Day 8 somatic sensation:

5 Basic types of sensory receptors

1. Mechanoreceptors- detect mechanical contraction of pressure on the receptors or adjacent to the receptors
e.g., muscle spindles
2. Thermoreceptors- detect changes in temp.
3. Nociceptors (pain receptors)- detect physical or chemical change occurring in tissues
4. Electromagnetic Receptors- detect light on the retina of the eye
5. Chemoreceptors- detect taste in mouth, smell in nose, oxygen level in arterial blood, osmolality of the blood,
fluids, carbon dioxide concentration and other factors that make up the chemistry of the blood

Receptor Potentials
- Whatever excitation in the neuron Changes in electrical of membrane; neurotransmitters
- Basic cause on change in membrane potential- changes in membrane permeability of receptors- allows
exchange of ions into the membrane therefore changes membrane potential
♤ WHEN TOUCHED: MORE – OUTSIDE MORE ++ INSIDE
♤ Free nerve endings- part of the nerve ang endings

Triggers or ways to excite sensory receptors:

1. mechanical deformation- such as membrane and opens ion channels
2. application of a chemical to the membrane- opens ion channels
- found in chemoreceptors
3. Change of the temperature membrane- alters permeability of membrane
4. effects of electromagnetic radiation- (light in retinal visual receptors) indirectly or directly cause changes in
receptor membrane characteristics
 Are not alpha and beta receptors (found in neurons)-attaches in neurotransmitters

Adaptation of receptors (characteristics)

 Initial high impulse rate response of receptors that gradually decreases and eventually stops with continuous
sensory stimulus application
 When there is continuous sensory stimulation receptors response initially with high impulse rate then slowly
decrease until membrane potential is low or none

Tactile and Position Senses (Classification of somatic senses)

1. Mechanoreceptive somatic senses- includes both tactile and position senses that is stimulated by mechanical
displacement of tissues
2. Thermoreceptive senses- detect heat and cold
3. Pain sense- activated by factors that damage the tissue

Tactile senses include:

- Touch, pressure, vibration, tickle senses

Position senses include:

- Static position and rate or movement senses

Other classification of somatic sensations

1. exteroreceptive sensations- sensations or stimuli coming from surface of body(skin)
2. Proprioreceptive sensations- Physical state of body e.g., tendon and muscle sensation, pressure from bottom of
feet, equilibrium (special sensation)
 3. visceral sensations- from visceral of body
- internal organs sensation
4. Deep sensations- from deep tissues (fascia, muscles, bones) deep pressure pain and vibration

Detection and transmission of tactile sensations

“3 principal differences among them”:
1. Touch sensation- tactile receptors in the skin or (tissue) immediately beneath the skin
2. pressure sensation- deformation of deeper tissues
3. vibration sensation- rapidly repetitive sensory signals

 some receptors for touch and pressure sensations can detect vibrations incision through rapid repetitive
sensory signals

Tactile receptors and their special characteristics

1. Free nerve endings- detect touch and pressure
♡ found anywhere the skin and many other tissue
♡ even light contact of cornea in the eye can elicit to blink.
2. Meisner's corpuscle- in non-hairy parts of the skin
- discern spatial location of touch sensation
- sensitive to movement of objects in the surface of skin
- low frequency vibration
- capsulated and myelinated
- elongated and capsulated nerve ending
- inside capsulation are blanching terminal nerve filaments
3. Merkel’s Disc- expanded tips of tactile receptors
- found in both non hairy and hairy skin
- steady state signals that allows one to determine continuous touch of objects against the skin
- used to dermine texture
4. Hair-end organs (touch receptors)- the text movement of objects on the surface of the body through the hair
follicles
◇ slight movement of the hair esp the villis will stimulate a nerve fiber entwining its base.
- detects initial contact with the body
5. Ruffin’s endings
- continuous signaling states of deformation of the tissues (heavy prolonged touch pressure signals)
- found on the deeper layers of the skin
- found in joint capsules and detect the degree of rotation of joint
- Multi branch and is capsulated (like Meisner’s)
6. Pacinian corpuscle
- lie immediately beneath the skin and deep in the fascial tissues
- Stimulated only by rapid local compression or vibration of the tissues
- Detecting tissue vibration or other rapid changes in the mechanical state of the tissues

