Integration of the nervous system functions
Compared to animals we have large complex brains that have the same basic function of receiving and sending signals, but we are also capable to unique complex functions: recording history, reasoning, planning, to a degree unparalleled in the animal kingdom.
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I. Sensation
II. Control of skeletal muscle
III. Brain Stem Function
IV. Other Brain functions
V. FX of aging of the nervous system
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B. Sensory tracts
C. Sensory areas of the cerebral cortex
D. Sensory processing
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• Sensation/perception
– Conscious awareness of FX of stimuli on sensory receptors
– Sensation requires 3 steps :
Stimuli originating inside or outside of the body are detected by sensory receptors & AP’s are propagated to the CNS via the nerves w/in the CNS AP’s to the cerebral cortex & to other areas of the CNS
Many AP’s reaching the cerebral cortex are ignored others are translated and person becomes aware of the stimuli
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• Senses : means by which the brain perceives information about the environment & the body
5 recognized senses :
1.
Smell
2.
Taste
3.
Sight
4.
Hearing
5.
Touch
1
Divided into 2 groups
2
• More specialized structure
• Specialized nerve endings
• Localized to specific organs
Provide sensory info about the body & environment
Provide sensory info for internal organs
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• Function:
– Mechanoreceptors, Chemoreceptors,
Thermoreceptors, Photoreceptors, & Nociceptors
• Location:
– Exteroreceptors, Visceroreceptors, &
Proprioceptors
• Structure:
– Free nerve endings, Tacile/Merkle disks, Hair follicle receptors, Pacinian Corpuscles, Meissner corpusle, Ruffini end organs, Muscle spindles, &
Golgi tendon apparatus
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1.
Mechanoreceptor :
– Mechanical stimuli (Compression, bending, or stretching)
– Fxn: touch, tickle, itch, vibration, pressure, proprioception, hearing & balance
2.
Chemoreceptors :
– Ligands bind to cell membrane receptors
– Fxn: Smell & taste
3.
Thermoreceptors :
– Responds to
D ’s in temp @ site of receptor
– Fxn: req’d for sense of temp
4.
Photoreceptors :
– Responds to light striking receptor cells
– Fxn: req’d for vision
5.
Nociceptors :
– (pain) responds to mechanical, chemical, or thermal stimuli, some can respond to more than 1.
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1. Exteroreceptors:
– Associated with the skin and detects the external environment
2. Visceroreceptors:
– Associated with the visceral organs & detects the internal environment
3. Proprioceptors:
– Associated with joints, tendons, & other CT & detects body position, mvmt, & extent of stretch or force of muscular contraction
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1. Free nerve endings
2. Tactile/Merkle Disk
3. Hair follicle receptors
4. Pacinian Corpuscle
5. Meissner corpusle
6. Ruffini end organs
7. Muscle spindles
8. Golgi Tendon Organ
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1. Free Nerve ending
– Branches with no capsule
2. Tactile/Merkel Disk
– Flattened expansions @ axon ends associated with
Merkel cells
3. Hair follicle receptor
– Wrapped around hair follicle or extending along axis each axons supplies X hairs and each hair has axons from X neurons
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4. Pacinian Corpuscle
– Onion shaped multilayered capsule with 1 central nerve process found deep in the dermis/ hypodermis/ associated with joints
5. Meissner corpuscle
– Several branches of 1 axon asso.’d w/ wedge shaped eptheliod cells & surrounded by a CT capsule
6. Ruffini end organs
– Branching axon w/numerous terminal knobs surrounded by
CT capsule
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7. Muscle Spindle
– Sk muscle fibers enclosed by LCT capsule w/sensory nerve endings in the center
– Proprioception asso w/detection of muscle stretch
8. Golgi End Organ
– Surrounds tendon & enclosed in delicate CT capsule
– Proprioception asso w/ stretch of tendon & imp in control of muscle contraction
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Primary
Directly conduct an AP
Secondary
Sensory receptor releases
NT, doesn’t carry AP
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A. Tonic Receptors:
• Accomidation/Adaptation:
– A decreased sensitivity to a continued stimulus
– slowly adapting receptors generate AP’s as long as the stimulus is applied and accommodate very slowly
– The response of the receptors or sensory pathways to a certain stimulus strength lessens from that which occurs when the stimulus was 1 st applied.
B. Phasic receptors:
– Rapidly adapting receptors accommodate rapidly & are most sensative to changes in stimuli
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• SC & brainstem have a # of sensory pathways that transmit
AP’s from the periphery to various parts of the brain.
