Nervous System Flashcards

Nervous System

Nervous System Functions & Organs

  • Function: Detects impulses from senses; control center.
  • Major Organs:
    • Brain
    • Spinal cord
    • Senses
    • Nerves

Organization of the Nervous System

  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Other nerves.
    • Cranial nerves: Originate in the brain.
    • Spinal nerves: Originate in the spinal cord.

Peripheral Nervous System (PNS) Divisions

  • Motor (Efferent) Division: Sends impulses from the CNS to muscles and glands.
    • Autonomic Nervous System: Involuntary muscle control.
    • Somatic Nervous System: Voluntary muscle control.
      • Sympathetic Division: Emergency situations ("fight or flight").
      • Parasympathetic Division: Reduces sympathetic response, provides resting functions.
  • Sensory (Afferent) Division: Sends impulses from senses to the CNS.

Major Functions of the Nervous System

  • Sensory input: Detects changes (stimuli).
  • Integration: Processes and interprets information.
  • Response: Activates muscles or glands.

Types of Nerve Cells

  • Neurons: Conduct impulses (10% of nerve cells).
  • Neuroglia ("nerve-glue"): Support, insulate, and protect neurons (90% of nerve cells).

Neuron Structure

  • Cell body: Contains the nucleus, cytoplasm, and organelles.
  • Processes:
    • Dendrites: Bring impulses towards the cell body.
    • Axons: Send impulses away from the cell body.
    • Axon terminals: Release neurotransmitters to pass impulses to the next neuron.

Types of Neurons (classification)

  • By number of processes:
    • Unipolar: Single process.
    • Bipolar: Two processes.
    • Multipolar: Many processes.
  • By function:
    • Afferent neurons: Carry impulses toward the CNS.
    • Efferent neurons: Carry impulses away from the CNS.
    • Interneurons: Connect afferent & efferent neurons.

Myelin Sheath Creation

  • Schwann cells wrap around the axon to form myelin.
  • Neurilemma: Outer layers of the Schwann cell.
  • Myelin sheath: Collective myelin wrappings with gaps called Nodes of Ranvier.

Functions of Neuroglia

  • CNS:
    • Astrocytes: Support & anchor neurons to capillaries.
    • Microglia: Immune response.
    • Ependymal cells: Secrete and circulate cerebrospinal fluid.
    • Oligodendrocytes: Myelin insulation.
  • PNS:
    • Satellite cells: Support and anchor neurons.
    • Schwann cells: Myelin insulation.

Nerve Impulse Transmission

  • Resting potential: Neuron's intracellular space is negatively charged, extracellular space is positively charged.
  • Action potential: Sodium rushes in, reversing charges (depolarization).
  • Repolarization: Potassium diffuses out.
  • Sodium-potassium pump: Restores ion concentrations to normal.
  • All-or-none response: either the threshold is met and the impulse proceeds, or it never starts.

Events at a Synapse

  • Synapse: Where 2 neurons meet; they don't touch (separated by the synaptic cleft).
  • Impulse stimulates vesicles to release neurotransmitters across the synaptic cleft.
  • Neurotransmitters cause channels to open in the next neuron, continuing the action potential.

Protection of the Central Nervous System

  • Meninges (3 layers of connective tissue)
    • Dura mater: Thick, tough layer
    • Arachnoid membrane: Thin, cobweb-like layer
    • Pia mater: Thin layer containing lots of blood vessels
  • Cerebrospinal fluid (CSF): Between arachnoid and pia mater; protects the brain, maintains the blood-brain barrier.

Cerebrospinal Fluid

  • Produced in ventricles within the brain.
  • There are 4 ventricles: 2 lateral ventricles, third ventricle & fourth ventricle.
  • CSF is constantly being produced, circulated and reabsorbed within these ventricles.
  • Choroid plexuses secrete CSF and is absorbed by arachnoid granulations into the blood.

Major Regions of the Cerebrum

  • Two hemispheres (right and left) connected by the corpus callosum.
  • Surface covered in ridges (gyri) and grooves (sulci).
  • Deeper grooves called fissures divide portions of the brain.

Layers of the Brain

  1. Cerebral cortex: "Gray matter" (cell bodies & dendrites).
  2. Cerebral medulla: "White matter" (myelinated axons).
  3. Basal nuclei: Islands of gray matter.

Functions of the Lobes within the Cerebrum

  • Frontal lobe: Voluntary movements, reasoning, decision-making, memory, planning, verbal communication.
  • Parietal lobe: Sensations, visual-spatial processing, body position.
  • Occipital lobe: Visual processing.
  • Temporal lobes: Memory, comprehension & pronunciation of words, sensations of smell and sound, emotional association of memories.

Structures in the Diencephalon

  • Thalamus: Relays sensory impulses to the cerebral cortex.
  • Hypothalamus: Autonomic processes, hormone control, part of the limbic system.
  • Pineal gland: It will be discussed in the endocrine system.

Structures in the Brain Stem

  • Midbrain: Relays information to cerebrum, controls body movements and posture.
  • Pons: Links cerebral cortex and cerebellum, carries information from one side of the brain to the other, central control of breathing.
  • Medulla Oblongata: Transmits impulses between spinal cord and brain, controls blood pressure, heart rate, swallowing, and coughing.

Function of the Cerebellum

  • Coordinates movements directed by the cerebrum, aids in “muscle memory”.

Structure and Function of the Spinal Cord

  • Extends from the medulla oblongata to the lumbar vertebrae.
  • Covered by meninges.
  • Relays impulses between the peripheral nervous system and the brain through 31 pairs of spinal nerves.
  • Dorsal horns receive impulses from afferent nerves, then pass the impulses through the ventral horns to the efferent nerves.
  • Dorsal and ventral roots contain the nerve fibers and join together to form a 2-directional spinal nerve.

Reflex Arc

  • Reflexes: Preprogrammed responses.
  • Involves:
    1. A receptor
    2. Sensory neurons
    3. Integration
    4. Motor neurons
    5. An effector
  • Reflexes can be somatic (involving skeletal muscles) or autonomic (involving smooth muscles).