NERVOUS SYSTEM

Dr. A. R. JoshiPROFESSOR OF

PHYSIOLOGY

Nervous System

Central Nervous System

• To control voluntary and conscious functions e.g. voluntary movements, appreciation of sensations etc.

Autonomic Nervous System

• To control in-voluntory functions e.g. beating of heart, movements of intestine etc.

Central Nervous System

• Anatomical Division :

Brain & twelve pairs of cranial nerves

Spinal Cord & thirty one pairs of spinal nerves

Brain• Forebrain - Cerebrum

- Thalamus - Hypothalamus

• Midbrain• Hindbrain - Pons

- Medulla - Cerebellum

(Grey matter outside & white matter inside)

Brain…

• Blood Supply : 700-800 ml/minute by Circle of Willis.● Brain is covered by three meninges.● Lymph is replaced by CSF, present in ventricles of brain & subarachnoid space.● There exits blood brain barrier.

Spinal Cord

• Parts : - Cervical - Thoracic - Lumbar - Sacral

Gray matter inside with anterior and posterior roots. White matter outside with anterior, lateral and posterior columns.

Physiological Division

• Sensory component

Receptor Sensory nerve Ascending tract Thalamus Parietal lobe

• Motor ComponentFrontal lobeDescending tractAnterior horn cellMotor nerveMuscle

Neuron• A functional unit of nervous system

• One way conduction in neuron

• Cell body is sensory

• Axon is motor

• Velocity of impulse depends upon

- Myelination

- Diameter

Synapse• Functional junction between two

neurons

•Transmission is via Neurotransmitter

•Excitatory NTs are Ach, Adr, NA

•Inhibitory NTs are Serotonin, GABA,

Dopamine, Glycine

•(Inhibition can be presynaptic or postsynaptic)

Properties of Synapse1. One way conduction

2. Fatigue

3. Delay

4. Excitation or Inhibition

5. Reciprocal inhibition or cross extensor reflex

6. Reverberation

7. Irradiation

Functions of Spinal cord1. Reflex action

2. Ascending tracts (Sensory)

3. Descending tracts (Motor)

4. Origin to ANS

5. Inhibitory neurons with different functions

Tracts in Spinal Cord

Tracts in Spinal cord

Dorsal Column Pathways

• Tract of Gall (Fasciculus Gracilis)

(Carrying fine sensations from lower extremities & trunk)

• Tract of Burdach (FasciculusCuneatus) (Carrying fine sensations from upper extremities & chest)

Dorsal Column Pathways…

Dorsal root ganglion (1st ordered neuron)↓

Dorsal column tract in spinal cord on the same side

↓

Nucleus Gracilis & Cuneatus (2nd ordered neuron)

(Crossing to opposite side) ↓

Medial lemniscus (Brain Stem) ↓

Thalamus (3rd ordered neuron) ↓

Parietal lobe (Sensory Cortex)

Ascending Tracts (Sensory)

1.Dorsal column tracts (Fine sensations)

• Fine touch,

• Tactile localization,

• Tactile discrimination

• Vibration sense,

• Sense of stereognosis,

• Joint position, Muscle movement

sense (Proprioception)

Spinothalamic Pathways

1. Lateral Spinothalamic Tract (Carrying pain & temp. sensation)

2. Ventral Spinothalamic Tract (Carrying crude touch & pressure sensation)

Spinothalamic pathways…

Dorsal root ganglion (1st ordered neuron) ↓

SG cells (2nd ordered neuron) in spinal cord

↓ (Crossing to opposite side)

↓Lateral & Ventral Spinothalamic tract

↓Thalamus (3rd ordered neuron)

↓ Parietal lobe (Sensory Cortex)

2. Spinothalamic tracts (Crude sensations)

• Crude touch,

• Pressure,

• Temperature,

• Pain

• Itch

• Sexual sensations

Damage to Sensory Tracts

1.Damage to Dorsal column tract Sensory ataxia

Loss of fine sensations Loss of vibration sense Astereognosis on the same side below the level of lesion

2. Damage to Spinothalamic tract

Crude sensations lost on opposite side

below the level of lesion

Descending Tracts (Motor)1. Pyramidal tracts:

Cortico-spinal fibers: Control of voluntary movements especially skilled movements of distal joints (e.g. writing, painting) and voluntary control of bladder and bowel

Corticonuclear fibres: Control of facial movements, eye-ball movements, mastication and speech.

Pyramidal tracts (Cortico-spinal)

Motor cortex (Broadman's area 4,6 and 8)

↓Corona radiata

↓Internal capsule (Common site of

damage)↓

Crus of Mid brain↓

Pyramids of Medulla - Crossing on opposite side

↓Crossed lateral Cortico-spinal tract

Hemiplegia

•Common site of damage- Internal capsule (damage to Charcot’s artery)

•Paralysis on opposite side

•Three stages seen

•Second stage-typical UMN type of paralysis

•Aphasia may be associated

•Supra-nuclear facial nerve palsy

Extra-pyramidal Tracts

1. Reticulo-spinal tracts

2. Vestibulo-spinal tracts

3. Rubro-spinal tract

4. Tecto-spinal tract

5. Olivo-spinal tract

Descending Tracts (Motor…)

Extra-pyramidal tracts: (Sub cortical origin )● Control of gross postural movements of proximal joints like pelvic girdle & shoulder girdle movements ● Control of anti-gravity muscles of lower extremities● Regulation of muscle tone.

