Comprehensive Notes on the Nervous System

Nervous System

Introduction

• The nervous system is complex, containing 10 billion nerve cells.

• It controls both voluntary and involuntary functions.

• It carries electrical messages throughout the body.

• It responds to external and internal receptors.

• Nerve cells (neurons) are microscopic and collected into macroscopic nerves.

• Neurons carry electrical messages all over the body.

General Structure

• The nervous system has two major divisions:

  • Central Nervous System (CNS):

    • Brain

    • Spinal cord

  • Peripheral Nervous System (PNS):

    • Cranial nerves

    • Spinal nerves

    • Plexuses

    • Peripheral nerves throughout the body

• Cranial and Spinal Nerves:

  • Sensory nerves: Carry messages toward the brain.

  • Motor nerves: Carry messages from the brain.

  • Mixed nerves: Carry both sensory and motor fibers.

• Sensory receptors are present.

• Autonomic Nervous System:

  • Carries impulses from the CNS to the organs.

  • Sympathetic nerves stimulate the body under stress.

  • Parasympathetic nerves balance the sympathetic system by slowing heart rate and lowering blood pressure.

Neurons, Nerves, and Glia

• Neuron: Individual nerve cell

  • Dendrite

  • Cell nucleus

  • Axon:

    • Myelin sheath

    • Neurilemma

  • Terminal end fibers (secrete neurotransmitters)

  • Neurotransmitters transfer impulse across the synapse.

• Ganglia: Small clusters of nerve cell bodies.

• Glia cells: Maintain the health of the nervous system but do not transmit impulses.

  • Four types of glial cells:

    • Astrocytes (astroglial cells)

    • Microglia (microglial cells)

    • Oligodendroglia (oligodendroglial cells)

    • Ependymal cells

The Brain

• Cerebrum:

  • Largest section of the brain.

  • Surface nerve cells are called the cerebral cortex.

  • Manages speech, vision, smell, movement, hearing, and thought.

• Cerebellum:

  • Coordinates voluntary movements.

  • Maintains balance.

• Thalamus:

  • Integrates and monitors impulses from the skin, including pain.

• Hypothalamus:

  • Controls body temperature, sleep, appetite, sexual desire, and emotions.

  • Regulates the release of hormones from the pituitary gland.

  • Monitors sympathetic and parasympathetic nervous systems.

• Brainstem:

  • Pons:

    • Bridges the cerebrum and cerebellum with the rest of the brain.

    • Houses nerves for the face and eyes.

  • Medulla Oblongata:

    • Connects the spinal cord to the brain.

    • Nerve tracts from side to side.

    • Regulates blood vessels, heart, and respiratory system.

Spinal Cord and Meninges

• Meninges (no details provided in the text)

• Spinal cord (no details provided in the text)

Vocabulary

• Acetylcholine: Neurotransmitter released at the ends of nerve cells.

• Afferent nerve: Carries messages toward the brain and spinal cord.

• Arachnoid membrane: Middle layer of the three membranes that surround the brain and spinal cord.

• Astrocyte: Glial cell that transports water and salts from capillaries.

• Autonomic nervous system: Nerves that control involuntary body functions of muscles, glands, and internal organs.

• Axon: Microscopic fiber that carries the nervous impulse along a nerve cell.

• Blood-brain barrier: Protective separation between the blood and brain cells that keeps substances from penetrating capillary walls and entering the brain.

• Brainstem: Posterior portion of the brain that connects the cerebrum with the spinal cord.

• Cauda equina: Collection of spinal nerves below the end of the spinal cord.

• Cell body: The part of a nerve cell that contains the nucleus.

• Central nervous system (CNS): The brain and spinal cord.

• Cerebellum: The posterior part of the brain that coordinates muscle movements and maintains balance.

• Cerebral cortex: Outer region of the cerebrum; contains sheets of nerve cells; gray matter.

