Medical Physiology-II. Organization of Nervous System.

WINDSOR UNIVERSITYSCHOOL OF MEDICINE

Dr.Vishal Surender.MD.

Medical Physiology-II

Organization of Nervous System

Nervous System…

• The nervous system regulates most body systems using direct connections called nerves. It enables you to sense and respond to stimuli

• The basic function of nervous system are:1. Receive sensory input internal or external 2. Integrate the input3. Responding to internal and external stimuli

Components of the Nervous

System • Nervous System = Central Nervous System (CNS) +

Peripheral Nervous System (PNS)

• CNS = Brain + Spinal Cord

• Plus all of cranial nerve II and the retina

• PNS = Neurons (and/or processes) and associated

non-neural cells outside the CNS – Somatic or autonomic motor neurons may have cell bodies in the

CNS

but with axons extending through the PNS – Sensory cells may have receptive endings, axons and cell bodies

in

the PNS but restricted parts of their axons extending into the CNS – Many autonomic neurons dwell entirely in the periphery

Central Nervous System

Peripheral Nervous System

Central Nervous System• Five Parts of the Brain

– Telecephalon • Lateral ventricles

– Diencephalon • Third ventricle

– Mesencephalon • Cerebral aqueduct

– Metencephalon • Rostral fourth ventricle

– Myelencephalon • Caudal fourth ventricle and

medullary • central canal (continuous

with the• spinal central canal)

Central nervous system (CNS) Five parts of the brain

Midbrain = Mesencephalon Pons + cerebellum = Metencephalon Medulla oblongata = Myelencephalon

Lobes of the Cerebral Hemispheres MRI - Lateral Lobes of the Cerebral Hemispheres - Lateral

Frontal lobeParietal lobe

Temporal lobeOccipital lobe

Cerebral Lobes: Lateral Aspect

• General Functional Considerations – Frontal (motor) – Parietal (somatosensory) – Temporal (auditory) – Occipital (visual)

(motor)(somatosensory)

(visual)(auditory)

Lobes of the Cerebral Hemispheres –MRI - Medial

Lobes of the Cerebral Hemispheres - Medial

Parietal lobe

Frontal lobe

Occipital lobe

Temporal lobe

Limbic lobe

Cerebral Lobes: Medial Aspect

Deep Cerebral Nuclei(Basal Ganglia)

Spinal Cord • Enlargements: Reflect larger numbers of cells subserving sensory or motor function related to the limbs.

Motor neurons tend to dwell in the gray matter of the ventral horn, whereas sensory neurons tend to aggregate dorsally.

Spinal Cord

Cervical

Thoracic

Lumbar

Sacral

Filum terminale

Cervical enlargement

Lumbar enlargement

Ventral sulcus

FibresCellbodies

Cuneate fasciculus

Gracile fasciculus

Dorsal horn

Ventral horn

Dorsal Column

Lateral Column

Ventral Column

Spinal Nerves

• Dorsal and ventral nerve roots exit the cord, joining in the vertebral

canal. • Because there are 8 cervical

spinal segments but only 7 cervical vertebrae, the 1st spinal nerve emerges rostral to the 1st

cervical vertebra, whereas the 8th

cervical nerve emerges caudal to the 7th cervical vertebra and hence rostral to the first thoracic

vertebra.

Peripheral Nerve - Structure

Fat

Blood vessels

Epineurium Perineurium

Endoneurium

Myelinated fibers

Unmyelinated fibers

Peripheral Nerve

Fascicles

Axon

No

de o

f Ra

nvie

r

Myelin sheath

Endoneurium

Cell body of Schwann cell

Important Sensory Pathways•Dorsal Column/Medial Lemniscus System - sensory

•Anterolateral System (spinothalamic tract) - sensory

Ventral sulcus

FibresCellbodies

Cuneate fasciculus

Gracile fasciculus

Dorsal horn

Ventral horn

Dorsal Column: Proprioception, Vibration, Tactile discrimination

Anterolateral System: Pain, Temperature, Pressure

Important Motor Pathways

• Corticospinal Tract - (lateral and anterior)

motor • Corticobulbar Tract - motor • Vestibulospinal (lateral and medial) Tract -

motor • Reticulospinal (lateral and medial) Tract -

motor • Rubrospinal Tract - motor

Your 43-yr-old female patient suffers a traumatic accident in which the dorsal columns of the spinal cord are damaged.

What function is lost? 1. Motor

2. Tactile discrimination

3. Nociception

Ventral sulcus

FibresCellbodies

Cuneate fasciculus

Gracile fasciculus

Dorsal horn

Ventral horn

Brodmann’s Areas - Left Hemisphere.

Vertebral and Basilar Artery

Picture taken from Ward Model

1 Anterior cerebral a.

2 Anterior communicating a.

3 Internal carotid a.

4 Middle cerebral a.

5 Posterior communicating a.

6 Posterior cerebral a.

7 Superior cerebellar a.

8 Basilar a.

9 Anterior inferior cerebellar a.

10 Vertebral a.

11 Posterior inferior cereballar a.

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3 4

567

8

9

10

11

Cerebro-Spinal Fluid

Properties • Is clear& colorless. • Is sterile only upto 5

lymphocytes/µL and no red blood cells (RBCs)

• Intracranial pressure (ICP) is 65 -200 mm H2O (5 – 15 mm Hg)

Functions of CSF • Reduces traction exerted

upon the nerves and blood vessels connected with the CNS.

• Provides a cushioning effect.

• Removal of metabolites. • Providing a stable ionic

environment.

Circulation of the CSF

Essential Neuroscience, Updated 1st Edition Allan Siegel, Ph.D; Hreday N. Sapru PhD

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Clinical Correlations

Hydrocephalus • Dilation of the ventricles (or hydrocephalus) occurs when

the circulation of CSF is blocked or its absorption is impeded, while the CSF formation continues to occur at a constant rate.

2 types

1. Non communicating (obstructive) Hydrocephalus

2. Communicating Hydrocephalus

Clinical Correlations • Transient Ischemic Attack (TIA). This is an acute loss of cerebral or monocular function with symptoms lasting under 24 hours. The origin is presumed to be a disorder of the cerebral circulation that leaves parts of the brain with an inadequate blood supply. Recovery of functions is likely. Predicted by stenosis if internal carotid artery and intermittent atrial fibrillation. Predicts stroke within a year. • Reversible Ischemic Neurological Deficit. This is an acute loss

of cerebral or monocular function with symptoms lasting longer than 24 hours due to inadequate blood supply of parts of the brain. Recovery of functions is likely.

• Stroke (Cerebrovascular Accident). This is a rapidly developing loss

of cerebral function due to cerebrovascular disturbance. The occurring

symptoms are irreversible or only partial reversible. In some patients the symptoms are global. The severity of loss ranges from partial recovery through permanent disability to coma and death.