Nervous System Reviewer

• Nerve Impulses


  • Electrical signals that travel through neurons
  • Your body's quicker means of communication
• Nervous System


  • The nervous system helps you receive information about what is happening inside and around your body and directs you to respond appropriately to a given situation
  • Nerves also control the endocrine glands in your body that produce hormones
  • Enables the body to gather information from the outside environment and respond quickly
  • Both the nervous and endocrine systems interact to coordinate the body's activities
  • Controls and interprets all the activities that happen in the body
  • The extraordinary amount of information that the body receives at any one time is flashed through the system in the form of millions of messages
  • Also busy monitoring breathing, blood pressure, and body temperature
  • Even during sleep
  • Keeps the body working properly despite the constant changes that take place around it
• Stimuli


  Changes that take place around the body
• Functions of the Nervous System


  • Gathers information both from the outside world and from inside the body
  • Transmits information to the processing areas in the brain and spinal cord
  • Processes information to determine the best response
  • Sends information to muscles, glands, and organs so they can respond correctly
• Responses to stimuli can be voluntary or involuntary
• Involuntary responses


  • Breathing
  • Blinking
  • Sneezing
• Voluntary responses


  • Opening an umbrella
  • Walking, Jumping, Running
  • Eating
• Neuron


  • The basic message-carrying unit of the nervous system
  • Hundreds of messages are carried by strings of special cells called neurons or nerve cells
  • Unlike most cells in the body, they do not reproduce. Once damaged, neurons cannot be replaced
  • The neurons you are born with are more than enough for a lifetime
• Parts of a Neuron


  • Cell Body / Soma
  • Cytoplasm / Axoplasm
  • Dendrites
  • Axon
  • Myelin Sheath
• Cell Body / Soma


  • Largest part of a neuron
  • Contains the nucleus (a large dark structure), which controls all the activities of the cell
  • The switchboard of the message-carrying neuron
• Cytoplasm / Axoplasm


  The cytoplasm of the neuron extends into 2 types of fiberlike structures
• Dendrites


  Receive and carry information toward the cell body
• Axon


  • A long, taillike fiber that extends from the cell body
  • The axon splits into many featherlike fibers, called axon terminals (ends)
  • Pass on messages to the dendrites of other neurons
  • They are usually found some distance from the cell body
  • Carries messages away from the cell body
  • Each neuron only has one axon, but it can have many dendrites
• Myelin Sheath


  • Covers the axon
  • Speeds up the travel of the nerve impulses
• Types of a Neuron

  • Sensory neurons (affarent neurons)
  • Interneurons (connector / association neurons)
  • Motor neurons (efferent neurons)
• Sensory neurons (affarent neurons)


  • Conduct nerve impulses toward the central nervous system
  • Function is to receive initial stimuli from receptors
  • Transmit information from the cells and organs that gather information about conditions in the internal and external environments
  • Sensory receptors are specialized sensory neurons
• Interneurons (connector / association neurons)


  • Conduct impulses within the central nervous system
  • Found in the spinal cord and in the brain
  • "Read" the impulses sent by the sensory neurons
  • Connect sensory neurons, motor neurons, and other interneurons
  • Determines what response should be generated. If a response is required, the interneuron passes the impulse
• Motor neurons (efferent neurons)


  • Conduct impulses away from the central nervous system
  • Nerve impulses transmitted by motor neurons cause muscles, organs, and glands to respond
  • Effectors are muscles, organs, and glands that respond to impulses from motor neurons
• Nerve Impulse


  A wave of chemical and electrical signal that is conducted along the membrane of a neuron
• Synapse


  • The tiny gap between 2 adjacent neurons and between neurons
  • Neurons do not touch one another
• Neurotransmitters


  • A nerve impulse is "ferried" across the synapse by a chemical signal in the form of chemical messengers called neurotransmitters, which are stored in small sacs
  • When a nerve impulse reaches the tip of an axon, the neurotransmitters are released into the synapse, carrying the nerve impulse across the gap
  • The neurotransmitter molecules bind to receptors on the next neuron
• Reflex


  • One of the simplest response of the nervous system
  • An automatic response to stimuli
  • Nerve impulses bypass the brain and travel directly to the spinal cord
  • The brain becomes aware of the event only after it has happened
  • A reflex that does not involve the brain is called a spinal reflex
• Divisions of the Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Central Nervous System (CNS)


