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ISLAMIC MEDICAL EDUCATION RESOURCES 04

0002-THE NERVOUS SYSTEMS (JIHAZ AL ASABI)

Lecture to 2nd year medical students on 12th February 2000 at the Kulliyah of Medicine, International Islamic University, Kuantan by Professor Omar Hasan Kasule Sr.

OUTLINE

1.0 ANATOMY and PHYSIOLOGY

A. Qur'anic Concepts

B. Central Nervous Systems

C. Peripheral Nervous System

D. Neurones And Synapses

E. Protection

 

2.0 INFORMATION INPUT,  PROCESSING, STORAGE, and OUTPUT

A. Sensory Modalities:

B. Sensory Receptors:

C. Sensory Stimuli:

D. Mapping Of Origin Of The Sensory Stimulus:

E. Processing Capacity:

 

3.0 HUMAN ACTIONS

A. Encephalization:

B. Motivation:

C. Autonomic Nervous System:

D. Motor Function:

E. Human Freedom Of Action:

 

4.0 HUMAN BEHAVIOR

A. Electro-Chemical Basis Of Human Behavior:

B. Genetic Basis Of Human Behavior:

C. Cultural Basis Of Human Behavior:

D. Human Responsibility For Behavior:

E. Artificial Pharmacological Effect On Human Behavior:

 

5.0 PATHOLOGY

A. Diseases Of The Brain

B. Diseases Of Cranial Nerves

C. Diseases Of The Spinal Cord

D. Diseases Of Peripheral Nerves

E. Diseases Of The Autonomic Nerves

 


1.0 ANATOMY and PHYSIOLOGY

A. QUR'ANIC CONCEPTS RELATING TO FUNCTIONS OF THE NS

FUNCTIONAL DESCRIPTION

The Qur’an did not describe the anatomy of the nervous system in a direct and explicit way but it dwelt on the functions of the nervous system. The functions of thought, memory, forgetting, and emotions were described in association with 4 Qur’anic phenomena: naasiyat, lubb, qalb/nafs, fuaad, and dhihn. These four can not be located anatomically.

 

NAASIYAT

The Qur’anic concept of nasiyat:  (11:56, 55:41, 96:15-16).

LUBB

Lubb & ayaat al llaah 3:19

Lubb  & ‘ibrat 12:111

Lubb & tadhkirat 13:19

Lubb & tadabbur 38:29

 

QALB

Importance of qalb: The human has only one qalb, ‘adam ta’addud al qalb (33:4). an indication that it is a master organ or function that directs others  Qalb and intention/purposive action (33:5). Qalb and responsibility, qalb & mas uliyat (2:225, 33:5).

 

Emotional functions of the qalb: Ulfat al qalb (3:10,  9:60). Ra afat al qalb (57:27). Rahmat al qalb (3:159, 57:27). Tanafur al quluub (14:59). Hasrat al qalb (3:156). Khawf al qalb (3:151, 59:3). Riibat al qalb (9:45, 9:110). Zaygh al qalb (3:7). Ghaldhat al qalb (3:159).

 

Intellectual functions of the qalb: Tadabbur al qalb (6:113 … 59:9). Tadabbur min al qalb (47:24), Tadhakkur al qalb (50:37). Hijaab al qalb (6:25 … 41:5). Ru uyat al qalb (22:48, 53:11-12). Dhann al qalb al sayyei (48:12). ‘Aql al qalb (22:46). Qalb & ‘ilm (2:97, 47:24). Qalb & fiqh (7:179, 63:3).

 

Sensory functions of qalb: Qalb & hawaas (2:7, 57:37). The eyes sleep but the qalb does not.

 

FUAD

Importance: Accountability,  suaal al fuaad (17:36). Ni’imat al fuaad (16:78)

 

Emotional functions: Faragh al fuaad (28:10)

 

Intellectual functions:

 

Sensory functions: Isighaau al fuaad (6:113). Fuad & samau (23:78). Fuaad & basar (23:78, 32:9, 46:26, 67:23)

 

Moral guidance/misguidance: Kadhb al fuaad (53:11). Thabaat al fuaad (11:120, 25:32). Hawa al fuaad 14:37.

 

Taqallub al fuaad (6:110).

 

DHIHN

Udhn and wa’ay 69:12

 

B. CENTRAL NERVOUS SYSTEMS

INTRODUCTION

The central nervous system (CNS): CNS consists of the brain and the spinal cord. There are 100 billion neurones in the brain. The brain has three parts: forebrain, mid-brain, and hind-brain.  CNS controls and co-ordinates body activity in response to internal and external environmental stimuli. It correlates sensory information, motor co-ordination, memory, and intellectual function. The modus operandi is sensory input followed by processing and then action.

