Neural integration the sensory pathways chapter 15
This presentation is the property of its rightful owner.
Sponsored Links
1 / 67

Neural Integration The sensory pathways Chapter 15 PowerPoint PPT Presentation


  • 195 Views
  • Uploaded on
  • Presentation posted in: General

Neural Integration The sensory pathways Chapter 15. Afferent Division of the Nervous System. Receptors Sensory neurons Sensory pathways. Afferent Division – location in CNS. Somatic Sensory info Sensory cortex of cerebrum Cerebellum Visceral Sensory info Reflex centers in brainstem

Download Presentation

Neural Integration The sensory pathways Chapter 15

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Neural integration the sensory pathways chapter 15

Neural IntegrationThe sensory pathwaysChapter 15


Afferent division of the nervous system

Afferent Division of the Nervous System

  • Receptors

  • Sensory neurons

  • Sensory pathways


Afferent division location in cns

Afferent Division – location in CNS

  • Somatic Sensory info

    • Sensory cortex of cerebrum

    • Cerebellum

  • Visceral Sensory info

    • Reflex centers in brainstem

    • Reflex centers in diencephalon


The somatic sensory system

The somatic sensory system

  • Sensory stimuli that reach the conscious level of perception

  • Specialized cells that monitor specific conditions in the body or external environment

  • General Senses:

    • Temp, pain, touch, pressure, vibration, proprioception

    • Simple receptors located anywhere on body

  • Special Senses:

    • Are located in sense organs such as the eye or ear

    • Olfaction, vision, gustation, hearing, equilibrium

    • Complex receptors located in specialized sense organs


General properties sensory division

General Properties: Sensory Division

Table 10-1 (1 of 2)


From sensation to perception

From Sensation to Perception


Sensory pathways from sensation to perception

Sensory Pathways – from sensation to perception

  • Stimulus as physical energy  sensory receptor

    • Receptor acts as a transducer

  • Intracellular signal  usually change in membrane potential

  • Stimulus  threshold  action potential to CNS

  • Integration in CNS  cerebral cortex or acted on subconsciously


Sensory receptors

Sensory Receptors

  • Transduction – conversion of environmental stimulus into action potential by sensory receptor

  • Receptors specific for particular type of stimulus

  • Specificity is due to structure of receptor


From sensation to perception1

From Sensation to Perception

  • A stimulus is a change in the environment that is detected by a receptor

  • Sensation: the awareness of changes in the internal and external environment

  • Perception: the conscious interpretation of those stimuli


Classification by location

Classification by Location

  • Exteroceptors

    • Respond to stimuli arising outside the body

    • Receptors in the skin for touch, pressure, pain, and temperature

    • Most special sense organs

  • Interoceptors (visceroceptors)

    • Respond to stimuli arising in internal viscera and blood vessels

    • Sensitive to chemical changes, tissue stretch, and temperature changes


Classification by location1

Classification by Location

  • Proprioceptors

    • Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles

    • Inform the brain of one’s movements


Four types of general sensory receptors

Four types of General Sensory Receptors

  • Pain: nociceptor

  • Temperature: thermoreceptor

  • Physical: mechanoreceptor

  • Chemicals: chemoreceptors

  • All can be found in both somatic (exteroceptors) and visceral (interoceptors) locations except:

    • Proprioceptors (a mechanoreceptor) are somatic only

      • report the positions of skeletal muscles and joints


Pain receptors nociceptors

Pain Receptors: Nociceptors

  • (noci = harm) sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)

  • Free nerve ending

  • Mode of Action:

    • Injured cells release arachidonic acid

    • Arachidonic acid is converted into prostaglandins by the interstitial enzyme cyclo-oxygenase

