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103 terms

Lec Test 2 chap. 15 & 16

Conscious or subconscious awareness of change in internal/external environment (somatic or visceral)
Conscious awareness (interpretation) of sensations and is primarily a function of the cerebral cortex
General Senses (somatic & visceral)
Temperature, pain, touch (tactile), pressure, vibration, proprioception
Special Senses
Olfaction (smelling), vision, gustation (taste), equilibrium, auditory
Labeled Line
The connection between the receptor & the cerebral cortex (1st-order, 2nd-order & 3rd-order neurons)
Conversion of a stimulus into a graded potential
The Process of Sensations
1. Stimulation of the sensory receptor (receptive field)
2. Transduction of the stimulus
3. Generation of nerve impulse (1st-order neurons)
4. Integration of sensory input (in cerebral cortex)
Concept of Receptive Field
An appropriate stimulus must occur within the sensory receptor's receptive field, meaning, the body region where stimulation activates the receptor & produces a response
Receptive Field
-Area is monitored by a single receptor or a receptor cell
-The larger the receptive field, the more difficult it is to localize a stimulus
Mapping of the Primary Somatosensory Area (distribution or sensory receptors)
Highest: Fingertips, lips, tip of tongue
Lowest: Posterior surface of the body
Classification of Sensory Receptors by Structure
1. Free nerve endings (bare dendrites, pain, thermoreceptors, itch & tickle)
2. Encapsulated nerve endings (dendrited enclosed in CT capsule, Pacinian corpuscles, Ruffini corpuscles & Meissners corpuscles, etc)
3. Receptor cells (special senses, hair cells, photoreceptors, & gustatory receptor cells)
Classification of Sensory Receptors by Location & Origin
1. Exteroceptive senses (senses associated w/ body surface, touch, pressure, temp, pain - Exteroceptors)
2. Interoceptive senses (associated w/ changes in viscera - Interoceptors)
3. Proprioceptive senses (associated w/ changes in muscles & tendons - Proprioceptors)
Classification of Sensory Recpetors by Stimulus
1. Chemoreceptors - respond to change in chemical concentrations
2. Nociceptors (pain) - tissue damage & extreme temps
3. Thermorecptors - change in temperature
4. Mechanoreceptors (tactile, baro-, proprioceptors) - stimulation by mechanical forces
5. Osmoreceptors - changes in osmotic pressure of body fluids
6. Photoreceptors - respond to light
Sensory Adaptation
Adjustment (reduction in sensitivity) of peripheral receptors or cortical neurons to a constant, monotonous painless stimulus
Rapidly Adapting Receptors
Smell, pressure & touch
Slowly Adapting Receptors
Pain, proprioceptors, receptors monitoring chemical composition of blood
Tactile Receptors in the Skin
1. Meissner corpuscle
2. Merkel's disc
3. Pacinian corpuscle
4. Ruffini corpuscle
5. Hair root plexus
6. Free nerve ending
Free Nerve Endings
-slowly adapting
-common in epithelial tissues
-situated between epidermal cells
-detect pain, temp, itch & tickle
Meissner's Corpuscle
-rapidly adapting, encapsulated
-abundant in hairless portions of skin, fingertips, eyelids, nipples, clitoris, penis, tongue, soles (dermal papillae)
-detect soft touch, low-frequency vibration
Hair Root Plexus
-rapidly adapting
-free nerve endings wrapped around hair follicles
-detect movements across the hairy body surface
Pacinian (lamellated) Corpuscle
-rapidly adapting
-common in deep dermis, submucosa, tendons, ligaments, subserosa, periosteum & viscera
-detect heavy, deep pressure
-most sensitive to pulsing or high-frequency vibration
Merkel's Disc (tactile disc)
-slowly adapting
-detect fine touch, pressure
-extremely sensitive receptors
-have very small receptive fields
-located in stratum basale
-aka. type 1 cutaneous mechanoreceptor
Ruffini Corpuscle
-slowly adapting
-detects deep pressure, stretching of movement
-located in reticular (deep) dermis, ligaments, tendons
-aka. type 2 cutaneous mechanoreceptor
Thermal Sensation (thermoreceptors)
-free nerve endings
-located in dermis, skeletal muscle, liver, hypothalamus
