Neurophysiology Series SENSORY FUNCTIONOF THE NERVOUS SYSTEMwww.physiology.sdu.edu.cn By Sawiji AmaniMobile phone: 081 328 028333E-mail: sawijiamani@gmail.com

Basic Sciences DepartmentMuhammadiyah Gombong UniversityCentral Java Indonesia

I Sensory pathwaysSensory systems allow us to detect, analyze and respond to our environmentascending pathwaysCarry information from sensory receptors to the brainConscious: reach cerebral cortexUnconscious: do not reach cerebral cortexSensations from body reach the opposite side of the brain

1. Sensory receptorsA: Free nerve endings (pain, temperature)

B: Pacinian corpuscle (pressure)

C: Meissners corpuscle (touch)

D: Muscle spindle (stretch)

Sensory receptors

Ruffini's endings respond to tension and stretch in the skin

Sensory receptors

Sensory receptors: organs which detect sensory stimuli .

Sensory stimuli: sensation modality (touch, sound, light, pain, cold, and warmth..etc)

Sensory receptors

Mechanoreceptors: detect mechanical compression or stretching of tissues Thermoreceptors: detect changes in temperature Nociceptors (pain receptors): detect tissue damage ( physical or chemical damage) Chemoreceptors: detect taste in the mouth, smell in the nose, oxygen level ..etc.Electromagnetic receptors (photoreceptor): detect light on the retina

2. Sensory pathways: 3 neurons1st: enters spinal cord from periphery2nd: crosses over (decussates), ascends in spinal cord to thalamus3rd: projects to somatosensory cortex

Two important pathway2.1. Spinothalamic pathway2.2. Dorsal column medial lemniscal pathway

2.1 Spinothalamic pathwayCarries pain, temperature, touch and pressure signals1st neuron enters spinal cord through dorsal root2nd neuron crosses over in spinal cord; ascends to thalamus3rd neuron projects from thalamus to somatosensory cortex

Spinothalamic PathwaySmall sensory fibres:Pain, temperature, some touchPrimary somatosensory cortex (S1)ThalamusMedullaSpinal cordSpinothalamic tract

Spinothalamic damage

2.2 Dorsal column pathwayCarries fine touch, vibration and conscious proprioception signals1st neuron enters spinal cord through dorsal root; ascends to medulla (brain stem)2nd neuron crosses over in medulla; ascends to thalamus3rd neuron projects to somatosensory cortex

Two-Point Discrimination

Dorsal column pathwayLarge sensory nerves:Touch, vibration, two-point discrimination, proprioceptionPrimary somatosensory cortex (S1) in parietal lobeThalamus MedullaMediallemniscusSpinal cordDorsal columnDorsal columnnuclei

Dorsal column damage

Dorsal column damage

Sensory ataxia

Patient staggers; cannot perceive position or movement of legs

Visual clues help movement

Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved. ataxia[ah-takse-ah] failure of muscular coordination; irregularity of muscular action. adj., adj atactic, ataxic.sensory ataxia: ataxia due to loss of proprioception (joint position sense), resulting in poorly judged movements and becoming aggravated when the eyes are closed.

Central Pathways

Sensory pathways cross the bodys midline (Silverthorn: 2007)

3.3 Spinocerebellar pathwayCarries unconscious proprioception signalsReceptors in muscles & joints1st neuron: enters spinal cord through dorsal root2nd neuron: ascends to cerebellumNo 3rd neuron to cortex, hence unconscious

Spinocerebellar tract damageCerebellar ataxia : ataxia due to disease of the cerebellum. Clumsy movementsIncoordination of the limbs (intention tremor)Wide-based, reeling gait (ataxia)Alcoholic intoxication produces similar effects!

4. Somatosensory cortex Located in the postcentral gyrus of the human cerebral cortex.

Lobus Parietalis: Fungsi & Asosiasi Somatosensoris Gyrus postsentral : korteks somatosensori primer Sentuhan/raba lembut, tekanan, nyeri & suhu, sensasi umum di kepala Sensory homunculus (representasi disproporsional)

Spatial orientation of signals.Each side of the cortex receives sensory information exclusively from the opposite side of the body (the exception: the same side of the face).

Spatial orientation of signals.2)The lips, face and thumb are represented by large areas in the somatic cortex, whereas the trunk and lower part of the body, relatively small area.3)The head in the most lateral portion, and the lower body is presented medially

Sensory homunculus (representasi disproporsional)

Sensory homunculus (representasi disproporsional)

II . Pain

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

International Association for the Study of Pain

Why feel pain?Gives conscious awareness of tissue damageProtection:Remove body from dangerPromote healing by preventing further damageAvoid noxious stimuliElicits behavioural and emotional responses

free nerve endings in skin respond to noxious stimuli

1. Nociceptors

NociceptorsNociceptors are special receptors that respond only to noxious stimuli and generate nerve impulses which the brain interprets as "pain".