    • Prostaglandins activate nociceptors

      • Many pain medications like aspirin function to inhibit cyclo-oxygenase

      • Pain levels are modulated by endorphins which inhibit CNS function


Thermoreceptors

Thermoreceptors

  • Detect temperature

  • Found in skin, skeletal muscle, liver, and hypothalamus

  • Consist of free nerve endings

  • Phasic receptors that adapt easily

    • Cold response are more superficial and receptors that respond to heat – deeper

    • Temperature out of the range of the thermoreceptors will activate nociceptors


Mechanoreceptors

Mechanoreceptors

  • Detect membrane distortion

    • Three receptor types:

      • Tactile Receptors

      • Proprioceptors

      • Baroreceptors


Mechanoreceptors tactile receptors

Mechanoreceptors - Tactile Receptors

  • Detect touch, pressure and vibration on skin

  • Detect hair movement

  • Detect fine touch

  • Detect deep pressure

  • respond to itch (respond among other to histamine) and light touch (detect changes in shape like bending)


Mechanoreceptors proprioceptors

Mechanoreceptors - Proprioceptors

  • Detect positions of joints and muscles

    • Muscle spindles

      • Modified skeletal muscle cell

      • Monitor skeletal muscle length

    • Golgi tendon organs

      • Dendrites around collagen fibers at the muscle-tendon junction

      • Monitor skeletal muscle tension

    • Joint capsule receptors

      • -Monitor pressure, tension and movement in the joint


Mechanoreceptors baroreceptors

Mechanoreceptors - Baroreceptors

  • Detect pressure changes

  • Found in elastic tissue of blood vessels and organs of digestive, reproductive and urinary tracts


Chemoreceptors

Chemoreceptors

  • Detect change in concentration of specific chemicals or compounds

    • pH, CO2, sodium etc.

    • Found in respiratory centers of the brain and in large arteries


Sensory receptors1

Sensory Receptors

Table 10-2


Processing of the sensory information

Processing of the sensory information

  • Levels of neural integration in sensory systems:

    • Receptor level — the sensor receptors

    • Circuit level — ascending pathways in the CNS

    • Perceptual level — neuronal circuits in the cerebral cortex


Processing at the receptor level

Processing at the Receptor Level

Perceptual level(processing in

cortical sensory centers)

3

Motor

cortex

Somatosensory

cortex

Thalamus

Reticular

formation

Cerebellum

Pons

Medulla

Circuit level

(processing in

ascending pathways)

2

Spinal

cord

Free nerve

endings (pain,

cold, warmth)

Muscle

spindle

Receptor level

(sensory reception

and transmission

to CNS)

1

Joint

kinesthetic

receptor

Figure 13.2


Processing at the receptor level1

Processing at the Receptor Level

  • The receptor must have specificity for the stimulus energy (as previously discussed)

  • The receptor’s receptive field must be stimulated

  • The stimulus need to be converted to a nerve impulse

  • Receptors have different levels of adaptation

  • Information is encoded in the frequency of the stimuli – the greater the frequency, the stronger is the stimulus.


The stimulation of the receptive field affects the discharge of the sensory neurons

The stimulation of the receptive field affects the discharge of the sensory neurons

  • The receptive field is the a specific physical area that, when stimulated, affect the discharge of the stimulus.

  • Most receptive fields activation will result in message sending – excitatory receptive field

  • Sensory receptors in the CNS can have inhibitory receptive field (example: vision fields to determine borders).

  • Sensory neurons of neighboring receptive field may exhibit

    • Convergence many sub-threshold stimuli to sum in the postsynaptic neuron

    • Overlapping with another receptor’s receptive field – sending 2 sensations from the same area (pressure and pain)

  • The smaller the receptive field the greater the ability of the brain to localize the site


Sensory neurons two point discrimination

Sensory Neurons: Two-Point Discrimination

(a)

Compass with pointsseparated by 20 mm

  • convergenceTwo-point discrimination

Skin surface

Primarysensoryneurons

Secondarysensoryneurons

One signal goes to the brain.

