequency of AP
Magnitude of each AP is the SAME but frequency can CHANGE
What increases the speed of conduction of action potentials?
Myelination
Myelin + fiber diameter = inc. speed of conduction
What influences the velocity of action potential propagation?
Fiber diameter
What is myelination?
Myelin = thick layer of lipids
Acts as insulation to “electrical transmission” along the axon
Advantages of saltatory conduction
- Faster bc have myelin
- Can keep the strength of the AP
What happens in saltatory conduction?
- Action potentials occurs at the 1st node
- Na+ flows into the axon through Na+ channels
- Local current flow depolarises adjacent node
- Second node reaches threshold & AP occurs
- Na+ gate opens & Na+ rushes in
- At the same time (as 5), outward flow of K+ restores 1st node to resting potential
so AP jumps from node to node
What is a synapse?
Junction b/w neurons
What are electrical synapses?
Neurons connected directly by gap junctions
What are chemical synapses?
Chemical messenger transmits information one way across a space separating two neurons
Most synapses in human NS are chemical synapses
Anatomy of chemical synapse
Presynaptic terminal - from the axon
Postsynaptic dendrite - receives
Synaptic cleft - space b/w the presynaptic terminal & postsynaptic dendrite
Steps in the synaptic transmission
- Depolarization:
Presynaptic terminal is depolarized –> AP travels down & reaches axon terminal (results in step 2) - Influx of calcium:
Opening of voltage-gated Ca2+ which results in influx of Ca2+ - Docking:
Ca2+ signals synaptic vesicles (contains neurotransmitters) to docking protein - Release of Neurotransmitter:
Once the synaptic vesicles dock, neurotransmitters are released into synaptic cleft - Binding of neurotransmitter to receptor:
On postsynaptic terminal
The binding of neurotransmitters to receptor usually results in that ion channel opening
What happens to the neurotransmitter after synaptic transmission?
Must be broken down/removed from the synapse
If it remains there, it will constantly activate post synaptic neuron
How many inputs can a neuron receive?
MULTIPLE inputs from MANY presynaptic axons
What are receptor channels?
Combined receptor & channel units
Present in postsynaptic neuron
Types of synapses
- Excitatory synapses
- Inhibitory synapses
What are excitatory synapses?
Generation of excitatory post-synaptic potential
Brings resting mbn potential closer to the threshold
What are inhibitory synapses?
Generation of inhibitory post-synaptic potential
Brings resting mbn potential away from threshold
How do drugs & diseases affect synaptic transmission?
- Can modify synaptic transmission
- Agonise/Antagonize the receptors
- Influence NS function by altering synaptic mechanisms (most affect neurotransmitter receptors by e.g. blocking/enhancing action/activating)
How are neurons linked?
Convergence
Divergence
Convergence pathway of neurons
Neuron may have many other neurons synapsing on it –> lots of signals converge
basically, one cell influenced by many others
Divergence pathway of neurons
Branching axon terminals so a single cell synapses & influences other cells –> signal diverted
basically, one cell influences many others
Functions of acetylcholine
PNS: Neuromuscular junctions, parasympathetic nerves
Usually generates excitatory post-synaptic potential
Function of dopamine
Involved in many pathways in CNS (such as muscle movement & reward pathway)
Function of glutamate
Primary excitatory neurotransmitter in CNS (excitatory post-synaptic potential)
Function of Gamma-aminobutyric acid (GABA)
Primary inhibitory neurotransmitter in CNS (inhibitory post-synaptic potential)
Effect of parasympathetic stimulation on organs
Just read through –> can think of it on the spot (slide 16 of neuro1)
Parasympathetic –> relax, chill, quiet
- Heart: Dec HR & dec force of contraction of atria
- Most innervated blood vessels: dilates vessels supplying to genitals
- Lungs: constricts bronchioles, stim mucus secretion
- Digestive tract: inc motility, stim. digestive secretions, relaxes sphincters (prevent forward movement of food)
- Urinary bladder: conttracts
- Eye: constricts pupil, adjusts eye for near vision
- Liver: none
- Adipose cells: none
- Exocrine glands: stim pancreatic exocrine secretion, stim large vol of watery saliva rich in enzymes
- Endocrine glands: stim insulin & glucagon secretion
- Genitals: controls erection
- Brain activity: none
