Nerves and Nerve Cells:
Neurons – is a basic cell of the nervous system. • Neurons carry nerve messages, or impulses, from one part of the body to another.
Structure of a Nerve Cell:
A neuron has three basic parts:
1. Body – controls the cell’s growth
2. Axon – is a long thin fiber that carries impulses away from the cell body Myelin – is a fatty material that insulates the axon and increases the speed at which an impulse travels
3. Dendrites – are short, branching fibers that carry nerve impulses toward the cell body.
• A nerve impulse begins when the dendrites are stimulated. The impulse travels along the dendrites to the cell body, and then away from the cell body on the axon.
• The impulse must cross a synapse to a muscle or another neuron.
Synapse – is the space between an axon and the structure with which the neuron communicates.
Types of Nerve Cells:
Sensory Neurons – pick up information about your external and internal environment from your sense organs and your body
Motor Neurons – sends impulses to your muscles and glands, causing them to react
Interneurons – are located only in the brain and spinal cord, pass impulses from one neuron to another
• The nervous system consists of two parts. Your brain and spinal cord make up one part, which is called the central nervous system.
1 • The peripheral nervous system, which is the other part, is made up of all the nerves that connect the brain and spinal cord to other parts of the body.
The Brain:
Brain – a moist, spongy organ weighing about three pounds is made up of billions of neurons that control almost everything you do and experience. The brain controls your sense experiences, actions, thoughts, and memory.
• The cranium protects the brain.
• Beneath the cranium are the meninges.
Meninges – three layers of membranes that cover the brain and give it further protection
Cerebrospinal fluid – a liquid found between the middle and inner meninges and in certain spaces within the brain, helps to cushion and protect the brain and spinal cord
The brain is divided into three areas or lobes:
1. Cerebrum – (center of intellect) is the large upper region that controls
- movement of skeletal muscles
- memory and reasoning and interprets the sense organs:
1. smells 2. tastes 3. sounds 4. sights 5. touch
• A deep grove divided the cerebrum into left and right sides, known as hemispheres.
Right cerebrum – controls muscles on the left side of the body.
Left cerebrum – controls muscles on the right side of the body.
If a person receives an injury to the left side of the brain of the cerebrum, which side of the body is affected?
2 Cerebellum (little brain) – located just beneath the back part of the cerebrum, coordinates the contraction of your muscles
Brain stem (medulla) – located below the cerebellum at the base of the cranium, acts as the body’s life support system and is the body’s most vulnerable. It controls heartbeat, digestion, breathing, body temperature and blood pressure.
Two small parts that extend out from the brain stem:
1. Thalamus – is a relay station for the senses, receiving impulses from the sense organs and modifying them before they reach the cerebrum.
2. Hypothalamus – regulates body temperature, sleep, water balance, blood pressure, and hormones.
3. Pons – controls awakening and sleeping
The spinal cord:
Spinal cord – nerve tissue that extends from the brain down the back just below the ribs.
The Peripheral Nervous System:
Peripheral nervous system includes all parts of the nervous system except the brain and spinal cord.
Cranial nerves – twelve pair of nerves that emerge from the brain and connect to various areas in the eyes, ears, nose, and face.
Spinal nerves – thirty-one pairs of nerves that branch off the spinal cord, passing through openings in the vertebrae
Peripheral nervous system consists of two parts:
1. Somatic nervous system (voluntary) – is responsible for actions that you can control 2. Automatic nervous system – (involuntary) regulates actions that happen automatically (example: heartbeat, breathing rate, digestion)
3 Control of Movement:
When you move, your muscles are at work. However, your nervous system controls movement by sending impulses to muscles that direct them to contract. Various factors can affect the way your nervous system controls muscle movement.
Two factors that affect the nervous system:
1. Coordination – is your brain storing information of various movements. Practice helps you improve the skill and the brain keeps adding information to this stored memory enabling your performance to improve over time.
2. Reflex – an automatic response of the nervous system to the environment
Disorders of the Nervous System:
Problems associated with the nervous system range from mild conditions to serious illnesses and injuries.
Damage to nerve cells are permanent, they can not replace themselves.
Neurologist – physician that studies brain disorders
EEG (electroencephalograghy) – measures the waves of electrical activity produced by the brain. Used in diagnosing seizures.
Injuries:
Concussion – a short loss of consciousness following a severe bump to the head, during which the soft brain tissue comes into contact with the skull
Coma – a prolonged period of deep unconsciousness that may result from severe brain injury, a disease, or a drug overdose
Paralysis – the loss of feeling in and the ability to move some part of the body
Quadriplegia – paralysis of the body from the neck down, including arms and legs
Paraplegia – paralysis of the lower body and legs
4 Infections:
Meningitis – An inflammation of the meninges of the brain and spinal cord
Rabies – An infection of the Central Nervous System transmitted from the bite of an infected animal.
Other Conditions:
Migraine headache – an especially severe, long lasting headache that may be caused by swelling of the brain’s blood vessel.
Cerebral palsy – nervous system damage that occurs before, during, or shortly after birth, resulting in lack of full control of the body movement.
Epilepsy – a disorder in which the brain’s impulses become disturbed and cause seizures
Seizure – an attack caused by a sudden storm of brain activity, during which a person may lose consciousness, the arms and legs may jerk, and the teeth may lock together.
Multiple sclerosis (MS) – an progressive condition in which patches of myelin are slowly destroyed, resulting in difficulty with muscular control, speech and vision problems, and sometimes paralysis.
Keeping the Nervous System Healthy:
• Rest, sleep, good nutrition, and daily exercise help keep the nervous system in good condition. • Avoid drugs and alcohol that cause permanent damage to the nervous system. • Injuries are the most common cause of brain and spinal cord damage.
You can avoid injuries by following a few basic rules:
1. Do not use drugs or alcohol. Never ride in a motor vehicle whose driver is under the influence of drugs or alcohol
2. Fasten your safety belt every time you ride in a car.
3. Before diving into water, be certain that it is deep enough and that there are no underwater hazards
5 4. Be sure to wear a protective helmet when you work on mechanical equipment, play contact sports, or ride a bicycle or motorcycle.
By following these safety guidelines, you will be helping to maintain the health of your nervous system.
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