transmission of tactile signals in peripheral nerve fibers

1. Type AB (A- beta) nerve fibers
- Meissner's corpus, Iggodome receptors, hair receptors, pacinian corpuscle, ruffini’s endings
2. type A- Delta myelinated fibers
- all free nerve endings
- small type
3. Type C fibers
- some free nerve endings
- for tickle sensations
- send signals in spinal cord and lower brainstem serving sensation of tickles.

Detection of vibration
1. high frequency- transmit signals type AB (A –beta) nerve fibers transmit impulses in a fast rate.
- Pacinian corpuscle
2. Low frequency- Meisner's corpuscle
- Type AB ( A- Beta)

Detection of tickle and itch by Mechanoreceptive free nerve endings (rapidly adapting)
- Found almost exclusively in superficial layers of the skin
- Very small type C fibers (slow type) (unmyelinated) Same with slow type of pain
Purpose: call attention to mild surface stimuli (ant crawling on skin or mosquito about to bite)
- Signals elicited will activate scratch reflex get rid of irritant (stretching hard enough to suppress each signal or
stimuli)

Sensory pathways for transmitting somatic signals into the CNS

Main: sensory signal- interesting spinal cord through dorsal root (sensory signal/enters) spinal nerves

Alternative pathways for sensory signals

1. Dorsal column-medial lemniscal system
- contains large, myelinated fibers
- Dorsal columns
- Cross at the level of the medulla
- Faster because of large, myelinated fibers
- Carries signals upward to medulla of the brain mainly in the dorsal columns of the cord
- Signals will synapse in the opposite side of the medulla (where there is crossing) then continue upward to the
brain stem and thalamus.

2. anterolateral system
- Anterolateral column
- cross immediately after entering the cord
- Synapse with other dorsal horn grey matter, cross in opposite side before going up
- slower because it contains smaller unmyelinated fibers

Carried sensations of:

1. Dorsal column- medial Lemniscal system (greater spatial orientation)
 Touch sensations requiring a high degree of localization of the stimulus
 Touch sensations requiring transmission of fine gradations of intensity
 Phasic sensations such as vibratory sensation
 sensations that signal movements against the skin
 position sensations from the joints
 pressure sensations correlated to fine degree of a judgment of pressure intensity

2. Anterolateral system (Less spatial orientation)

 Pain
 Thermal sensations including both warm and cold sensation
 Crude Touch and pressure sensations capable only of crude localizing ability on the surface of the body
  Tickle and itch sensations
 sexual sensations
- Ability to transmit a large number or wide spectrum of sensory modalities

Somatosensory cortex- 50 different areas

 Brodmann’s Area- (50 areas)
1. Anterior half of parietal lobe
- Reception and interpretation of some somatosensory signals
2. Posterior half of parietal lobe
- Higher form of level of interpretation
3. Occipital Lobe
- visual signals terminate
4. Temporal Lobe
- auditory signal terminate
Note:
♧ Primary Somatosensory Area – detection and reception of sensations
♧ Secondary somatosensory Area – interpret sensations coming from the primary

Somatosensory areas I and II

- Distinct spatial orientation of different body parts found in these areas
1. Somatosensory I
- more extensive
- much more important
- high degree of localization of parts of body
- sometimes called the somatosensory cortex

2. Somatosensory II
- localization is poor
- less extensive
- projections from somatosensory I is needed for this function
- if removed, it has no effect on somatosensory I

Spatial orientation in somatosensory area I (parietal lobe)

