Download Nervous System

Nervous System
Functions of the Nervous Systems
 Your nervous system controls all of your body’s actions
and functions.
 It senses changes not only within your body but also
outside of it in your environment
 Enables you to respond within fractions of a second.
Structure of the Nervous System:
Two main divisions:
 Central Nervous System (CNS)
 Peripheral Nervous System (PNS)
 PNS gathers information from inside and outside your
body
 CNS receives and analyzes this information and initiates
responses.
 PNS then picks up and carries the response signal
o This information is transmitted throughout your body
by means of electrical charges or impulses.
o These impulses travel at speeds up to 280 miles per
hour.
o The messengers and receivers of these transmissions
are neurons, or nerve cells.
Functions of Neurons:
Three main types:
 Sensory Neurons
 Motor Neurons
 Interneurons
 Sensory neurons carry signals from sense receptors in the
CNS
 Motor neurons carry signals from the CNS to muscles or
glands
 Interneurons form all the electrical connections within the
CNS itself
Unlike other cells, neurons cannot replace themselves. If the
cell body of neuron is damaged or degenerates, the cell dies.
Each neuron is made up of three basic parts:
Cell body:
 Consists of a nucleus
o Control center of the cell
o In a sack of fluid contained within a outer skin called
the cell membrane
o Nucleus receives and sends nerve impulses.
o It also regulates the amount and type of proteins
made in the cell
 Dendrites:
o Are branching projections of the cell body
o Receive and carry impulses toward the cell body
 Axons:
o Every neuron has threadlike extension
o Carries impulses away from the cell body
o Branches at its end to form terminals though which
signals are sent to targets cells, such as the dendrites
of other neurons, muscles cells, or glands
o Vary in length from a fraction of an inch to several
feet.
o Most axons have a coating or sheath of fatty material
call myelin.
o The myelin sheath insulates the nerve fiber and
speeds the transmission of impulses
The Central Nervous System
Made up of two main parts
Spinal Cord:
 Cylinder of nerve tissue about 18 inches long and about as
thick as your index finger
 Runs down the central canal in the spine
 Downward extension of the brain
 Protected by cerebrospinal fluid that acts like a shock
absorber.
 Protected by three layers of connective membranes called
the spinal meninges.
Brain:
 Largest, most complex part of your nervous system.
 Helps you receive and process messages
 Weighs about three pounds.
 Contains 100 billion neurons
 Uses more then 20 percent of the oxygen you inhale.
 Protected by 8 cranial bones
 Protected by three layers of membranes called cranial
meninges.
Brain has three main divisions:
Cerebrum:
 Most complex part of the brain
 Site of most conscious and intelligent activities
 Outer layer, or cortex, is where conscious thought takes
place.
 Divided into two halves called the cerebral hemispheres
o Right hemisphere controls the muscular activities
of and receives sensory input from the left half of the
body
o Right hemisphere is concerned with imagination
and visual thinking artistic activities, and emotional
responses such as color appreciation.
o Left hemisphere does the same for right half of the
body.
o Left hemisphere is mainly responsible for language,
logic, arithmetic calculation, analysis, and critical
thinking.
Each hemisphere has four lobes.
 The frontal lobe controls voluntary movements and also
has a role in the use of language. The prefrontal areas of
this lobe are believed to be involved with intellect and
personality.
 The parietal lobe is involved with a wide variety of
sensory information: heat, cold, pain, touch, and body
position in space
 The occipital lobe contains the sense of vision.
 The temporal lobe contains the senses of hearing and
smell as well as memory, thought, and judgment.
Cerebellum:
 Second largest part of the brain
 Located beneath the occipital lobes of the cerebrum
 Divided into two hemispheres
 Concerned mainly with maintaining posture, balance, and
coordinating skeletal muscle movement.
 Receives impulses from the balance organs of the inner ear
and from muscles.
 After receiving this information, the cerebellum refines the
orders sent to muscles from the motor cortex in the
cerebrum to ensure smooth, coordinated movements and
balance.
Brain Stem:
 3 inches long
 Acts partly as a pathway from messages traveling between
other parts of the brain and spinal cord.
 Connects with 10 of the 12 pairs of the cranial nerves and
controls basic functions such as breathing, heartbeat, and
eye reflexes.
Brain stem consists of three main parts:
Medulla Oblongata:
 Lowest part of the brain stem
 Contains vital controls centers that regulate:
 Heartbeat
 Breathing
 Blood pressure
 Digestion
 Swallowing
 Vomiting
 Sneezing
 Coughing
 Relays taste sensations from the tongue and is
involved in speech and in 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 as
well as the signals that move the jaw and adjust facial
expressions.
Midbrain:
 Shortest part of the brain
 Contains the nuclei of the two pairs of cranial nerves that
control eye movement and pupil size
 Reflexive response of turning your head when you hear an
unexpected loud noise
 Thalamus and hypothalamus are closely associated with
the brain stem
o Thalamus: Receives information from different sense
organs such as the eyes and ears.
o Hypothalamus: Controls body temperature, stimulates
appetite, and regulates sleep.
The Peripheral Nervous System:
 Means located away from the center
 Consisted of nerves that fan out from the central nervous
system to the muscles, skin, internal organs, and glands.
 PNS carries messages between the CNS and the rest of the
body.
 Consists of 12 pairs of cranial nerves that branch from the
brain and 31 pairs of spinal nerves that branch from the
spinal cord.
PNS is composed of two subdivisions:
Autonomic Nervous System (ANS)
 Is responsible for controlling the involuntary functions of
the body, such as sweating, digestion, and heart rate.
 Consists of a network of nerves divided into 2 parts
o Sympathetic Nervous System
o Parasympathetic Nervous System
Sympathetic Nervous System:
 Responds to the body’s needs during increased activity and
in emergencies (Fight or Flight response)
Parasympathetic Nervous System:
 Opposes the actions of the sympathetic system by slowing
body functions
Somatic Nervous System:
 Includes cranial and spinal nerves that transmit impulses
from the CNS to the skeletal muscles.
 Voluntary responses; responses that are under your
control.
Reflex Action:
 Occurs automatically, without conscious thought or effort.
Care of the Nervous System:
 You need to exercise regularly
 Proper Nutrition
 Adequate rest and sleep
 Avoid using alcohol and other drugs
Problems of the Nervous System:
 Head and spinal cord injuries
o Paraplegic: Paralysis of the lower body
o Quadriplegic: Paralysis of both arms and legs
 Degenerative Diseases
o Parkinson’s disease: caused by degeneration of the
nerve cells within the brain that modify nerve impulses
transmitted from the motor area of the brain.
o Multiple Sclerosis: It involves the destructions of the
myelin sheath that surrounds nerves fibers
o Alzheimer’s Disease: General mental deterioration.
Patients gradually lose their memory and powers and
judgments.
o Epilepsy: Is a disorder of the nervous system that is
characterized by recurrent seizures.
 Grand Mal Seizures: Usually last about 2-5 minutes
and fall to the floor, unconsciousness.
 Petit Mal Seizures: Often pass unnoticed; usually
people have a blank stare for about 30 seconds.
o Cerebral Palsy: Disorder that are the result of damage to
the brain before birth, during birth, in the newborn
period, or in early childhood