Figure 10-3a


Sensory neurons two point discrimination overlapping

(b)

Compass with pointsseparated by 20 mm

Skin surface

Primarysensoryneurons

Secondarysensoryneurons

Two signals go to the brain.

Sensory Neurons: Two-Point Discrimination - overlapping

Figure 10-3b


Receptive fields of sensory neurons overlapping

Receptive Fields of Sensory Neurons - overlapping

Primary sensoryneurons

The primary sensory neuronsconverge on one secondarysensory neuron.

Information from thesecondary receptivefield goes to the brain.

Secondarysensoryneuron

The receptive fields of three primary sensory neuronsoverlap to form one large secondary receptive field.

SECTION THROUGH SPINAL CORD

Figure 10-2


Properties of stimulus location

Properties of Stimulus: Location

  • Lateral inhibition enhances contrast and makes a stimulus easier to perceive

Stimulus

Stimulus

Pin

Skin

A

B

C

Frequency of action potentials

Tonic level

Primary neuronresponse is proportionalto stimulus strength.

Primarysensoryneurons

Pathway closest tothe stimulus inhibitsneighbors.

Secondaryneurons

A

B

C

Frequency of action potentials

Inhibition of lateralneurons enhancesperception of stimulus.

Tonic level

Tertiaryneurons

A

B

C

Figure 10-6


Neural integration the sensory pathways chapter 15

Transduction allows sensory receptors to respond to stimuli – converting sensation into a nerve impulse

  • Sensory transduction – the process that enables a sensory receptor to respond to a stimulus.

  • The sensory transduction induces a receptor potential in the peripheral terminal of the sensory neuron

  • A receptor potential is a depolarization event that if brings the membrane to a threshold, will become a nerve impulse (AP)

  • The conversion from receptor potential to AP happens in the trigger zonethat can be in the first node of Ranvier.

  • In some cases, the peripheral terminal is a separate sensory cell (ex. Photo receptors). In this case there is an involvement of a synapse and NT


Receptors adaptation

Receptors adaptation

  • The duration of a stimulus is coded by duration of action potentials.

  • A longer stimulus generates longer series of APs.

  • If a stimulus persists, some receptors adapt or stop responding

  • There are 2 classes of receptors according to how they adapt:

    • Tonic receptors – slowly adapting – they fire rapidly when first activated, than they slow and maintain firing as long as the stimulus is present (baroreceptors, proprioceptors)

    • Phasic receptors – rapidly adapting receptors – rapidly firing when first activated but stop firing if the strength of stimulus remains constant

      • This type of reaction allows the body to ignore information thatwas evaluated and found not to be a threat to homeostasis (smell)


Tonic receptors

Tonic Receptors

  • Always active

  • Signal at different rate when stimulated

  • Monitor background levels

Figure 10-8a


Phasic receptors

Phasic Receptors

  • Activated by stimulus

  • Become active for a short time whenever a change occurs

  • Monitor intensity and rate of change of stimulus

Figure 10-8b


Receptors adaptation1

Receptors adaptation

  • The mechanisms for receptors’ adaptation depends on the receptors:

    • Potassium channels in the receptor’s membrane open causing the membrane repolarization

    • Sodium channels inactivated stopping depolarization

    • Accessory structure may contribute to decrease sensitivity (muscle in the ear contract and limit the movement of the auditory oscicles)


Processing at the circuit level

Processing at the circuit Level

Perceptual level(processing in

cortical sensory centers)

3

Motor

cortex

Somatosensory

cortex

Thalamus

Reticular

formation

Cerebellum

Pons

Medulla

Circuit level

(processing in

ascending pathways)

2

Spinal

cord

Free nerve

endings (pain,

cold, warmth)

Muscle

spindle

Receptor level

(sensory reception

and transmission

to CNS)

1

Joint

kinesthetic

receptor

Figure 13.2


Processing at the circuit level1

Processing at the circuit Level

  • A sensory pathway is a set of neurons arranged in series.

