classification of fibers

The _____, described by Erlanger and Gasser, applies to both sensory (afferent) and motor (efferent) nerve fibers and uses a lettered nomenclature of A, B and C.

first system

The first system, described by _____, applies to both sensory (afferent) and motor (efferent) nerve fibers and uses a lettered nomenclature of A, B and C.

Erlanger and Gasser

The first system, described by Erlanger and Gasser, applies to both sensory (afferent) and motor (efferent) nerve fibers and uses a lettered nomenclature of ______

A, B and C.

The _____, described by Lloyd and Hunt, applies only to sensory nerve fibers and uses a Roman numeral nomenclature of I, II, III, and IV.

second system

The second system, described by _____, applies only to sensory nerve fibers and uses a Roman numeral nomenclature of I, II, III, and IV.

Lloyd and Hunt

The second system, described by Lloyd and Hunt, applies only to sensory nerve fibers and uses a Roman numeral nomenclature of _____

I, II, III, and IV.

enumerate the classification of fibers

TYPE A

TYPE B

TYPE C

- Typical large and medium sized, myelinated fibers

- High velocity

TYPE A

a classification of fibers typical large and medium sized, myelinated fibers

TYPE A

a classification of fiber in axonal diameter that has high velocity

TYPE A

Intermediate, myelinated fibers

TYPE B

- Small, unmyelinated fibers

- Conduct impulses at a low velocity

- 1⁄2 of sensory fibers in most peripheral nerves

TYPE C

Small, unmyelinated fibers

TYPE C

Conduct impulses at a low velocity

TYPE C

1⁄2 of sensory fibers in most peripheral nerves

TYPE C

Primary muscle spindle afferents (Extrafusal fibers), motor fibers to motor neurons, Proprioception

A-alpha (a)

Cutaneous touch and pressure afferents

A-beta (B)

Motor fibers to muscle spindles (Intrafusal fibers)

A-gamma (y)

Thinly myelinated, cutaneous temperature (cold)

A-delta (d)

Preganglionic autonomic

B

Unmyelinated cutaneous pain afferents (slow), and temperature

Postganglionic sympathetic

C

Fibers from the annulospiral endings of muscle spindles

Group Ia (A-alpha)

Fibers from the Golgi tendon organs

Group Ib (A-alpha)

fibers from most discrete cutaneous tactile receptors and from the flower-spray endings of the muscle spindles

Group II (A-beta and A-gamma)

fibers carrying temperature, crude touch, and pricking pain sensations

Group III (A-delta)

unmyelinated fibers carrying pain, itch, temperature, and crude touch sensations

Group IV (c)

what are the transmission of signals of different intensity?

spatial summation

temporal summation

Increase in signal strength is transmitted by using progressively greater number of fibers

SPATIAL SUMMATION

Increase in signal strength by increasing the frequency of nerve impulses in each fiber

TEMPORAL SUMMATION

what are the tactile sensations?

touch sensation

pressure sensation

vibration sensation

• Touch, pressure, vibration, tickle

• All detected by the same receptors but are separate sensations

• 3 differences:

a. Touch sensation generally results from stimulation of tactile receptors from skin beneath

b. Pressure sensation results from deformation of deeper tissues

c. Vibration sensation results from rapidly repetitive sensory signals

Tactile Sensations

Touch, pressure, vibration, tickle

Tactile Sensations

All detected by the same receptors but are separate sensations

Tactile Sensations

generally results from stimulation of tactile receptors from skin beneath

Touch sensation

results from deformation of deeper tissues

b. Pressure sensation

results from rapidly repetitive sensory signals

c. Vibration sensation

what are the tactile/cutaneous receptors?

free nerve endings

meissner’s corpuscle

merkel’s disc

ruffini’s endings

pacinian corpuscle

hair end organ

krause’s end bulbs

• Simplest and most common

• Found everywhere in the skin

• Abundant in epithelial and connective tissues

• Perception of pain, temperature, touch, pressure, tickle, and itch sensations

Free Nerve Endings

• Elongated, encapsulated nerve endings of a large myelinated sensory nerve fiber (TYPE A β)

• Present in non-hairy parts of the skin, located in the dermis

• Abundant in fingertips and toes, tongue and lips

• Sensitive to movements of objects over the surface of the skin and discriminative touch

Meissner’s Corpuscle

• Expanded tip tactile receptor

• Hairy parts of the skin, located at the basal epidermis

• Sensitive to low-intensity touch, as well as to the velocity of touch, and respond to constant indentation of the skin superficially (pressure).

