AP1 Chapter 14 1

Chapter 14Integration 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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Chapter 14 Outline

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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I. Sensation

A. Sensory receptors

B. Sensory tracts

C. Sensory areas of the cerebral cortex

D. Sensory processing

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I. Sensation• 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

Divided into 2 groups

Provide sensory info about the body &

environment

•More specialized structure•Specialized nerve endings•Localized to specific organs

Provide sensory info for internal

organs

1 2

5 recognized senses:1. Smell 2. Taste3. Sight4. Hearing5. Touch

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Sensory receptors can be categorized in various ways

• 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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Function: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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Location

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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Structure

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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Structure

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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Structure

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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Structure

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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Responses of Sensory receptors:Primary vs. Secondary Receptors

Primary

Secondary

Directly conduct an AP

Sensory receptor releases NT, doesn’t carry AP

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Responses of sensory receptors

• Accomidation/Adaptation:– A decreased sensitivity to a

continued stimulus– The response of the receptors

or sensory pathways to a certain stimulus strength lessens from that which occurs when the stimulus was 1st applied.

A. Tonic Receptors: – slowly adapting receptors

generate AP’s as long as the stimulus is applied and accommodate very slowly

B. Phasic receptors:– Rapidly adapting receptors

accommodate rapidly & are most sensative to changes in stimuli

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I. Sensation: Sensory Tracts• 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:

1. Anteriolateral system

2. Dorsal-column/medial lemniscal system

• Ascending tracts involved with unconsciouss perception:• Spinocerebellar, spinoolivary,

spinomesencephalic, & spinoreticular tracts

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I. Sensation: 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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I. Sensation: 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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I. Sensation:Sensory Tracts

• Trigeminothalamic Tract– Joins with spinothalamic

tract as they both pass thru brainstem

– Afferent fibers from• Trigeminal nerve (1o)• 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. 1oly 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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I. SensationSensory Tracts

• 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 tracts1. 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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I. SensationSensory Tracts

• 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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C. Sensory Areas of the Cerebral Cortex• 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

Figure 14.11 pg 481

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C. Sensory areas of the cerebral cortex• 1o 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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C. Sensory areas of the cerebral cortex• 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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D. S

enso

ry P

roce

ssin

g• Association Areas are involved in the process of

recognition (Process sensory input from the primary sensory areas)– They are normally adjacent to their 1o 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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II. Control of Skeletal Muscles

A. Motor areas of the cerebral cortex

B. Motor Tracts

C. Modifying and refining motor activities

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II. Control of Skeletal Muscle• 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)

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

• 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

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II. Control of Skeletal MusclesVoluntary 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

iStimulate LMN

iStimulate skeletal muscle

contraction

Cerebral cortex interacts with Basal nuclei & cerebellum to

plan, coordinate, & execute mvmts

A. Motor Areas- Cerebral Cortex1. *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 28AP1 Chapter 14

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B. Motor TractsDescending pathways w/axons carrying AP’s from regions of the cerebrum/cerebellum to

brainstem & SC

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2 divisions

Direct Pathways/Pyramidal System

Corticospinal TractCorticobulbar Tract

LateralCorticospinal Tract

AnteriorCorticospinal Tract

Indirect Pathways/Extrapyramidal System

Rubrospinal

Vestibulospinal Reticulospinal

Tectospinal

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Direct Pathway

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Maintenance of muscle tone & controlling the speed & precision of skilled mvmts, 1oly fine mvmts involved in dexterity*

Corticobulbular Tracts

CorticospinalTracts

Control eye & tongue mvmts, mastication, facial expression & palatine, pharyngeal, & laryngeal mvmts

Mvmts below the head esp the hands

Lateral Corticospinal

Tracts

AnteriorCorticospinal

Tracts

Mvmt of neck, trunk & limbs (push-ups, moving with a hola hoop.)

Mvmt of the neck & upper limb extremities(Typing)

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*Indirect Pathway

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Less precise (unconscious) control of motor fxns especially those involved in overall body coordination & cerebellar fxn such as posture

RubrospinalTracts

TectospinalTracts

•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

•Maintenance of upright posture /balance•Extension of upper limbs when falling down

VestibulospinalTracts

ReticulospinalTracts

•Posture Adjustment/ Walking•Maintenance of posture while standing on 1 foot

•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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Dire

ct v

s. In

dire

ct

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C. Modifying & refining motor activities

• 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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Cerebellar Comparator FXN

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III. Brain stem fxnsMajor 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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III. Brainstem (Bnsm) fxns

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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B. RAS Fxns of the Bnsm• 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

• 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.

Parasympathetic Output & Reflexes

• Reflexes controlled via the reticular formation:– Visual reflexes (pupil size)

• Passin’ thru– Sneeze reflex– Salivary glands stimulation

to salivate– Gag reflex– Cough reflex– Heart rate– Respiration– Digestion

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IV. Other brain functions• 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

AP1 Chapter 14 40A. S

peec

h- 2

maj

or a

reas

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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B. Right & Left Cerebral cortex

Rt. CerebralHemisphere

Lt. CerebralHemisphere

•Motor Output goes to the left side•Sensory input comes from the left side•Spatial perception, facial recognition, & musical ability

•Motor Output goes to the right side•Sensory input comes from the right side• mathematics & speech

Commissure: band of tracts that connect the 2 hemisphere for info sharing

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C. B

rain

wav

es &

sle

ep• 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

• 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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D. Memory: 3 types1. 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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D. Memory: Long termDeclarative

• Retention of facts• 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)

Procedural• Involves the development

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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D. M

emor

y: L

ong

term

• 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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D. Limbic System• Influences emotions, innate responses to

emotions, motivation, mood & sensations of pain & pleasure

• Associated with basic survival (reproduction, food H2O)

• 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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V. FX of Aging on the NS

• General decline in sensory & motor fxns • Short term memory is decreased• Thinking ability doesn’t D