  • The circuit level role is to deliver the impulses to the appropriate region in the cerebral cortex.

  • The ascending tract typically consists of 3 neurons

  • First order neurons

    • cell bodies in a ganglion (dorsal or cranial)

    • Impulses from skin and proprioceptors to spinal cord or brain stem to a 2nd order neuron

  • Second order neuron

    • In the dorsal horn of the spinal cord or in the medulary nuclei

    • Transmit impulses to thalamus or cerebellum

  • Third order neurons

    • Cell bodies in the thalamus (no 3rd-order neurons in the cerebellum)

    • Transmit signals to the somatosensory cortex of the cerebrum


Pathways for somatic perception

Pathways for somatic perception

  • Receptors for the somatic sensations are found both in the skin and viscera

  • Receptor activation triggers AP in the 1st order neuron

  • In the spinal cord, sensory neurons synapse with interneurons – 2nd order neurons

  • All 2nd order neurons cross overat some point (sensations are being integrated in the opposite side)

  • The synapse between the 2nd and the 3rd happens in the thalamus

  • The axons of the 3rd order neurons project to the appropriate somatosensory area in the cerebral cortex


Processing at the circuit level2

Processing at the circuit Level

  • Impulses ascend in :

    • Non specific pathway that in general transmit pain, temperature and touch

      • Give branches to reticular formation and thalamus on the way up

      • Sends general information that is also involved in emotional aspects of perception

  • Specific ascending pathways involve in more precise aspect of sensation


Thalamic function

Thalamic Function

  • The thalamus is the “gateway to the cerebral cortex”

  • Major relay station for mostsensory impulses that arrive to the primary sensory areas in the cerebral cortex:

    • taste, smell, hearing, equilibrium, vision, touch, pain, pressure, temperature

  • Contributes to motor functions by transmitting information from the cerebellum and basal ganglia to the cerebral primary motor area

  • Connects areas of the cerebrum

  • Impulses of similar function are sorted out, edited, and relayed as a group


3 major somatosensory pathways 1 spinothalamic pathway

3 major somatosensory pathways –1) spinothalamic pathway

  • Conscious sensation of poorly localized sensations

    • Anterior spinothalamic tracts – crude touch and pressure

    • Lateral spinothalamic tracts – pain and temperature

  • 1st order neurons synapse with the 2nd in the posterior gray horn at the level of entrance

  • The 2nd cross before ascending to the thalamus

  • 3rd order synapse at the level of the primary somatosensory cortex


Neural integration the sensory pathways chapter 15

http://webanatomy.net/anatomy/spinothalamic.jpg


3 major somatosensory pathways 2 posterior column pathway

3 major somatosensory pathways - 2) Posterior column pathway

  • Sensation of precise touch, vibration and proprioception

  • Includes

    • Left and right fasciculus gracilis (inferior part of the body)

    • Left and right fasciculus cuneatus (superior part of the body)

  • First order neurons enter the CNS at the dorsal roots and the sensory roots of cranial nerves.

  • Synapse with 2nd order in the medulla

  • 2nd order neurons cross over in the brain stem

  • 3rd order in the thalamus where the stimuli are sorted by the nature of stimulus and the region of body involved


  • Neural integration the sensory pathways chapter 15

    http://webanatomy.net/anatomy/gracilis_cuneatus.jpg


    3 major somatosensory pathways 3 the spinocerebellar pathway

    3 major somatosensory pathways – 3) The spinocerebellar pathway

    • Information about muscle, tendon and joint position from the spine to the cerebellum

    • This information is subconscious

    • 1st order neurons synapse in the dorsal horn

    • 2nd order neurons ascend via anterior and posterior spinocerebellar tracts to the cerebellar cortex

    • Used to coordinate movements

    • In this pathway there is no 3rd order neuron


    Neural integration the sensory pathways chapter 15

    http://webanatomy.net/anatomy/spinocerebellar.jpg


    Somatic senses pathways

    Somatic Senses Pathways

    Sensations are perceivedin the primary somaticsensory cortex.

