The Nervous System

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The Nervous System
Unit K
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Central Nervous System

• Communication and coordination system of the body
• Seat of intellect and reasoning.
• Consists of the brain, spinal cord, and nerves.

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Neuron

• -Nerve cell
• -Transmits a message from one cell to another
• -Has a nucleus, cytoplasm, and cell membrane

Dendrites Nerve cell processes that carry
impulse to cell bodymay be one or more
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• Myelin Sheath
• Myelin is a fatty substance that protects axon
• speeds transmission along axon - Called
  neurilemma

• Axon
• -Carries impulses away from the cell body
• -Only one on a neuron

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NERVE IMPULSE

• A STIMULUS creates an IMPULSE.
• Impulse to dendrite to axon to neurotransmitter
  to synapse.

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SYNAPSE

• A space between neurons, messages go from one
  cell to another.

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SENSORY NEURONS (AFFERENT)

• Emerge from the skin or sense organs.
• Carry impulses to spinal cord and brain.

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MOTOR NEURONS (EFFERENT)

• Carry messages from brain and spinal cord to
  muscles and glands.

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ASSOCIATIVE NEURONS (INTERNEURONS)

• Carry impulses from sensory neurons to motor
  neurons.

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NEUROGLIA

• Cells that insulate, support and protect the
  neurons, nerve glue.

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CENTRAL NERVOUS SYSTEM
Divisions of the Nervous System

• The brain and spinal cord

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Autonomic Nervous System

• Peripheral nerves and ganglia
• Supplies heart muscle, smoother muscle and
  secretory glands
• Involuntary i.e. automatic responses to injury
  like shock and increased heart rate

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Peripheral Nervous System (PNS)

• Cranial nerves and spinal nerves are part of the
  PNS

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The Brain

• 3lb mass of soft nervous tissue
• 100 billion neurons
• Protected by skull, 3 membranes called meninges,
  and cerebrospinal fluid (shock absorber)

Cerebrum
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• Adequate blood supply is needed, brain tissue
  will die in 4-8 mins without O2
• Divided into 4 major parts cerebrum,
  diencephalon (near midbrain), cerebellum, brain
  stem

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Coverings of the Brain (MENINGES)

• Meninges surrounds the brain and spinal cord

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• DURA MATER- outer brain covering, lines inside of
  skull, tough, fluid-containing - dense fibrous
  connective tissue
• Layers dura mater, subdural, arachnoid,
  subarachnoid, pia mater

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Coverings contd

• Subdural space
• is between the dura and arachnoid space

Next layer is the Arachnoid layer - middle layer
resembles fine cob web
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• SUBARACHNOID SPACE- between arachnoid and pia
  mater, filled with CEREBROSPINAL FLUID which acts
  as a liquid shock absorber and as a source of
  nutrients for the brain

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Coverings contd

• PIA MATER
• innermost layer of the meninges
• covers the brains surface, comprised of blood
  vessels held together by connective tissue

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Ventricles of the Brain

• Brain contains four cavities filled with
  cerebrospinal fluid called CEREBRAL VENTRICLES.

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Ventricles of the Brain (cont.)

• CHOROID PLEXUS- network of blood vessels lining
  the ventricles which helps in the formation of
  cerebrospinal fluid.
• CEREBROSPINAL FLUID
• Forms inside ventricles of the brain.
• Serves as a liquid shock absorber

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• BLOOD-BRAIN BARRIER- choroid plexus capillaries
  prevent substances (like drugs) from penetrating
  brain tissue this makes infections, like
  meningitis, difficult to cure.
• LUMBAR PUNCTURE- removal of CSF from spinal
  canal, needle puncture between 3rd and 4th lumbar
  vertebrae.

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CEREBRUM

• Largest part of the brain
• Divided into R and L hemispheres by deep groove
• CONVULTIONS- elevated folds on the surface of the
  cerebrum, they increase the surface area of the
  brain

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SULCI - fissure or grooves separating cerebral
convolutions Divided into four lobes FRONTAL
(voluntary muscle movement), PARIETAL, OCCIPITAL
and TEMPORAL
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CEREBRAL FUNCTION

• Conscious thought, judgment, memory, reasoning,
  and will power.
• - responsible for maintaining consciousness,
• decision making, recalling information
• and normal speech
• These people were not
• using their cerebrum.

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• DIENCEPHALON
• Located between cerebrum and midbrain
• Composed of THALAMUS and HYPOTHALAMUS

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• Vital functions of the hypothalamus
• 1. Autonomic nervous control
• 2. Temperature control
• 3. Appetite control
• 4. Emotional state
• 5. Sleep control

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• CEREBELLUM
• 2nd largest part of brain
• Composed of two hemispheres
• below the cerebrum
• Controls all body functions related to skeletal
  muscles, including
• Balance, walking
• Muscle tone
• Coordination of muscle movements

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• Controls all body functions related to skeletal
  muscles, including
• Balance, walking
• Muscle tone
• Coordination of muscle movements

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BRAIN STEM

• Made up of PONS, MEDULLA and MIDBRAIN
• Pons in front of cerebellum, between midbrain
  and medulla contains center that controls
  respiration
• Midbrain controls vision and hearing
• Medulla oblongata bulb-shaped structure between
  pons and spinal cord, inside the cranium above
  foramen magnum (opening in vertebral column)
• - Responsible for
• 1. Heart rate
• 2. Blood pressure

