Unit H: Nervous System

Neuron

• This is a nerve cell

• Functions to transmit a message from one cell to the next

• It contains a nucleus, cell body, cytoplasm, and a cell membrane

Dendrites carry messages towards the body.

• Extension of the neuron

• It is possible to have more than one dendrite on a nerve cell

• Is a path along which nerve impulses travel

Axons carry messages away from the cell body

• Another extension of nerve cell

• Only one axon per cell

• This covering produces a fatty substance called Myelin (AKA White Matter) which protects the axon

• Another path for nerve impulses to travel alone a nerve cell

• Covered by Neurolemma (also called Myelin Sheath) that speeds up the nerve impulse as it travels along the axon

Nervous Tissue

• All neurons possess the characteristics of being able to react when stimulated and of being able to pass (transmit) the nerve impulse generated on to other neurons

• Irritability – The ability to react when stimulated

• Conductivity – The ability to transmit  a disturbance to distant points

Types of Neurons

• Sensory (Afferent) Neurons – emerge from the skin or sense organs and carry messages or impulses towards the spinal cord and brain.

• Motor (Efferent)Neurons – carry messages away from the brain and spinal cord to the muscles and glands.

• Associative (Interneurons) – carry impulses from the sensory neuron to the motor neuron.

Synapse

• The area of the neuron where the message goes from one cell to the next.

• Messages go from the axon of one cell to the dendrite of another.

• They never touch!!!

• Synaptic cleft – the space between the cells.

• Conduction accomplished through neurotransmitters at the end of the axon

• Neurotransmitters-special chemicals that make it possible for messages to cross the synapse of a neuron to a target receptor

  • Epinephrine

  • Norepinephrine

  • Acetylcholine

Day 2: Division 1 - Central Nervous System (Brain and Spinal Cord)

• Protected by the skull, meninges, and the cerebrospinal fluid (CSF).

• Divided into 4 major parts: cerebrum, diencephalon, cerebellum, brain stem

• Adequate blood supply is needed, brain tissue will die in 4-8 mins with O₂

• Cerebral cortex (outer) made up of gray matter  with the highest center of reasoning & intellect.

• Deeper part of cerebral cortex is made up of myelinated nerve tracts  and is called white matter
  

• Cerebrum: Divided into two hemispheres (right and left)

  • Frontal lobe: Motor, Speech, Personality, Emotions, Intellect

  • Occipital lobe: Vision

  • Parietal lobe: Sensory: Pain, Heat, Cold, Touch Distance, Size, and Shapes

  • Temporal lobe: Hearing/Auditory & Smell/Olfactory

Structural Components:

CONVOLUTIONS (gyri) – elevated folds on the surface of the cerebrum, they increase the surface area of the brain

• Grooves separating cerebral convolutions are called

  • Fissures-deep  

  • Sulci-shallow

General Functions:

• Conscious thought, judgment, memory, reasoning, and will power.

Diencephalon

• Located between the cerebrum and the midbrain

• Damage could result in increased sensitivity to pain, or total loss of consciousness.

Structures include:

• Thalamus

  • Acts as a relay station for incoming and outgoing nerve impulses from sensory organs and from areas of the brain

• Hypothalamus

  • Autonomic nervous control (involuntary)

  • EXAMPLES:

    • Heart control: BP

    • Temperature control

    • Appetite control

    • Water Balance (thirst area)

    • Emotional state

    • Sleep control

    • Contractions for labor

    • Gastrointestinal Control

Limbic System - Tope of Brain Stem

• It influences unconscious and instinctive behaviors that relate to survival.

• And emotional control.

• Hippocampus helps to store and retain short-term memory.

• FYI>>>>Composed of the amygdala, hippocampus, cingulated gyrus, and other intricate structures.

Brain Stem

• Midbrain

• Pons

• Medulla Oblongata

Midbrain

• Involved with vision and hearing

Pons

• Pathway for nerve impulses between the cerebrum and cerebellum

Medulla Oblongata

• Controls the heart rate, respiration rate and depth

• Swallowing and vomiting

Cerebellum

• Located behind the pons and below the cerebrum

• Damage to the Cerebellum could result in motor impairment.

Functions:

• Maintenance of balance

• Maintenance of muscle tone

• Coordination of muscle movement

BESS Test

Balance Error Scoring System (BESS):

• Clinical Test Battery

  • Six 20 second trials using 3 different stances (double, single, tandem) on 2 different surfaces (firm, foam)

• Record Errors

  • Hands lifted off iliac crests

  • Opening eyes

  • Step, stumbles, or falls

  • Moving into >30 degrees of hip flexion or abduction

  • Remaining out of testing position for >5 seconds

Meninges

• Dura Mater-Outermost Layer

• Subdural space

• Arachnoid-Middle Layer

• Subarachnoid Space

• Pia Mater-Innermost Layer

Cerebral Spinal Fluid (CSF)

• CSF – acts as a shock absorber and source of nutrients for the brain

  • The average person has 140 to 270 mL of CSF.