-same pathway as pain (lateral spinothalamic pathway)
-adapts fast followed by slow
Warm Receptors
-sensitive to temps between 32-48 C (90-118 F)
-unresponsive to temps above 48 C
Cold Receptors
-sensitive to temps between 10-40 C (50-105 F)
-located in stratum basale, more abundant than warm
Pain Receptors (nociceptors)
Respond to temps above 48 C and below 10 C
-free nerve endings w/ large receptive field
-widely distributed throughout body
-common in superficial skin, joint capsules, within periostem of bones, around walls of blood vessels
-absent in the brain
-stimulated by tissue damage (k+, kinins or prostaglandins), chemical or mechanical forces, or extreme temps
-do not adapt readily
Visceral Pain
-may exhibit "referred pain"
-we can't localize it well
Somatic Pain
-caused by injury of muscle or skin
Types of Pain Sensations
1. Acute (fast) pain
2. Chronic (slow) pain
3. Phantom pain
Aute (Fast) pain
-carried by type A fibers
-happens within 0.1 second after stimulus
-fibers conduct impulses rapidly
-acute or sharp pain
-well localized
Chronic (Slow) Pain
-carried by type C fibers (thin, unmyelinated)
-fibers conduct impulses slower
-associated w/ dull, aching (throbbing) pain
-difficult to pinpoint
-begins 1 second after fast
-persists longer
Phantom Pain
-labeled lines are involved
-hpersensitive & hyperexcitable neurons send signal to sensory cortex
Referred Pain
-projection of the pain impulses originating from the viscera onto the body surface
-most of the time the projection of pain doesn't correspond w/ projection of organ onto the body surface
-may occur due to sensory impulses from 2 regions following a common nerve pathway to the brain
-pure somatic sensation
-monitor degree of muscle contraction (muscle spindles) & tension in tendons & joints (golgi tendon organs)
-don't adapt readily
-not in viscera
-you can't tell where your spleen, appendix or pancreas are
Muscle Spindles
-monitor stretch (length) of muscles
-used by CNS to set muscle tone
Golgi Tendon Organs
-monitor muscle tension
-initiate tendon reflexes
-reduce damage to muscle & tendon through feedback reflexes causes muscle to relax
Joint Kinesthetic Receptors in synovial capsules
-monitor joint position & movements
-initiate protective reflexes
-free nerve endings
-rapidly adapting
-found in elastic tissues (aortic & carotid bodies)
-monitor blood pressure
-found in both central & peripheral NS
-detect dissolved chemical substances
-carotid & aortic bodies contain chemoreceptors detecting blood levels of pH, O2 & CO2
Organization of the Somatosensory Pathways
Sensory pathways are ascending (afferent - sensory)
1.1st-order neurons:
-sensory neuron delivers sensations to the CNS
-cell body is located in dorsal root ganglion or cranial nerve ganglion
-synapses w/ 2nd-order neuron in CNS (spinal cord or brain)
2. 2nd-order neuron:
-body is located in CNS
-axon of the 1st-order neuron synapses on it
-synapses w/ 3rd-order neuron in thalamus
-may be located in spinal cord or brain stem
-decussates (crosses over)
3. 3rd-order neuron:
-cell body located in thalamus
-if the sensation is to reach our awareness, the 2nd-order neuron synapses on it
-then synapses w/ neurons in cerebral cortex
Tracts (pathways) of the Spinal Cord
1. Ascending tracts - conduct sensory impulses from periphery to the brain
2. Descending tracts - conduct motor impulses from the brain to motor neurons reaching muscles & glands
Ascending (Somatosensory) Pathways
-carry sensory info from soma: skin & musculature of body wall, head, neck & limbs
-Has 4 major pathways
1. The Dorsal Column-Medial Lemniscus Pathway (DCML)
a. Fasciculus Gracilis
b. Fasciculus Cuneatus
-carry sensations of highly localized: fine touch, pressure, vibration, proprioception, stereognosis
-weight & 2-point discrimination: FG from the lower part & FC from the upper part
-1st-order neuron bodies are within the dorsal roots of spinal nerves & the sensory roots of cranial nerves
-2nd-order neuron bodies are in the gracile nucleus or cuneate nucleus in medulla & decussates at medulla