 

THE BRAIN

Size of the brain and area: The adult human brain is 2.5% of body weight. Male have a bigger brain because of bigger muscle mass. There is no relation between brain size and intelligence. The total cortical surface area is 2200 square meters. It is increased by the gyri and sulci. The human brain is superior to that of other mammals because it has the highest brain to body weight ratio. The ratio of the brain to the weight of the body is highest in infancy when the brain is the most rapidly-growing organ. It falls progressively after the brain has completed its growth. In old age there is atrophy of brain cells and decrease of brain weight.

 

Parts of the brain:  The brain has 3 main areas: cerebrum, cerebellum and the medulla oblongata. The cerebrum is responsible for recognition, memory, imagination, creative thoughts, and abstract reasoning. The main functional areas of the cerebrum are: olfactory, optical, auditory, sensory input, motor. There is also somatotopic representation of parts of the body. The cerebellum coordinates activity of voluntary muscles as well as posture and equilibrium. The cerebellum is mid-way between the cerebral cortex whose actions are very voluntary and the medulla oblongata whose actions are mostly involuntary. The medulla oblongata has several important centers: vasomotor (BP control), cardiac (heart rate and heart force), respiratory, vomiting, temperature, posture and balance, and chemoreceptors. The hypothalamus controls homeostatic mechanisms. The pituitary, directly under hypothalamic control, is the master gland of the body.

 

Histology: The cerebrum has gray and white matter. A normal individual has 10E11 - 10E13 neurones in the brain. These provide a large ability to store and process a lot of information. Brain cells are either neurones or glial cells. Glial cells are supportive or connective cells. The following are the commonest types of glial cells: schwann cells, oligodendrocytes, microglia, epindyma, and astrocytes.

 

Hierarchy: The 3 parts of the brain parallel the hierarchy of sophistication. The least sophisticated is the medulla, the most sophisticated is the cerebrum, and the cerebellum is in between. The medulla controls automatic largely unconscious but essential functions. The cerebrum deals with intellectual functions. The human cortex is more sophisticated than that of animals. The human also relies less on the cerebellum and the medulla than other animals. The human cortex is able to override the autonomic functions of the medulla and cerebellum.

 

Parity: The brain follows the principal of parity in having two hemispheres. In any one individual only one of the hemispheres is dominant. One hemisphere can take over the functions of the other in cases of damage.

 

Specialization and mapping: Each part of the brain has specific sensory, motor, and informational processing functions. The science of brain mapping has enabled us to recognize and localize those areas.

 

Blood and oxygen supply: The brain is very important and therefore has special circulatory and metabolic systems. These must be very reliable because any malfunction of the brain especially the cortex has far more reaching effects than malfunction of other parts of the body. The brain is 2% of body-weight but receives 15% of cardiac output and 20% of oxygen consumption.. The brain uses 103 g of glucose per day which is equivalent 3.4 liters of oxygen a day. The brain is very sensitive to hypoxemia.

 

Metabolism: Of all tissues the brain is the most dependent on glucose as a source of energy. Lipids have no metabolic role in the brain. The brain is thus very sensitive to hypoglycemia.

 

C.     PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system (PNS): The PNS is an extension of the CNS in the organs and tissues. The PNS is largely under the control and direction of the CNS. PNS consists of 31 pairs of spinal nerves from the spinal cord and 12 pairs of cranial nerves. It collects information that is transmitted eventually to CNS. It conveys CNS commands to the periphery. Some parts of the PNS like intestinal plexuses are autonomic and are not under the influence of CNS.

 

D. NEURONES AND SYNAPSES

Energy transduction: Neurones and synapses illustrate the phenomenon of transduction of energy. Neurones are excited by electrical, chemical, and mechanical stimuli. The action potential is a propagated electrical charge. Nerve conduction is slower than the electrical current (why?). The action potential is all-or-none. It requires a threshhold stimulus. The speed of conduction and excitability of nerve fibers increase with fiber diameter. Myelinated fibers conduct faster than non-myelinated ones.

 

Types of neurones: Neurones vary in structure and function. Nerve fibers can be divided into three categories depending on their speed of conduction: alpha are the fastest and are myelinated. Beta are myleinated but not as fast as aplha. Theta are the slowest and are non-myelinated.

 

Synapses and neuro-transmitters: Neurotransmitters help transfer impulses across synapses. Among the neurotransmitters are: acetylcholine, dopamine, nor-epinephrine, 5HT, adenosine, glutamate, GABA, segothionine, glycine, aspartate.

