THE NERVOUS
SYSTEM
Functions
 The body’s communication network and
control center
 Controls all actions and functions of the body
 Senses change and allows your body to
respond within a fraction of a second
Neurons
 Sensory Neurons: carry signals from sense
receptors into the CNS
 Motor Neurons: carry signals from CNS to
muscles or glands
 Interneurons: form all the electrical
connections within the CNS itself
Structure
 Two main divisions : central nervous system
and peripheral nervous system
Central Nervous System
 Contains the brain and the spinal cord
 Receives and analyzes information and
initiates the responses of the body
 Parts of the brain include the cerebrum,
cerebellum and brain stem
Cerebrum
 Site of the most conscious and intelligent
activities
 Conscious thoughts take place on the outer
layer of the brain or the cortex
 Divided into two hemispheres: Right and Left
 The right hemisphere controls the left side of
the body and the left hemisphere controls the
right half of the body
Cerebellum
 Second largest part of the brain
 Divided into two hemispheres
 Helps with maintaining balance, posture and
coordinating skeletal muscle movement
The Brain Stem
 3 inch long stalk of nerve cells and fibers that
connects the spinal cord to the rest of the
brain
 Pathway for messages traveling between
other parts of the brain and the spinal cord
 Controls breathing, heartbeat, and eye
reflexes
 Consists of the medulla oblongata, pons,
midbrain, thalamus, and hypothalamus
Medulla Oblongata
 Lowest part of the brain stem
 Contains vital control centers that control
heartbeat, breathing, blood pressure, and
digestion
 Also controls swallowing , vomiting,
sneezing, and coughing
 Involved in speech and tongue movements
Pons
 Above the medulla
 Serves mainly as a pathway for nerve
impulses passing to and from the cerebrum
 Relays sensory information from the ear,
face, and teeth
 Adjusts facial expressions
Midbrain
 The shortest part of the brain stem, lies
above the pons
 Controls eye movements and the size and
reactions of the pupils
Thalamus
 Located above midbrain
 Relay center for incoming sensory impulses
 Receive information from the eyes and ears
 Through the spine, also receives information
from touch and pressure receptions
Hypothalamus
 Under the thalamus, -hypo- means under
 Regulates body temperatures, stimulates
appetites for food and drink, and regulates
sleep
 Controls secretions from pituitary glands that
control processes such as metabolism and
sexual development
Peripheral Nervous System
 main parts:
1. Autonomic nervous system
2. Somatic nervous system
Autonomic Nervous system
 Responsible for controlling the involuntary
functions of the body such as sweating
digestion, and heart rate
 Divided into two parts: Sympathetic
Parasympathetic
Sympathetic
 Responds tot the body’s needs during
increased activity and emergencies
 “Fight or Flight” response
 During the fight or flight response heartbeat
and breathing rate quickened
 Blood flow to the muscles increase
Parasympathetic Nervous system
 Slows body functions
 Slows down heartbeat, opens blood vessels,
and lowers blood pressure
Somatic Nervous System
 Includes cranial and spinal nerves that
transmit impulses from the CNS to the
skeletal muscles
 Voluntary : responses that are under your
control
Reflex Action
 A reflex is a spontaneous response of the
body to a stimulus
 Occurs automatically
 Ex: when the doctor taps your knee and it
makes your leg kick
 Ex: when your hand touches a hot stove an
impulse is send to your brain and to take your
hand off