Lect 15
The Autonomic Nervous System
1. Describe about autonomic nervous system
• The autonomic nervous system (ANS) operates via reflex arcs.
• Regulate activity of smooth muscle, cardiac muscle & certain glands
• Receives input from limbic system and other regions of the cerebrum
• Operation of the ANS to maintain homeostasis, however, depends on a continual flow of sensory afferent input, from receptors in organs, and efferent motor output to the same effector organs.
• Structurally, the ANS includes autonomic sensory neurons, integrating centers in the CNS, and autonomic motor neurons.
• Functionally, the ANS usually operates without conscious control.
• The ANS is regulated by the hypothalamus and brain stem.
ANS:
• The output (efferent) part of the ANS is divided into two principal parts:
– the sympathetic division
– the parasympathetic division
– Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation.
• Dual innervation
– one speeds up organ
– one slows down organ
– Sympathetic NS increases heart rate
– Parasympathetic NS decreases heart rate
2. Sympathetic ANS vs. Parasympathetic ANS
A. Sympathetic NS SNS
Structures of Sympathetic NS
• Preganglionic cell bodies at T1 to L2/3
• Postganglionic cell bodies
– sympathetic chain ganglia along the spinal column
– prevertebral ganglia at a distance from spinal cord
• celiac ganglion
• superior mesenteric ganglion
• inferior mesenteric ganglion
Organs Innervated by Sympathetic NS
• Structures innervated by each spinal nerve
– sweat glands, arrector pili mm., blood vessels to skin & skeletal mm.
• Thoracic & cranial plexuses supply:
– heart, lungs, esophagus & thoracic blood vessels
– plexus around carotid artery to head structures
• Splanchnic nerves to prevertebral ganglia supply:
– GI tract from stomach to rectum, urinary & reproductive organs
Sympathetic Responses
• Dominance by the sympathetic system is caused by physical or emotional stress -- “E situations”
– emergency, embarrassment, excitement, exercise
• Alarm reaction = flight or fight response
– dilation of pupils
– increase of heart rate, force of contraction & BP
– decrease in blood flow to nonessential organs
– increase in blood flow to skeletal & cardiac muscle
– airways dilate & respiratory rate increases
– blood glucose level increase
• Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland
B. Parasympathetic NS PSNS
Anatomy of Parasympathetic NS
• Preganglionic cell bodies found in
– 4 cranial nerve nuclei in brainstem
– S2 to S4 spinal cord
• Postganglionic cell bodies very near or in the wall of the target organ in a terminal ganglia
Parasympathetic Sacral Nerve Fibers
• Form pelvic splanchnic nerves
• Preganglionic fibers end on terminal ganglia in walls of target organs
• Innervate smooth muscle and glands in colon, ureters, bladder & reproductive organs
Parasympathetic Responses
• Enhance “rest-and-digest” activities
• Mechanisms that help conserve and restore body energy during times of rest
• Normally dominate over sympathetic impulses
• SLUDD type responses = salivation, lacrimation, urination, digestion & defecation and
3 “decreases”--- decreased Heart Rate, diameter of airways and diameter of pupil
• Paradoxical fear when there is no escape route or no way to win
– causes massive activation of parasympathetic division
– loss of control over urination and defecation
SUMMARY
• The sympathetic responses prepare the body for emergency situations (the fight-or-flight responses).
• The parasympathetic division regulates activities that conserve and restore body energy (energy conservation-restorative system). becaz resting
3. Somatic and autonomic nervous system
• The somatic nervous system contains both sensory and motor neurons.
• The somatic sensory neurons receive input from receptors of the special and somatic senses.
• Somatic motor neurons innervate skeletal muscle to produce conscious, voluntary movements.
• The autonomic nervous system contains both autonomic sensory and motor neurons.
• The ANS also receives sensory input from somatic senses and special sensory neurons.
• The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities of cardiac muscle, smooth muscle, and glands.
