SENSORY SYSTEM

NUR ALYA SYAFIQA BINTI MOHD NAZIM A164672

GAN JIN YING A164917

Part of the nervous system – responsible for processing sensory information.

Consists of 3 things:

  1. sensory receptor (GENERAL SENSE)
  • Chemoreceptors – respond to changes in chemical concentrations
  • Pain receptors (nociceptors) – respond to tissue damage
  • Thermoreceptors – respond to changes in temperature
  • Mechanoreceptors – respond to mechanical forces
  • Photoreceptors – respond to light
  • Osmoreceptors – respond to changes in solute concentration

2. Neural pathways

3. Parts of the brain involved in sensory perception

  • Proprioception : Sense of the body awareness. Our body senses propriocepton through messages sent from sensory receptors in our muscles and joints .
  • Vestibular : Sense of balance and motion, located in the middle ear. At the most basic level, the vestibular system is activated any time we move our head.
  • Tactile : Sense of touch, located in sensory receptors in our skin and mouth.
  • Visual : Sense of vision, but it’s more than just about being able to see clearly.
  • Auditory : Sense of hearing but again, it’s more than just able to hear accurately.
  • Olfactory : Sense of smell, influences sense of taste
  • Gustatory : Sense of taste

Sensory neurons (afferent neurons)

Neurons that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials (sensory transduction).

The cell bodies of the sensory neurons are located in the dorsal ganglia of the spinal cord.

This sensory information travels along afferent nerve fibers in an afferent or sensory nerve, to the brain via the spinal cord.


FIRST ORDER NEURONS

  • conduct impulses from receptors of the skin and from proprioceptors (receptors located in a join, muscle or tendon) to the spinal cord or brain stem.
  • Synapses with second order neuron
  • Located at dorsal root ganglion

SECOND ORDER NEURONS

  • Conduct impulses from the brain stem and spinal cord to the thalamus
  • Axons of second-order neurons decussate (cross over to the opposite side) in the brain stem or spinal cord before ascending to the ventral posterior nucleus of the thalamus
  • Thus, all somatic sensory information from one side of the body reaches the thalamus on the opposite side

SENSORY TRACTS OF SPINAL CORD

Consists of :

  • Spinothalamic tracts
    • Lateral
      • pain & temperature
    • Anterior
      • light touch & pressure
  • Dorsal column tract
    • deep touch & pressure
    • proprioception
    • vibration sensation
  • Spinocerebellar tract
    • posture & coordination

THIRD ORDER NEURON

  • arise from the thalamus and pass through the internal capsule
    • thalamocortical fibres pass through the medial part of the posterior limb of the internal capsule
  • Enters the postcentralgyrus
    • sensory cortex of the cerebrum
    • behind the central sulcus
    • Same homunculus arrangement
      • more sensitive areas in the body have a greater representation

Flow of arrangement of the dorsal column tracts:

1st order neuron:

  • Arise from the sensory receptors of the body
  • Fibres enter the dorsal column of the SAME side (post column of spinal cord)
    • ascends to the medulla oblongata
  • Enters medulla oblongata

2nd order neuron:

  • Starts at the gracile&cuneate nucleus of the medulla oblongata
  • crosses to the opposite side of the medulla oblongata
  • Ascends through the brain stem
  • Ends in the ventral posterolateral nucleus of the thalamus

3rd order of nucleus:

  • Arise from the thalamus
  • Pass through the internal capsule
  • Reaches the postcentralgyrus

1st order neuron:

  • Arise from sensory receptors of the body
  • The fibres enter the white mater and ends at the substantiagelatinosa

2nd order neuron:

  • The fibres of 1st order neuron synapse with the 2nd order neuron at the substantiagelatinosa
  • fibres then cross to the opposite side
    • Pain & temperature fibres
      • enters the lateral spinothalamic tract
    • Light touch & pressure fibres
      • enters the anterior spinothalamic tract
  • tracts ascends to brainstem
    • to medulla oblongata, pons and midbrain
    • tracts flattened in the brainstem
  • Reaches the ventral posterolateral nucleus of the thalamus

3rd order neuron:

  • arise from the thalamus and pass through the internal capsule
  • Enters the postcentralgyrus
    • sensory cortex of the cerebrum
    • behind the central sulcus
    • Same homunculus arrangement
      • more sensitive areas in the body have a greater representation

COMMON DISORDER AFFECTING OUR SENSES
(GENERAL & SPECIAL SENSE)

Hyperalgesia

  • a condition where a person develops an increased sensitivity to pain.
  • Signs & Symptoms
    • Increasingly extreme reaction to painful stimuli without any new injuries or worsening of a medical condition.
    • Increasing pain medication will not reduce the amount of pain a person feels
    • Sometimes, increasing the pain medication makes the person’s pain worse.

Meniere’s Disease

  • a disorder of the inner ear
  • can develop at any age, but more likely to happen to adults between 40 and 60 years of age
  • CAUSES:
    • Build up of endolymph in the labyrinth
    • Factor affect the fluid ( endolymph ) :
    •    – Improper fluid drainage, perhaps because of a blockage or anatomic
    •      abnormality
    •    – Abnormal immune response
    •    – Allergies
    •    – Viral infection
    •    – Genetic predisposition
    •    – Head trauma
    •    – Migraines
  • Signs & Symptoms
    • Recurring episodes of vertigo
    • Hearing loss
    • Ringing in the ear (tinnitus)
    • Feeling of fullness in the ear

Ageusia

  • Inability to taste, particularly the loss of ability to detect sweetness, sourness, bitterness and saltiness
  • CAUSES:
  • Neurological damage – Tissue damage to the nerves that support the tongue can cause ageusia, especially damage to the glossopharyngeal nerve
  • Deficiency of vitamin B3 (niacin) and zinc
  • Signs and Symptoms
  • Dry mouth

DISEASE/ PROBLEM RELATED TO SENSORY TRACT OF SPINAL CORD, BRAIN STEM AND SECOND ORDER NEURON

SPINAL CORD TUMOR

  • cause weakness,paralysis or numbness.
  • People with numbness may be unable to feel light touch, pain, temperature or vibration.

BROWN-SEQUARD SYNDROME

  • Caused by- damage to one half of the spinal cord.
  • Resultingin
    • paralysis and loss of proprioception on the same side as the injury or lesion.
    • loss of pain and temperature sensation on the opposite side as the lesion.

ANTERIOR SPINAL ARTERY SYNDROME

  • Characterized by loss of motor function below the level of injury, loss of sensations carried by the anterior columns of the spinal cord ( pain and temperature), and preservation of sensations carried by the posterior columns ( fine touch, vibration and proprioception ).

DISEASE/ PROBLEM RELATED TO THIRD ORDER NEURON

APRAXIA

  • characterized by the loss of the ability to carry out learned purposeful movements, despite knowing what is expected and having the physical ability and desire to do so.
  • CAUSES of acquired apraxia are:
    • Brain tumor
    • Condition that causes gradual worsening of the brain and nervous system (neurodegenerative illness)
    • Dementia
    • Stroke
    • Traumatic brain injury
  • SIGNS & SYMPTOMS
    • Distorted, repeated, or left out speech sounds or words. The person has difficulty putting words together in the correct order.
    • Struggling to pronounce the right word
    • More difficulty using longer words, either all the time, or sometimes
    • Ability to use short, everyday phrases or sayings (such as “How are you?”) without a problem
    • Better writing ability than speaking ability

CENTRAL PAIN SYNDROME

  • caused by damage to or dysfunction of the central nervous system (CNS), which includes the brain, brainstem, and spinal cord. 
  • results from damage to the pain-transmission pathway from the level of the spinal cord up to the cortex, the grey matter that covers the cerebral hemispheres.
  • can be caused by stroke, multiple sclerosis, tumors, epilepsy, brain or spinal cord trauma, or Parkinson’s disease. 

ATAXIA

  • A neurological disorder in coordination and balance.
  • Lack of coordination of muscle movements resulting in the impairment or inability to perform voluntary activities. 
  • Many conditions can cause ataxia, including alcohol abuse,  certain medications, stroke, tumor, cerebral palsy, brain degeneration and multiple sclerosis.
  • Inherited defective genes also can cause the condition.