• Responsible for giving steady state signals to determine continuous touch of objects against the skin

Merkel’s Disc

• Located on deeper layers of the skin (dermis)

• Multibranched, encapsulated endings

• Adapt very slowly

• Important for signaling continuum state of deformation of the tissues

• Perception of touch and pressure. They also detect warmth.

• Found in joint capsules – signal degree of joint rotation, assist with position sense

Ruffini’s Endings

• Immediately beneath the skin and deep in fascial tissues of the body (subcutaneous tissue and below)

• Rapid local compression of tissue

• Important in detecting tissue vibration or other rapid change in mechanical state of the tissues, and also deep pressure

• Help relay proprioceptive information about joint positions

Pacinian Corpuscle

• Hair and its basal nerve

• Slight movement of any hair on the body that stimulates a nerve fiber entwinning its base

• These receptors are sensitive to mechanical movement and touch

Hair End Organ

• They are located in the dermis and conjunctiva of the eye.

• They are believed to be low-threshold mechanical receptors that may play a contributing role in the perception of touch and pressure

• May also contribute to detection of cold

Krause’s End-bulbs

Simplest and most common

Free Nerve Endings

Found everywhere in the skin

Free Nerve Endings

Abundant in epithelial and connective tissues

Free Nerve Endings

Perception of pain, temperature, touch, pressure, tickle, and itch sensations

Free Nerve Endings

Elongated, encapsulated nerve endings of a large myelinated sensory nerve fiber (TYPE A β

Meissner’s Corpuscle

Present in non-hairy parts of the skin, located in the dermis

Meissner’s Corpuscle

Abundant in fingertips and toes, tongue and lips

Meissner’s Corpuscle

Sensitive to movements of objects over the surface of the skin and discriminative touch

Meissner’s Corpuscle

Expanded tip tactile receptor

Merkel’s Disc

Hairy parts of the skin, located at the basal epidermis

Merkel’s Disc

Sensitive to low-intensity touch, as well as to the velocity of touch, and respond to constant indentation of the skin superficially (pressure).

Merkel’s Disc

Responsible for giving steady state signals to determine continuous touch of objects against the skin

Merkel’s Disc

Located on deeper layers of the skin (dermis)

Ruffini’s Endings

Multibranched, encapsulated endings

Ruffini’s Endings

Adapt very slowly

Ruffini’s Endings

Important for signaling continuum state of deformation of the tissues

Ruffini’s Endings

Perception of touch and pressure. They also detect warmth.

Ruffini’s Endings

Found in joint capsules – signal degree of joint rotation, assist with position sense

Ruffini’s Endings

Immediately beneath the skin and deep in fascial tissues of the body (subcutaneous tissue and below)

Pacinian Corpuscle

Rapid local compression of tissue

Pacinian Corpuscle

Important in detecting tissue vibration or other rapid change in mechanical state of the tissues, and also deep pressure

Pacinian Corpuscle

Help relay proprioceptive information about joint positions

Pacinian Corpuscle

Hair and its basal nerve

Hair End Organ

Slight movement of any hair on the body that stimulates a nerve fiber entwinning its base

Hair End Organ

These receptors are sensitive to mechanical movement and touch

Hair End Organ

They are located in the dermis and conjunctiva of the eye.

