100 BIPN Dr. Fortes TA Jing Wang Handout4 [e-mail] OH Wed 4-5 @ Caf Roma 1. Sensory Receptors A. Special Senses - sensory stimuli reaching the conscious level of perception i. Vision, taste, smell, hearing, equilibrium/postural ii. Sensory neurons project into thalamus for processing, relaying stimuli to respective brain regions; (a) **Olfactory information goes directly to cerebrum, bypasses thalamus B. Receptors - classified according to stimulus type i. Mechanoreceptors ion channels; respond to pressure, vibrations, sound, stretch (a) Ex: increase in cytosolic osmolarity causes cell volume to increase, which stretches MB, activating mech-R ii. Thermoreceptors respond to temperature (cold or hot) and chemicals (chili oil, menthol/mint) (a) Cold receptors respond to temp below 37C; Warm receptors respond to temp above ~45 iii. Chemoreceptors respond to chemical ligands that bind to the receptor (O 2, CO2, pH, glucose) iv. Photoreceptors respond to light v. Nociceptors respond to noxious stimuli, pain (Very hot/cold or very strong mechanical/chemical stimulus) C. Fig 8-13: Intensity of stimulus is coded by the number of receptors activated and in the frequency of APs fired D. Tonic Receptors slowly adapt to a stimulus, or not at all constantly function i. As long as the stimulus is present, the receptor continues to transmit signals baroreceptors, nociceptors (a) Ex: Maintains state of contractility of skeletal muscle under a constant mechanical stimulus E. Phasic Receptors rapidly adapt to a continuous stimulus, prevents overwhelming the brain with stimuli i. Fire at initial stimulus or a change in the stimulus intensity, but then stop when stimulus becomes constant, fire again when stimulus is removed/changes intensity (a) Ex: dip hand in warm water -> adapt to temp until you remove your hand (b) Ex: smell odor/perfume, but rapidly adapt and don't smell it anymore until intensity of the smell changes
2.
Somatosensory Pathways A. Types of Receptors i. Touch: fine, coarse, pressure ii. Proprioceptors: state/orientation of body parts in space iii. Thermoreceptors: heat/cold iv. Nociceptors: variety of stimuli felt as pain, have bare nerve endings B. Types of Fibers: classified by conduction velocities i. Type A: large, myelinated (a) : up to 120m/sec; mainly motor neurons (b) : 30-70m/sec: fast touch, vibration, pressure response (c) : 12-13m/sec: fast pain response ii. Type C: small, unmyelinated (a) Conductance velocities from 0.1-2m/sec (b) Slow pain fibers, autonomic neurons C. Spinal Chord Tracts; Corticosinal(motor)
Dorsal columns (sensory)
Spinothalamic
D.
Quaternary neurons: connects thalamus to somatosensory cortex in parietal lobe i. Size of cortical structures are proportional to the amount of neurons/sensory acuity for the associated areas of the body
E.
Pain Modulation: fig 10-12 i. Absence of pain (a) No input from C fibers interneuron suppresses pain pathway by inhibiting 2 neuron in spinal chord ii. Strong pain (a) 1 neuron ( C fiber) activated by pain stimulus NT release (b) C fiber inhibits inhibitory neuron allows activation of 2 neuron in pain pathway (c) C fiber stimulates 2 neuron
3.
The Peripheral Nervous System network of nerves entering and exiting the central nervous system. Sensory neurons carry information receptors at the periphery to the CNS Afferent neurons Motor neurons carry information from the CNS to periphery (muscles, glands) Efferent neurons. Ganglion cluster of nerve cell bodies in the PNS Nerves collection/bundle of axons running between the CNS and the peripheral target cells A. Somatic Nervous System subdivision of PNS that carries sensory and motor information at the conscious level. i. Flow of information along the spinal nerves: (a) Sensory Pathway sensory neurons carry info (pain, temp, taste, smell...) from receptors at periphery to CNS i Dorsal Root Ganglia running along next to the spinal chord are clusters of the somas of these neurons (b) Motor Pathway motor neurons (somas in spinal chord) carry information from the CNS to the muscles, glands (c) Interneurons neurons that lie entirely in the CNS; i in the spinal chord, neurons can synapse directly with a motor neuron, ii they can also synapse with an interneuron, which then synapses with a motor neuron
B.