 Each lateral side of cortex- almost exclusively receive signals from the opposite side of the body
 size or coverage on motor humunculus depends on the number of specialized nerve endings present
LARGE AREAS IN THE SOMATIC CORTEX
• Lips - greatest of all (sensory) A LOT OF RECEPTORS
• Face
• Thumb
RELATIVELY SMALL AREAS IN THE SOMATIC CORTEX
• Trunk
•Lower Body Parts

LATERAL components
- Face, lips, mouth and nose
Medially components
- the head, neck, shoulders and other lower extremities/parts
Layers of somatosensory cortex
1. Layer I- surface
2. Layer IV- first enters the (cortex) somatosensory receptors

Functions of Somatosensory Area I

- detection of sensation signals
If removed:
- Unable to localize discretely the diff. Sensations
- Unable to judge diff. Degrees of pressure
- Unable to judge the weight of objects
- Unable to judge shapes or forms- (astereognosis)
- Unable to judge textures
 There's still ability to determine pain and temp. Of ranging degrees but poor localization of the sensation on
the body

Somatosensory Association area

 Brodmann’s area 5 and 7 (located in parietal cortex; behind somatosensory I)
- Deciphering deeper meanings of the sensory info.
If removed:
1. amorphosynthesis
- Forgets to use the other side for motor functions
- Recognize only one side of the object and forgets that the other side even exist
- Loses use of the other side of the body

Method to use when determining tactile discrimination

1. Two- Point discrimination
- Tip of fingers (very sensitive) 1-2 mm
- On the Back- 30-70mm
- Tests the number of specialized tactile receptors

Position senses (Proprioceptions)

Proprioception subtypes
1. Static- continuous for perception of the orientation of different parts of the body
2. Kinesthesia (dynamic proprioception)- rate of movement sense
☆ Both positions will depend on knowing the degree of Angulation on all joints and the rate of change of these
Angulations

Position sensory receptors- detect degree of Angulation/ change in angulation

1. Skin tactile receptors and deep receptors
2. Fingers-skin > deep receptors
3. larger joints- deep > Skin receptors

Dermatomes- segmental field

- innervated by level of their spinal nerves
- Adjacent dermatomes usually overlaps
- Anal region – lies in s55 (distal part in embryonic stage)
- Used to determine the level of spinal nerves injured
- dermatomal sensation problem
Pain (Headache and thermal sensations)
2 major types
1. Fast pain- only superficial
- it's not felt on deep tissues
- 0.1 sec pain stimulus
- a.k.a. sharp pain, pricking pain, acute pain, electric pain

2. Slow pain- tissue destruction (skin and deep tissue or organ) (prolonged)
- after one second or more
- increases slowly
- aka burning pain, aching pain, throbbing pain, nauseous pain and chronic pain
3. Combination of Fast and Slow pain
- Poking on the side

Pain receptors in skin and other tissues

- All free nerve endings
- Widespread in the superficial layers of the skin, and internal tissues (deep pain receptors below)
- Deep pain receptors: periosteum, arterial walls, the joint surface says and the falx and then tentorium in the
cranial vault

Mechanical, Thermal and chemical stimuli- and illicit pain

1. Mechanical & Thermal- fast stimuli
2. Chemical- bradykinin, serotonin, histamine, potassium ions, acids, acetylcholine, and proteolytic enzymes
3. Prostaglandins and substance P
- Slow suffering type of pain after tissue injury
- Enhance the sensitivity of pain endings
- Do not directly excite pain endings

Non adaptive nature of pain receptors

 Hyperalgesia- enhanced sensitivity of pain

Note: slow continuous stimulation of pain increase intensity of pain

Rate of tissue damage

- average person perceives pain when skin is heated above 45 degrees Celsius
- he should begin to be damaged by heat
- Pain resulting/ intensity of pain from heat is related to rate of tissue damage
- Rate of Tissue damage = Amount of Pain

