Nervous System Overview Quiz

Nervous System Overview

• The nervous system allows communication between cells through sensory input, integration of data, and motor output.
• Two cell types are neurons and neuroglia.

Nervous Divisions

• Two divisions:
  • Central nervous system (CNS): Composed of the brain and spinal cord.
  • Peripheral nervous system (PNS): Includes nerves and ganglia (collections of cell bodies).

Types of Neurons

• Three types:
  • Sensory neurons: Carry impulses from sensory receptors to the CNS.
  • Interneurons: Receive information within the CNS and send it to motor neurons.
  • Motor neurons: Carry impulses from the CNS to effectors (glands or muscle fibers).

Neuron Structure

• Cell body: Contains the nucleus and most organelles.
• Dendrites: Short extensions that carry impulses to the cell body.
• Axon (nerve fiber): A long extension that carries impulses away from the cell body.

Myelin Sheath

• A lipid covering on long axons that increases the speed of nerve impulse conduction, provides insulation, and aids regeneration (in the PNS).
• Schwann cells: Neuroglia that form the myelin sheath in the PNS.
• Nodes of Ranvier: Gaps between myelination on the axons.
• Saltatory conduction: Conduction of the nerve impulse from node to node.

The Nerve Impulse: Resting Potential (RP)

• Resting potential: The state when the axon is not conducting a nerve impulse.
• More positive ions are outside the membrane than inside.
• Negative charge of -70 mV inside the axon.
• More sodium (Na+) ions outside the axon than inside.
• More potassium (K+) ions inside the axon than outside.

The Nerve Impulse: Action Potential

• Action potential: A rapid change in the axon membrane that enables a nerve impulse to occur.
• Sodium gates open, allowing sodium (Na+) ions to enter.
• Depolarization: The interior of the axon loses its negative charge (-55 mV, then +35 mV).
• Potassium gates open, allowing potassium (K+) ions to leave.
• Repolarization: The interior of the axon regains its negative charge (-70 mV).
• Wave of depolarization/repolarization travels down the axon.

The Synapse

• A synapse is a small gap between a sending neuron (presynaptic membrane) and a receiving neuron (postsynaptic membrane).
• Transmission across the synapse is accomplished by neurotransmitters (e.g., acetylcholine (ACh), dopamine, or serotonin).
• Neurotransmitters are stored in synaptic vesicles in the axon terminals.

Synaptic Transmission

• Nerve impulse reaches the axon terminal.
• Calcium ions enter the axon terminal and stimulate synaptic vesicles to fuse with the presynaptic membrane.
• Neurotransmitters are released and diffuse across the synapse.
• Neurotransmitters bind to the postsynaptic membrane, either inhibiting or exciting the neuron.

Synaptic Integration

• Integration is the summation of inhibitory and excitatory signals received by a postsynaptic neuron.
• Neurons receive multiple signals.

Central Nervous System (CNS)

• Includes the brain and spinal cord.
• Protected by: bones (skull and vertebral column), meninges (three protective membranes), cerebrospinal fluid (CSF) which cushions and protects.
• CNS is composed of:
  • Gray matter: Contains cell bodies and nonmyelinated fibers.
  • White matter: Contains myelinated axons.

CNS: Spinal Cord

• Extends from the brain's base along the vertebral canal.
• Functions in communication between the brain and most of the body.
• Center for reflex arcs.
• Gray matter is butterfly-shaped, white matter surrounds it.

CNS: Brain

• Four major parts:
  • Cerebrum
  • Diencephalon
  • Cerebellum
  • Brain stem

CNS: Cerebrum

• Cerebral hemispheres: Major structures of the cerebrum.
• Cerebral cortex: The thin, outer layer of gray matter.
  • Primary motor area: Voluntary control of skeletal muscles.
  • Primary somatosensory area: Processes sensory information from skeletal muscles and skin.
  • Association areas: Integration occurs here.
  • Processing centers: Perform higher-level analytical functions (e.g., Wernicke's and Broca's areas involved in speech).

CNS: Diencephalon

• Includes the hypothalamus and thalamus.
  • Hypothalamus: Maintains homeostasis (e.g., hunger, sleep, thirst, body temperature, and water balance) and controls the pituitary gland.
  • Thalamus: Receives all sensory input except smell; involved in memory and emotions.
  • Pineal gland: Secretes melatonin and controls daily rhythms.

CNS: Cerebellum

• Receives and integrates sensory input from eyes, ears, joints, and muscles; provides information about the current position of the body.
• Functions: Maintains posture, coordinates voluntary movement, allows learning of new motor skills.

CNS: Brain Stem

• Includes the midbrain, pons, and medulla oblongata.
  • Midbrain: Relay station between the cerebrum and spinal cord or cerebellum, has reflex centers.
  • Pons: A bridge between the cerebellum and the CNS; regulates breathing rate; reflex center for head movements.
  • Medulla oblongata: Contains reflex centers for regulating breathing, heartbeat, and blood pressure.
  • Reticular formation: A major component of the reticular activating system (RAS) that regulates alertness.

Limbic System

• Connects primitive emotions (fear, pleasure) with higher functions (reasoning).
• Can cause strong emotional reactions, but conscious thought often overrides.
  • Amygdala: Imparts emotional overtones.
  • Hippocampus: Important for learning and memory.

Peripheral Nervous System (PNS)

• Includes cranial nerves (12 pairs), spinal nerves (31 pairs), and ganglia outside the CNS.
  • Spinal nerves: Conduct impulses to and from the spinal cord.
  • Cranial nerves: Conduct impulses to and from the brain.
• Two divisions:
  • Somatic division: Serves the skin, skeletal muscles, and tendons.
    • Reflexes: Automatic responses.
  • Autonomic division: Regulates involuntary muscles (e.g., cardiac and smooth muscles) and glands.
    • Two divisions:
      • Sympathetic division: Coordinates the "fight or flight" response.
      • Parasympathetic division: Counters the sympathetic system to bring the body back to a relaxed state.