Autonomic Nervous System regulates organ systems at an unconscious level: homeostatic balance i. Main Centers: (a) Hypothalamus: master gland i Temperature regulation, water balance via osmoreceptors, eating behavior (b) Pons: 2 respiratory centers, blood pressure center (c) Medulla: 1 respiratory center ii. Preganglionic fibers (a) Cell body in the CNS (grey matter) (b) Axons exit CNS, synapse with cell bodies of postganglionic fibers at ganlia (c) Always release Ach onto nicotinic Ach receptors on postganglionic fibers iii. Postganglionic fibers the axons running from the ganglia to the target organs (a) Cell body in ganglia (b) Axons synapse with effector cells in PNS (c) Release either Ach or Norepinephrine (NE) onto target cells iv. Parasympathetic Nervous System - Responsible for day-to-day activities (a) `Rest/digest' i Stimulates: GI tract to digest food: secretions, motility (smooth muscle); sexual arousal ii Inhibits: heart rate, respiratory rate (b) Ach as main NT, muscarinic cholinergic fibers inervate effector cells (c) Long preganglionc fibers, short postganglionic fibers ganglions close to target organs (d) Cranio-sacral: i Pons/medulla: vagus nerve to thoracic/abdominal organs, round muscles of eye ii S2-S4: pelvic organs, genitalia, urinary bladder, rectal/anal/urinary sphincters, contraction in bladder/genitals v. Sympathetic Nervous System (a) `4 F's' Fight, Flight, Fright, Sex i Stimulatory: increase heart rate, strength of contraction, blood pressure, dilate pupil, orgasm ii Inhibitory: GI tract slows secretions, motility; sexual arousal (b) Norepinephrine as main NT, adrenergic fibers (c) Short preganglionic fibers, long postganglionic fibers ganglia right next to spinal chord (d) Thoraco-lumbar: T1-L2: everything in the body
Autonomic Neurotransmitters A. Preganglionic neurons (both para/symp branches) release Ach onto cholinergic nicotinic receptors (n-Ach-R) B. Parasympathetic Postganglionic neurons release Ach onto cholinergic muscarinic receptors (m-Ach-R) on target cells i. Activation/inhibition depending on the receptor (GCPR) (a) Heart (pace maker cells): G subunit opens K+ ch. to hyperpolarize MB of pacemaker cell (b) GI tract: G subunit causes smooth muscle contraction and secretion of gastric juices C. Sympathetic Postganglionic neurons release NE onto adrenergic receptors D. Adrenergic receptors are GPCRs that come in 2 forms: Fig Tables 11.9,10; 11-2,3 i. Alpha receptors () more sensitive to NE that to Epinephrine (a) 1 stimulatory: activate phospholipase C, which catalyzes: breakdown of PIP2 -> generate IP3, DAG ++ i DAG remains in the MB, activates enzymes to open Ca ch ++ ii IP3 released into cytosol, opens Ca ch on ER ++ iii 1's generally increase intracellular [Ca ], causing muscle contraction or secretion(exocytosis) (b) 2 inhibitory: decrease cAMP, cause smooth muscle to relax (GI tract) or decrease secretion(pancreas) ii. Beta receptors () modulate cAMP levels (a) 1 stimulatory: increase cAMP cause smooth/cardiac muscle contraction i innervated by sympathetic neurons ii respond equally to NE from vagus nerve and E from circulation (adrenal medulla) (b) 2 inhibitory: decrease cAMP smooth muscle relaxation vasodilation, bronchodilation i in tissue not innervated by sympathetic neurons respond more to E than NE ii vasodilation increased blood flow to muscles, lungs iii bronchodilation increased ventilation (decreased resistance to air flow) (c) 3 Adipose tissue Somatic Motor Reflexes 1. Monosynaptic reflex: stimulus sensed by sensory neuron, enters dorsal root, synapses onto motor neuron (no interneurons) 2. Polysynaptic reflex: At least one interneuron between sensory neuron and motor neurons; the more synapses, the slower the reflex 3. Autonomic Reflex: form of polysynaptic reflex A. Sensory neuron interneuron preganglion neuron postganglionic neuron target cell response 4. Muscle Spindles: embedded between skeletal muscle fibers; sense length of skeletal muscle A. Tonically active sensory neurons wrapped around central non-contractile portion of intrafusal fibers B. Longitudinal stretching of spindle fibers mechanically deforms nerves increases AP frequency C. APs sent to dorsal root ganglion, into spinal chord; synapse directly with A and A motor neurons D. Alpha motor neurons innervate extrafusal (skeletal muscle) fibers increase tension i. Extrafusal contraction shortens intrafusal fibers decrease APs to alpha motor neurons E. Gamma motor neurons innervate contractile portion of intrafusal fibers maintains stretch on