-3rd-order neuron bodies are in the thalamus and projects to the primary somatosensory area of cerebral cortex
Medial Lemniscus
A thin ribbonlike projection tract that extends from the medulla to the ventral posterior nucleus of the thalamus
2. The Anterolater (Spinothalamic) Pathway
Provides conscious sensations of poorly localized: touch, pressure, pain, temp, phantom pain, itch, tickle, referred pain
a. Anterior Spinothalamic Tract
-carries crude touch & pressure sensations
b. Lateral Spinothalamic Tract
-carries pain & temperature
-conveys impulses from limbs, trunk, neck & posterior head to the primary somatosensory area of cerebral cortex
-1st-order neuron cell bodies are in the doral root ganglion
-2nd-order neuron cell bodies are in posterior gray horn of spinal cord and decussates at the spinal cord
-3rd-order neuron bodies are in the ventral posterior nucleus of the thalamus and then they project to the primary somatosensory area of the cerebral cortex
3. Trigeminothalamic Pathway
Transmits impulses for most somatic sensations from the face, nasal cavity, oral cavity & teeth to the cerebral cortex
-1st-order neuron cell bodies are in the trigeminal ganglion
-2nd-order neuron cell bodies are in the pons or medulla and decussate in the pons or medulla before ascending to the ventral posterior nucleus of the thalamus
-3rd-order neuron cell bodies are in the thalamus and they project to the primary somatosensory area of cerebral cortex
4. Spinocerebellar Pathways
The cerebellum receives subconscious proprioceptive info about position of: skeletal muscles, tendons, joints (balance, posture) & actual movements
-Posterior Spinocerebellar Tract
-Anterior Spinocerebellar Tract
Posterior Spinocerebellar Tract
Contain axons that don't decussate
-axons reach cerebellar cortex via inferior cerebellar peduncle of the same side
Anterior Spinocerebellar Tract
Dominates by axons that decussate within the cord
-contains some amount of uncrossed axons as well
-sensations reach cerebellar cortex via superior cerebellar peduncle
-many axons that did cross over ascend to the cerebellum and cross over again synapsing ipsilaterally to the original stimulus side
Organization of Visceral Sensory Pathways
1st-order neuron:
-goes along the autonomic motor neurons
-with CN V, VII, IX, X in the head and neck
-cross-over (decussation)
2nd-order neuron:
-terminates in the solitary nuclues (medulla)
3rd-order neuron:
-usually doesn't exist because there is no conscious awareness of the sensation
*Carry visceral sensory info from mouth, palate, pharynx, larynx, trachea, esophagus, and associated vessels & glands
Somatic Motor (descending) Pathways Overview
Control of body movement
-motor portions of cerebral cortex
--initiate & control precise movements
-basal ganglia help establish muscle tone & integrate semivoluntary autonomic movements
-cerebellum helps make movements smooth & helps maintain posture & balance
Somatic motor pathways
-direct pathway from cerebral cortex to spinal cord & out to muscles
-indirect pathway includes synapses in basal ganglia, thalamus, reticular formation & cerebellum
Organization of the Somatic Motor Pathways
Carry motor impulses (commands) from the brain to the skeletal musculature
-Upper Motor Neuron (UMN): Is in charge of LMN, its body is in the CNS (Primary Motor Cortex)
-Lower Motor Neuron (LMN): Its body is in a nucleus of the brain or in the anterior gray horns of the spinal cord, it becomes part of a peripheral nerve
-LMN is also called the "Final Motor Pathway" because it receives input from 4 sources
-all excitatory & inhibatory signals that control movement converge on the LMNs that extend out of the brain stem & spinal cord to innervate skeletal muscles in the body
-from the brain stem, axons of LMNs extend through cranial nerves to innervate skeletal muscles of the face & head
-from the spinal cord, axons extend through spinal nerves to innervate skeletal muscles of the limbs & trunk
-only LMNs provide output from the CNS to skeletal muscle fibers