• Each is involved with specific modalities (type of info transmitted)
• Names indicate their origin & termination
– 2 Major ascending tracts involved in conscious perception of external stimuli:
• Ascending tracts involved with unconsciouss
1.
Anteriolateral system
2.
Dorsal-column/medial lemniscal system perception:
• Spinocerebellar, spinoolivary, spinomesencephalic, & spinoreticular tracts
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Sensory Tracts
• Anterolateral Pathway
– All originate from cutaneous receptors
– Crossing over may occur near the level of neuron entry a) Spinothalamic
• Modaility (M) pain, temp, light touch, pressure, tickle, & itch
•
Termination (T) Cerebral cortex b) Spinoreticular
• (M) Pain
•
(T) Reticular formation & thalamus c) Spinomesencephalic
•
(M) Pain & touch
• (T) mesencephalon & superior colliculus
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Sensory Tracts
• Dorsal-column/Medial-lemniscal
System
– Fasciculus gracilis
• Conveys impulses from nerve endings below the midthorax
– Fasciculus cuneatus
• Conveys impulses from below midthorax
– (M) proprioception, 2-point discrimination, pressure, & vibration
– (O) Joints, tendons, muscles
– (T) Cerebral cortex & cerebellum
• Contralateral
– Involved in conscious awareness of proprioception but also unconscious neuromuscular fxns
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Sensory Tracts
• Trigeminothalamic Tract
– Joins with spinothalamic tract as they both pass thru brainstem
– Afferent fibers from
• Trigeminal nerve (1 o )
• ear, tongue, cranial nerves 7,
9, &10
– Info from face, nasal cavity,
& oral cavity
• Pain, temp, light touch, pressure, tickle, itch, touch, proprioception, 2-p discrimination, & vibration
• Spinoolivary tracts:
– Project to:
• Olivary nucleus
• Cerebellum
– AP’s contribute to coordintion of mvmt asso.
1 o ly w/mvmt & balance
• Spinotectal tracts:
– End @ superior colliculi of the midbrain
– AP’s involved in reflexes that turn head & eyes toward point of cutaneous stimulation
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• Spinocerebellar (SpCB) System
– Carry proprioceptive info to cerebellum so info concerning actual mvmt can be monitored & compared w/cerebral info rep’ing intended mvmts
– Two tracts
1.
Posterior SpCB tract
– Info from thorax, upper limbs, & upper lumbar region  cerebellum
2.
Anterior SpCB tract
– Info from lower truck & lower limbs
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• Descending Pathways that modify sensation
– Corticospinal plus other descending tracts send collateral branches to the thalamus, reticular formation, trigeminal nuclei & spinal cord
• Neuromodulators from these regions decrease the frquency of AP’s to sensory tracts via the cerebral cortex & other brain regions
• This may reduce the conscious perception of sensations
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Figure 14.11 pg 481
• Sensory pathways project to specific regions of the cerebral cortex where sensations are perceived
• Must be intact for conscious perception, localization, & identification of a stimulus
• Projection: although cutaneous sensations are integrated within the cerebrum, they are perceived as though on the surface of the body
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• 1 o Somatic Sensory Cortex
(PSSC)
– This pattern can be found in both hemispheres
– NOTICE the size of the areas corresponding to the sensory regions
– The size of the region is related to the # of sensory receptors in that area of the body
– THUS: the density of sensory receptors in the face is > than that seen in the legs (just look at how much area is dedicated to it.)
• THUS the greater the area of the
SSC the more sensory receptors in that area of the body
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• Taste Area
– Taste sensations are perceived
– located at the end of the inferior end of the postcentral gyrus
• Olfactory cortex:
– Here conscious & unconscious responses to odor are initiated
– (not shown) inferior surface frontal lobe
• Primary Auditory cortex
– Here auditory stimuli are processed by this part of the brain
– Superior Temporal Lobe
• Visual Cortex
– Portions of visual images are processed by this part of the brain (Color, shape & mvmt are processed separately rather than a complete color motion picture)
– Located in the occipital lobe
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• Association Areas are involved in the process of recognition (Process sensory input from the primary sensory areas)
– They are normally adjacent to their 1 o sensory area.
– There are 3 a.
Auditory Association Area b.
Somatic Sensory Association Area c.
Visual Association Area
Also interconnected w/other parts of the brain
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A. Motor areas of the cerebral cortex
B. Motor Tracts
C. Modifying and refining motor activities
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• Reflexes (occur w/o conscious thought)
• Voluntary Mvmts:
– Mvmts consciously activated to achieve a specific goal (*)
– AP’s mv from upper motor neurons (UMN) to lower motor neurons (LMN)
• Motor Syst of brain & SC responsible for maintaining: a.