 

E. PROTECTION

Because of its importance, CNS has extra protection from mechanical, chemical, and microbial injury. Extra protection becomes necessary because the nervous system is very important repair mechanisms are limited. There is no renegeration of damaged neurones in the CNS. Only limited regeneration is possible in the PNS.

 

Mechanical injury could be due to direct mechanical trauma. It could also be due to gravity or acceleration forces. Mechanical protection consists of the bony cranium, the vertebral column, the meninges, and fluids. The meninges provide additional mechanical protection. Three layers of meninges (dura mater, pia mater, and arachnoid) ensure protection from sudden movements. The CSF is protective by cushioning CNS from sudden or violent mechanical movements.

 

Chemical injury is due to toxins. The blood-brain barrier protects the sensitive neurones from endogenous and exogenous toxins, ensures that the environment of the neurones is constant, and prevents escape of neurotransmitters into the general circulation. It also makes it difficult for infective organisms to enter the brain. The blood-brain barrier protects the brain cells from sudden changes in the chemical environment.

Microbial injury could be due to infective organisms: The blood brain barrier provides some protection against entry of infective organisms.

 

2.0 INFORMATION INPUT,  PROCESSING, STORAGE, and OUTPUT

A. SENSORY MODALITIES:

PRINCIPAL SENSORY MODALITIES:

The principal sensory modalities in humans are: vision, hearing, smell, taste, acceleration (rotational & linear), touch-pressure, temperature, pain, joint position (propioception), muscles (tension, length), arterial blood pressure, central venous pressure, lung inflation, arterial P-O2, arterial P-CO2, glucose concentration, pH of CSF, and osmotic pressure of plasma.

 

HIERARCHY OF SENSORY MODALITIES:

Some senses are higher than others. The criterion used is the proportion of sensory input from the environment. Vision and hearing are in this sense are higher senses and are the most frequently mentioned by the Qur’an. Smell is not as important in humans as it is in other animals. Animals rely more on their sense of small than do humans and have a relatively larger olfactory area in the brain. Insects for example use pheromones to communicate. Studies of pheromones in humans are not yet conclusive.

 

B. SENSORY RECEPTORS:

Human sensory receptors can be classified as: exteroceptive, interoceptive, and propioceptive. Some receptors are in direct contact with the external environment (extero-ceptors) such as the 5 major senses: vision, hearing, taste, smell, and touch or pressure. Some receptors are in the internal environment (inter-ceptors) such as osomoreceptors, baroreceptors, and chemoreceptors. Information from both the internal and external environments is picked up by these receptors. Propioceptors in muscles and joints detect movements and provide information about position in space.

 

C. SENSORY STIMULI:

FORMS OF SENSORY STIMULI:

The sensory stimulus is in the form of energy (mechanical, thermal, photo, electromagnetic, or chemical). This energy is eventually transformed into electro-chemical action potentials in the sensory neurones. In the end all sensory stimuli have the same common pathway. The brain is able to distinguish them depending on the efferent neurones and the intensity of the message.

 

CONCEPT OF THRESHHOLDS:

It is part of Allah’s design to protect the CNS from unnecessary overstimulation that there is a threshhold stimulation that results into an action potential. Sub-threshold stimuli are thus ignored. The threshold level varies by sensory modality and even within the same sensory modality by location. All these variations are determined by the relative importance of the sensory information.

 

INTENSITY AND DURATION OF STIMULUS:

Detection of changes in intensity of sensory stimuli varies by sensory modality and duration. If a stimulus is continuous there is adaptation. Rate receptors incorporate time of events.

 

D. MAPPING OF ORIGIN OF THE SENSORY STIMULUS:

A neurone from a particular region of the body send its stimulus to a known part of the brain which enables the brain to locate the source of the stimulus. However in cases of referred pain, this does not apply. The explanation is related to embryological dermatomes. Referred pain is a blessing from Allah. It can enable location of internal pain from the surface of the body.

 

E. PROCESSING CAPACITY:

The massive information input into the brain is processed rapidly with no mistakes. Study of the processing speeds of modern computers makes us appreciate the power of Allah. However sophisticated they may be they do not even approach the processing capacity of the human brain.

 

3.0 HUMAN ACTIONS

A. ENCEPHALISATION:

Human intellectual superiority is explained by the greater role of the cortex in many functions. The cortex controls higher functions of human thought: learning, memory, judgment, and language. In general anesthesia and other situations such as drug and alcohol intoxication in which the psyche is altered, the cortex is depressed first affecting the higher functions that distinguish humans from animals.

