IPHY 3430 Exam 2 [Nervous] Flashcards
Nervous system
- communication system
-coordinates body function; electrical signals[graded potentials & action potentials]
chemical signals; neurocrines[neurohormone, neurotransmitter, neuromodulators]
organization of NS
- CNS
- PNS: sensory[afferent] & motor[efferent; somatic division & autonomic division(sympathetic and parasympathetic branch)]
- Enteric Nervous system(digestion)
Nervous system cells
neurons: basic signaling molecule
glial cells: provide support for neurons(many types of glial cells bu we focus on oligodendrocytes and schwann cells)
3 functional groups of neurons
afferent(sensory)
interneuron(there can be many or none)
Efferent (motor) neuron
Organization of a neuron
Dendrtite= input (receive incoming signals)
soma(cell body) = contains nucleus
trigger zone = “initial segement”; integration
axon = conduction(long distance); myelin and nodes of ranvier
Presynaptic (axon) terminal = output(talk to target cell)
Oligodendrocytes vs schwann cells
oligodendrocytes: form myelin in the CNS, wrap up to 15 axons
schwann cells: form myelin in PNS, wrap 1 axon
how are neurons connected? (labeled lines)
presynaptic cell: delivers signal at synapse
postsynaptic cell: receives signal at synapse
2 Electrical signals in neurons
Graded potential = local signals, purpose is to carry info from input region to trigger zone
Action potential = long distance signals, purpose is to carry info to presynaptic axon terminal
Integrative action
where there is both action and graded potentials
are electrical signals temporary changes in membrane potential?
yes, due to temporary (transient) changes in membrane permeability via gated ion channels.
- chemically-, mechanically- , voltage- gated.
Do electrical signals appreciably change ion concentrations ?
No, they do change separation of charge across the membrane(membrane potential)
Graded Potentials
- originate in input region due to opening of gated channels
- decrease in amplitude(lose “strength”, “decay”) as travel
excitatory vs inhibitory
*Graded potentials can be both
excitatory- depolarize cell & make it easier to produce action potential
inhibitory- hyperpolarize cell & make it harder to produce action potential
different names for graded potentials
receptor potential: input region of sensory neuron
synaptic potential (Excitatory postsynaptic potential[EPSP], inhibitory postsynaptic potential [IPSP]): input region of interneuron and motor neuron
End-plate potential: input region of skeletal muscle
graded potential strength and duration
graded potentials vary in amplitude & duration to convey information about stimulus amplitude & duration.
- amp: typically 0.1-10mV
- duration: typically 2-10 msec
Where are graded potentials summated?
Graded potentials travel to trigger zone (integrative
site) & summate.
- typical neuron receives ~1000-10,000 inputs
- decision: action potential
integration at trigger zone from graded potential
determines whether action potentials produced & information is passed along
- action potential threshold [subthreshold, suprathreshold]
- both action and graded potentials at trigger zone(transition from local to long distance)
Purpose of action potentials
carry info from trigger zone to synapse(presynaptic terminal)
- log distance; dont decrease in amplitude(strength as propagate, “regenerated”
all-or- none(summate)- decisions been made.
typically ~1ms,~100mV but can vary based on ion flow.
how to Action potentials convey info?
Frequency: codes for stimulus amplitude (intensity,strength)
Duration of spike train: codes for stimulus duration
How are action potentials produced
Gated ion channels; produced by sequential opening & closing of voltage -gated ion channels.
- you need to let it rest before you try and produce another action potential, can’t summate
Gated ion channels for action potentials
Hodgkin-Huxley channels:
H-H Na+: closed(resting), open, inactive(refractory)
- time dependant
H-H K+ : closed, open
Action potential threshold
Action produced when trigger zone is depolarized above threshold because of positive feedback, Na+ comes in and tries to depolarize into its equilibrium potential.
Similarities between Na+ and K+ channels
differences: time responds to stimulus, reason ion stops flowing, # gates- inactivation- time(~1 msec)
similarities: voltage dependant; depolarize (~15-20mV) -> open - repolarize -> closed
Termination of positive feedback cycle
Two processes to repolarize cell
1) inactivation of voltage - gated Na+ channels
2) opening of voltage- gated K+ channels
Refractory periods
- not all channels reset at the same time
Absolute refractory: when there is no chance to summate an action potential
relative refractory period: some channels are ready but some are not, you can get a small action potential. Na+ channels are time dependant so not all of them are ready, - to produce full action potential it takes about 2 msec
Action potential propagation
like dominos, the same action potential does not move, it just triggers the next one
- voltage- gated Na+ channels open & Na+ flows in, depolarizing that part of the axon; passive current flow depolarizes neighboring region[like water flowing along a pipe]
Speed of action potential
2 mechanisms increase conduction velocity.
