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 input 3.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

Cerebral Lobes: Lateral Aspect General Functional Considerations –Frontal (motor) –Parietal (somatosensory) –Temporal (auditory) –Occipital (visual) (motor) (somatosensory) (visual) (auditory)

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. 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 Node of Ranvier Myelin sheath Endoneurium Cell body of Schwann cell

Important Sensory Pathways Dorsal Column/Medial Lemniscus System - sensory Anterolateral System (spinothalamic tract) - sensory 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

Brodmann’s Areas - Left Hemisphere.

Cerebro-Spinal Fluid Properties Is clear& colorless. Is sterile only upto 5 lymphocytes/µL and no red blood cells (RBCs) Intracranial pressure (ICP) is mm H 2 O (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

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 t hat 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.