All somatic motor pathways consist of a single motor neuron
Autonomic motor pathways consists of two motor neurons in series
SUMMARY
• Somatic nervous system
– consciously perceived sensations
– excitation of skeletal muscle
– one neuron connects CNS to organ
• Autonomic nervous system
– unconsciously perceived visceral sensations
– involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion
– two neurons needed to connect CNS to organ
• preganglionic and postganglionic neurons
4. Basic Anatomy of ANS
• Preganglionic neuron (myelinated)
– cell body in brain or spinal cord
• Postganglionic neuron (unmyelinated)
– cell body lies outside the CNS in an autonomic ganglion
5. ANS Neurotransmitters
• Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released
A. Adrenergic Neurons and Receptors
• Adrenergic neurons release norepinephrine (NE)
– from postganglionic sympathetic neurons only
• Excites or inhibits organs depending on receptors
• NE lingers at the synapse until enzymatically inactivated by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)
B. Cholinergic Neurons and Receptors
• Cholinergic neurons release acetylcholine (ACh)
– all preganglionic neurons
– all parasympathetic postganglionic neurons
– few sympathetic postganglionic neurons (to most sweat glands)
• Excitation or inhibition depending upon receptor subtype and organ involved.
• Cholinergic receptors are integral membrane proteins in the postsynaptic plasma membrane.
• The two types of cholinergic receptors are nicotinic and muscarinic receptors.
– Activation of nicotinic receptors causes excitation of the postsynaptic cell.
• Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells (and at NMJ.)
– Activation of muscarinic receptors can cause either excitation or inhibition depending on the cell that bears the receptors.
• Muscarinic receptors are found on plasma membranes of all parasympathetic effectors
6. Physiological Effects of the ANS
• Most body organs receive dual innervation
– innervation by both sympathetic & parasympathetic
• Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels
• Some organs have only sympathetic innervation
– sweat glands, adrenal medulla, arrector pili mm & many blood vessels
– controlled by regulation of the “tone” of the sympathetic system
7. Autonomic or Visceral Reflexes
• A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously.
– changes in blood pressure, digestive functions etc
– filling & emptying of bladder or defecation
• Autonomic reflexes occur over autonomic reflex arcs.
Components of that reflex arc:
– sensory receptor
– sensory neuron
– integrating center
– pre & postganglionic motor neurons
– visceral effectors
8. Control of Autonomic NS
• Not aware of autonomic responses because control center is in lower regions of the brain
• Hypothalamus is major control center
– input: emotions and visceral sensory information
• smell, taste, temperature, osmolarity of blood, etc
– output: to nuclei in brainstem and spinal cord
– posterior & lateral portions control sympathetic NS
• increase heart rate, inhibition GI tract, increase temperature
– anterior & medial portions control parasympathetic NS
• decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility
https://www.youtube.com/watch?v=8p6vxRtWHO0
https://www.youtube.com/watch?v=zZ80T1BtumQ
https://www.youtube.com/watch?v=D96mSg2_h0c
https://www.youtube.com/watch?v=71pCilo8k4M
Lect 16 & 17
Sensory & The Special Senses
1. Is Sensation Different from Perception?
• Sensation is a conscious or unconscious awareness of external or internal stimuli.
• Sensation is any stimuli the body is aware of
– Chemoreceptors化学物质, thermoreceptors温度, nociceptors疼, baroreceptors血压/pressure
• Perception is the conscious awareness & interpretation of a sensation.
– precisely localization & identification
– memories of our perceptions are stored in the cortex
2. Sensory Modalities
• Sensory Modality is the property by which one sensation is distinguished from another.
• Different types of sensations
– touch, pain, temperature, vibration, hearing, vision
– Generally, each type of sensory neuron can respond to only one type of stimulus.
• Two classes of sensory modalities
– The general senses include both somatic and visceral senses, which provide information about conditions within internal organs.
– The special senses include the modalities of smell, taste, vision, hearing, and equilibrium.