- diameter of axon; the bigger the faster
- myelination, prorogations are faster when there is myelin on that section. Nodes of ranvier have teh ion channels so it is slower on those portions
saltatory conduction
myelinated axons
- nodes of ranvier; no nodes, where voltage gated channels and regeneration of action potential happens
how do action potentials convey info to synapse
action potentials propagate unfailingly over long
distances to output region (synaptic/axon terminal)
types of synapses
electrical: gap junctions, synchronize activity, rapid bidirectional signal conduction
Chemical: majority of synapses, most neurotransmitters stored in vesicles &exocytosed due to action potential [neurotransmitter diffuses across synaptic cleft.], slower but more flexible & allows amplification
purpose of action potential
open voltage gated Ca++ channels for exocytosis.
- uses hydrogen ion gradient and uses it as secondary active transport for exocytosis.
Neurotransmitter/ neurocrine secretion
-Release of neurotransmitter/neurocrine depends on frequency of action potentials, & duration of spike train
-Major neurocrines of peripheral nervous system (PNS):
acetylcholin(ACh), norepinephrine (NE), epinephrine (E)
types of postsynaptic receptors
nicotinic, muscarinic, AchR
- 2 types:
ionotropic (directly gated, channel protein)
• metabotropic (indirectly-gated, GPCR/RE)
- response maybe be excitatory or inhibitory
• EPSP/IPSP – excitatory/inhibitory post-synaptic potential
EPSP: depolarization (Na+)
IPSP: hyperpolarization (Ca++)
Termination of neurotransmitter activity
inactivate, reuptake, diffuse away. pump out Ca++
Afferent Division of PNS
Detects, encodes & transmits signals about internal & external environment to CNS
sensory receptors
classified based on nature of stimulus(type of energy) that receptor responds to & transduces
types of senses
special senses, somatic senses, visceral senses
special sense
have specialized organs devoted to them: eye, ear, nose, tongue; taste, vision, hearing, equilibrium, smell.
somatic senses
somatosensory receptors - collect information from surface of
body (cutaneous sensations), and muscles & joints
(proprioceptive sensations => body position)
• cutaneous: touch, pain, skin temperature
• proprioception: e.g., muscle length & force, joint position
visceral sense
• interoceptors sense/detect stimuli within internal organs
(viscera) such as blood vessels, gut, etc.
• e.g., chemoreceptors, baroreceptors, osmoreceptors
• monitor internal environment, e.g., blood glucose, blood
osmolarity, blood pressure, internal temperature
phasic vs, tropic receptors
Phasic: rapid adapting, on off cells, don’t tell you how long something has been on/off for. just tells you something is on/off
Tonic: slowly adapting, stays active throughout the entire time of stimulus
Receptive fields
Region w/in which a sensory neuron sense a stimulus: how you keep track of where signal came from.
Sensory transduction
Stimulus alters receptor cells permeability leading to a graded potential
- transduction occurs via : ionotropic and metabotropic channels
ionotropic channels
directly gated: mechanical, chemical, voltage
Metabolic channels
indirectly gated: GPCR, receptor enzyme.
Tastant transduction: why don’t we get confused on what flavors are which?
each taste cell only sense one type of ligand: salt, sour, bitter, sweet, or umami
G-protein: metabotropic[bitter, sweet, umami, fat]
tastant: transducing channels, ionotropic[salt(NA+), sour(H+)
spinal cord organization for afferent signals.