• Cerebrospinal fluid: Circulates throughout the brain and spinal cord.

• Cerebrum: The largest part of the brain; responsible for voluntary muscle activity, vision, speech, taste, hearing, thought, and memory.

• Cranial nerves: Twelve pairs; carry messages to and from the brain with regard to the head and neck (except the vagus nerve).

• Dendrite: Microscopic branching fiber of a nerve cell; the first part to receive the nervous impulse.

• Dura mater: The thick, outermost layer of the meninges surrounding and protecting the brain and spinal cord.

• Efferent nerve: Carries messages away from the brain and spinal cord; motor nerve.

• Ependymal cell: Glial cell that lines the membranes within the brain and spinal cord; helps form cerebrospinal fluid.

• Ganglion: Collection of nerve cell bodies in the peripheral nervous system.

• Glial cell: Supportive and connective nerve cell that does not carry nervous impulses; can reproduce itself.

• Gyrus: Sheet of nerve cells that produces a rounded ridge on the surface of the cerebral cortex; convolution.

• Hypothalamus: The portion of the brain beneath the thalamus; controls sleep, appetite, body temperature, and pituitary gland secretions.

• Medulla oblongata: The part of the brain just above the spinal cord; controls breathing, heartbeat, and size of blood vessels.

• Meninges: Three protective membranes that surround the brain and spinal cord.

• Microglial cell: Phagocytic glial cell that removes waste products from the central nervous system.

• Motor nerve: Carries messages away from the brain and spinal cord to muscles and organs; efferent nerve.

• Myelin sheath: Covering of white fatty tissue that surrounds and insulates the axon of a nerve cell; speeds impulse conduction.

• Nerve: Macroscopic cord-like collection of fibers (axons and dendrites) that carry electrical impulses.

• Neuron: Nerve cell that carries impulses throughout the body; parenchyma of the nervous system.

• Neurotransmitter: Chemical messenger released at the end of a nerve cell; stimulates or inhibits another cell.

• Oligodendroglial cell: Glial cell that forms the myelin sheath covering axons; oligodendrocyte.

• Parasympathetic nerves: Involuntary, autonomic nerves that regulate normal body functions such as heart rate, breathing, and muscles of the gastrointestinal tract.

• Parenchyma: Essential, distinguishing tissue of any organ or system; for the nervous system, neurons and nerves that carry impulses.

• Peripheral nervous system: Nerves outside the brain and spinal cord; cranial, spinal, and autonomic nerves.

• Pia mater: The thin, delicate inner membrane of the meninges.

• Plexus: A large, interlacing network of nerves.

• Pons: The part of the brain anterior to the cerebellum and between the medulla and the rest of the midbrain.

• Receptor: An organ that receives a nervous stimulus and passes it on to afferent nerves; the skin, ears, eyes, and taste buds are receptors.

• Sciatic nerve: The nerve extending from the base of the spine down the thigh, lower leg, and foot.

• Sensory nerve: Carries messages toward the brain and spinal cord from receptors; afferent nerve.

• Spinal nerves: Thirty-one pairs arising from the spinal cord.

• Stimulus: An agent of change (light, sound, touch) in the internal or external environment that evokes a response.

• Stroma: Connective and supporting tissue of an organ; glial cells are the stromal tissue of the brain.

• Sulcus: Depression or groove in the surface of the cerebral cortex; fissure.

• Sympathetic nerves: Autonomic nerves that influence bodily functions involuntarily in times of stress.

• Synapse: The space through which a nervous impulse travels between nerve cells or between nerve and muscle or glandular cells.

• Thalamus: Main relay center of the brain; conducts impulses between the spinal cord and the cerebrum.

• Vagus nerve: Tenth cranial nerve; branches reach to the larynx, trachea, bronchi, lungs, aorta, esophagus, and stomach.

• Ventricles of the brain: Canals in the brain that contain cerebrospinal fluid.