Ventricles

• Lined cavities deep within the brain

• Filled with cerebrospinal fluid

• Choroid plexus – blood vessels that make cerebrospinal fluid

Surrounded by:

1. Vertebrae

2. Meninges

3. Cerebrospinal fluid

Functions as:

1. Reflex center

2. Conduction pathway to and from the brain

Division 2: Peripheral Nervous System - Cranial and Spinal Nerves

• It connects the CNS to the various body structures

• Functions – Control the automatic (involuntary) activities of the body

  • Act as the reflex center of the body

Knee Jerk Reflex

• The knee-jerk reflex is called a monosynaptic reflex because there is only one synapse in the circuit needed to complete the reflex. It only takes about 50 milliseconds between the tap and the start of the leg kick. That is fast! The tap below the knee causes the thigh muscle to stretch. Information is then sent to the spinal cord. After one synapse in the ventral horn of the spinal cord, the information is sent back out to the thigh muscle that then contracts.

Cranial Nerves

• 12 pairs

• Designated by number and name

• Name may give clue to its function

• Functions are concerned mainly with activities of the head and neck

• Sensory (afferent); Motor (efferent); Mixed (both) Nerves

Spinal Nerves

• 31 pairs

• All are Mixed nerves

• Named in relation to their location on the spinal cord

• Carry messages to and from the spinal cord and brain to all parts of the body

Cranial Nerve Assessment

I. Olfactory (s) – smell

II. Optic (s) – vision

III. Occulomotor (s/m) – blink; pupil reaction

IV. Trochlear (s/m) – eyeball movement

V. Trigeminal (s/m) – chewing

VI. Abducens (s/m) – eyeball movement

VII. Facial (s/m) – smile

VIII. Vestibulocochlear (s) – balance/snaps

IX. Glossopharyngeal (s/m) – saliva/BP

X. Vagus (s/m) – sharp/dull

XI. Accessory (s/m) – yes/no/so-so/swallow

XII. Hypoglossal (s/m) – stick out tongue/swallow

Vagus-supplies heart, lung, respiratory tract, GI tract, ear!

Autonomic Nervous System

• Includes nerves and plexuses which carry impulses to all smooth muscle, secretory glands and heart muscle.

• Regulates the activities of the heart, blood vessels, respiratory organs, alimentary canal, kidneys, urinary bladder and reproductive organs.

• Usually not under conscious control. They are automatic.

• Strongly influenced by emotion.

• During periods of fear, anger or stress, the sympathetic division acts to prepare the body for action.

• The effects of the parasympathetic counteract the effects.

• Operate as a pair, to keep the body balanced and functioning properly.

Sympathetic

• Referred to as the “fight or flight system”

• When the body perceives it is in danger or under stress, it prepares to run away or stand and fight.

Parasympathetic

• Helps to restore balance in the body afterwards.

The somatic nervous system is responsible for all voluntary muscle contractions and sensory information processing.

• The somatic nervous system innervates all sensory organs, including the eyes, ears, tongue, and skin, as well as all the skeletal muscles, and the muscles attached to the bone and used for voluntary movement.

Diseases and Disorders

Alzheimer’s Disease

Greatest Risk Population: Elderly and Genetics

Symptoms: Difficulty Remembering

Causes: Unknown, could be viral, plaque spots where neurons are dead, low production of neurotransmitter acetylcholine

Treated or Prevention: Continued education, cardiovascular exercise, estrogen replacement therapy, antioxidants such as vitamins C, E, and beta carotene and the use of anti - inflammatory agents

Parkinson’s Disease

• A progressive disorder that affects movement

Cause: Decrease in the neurotransmitter dopamine

Symptoms: Tremors, shuffling gait, pill-rolling, muscular rigidity

Who is most likely to have this disorder: Ages 40-60, Men, Heredity

Treatment: L-DOPA drugs or brain stimulation

Cerebral Palsy

• Problem with voluntary muscular activity result of brain problem (usually no problem with intellect)

Cause: Unknown (birth injury or abnormal brain development

Treatment: Therapy (through therapists and neurologists)

Multiple Sclerosis

• Chronic inflammatory disease attacking the myelin sheath of the axon

What are the symptoms?

• Weakness, numbness, double vision, speech problems, loss of coordination, nystagmus (eye tremors), paralysis

Who is most likely to develop it?

