Neurophysiology Flashcards
What part of the neuron receives incoming signals
Dendrites
A synapse is
A gap between one neuron and the next
The axon hillock is
The signal integration centre of the neuron
Direction of signal in a neuron
Dendrite —> cell body (soma) —> axon hillock —> axon —> jumps across nodes of ranvier —> synapse
Axons may or may not be wrapped in a
Myelin sheath
A collection of cell bodies (soma) is called
Ganglia
Three types of neurons
-multipolar
-bipolar
-unipolar
Multipolar neuron
Many dendrites entering the cell body (soma)
Bipolar neuron
Two processes coming off a cell body (ie. one dendrite, one axon)
Unipolar neuron
One process off the cell body (soma)
Each nerve is made of many types of
Axons
Myelination increases
Speed of transmission
Axons have different
Conduction velocities (an increase in axon diameter will increase velocity)
Sensory (afferent) nerves
From the sensory organ TO the CNS
Motor (efferent) nerves
From the CNS TO the muscles
True or False: a nerve is either sensory (afferent) OR motor (efferent)
False. Most nerves are a mix of both
An impulse is conducted along both
Pre- and post-synaptic neurons (ie. the gap in between neurons)
The nervous system coordinates and regulates incoming (afferent) and outgoing (efferent) information via
Signal (electrical) transmission
Electrically charged molecules are called __. Give three examples and where they are located
Ions
Sodium (Na+) - outside the cell
Potassium (K+) - inside the cell
Chloride (Cl-) - outside the cell
Different ion concentrations on different sides of the membrane creates an
Electrical gradient
Ions have the ___ to move across the membrane, creating a ____
Potential; membrane potential
An electrochemical gradient is established based on these 3 things:
-diffusion of ion DOWN its concentration gradient
-electric charge of the ion (ie. is it positive or negative)
-membrane pumps for that particular ion
Ions wants to move
Down their concentration gradient/electrical membrane (ie. from high concentration to low concentration)
Two types of transport proteins on the semi-permeable membrane
-Channel proteins
-Carrier proteins
Channel proteins vs. Carrier proteins
Channel Proteins: provide a narrow channel for ions to pass through
Carrier Proteins: physically bind to a substance on one side of the membrane and release it on the other
Channel proteins help to
Facilitate passage of ions (sodium and chloride) across the membrane
Ions will follow their concentration gradient until
A dynamic equilibrium is reached
The sodium-potassium pump requires
Energy (ie. it is Active Transport)
Sodium-Potassium pump exchanges
3 Na+ for 2 K+
The resting membrane potential of a mammalian neuron is
—70mV
What part of the cell membrane is positive? What part is negative?
-outside of cell is slightly more positively charged
-inside of cell is slightly more negatively charged
The resting membrane potential in neurons (-70mV) is due to 3 factors:
-cell membrane is “leakier” to K+ (ie. more channels are available for potassium)
-ions diffuse to reach dynamic equilibrium (Na+ diffuses in, K+ diffuses out)
-pumping of both ions by Na-K pump
Neurons are unique in that their resting membrane potential
Can be altered by surrounding pre-synaptic neurons
Three types of membrane states
-Depolarization
-Hyperpolarization
-Repolarization
Membrane states are determined by
The type of neurotransmitter
Depolarization (4)
-charge difference between the inside and outside decreases
-membrane potential becomes less negative
-either positive ions ENTER the cell or negative ions LEAVE the cell
-excitatory post-synaptic potential (EPSP)
Hyperpolarization (3)
-membrane potential becomes more negative
-either positive ions ENTER the cell or negative ions LEAVE the cell
-inhibitory post-synaptic potential (ISPS)
When the cell membrane returns to its resting potential, it is called
Repolarization
Each nerve has its own sown
Threshold potential
Excitatory post-synaptic potential (EPSP)
-when pre-synaptic neuron depolarizes the post-synaptic neuron to its threshold
No summation summation is when
One neuron receives one signal
Spatial summation is when
Multiple neurons are giving a signal
Temporal summation is when
One neuron is giving off multiple signals
A signal will be sent along the axon when
The threshold is reached
Conductance (movement) of Na+ into the cell will (2)
-excite (depolarize)
-increase action potential
The resting membrane potential is ___
—70mV
The absolute refractory period is when
There is no way to generate another action potential
The relative refractory period is when
Another action potential can be generated but needs more excitation as Hyperpolarization has lowered the resting membrane potential