Body’s posture & balance b. Moving: trunk, head, limbs, & eyes c. Communicating thru facial expressions & speech a.
UMN: cell bodies w/in cerebral cortex and connect directly or indirectly (internerons) to LMN b.
LMN: cell bodies synapse with
UMN in the 1.
anterior horns of the gray matter (SC) or 2.
cranial nerve nuclei of brainstem then axons leave
CNS & extend thru the PNS nerves to supply ske. muscle
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Voluntary Movements Depend on
Initiation of of most voluntary mvmts begin in the premotor area of cerebral cortex & involve the stimulation of the UMN’s
UMN form descending tracts i
Stimulate LMN i
Stimulate skeletal muscle contraction
Cerebral cortex interacts with
Basal nuclei & cerebellum  to plan, coordinate, & execute mvmts
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A. Motor Areas- Cerebral Cortex
1. *Primary Motor Cortex
(PMC)
– Although only 30% of the UMN are located in the PMC, AP’s from PMC control many voluntary mvmts
– The higher the # of MU (that have few muscle fibers) the more precise the movement
2. Premotor Area:
– Staging area where motor fxns are organized b4 they are initiated in the (PMC)
– Which muscles must contract, in what order to contract, & to what degree do they contract
3. Prefrontal Area:
– Involved in motivation & foresight to plan and initiate mvts
– Involved in motivation & regulation of emotional behavior & mood
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Descending pathways w/axons carrying AP’s from regions of the cerebrum/cerebellum to brainstem & SC
2 divisions
Direct Pathways/Pyramidal System Indirect Pathways/Extrapyramidal System
Rubrospinal Tectospinal
Corticobulbar Tract Corticospinal Tract
Vestibulospinal Reticulospinal
Anterior
Corticospinal Tract
Lateral
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Maintenance of muscle tone & controlling the speed & precision of skilled mvmts,
1oly fine mvmts involved in dexterity*
Corticobulbular
Tracts
Control eye & tongue mvmts, mastication, facial expression & palatine, pharyngeal,
& laryngeal mvmts
Lateral
Corticospinal
Tracts
Mvmt of neck, trunk & limbs
(push-ups, moving with a hola hoop.)
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Corticospinal
Tracts
Mvmts below the head esp the hands
Anterior
Corticospinal
Tracts
Mvmt of the neck & upper limb extremities
(Typing)
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Less precise (unconscious) control of motor fxns especially those involved in overall body coordination & cerebellar fxn such as posture
Rubrospinal
Tracts
•Mvmt coordination
•Positioning digits & palm when reaching out to grasp
•Reg’ing fine motor control of muscles in the distal part of the upper limbs
Vestibulospinal
Tracts
•Maintenance of upright posture /balance
•Extension of upper limbs when falling down
Reticulospinal
Tracts
•Posture
Adjustment/
Walking
•Maintenance of posture while standing on 1 foot
Tectospinal
Tracts
•Mvmt of head and neck in response to visual & auditory reflexes
•Mvmt of head & neck away from a sudden flash of light
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• Basal Nuclei
– Important in planning, organizing, & coordinating motor mvmts & posture.
– Links to both the thalamus & cerebral cortex
• These form feedback loops
• Can be stimulatory/inhibitory
– Disorder
• Cerebellum a. Vestibulcerebellum:
– Controls balance & eye mvmt b. Spinocerebellum:
– Corrects discepancies btwn intended & actual mvmts (Comparator) c. Cerebrocerebellum:
– Can “learn” highly specific complex motor activites
(piano/baseball)
– Also involved in cognitive fxns
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Major ascending & descending pathways project thru the brainstem
A. Sensory input projecting through the brainstem
B. RAS functions of the brainstem
C. Vital fxns controlled in the brainstem
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A. Sensory Input
Projecting Thru the
BnSm
– Sensory axons project thru the BnSm from the ascending SC pathways
– Sensory nuclei from cranial nerves (CN) 3-
10 & 11
– Nuclei of the reticular formation
• Cranial Nerve (CN) 2  Vision
• CN 5  tactile sensation from face, nasal & oral cavities
• CN 7  Taste
• CN 8  Hearing and balance
• CN 9  Taste and tactile sensation in the throat
• CN 10  Taste and tactile sensation in the larynx; visceral sensation in the throat and abdomen
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• Reticular activating system
(RAS)
– Can be stimulated by inputs from the cerebral cortex
(mental activities), & a variety of sensory inputs from stimuli such as visual
(flashes of light), auditory
(ringing alarm), olfactory
(burning/coffee), & sematosensory (splashing cold H2O on/touching your face).
