Neuro Exam 2

SC tracts, sensory receptors, pain

sensory receptor

specialized nerve cell designed to respond to a specific sensory stimulus (touch, pressure, pain, temperature, light, sound, position in space)

3 Types of Sensory Receptors

1. exteroceptors

2. interoceptors

3. proprioceptors

Exteroceptors

sensory receptors that receive stimuli from the external world

• ex: visual, auditory, tactile, olfactory, and gustatory receptors

Interoceptors

sensory receptors that receive information from inside the body (viscera, hollow organs, glands, etc.)

What type of receptor would detect body sensations such as stomach pain, pinched spinal nerves, or processes within the deep layers of skin?

interoceptors

Proprioceptors

sensory receptors located in the muscles, tendons, and joint of the body and in the utricles, saccules, and semicircular canals of the inner ear; detect body position and movement

Developmental Classifications of Sensory Receptors

1. protopathic

2. epicritic

Protopathic Sensory Receptors

receptors that identify gross bodily sensations rather than specific regions of sensations

• cannot locate precise origin of pain

• detects crude touch and dull pain

Epicritic Sensory Receptors

receptors that detect sensation with precision, accuracy, and acuteness

• can locate the precise origin of pain

• detect discriminative touch, sharp pain, and exact joint position

• allows organism to detect imminent danger

What is the difference between protopathic and epicritic sensory receptors?

• protopathic detect crude touch and dull pain and are unable to determine the precise origin of pain

• epicritic detect discriminative touch, sharp pain, and exact joint positioning and can locate the precise origin of pain

T or F: Protopathic sensory receptors can locate the exact origin of pain

false

T or F: Epicritic sensory receptors can locate the exact origin of pain

true

Do protopathic or epicritic sensory receptors allow the organism to detect imminent danger?

epicritic

A child who does not receive adequate sensory stimulation from the environment, or the sensory information is dulled may show more self-stimulating behaviors.

What sensory system is dominant?

protopathic sensory system

A child who is hypersensitive to sensation from the environment may display tactile defensiveness (e.g. dislike the feeling of wet clothes) and/or gravitational insecurity (e.g. swinging is frightening).

What sensory system is dominant?

epicritic sensory system

Sensory Receptors Classified by Anatomical Position

1. cutaneous reeptors

2. proprioceptors

3. visceral receptors

4. special sense receptors (visual, auditory, olfactory, gustatory, equilibrium)

Cutaneous Receptors (function, location, type, occupational implications)

• function: respond to pain, temp, pressure, vibration, and discriminative touch

• location: superficial and deep layers of skin

• type: exteroceptors and interoceptors

• occupational implications: development of ulcers; burns; difficulty detecting trains, trucks, or earthquakes; distinguishing objects in one’s pocket

Proprioceptors (function, location, type, occupational implications)

• function: detect muscle length, tendon joint position, deep muscular and joint pain, tendonitis

• location: muscles, tendons, and joints

• type: proprioceptors

• occupational implications: fall risk, impaired muscle tone affecting AROM in the limbs and trunk

Visceral Receptors (function, location, type, occupational implications)

• function: respond to pressure and pain from internal organs

• location:

• type: interoceptors

• occupational implications: at risk for missed identification of serious injury or illness due to impaired pain detection in internal organs

Special Sense Receptor: Visual Receptors (function, types, occupational implications)

• function: respond to light information from external environment

• type: exteroceptors

• occupational implications: difficulty visually identifying all environmental stimuli (e.g. dangerous crossing the street)

Rods and Cones

visual receptors

Special Sense Receptor: Olfactory Receptors (function, location, type, occupational implication)

• function: respond to scent and odor stimuli from the ext. environment

• location: mucous lining of the nasal cavity

• type: exteroceptors

• occupational implications: difficulty smelling spoiled food, mold, burning, gas leaks, etc.

What are the olfactory receptors?

hair cells found in the mucous lining of the nasal cavity

Special Sense Receptor: Auditory Receptors (function, location, type, occupational implications)

• function: respond to sound stimuli from the external environment

• location: cochlea of ear

• type: exteroceptors

• occupational implications: difficulty participating in social communication; difficulty detecting alert signals (smoke alarm, carbon monoxide detector, horns, etc)

Special Sense Receptor: Gustatory Receptors (function, location, type, occupational implications)

• function: respond to taste stimuli from the external environment

• location: tongue

• type: exteroceptors

• occupational implications: difficulty detecting burnt or spoiled food

What are the gustatory receptors?

the taste buds

Special Sense Receptors: Equilibrium (function, location, type, occupational implications)

• function: provide info about the position of the head in space in relation to the body