Importance of chemical pain stimuli

1. Bradykinin (most painful)
- intensity of pain correlate to the increase of K+ ion concentrations or proteolytic enzymes that directly attack
the nerve endings and excite making the nerve ending permeable to ions.
- Chemical more painful than others.
- Agent that causes pain after tissue damage.
Cause of Pain
1. Tissue Ischemia
- flow of blood and tissue is blocked, tissue should become painful
- Greater rate of metabolism, faster pain appears
- Accumulation of lactic acid
Anaerobic metabolism- lactic acid (byproduct)

2. muscle spasm (common in clinical pain)

- mechanical stimulation of pain receptors
- Indirect effect of ischemia
- Partially solved

2 pathways for transmission of pain signals in CNS

1. Fast (Sharp) fibers

- Elicited by mechanical/thermal pain stimuli
- Transmitted in the Peripheral nerve to the spinal cord by small type A delta fibers

2. Slow (Chronic pain) fibers

- Stimulated by all three but commonly chemical
- Transmitted in spinal cord by small type C fibers

Double pain Stimulation – first is fast pain followed by a slow pain

Sharp Pain- important in making the person react immediately to stay away from the stimulus
Slow Pain – become greater over time cause intolerable pain.

Pain suppressions (Analgesia)

- Degree of how people react to pain will vary by activating pain control system like the Analgesia System.

Analgesia System- prevents or inhibits signals from type C and A-Delta pain fibers
○ Enkephalin - inhibit type C & A-delta fibers
○ Serotonin – neurotransmitter (inhibitory) secrete Enkephalin
3 major components
• Periaqueductal Gray
• Periventricular Areas of the Mesencephalon
• Upper Pons

♤ Periaqueductal gray and periventricular areas > raphe magnus nucleus > pain inhibitory complex of the spinal cord
 can block reflexes such as withdrawal reflexes

Inhibition of pain transmission by simultaneous tactile sensory signals

 large type A- Beta
- depress transmission of pain from same area
- local lateral inhibition of spinal cord
- Rubbing relieve pain
- Simultaneous psychogenic excitation of central Analgesian system basis of pain relief by acupuncture
- Liniments – uses tactile sensory fibers; suppress painful stimuli
Treatment of pain by electrical stimulation
 TENS – electric Stimulation of skin surface that will stimulate tactile skin receptors it will suppress pain.
 Tactile receptors- through A-beta fibers, these fibers has the ability to Laterally inhibit the pain fibers.

Referred pain (most common type of pain)

- pain remote to the area causing the pain such as chest pain
- Cause: Branches of visceral pain fibers will synapse in the spinal cord of the same neuron that receives pain
signals from the skin.

Visceral pain- highly localization of visceral damage will seldomly cause severe pain
- Pain from viscera is one of the few criteria that can be used in diagnosing visceral inflammation, infectious
disease and other Visceral ailments.
- Differs from surface pain in diff kinds of aspects
□ one difference from viscera and surface pain is that:
■ highly localize type of damage to the viscera will seldom cause SEVERE PAIN.
Note: all visceral pain that originate in the thoracic and abdominal is transmitted by the Type C Pain fibers can only
transmit chronic aching pain.
Cause of Visceral pain:
1. Ischemia – cause extreme pain in 1 touch
2. Chemical stimuli- enzymes such as lactic acid etc.
- such as damaging substances leaking to GI tract into cavities destroying the peritonium cavity
3. Spasm of hollow visces- compression of blood vessels leading to cramping
4. Overdistension- overfilling or over distention, cause collapse in blood vessels
5. Insensitive Viscera- all internal organs are not capable of being sensations
- liver parenchyma – liver capsule is extremely sensitive to both direct trauma and stretching to cause pain.
- alveoli of the lungs – bronchi and parietapleura are very sensitive to pain