 

B. UNCONSCIOUS ACTION

The human organism is such a complicated system with millions of activities. If all these activities were part of the conscious will, the system would be overwhelmed. Humans must have the humility to know that they have very little conscious control over their bodies. Humans do not consciously control individual muscle movements, glandular secretions, or metabolic activities.

 

C. AUTONOMIC ACTION:

The existence of the autonomic nervous system enables many background life-sustaining activities to continue without sensory input into the cerebrum. Most neuronal sensation and activity is not under conscious control. It is part of the autonomic nervous system (ANS). ANS consists of sympathetic, parasympathetic, and the enteric NS. It is characterized by rapid, automatic, reflex response with no conscious control. The sympathetic and parasympathetic systems have opposite effects and are finely balanced. This is an illustration of the Qur’anic concept of tadaf’u without which human physiology and human civilization would collapse.

 

D. MOTOR FUNCTION:

NEURO-MUSCULAR UNIT

The functional unit of the neuromuscular unit is the motor unit which consists of: the lower motor neurone that arises from the spinal cord, the axon of the lower motor neurone, and the multiple muscle fibers that are innervated. Muscles with fine movements have a higher neurone to muscle ratio (1:10) than those with relatively coarse and stereotypees movements (1:2000). Innervation of muscles: Each muscle has its neurones. The innervation is embryologically derived (dermatomes).

 

TYPES OF MUSCLES

somatic, vesceral, and neuro-endocrine.

 

CONTROL OF STRIATED MUSCLES:

Skeletal muscles are controlled at three levels: spinal cord in simple reflexes, brain stem, and the cerebral hemisphere. Reflexes are automatic muscular contractions that protect the body. They are at the spinal level without cerebral involvement. Examples are the knee jerk and the withdrawal reflex.The spinal reflexes are: flexor/withdrawal, crosse-extensor, stretch (myotatic), and tendon (inverse stretch reflex). There is mapping of muscles in the motor cortex. Fingers, lips, the tongue, and vocal cords have more neurones than the elbow, trunk and ankle. The cortex is aware of the autonomic or reflex activity of muscles and can intervene to override them.

 

E. HUMAN FREEDOM OF ACTION:

The Qur'an mentions that the human has freedom of action (p. 841 4:66, 17:18-19, 17:84, 41:40, 73:19, 74:37, 76:29, 78:34, 81:28, 92:4-10).

 

Human freedom of action is limited. The observation that most mechanical and metabolic activities in the body are under autonomic, reflex, and endocrine control is further indication of the limitations of human will in actions. The human is not able to control many of the emotions.

 

4.0 HUMAN BEHAVIOUR

A. ELECTRO-CHEMICAL BASIS OF HUMAN BEHAVIOR:

ORGANIC BASIS:

Many phenomena in the nervous system related to behavior can be explained by organic factors. More are likely to be explained in the future. The un-explained phenomena reflect the impact of nafs, the essence of the human. The nafs can over-ride the organic factors. Drugs react with CNS transmitters to produce behavior or mental state changes. Thus proves that human behavior has a chemical basis. Neurohormones also control behavior.

 

RAGE:

Rage and aggression have an organic basis. Noradrenaline stimulates rage in the amygdala. Serotonin inhibits rage through the forebrain. Acetylcholine is involved in rage at the hypothalamic level. The directive of the prophet to sit down or get wudhu when angry is understood I this sense. Wudhu and sitting down may have a relaxing effect mediated either directly or through the cerebral cortex.

 

MOOD:

Normal mood is when the state of the mind is in tune with the environment. The affective state is a balance between amine-containing and actylcholine-containing neurones in the brain-sotem and the forebrain.  Depression and mania are imbalance disorders. The following chemicals play a role in mood: serotonin, catecholamines, cyclic AMP, and acetylcholine.

 

 

DIFFERENCES AMONG PEOPLE:

The observed differences in behavior and emotional reactions between men and women may be explainable on the basis of neuro-hormonal differences. Differences among ethnic groups could also be similarly explained.

 

B. GENETIC BASIS OF HUMAN BEHAVIOR:

The anatomical and chemical factors that affect human behavior are genetically controlled. Genetic control of behavior can not be perfect or over-riding because that would nullify any human responsibility for misbehavior. Processes originating in the nafs and qalb can override the genetic and neuro-homoral mechanisms to impose human will on behavior. This override usually acts through the cortex but other mediums are possible.

 

A dangerous trend in genetic research is the discovery of specific genes for human sexual and addictive misbehavior. Genes have been defined for homosexuality and alcohol addiction. If the results of these studies are interpreted in a secular way, they will disempower humans and prevent them from struggling to improve by fighting evil promptings of their nafs.