• location: semicircular canals, utricles, and saccules of the inner ear

• type: proprioceptors

• occupational implications: impaired balance; fall risk; positional vertigo

Sensory Receptors Classified by Structural Design

1. mechanoreceptors

2. thermoreceptor

3. chemoreceptors

4. photoreceptors

Mechanoreceptors

sensory receptors that detect mechanical pressure and/or deformation

• detect deep touch, pressure, vibration, proprioception, equilibrium, and audition

• several types

Types of Mechanoreceptors and what they detect

1. Pacinian Corpuscles (rapid vibration)

2. Meissners Corpuscles (light touch and texture change)

3. Merkel Discs (sustained pressure)

4. Ruffini Endings (deep pressure, tension, deep skin layers)

5. Free Nerve Endings (touch, pressure, stretch)

6. Baroreceptors (stretch of blood vessles)

7. Ligamentous Receptors (ligament stretch)

Pacinian Corpuscles

mechanoreceptor that detects rapid vibration

Meissners Corpuscles

mechanoreceptors that detect light touch and texture change

Merkel Discs

mechanoreceptors that detect sustained pressure

Ruffini Endings

mechanoreceptors that detect deep pressure and tension from deep skin layers

Free Nerve Endings

mechanoreceptors that detect touch, pressure, and stretch

Barorecptors

mechanoreceptors that detect the stretch of blood vessels

Ligamentous Receptors

mechanoreceptors that detect ligament stretch and proprioception

Thermoreceptors

sensory receptors that are stimulated by changed in temp

While thermoreceptors are found throughout the body, where are the highest density of cold receptors found?

facial skin, tongue, bladder, and cornea

What are the special pain receptors that detect change in harmful temps called?

nociceptors

Chemoreceptors

sensory receptors that detect changes in chemical stimuli from the environment

• 2 types: direct and distance

Direct Chemoreceptors

respond to immediate contact

• ex: taste buds are stimulated when they make contact with food

Distance Chemoreceptors

repond to gaseous molecules that emerge from a distant odorant

• ex: olfactory receptors respond to the gaseous molecules (scent of cookies) given off by the distant odorant (cookies)

Two Categories of Chemoreceptors

1. direct

2. distance

Photoreceptors

sensory receptors located in the retina that detect light from the environment

• two forms: rods and cones

Rods

visual receptors / photoreceptors that are responsible for night vision and black-and-white vision

• located in the retina periphery

Where are the rods located?

retina periphery

Where are the cones located?

fovea (central region of the eye)

Cones

visual receptors / photoreceptors that work in daytime lighting and are responsible for color vision

Large Receptor Fields (function, location, cortical representation)

• function: gross discrimination of sensation

• location: body regions with less discrimination (legs, abdomen, arms, back)

• representation: small

Small Receptor Fields (function, location, cortical representation)

• function: fine discrimination of sensation

• location: body regions with greatest sensitivity (lips, hands, face, soles of feet)

• representation: large

What areas of the body have small receptor fields?

lips, hands, face, soles of feet

What areas of the body have large receptor fields?

legs, abdomen, arms, back

T or F: Both large and small receptor fields are represented on both right and left sides of the brain

true

How does our brain allocate sensory and motor function to the various aspects of the body?

Sensory Homunculus and Motor Homunculus

T or F: Small receptors fields have large cortical representaiton in the brain

true

T or F: Large receptor fields have large cortical representation in the brain

false

Motor Cortex

variety of areas that control motor movement, including the primary motor cortex which holds the motor homunculus

Association Cortex

area that includes higher order functions that contribute to motor planning, spatial awareness, planning responses, etc.

How do the basal ganglia and cerebellum help mediate movement?

they do not directly communicate with the cerebrum—instead the thalamus acts as a relay station between the basal ganglia/cerebellum and the cerebral cortex

Describe the Organization of Motor Systems

Four Levels:

1. Motor Cortex: controls motor movement and hold the motor homunculus (motor map of the body)

2. Association Cortex: includes higher-order functions that contribute to motor planning, spacial awareness, planning responses, etc.

3. Spinal Cord: receives info from the brainstem

4. Brainstem: assists with coordination of movement to be sent to the SC

UMN

carry info from the cortex to cranial nerve nuclei in the brainstem or to cell bodies in the ventral horn

UMN are part of the (CNS/PNS)

CNS

UMN Lesions

Below Level of Lesion:

• increased muscle tone

• hyperreflexia (exaggerated DTRs)

• clonus

• Babinski Sign

At Level of Lesion:

• flaccidity

LMN

carries info from cell bodies in the anterior horn to the skeletal muscles in the periphery

the LMNs are considered part of the (CNS/PNS)

PNS

LMN Lesions

• paralysis or paresis of movement

• hypotonia

• hyporeflexia (decreased) or areflexia (absent)

• fibrillations and/or fasciculations

• muscle atrophy

Spinal Cord Tracts

bundle of nerve fibers within the spinal cord that carry specific sensory or motor info either up towards the brain (ascending tracts) or down from the brain to the body (descending tracts)

What is termed the “highway” for neural signals to travel along the SC?