3. Sensory Receptors
• Receptor Structure may be simple or complex
– General Sensory Receptors (Somatic Receptors)
• no structural specializations in free nerve endings that provide us with pain, tickle, itch, temperatures
• some structural specializations in receptors for touch, pressure & vibration
– Special Sensory Receptors (Special Sense Receptors)
• very complex structures---vision, hearing, taste, & smell
4. Alternate Classifications of Sensory Receptors by
A. Structural classification
•Free nerve endings
-pain, temperature, tickle, itch & light touch
•Encapsulated封装的 nerve endings
-pressure, vibration & deep touch
•Separate sensory cells
-vision, taste, hearing, balance
B. Type of response to a stimulus/classification by response
• Generator potential
– free nerve endings, encapsulated nerve endings & olfactory/smell receptors produce generator potentials
• Receptor potential
– vision, hearing, equilibrium and taste receptors produce receptor potentials
• Amplitude of potentials vary with stimulus intensity
C. Location of receptors & origin of stimuli/classification by location
• Exteroceptors
– near surface of body
– receive external stimuli
– hearing, vision, smell, taste, touch, pressure, pain, vibration & temperature
• Interoceptors
– monitors internal environment (BV or viscera)
– not conscious except for pain or pressure
#pH
• Proprioceptors
– muscle, tendon, joint & internal ear
– senses body position & movement
D. Type of stimuli they detect/classification by stimuli
• Mechanoreceptors
– detect pressure or stretch
– touch, pressure, vibration, hearing, proprioception第六感, equilibrium & blood pressure
• Thermoreceptors detect temperature
• Nociceptors detect damage to tissues
• Photoreceptors detect light
• Chemoreceptors detect molecules
– taste, smell & changes in body fluid chemistry--respiratory, cardiovascular
5. Somatic sensation
Tactile Sensations
• Tactile sensations are touch, pressure, and vibration plus itch and tickle.
• receptors include
– corpuscles of touch (Meissner’s corpuscles),
– hair root plexuses,
– type I (Merkel’s discs)
– type II cutaneous (Ruffini’s corpuscles)
– mechanoreceptors,
– lamellated (Pacinian) corpuscles,
– free nerve endings
A. Touch
• Crude touch refers to the ability to perceive that something has simply touched the skin
• Discriminative touch (fine touch) provides specific information about a touch sensation such as location, shape, size, and texture of the source of stimulation.
• Receptors for touch include corpuscles of touch (Meissner’s corpuscles) and hair root plexuses; these are rapidly adapting receptors.
• Type I cutaneous mechanoreceptors (tactile or Merkel discs) and type II cutaneous mechanoreceptors (end organs of Ruffini) are slowly adapting receptors for touch.
B. Pressure and Vibration
• Pressure is a sustained sensation that is felt over a larger area than touch.
– Pressure sensations generally result from stimulation of tactile receptors in deeper tissues and are longer lasting and have less variation in intensity than touch sensations
– Receptors for pressure are type II cutaneous mechanoreceptors and lamellated (Pacinian) corpuscles.
• Like corpuscles of touch (Meissner’s corpuscles), lamellated corpuscles adapt rapidly.
• Vibration sensations result from rapidly repetitive sensory signals from tactile receptors
– receptors for vibration sensations are corpuscles of touch and lamellated corpuscles, which detect low-frequency and high-frequency vibrations, respectively.
C. Itch and Tickle
• Itch and tickle receptors are free nerve endings.
– Tickle is the only sensation that you may not elicit on yourself.
