week 6 Flashcards
is the ANS the afferent of efferent nervous system?
efferent
whats the primary function of the ANS? and what are the two divisions of the ANS that help achieve this goal?
primary function = maintain homeostasis
two divisions = parasympathetic and sympathetic
very briefly, what are the roles of the parasympathetic and sympathetic nervous systems?
parasympathetic = rest and digest
sympathetic = flight or flight
what is dual innervation?
the fact that BOTH divisions of the ANS innervate most effector organs
what are the two types of neurons from CNS to effector organs? what structure facilitates communication bw these neurons?
preganglionic and postganglionic neurons
autonomic ganglia
T or F: the soma of the preganglionic neuron sits in the PNS
false – sits in CNS
T or F: all adrenergic receptors are G-protein linked receptors
true!
what is the neurostransmitter associated with:
a) (para and sympa) preganglionic neurons
b) para postganglionic neurons
c) sympa post ganglionic neurons
a) acetylcholine (+ sometimes epinephrine for sympa)
b) acetylcholine
c) norepinephrine
SYMPA: preganglionic neurons emerge from ____ region of spinal cord, originate in a region of gray matter called the ___ or the _______.
thoracic/upper lumbar
lateral horn or the intermediolateral cell column
what is the sympathetic chain?
links sympathetic system to organs (short axons for pre neurons, long axons for post neurons)
PARASYMPA: pre neurons originate from _____ spinal cord.
brainstem/sacral
what is the parasympathetic chain
no such thing!
instead: have very long pre neuron, synapsing with post neuron in autonomic ganglia near effector organ.
what is a neuroeffector junction?
junction bw postganglionic neuron and effector organ
where are neurosransmitters stored in neuroeffector junctions
vesicles inside varicosities
T or F: one axon has several varicosities and releases neurotransmitter from ALL
true
describe the events occurring at the neuroeffector junction (6)
- AP arrives at varicosity.
- VGCC open.
- Ca2+ triggers exocytosis of neurotransmitter.
- neurotransmitter binds with receptors on effector organ.
- response in effector organ occurs.
- neurotransmitter is degraded and diffuses away; reuptake occurs.
___ in parasympathetic activity are coupled with ___ in sympathetic activity (and vice versa).
increases
decreases
(always opposites)
what kind of physiological activity takes place due to parasympa system? (3)
- increased gastrointestinal activities
- decreased heart rate
- decreased BP
what kind of physiological activity takes place due to sympa system? (6)
- increased heart rate
- increased BP
- mobilizes energy stores
- dilates pupils
- decreases gastrointestinal/urinary functions
- releases epinephrine
where does the sympa system release epinephrine from?
adrenal medulla
what are MAOIs? (3)
- powerful antidepressants that increase amount of norepinephrine by reducing its degradation.
- also acts in PNS… therefore, see increased heart rate and other symptoms.
- often reserved as last resort for these reasons.
at rest, which system dominates?
parasympa
why do autonomic/visceral reflexes occur?
bc ANS is linked to the sensory system to produce functional reflexes. these are negative feedback loops that aim to maintain homeostasis (full bladder example)
pick an example of an autonomic reflex and describe how it works
- pupillary light refllex
- too bright = parasympa reflex to circular muscles (constriction)
- too dark = sympa reflex to radial muscles (dilation)
what is baroreflex?
- maintainence of BP at constant levels.
- ex. decreased BP will cause heart rate to increase to restore BP.
- controlled by ventrolateral medulla and muscle sympa effects (noradrenergic vasoconstriction).
areas of the brain that regulate autonomic function (3)
medulla
hypothalamus
pons
efferent neurons of somatic nervous system are aka…
motor neurons!
describe the parasympa vs sympa effects for:
a) heart
b) urinary bladder
c) skin
a) parasympa: decreases everything, sympa: increases everything
b) parasympa: wall contracts/sphincter relaxes, sympa: wall relaxes/sphincter contracts
c) both make sweat glands secrete, but only sympa makes hairs stand up (piloerector muscles)
what is a neuromuscular junction?
the synapse between a motor neuron and a muscle fiber
what are the neuromuscular junction equivalents for axon terminals?
terminal bouton
what is the motor end plate
specialized muscle membrane at junction (where motor neurons end)
T or F: all motor neurons release serotonin and are inhibitory?
false!!!
acetylcholine
excitatory
which toxins result in muscle spasms? which toxins result in muscle paralysis?
spasms = latroxin (black widow venom)
paralysis = crotoxin (rattlesnake venom) and curare.
activation of motor neuron depends on _____
summation of EPSPs/IPSPs
describe the events occurring at the neuromuscular junction (8)
- AP arrives at terminal bouton.
- VGCC open.
- Ca2+ enters cell triggering release of ACh.
- ACh diffuses across cleft and binds to nicotinic receptors on motor end plate.
- ACh triggers opening of channels for small sodium and potassium cations.
- depolarization.
- AP in muscle cell.
- AP spreads thru muscle causing contraction.
describe crossbridge cycle process (5)
- actin binds to myosin (Pi released)
- power stroke
- rigor (myosin in low-energy form, ADP released)
- unbinding of myosin and actin (ATP required/hydrolisized)
- cocking of myosin head (myosin in high-energy form)
what is excitation-contraction coupling?
sequence of events whereby an AP in the sarcolemma causes contraction.
- ACh binds to motor plate, eliciting AP in muscle cell.
- AP propagates along sacrolemma.
- AP triggers Ca2+ release.
- Ca2+ binds to troponin, exposing myosin-binding sites.
- crossbridge cycle begins.
- Ca2+ transported back
how is contraction terminated?
Ca2+ leaves binding sites via ATPase (pump) which moves it to sarcoplasmic reticulum
T or F: a twitch is an all-or-nothing event
true
phases of muscle twitch (3)
LATENT PERIOD = muscle excited… AP spread through muscle and calcium released, but has not arrived yet
CONTRACTION PHASE = intracellular calcium levels increase; more crossbridges forming.
RELAXATION PHASE = calcium pumped back into SR. intracellular calcium level falls. fewer crossbridges.
what is tetanus? what muscles does this occur in?
APs fire so close you get fused tetanus (maximum force reached). occurs only in skeletal muscles; not cardiac
parasympathetic system:
- pre AND post neurons release ACh
- post neurons have nicotinic ACh receptors
- effector organs have muscarinic ACh rceptors
sympathetic system:
- pre neurons release ACh… note: can also release ACh directly onto receptors of adrenal gland, which then release E
- post neurons have nicotinic ACh receptors
- post neurons release NE
- effector muscles have adrenergic NE receptors