Parietal Pain- cause by visceral disease

 Sharp- parietal (surface)
 Slow- visceral (Inside)

Note: 2 types of Pericardium: parietal and visceral

Some clinical abnormalities of pain and other somatic sensations (clinical application)
1. Hyperalgesia- hypersensitivity to pain
 Primary- sunburn (increase sensitivity of pain receptors)
♤ pain endings by local tissue products from burns
 Secondary- lesions in the spinal cord or thalamus (facilitation of Sensory transmission)
- Facilitation of transmission of pain signals
2. Herpes Zoster (Shingles)
- herpes virus infects dorsal root ganglia (sensory)
- severe pain in dermatomal zone
-causes neuronalcytoplasmic flow out
- vesicular rash
3. Tic Doulourex
- Trigeminal neuralgia (both sensory and motor nerves)
- Lancing or stabbing type of pain
- sudden electrical shop
- mechanical stimuli- illicited
In order to block pain:
- Cutting peripheral nerve from hyper sensitive area without involving motor portion
- Leaves no sensation after removal (analgesic area)
4. Headaches- deep cranial structural pain
- inside and outside pain stimuli of cranium
- not caused by damage of brain itself
- pain in the eye area or around eye orbit / nasal sinus (retro orbital Pain)
5. Pain sensitive areas in the cranial vault
- brain tissues( cortex)- almost insensitive to pain (only prickling feeling)
Areas that can elicit pain:
- Venous sinus (tugging)
- Dura(stretching)- Headache
- Tentorium-
- Blood vessels of the meninges- headache
 Middle Meningeal artery
- Migraine (cause is pulsation of blood vessels or overstretching)

Areas in the head to which the Intracranial headache is referred

1. Above the Tentorium- Front half
- headache
- enters the spinal cord through the or travels through the cranial nerve V
- Cerebral vault headache (Supratentorial)
1. Below the Tentorium
- enters the spinal cord through or travels through the cranial nerve VIII, IX and C2
- below the brainstem and cerebellar vault headache (Subtentional)- below the ears slightly
 Subtentorial pain- occipital

Types of intracranial headache

1. Meningitis- inflammation of dura and the venous sinus (Severe)(extreme headache- entire head)
2. low CSF- distortion of dural surfaces
- Removal of 20ML fluid in spinal canal
- Decreases floating stability of brain
3. Migraine- abnormal vascular function (special type of headache) (medication: unknown)
 Prodrome- 30-60 mins. Before Headache (Hallucinations, nauseous)
 Theory 1- tension or emotion> vasoplasm>ischemia> prodrome>exhaustion of Smooth muscle
vasospasm>vasodilation> pulsation> Headache
 Other Theory- Spreading cortical depression, psychological abnormalities and vasospasm caused by excess local
potassium
4. Alcoholic headaches- meningeal irritation
- too much alcohol consumption (hungover)
- toxic to tissues
- dehydration can also play a role – hydration can attenuate but not abolish headache

Extracranial types of headaches

1. muscle spasm- common cause of headache (emotional tension- contracts the muscle of the brain)
2. Irritation of nasal and accessory nasal structures- sinus infections
- sensitive to pain
-irritation progresses
- retro orbital pain (behind the eye pain)
 3. Eye disorders
- extreme contraction of eye ciliary muscles and reflex spasm of facial and extraocular muscles
- excessive exposure to light rays (UV)
- headache last 24-48 hrs
- focus on intense light can burn the retina and cause headache

Thermal sensations (receptors)

1. Cold receptors
- 3 to 10 times more than warmth
- transmitted by type A-delta myelinated
- some type C
2. Warmth receptors
- Free nerve endings
- Transmitted by Type C fibers (unmyelinated)
3. Pain receptors
- extreme degrees of heat and cold
- elicited in temperatures 45 degrees and above

Adaptation of thermal receptors

- temperature of skin is falling, you feel colder than when temperature remained the same
- respond to changes