    4

    4

    Sensory pathwayssynapse in the thalamus.

    3

    3

    THALAMUS

    MEDULLA

    2

    Fine touch, vibration,and proprioceptionpathways cross themidline in the medulla.

    2

    Fine touch,proprioception,vibration

    KEY

    Pain, temperature, andcoarse touch cross themidline in the spinal cord.

    1

    1

    Nociception,temperature,coarse touch

    Primary sensory neuron

    Secondary sensory neuron

    Tertiary neuron

    Figure 10-9, steps 1–4

    SPINAL CORD


    Processing at the perceptual level

    Processing at the Perceptual Level

    Perceptual level(processing in

    cortical sensory centers)

    3

    Motor

    cortex

    Somatosensory

    cortex

    Thalamus

    Reticular

    formation

    Cerebellum

    Pons

    Medulla

    Circuit level

    (processing in

    ascending pathways)

    2

    Spinal

    cord

    Free nerve

    endings (pain,

    cold, warmth)

    Muscle

    spindle

    Receptor level

    (sensory reception

    and transmission

    to CNS)

    1

    Joint

    kinesthetic

    receptor

    Figure 13.2


    Processing at the perceptual level1

    Processing at the Perceptual Level

    • Interpretation of sensory input occurs in the cerebral cortex

    • The ability to identify the sensation depends on the specific location of the target neurons in the sensory cortex not on the nature of the message (all messages are action potentials)


    The cns integrate sensory information

    The CNS integrate sensory information

    • Most of the somatic sensory information enters the spinal cord and travels via ascending pathways to the brain

    • Some information goes directly to the brain through the cranial nerves

    • Autonomic sensory information does not arrive conscious perception


    Main aspects of sensory perception

    Main Aspects of Sensory Perception

    • Perceptual detection – detecting that a stimulus has occurred and requires summation

    • Magnitude estimation – the ability to detect how intense the stimulus is

    • Spatial discrimination – identifying the site or pattern of the stimulus

    • Feature abstraction – used to identify a substance that has specific texture or shape

    • Quality discrimination – the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)

    • Pattern recognition – ability to recognize patterns in stimuli (e.g., melody, familiar face)


    Somatosensation perception

    Somatosensationperception

    • The specific sensation depends on the 2nd and 3rdneurons

    • The ability to localize the specific location of a stimulus depends on the stimulation of a specific area in the primary somatosensory cortex

    • A sensory “homunculus” (little human) is a functional map of the primary somatosensory cortex


    Somatosensory association cortex

    Somatosensory Association Cortex

    • Located posterior to the primary somatosensory cortex and has connection with it

    • Integrates sensory information like temperature and pressure coming from the primary somatosensory cortex.

    • Forms understanding of the stimulus like size, texture, and relationship of parts

    • Ex.: putting the hand in the pocket and feeling something. The center integrate previous information to identify objects without seeing them


    The main sensory areas in the cerebral cortex

    The main Sensory Areas in the cerebral cortex

    Figure 12.8a


    Properties of the sensory system summary

    Properties of the sensory system - summary

    • Stimulus – works on a receptor

      • The receptor is a transducer that converts the stimulus into a change of membrane potential

    • The message from the receptor will be sent in the form of action potential to the CNS

    • Stimuli that will reach the cerebral cortex will be come conscious

    • Somatosensory information ascends the spinal column along several pathways, which synapse at the midbrain &/or thalamus before reaching the cortex

    • Sensory processes have different sub-modalities of somatosensory information

    • Later stages of processing combine information across the sub-modalities, & with information from other senses


    Pain pathways

    Pain pathways

    • Pain is a protective mechanism

    • Pain is a subjective perception

    • It is individual and can vary depending on emotional state

    • Types of pain sensations:

      • Fast pain – sharp and localized – in superficial parts of the body (cut, burn)