sensory nerves for sustained contractions F. Monitor static length of muscle: maintain basal muscle tone i. Stretch = increased muscle length increased AP frequency to alpha neurons G. Monitor dynamic length of muscle: sustained tension against load i. Change in length over time modulated increases in AP frequency 5. Golgi Tendon: sense stretching in tendon; prevent damage to muscle from excess contraction or too much force of contraction/tension A. Sensory neurons with free nerve endings interweave within collagen fibers in tendon B. Longitudinal stretching of collagen fibers compresses nerves AP to interneurons in spinal chord; EPSPs C. Inhibitory interneuron: inhibits alpha motor neuron of the synergist muscle (contracted muscle) decrease or stop contractions 6. Knee Jerk Reflex: A. Sensory neuron activates extensor (quadriceps) alpha motor neurons B. Inhibitory interneuron synapses onto flexor (hamstrings) C. Agonist muscles: work together as a group to provide movement D. Antagonist muscles: work against each other (flexors and extensors) E. Brain has inhibitory fibers to alpha motor neurons (uses glycine) 7. Withdrawal Reflex: protective reflex; sometimes complex (stepping on a nail) A. Contralateral and ipsilateral effects
4.
Sensory neuron activates alpha motor neurons of flexors (hamstrings) on ipsilateral side and extensors (quads) on contralateral side C. Sensory neuron inhibits alpha motor neurons of extensors on ipsilateral side and flexors on contralateral side D. Allows person to maintain balance on one foot 8. Postural Reflex: occurs around brainstem to cerebellum A. input from vision, vestibular apparatus, proprioceptors B. output goes down descending tracts maintains posture, equilibrium (unconscious reflex) 9. Axons of Motor Neurons A. Pass through midbrain B. Cranial nerves can go through mesencephalon C. Somatic nerves to medulla and cross in pyramids i. Corticospinal tract: voluntary movement ii. Extrapyramidal tract: fine movement; tracts go down and cross later at spinal chord
B.
Which of the following is NOT TRUE of Acetylcholine? A. Main excitatory NT at the neuromuscular junction B. Inhibitory in the heart C. Excitatory in the GI tract D. Has G-protein coupled receptors in skeletal muscle E. Has G-protein coupled receptors in myocardial cells 2. Which of the following is NOT a Parasympatheic response? A. Decreased heart rate B. Dilation of the pupils C. Constriction of the bronchioles D. Sexual arousal E. Increased salivation 3. Which of the following is TRUE? A. Tonic receptors only respond to a change in stimuli B. Phasic receptors are quick to adapt to stimuli C. Nociceptors, proprioceptors, and muscle-stretch receptors are phasic receptors D. Both A and B E. Both B and C
1.
Problems 1. You're playing doctor with a friend and test the acuity of his touch receptors. With his/her eyes closed, you lightly touch his skin with two closely placed pencil tips. At some locations, s/he tells you that he feels two separate pencil tips on his/her skin, while at other locations, s/he only feels one. Explain why s/he sometimes feels one tip, and sometimes two. 2. What would be the symptoms if nerve damage occurred in the following pats of the spine? A. Dorsal horn in the lumbar spinal section. B. Lateral horn of the cervical spinal section 3. Your worst nightmare has occurred. You just checked your mam phys midterm score on webct, and you run away from your computer in horror. Which autonomic nervous system is activated? List the appropriate change in your organs, the corresponding types of receptors involved, and whether it is excitatory or inhibitory. Effector Organ Response to Stimulus Adrenergic Receptor Excitatory or Inhibitory Pupil of eye Heart Lung GI tract Adipose tissue Urinary bladder
4.
Which of the following is a correct pathway of a reflex arc?
Receptor afferent neuron interneuron efferent neuron effector organ Effector organ afferent neuron efferent neuron interneuron receptor C. Receptor efferent neuron interneuron afferent neuron effector organ D. Interneuron afferent neuron receptor effector organ efferent neuron Receptor interneuron afferent neuron efferent neuron effector organ
A. B.
5.
You are in the garage without shoes on, and your left foot steps on a small nail. You immediately retract your foot, but you don't fall. Diagram or describe the reflex that occurred on both ipsilateral and contralateral sides from the stimulus. Inclues the afferent and efferent paths and their effect on flexor and extensor muscles of the thigh.