Comprehensive Notes on Nervous System Functions and Neuroglia lecture

Central Nervous System Functions

• Brain and spinal cord process sensory information from external and internal environments.
• Receptors detect changes and generate sensory nerve impulses (action potentials).
• Sensory impulses are sent to the CNS for interpretation.
• CNS processes incoming information and decides whether to generate a response.
• Motor nerve impulses (motor commands) are generated as a response.
• Higher-level functions like memory, intelligence, learning, and emotional states are centered in the CNS.

Peripheral Nervous System

• Composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves.
• Delivers sensory information to the CNS.
• Carries motor impulses from the CNS to peripheral tissues.
• A nerve is a collection or bundle of axons.

Enteric Nervous System (ENS)

• Part of the nervous system found in the gut.

Divisions of the Peripheral Nervous System

• Afferent Division: Carries sensory information (sensory).
• Efferent Division: Carries motor commands (motor).

Efferent Division Synapses

• Motor nerves synapse with:
  • Muscle fibers (skeletal, cardiac, or smooth).
  • Glandular cells (causing glandular secretion).
  • Adipose tissue (acting like an endocrine organ).

Receptors

• Detect changes in the environment (stimuli).
• Respond to stimuli. Can be simple nerve endings or specialized cells (e.g., eyes and ears).

Effectors

• Muscle fibers, glandular cells, and adipose tissue.
• Motor nerve impulses affect these, bringing about a response.

Divisions of the Efferent (Motor) Part of the Peripheral Nervous System

Somatic Nervous System:

• Controls skeletal muscle contraction.

Autonomic Nervous System:

• Subconscious control.
• Controls cardiac muscle, smooth muscle, glandular secretion, and hormonal activity from adipose tissue.
• Two divisions:
  • Sympathetic: Dominant during fight or flight responses (stress).
    • Increases heart rate, blood pressure, and respiratory rate; decreases digestive activity.
  • Parasympathetic: Dominant during rest and digest.
    • Decreases heart rate, blood pressure, and respiratory rate; increases digestive efficiency.

Enteric Nervous System (Continued)

• Found in the walls of the digestive tract (100 million cells).
• Coordinates local reflexes in the gut.
• The autonomic nervous system can influence the ENS.

Neurons

• Functional cells that create and carry nerve impulses (action potentials).

Major Parts of a Neuron

• Cell Body (Soma):
  • Contains a single nucleus.
  • Cytoplasm called perikaryon.
  • Numerous mitochondria and strong collections of rough endoplasmic reticulum (rough ER).
  • Dense areas of rough ER and ribosomes make the nervous system appear gray (gray matter).
  • Cytoskeleton contains neurofilaments, tubules, and fibrils.
• Dendrites:
  • Short, highly branched processes with dendritic spines.
  • Receive information at synapses.
  • The dendrites are always numerous and highly branched, relatively short processes
• Axon:
  • Single long slender process where the action potential is propagated.
  • At the terminal parts of the axon, we now have these slender divisions called the plural term is telodendria.

Axon Structure

• Axon Hillock: Thick area where the axon attaches to the cell body.
• Initial Segment: Part of the axon just distal to the axon hillock.
• Telodendria: Slender divisions at the terminal parts of the axon.
• Axon Terminals (Synaptic Terminals): Expanded bulb portions at the end of telodendria.
  • Contain vesicles that store neurotransmitters.

Synapses

• Presynaptic Cell: Neuron carrying the impulse towards the synapse.
• Postsynaptic Cell: Neuron receiving the impulse.

Structural Classification of Neurons

• Anaxonic Neuron:
  • Axon is not obvious; wrapped in connective tissue with dendrites.
• Bipolar Neuron:
  • Two distinct processes separated by the cell body.
• Unipolar Neuron:
  • Cell body is off to the side with a single elongated process.
• Multipolar Neuron:
  • Numerous dendrites and a single axon.
  • Most common type of neuron.

Functional Classification of Neurons

• Classified based on the information they carry.
  • Sensory neurons, motor neurons and interneurons

Sensory Neurons

• Carry sensory information from receptors.
• Cell bodies are grouped together in ganglia (peripheral nervous system).
• In the central nervous system, clusters of nerve cell bodies are called nuclei.

Types of Receptors

When you use the term again, remember, a stimulus. A stimulus for stress. That's what it is. It's a change in the environment

• Interoceptors: Monitor internal conditions (pain, pressure, blood pressure, pH).
• Exteroceptors: Monitor the external environment (eyesight, hearing, skin surface).
• Proprioceptors: Monitor the position of joints and skeletal muscles.

Motor Neurons

• Part of the efferent system.
• Somatic Motor Neurons: Control skeletal muscle.
• Visceral Motor Neurons: Carry motor impulses to heart, smooth muscle, and adipose tissue.

Interneurons

• Found in the brain and spinal cord, and some in autonomic ganglia.
• Located between the sensory and motor systems.
• Responsible for interpreting sensory information and higher-level functions (memory, learning, emotional states).

Neuroglia (Glial Cells) in the Central Nervous System

• Cells responsible for protecting and allowing neurons to function.

Types of Neuroglia

• Astrocytes:
  • Create and maintain the blood-brain barrier.
  • Mediate limited repair in the brain.
  • They line the central canal to the spinal cord
• Ependymal Cells:
  • Line the central canal of the spinal cord and ventricles of the brain.
  • Produce and monitor cerebrospinal fluid.
• Oligodendrocytes:
  • Produce myelin in the CNS, increasing the speed of nerve impulses.
  • Myelin creates white matter in the nervous system.
  • Myelin is not continuous; there are myelinated areas (internodes) and small gaps (nodes).
  • Only axons are myelinated, not dendrites or cell bodies.
  • White matter contains myelinated axons; gray matter contains non-myelinated axons, cell bodies, and dendrites.