        • Rapidly transferred to CNS by small myelinatedfibers (within 0.1 seconds after stimulus applied)

    • Slow pain – more diffused pain (associated with tissue destruction)

      • Carried by small unmyelinated fibers

  • Often fast pain will follow a slow one


  • Pain pathways1

    Pain pathways

    • Pain from the body – via spinal cord

    • Pain from face – via trigeminal (V) that enters the pons, descend to the medulla where they cross over and ascend to the thalamus

    • The ascending pathway sends branches not only to thalamus and the cerebral cortex but also to the limbic system (emotions) and hypothalamus (autonomic reaction)

    • The result is that pain may be accompanied by emotional distress and autonomic reactions such as nausea, vomiting or sweating


    Pain perception

    Pain perception

    • Pain can be felt in skeletal muscle when anaerobic metabolism

    • In cardiac muscle, pain is a result of ischemia (lack of oxygen due to reduced blood flow) during myocardial infraction (heart attack)

    • Visceral pain is poorly localized and called referred pain


    Pain perception the gate control theory

    Pain perception – the gate control theory

    • Pain perception is subjected to modulation that can happen in several levels of the nervous system

    • Pain can be magnified by past experiences

    • Pain can be suppressed when in emergencies when surviving depends on ignoring the injury

      • http://www.youtube.com/watch?v=IlCstuhpteo

        • (minute 13.41)


    The gate control theory of pain

    The Gate-Control Theory of Pain

    • Pain can be suppressed in the dorsal horn level.

    • Normally, tonically active inhibitory interneuron inhibit ascending pathways for pain

    Figure 10-12a


    The gate control theory of pain modulation

    The Gate Control Theory of Pain Modulation

    • Fibers from nociceptors synapse on the inhibition interneuron

    • When activated, the fibers send message to block the interneurons and pain travels to the brain

    Figure 10-12b


    The gate control theory of pain modulation1

    The Gate Control Theory of Pain Modulation

    • In the gate control theory of pain modulation fibers carrying sensory information about mechanical stimuli help block pain transmission

    • Those fibers synapse on the interneuron and increase its inhibitory activity

    • If both pain stimulus and nonpainful stimulus arrive at the same time, there will be partial inhibition of pain

    • The sensation of pain will be perceived by the brain as lower

    • Explains why rubbing a bumped elbow lessens the pain feeling

    Figure 10-12c


    Visceral sensory pain pathways

    Visceral sensory pain pathways

    • Collected by interoceptors within the closed ventral body cavities

    • The interoceptors include nociceptors, thermoreceptors, tactile receptors, baroreceptors and chemoreceptors

    • The axons of the 1st order neuron usually travel with the autonomic motor fibers innervating the same visceral structures

    • 2nd order neurons within the spinal cord use the spinothalamic pathway and arrive to the medulla oblongata

    • Cranial nerves V, VII, IX and X carry visceral sensory information also to the medulla

      • (all parasympathetic will be discussed with the ANS)


    Referred pain

    Referred Pain

    Skin(usual stimulus)

    Primary sensoryneurons

    Kidney(uncommon stimulus)

    Secondarysensoryneuron

    Ascending sensorypath to somatosensorycortex of brain

    (b)

    Figure 10-13b


    Sensory pathways

    Sensory Pathways

    Primary somaticsensory cortex

    Gustatory cortex

    Olfactory cortex

    Olfactory bulb

    Auditorycortex

    Visualcortex

    1

    Olfactory pathways fromthe nose project throughthe olfactory bulb to theolfactory cortex.

    Eye

    2

    Cerebellum

    Most sensory pathways projectto the thalamus. The thalamusmodifies and relays informationto cortical centers.

    2

    1

    Thalamus

    Nose

    Sound

    Brainstem

    Equilibrium

    3

    3

    Equilibrium pathways projectprimarily to the cerebellum.

    Tongue

    Somaticsenses

    Figure 10-4


  • Login