spinal cord is organized to keep track of information
-somatotopy: “body map”
Sensory spinal cord: dorsal root, dorsal horn[ somatic, visceral]
Decussation
“crossover”
sensory info decussates (crosses over) to other side of nervous system
• “upper” medulla: fine touch, proprioception, vibration
-dorsal column-medial lemniscus tract
• “lower” spinal cord: nociception (pain), temperature, coarse touch
- anterolateral tract
Thalamus
- relay station - (with exception of olfaction)
* many nuclei – each for one type of sensory information
Somatosensory organization
Somatosensory projections from body maintain body map
- CNS integrates sensory information
- highest sensory signals when we are born come from the mouth and hands, so that takes a big part of the min-body map
Brain areas
CEREBELLUM FOREBRAIN: - cerebrum ------cerebral cortex; frontal lobe, parietal, occipital, temporal, ------basal nuclei (voluntary movement) -diencephalon; hypothalamus, thalamus BRAIN STEM - medulla oblongata - pons - midbrain[eye movement]
Autonomic control centers
Hypothalamus: receives visceral sensory inputs & control autonomic sys, temp control, water balance, eating behavior
Pons & medulla: control autonomic sys (ANS) output to periphery; bladder control, sec respiratory control, BP, respiratory center
Cerebellum
muscle(voluntary movement)
where is sensory information processed?
cerebral cortex
- parietal lobe: info from skin, musculoskeletal system, viscera, and taste buds
- frontal lobe: coordinates info from other association areas, controls some behaviors
- temporal lobe: auditory association area, taste and smell
- occipital lobe: vision
Efferent (motor) divisions
somatic and autonomic
what part of the brain controls somatic motor neuron?
Motor cortex; then descends spinal cord
- corticospinal tracts: most cross (decussate)at medulla(pyramidal tract)
- somatotopy maintained
what does somatic motor division control?
SKELETAL MUSCLE
somatic (alpha) motor neurons
• control skeletal muscle contractions (mostly voluntary)
• tonic
• neuron originates in CNS (ventral horn)
• leave ventral horn via ventral root to synapse onto skeletal muscle
Neuromuscular junction
somatic(a) motor neuron releases acetylcholine
- always excitatory
Skeletal muscle fiber membrane (sarcolemma) contain nicotinic acetylcholine receptors (nAChR)
end plate potential
Binding of acetylcholine (ACh) to nicotinic receptor
(nAChR) opens ion channels leading to depolarization of muscle membrane
- excitatory (Na+)
** graded potential = end plate potential
Events at Neuromuscular junction
End-plate potential causes voltage-gated Na+ channels to open in muscle membrane (sarcolemma) leading to muscle (sarcolemmal) action potential …. ->muscle contraction
Life cycle of acetylcholine at neuromuscular junction
acetyltransferase(enzyme)
- acetyl CoA & choline
- acetyl CoA comes from citric acid cycle
- choline comes from diet(recycled)
Termination of acetylcholine pathway
Acetylcholinesterase (AChE)
- breaks it down to acetate and choline
Neurocrine Naming
Need to differentiate cell that makes & releases
signal versus cell that has receptors for signal
examples:
• cholinergic (relates to acetylcholine)
• cholinergic neuron – makes & releases acetylcholine as signal
• cholinergic receptor – binds & responds to acetylcholine
• subtypes: nicotinic, muscarinic
• adrenergic (relates to epinephrine/norepinephrine)
• adrenergic neuron - makes & releases E / NE as signal
• adrenergic receptor – binds & responds to E / NE
• subtypes: alpha, beta
• dopaminergic, serotonergic, GABAergic, glycinergic,
histaminergic, glutamatergic,….
what does Autonomic neurons control?
Control - cardiac & smooth muscles - many glands - lymphoid & some adipose tissue Mostly involuntary - regulate/influence visceral functions
Autonomic Division branches
Parasympathetic and sympathetic
Most effectors connected to both
branches (antagonistic control)
• excitatory & inhibitory effects (unlike somatic branch)
• act simultaneously
• shifts in predominance due to mental & physiological states
• autonomic tone* (background activity; balance between 2 branches)
Autonomic Nervous system
creates autonomic, endocrine, & behavioral responses
- influenced by: cerebral cortex, limbic system
works closely w/ endocrine system to maintain homeostasis
Antagonistic control of autonomic NS
Most internal organs are under antagonistic control.