Adequate StimulationTemperatureMechanical damageChemicals (released from damaged tissue) Bradykinin, serotonin, histamine, K+, acids, acetylcholine, and proteolytic enzymes can excite the chemical type of pain. Prostaglandins and substance P enhance the sensitivity of pain endings but do not directly excite them.Nociopectors

Hyperalgesia: The skin, joints, or muscles that have already been damaged are unusually sensitive. A light touch to a damaged area may elicit excruciating pain;

Primary hyperalgesia occurs within the area of damaged tissue; Secondary hyperalgesia occurs within the tissues surrounding a damaged area.

2. Localization of PainSuperficial Somatic Pain arises from skin areasDeep Somatic Pain arises from muscle, joints, tendons & fasciaVisceral Pain arises from receptors in visceral organslocalized damage (cutting) intestines causes no paindiffuse visceral stimulation can be severedistension of a bile duct from a gallstonedistension of the ureter from a kidney stone

Most pain sensation is a combination of the two types of message. If you prick your finger you first feel a sharp pain which is conducted by the A fibres, and this is followed by a dull pain conveyed along C fibres.

3. Fast and Slow Pain

Fast pain (acute)occurs rapidly after stimuli (.1 second)sharp pain like needle puncture or cutnot felt in deeper tissueslarger A nerve fibersSlow pain (chronic)begins more slowly & increases in intensityin both superficial and deeper tissuessmaller C nerve fibers

Impulses transmitted to spinal cord byMyelinated A nerves: fast pain (80 m/s)Unmyelinated C nerves: slow pain (0.4 m/s)

Impulses ascend to somatosensory cortex via:Spinothalamic pathway (fast pain)Reticular formation (slow pain)

4. Visceral painNotable features of visceral pain:Often accompanied by strong autonomic and/or somatic reflexesPoorly localized; may be referred referred painMostly caused by distension of hollow organs or ischemia (localized mechanical trauma may be painless)

Afferent innervation of the viscera.Often anatomical separation nociceptive innervation (in sympathetic nerves) from non-nociceptive (predominantly in vagus). Many visceral afferents are specialized nociceptors, as in other tissues small (Ad and C) fibers involved. Large numbers of silent/sleeping nociceptors, awakened by inflammation. Nociceptor sensitization well developed in all visceral nociceptors.

Referred painPain originating from organs perceived as coming from skin

Site of pain may be distant from organ

Convergence theory: This type of referred pain occurs because both visceral and somatic afferents often converge on the same interneurons in the pain pathways.

Excitation of the somatic afferent fibers is the more usual source of afferent discharge,

so we refer the location of visceral receptor activation to the somatic source even though in the case of visceral pain.

The perception is incorrect.The convergence of nociceptor input from the viscera and the skin.Referred pain

5. Pain Gate TheoryMelzack & Wall (1965)

A gate, where pain impulses can be gated

The synaptic junctions between the peripheral nociceptor fiber and the dorsal horn cells in the spinal cord are the sites of considerable plasticity.

A gate can stop pain signals arriving at the spinal cord from being passed to the brain

Reduced pain sensationNatural pain relief (analgesia)

How does pain gate work?The gate = spinal cord interneurons that release opioids.

The gate can be activated by:

Simultaneous activity in other sensory (touch) neuronsDescending nerve fibers from brain

Applications of pain gateStimulation of touch fibres for pain relief:TENS (transcutaneous electrical nerve stimulation)AcupunctureMassage

Release of natural opioidsHypnosisNatural childbirth techniques

6. Pain ReliefAspirin and ibuprofen block formation of prostaglandins that stimulate nociceptorsNovocain blocks conduction of nerve impulses along pain fibersMorphine lessen the perception of pain in the brain.

Phantom Limb Sensation(Tortora & Derrickson, 2006:552)Patients who have had a limb amputated may still experience sensations such as itching, pressure, tingling, or pain as if the limb were still there. This phenomenon is called Phantom Limb Sensation.Why so?

Some Explanations (Tortora & Derrickson, 2006:552) The cerebral cortex interprets impulses arising in the proximal portions of sensory neurons that previously carried impulses from the limb as coming from the nonexistent (phantom) limb.The brain itself contains networks of neurons that generate sensations of body awareness.Neurons in the brain that previously received sensory impulses from the missing limb are still active, giving rise to false sensory perceptions.

(Tortora & Derrickson, 2006:552)Phantom limb can be very distressing to an amputee.Many report that the pain is severe or extremely intense, and that it often does not respond to traditional pain medication therapy.In such cases, alternative treatments may include electrical nerve stimulation, acupuncture, and biofeedback.

Analgesia: Relief from Pain (Tortora & Derrickson, 2006:553) Pain sensations sometimes occur out of proportion to minor damage, persist chronically due to an injury, or even appear for no obvious reason.In such cases, analgesia (an- = without; -algesia = pain) or pain relief is needed.Analgesic drugs such as aspirin and ibuprofen (for example, Advil or Motrin) block formation of prostaglandins, which stimulate nociceptors.

(Tortora & Derrickson, 2006:553)Local anesthetics, such as Novocaine, provide short-term pain relief by blocking conduction of nerve impulses along the axons of first-order pain neurons.Morphine and other opiate drugs alter the quality of pain perception in the brain; pain is still sensed, but it is no longer perceived as being so noxious.Many pain clinics use anticonvulsant and anti depressant medications to treat those suffering from chronic pain.

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