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).