Exceptions - only innervated by sympathetic
branch (tonic)
• (sweat glands)
• smooth muscle of most blood vessels
Autonomic pathways consist of…
All autonomic pathways consist of 2 neurons in series
2 neurons that synapse in an autonomic ganglion
CNS -> preganglionic neuron -> autonomic ganglion (mini- integrating center) -> postganglionic neuron -> target tissue
2 autonomic neuron pathways
sympathetic ganglia and parasympathetic ganglia
sympathetic ganglia
- close to spinal cord
- short preganglionic neurons
- thoracic & lumbar segments
- long postganglionic neurons
parasympathetic ganglia
- vagus nerve is major tract: contains ~75% of fibers
- located primarily on or near target organs
- long preganglionic neurons
- brain stem & sacral region
- short postganglionic neurons
ANS: Neurotransmitters and receptors
receptors: cholinergic [ nicotinic and muscarinic ] and adrenergic [ alpha and beta ]
- sympathetic pathways use CNS -> acetylcholine release from preganglionic neuron -> nicotinic receptor on autonomic ganglion-> norepinephrine released from postganglionic neuron -> target cell.
- parasympathetic use CNS ->preganglionic neuron -> acetylcholine -> nicotinic receptor on autonomic ganglia -> Acetylcholine released from postganglionic neuron -> GPCR
Varicosities
where autonomic post ganglionic neurons end. It contains neurotransmitter & release it over the surface of the target cell
Life cycle of norepinephrine at sympathetic neuroeffector junction
neuro effector junction: catecholamines are derived from tyrosine(amino acid) -> pump norepinephrine into vesicles by secondary active transport -> the rest is the same as the neuromuscular junction
pancreas and the ANS
Pancreas is innervated by both branches, para and sympathetic.
Parasympathetic: increases activity due to food in digestive tract
- insulin secretion via IP3-Ca++ pathway [ feedforward response]
Sympathetic : inhibits the insulin secretion by decreasing cAMP
- effect; increased blood glucose available to fuel muscle activity for fight or flight
Arterioles: receptor type determination
alpha and Beta adrenergic receptors on arterioles:
- B2 receptors cause vasodilation- decreases cAMP
- a receptors cause vasoconstriction - activates PLC
certain organs during fight or flight with receives one of the responses, muscles will dilate, urinary will constrict
what stays longer; epinephrine or norepinephrine?
Norepinephrine
termination of Norepinephrine
diffuses away or use active transport to move it back into the cell it came from or neighboring glial cells
Adrenal Medulla
a specialized neuroendocrine gland that secretes epinephrine into blood
reflexes
involuntary responses triggered by a sensory stimulus
classifications of reflexes
- efferent division: somatic vs. autonomic
- integrating region in CNS: spinal (spinal cord) vs. cranial (brain)
- time develops: innate (born - e.g., patellar tendon) vs. learned (conditioned) (acquired thru experience - e.g., Pavlov’s dog)
- number of neurons: monosynaptic vs. polysynaptic
Autonomic reflexes
involve autonomic neurons & targets (internal organs) ex: • urination/defecation • salivating • vomiting • sneezing • coughing • swallowing • gagging • blushing • heart rate • blood pressure ****THEY CAN BE LINKED TO EMOTION[ GUT FEELING, BUTTERFLIES IN STOMACH]
Skeletal reflexes
involve proprioceptors & somatic motor neurons
spinal reflexes:
• CNS integrates input signal
• mono- or polysynaptic pathways
• efferent neuron - somatic (alpha) motor neurons
• effectors - skeletal (extrafusal) muscle fibers
- mediated by Golgi tendon organ and muscle spindle organ
Proprioceptors (skeletal muscle reflex)
• sensory receptors in skeletal muscle, joint capsules, & ligaments
• sense body position & change
non voluntary response, its a reflex
Golgi tendon organ
monitors muscle force and mediates tendon reflex
- regulates muscle force,
- locates near the tendon
• innervated by sensory neuron (Ib afferent)
• mechanically-gated channels -> graded (receptor) potential
Muscle spindle organ
monitors muscle length and mediates stretch reflex (patellar , knee jerk)
- regulates muscle length
- located within muscle fibers
• innervated by sensory neuron (Ia afferent)
• mechanically-gated channels -> graded (receptor) potential
Postural control!!!
Ex: patellar stretch reflex
Golgi tendon reflex and muscle relaxation
this happens to prevent muscle damage, when there is too much force, the golgi relaxes the muscles.
polysynaptic pathway
• Ib afferent -> Ib inhibitory interneuron -> motor neuron
Muscle tone
muscle spindles monitor muscle length