Conductance (movement) of K+ out of the cell will (2)
-inhibit (hyperpolarize)
-decrease action potential
A signal needs to propagate (jump) across an axon via
Saltatory Conduction
Saltatory Conduction (3)
-fast transport of a signal along the axon
-jumping of action potential from one Node of Ranvier to another (ie. jumps over myelin sheath)
-a high concentration of Na+ will produce a passive speed
The myelin sheath is called ___ in the CNS and ___ in the PNS
CNS: Oligodendrocytes
PNS: Schwann Cells
The myelin sheath acts as an
Insulator - there is less current lost across the axon and allows the signal to jump
The gap between one neuron and the next is called the
Synaptic Cleft
Two types of synapses:
-electrical
-chemical (can be ionotrophic or metabotrophic)
The more common type of synapse is
Chemical
Electrical Synpase (3)
-quick, fast response (defensive reflexes, escape behaviours)
-signal is directly transferred from one neuron to the next (narrow gap junction between pre- and post-synaptic cells) via CONNEXONS
-instantaneous via electrotonic current speed
Connexons (3)
-connection between two interacting membranes
-direct transfer of ions between the pre- and post-synaptic cells in both directions
-modulated by intracellular Ca2+ (low concentration opens connexon, high concentration closes it)
Chemical neurotransmission can be (2)
-ionotrophic
-metabotrophic
Connexons will open/close based on
Ca2+ concentration (high = closed, low = open)
Which part of the neuron receives information from the surrounding cells
Dendrite
Action potentials are transmitted along which part of a neuron
Axon
What happens when an inhibitory post-synaptic potential (IPSP) is generated after excitatory post-synaptic potential (EPSP)?
The membrane is more hyperpolarized
During chemical neurotransmission, Ca2+ ions are necessary for
Fusing the pre-synaptic vesicle with the pre-synaptic membrane, thus releasing the neurotransmitter
Acetylcholinesterase rapidly breaks down
Acetylcholine into choline and acetate
An unbound transmitter is either (3)
-degraded
-recycled
-diffused out of synaptic cleft
Calcium entering the cell allows the vesicle to
Release its neurotransmitter out into the synaptic cleft to bind to the post-synaptic receptor
Ligand-gated channels ion the post-synaptic cell will either
-excite (depolarize)
-inhibit (hyperpolarize)
A receptor is named after
The neurotransmitter that binds to it (ex. Nicotinic Acetylcholine Receptor)
A neurotransmitter binding causes
A conformational change in pore proteins (ie. opens ion channel and allows ions to cross the cell membrane)
Ligand-gated ion channels that are permeable to Na+, K+, and Ca2+
-are excitatory (EPSP)
-depolarize (ie. closer to threshold)
Ligand-gated ion channels permeable to Cl-
-are inhibitory (IPSP)
-hyperpolarize (ie. away from threshold
Metabotrophic receptors (4)
-no pore
-neurotransmitter binds and changes shape of receptor, activating a signal transduction pathway
-slower than ionotrophic receptors (more long term effects)
-activates a second messenger system
An example of an ionotrophic receptor is
Nicotinic receptor
An example of a metabotrophic receptor is
Muscarinic receptor
Cholinergic receptors only bind to
Acetylcholine
The neuromuscular junction is between
A motor neuron and skeletal muscle
The neurotransmitter acetylcholine will only bind to
Cholinergic receptors
Adrenergic receptors only bind with
-Adrenalin
-Noradrenalin
Binding to alpha 1 adrenergic receptors causes
Smooth muscle contraction
Binding to alpha 2 adrenergic receptor will either
-inhibit the release of the transmitter
-contract smooth muscle
Binding to the beta adrenergic receptor will cause (3)
-heart muscle contraction
-smooth muscle relaxation
-glycogenolysis
One neurotransmitter can have
Many effects based on the receptor and target tissue
Mitochondria synthesizes
Acetylcholine
The neurotransmitters Adrenalin and noradrenalin bind to
Adrenergic receptors
The neuromuscular synapse steps (8)
- Action potentials arrive at the axon terminal
- Voltage gate Ca2+ channels open
- Ca2+ enters the cell
- Ca2+ signals vesicle
- Vesicles move to membrane
- Docked vesicles release their neurotransmitter via Exocytosis
- Neurotransmitter diffuses across the synaptic cleft and bind to receptors
- Binding of neurotransmitters to receptor activates a signal transduction pathway
When AChesterase breaks down ACh into ___ and ___, it ___
-choline and acetate
-terminates the signal in the post-synaptic cell
Termination of a signal occurs via
Acetylcholinesterase breaking down acetylcholine into acetate and choline
Once the signal is terminated, what happens to acetate and choline?
