Nervous System Introduction and Tissue

Nervous System Introduction

• The nervous system is complex, controlling and coordinating all body systems
• Diseases and injuries can affect various parts of the nervous system, leading to diverse presentations
• Anatomical divisions include the central nervous system (CNS), peripheral nervous system (PNS), and autonomic nervous system (ANS)
• CNS comprises the brain and spinal cord
• PNS includes nerves outside the spinal cord, both motor and sensory
• ANS has two subdivisions: sympathetic and parasympathetic systems

Nervous Tissue

• Neurons (nerve cells) are fundamental units of nervous tissue
• Neuron types include afferent (sensory), efferent (motor), and interneurons
• Upper motor neurons are in the cerebral cortex, brainstem, and cerebellum
• Lower motor neurons in spinal cord's anterior horn
• Neuron lesions (injuries) can be upper or lower, with different clinical signs
• A neuron is made up of a cell body, axon, and dendrites
• Axons transmit signals away from the cell body
• Dendrites carry signals toward the cell body
• Synapses are junctions between neurons where neurotransmitters are released
• Electrical signals travel along axons and dendrites, based on specific sensory stimuli

The Central Nervous System (CNS)

• CNS includes the brain and spinal cord for maximum protection
• Skull surrounds the brain, and vertebrae surround the spinal cord
• The foramen magnum aligns in vertebral foramen
• Meninges are protective membranes surrounding the CNS
• Dura mater is the outermost tough layer
• Arachnoid mater is the middle, thinner layer
• Pia mater is the innermost, thin, delicate layer with blood vessels
• CSF (cerebrospinal fluid) circulates between arachnoid and pia mater; providing shock absorption
• Brain has four ventricles that contain a capillary network which produces CSF
• Cerebrum is the largest brain part for cognitive functions like motor control, speech, and personality; is divided into right and left hemispheres
• Left and right hemispheres are connected by the corpus callosum
• Four lobes within the cerebrum (frontal, parietal, occipital, and temporal)
• Frontal lobe controls movement, speech, and personality, while the occipital lobe interprets visual input.
• Thalamus is a relay station for body sensations
• Hypothalamus regulates hormones and behavior
• Brainstem (midbrain, pons, medulla oblongata) contains fiber tracts from the brain and spinal cord
• Cerebellum is behind the pons and medulla, controls muscle tone, coordination, balance

The Peripheral Nervous System (PNS)

• PNS carries information between CNS and the body
• Includes cranial nerves and spinal nerves, which transmit sensory and motor impulses
• 12 pairs of cranial nerves, classified as sensory, motor, or mixed
• 31 pairs of spinal nerves, branching into dorsal and ventral rami
• Dorsal rami supply posterior trunk
• Ventral rami form plexuses (like cervical, brachial, and lumbosacral) to provide nerves to the limbs
• Cranial nerves innervate the head and neck
• Peripheral nerves connect the spinal cord and the limbs

Dermatomes and Myotomes

• Dermatomes are areas of skin innervated by specific spinal nerves or spinal cord segments
• Myotomes are muscles innervated by specific spinal nerves

Autonomic Nervous System

• The ANS controls involuntary functions such as digestion, reproduction, heart, and lungs.
• The ANS is composed of sympathetic and parasympathetic systems that have opposing effects
• Sympathetic system prepares the body for action ("fight-or-flight"), and the parasympathetic system conserves energy.