SC tracts

Where are spinal cord tracts located?

white matter

How are SC tracts named?

place of origin and destination

Ascending Spinal Nerves

carry sensory information from the periphery (sensory receptor) to the SC

How do ascending spinal nerves enter the SC? What do they do once they enter?

enter the SC through the dorsal root/rootlets (PNS) > enter the dorsal horn and synapse with an interneuron (CNS) > interneuron synapses with an ascending SC tract (CNS)

Ascending Spinal Cord Tracts

carry sensory information up the SC, to the brainstem, thalamus, and cortex

• (some carry infor from brainstem to cerebellum)

T or F: While most ascending SC tracts carry sensory info to the brainstem, thalamus, and cortex, some carry info from the brainstem to the cerebellum

true

Dorsal Columns Function

carries conscious info regarding fine touch, vibration, and proprioception to the cortex

Dorsal Column Decussation

caudal medulla level

Lesions to the dorsal column below the caudal medulla would result in…

ipsilateral loss of fine touch, vibration, and proprioception

Lesions to the dorsal column about the caudal medulla would result in…

contralateral loss of fine touch, vibration, and proprioception

The client has difficulty distinguishing between coins when reaching into his pocket, has developed a umber of pressure sores, comes dangerously close to fragile items in an antique store, and is unable to detect when his car has started.

What tract is likely to be lesioned?

Dorsal Columns

Lateral Spinothalamic Tract Function

carries conscious sensory info to the cortex regarding pain and temp

Lateral Spinothalamic Tract Decussation

SC Level (as soon as the spinal nerve enters the cord and synapses on tract)

Your client often burns himself when showering and is unable to detect the development of pressure sores, a foot that fell off the footplate, or his hand caught in wheelchair spokes.

What tract is likely damaged?

lateral spinothalamic

The Lateral Spinothalamic Tract is a (ascending/descending) tract

ascending

The Dorsal Columns is a (ascending/descending) tract

ascending

Name the Ascending Sensory SC Tracts

1. Dorsal Columns

2. Lateral Spinothalamic

3. Anterior Spinothalamic

4. Posterior Spinocerebellar

5. Anterior Spinocerebellar

6. Cuneocerebellar

7. Rostral SPinocerebellar

Name the Descending Motor SC Tracts

1. Lateral Corticospinal Tract

2. Anterior Corticospinal Tract

3. Corticobulbar Tract

4. Rubospinal Tract

5. Medial Reticulospinal Tract

6. Lateral Reticulospinal Tract

7. Vestibulospinal Tract

What SC tracts collect proprioception from the LE?

posterior spinocerebellar and anterior spinocerebellar

What SC tracts collect proprioception info from the UE?

cuneocerebellar and rostral cerebellar

The brain has bilateral representation of unconscious proprioception. What does this mean?

• the posterior and anterior spinocerebellar tracts both detect proprioception info from the LE

• the cuneocerebllar and rostral cerebellar tracts both detect proprioception info from the UE

• If one tract of each set is lost, the other will still send proprioceptive info the cerebellum. An individual will not lose unconscious proprioceptive info from UE or LE unless both tracts in the set are lost

T or F: While most descending SC tracts carry motor info from the cortex, through the internal capsule, thalamus, and brainstem to the SC, some motor SC tracts actually originate in the cerebellum or brainstem

true

When descending SC tracts are ready to exit the cord, they synapse with…

an interneuron in the ventral horn which then synapses on a motor neuron in the ventral horn which then synapses on a descending motor spinal nerve and exits the SC through the ventral root

Pyramidal Tracts

descending motor SC tracts that (1) originate in the cerebral cortex, (2) travel through the pyramids of the medulla oblongata, and (3) control voluntary muscle movement in the face and body

List the Pyramidal Tracts

1. Lateral Corticospinal

2. Anterior Corticospinal

3. Corticobulbar

Extrapyramidal Tracts

descending motor tracts that (1) originate in the brainstem, (2) do not travel through the pyramids, and (3) control involuntary muscle movement (balance, posture, muscle tone)

(Pyramidal/Extrapyramidal) tracts originate in the brainstem

Extrapyramidal

(Pyramidal/Extrapyramidal) tracts originate in the cortex

pyramidal

(Pyramidal/Extrapyramidal) tracts control voluntary muscle movement of the face and body.

pyramidal

(Pyramidal/Extrapyramidal) tracts control involuntary muscle movement (balance, posture, tone)

extrapyramidal

(Pyramidal/Extrapyramidal) tracts include the basal ganglia and cerebellum

extrapyramidal