Neuron and Nervous System PDF

 Neuron The basic structural and functional unit of the nervous system is the neuron or the nerve cell. Nerve cells are the largest cells in the body. A neuron is a specialized cell to conduct impulses called nerve impulses. Structure of a Neuron Synapse acts li...

 Neuron The basic structural and functional unit of the nervous system is the neuron or the nerve cell. Nerve cells are the largest cells in the body. A neuron is a specialized cell to conduct impulses called nerve impulses. Structure of a Neuron Synapse acts like one way valves Nerves  Nerves A cord like whitish structure with a number of axons bundled together is called a nerve. Nerves are a cluster of neurons enclosed within the sheath Each axon in the bundle remains separated from each other because of the covering of myelin sheath. It prevents mixing of adjacent impulses in the fibres. The nerves are of different types depending on their function. Three - Autonomic Nervous System  - The messages from the sense organs are transmitted to the central nervous system for processing and then appropriate action is taken in response to the environment.  Brain It is the highest coordinating centre in the body. Location in the skull at the top of the spinal cord. Protection – Bony Skull / Cranium It is enclosed in three layers of tissues and is surrounded by a special shock-proof tissue is called as meninges. Cerebrospinal fluid Forebrain Cerebrum Largest and uppermost part of brain It consists of sensory areas to receive impulse from sense organs Cerebrum is divided into two large, deeply-convoluted parts called cerebral hemispheres.  Functions: Responsible for thinking and reasoning It controls our thoughts, memory, intelligence, learning, consciousness and will power. Midbrain – Auditory and visual processing Pons also controls sleep , and dreams  Cerebellum second largest part of the brain. Located below and behind the cerebrum and above the medulla oblongata.  It has no convolutions, instead, it has numerous furrows. Like the cerebrum, it also has an outer cortex made up of grey matter. Centrally, cerebellum has white matter which, in median section appears like a branching tree.  Functions It maintains balance of the body and coordinates muscular activities. It coordinates the movement of voluntary muscles.  Medulla Oblongata It is the lowest portion of the brain and lies beneath the cerebellum. It connects the brain to the spinal cord.  Functions All the information to and from our brain passes through the medulla. It controls functions like the heart beat, breathing, swallowing and coughing. Damage to the medulla leads to immediate death because of the failure to pursue essential involuntary actions. Spinal Cord  The spinal cord extends from the medulla to almost the whole length of the backbone. It is a tube like structure about 16-18 inches long. The vertebral column protects the spinal cord. Three layers of meninges protect the spinal cord in addition to the vertebral column. Cerebrospinal fluid fills the spaces between the meninges.  The section of the spinal cord shows two similar halves fused together to form the central canal. The central canal is surrounded by H-shaped grey matter (made up of cell bodies) while its outer part contains white matter (made up of nerve fibres). Functions Transmits signals from the brain to other body parts and vice versa. Controls involuntary functions like heartbeat, bladder functioning, etc. Manage reflex actions. PNS – Peripheral Nervous System Communication between the central nervous system and the other parts of the body is called peripheral nervous system (PNS).  Autonomic Nervous System It is a system that helps the body to deal with stress and works without conscious control. It consists of two main branches: sympathetic and parasym- pathetic systems. These systems are antagonistic but complementary to each other.  Sympathetic nervous system The sympathetic nervous system is often called the fight or flight division. It results in increased alertness and metabolic activities to prepare the body for an emergency situation. Functions: It regulates responses during physical activity or emotional stress such as increased heart rate, dry mouth, cold skin and blood supply to arteries. Parasympathetic nervous system The parasympathetic nervous system (PNS) is also called the rest and digest division. It conserves and restores body energies during rest or during the time when we take meals. Functions: This system is responsible for the dilation of blood vessels, slowing down of the heartbeat and constriction of the pupil of the eyes. Action due to response to stimuli Reflex action Involuntary action Voluntary action  Reflex Action Reflex is a special characteristic feature which helps to survive dangerous situation in our surroundings. The nerve pathway through which a reflex action occurs is called reflex arc. The reflex arc involves three neurons - sensory neurons, interneurons and motor neurons. Reflex Arc