ANATOMY OF NERVOUS SYSTEM BY DR Noha Elsayed

INTRODUCTION DEFINITION The system which controls the sensory and motor functions of the body is called nervous system. CLASSIFICATION Nervous system can be classified in two ways 1. Anatomically (according to the structure) 2. Functionally (according to the function)

Anatomically Nervous system is divided into 1 Central nervous system Brain (Cerebrum,Cerebellum, Brainstem ) midbrain, pons, medulla oblongata Spinal cord 2. Peripheral nervous system 12 pairs of cranial nerves 31 pairs of spinal nerves 2 sympathetic trunks

Cranial nerves These nerves arise from brain within the cranial cavity and supply the face,its parts, digestive system, respiratory system and heart. Spinal nerves These nerves arise from the spinal cord and control the functions of rest of the body.

Functionally Nervous system can be classified into 1. Somatic nervous system Controls the voluntary function of the body like moving the arms, blinking the eyes etc 2. Autonomic nervous system Controls the involuntary activities of the body like heart beating, movement of the digestive tract etc Autonomic nervous system further divides into a. Sympthatic nervous system (works in danger) b. Parasympathetic nervous system (works in normal life)

Functional unit of nervous system o Neuron is the functional unit of the nervous system. All the functions of nervous system depends on the neuron. o Neuroglia (supporting cells)  Astrocytes  Ependymal cells  Microglial cells  Oligodendrocytes Definition It is defined as 1. The cell which carries the messages from the brain and spinal cord to the rest of the body or 2. The cell which transmits the nerve impulses.

Anatomy of a Neuron Each neuron contains: - Cell body with nucleus - Cell body with nucleus - Dendrites : fibers that receive messages from other neurons - Dendrites : fibers that receive messages from other neurons - Axons : fibers that send messages to other neurons - Axons : fibers that send messages to other neurons

Neurons do NOT touch; there is a gap between them called a synapse Neurons do NOT touch; there is a gap between them called a synapse Messages are sent across the synapses by special chemicals called neurotransmitters Messages are sent across the synapses by special chemicals called neurotransmitters

TYPES OF NEURONS INTERNEURON- located entirely within CNS,integrates functions in CNS Sensory (from sensory receptor to CNS) Motor (from CNS to effector organ)

Sensory (Afferent) vs. Motor (Efferent) e.g., skin e.g., muscle sensory (afferent) nerve motor (efferent) nerve Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS Neurons that transmit commands from the CNS to the muscles, glands, and organs

The Nervous System: Anatomy and Physiology In unmyelinated axons, electrical signals propagate along the entire axon membrane. Myelinated nerves are surrounded by a myelin sheath, manufactured by Schwann cells. ◦ Narrow gaps between these cells are the nodes of Ranvier.

Neurologic Structures A neuromuscular junction is the connection between a motor neuron and a muscle fiber. ◦ A motor end plate formed by specialized muscle fiber membranes

The Central Nervous System Meninges ◦ Tough membranes, enclose entire CNS  Dura mater: outer, toughest layer  Arachnoid: second layer  Pia mater: innermost layer ◦ In between cerebrospinal fluid (CSF)

Physiology of Sensation Ability to gather and process information about the body and the external environment is important ◦ Generated and transmitted by sensory receptors ◦ Message is processed and:  Brought to conscious thought  Generates an automatic response (reflex)  Discarded as unimportant

General Senses Monitored by receptors in different tissues ◦ Nociceptors monitor pain. ◦ Mechanoreceptors monitor physical properties. ◦ Proprioceptors track position in space. ◦ Baroreceptors measure changes in pressure. ◦ Chemoreceptors measure chemicals in the body.

Special Senses Sense of taste ◦ Taste receptors respond to sweet, salty, sour, and bitter

Special Senses Sense of smell ◦ Upper nasal cavity contains olfactory receptors

Special Senses Sense of sight ◦ Eyeball is the source of information the brain processes into pictures ◦ Image is brought into focus by altering shape and thickness of the lens  Distortion of the lens causes difficulty focusing on an object.

Special Senses Sense of hearing ◦ External ear collects sounds into the ear canal ◦ Sound waves travel through the ear canal to the tympanic membrane or eardrum.

Special Senses Sense of balance ◦ Vestibular system is contained within the inner ear.  Composed of fluid-filled sacs (otoliths) and fluid-filled passageways (semicircular canals)  Structures are used by the CNS to collect information about movement and orientation.