Nervous system One of the two main communication systems in the body Coordinates all the activities of the body carrying messages from one cell to the next Enables the body to respond and adapt to changes that occur inside and outside the body Basic structural unit is the NEURON or nerve cell

The Nervous System Each neuron consists of: The cell body. Dendrites. The axon.

Neurons Cell body consists of nucleus Dendrites consist of nerve fibers that carry impulses toward the cell body Axon is a single nerve fiber that carries impulses away from the cell body Myelin sheath covers the axon (fat covering) that insulates and maintains the axon Nodes of Ranvier are areas where no myelin is present

The axon of one neuron lies next to the dendrites of another neuron The spaces between them are called synapses Impulses coming from one axon “jump” the synapse to get to the dendrite of another neuron which carry it in the right direction Special chemicals, neurotransmitters, found at the end of each neuron allow impulses to pass from one neuron to another so impulses can follow many different routes

Nerve fibers Nerves are a combination of many nerve fibers found in the brain and spinal cord 3 types: Afferent – sensory nerves Nerves carry messages from body to the brain and spinal cord Efferent – motor nerves carries messages from the brain and spinal cord to the body Associative - interneurons Carries impulses from the sensory neuron to the motor neuron

3 Divisions Central nervous system Peripheral nervous system Brain Spinal cord Peripheral nervous system Nerves Autonomic nervous system Controls involuntary body functions Includes peripheral nerves and ganglia (group of cell bodies outside the CNS that carry impulses to involuntary muscles and glands)

Central nervous system BRAIN – mass of nerve tissue protected by membranes and skull Cerebrum Largest and highest section Has convolutions (folds) that separates the lobes 4 lobes: Frontal Parietal Temporal Occipital

Frontal lobe Links all components of behaviors Impulse control Injury here may cause lose of function on one side of the body Speech may become halted or disorganized Personality changes can occur Social rules are disregarded Sustained attention and “insight” are affected

Temporal lobe Perceives and recognizes verbal material Most commonly injured Causes misunderstandings in what is said Emotional changes such as unexplained panic or tearfulness can occur Left temporal lobe involved in production of speech, naming and verbal memory Right temporal lobe involves musical ability, foreign language, visual memory and comprehension of the environment

Parietal lobe Construction of language Recall of long term memories may be mixed up in time and sequencing Easily lost or confused about left/right Difficulty recognizing and naming what they see May affect ability to read, write or perform calculations Conscious sensation and voluntary movement is affected Injury to front part of the lobe may cause loss of body sensation

Occipital lobe Injury usually results in blindness to part or all of the visual field People may experience “blind spots” or “holes” May misperceive pictures they see Recognition of colors may be distorted

Cerebellum Diencephalon Below cerebrum Responsible for muscle coordination, balance and posture, muscle tone Diencephalon Section between the cerebrum and midbrain Contains 2 structures Thalamus – acts as a relay center and directs sensory impulses to the cerebrum Hypothalamus – regulates and control the autonomic nervous system, temperature, appetite, water balance, sleep, etc. Also involved in emotions such as fear, anger, pleasure, pain and affection

Midbrain Pons Medulla oblongata Below the cerebrum and top of the brain stem Responsible for conducting impulses between brain parts and certain eye and auditory reflexes Pons Below the midbrain and in the brain stem Responsible for conducting messages to other parts of the brain, chewing, tasting, saliva production and assists with breathing Medulla oblongata Lowest part of the brain stem Connects with the spinal cord and is responsible for breathing, heartbeat, swallowing, coughing and blood pressure

Spinal cord Meninges Continues down from the medulla oblongata Ends at the first or second lumbar vertebrae Surrounded and protected by vertebrae Responsible for many reflex actions and carrying afferent and efferent nerves Meninges 3 membranes that cover and protect the brain and spinal cord Dura mater – outer layer Arachnoid membrane – middle, delicate layer Pia mater – attached to the brain and contains blood vessels that nourish the nerve tissue

Filled with fluid called cerebrospinal fluid The brain has 4 ventricles (hollow spaces that connect with each other and the space under the arachnoid membrane) Filled with fluid called cerebrospinal fluid Circulates continuously Serves as shock absorber to protect brain and spinal cord Carries nutrients to parts of the CNS and helps remove waste products

Peripheral Nervous System Consists of the somatic and autonomic nervous systems Somatic nervous system 12 pairs of cranial nerves 31 pairs of spinal nerves Spinal nerves carry messages to and from the spinal cord and are mixed nerves (both afferent and efferent)

Autonomic Nervous System Branch of peripheral nervous system Maintains balance in the involuntary functions of the body and allows the body to react in times of emergency 2 divisions: Sympathetic Parasympathetic Work together to maintain homeostasis

In times of emergency the sympathetic nervous system prepares the body to act Increased heart rate Increased respirations Increased blood pressure Decreased digestion After the emergency, the parasympathetic nervous system counteracts actions of the sympathetic nervous system Decreased heart rate Decreased respirations, etc.

Diseases/disorders Traumatic disorders – caused by injury: Concussion. Brain contusion. Congenital disorders – present at birth: Spina bifida. Hydrocephalus. Cerebral palsy. Cerebrovascular accident (CVA). Encephalitis. Epilepsy. Meningitis. Multiple sclerosis (MS) Neuralgia. Paralysis. Parkinson’s disease. Dementia. Alzheimer’s disease.

Epilepsy Seizure syndrome Disorder associated with abnormal electrical impulses in the neurons of the brain Causes Trauma Toxins Idiopathic (spontaneous) Treated with medications

Parkinson’s disease Chronic, progressive degeneration of brain cells usually in people over 50 y.o. Tremors, stiffness, muscular rigidity, forward leaning position, shuffling gait, mood swings, etc. Treatment is supportive and symptomatic

Shingles Herpes zoster Inflammation of nerve cells caused by herpes virus Same virus that causes chicken pox Occurs in thoracic area on one side of the body and follow path of affected nerves Itching, fever, increased skin sensitivity Treatment is to relieve pain and itching until inflammation subsides

Dementia General term defining a loss in at least two areas of complex behavior such as language, memory, visual/spatial abilities or judgment Does not mean that everyone that is forgetful has dementia

Alzheimer’s disease Progressive disease where initial symptom is usually a problem with remembering recently learning information Nerve endings in the cortex of the brain degenerate and block signals Cause is unknown and has 3 stages: 1st stage lasts 2-4 years and involves short-term memory loss, anxiety and poor judgment 2nd stage lasts 2-10 years and increases memory loss, difficulty recognizing people, motor problems, loss of social skills 3rd stage lasts 1-3 years and includes inability to recognize self, weight loss, seizures, mood swings, and aphasia (loss of speech).