-4 neural circuits (somatic motor pathways) participate in control of movement by providing input to LMNs
1. Local Circuit Neurons (interneurons)
-located close to the LMN cell bodies in the brain stem & spinal cord
-receive input from somatic sensory receptors (nociceptors, muscle spindles etc) as well as from higher centers in the brain
-coordinate rhythmic activities & local reflexes
2. UMNs
-input to local circuits & LMNs
-most UMNs synapse w/ local circuit neurons, which in turn synapse w/ LMNs (some synapse directly w/ LMNs)
-cell bodies are in cerebral cortex & motor nuclei of brain stem
-planning & initiating directing sequence of voluntary movements (cortex)
-regulate muscle tone, posture, balance, head & body orientation (brain stem)
-both basal ganglia & cerebellum exert influence on UMNs
3. Basal Ganglia Neurons
-assist movement by providing input to UMNs
-Neural circuits interconnect the basal ganglia w/ motor areas of cerebral cortex (via the thalamus) & brain stem
-help initiate , terminate & suppress movements
-helps establish a normal level of muscle tone
4. Cerebellar Neurons
-aid movement by controlling activity of UMNs
-coordinates body movements
-balance & posture
Direct Motor Pathways (a.k.a. pyramidal)
-provide input to LMN via axons that extend directly from the cerebral cortex
a. Corticospinal
b. Corticobulbar
-conscious precise movements
Indirect Motor Pathways (extrapyramidal)
-provides input to LMN from basal ganglia, thalamus, cerebellum, reticular formation & nuclei in brain stem
a. Rubrospinal
b. Tectospinal
c. Reticulospinal
d. Vestibulospinal
-subconscious movements
Direct Descending Pathways
3 Pyramidal Tracts:
1. Lateral Corticospinal
-has the majority of axons
-decussates in the medulla
-switches to the body of LMN in anterior gray horn of spinal cord
-innervates distal muscles of extremities (precise movement of hands & feet)
2. Anterior Corticospinal
-10% of axons
decussates at the level of LMN
-innervates proximal muscles of the extremities & trunk & neck
3. Corticobulbar
-UMN & LMN synapse & decussate in brain stem; some don't decussate
-provide input to LMN in CN-III to XII
-controls skeletal muscles in head through cranial nerves
-controls movements of eyes, tongue, chewing, expressions & speech
Indirect Descending Pathways
1. Rubrospinal: from red nucleus; distal skeletal muscles of upper extremities
2. Tectospinal: from superior colliculus; reflex movement of the head in response to visual stimulus or sound
3. Vestibulospinal: from vestibular nucleus; skeletal muscles of trunk & proximal extremities to maintain posture & balance in response to head movements (ipsilateral)
4. Medial & Lateral Reticulospinal: from reticular formation; skeletal muscles of the trunk & proximal parts of extremities; maintain posture & balance in motion (ipsilateral)
Basal Ganglia
-normally inactive
-release ACh
-substantia nigra releases Dopamine
-usually active
-release GABA
-inhibit UMNs
The Role of Cerebellum in movements
The cerebellum is active in:
-learning & performing rapid, coordinated, highly skilled movements
-maintaining proper posture & equilibrium
Detects sensory input of:
-visual input
-vestibular & auditory input
-motor pathways
-connects w/ spinocerebellar pathways
-monitoring intent for movement
-monitoring actual movement
-comparing intent w/ actual performance
-sending out corrective signals
Somatic NS
Sensory input from: exteroceptors
Control of motor output: voluntary
Motor neuron pathway: 1 neuron (from CNS to effector organ)
NT: ACh only
Effector organs: skin, skeletal muscles
Responses: always excitatory
Autonomic NS
Sensory input from: interoceptors (visceral receptors)
Control of motor output: involuntary
Motor neuron pathway: 2 neurons (from CNS to ganglia & postganglionic ganglia to effector organ)
NT: ACh & NE
Effector organs: smooth, cardiac muscles & glands
Responses: excitatory or inhibitory
Autonomic Nervous System
-functions without conscious effort
-controls visceral activities
-regulates smooth, cardiac muscles & glands
