Neurology S3 Flashcards
Types of sensation
General:
(a) Body surface, that belong to the somatomotor NS:
1- Tactile (touch, pressure, vibration)
2- Thermal (warm, cold)
3- Pain
4- Proprioception (position sense)
(b) Visceral (General Visceral Afferent – GVA), that belong to autonomic NS: form internal organs, viscera, glands & blood vessels)
Special:
Like: smell, taste, vision, hearing, balance
Types of 1 st order neurone
Free Nerve Ending cold
Encapsulated Nerve Ending pressure stimulation
With Specialised Cell gestation (with sugar )
Deep receptors
Proprioceptors receptors
Unconsciuos Proprioceptors (sense of position) Muscle spindle : Senses the length of the muscle Golgi tendon organ : Senses the tension of the tendons
Which sensation carried by ascendingdorsal columns
Lateral spinothalmic tract
Ventral spinothalmic tract
Deep / fine touch ,vibration ,proprioception
Pain & T
Light touch / crude touch ,pressure
UNCONSCIOUS SENSATION FROM THE LIMBS & BODY
Spinocerebellar – anterior & posterior
unconscious proprioception
Cuneocerebellar
unconscious proprioception
بس الڤينترال سبلاي الكونترا لاترال سايد
DORSAL COLUMN – MEDIAL LEMNISCAL TRACT
Fine touch
Cutaneous receptors, e.g.:
Conscious proprioception
Meissner’s corpuscle – stroking Merkel disk – pressure Pacinian Corpuscle – vibration Ruffini ending – skin stretch Hair receptors - stroking
Muscle & joint receptors, e.g.
Muscle spindle – muscle length/limb movement Golgi tendon organ – muscle contraction Joint receptors – joint movement
DORSAL COLUMN – MEDIAL LEMNISCAL TRACT
1 st order afferent neuron
2
3
DORSAL COLUMN – MEDIAL LEMNISCAL TRACT 1 st order afferent neuron
Cell body – dorsal root ganglion Spinal cord – ascends in dorsal columns (fasciculi gracilis & cuneatus) of ipsilateral cord Termination – medulla: nuclei gracilis & cuneatus
2 nd order afferent neuron
Cell body – nuclei gracilis & cuneatus Decussates in the medulla Termination – thalamus (ventral posterolateral nucleus)
3 rd order afferent neuron
Cell body - thalamus Termination – contralateral somatosensory cortex (postcentral gyrus)
ANTEROLATERAL SYSTEM sensation
Pain
Nociceptors, (all free-ending afferents) e.g.:
Mechanical – sharp pain Thermal – burning pain Thermal – cold/freezing pain
Temperature
Thermo-receptors (free-ending afferents) e.g.:
Thermal - cool Thermal - warm
Crude Touch
Mechanoreceptors
Free-ending afferents – crude touch/pressure Merkel disks – crude touch/pressure
ANTEROLATERAL SYSTEM
1st order N
2
3
1 st order afferent neurons
Cell body – dorsal root ganglion Spinal cord – enter dorsolateral tract Terminations – dorsal horn laminae I, II (substantia gelatinosa), and V
2 nd order afferent neuron
Cell body – dorsal horn, laminae I & V Decussates in the spinal cord Terminations– thalamus (ventral posterolateral nucleus). Also, reticular system & midbrain
3 rd order afferent neuron (spinothalamic tract)
Cell body - thalamus ( VPL nucleus) Termination – contralateral somatosensory cortex (postcentral gyrus)
SPINOCEREBELLAR TRACTS
1st order N
2
1 st order afferent neuron
Group I and II (musculo-skeletal) Cell body – dorsal root ganglion Terminate – dorsal horn
2 nd order afferent neuron
Anterior tract - decussates in the cord, re-crosses & terminates in the ipsilateral cerebellum
Posterior tract – remains ipsilateral & terminates in the cerebellum
Stimulus modalities
, and the qualities
Stimulus modalities are the stimulus that the receptors respond to, such as light, touch, temperature, and the qualities are simply the subdivision of a modality, such as taste can be divided into sweet, sour etc. Sensory receptors are modality specific, meaning that they only respond to the type of stimuli they are specialised for. The eyes respond preferentially to light yet any mechanical stimulus (blow to the head) may cause the individual to “see stars”.
لماذا لا يشعر مريض الحروق من الدرجة الثالثة بآلام في البداية
any third degree burn will destroy all of these pain receptors such that the patient will not feel any pain initially with a full thickness burn.
Sensory Transduction
When a stimulus impinges upon a receptor, it causes a change in its membrane potential which is proportional to stimulus intensity. This change affects the action potential generating regions of the nerve, to set off a series of action potentials which encode information about the intensity and duration of the stimulus. This is achieved by two mechanisms:
Frequency coding, whereby strength can be determined by rate of action potential stimulus (i.e. increased frequency of action potential means a stronger stimulus) Activation of neighbouring cells, as a stronger stimulus will activate neighbouring cells to a greater degree
Receptor Adaptation
Tonic receptors will respond continuously to the presence of an adequate stimulus (e.g. pain receptors) whereas phasic receptors rapidly adapt to a stimulus so that action potential firing so that the action potential frequency in the afferent nerve decreases during a maintained stimulus (e.g. touch receptors).
Convergence and divergence
Convergence and divergence are two terms which can also be applied to acuity. Convergence decreases acuity whereas divergence causes amplification.