SUMMARY
• Touch
– crude touch is ability to perceive something has touched the skin
– discriminative touch provides location and texture of source
• Pressure is sustained sensation over a large area
• Vibration is rapidly repetitive sensory signals
• Itching is chemical stimulation of free nerve endings
• Tickle is stimulation of free nerve endings only by someone else
6. Meissner’s Corpuscle
• Dendrites enclosed in CT in dermal papillae of hairless/glabrous skin
• Discriminative touch & vibration-- rapidly adapting--dynamic stimulus
• Generate impulses mainly at onset of a touch
#layered disk, beta nerve fibers, light touch, position sense
https://www.youtube.com/watch?v=AwzIHhBljts
7. Hair root plexus
•Free nerve endings found around follicles, detects movement of hair
8. Merkel’s Disc
• Flattened dendrites touching cells of stratum basale
• Used in discriminative touch (25% of receptors in hands)
#superficial layer
https://www.youtube.com/watch?v=pOZ_ATlwBYQ
9. Ruffini Corpuscle/endings
• Found deep in dermis of skin
• Detect heavy touch, continuous touch, & pressure
#encapsulated, reticular dermis, dense connective tissue
https://www.youtube.com/watch?v=AUa7pD7YF38
10. Pacinian/lamellar Corpuscle
• Onion-like connective tissue capsule enclosing a dendrite
• Found in subcutaneous tissues & certain viscera--joints, ligaments
• Sensations of deep touch/pressure or high-frequency vibration
#deep skin layer, quick adapt=constantly changing stimulus, diabetes=loss vibration
https://www.youtube.com/watch?v=T6QTNWbZl2U
11. Thermal Sensations
• Free nerve endings with 1mm diameter receptive fields on the skin surface
– Cold receptors in the stratum basale respond to temperatures between 50-105 degrees F
– Warm receptors in the dermis respond to temperatures between 90-118 degrees F
• Both adapt rapidly at first, but continue to generate impulses at a low frequency
• Pain is produced below 50 and over 118 degrees F.
#phasic=quick adapt
#3-4x more cold than worm receptors
12. Pain Sensations
• Pain receptors (nociceptors) are free endings that are located in nearly every body tissue
– Free nerve endings found in every tissue of body except the brain
– adaptation is slight if it occurs at all.
• Stimulated by excessive distension, muscle spasm, & inadequate/not enough blood flow
• Tissue injury releases chemicals such as K+, kinins or prostaglandins that stimulate nociceptors
#tonic
13. Proprioceptive or Kinesthetic Sensations
• Receptors located in skeletal muscles, in tendons, in and around joints, and in the internal ear convey nerve impulses related to muscle tone, movement of body parts, and body position. This awareness of the activities of muscles, tendons, and joints and of balance or equilibrium is provided by the proprioceptive or kinesthetic sense.
• Awareness of body position & movement
– walk or type without looking
– estimate weight of objects
• Proprioceptors adapt only slightly
• Sensory information is sent to cerebellum & cerebral cortex +thalamus
– signals project from muscle, tendon, joint capsules & hair cells in the vestibular apparatus
– receptors discussed here include muscle spindles, tendon organs (Golgi tendon organs), and joint kinesthetic receptors (Figure 16.4).
SUMMARY
https://www.youtube.com/watch?v=0SErqVGcAR0
https://www.youtube.com/watch?v=kBr0Yj_vMQg
https://www.youtube.com/watch?v=AG7Ev2hJGFk
https://www.youtube.com/watch?v=KJB_WNR-DBw
https://www.youtube.com/watch?v=BnXz70i0St4
https://www.youtube.com/watch?v=uOaiaYDoUnA
______
1. Chemical Senses
• Interaction of molecules with receptor cells
• Olfaction (smell) and gustation (taste)
• Both project to cerebral cortex & limbic system
– evokes strong emotional reactions
2. Olfactory Epithelium
• The receptors for olfaction, which are bipolar neurons, are in the nasal epithelium in the superior portion of the nasal cavity.
• They are first-order neurons of the olfactory pathway.
• Supporting cells are epithelial cells of the mucous membrane lining the nose.
• Basal stem cells produce new olfactory receptors.
3. Cells of the Olfactory Membrane
• Olfactory receptors
– bipolar neurons with cilia or olfactory hairs
• Supporting cells
– columnar epithelium
• Basal cells = stem cells
– replace receptors monthly
• Olfactory glands
– produce mucus
4. Gustatory Sensation: Taste
• Taste is a chemical sense.
– To be detected, molecules must be dissolved.
– Taste stimuli classes include sour, sweet, bitter, and salty.
• 10,000 taste buds found on tongue, soft palate & larynx
• 3 cell types: supporting, receptor & basal cells
5. Physiology of Taste
• Receptor potentials developed in gustatory hairs cause the release of neurotransmitter that gives rise to nerve impulses.