-coordinates CV, respiratory, digestive, urinary & reproductive systems

Two Antagonistic Divisions:
1. Sympathetic - prepares body for fight or flight stress situations (mobilizes & spends energy)
2. Parasympathetic - prepares body for resting & digesting activities (conserves & stores energy)
Autonomic Nerve Fibers
-sensory (most are interoceptors)
-motor (efferent)
Preganglionic fibers:
-axons of preganglionic neurons
-cell bodies in CNS (lateral gray horn of spinal cord or nuclei of cranial nerves)
-synapse in autonomic ganglion
-release ACh
Postganglionic Fibers:
-axons of postganglionic neurons
-cell bodies in ganglia (postganglionic neurons)
-synapse w/ effector organs
-release NE & ACH
Sympathetic Division
a.k.a. Thoracolumbar Division
-bodies of preganglionic neuron are located in the lateral gray horns of T1-L2
Preganglionic fibers:
-short & myelinated
-leave spinal nerves through white rami (myelinated)
-enter ganglia
Sympathetic Ganglia
1. Paravertebral ganglia and fibers that connect them make up the sympathetic trunk
2. Prevertebral (collateral) ganglia synapse with postganglionic neurons
3. Adrenal medulla is a modified ganglion
Sympathetic Trunk Ganglia (paravertebral)
-located on both sides of vertebral column
-innervate head, heart, lungs, liver, stomach (everything)
-cervical ganglia & thoracic ganglia
Splanchnic Nerve
Some sympathetic preganglionic axons pass through the sympathetic trunk without terminating in it. Beyond the trunk, they form splanchnic nerves which extend to outlying prevertebral ganglia
Prevertebral (collateral) Ganglia
-located anteriorly to vertebrae (in the abdominal cavity, associated w/ major blood vessels)
-forms 5 ganglia
1. Celiac Ganglion
Innervates: stomach, liver, gallbladder, adrenal gland, pancreas & spleen
2. Aortico-renal Ganglion
Innervates: kidneys & ureters
3. Superior Mesenteric Ganglion
Innervates: small intestine, proximal 2/3 of large intestine
4. Renal Ganglion
Innervates: kidneys & ureters
5. Inferior Mesenteric Ganglion
Innervates: the rest of large intestine, rectum, urinary bladder, reproductive organs
Adrenal Medulla
-modified ganglion
-secretes Epinephrine & NE into blood vessels
Autonomic Neurotransmitters
Cholinergic neurons release ACh
Cholinergic Neurons include:
1. all sympathetic & parasympathetic preganglionic neurons
2. sympathetic postganglionic neurons that innervate most sweat glands
3. all parasympathetic postganglionic neurons
Cholinergic Neurons
Nicotinic receptors are present in the plasma membrane of dendrites & cell bodies of both sympathetic & parasympathetic postganglionic neurons
Muscarinic receptors are present in plasma membranes of all effectors (smooth, cardiac muscle & glands) innervated by parasympathetic postganglionic axons
-Both bind to ACh
Adrenergic Neurons
Release the NT norepinephrine
-Most sympathetic postganglionic neurons are adrenergic
-NE can either be a NT or a hormone released into the blood by chromaffin cells of the adrenal madulla
-Epinephrine is released as a hormone
Alpha1: Smooth muscle fibers in BV that serve salivary glands, skin, mucosal membranes, kidneys, & abdominal viscera; radial muscle in iris of eye; sphincter muscles of stomach & urinary bladder.
Salivary glands
Sweat glands on palms & soles
-Excitation--> contraction, which causes vasoconstriction, dilation of pupil, & closing of phincters.

-Secretion of k+ & water
-Increased sweating
Alpha2: Smooth muscle fibers in some BV
Cells of pancreatic islets that secrete the hormone insulin (beta cell)
Platelets in blood
-Inhibition--> relaxation--> vasodilation
-Decreased insulin secretion

-Aggregation to form platelet plug
Beta1: Cardiac muscle fibers
Juxtaglomerular cells of kidneys
Posterior pituitary
Adipose cells
-Excitation-->increased force & rate of contraction
-Renin secretion
-Secretion of antidiuretic hormone
-Breakdown of triglycerides-->release of fatty acids into blood
Beta2: Smooth muscle in walls of airways; in BVs that serve the heart, skeletal muscle, adipose tissue, & liver; & in walls of visceral organs, such as the urinary bladder.