Paraplegia

• Paralysis of both lower extremities • Most of the cases are spastic • Three stages are seen • It is UMN type of lesion• Features of complete & incomplete transection may differ.

UMN & LMN concept

• UMN : 1st Neuron in motor pathway terminating on LMN

e.g.: Pyramidal & extrapyramidal tract neurons

• LMN : Last neuron in motor pathway directly supplying muscle

e.g. Anterior horn cells & cranial nerve nuclei

UMN Lesion (features)1. Rigidity or spasticity

2. Hypertonia

3. Deep reflexes are exaggerated

4. No atrophy

5. Positive Babinski’s sign

e.g. Hemiplegia or Paraplegia

LMN Lesion (features)1. Flaccidity

2. Hypotonia

3. All reflexes lost

4. Atrophy seen

5. No Babinski’s sign

eg.Poliomyelitis

Spinal cord lesions

Causes:• Traumatic e.g. fracture of

vertebrae• Infective e.g. tuberculosis• Degenerative e.g. motor neuron disease• Vascular e.g. atherosclerosis• Neoplastic e.g. meningioma

Spinal cord lesions (classification)

1.Lesions of roots:

Anterior or posterior root lesions

2.Lesions of cord proper:

(a) Complete trans-section

(b) Incomplete trans-section including Hemi-section

(Brown Sequard syndrome)

Spinal cord Lesions (Stages)

1. Stage of Spinal Shock For 2-3 wks. Picture like LMN

lesion2. Stage of Reflex Activity

Can remain life long Picture like UMN

lesion3. Stage of Reflex Failure

Complications causing irreversible

damage Picture like LMN lesion

Complete transection1. Paraplegia in Flexion

2. Flexor reflexes return first

3. Mass reflex present

Incomplete transection1. Paraplegia in Extension

2. Extensor reflexes return first

3. Mass reflex absent

Principles of Treatment

1. Treat the basic Cause2. Maintain the Vital functions3. Take care of

• Nutrition • Bladder• Bowel• Bed sores

4. Start Physiotherapy as early as possible

Functions of Cerebral Cortex

Frontal lobe( Motor Functions)

1. Control of Voluntary movements

2. Control of Speech and writing

Prefrontal lobe ( Intellectual Functions)

1. Memory and intelligence

2. Thinking and solving of problems

3. Prediction and future planning

Parietal lobe ( Sensory functions)

1. Appreciation of fine sensations

2. Stereognosis, barognosis

3. Appreciation of taste sensation

Temporal lobe ( Auditory functions)

1. Appreciation of hearing

2. Behavioral functions like fear and

rage

Occipital lobe (Visual functions)

Appreciation of vision including colors

Functions of Hypothalamus

1. Endocrine control on Pituitary gland

2. Regulation of

•Food intake

•Thirst

•Body temperature

•Sex behavior

•Circadian rhythms

•ANS

Sleep & wakefulness• Temporary state of

unconciousness

• Neuronal fatigue of ARAS

• REM & NREM patterns

• Essential for life

• Drugs can modify

REM Sleep NREM Sleep

1. Person wakes up in 1. Person goes

to sleep this pattern in this pattern

2. Duration less 2. Duration more

3. Eyeballs move 3. No movement

4. Dreams occur 4. Do not occur

5. Difficult to arouse 5. Easy to arouse

6. EEG –Beta pattern 6. EEG –Delta

pattern

Functions of Basal Ganglia

1. Regulation of muscle tone

2. Inhibition of motor cortex

3. Timing and scaling of movements

4. Involuntary associative

movements

5. Regulation of gross intentional acts

ParkinsonismDeficiency of Dopamine at Corpus

Striatum due to damage to Nigro-strial

tract

Features: 1.Akinesia

2. Rigidity

3. Pill rolling tremors

4.Jerky gait

5. Mask face

Treatment of Parkinsonism

1. Treat the basic cause

2. L-dopa and carbi-dopa group of drugs

3. Anticholinergic drugs

4. Stop Phenothiasines

5. Other drugs like Amantadin,

Bromocriptin

6. Transplantation of Adrenal medulla

Functions of Cerebellum1. Co-ordination of Voluntary movements

2. Timing, planning and scaling of

movements

3. Regulation of Muscle tone

4. Regulation of Posture and Equilibrium

5. Regulation of Conjugate eyeball

movements

6. Inhibition of Motor cortex

Cerebellar Signs1. Nystagmus

2. Dysmetria

3. Dysdiadochokinesis

4. Motor ataxia

5. Drunken-man’s gait

6. Pendular knee jerk

Abnormal Gaits1. Circumduction gait in Hemiplegia

2. Spastic gait in Paraplegia

3. Flaccid gait in Poliomyelitis4. Drunken-man’s gait in Cerebellar

syndrome

5. Jerky gait in Parkinsonism6. High steppage gait in Dorsal column

damage