Consciousness (Physiological Point of View)

transcript

by:Alvin Lee Jin Wen

Ahmad Sallehuddin Mukhtarruddin

Introduction• Generally consciousness is the relation between the

mind and the world it interact.• It is difficult to really define consciousness as it can

be view from :1. Philosophical point of view2. Scientific (physiological point of view)

`• The study of human consciousness was long considered outside

the province of science , more appropriate as a subject for philosophy or religion. One reason for this view is consciousness is both broad-encompassing our awareness of ourselves and experiences- and subjective.

• Over the past decade however neuroscientist began studying consciousness using MRI , PET scan etc.

• It is now possible to compare activity in the human brain during different state of consciousness – e.g. before/ after seeing an object.

• These studies does not pinpoint a “consciousness centre” in the brain rather they offer an increasingly detailed picture of how neuronal activity correlates with consciousness experience.

• Physiologically, we opt to find Neuro-Correlates of Consciousness (NCC) to explain the consciousness phenomenon.

1. Reticular Activating System (RAS)

• “The system of cells of the reticular formation of the medulla oblongata that receives collaterals from the ascending sensory pathways and projects to higher centres ; they control the overall degree of CNS activity including wakefulness , attentiveness , and sleep” Saunders Comprehensive Veterinary Dictionary 3rd Ed.

• It used to be thought that wakefulness depended only on the direct reception of afferent (sensory) stimuli at the cerebral cortex

• Physiologists had proposed that some structure deep within the brain controlled mental wakefulness and alertness.

• RAS Comprised of the– Motor system (reticulo-spinal system)– Sensory systems (RAS)– Vital centres

• The RAS stimulates the whole brain to cause arousal (wakefulness)– It’s output is suppressed in sleep & comaStimulated by :

• Input from the cortex (corticofugal fibres)• OREXINS

– Peptides released by hypothalamic neurons just before waking

2. Medical Approach Assessing Consciousness

• Derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs.

• The medical approach focuses on the amount of consciousness a person has: in medicine, consciousness is assessed as a "level" ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end

2 ways of assessing consciousness in medicine:1.Simple procedure that requires minimal training.• 1.1 Asking whether the patient is able to move and react to

physical stimuli• 1.2 Asking whether the patient can respond in a meaningful

way to questions and commands• 1.3 Asked for name, current location, and current day and

time• A patient who can answer all of these questions is said to be

"oriented times three" (sometimes denoted "Ox3" on a medical chart), and is usually considered fully conscious.

2.A more complex procedure that requires substantial expertise.• 2.1 Known as a neurological examination and is usually

carried out by a neurologist in a hospital setting.• 2.2 Examination runs through a precisely delineated series of

tests, beginning with tests for basic sensor motor reflexes, and culminating with tests for sophisticated use of language.

• 2.3 Glasgow Coma Scale which yields a number in the range 3—15, with a score of 3 indicating brain death (the lowest defined level of consciousness), and 15 indicating full consciousness.

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IMPAIRMENT OF CONCIOUSNESS

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How conciousness may be impaired?brain’s ability to adjust its activity and consciousness levels can be impaired in several ways:- Severe sleep deprivation- After a seizure (Epilepsy)- both cerebral hemispheres are suddenly

and severely damaged- the reticular activating system

malfunctions- blood flow or the amount of nutrients (such

as oxygen or sugar) going to the brain decrease

- When toxic substances impair the brain (liver & kidney failure)

- Drugs-morphine-diazepam-antipsychotic drugs

Periods of impaired consciousness can be short or l o n g . The level of impairment can range from slight to severe:

a)Lethargy- slight reduction in alertness or clouding of consciousness. People tend to be less aware of what is happening around them and to think more slowly.

b)Obtundation- moderate reduction in alertness or clouding of consciousness.

c) Stupor- excessively long or deep sleep-like state. A person can be aroused from it only briefly by vigorous stimulation, such as repeated shaking, loud calling, pinching, or sticking with a pin.

d) Coma- state of complete unresponsiveness. A person cannot be aroused at all. A person in a deep coma lacks even the most basic responses, such as avoidance of pain. Reflexive behavior present

How conciousness may be impaired?brain’s ability to adjust its activity and consciousness levels can be impaired in several ways:- Severe sleep deprivation- After a seizure (Epilepsy)- both cerebral hemispheres are suddenly

and severely damaged- the reticular activating system

malfunctions- blood flow or the amount of nutrients (such

as oxygen or sugar) going to the brain decrease

- When toxic substances impair the brain (liver & kidney failure)

- Drugs-morphine-diazepam-antipsychotic drugs

Periods of impaired consciousness can be short or l o n g . The level of impairment can range from slight to severe:

a)Lethargy- slight reduction in alertness or clouding of consciousness. People tend to be less aware of what is happening around them and to think more slowly.

b)Obtundation- moderate reduction in alertness or clouding of consciousness.

c) Stupor- excessively long or deep sleep-like state. A person can be aroused from it only briefly by vigorous stimulation, such as repeated shaking, loud calling, pinching, or sticking with a pin.

d) Coma- state of complete unresponsiveness. A person cannot be aroused at all. A person in a deep coma lacks even the most basic responses, such as avoidance of pain. Reflexive behavior present

Coma-brain oxygen utilization is below normal resting levels

(in sleep, the brain is active and oxygen consumption is comparable to the waking state)

ComaCaused by:

A)traumaB)tumoursC)metabolic disorders

-hypoglycaemia (hyperosmolar coma)-drug overdose-liver and kidney failure-fluids & electrolytes imbalance

-hypernatraemia (>Na+)-hypokalaemia (<K+)-water intoxication

-myxoedema (hyperthyroidism) D)Depression of the reticular activating system (RAS)

Clinically assessed using Glasgow Coma Scale (GCS)Four Score Coma Scale

eye & motor responsesbrain stem reflexesrespiration. Total unresponsiveness to sensory stimuli for an extended period

1 2 3 4 5 6

Does not open eyes

Opens eyes in response to painful stimuli

Opens eyes in response to voice

Opens eyes spontaneo-usly

N/A N/A

VerbalMakes no sounds

Incomprehensible sounds

Utters inappropriate words

Confused, disoriented

Oriented, converses normally

Makes no movements

Extension to painful stimuli (decerebrate response)

Abnormal flexion to painful stimuli (decorticate response)

Flexion / Withdrawal to painful stimuli

Localizes painful stimuli

Obeys commands

Glasgow Coma Scale

Severe, with GCS ≤ 8Moderate, GCS 9 - 12Minor, GCS ≥ 13.

Consciousness (Physiological Point of View)

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