 

C. CULTURAL BASIS OF HUMAN BEHAVIOR:

Early learning and conditioning have an imprint on human behavior. Early learning experiences in the family may act at the cognitive level or may actually impact the architecture of neuronal networks in the brain during the plastic phase.

 

D. HUMAN RESPONSIBILITY FOR BEHAVIOR:

Although there are anatomical and chemical bases for human behavior, humans still have responsibility for their actions. This is because the nafs can over-ride the chemical and anatomical factors. Denial of this over-ride turns humans into animals with no responsibility for actions.

 

E. ARTIFICIAL PHARMACOLOGICAL EFFECT ON HUMAN BEHAVIOR:

Alcohol and other pharmacologically active substances affect human behavior. More research is needed on the impact of the ordinary diet that people take which may explain some culturally-determined patterns of behavior. The diet or environmental pollutants may have an effect on the internal chemical milieu affecting behavior of individuals or groups in specific ways.

 

5.0 PATHOLOGY

A. DISEASES OF THE BRAIN

PATHO-PHYSIOLOGICAL COMPLICATIONS

 (a) Herniation due to increased ICP (b) cerebral edema (c) hydrocephalus, enlargement of ventricles.

 

DEVELOPMENTAL ANOMALIES

Neural tube defects: anencephaly, encephalocele, spina bifida, myelomeningocele.

 

Fore-brain abnormalities: Polymicrogyria is loss of convolutions. Megalencephaly is increase of brain volume. Agenesis of the corpus callosum.

 

Posterior fossa abnormalities: Arnold-Chiari malformation.

 

Syringomyelia and hydromyelia

 

PERINATAL BRAIN INJURY:

(a) Cerebral palsy is non-progressive neurologic motor deficit with origin in the perinatal period. (b) intraparenchymal hemorrhage.

 

TRAUMATIC INJURY

 (a) Skull fracture. (b) Parenchymal injuries (concussion, confusion and laceration, white matter injury). (c) Traumatic vascular injury: epidural hematoma, subdural hematoma, sub-arachnoid hemorrhage

 

DEGENERATIVE

CVD: hypoxia, ischemia, and infarction. HT intracerebral hemorrhage.

Dementias (Alzheimer's and Pick's), Parkinson's disease, Huntington's disease, Friedrich's  Ataxia, Ataxia telengiectasia

Demyelinating Disease: The frequency of MS increases with distance from the equator

 

INFECTIONS

 (a) meningitis (acute bacterial, viral) (b) Brain abscess (c) sub-dural empyema (d) chronic meningo-encephalitis (TB, chronic meningitis, neuro-syphilis), (e) viral encephalitis (arbo virus, HSV, VZ, CMV, polio, rabies, HIV). (f) fungal

 

METABOLIC

Inborn errors of metabolism: Leukodystrophies eg Krabbe's disease

Toxic conditions: Vitamin deficiencies eg B-1 and B-12, carbon monoxide poisoning, methanol, ethanol, methotrexate, radiation.

Metabolic disorders: Hypoglycemia, hyperglycemia, hepatic encephalopathy

 

NEOPLASTIC

Tumors: astrocytoma, oligodendroglioma, ependynoma

 

B. DISEASES OF CRANIAL NERVES

OPTIC NEURITIS

Vitamin

Toxic

Infective

TRAUMA eg Bell’s palsy

 

C. DISEASES OF THE SPINAL CORD

 

D. DISEASES OF SPINAL NERVES

INFLAMMATORY NEUROPATHIES

(a) Acute inflammatory demyelinating polyradiculoneuropathy (Guillain-Barre) 1-2 cases/100,000. Two thirds of the cases are preceded by influenza-like illness. (b) Chronic inflammatory demyelinating polyradiculoneuropathy

Infectious polyneuritis: (a) leprosy (b) diphtheric neuropathy

 

HEREDITARY NEUROPATHIES:

Hereditary motor and sensory neuropathy

 

ACQUIRED METABOLIC AND TOXIC NEUROPATHIES:

(a) adult-onset diabetes mellitus (b) renal failure (uremic neuropathy) (c) chronic liver disease (d) chronic respiratory insufficiency (e) Thyroid dysfunction (f) vitamin deficiency (thiamine, B-12, B-6, E) (g) malignant infiltration (h) toxic: ethanol and organophosphates

 

TRAUMATIC:

 

DEGENERATIVE

Axonal degeneration leads to atrophy of muscle atrophy (denervation atrophy). Proximal stumps of degenerated axons can regenerate leading to some functional recovery. Muscles can be renervated.

 

E. DISEASES OF THE AUTONOMIC NERVES

Professor Omar Hasan Kasule Sr. February 2000