  • Command center of the entire body
  • Processes information and sends instructions to other parts of the body
  • All the information gathered by sensory receptors is delivered to the central nervous system through nerve impulses
  • Responds by sending nerve impulses to the motor nerves of the peripheral nervous system
• Parts of the Central Nervous System


  • The Brain
  • The Cerebrum
  • The Cerebellum
  • The Brain Stem
  • Spinal Cord
• The Brain


  • Delicate organ that is protected by and encased in a bone called the skull
  • Wrapped in three layers of connective tissue that nourishes and protects it
  • It is bathed with fluid called cerebrospinal fluid that cushions it against sudden impact
  • Appears gray because it is mostly composed of gray matter, which is because of the presence of billions of cell bodies
  • Underneath the gray matter is white matter, which is due to the myelinated axons
  • Despite the presence of billions of neurons, the mass of the brain is about 1.4 kilograms only
• The Cerebrum


  • Makes up 85% of the brain
  • Its surface is called the cerebral cortex, which is lined with deep, wrinkled grooves
  • Area where learning, intelligence, and judgment occur
  • The cerebral cortex controls all the voluntary activities of the body
  • Also shapes the attitudes, emotions and even the personality of an individual
  • Divided into 2 halves joined by the corpus callosum: Right Hemisphere (Artistic ability, Controls the movement of the left side) and Left Hemisphere (Mathematical or logical ability, Controls the movement of the right side)
• The Cerebellum


  • The second largest part of the brain and is located behind the brain stem
  • Coordinates the actions of the muscles and maintains balance
  • Maintains motor movements
  • Coordinates balance, equilibrium, and posture
• The Brain Stem


  • Connects the spinal cord to the rest of the brain
  • Coordinates many survival functions of the body such as breathing, heart rate, sleep, and wakefulness
  • 3 distinct regions make up the (lower) brain stem: medulla oblongata, midbrain, and pons
  • Medulla Oblongata (Controls involuntary actions such as heartbeat, breathing, and blood pressure)
  • Midbrain (Processes visual and auditory reflexes)
  • Pons (Control respiratory functions)
  • Thalamus (Serves as a relay station by directing incoming messages from the spinal cord to the appropriate parts of the brain)
  • Hypothalamus (Monitors internal conditions such as water content and temperature, Acts as the link between the endocrine and nervous systems)
• Spinal Cord


  • A tubelike organ of neurons and blood vessels
  • Located inside the backbone
  • About 1.8 cm wide, nearly the same size as a garden hose
  • Covered with protective membranes called meninges
  • Relays nerve impulses to and from the brain
  • Impulses from the peripheral nervous system are carried to the spinal cord, which then brings the message to the brain
  • The brain, in turn, sends impulses down the spinal cord to the motor nerves of the peripheral nervous system
• Peripheral Nervous System (PNS)


  • Links the central nervous system to the rest of the body
  • Made up of a network of bundled ropelike structures called nerves
  • Gathers and delivers information to and from the CNS
  • Consists of 43 pairs of nerves
  • Divided into the Somatic Nervous System and Autonomic Nervous System
• Somatic Nervous System


  • Nerves under the direct control of the conscious mind
  • Responsible for the mediation of spinal reflexes, which are involuntary
• Autonomic Nervous System


  • Controls the body activities that are involuntary
  • Happen automatically without thinking about them
  • Directs motor nerve fibers in smooth muscles, cardiac muscles, and the glands
  • 2 divisions that have opposite effects on the organs they control: parasympathetic and sympathetic
  • Their antagonistic nature maintains stability in the body by keeping the activities in balance
• Parasympathetic


  • Most active under normal conditions
  • Keeps the body functioning even when the person is not active
  • Rest and digest
• Sympathetic


  • Dominates in times of physical and emotional stress or whenever the body requires some action
  • Controls the "fight-or-flight" response
  • Increases blood pressure, heart rate, and breathing rate
• Infections of the Nervous System


  • Encephalitis
  • Meningitis
  • Rabies
  • Tetanus
• Encephalitis


  • Acute infection and inflammation of the brain
  • Caused by a virus such as herpes simplex virus (HSV) and enterovirus
• Meningitis


  An inflammation of the meninges and the membranes surrounding the brain and the spinal cord
• Rabies


  A viral infection transmitted through bites by infected animals such as dogs and cats
• Tetanus


  A disease caused by certain bacteria found in soil contaminated with animal waste