Click for picture
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SPINAL CORD

• Begins at foramen magnum and continues down to
  2nd lumbar vertebrae
• White and soft, in spinal canal
• Surrounded by cerebrospinal fluid
• FUNCTIONS AS
• Reflex center
• Conduction pathway to and from the brain

Injury to spinal cord difficulty with movement
(paraplegia paralysis of legs) and problems
breathing
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Peripheral Nervous System

• All of the nerves outside the central nervous
  system
• NERVES
• Contains sensory and motor nerves (afferent and
  efferent)

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Cranial Nerves

• 12 pairs
• Begin in the brain
• Designated by number and name

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On Old Olympus Towering Top A Finn
And German Vault And Hop
Mnemonic for the 12 cranial nerves
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• SPINAL NERVES
• Originate at spinal cord and go through openings
  in vertebrae
• 31 pairs of spinal nerves
• All are mixed (afferent and motor) nerves
• Named in relation to their location on the spinal
  cord

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• AUTONOMIC NERVOUS SYSTEM
• Regulates activities of visceral organs (i.e.
  beating of heart)
• Not subject to conscious control
• SYMPATHETIC NERVOUS SYSTEM- the fight or flight
  system- when the body perceives danger, SNS sends
  message to adrenal medulla (above kidney) to
  secrete adrenaline - heartbeat increases, resp
  rate increases, etc

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• Parasympathetic Nervous system counters SNS
  decreases heart rate, decreases respiratory rate,
  etc
• REFLEX
• Unconscious and involuntary
• In a simple reflex, only a sensory nerve and
  motor nerve involved example knee-jerk
  reflex

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Disorders of the Nervous System

• MENINGITIS
• Inflammation of the lining of the brain and
  spinal cord
• May be bacterial or viral
• Symptoms- headache, fever and stiff neck, nausea
  and vomiting
• In severe form, may lead to paralysis, coma and
  death
• If bacterial, may be treated with antibiotics
• Dx by removing csf with a needle lumbar puncture

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• EPILEPSY
• Seizure disorder of the brain, characterized by
  recurring and excessive discharge from neurons
• Seizures believed to be result of spontaneous,
  uncontrolled electrical activity of neurons
• Cause Uncertain
• Victim may have hallucinations and seizures
• Grand mal severe, convulsive seizure
• Petit mal - milder

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CEREBRAL PALSY

• Disturbance in voluntary muscular action due to
  brain damage.
• May be due to birth injury or abnormal brain
  development
• Spastic Quadriplegia- spastic paralysis in all
  four limbs.
• Sx- head rolling, grimacing,
• difficult speech and swallowing
• No impairments of intellect.

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• POLIOMYELITIS
• Viral disease of nerve pathways of spinal cord-
  causing progressive muscle weakness leading to
  paralysis
• Almost eradicated in USA (vaccine)
• DEMENTIA
• Loss of 2 areas of complex behavior, such as
  languages, memory, visual and spatial abilities,
  or judgment
• Interferes with persons daily life.

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HYDROCEPHALUS

• Increased volume of cerebrospinal fluid within
  ventricles of the brain.
• Usually, blockage in 3rd and 4th ventricle
• Enlargement of the head, usually noticed at
  birth.
• Bypass or shunt performed to relieve pressure.

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• ALZHEIMERS DISEASE
• Progressive disease that begins with problems
  remembering characterized by early senility,
  confusion, and loss of recognition of persons
• Nerve endings in cortex of brain degenerate and
  block signals that pass between nerve cells
• Abnormal fibers build up creating tangles

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• Cause Unknown
• 1st stage (2-4 yrs) involves confusion,
  short-term memory loss, anxiety, poor judgment
• 2nd stage (2-10 yrs) increase in memory loss,
  logic problems, and loss of social skills
• 3rd stage (1-3 yrs) inability to recognize
  oneself, weight loss, seizures, mood swings and
  aphasia

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• PARKINSONS DISEASE
• Symps - tremors, shuffling gait, pill-rolling,
  and muscular rigidity.
• Decrease in neurotransmitter dopamine
• RX- L-dopa and other drugs to treat symptoms.

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• MULTIPLE SCLEROSIS (MS)
• Chronic inflammatory disease of CNS - autoimmune
• Immune cells attack myelin sheath of axon-myelin
  sheath destroyed, leaving scar tissue on nerve
  cellstransmission of nerve impulses blocked.

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• Cause- UNKNOWN
• Sx- weakness of extremities, numbness, double
  vision, nystagmus, speech problems, loss of
  coordination, possible paralysis.
• Typically strikes young adults age 20-40, mostly
  women
• Rx- Avonex- slows progression

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Cerebral Vascular Accident

• Stroke or CVA
• Interruption of blood and O2 to the brain
  blockage of blood to the brain
• Tissue death
• Third leading cause of death in USA

• PARALYSIS- loss of power of motion or sensation
• HEMIPLEGIA- paralysis on one side of the body

Symptoms ?
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• Risk Factors
• Smoking
• Hypertension
• Heart disease
• Family history
• Causes of CVA
• 90 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

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• SYMPTOMS
• Hemiplegia on the opposite side of the body
• Sudden, severe headache
• Dizziness
• Sudden loss of vision in one eye
• Aphasia
• Dysphasia
• Coma
• Possible death