• Mechanism
– dissolved substance contacts gustatory hairs
– receptor potential results in neurotransmitter release
Odorant molecules dissolve in mucus secreted by the olfactory epithelium and bind to receptors, triggering a generator potential. In some cases the binding activates a G protein in the plasma membrane that activates adenylate cyclase that opens sodium ion channels. Axons of the receptors (first-order neurons) transmit impulses via cranial nerve I through the olfactory foramina of the cribiform plate and terminate in the olfactory bulbs, where they synapse with second-order neurons. These axons form the olfactory tracts, which transmit impulses to the olfactory area in the temporal lobe. Other important brain areas include the limbic system, the hypothalamus, and the orbitofrontal area.
6. Vision
Accessory Structures of Eye - Overview
• More than half the sensory receptors in the human body are located in the eyes.
• A large part of the cerebral cortex is devoted to processing visual information.
• Eyelids or palpebrae
– protect & lubricate
– epidermis, dermis, CT, orbicularis oculi m., tarsal plate, tarsal glands & conjunctiva
• Tarsal glands
– oily secretions
• Conjunctiva
– palpebral & bulbar
– stops at corneal edge
8. Extraocular Muscles
• Six muscles that insert on the exterior surface of the eyeball
9. Tunics (Layers) of Eyeball
• The eye is constructed of three layers.
A. Fibrous Tunic (outer layer)
B. Vascular Tunic (middle layer)
Muscles of the Iris
• Constrictor pupillae (circular) are innervated by parasympathetic fibers while Dilator pupillae (radial) are innervated by sympathetic fibers.
• Response varies with different levels of light
Photoreceptors
• shapes of their outer segments differ
• Rods /rod shaped
– specialized for black-and-white vision in dim light
– allow us to discriminate between different shades of dark and light
– permit us to see shapes and movement.
– shades of gray in dim light
– 120 million rod cells
– shapes & movements
– distributed along periphery
• Cones /cone shaped症状：近视
– specialized for color vision and sharpness of vision (high visual acuity) in bright light
– most densely concentrated in the central fovea, a small depression in the center of the macula lutea.
– sharp, color vision
– 6 million
– fovea of macula lutea
• densely packed region
• at exact visual axis of eye
• 2nd cells do not cover cones
• sharpest resolution (acuity)
• The macula lutea is in the exact center of the posterior portion of the retina, corresponding to the visual axis of the eye.
– The fovea is the area of sharpest vision because of the high concentration of cones.
– Rods are absent from the fovea and macula and increase in density toward the periphery of the retina.
• Named for shape of outer segment
• Receptors transduce light energy into a receptor potential in outer segment
• Photopigment is integral membrane protein of outer segment membrane
– photopigment membrane is folded into “discs” & replaced at a very rapid rate
Layers of Retina
• Pigmented epithelium
– nonvisual portion
– absorbs stray light & helps keep image clear
• 3 layers of neurons (outgrowth of brain)
– photoreceptor layer--rod, cone
– bipolar neuron layer--horizontal, bipolar, amacrine cell
– ganglion neuron layer--ganglion cell
• 2 other cell types (modify the signal)
– horizontal cells
– amacrine cells
Pathway of Nerve Signal in Retina
• Light penetrates retina
• Rods & cones transduce light into action potentials
• Rods & cones excite bipolar cells
• Bipolars excite ganglion cells
• Axons of ganglion cells form optic nerve leaving the eyeball (blind spot)
• To thalamus & then the primary visual cortex
process of image formation on the retina
Refraction:
• bending of light as medium changes to focus light into central fovea
Accommodation of lens for near/distance vision:
• shape of lens changed by ciliary muscle to make light focus on retina
Constriction of pupil:
• ANS reflex to prevent scattering of light through edges of lens
Convergence of eyes:
• to focus both eyes on same object and provide binocular (3D) vision
• Images are focused on the retina upside-down and mirror-image, and the brain then translates this information.