Krause’s End-bulbs

They are believed to be low-threshold mechanical receptors that may play a contributing role in the perception of touch and pressure

Krause’s End-bulbs

May also contribute to detection of cold

• Almost all tactile receptors involved

• Different receptors detect different frequencies of vibration

• Pacinian: 30 to 800 cycles per second

• Meissner: 2 up to 80 cycles per second

Detection of Vibration

Almost all tactile receptors involved

Detection of Vibration

Different receptors detect different frequencies of vibration

Detection of Vibration

Pacinian’s vibration

: 30 to 800 cycles per second

Meissner’s vibration

• : 2 up to 80 cycles per second

• Very sensitive, rapidly adapting mechanoreceptive free nerve endings

• Found almost exclusively in superficial layers of the skin

• Transmitted by small type C unmyelinated fibers

Detection of Tickle and Itch

Very sensitive, rapidly adapting mechanoreceptive free nerve endings

Detection of Tickle and Itch

Found almost exclusively in superficial layers of the skin

Detection of Tickle and Itch

Transmitted by small type C unmyelinated fibers

Detection of Tickle and Itch

Tickle and Itch are transmitted by what classification of fiber?

small type C unmyelinated fibers

• Posture, position sense, proprioception, muscle tone, and speed and direction of movement.

• Muscle Receptors – Muscle Spindle, Golgi Tendon Organs, Free nerve endings, Pacinian corpuscles

• Joint Receptors – Golgi-Type endings, Ruffini endings, Paciniform endings, Free nerve endings

Deep Sensations

Posture, position sense, proprioception, muscle tone, and speed and direction of movement.

Deep Sensations

Enumerate the muscle receptors

– Muscle Spindle, Golgi Tendon Organs, Free nerve endings, Pacinian corpuscles

Enumerate the joint receptors

– Golgi-Type endings, Ruffini endings, Paciniform endings, Free nerve endings

• The muscle spindle fibers (intrafusal fibers) lie in a parallel arrangement to the muscle fibers (extrafusal fibers).

• They monitor changes in muscle length (Ia and II spindle afferent endings) as well as velocity (Ia ending) of these changes.

• The muscle spindle plays a vital role in position and movement sense and in motor learning

Muscle Spindles

The muscle spindle fibers (intrafusal fibers) lie in a parallel arrangement to the muscle fibers (extrafusal fibers).

Muscle Spindles

They monitor changes in muscle length (Ia and II spindle afferent endings) as well as velocity (Ia ending) of these changes.

Muscle Spindles

The muscle spindle plays a vital role in position and movement sense and in motor learning

Muscle Spindles

Tell me something about the muscle spindle anatomy

Muscle Spindle Anatomy

• Extrafusal fibers (regular muscle fibers) and Intrafusal fibers (3-10 small muscle fibers)

• Sensory portion:

  • Primary Ending (Type Ia) → Annulospiral ending, supplies the nuclear bag and nuclear chain; have rapidly adapting responses to changes in muscle length

  • Secondary Ending (Type II) → Flower-spray ending, supplies the nuclear chain; produce sustained responses to constant muscle lengths

• Motor portion:

  • Plate endings à Nuclear bag intrafusal fiber

  • Trail endings à Nuclear chain intrafusal fiber

What are under the sensory portion of the muscle spindle anatomy?

Primary ending (Ia)

Secondary ending (II)

Annulospiral ending, supplies the nuclear bag and nuclear chain; have rapidly adapting responses to changes in muscle length

• Primary Ending (Type Ia) →

Flower-spray ending, supplies the nuclear chain; produce sustained responses to constant muscle lengths

• Secondary Ending (Type II) →

What are under the motor portion of the muscle spindle anatomy?

Plate endings

trail endings

Where do plate endings go?

Nuclear bag intrafusal fiber

Where do trail endings go?

Nuclear chain intrafusal fiber

• Located in series at both the proximal and distal tendinous insertions of the muscle.

• function to monitor tension within the muscle.

• Protective mechanism by preventing structural damage to the muscle in situations of extreme tension.

  1. Inhibition of the contracting muscle and

  2. facilitation of the antagonist.

Golgi Tendon Organs

Located in series at both the proximal and distal tendinous insertions of the muscle.

Golgi Tendon Organs