• CN’s 2,5,&8 stimulate wakefulness & consciousness
• RAS is involved in sleep wake
– Maintain alertness & attention
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C. Motor Output & reflexes projecting thru the Bnsm
Somatic Motor Output &
Reflexes
Parasympathetic Output &
Reflexes
• Reflexes:
– Eyes/neck mvmt in response to visual & auditory stimuli or tactile stimulation
• Passin’ thru
– Eyes: move & look toward on object, tracking a moving object
– Chewing, how hard or soft something is and changing mvmt accordingly control of tongue for chewing & speech
– Facial muscles for expressions
– Pharynx & larynx associated with swallowing & speech.
• Reflexes controlled via the reticular formation:
– Visual reflexes (pupil size)
• Passin’ thru
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– Sneeze reflex
– Salivary glands stimulation to salivate
– Gag reflex
– Cough reflex
– Heart rate
– Respiration
– Digestion
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• Brain is capable of many fxns besides sensory input & muscle control. Speech, mathematical & artistic abilities, sleep memory, emotions, & judgement
A. Speech
B. Right & Left cerebral cortex
C. Brainwaves and sleep
D. Memory
E. Limbic System
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1. Wernicke’s Area
• Portion of the parietal lobe
• Sensory speech area
• Req’d for understanding & formulating coherent speech
2. Broca’s Area
• Inferior part of the frontal lobe
• Motor speech area
• Initiates the complex series of mvmts necessary for speech
Connected to each other by a bundle of neurons known as arcuate fasciculus
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Commissure: band of tracts that connect the 2 hemisphere for info sharing
Rt. Cerebral
Hemisphere
•Motor Output goes to the left side
•Sensory input comes from the left side
•Spatial perception, facial recognition, & musical ability
Lt. Cerebral
Hemisphere
•Motor Output goes to the right side
•Sensory input comes from the right side
• mathematics & speech
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• Electroencephalogram:
(EEG)
– Can record simultaneous Ap’s in large #’s of neurons & displays wave-like patterns known as brain waves.
– Most normal people don’t have a regular pattern but there are 4 regular patterns seen at specific times: a) Alpha b) Beta c) Theta d) Delta
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• These waves can be used as a diagnostic tool to diagnose brain disorders
• Patterns also vary during the 4 stages of sleep.
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1. Sensory memory:
– Lasts less than a sec & involves transient
D ’s in membrane potential
– Retention of sensory input received by the brain while something is scanned, evaluated, & acted on
2. Short term memory
– Lasts sec’s to min’s if considered important enough to move from 1 to 2.
– Limited by the # of bits of info that can be stored at 1 time
– New info may cause loss of old
– Physiology: short term
D ’s in membrane potential (longer than 1) but can be eliminated by new info entering the cell
3. Long term memory
– Lasts hours to years to a lifetime
– There are 2 types: a.
Declarative/ Explicit b.
Procedural/ Implicit/
Reflexive
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Declarative
• Retention of facts
Procedural
• Involves the development
• Accessed via the hippocampus, amygdala, or amygdaloid nuclear complex
– H : involved in retrieving the actual memory*
– A : involved in the emotional overtones of that memory *
– Emotions may also serve as a switch for storing or not storing a memory
• Memories appear to be compartmentalized* in the cerebrum
– This also makes retrieval complex (put a puzzle together)
AP1 Chapter 14 of skills like riding a bike or playing the piano.
• Primarily stored in cerebellum & premotor area of the cerebrum
(only small amounts are lost thru time) #
• Conditioned/Pavlovian reflexes are implicit (but cerebellar lesions cause their loss)
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• Physiology of long term memory:
– D ’s in the neuron (long term potentiation) which facilities future transmission of AP’s.
– The neuron grows new axons to increase the number of synapse. (especially seen in development of skills)
• Repetition of info association with new info with existing memories assist in the transfer from short to long term memory
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• Influences emotions, innate responses to emotions, motivation, mood & sensations of pain & pleasure
• Associated with basic survival (reproduction, food H
2
O)
• Damage:
– Voracious appetite
– Increased sexual activity (often inappropriate)
– Docility (loss of fear and anger)
– Temporal lobe damage (Loc of Limbic System)
• Can also result in loss of memory formation
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• General decline in sensory & motor fxns
• Short term memory is decreased
• Thinking ability doesn’t D
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