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BIOLOGY 2A03 Study Guide - Midterm Guide: Troponin, Myofibril, Thermoreceptor


Department
Biology
Course Code
BIOLOGY 2A03
Professor
Graham R.Scott
Study Guide
Midterm

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PNS: Sensory Systems
Sensory Receptors: can be specialized endings of afferent neurons or a separate cell that synapses with an afferent neuron
(i.e. photoreceptors, chemoreceptors, thermoreceptors, mechanoreceptors, baroreceptors, stretch receptors, nociceptors)
Sensory Unit: comprises a single afferent neuron and all of the receptors with which it is associated
Receptor Potential: the GP induced by a stimulus in a sensory receptor; they tend to adapt over time
First-order Neuron : afferent neuron that transmits information from the periphery to the CNS
Second-order Neuron : interneurons that receive and integrate signals from afferent neurons (convergence) –
transmit to thalamus
Third-order Neuron : synapses with second-order neuron; transmit information to cerebral cortex – sensory
perception occurs
Temperature Receptors: free nerve endings in the skin; sense skin temperature in the normal range (20-45 C);
nociceptors detect tissue-damaging temperatures (>45 C); transient receptor potential (TRP)- temperature-sensitive ion
channels respond to temperature changes
Thermoreceptors : synapse with interneurons in the spinal cord; thermal signal sent to thalamus (relay station) 
thermoregulatory control centre in the hypothalamus
oEx . Chili peppers: contain capsaicin that triggers pain receptors in the tongue – produces the same
sensation heat would cause
Vision Receptors: photoreceptors in the eye sense light via rhodopsin which interacts with a G-protein; light sensed by a
reduction in action potential frequency of afferent neurons – reduces G-protein activation, closing Na channels
(hyperpolarization) reducing stimulation of bipolar cells) (photoreceptor cells synapse with bipolar neurons which synapse
with ganglion cells that synapse with axons of optic nerve) – optic nerve (cranial nerve II transmits information to
thalamus which relays it to visual cortex)
oRods : detect dim light, non-colour vision
oCones : detect bright light, colour vision
Autonomic Nervous System (ANS): autonomic control areas located in brainstem and hypothalamus receive input from
afferent neurons
oSympathetic Nervous System (SNS) : “fight or flight” response; stimulates CVS
oParasympathetic Nervous System (PSNS) : “rest and digest” response; inhibits CVS
Anatomy of ANS
oPre-ganglionic neurons : cell body located in brainstem/spinal cord; axons project to autonomic ganglia (thinly
myelinated); PSNS – located at the target organ; SNS – paravertebral in sympathetic chain
oPost-ganglionic neurons : cell body in autonomic ganglia (unmyelinated) projects to visceral effector
Parasympathetic Nervous System: efferent signals are transmitted primarily in the vagus nerve and other/pelvic nerves;
pre-ganglionic neurons pass uninterrupted to the target organ; post-ganglionic neurons are short and innervate target
tissue; *Ach final neurotransmitter – rapidly broken down by acetylcholinesterase (high activity in blood)
Sympathetic Nervous System: efferent signals transmitted via spinal nerves; pre-ganglionic neurons exit spinal cord,
synapse in the sympathetic chain/collateral ganglia; post-ganglionic neurons exit sympathetic chain/collateral ganglia and
innervate target tissue; *norepinephrine final transmitter
oPreganglionic axon bypasses both the chain and collateral ganglions and travels directly to the adrenal medulla
(chromaffin cells) – synapses with a modified cluster of postganglionic cell bodies (do not possess
dendrites/axons) – release epinephrine and norepinephrine into the blood when stimulated
oChromaffin cells release 80% adrenalin, 20% noradrenalin, small amount of dopamine

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Cholinergic Receptors
Nicotinic Receptors : ionotropic expressed by post-ganglionic neurons, chromaffin cells and skeletal muscle – high
affinity for nicotine; ligand ACh released from pre-ganglionic neurons
oAch allows Na to diffuse into the cell – depolarizing, excitatory
Muscarinic Receptors (GPCR) : metabotropic receptors expressed by effector organ of PSNS – high affinity for
muscarine in mushrooms
oExcitatory or inhibitory – coupled to G-protein and second messenger
Adrenergic Receptors (GPCR): activate/inhibit second messengers; bind to epinephrine/norepinephrine; metabotropic
-receptorsα : α1 and α2; greater affinity for norepinephrine; stimulatory
oBinding to α
1: G-protein activates phospholipase C which catalyzes the conversion of PIP2 to IP3 and
DAG – triggers release of Ca, causing a response in the cell
oBinding to α
2: Gi decreases activity of adenylate cyclase, suppressing synthesis of cAMP
-receptorsβ : activates Gs increasing activity of adenylate cyclase, increasing cAMP production
oβ1, β3: equal affinity, stimulatory
oβ2: greater affinity for epinephrine, inhibitory
Muscular System
Skeletal Muscle: connected to at least two bones via tendons – continuous with epimysium (exceptions: facial muscle,
larynx, urethral sphincter)
oComposed of muscle fibers surrounded by endomysium (elongated, multinucleated cells organized into fascicles
by perimysium)
oTransverse Tubule (T-Tubules) : invagination of sarcolemma – network within muscle cells; connects outside to
inside; AP can be transmitted into the interior; allows for increased speed and coordination of muscle contractions
– activates inside as quickly as outside
oSarcoplasmic Reticulum : store Ca; tight regulation with T-tubules
oMitochondria : increased mitochondria with increased energy demand of certain muscles; based on proximity to
oxygen supply – located subsarcolemmal (next to sarcolemma) or intermyofibrillar (interspersed with myofibrils)
Myofibrils: bundles of protein fibers (contractile proteins); ability to shorten; organized in sarcomeres
-Actin Myofilament (thin)
Fibrous Actin (F-Actin) : 2 strands arranged in a double helix – composed globular actin (G actin- each
monomer has an active site to which myosin molecules can bind to)
Tropomyosin : elongated, regulatory protein that winds along the groove of the F-helix; controls whether the
active sites are available/regulates myosin head binding
Troponin : consists of Ca, tropomyosin and actin binding sites; regulates tropomyosin movement
-Myosin Myofilament (thick)
Composed of many myosin molecules (dimer of 2 subunits) with staggered heads along the filament; bare
zone present in the middle of the filament devoid of cross-bridges
Rod : gives strength and support; composed of two myosin heavy chains wound together
2 Myosin Heads that extend laterally – ATPase site and actin-binding sit (cross-bridge site)
Hinge Region : where the heads attach to the rod; allows for action of bending
Sarcomeres: smallest functioning unit of a muscle; extends from one z-disk to an adjacent z-disk; organized myofibrils
within sarcomere produces a striated pattern
-Z-Disk : fibrous disk organized in a zig-zag pattern – anchor actin myofilaments
-I-Band : includes a z-disk and extends from each side of the z-disk to the ends of the myosin heads – region where
actin doesn't overlap myosin
-A-Band : extends the length of the myosin myofilaments within a sarcomere; actin and myosin overlap at both
ends; in a cross section, each myosin myofilament is surrounded by 6 actin myofilaments
-H-Zone : center of A-band; actin and myosin myofilaments do not overlap – only myosin present
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