C. Nervous Tunic (inner layer)
10. Hearing and equilibrium
A. The external (outer) ear collects sound waves.
• The external (outer) ear collects sound waves and passes them inwards
• Structures
– auricle or pinna
– external auditory canal
– tympanic membrane or eardrum
B. The middle ear (tympanic cavity) is a small, air-filled cavity in the temporal bone that contains auditory ossicles (middle ear bones, the malleus, incus, and stapes), the oval window, and the round window.
• Air filled cavity in the temporal bone
• Separated from external ear by eardrum and from internal ear by oval & round window
• 3 ear ossicles connected by synovial joints
– malleus attached to eardrum, incus & stapes attached by foot plate to membrane of oval window
– stapedius and tensor tympani muscles attach to ossicles
• Auditory tube leads to nasopharynx
– helps to equalize pressure on both sides
C. The internal (inner) ear is also called the labyrinth because of its complicated series of canals.
• The bony labyrinth is a series of cavities in the petrous portion of the temporal bone.
• It can be divided into three areas named on the basis of shape: the semicircular canals and vestibule, both of which contain receptors for equilibrium, and the cochlea, which contains receptors for hearing.
11. Physiology of Hearing - Overview
• Auricle collects sound waves
• Eardrum vibrates
– slow vibration in response to low-pitched sounds
– rapid vibration in response to high-pitched sounds
• Ossicles vibrate since malleus is attached to the eardrum
• Stapes pushes on oval window producing fluid pressure waves in scala vestibuli & tympani
• Pressure fluctuations inside cochlear duct move the hair cells against the tectorial membrane
• Microvilli are bent producing receptor potentials
• The auricle directs sound waves into the external auditory canal.
• Sound waves strike the tympanic membrane, causing it to vibrate back and forth.
• The vibration conducts from the tympanic membrane through the ossicles (through the malleus to the incus and then to the stapes).
• The stapes moves back and forth, pushing the membrane of the oval window in and out.
• The movement of the oval window sets up fluid pressure waves in the perilymph of the cochlea (scala vestibuli).
• Pressure waves in the scala vestibuli are transmitted to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear.
• As the pressure waves deform the walls of the scala vestibuli and scala tympani, they push the vestibular membrane back and forth and increase and decrease the pressure of the endolymph inside the cochlear duct.
• The pressure fluctuations of the endolymph move the basilar membrane slightly, moving the hair cells of the spiral organ against the tectorial membrane; the bending of the hairs produces receptor potentials that lead to the generation of nerve impulses in cochlear nerve fibers.
• Pressure changes in the scala tympani cause the round window to bulge outward into the middle ear.
12. Physiology of Equilibrium (Balance)
• Static equilibrium
– maintain the position of the body (head) relative to the force of gravity
– macula receptors within saccule & utricle
• Dynamic equilibrium
– maintain body position (head) during sudden movement of any type--rotation, deceleration or acceleration
– crista receptors within ampulla of semicircular ducts
13. Otolithic Organs: Saccule & Utricle
• The maculae of the utricle and saccule are the sense organs of static equilibrium.
• They also contribute to some aspects of dynamic equilibrium
14. Detection of Position of Head
• Movement of stereocilia or kinocilium results in the release of neurotransmitter onto the vestibular branches of the vestibulocochler nerve
15. Crista: Ampulla of Semicircular Ducts
• Small elevation within each of three semicircular ducts
• Hair cells are covered with cupula (gelatinous material)
• When you move, fluid in canal tends to stay in place, thus bending the cupula and bending the hair cells - and altering the release of neurotransmitter
16. Detection of Rotational Movement
• Nerve signals to the brain are generated indicating which direction the head has been rotated
SUMMARY
https://pressbooks.bccampus.ca/dcbiol12031209/chapter/14-1-sensory-perception/
https://www.youtube.com/watch?v=EkfmBjMOnaQ
https://www.youtube.com/watch?v=475aOnD8rik
https://www.youtube.com/watch?v=wQJbsOWc344
https://www.youtube.com/watch?v=gUNNPIY55OA
https://www.youtube.com/watch?v=m_9SqIQ0BQQ
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