Choline: presyanptic cell takes up and recycles
Acetate: diffuses out of the synapse
The central nervous system includes
The brain and spinal cord
The CNS functions include (5)
-gather and process information
-organize reflex response
-behavioural responses
-voluntary movements
-higher cognitive functions
The peripheral nervous system includes
Everything outside the brain and spinal cord
PNS functions include (3)
-carry incoming sensory information
-outgoing signals for physiological and behaviour responses
-autonomic (not conscious) and somatic (conscious) divisions
The peripheral nervous system is divided into
-autonomic (involuntary)
-somatic (voluntary)
The autonomic peripheral nervous system can be further subdivided into
-parasympathetic
-sympathetic
-enteric (GIT)
Involuntary control of glands and smooth muscle is controlled by
Autonomic nervous system
Afferent
Incoming (from sensors to the CNS)
Voluntary control of skeletal muscle is controlled by
Somatic nervous system
Efferent
Outgoing (from the CNS to the effectors)
Nerves are organized into
Spinal and cranial nerves
Spinal nerves (2)
-branch from spinal cord
-36 pairs in the dog)
There are ___ pairs of cranial nerves
12
Cranial nerves (2)
-12 pairs of nerves emerging from the brain
-mostly head/neck control (sight, smell, taste, etc.)
Somatic Efferent Pathway (2)
-one neuron
-signal from CNS to target (skeletal muscle)
Autonomic Efferent Pathway (2)
-two neurons (a myelinated pre-synaptic nerve and an unmyelinated post-synaptic nerve)
-from CNS to target (smooth muscle)
The autonomic ganglia of the sympathetic nervous system are predominantly located
Close to the spinal cord in the sympathetic chain
Acetylcholine released from preganglionic neurons bind to which receptor in the sympathetic nervous system
Nicotinic Type 2
Sympathetic Nervous System (4)
-preganglionic nerve exits CNS in thoracolumbar region
-ganglia are near spinal column
-short pre-ganglionic nerve
-lost post-ganglionic nerve
Parasympathetic Nervous System (4)
-preganglionic nerve exits CNS in brain stem and sacral region
-ganglia are close to effector tissue
-long pre-ganglionic nerve
-short post-ganglionic nerve
The vagus nerve (cranial nerve 10) supplies
Thoracic and abdominal regions
In the PNS, fibres leave the CNS via
Cranial nerves (supply the facial glands and eyes) and lower spinal cord nerves (supply urinary, GI, and reproductive systems)
In the somatic nervous system (3)
-cell body (soma) is IN the spinal cord
-one nerve extends to the muscle fibre
-neurotransmitter released is Acetylcholine
In the Somatic nervous system, acetylcholine (2)
-is the only neurotransmitter released
-crosses the synaptic cleft and binds to a Nicotinic Type 1 Acetylcholine receptor which opens its ion channel
In the sympathetic nervous system, acetylcholine binds to
Nicotinic type 2 receptor
Preganglionic fibres in the sympathetic nervous system are
Short and unmyelinated
Postganglionic fibers of the sympathetic nervous system (2)
-long and unmyelinated
-can be adrenergic or Cholinergic
In the sympathetic nervous system, it is more common that ___ binds to ___
Norepinephrine binds to adrenergic receptors (alpha or beta)
Three types of adrenergic receptors are
-alpha 1
-alpha 2
-beta
In the sympathetic nervous system, it is less common that ___ binds to ___
Acetylcholine binds to Cholinergic receptors (muscarinic type 3)
A type of Cholinergic receptor is
Muscarinic type 3 receptor
Adrenaline and noradrenaline are
Catecholamines
Adrenaline is a ___ that causes (3)
Catecholamine
-strong increase in HR
-weak increase in arterial pressure
-increased metabolism
Sympathetic hormones include
The catecholamines (Adrenalin and noradrenaline)
The thoracic splanchnic nerves end on modified neuronal cells
Chromaffin cells
Noradrenaline is a ___ and causes (5)
Catecholamines
-blood vessel constriction
-increased HR
-GI inhibition
-pupil dilation
-increased arterial pressure
The first nerve is always ___ and releases
Cholinergic; acetylcholine
The first synapse is always
Nicotinic
Nicotinic receptor in Somatic nervous system is ___ while in the autonomic nervous system it is ___
SNS: Type 1
ANS: Type 2