• Adults 20-40

• Mostly Women

How is it treated?

• Rest, exercise program, low stress, drugs like Avonex (interferon)

What is the prognosis?

• Can slow but not eliminate

What is epilepsy?

• Seizure disorder of the brain (grand mal-convulsions or petit mal-daze)

What is the cause?

• Unknown

What are the symptoms?

• Seizures , hallucinations, loss of consciousness

How is it treated?

• Medications called anticonvulsants

What is Hydrocephalus?

• Increased volume of CSF in the ventricles of the brain

What is cause?

• Blockage in ventricles

What are symptoms?

• Enlarged head

How is it treated?

• A bypass or shunt to divert spinal fluid

What is paralysis?

• Loss of movement or feeling

What is the cause?

• Injury or trauma to the spinal cord (nerve is disabled)

What are the symptoms?

• Depends on the location of the injury to the spinal cord

What is the prognosis?

• Realignment/stabilization, surgery, special medication, and rehabilitation

Spinal Cord injury:

• Quadriplegic-loss to trunk and all 4 limbs

• Paraplegic- loss could include part of the trunk and both legs

Neuritis

What is Neuritis?

• neur- -itis (nerve inflammation)

What are symptoms?

• Pain, hypersensitivity, loss of sensation, muscular atrophy, weakness, and paresthesia (tingling or crawling of skin)

What is cause of Neuritis?

• Infection, chemical, alcoholism from lack of Vitamin B, or improper Diet

How is it treated?

• Analgesics (pain medicine)

Meningitis

What is meningitis?

• Inflammation of the lining of the brain and spinal cord

What causes of meningitis?

• Bacterial or viral

What are the symptoms?

• Headache, fever, and stiff neck

How is it treated?

• Antibiotics

What is Poliomyelitis?

• Disease of the motor nerves in the spinal cord

What is the cause?

• Virus contaminated food or water

What is the impact of this disorder?

• Paralysis

How can it be prevented?

• Vaccine

How is it treated?

• Bedrest, pain medicine, ventilators

What is the prognosis?

• Mostly eliminated in the US but can lead to death

Cerebrovascular Accident

• Stroke or CVA

• Interruption of blood and oxygen to the brain

• Risk factors: Smoking, Hypertension, Heart disease; Family history

• 90% are caused by blood clots

• Clots lodge in carotid arteries, blocking the flow of blood to the brain

• 10% caused by ruptured blood vessels in the brain

Symptoms and Treatment of CVA (stroke)

• Hemiplegia—on opposite side of the body

• Sudden, severe headache

• Dizziness

• Sudden loss of vision in one eye

• Aphasia (can’t find the right words)

• Dysphagia (trouble speaking)

• Coma

• Possible death

Treatment: Get to the hospital immediately

CT done to determine etiology

If a clot, treatment aimed at dissolving clot

Traumatic Brain Injury (TBI)

• Sudden damage to the brain caused by a blow or jolt to the head

• Common causes include car or motorcycle crashes, falls, sports injuries, and assaults

• Ranges from mild concussions to severe permanent brain damage

• Those who survive a brain injury can face lasting effects in their physical and mental abilities as well as emotions and personality

• Most people who suffer moderate to severe TBI will need rehabilitation to recover and relearn skills.

Concussion

• Mild traumatic brain injury

• Caused by an impact to your head or after a whiplash-type

• Symptoms include headaches and problems with concentration, memory, balance and coordination

• Particularly common in contact sports, such as football

• An athlete with suspected concussion should not return to play until undergoes medical evaluation by a healthcare professional trained in managing concussions

West Nile Virus

• A virus that can caused by mosquitos

What is the symptoms?

• Encephalitis or Meningitis

Where is the greatest incidence of West Nile virus?

• Africa, Middle East, Parts of Asia (where mosquito population is high)

What are the risk factors?

• Visiting areas high in mosquitos, time of year, time outdoors

How is it prevented?

• Wear protective clothing, insect repellant, screens on windows and doors, prevent standing water, change out standing water areas

How is it treated?

• Treat the symptoms , Interferon (new)

Encephalitis

• Inflammation of the brain.

What are the symptoms?

• Mild flu-like symptoms (fever, fatigue, body aches)

Who is more likely to get encephalitis?

• Anyone- infants to older adults- people with weakened immune systems

What are complications of Encephalitis ?

• Brain damage, hearing loss, blindness, and/or death

What causes it?

• Exposure to viruses, bacteria, fungus, parasites. In US, most cases stem from West Nile Virus.

How is it treated?

• People with encephalitis receive immediate, aggressive medical treatment. The disease can progress quickly and cause irreversible neurological damage.