Quick Quiz Answers

• Question 1: B. gyrus

• Question 2: A. pia mater

• Question 3: D. Neuralgia

• Question 4: B. Epidural

Terminology: Combining Forms

Organs and Structures

• cerebell/o: cerebellum

• cerebr/o: cerebrum

• dur/o: dura mater

• (encephal/o): brain

• gli/o: glial cells

• lept/o: thin, slender

• mening/o, meningi/o: membranes, meninges

• my/o: muscle

• myel/o: spinal cord

• neur/o: nerve

• pont/o: pons

• radicul/o: nerve root

• thalam/o: thalamus

• thec/o: sheath (refers to meninges)

• vag/o: vagus nerve

Symptoms

• alges/o, -algesia: excessive sensitivity to pain

• -algia: pain

• caus/o: burning

• comat/o: deep sleep

• esthesi/o, -esthesia: feeling, nervous sensation

• kines/o, -kinesia: movement

• -kinesis, kinetic: movement

• -lepsy: seizure

• lex/o: word, phrase

• -paresis: slight paralysis

• -phasia: speech

• -plegia: paralysis

• -praxia: action

• -sthenia: strength

• syncop/o: cut off

• tax/o: order, coordination

Pathology

Congenital Disorders

• Hydrocephalus

• Spina bifida

  • Spina bifida cystica

  • Spina bifida occulta

Degenerative Movement and Seizure Disorders

• Alzheimer disease (AD)

• Amyotrophic lateral sclerosis (ALS)

• Epilepsy

• Huntington disease (Huntington chorea)

• Multiple sclerosis (MS)

• Myasthenia gravis (MG)

• Palsy

• Parkinson disease

• Tourette syndrome

Infectious Disorders

• Herpes zoster (shingles)

• Meningitis

• Human immunodeficiency virus (HIV) encephalopathy

Traumatic Disorders

• Cerebral concussion:

  • Temporary brain dysfunction after injury.

  • There may be no evidence of structural damage or loss of consciousness.

  • Rest is important for healing; usually clears within 24 hours.

• Cerebral contusion:

  • Bruising of brain tissue through direct trauma.

  • Associated with skull fracture, edema, and increased intracranial pressure.

  • Neurological deficits persist longer than 24 hours.

Vascular Disorders

• Cerebrovascular accident (CVA):

  • Thrombotic: Blood clot in an artery leaving the brain.

  • Embolic: Dislodged clot that travels to the cerebral arteries.

  • Hemorrhagic: Blood vessel breaks and bleeding occurs.

• Migraine: A severe, recurring, unilateral, vascular headache.

Clinical Procedures

X-ray Tests:

• Cerebral angiography

• Computed tomography (CT) of the brain

• Myelography

Other Procedures:

• MRI—Magnetic resonance Imaging

• PET—Positron emission scan

• EEG—Electroencephalography

Abbreviations

• AD: Alzheimer disease

• AFP: alpha-fetoprotein

• ALS: amyotrophic lateral sclerosis

• AVM: arteriovenous malformation

• BBB: blood brain barrier

• CNS: central nervous system

• CT: computed tomography

• CSF: cerebrospinal fluid

• CVA: cerebrovascular accident

• EEG: electroencephalogram

• GABA: gamma-aminobutyric acid (neurotransmitter)

• ICP: intracranial pressure; normal pressure is 5 to 15 mmHG

• LP: lumbar puncture

• MAC: monitored anesthetic care

• MG: myasthenia gravis

• MRA: magnetic resonance angiography

• MRI: magnetic resonance imaging

• 1/2 P: hemiparesis

• PCA: patient-controlled anesthesia

• PNS: peripheral nervous system

• PET: positron emission tomography

• Sz: seizure

• TBI: traumatic brain injury

• TENS: transcutaneous electrical nerve stimulation

• TIA: transient ischemic attack

• TLE: temporal lobe epilepsy

• tPA: tissue plasminogen activator