Ciliary muscle in eye
Hepatocytes in liver
-Inhibition--> relaxation, which causes dilation of airways, vasodilation, & relaxation of organ walls

-Inhibition--> relaxation
-Glycogenolysis (breakdown of glycogen into glucose)
Beta3: Brown adipose tissue
-Thermogenesis (heat production in kids)
Stimulates alpha receptors more than beta receptors; epinephrine is a potent stimulator of both
Parasympathetic Division
a.k.a.-Craniosacral Division
-Generally concerned with relaxation, digestion & replenishing energy (rest & digest)
Preganglionic Fibers:
-long & myelinated
-in cranial part, cell bodies are in nuclei of CN-III,VII,IX&X
-in sacral part, cell bodies are in lateral gray horns of S2-S4
-preganglionic fibers of thorax & abdomen in CN-X make up 75% of parasympathetic outflow
-no white or gray rami involved
Postganglionic Fibers:
-short & unmyelinated
-synapse w/ effector organs
-release ACh
-receptors are cholinergic (muscarinic or nicotinic)
Parasympathetic Ganglia
1. Terminal - near effector organ (associated w/ cranial part)
2. Intamural - within the organs (associated w/ sacral part)
Sacral division
-form pelvic splanchnic nerves
-preganglionic fibers are not part of ventral roots
Parasympathetic Division Ganglia (4)
1. CN III--> Ciliary ganglion innervates:
-circular (sphincter) pupillae muscle-->pupillary constriction
2. CN VII--> Pterygopalatine innervates:
-nasal mucosa, palate, pharynx, lacrimal glands
3. CN VII--> Submandibular innervates:
-submandibular & sublingual salivary glands--> salivation
4. CN IX--> Otic innervates:
-parotid salivary glands--> salivation
Plexuses associated with CN X
-heart, airways, liver, stomach, pancreas, small intestine, proximal 1/3 of large intestine
CN X produces 75% of parasympathetic outflow
Sacral part of Parasympathetic division
-preganglionic fibers of pelvic nerves
-pelvic splanchnic nerves innervate distal 2/3 of colon, urinary bladder & reproductive organs
Autonomic NT
Cholinergic receptors:
-bind ACh
-found in ganglia of PSNS & SNS
-found in effectors of PSNS & SNS
-found in somatic NS
a. Muscarinic (effector organs in PSNS & some SNS)
-excitatory or inhibitory
b. Nicotinic (all autonamic ganglia)
-only excitatory
Dual Innervation
Innervation by both PSNS & SNS
Most organs except:
-major BV
-sweat glands
-adrenal medulla
-arrector pili muscle
these are sympathetic only
Autonomic Tone
Is background balance between sympathetic & parasympathetic NS
-it's controlled by hypothalamus
-2 autonomic divisions have opposing effects due to actions of postganglionic actions
-in resting condition PSNS dominates
-in a crisis SNS kicks in
Autonomic Tone continued
-organs that have sympathetic innervation only maintains autonomic tone
-amount of released NE also maintains tone
-less NE = less sympathetic stimulation = weaker autonomic tone
-more NE = more sympathetic stimulation = stronger tone
what will happen w/ diameter of major BVs when autonomic tone is a) increasing & b) decreasing
**a) BVs will constrict and cause a rise in HR & BP (sympathtic)
**b) BVs will dilate & cause a decrease in HR & BP (parasympathetic)
Autonomic Reflexes
1. BP control reflex: (SNS)
-adjustment of HR, FOC, blood vessel diameter
2. Reflex-control of respiration: (SNS)
-control of diameterof bronchi
-RR control
-respiratory depth
3. Reflex control of digestion: (PSNS)
-gastrointestinal motility
-GI smooth muscle tonus
4. Reflex-control of defecation & urination: (PSNS)
-Para- pees, poops & performs
Control of Autonomic Activity
-controlled largely by CNS (not cortex)
-Medulla regulates cardiac, vasomotor, & respiratory activities
-Hypothalamus regulates visceral functions, autonomic tone
-Limbic system & Cerebral Cortex control emotional responses
Autonomic Plexuses
-These are tangled networks of sympathetic & parasympathetic neurons which lie along major arteries
*Major autonomic plexuses:
-celiac (biggest)
-superior mesenteric
-inferior mesenteric