The Nervous System
I. Functions
A. Your body’s communication network and control center.
1. Controls all of your body’s actions and functions
II. Structure of the Nervous System
A. Two Main Parts
1. Central Nervous System (CNS)
a. receives and analyzes information gathered by the PNS and initiates responses
2. Peripheral Nervous System (PNS)
a. gathers information from inside and outside the body and picks up and carries the response signals.
The Peripheral Nervous System
A. Consists of nerves that fan out from the CNS to the muscles, skin, internal organs, and glands.
B. Two Subdivisions
1. Autonomic Nervous System
a. controls involuntary functions such as sweating, digestion, heart rate
b. sympathetic nervous system
1. responds to the body’s needs during increased activity and in emergencies
2. prepares body for fight or flight response (heart and breathing rate increases)
c. parasympathetic nervous system
1. opposes actions of sympathetic system
2. slows down heartbeat, opens blood vessels, and lowers blood pressure
2. Somatic Nervous System
a. actions under your control (skeletal muscle movement)
C. Reflex Action
1. spontaneous response of the body to a stimulus
2. occurs automatically
B. Neurons
1. information gathered by the PNS and sent to the CNS and then back to the PNS is transmitted through your body by electrical charges that travel up to 248 MPH. The messengers and receivers of these transmissions are neurons.
2. Three types of neurons
a. sensory neurons – carry signals from sense receptors (muscles and glands) into the CNS.
b. motor neurons – carry signals from the CNS to muscles or glands.
c. interneurons – form all the electrical connections within the CNS
3. Three parts of a neuron
a. cell body – consists of a nucleus (control center). The nucleus receives and sends nerve impulses.
b. dendrites – branching projections of the cell body. Receive and carry impulses toward the cell body.
c. axons – extension of the neuron that carries impulses away from the cell body. Most axons have a myelin sheath that insulates the nerve fiber and speeds the transmission of impulses.
III. The Central Nervous System
A. Spinal Cord
1. cylinder of nerve tissue about 18 inches long and as thick as your index finger
2. runs down the central canal of the spine and is protected by vertebrae and cerebrospinal fluid
3. relays messages from all parts of the body to the brain and from the brain to muscles and glands
B. Brain
1. the largest, most complex part of your nervous system
2. helps you receive and process messages, think, remember, reason, and coordinates muscle movement
3. three main divisions
a. cerebrum
1. largest, most complex part of the brain
2. site of most conscious and intelligent activities
3. sensory information- heat, cold, pain, touch, and body position. Vision, hearing, smelling, memory, judgment, thought
b. cerebellum
1. second largest part of the brain
2. maintains posture, balance, coordinates skeletal muscle movement
c. brain stem
1. connects spinal cord to rest of the brain
2. controls breathing, heartbeat, eye reflexes
3. activities are not under conscious control
4. main parts
a. medulla oblongata – heart rate, breathing, blood pressure, digestion
b. pons – relays sensory information from the ear, face, and teeth, and controls movement of the jaw and adjusts facial expressions
c. midbrain – controls eye movement and the size and reactions of the pupils
C. Cerebrospinal Fluid
1.clear watery substance that surrounds brain and spinal cord
2. acts as a shock absorber
3. allows for exchange of nutrients/waste between blood and nervous tissue
D. Meninges
1. Three layers of tissue that cover the brain & spinal cord
2. provide a small amount of protection
IV. Disorders of the Nervous System
A. Epilepsy
-brain disorder causing seizures
-chemicals in cerebrum cause uncontrolled movements
B. Cerebral Palsy
-faulty development or damage to motor areas of the brain
-disrupts the brain’s ability to control movement
C. Multiple Sclerosis
-destruction of myelin sheath
-causes disrupted transmission of messages between the brain, spinal cord, & rest of body
-diminished or lost function
D. Stroke
-blood flow to the brain is disrupted by a blood clot
-brain does not get the oxygen and nutrients it needs
-loss of brain function – speech, movement, memory
E. Alzheimer’s
-degeneration of brain tissue
-results in impaired memory, thinking, and behavior
-personality and behavior changes
-no known cause – age and family history