Nervous System Lecture Notes (VETM 1502)

Nervous System Lecture Notes (VETM 1502)

• The nervous system is composed of a central and peripheral nervous systems
• The central nervous system is made up of neurons in the brain and spinal cord
• Groups of neuronal cell bodies are called nuclei
• Groups of axons are arranged into tracts
  • White matter is myelinated axons
  • Gray matter includes cell bodies, dendrites, and unmyelinated axons
• CNS sensory neurons carry information towards the CNS (ascending pathways) and away from CNS (descending pathways)
  • These sensory neurons carry information to the cerebellum, brainstem, and cerebrum for interpretation
  • Information is carried in ascending and descending pathways to communicate with the external environment

Learning Objectives

• Understand the importance of different nervous system divisions and their roles
• Explain the central and peripheral nervous systems
• Discuss ascending and descending pathways in the CNS
• Differentiate between the somatic and autonomic nervous systems
• Differentiate between the sympathetic and parasympathetic nervous systems

CNS Pathways

• Ascending pathways: Sensory information from the body periphery travel up the spinal cord to higher brain centers such as the somatosensory cortex or cerebellum
  • This information carries sensations from various receptors such as pain, thermal, tactile, muscle, and joint (proprioceptors)
  • The sensory information reaches higher levels in the brain and contributes to consciousness and voluntary decisions
• Descending pathways: Carry motor commands from higher brain areas to the muscles and glands in the periphery
  • The descending pathways utilize upper and lower motor neurons
  • Upper motor neurons originate in the brain and brainstem
  • Lower motor neurons originate in the spinal cord

Ascending Pathways - Specific Tracts

• Dorsal column medial lemniscus system (DCML)
  • Fasciculus gracilis
  • Fasciculus cuneatus
• Spinothalamic tracts
  • Lateral spinothalamic tract
  • Anterior spinothalamic tract
• Spinoreticular tract
• Spinocervicothalamic tracts
• Spinocerebellar tracts: Transmit proprioceptive information to the cerebellum for coordination

CNS Pathways - Continued (Descending)

• Descending pathways carry motor signals from the brain to skeletal and smooth muscles
• They consist of upper and lower motor neurons

Pyramidal System (Corticospinal)

• Produces fine movements requiring concentration and conscious thought.
• Plays a role in skillful movements, grooming, and control of facial muscles
• The pathways arise from the cerebral cortex and then descend to the spinal cord via the internal capsule and brainstem
• Composed of direct connections with no synapses in the brainstem (no synapses between the cortex and the muscles)
• Some fibers cross over to the opposite side of the body in the medulla oblongata, while others remain on the same side

Extrapyramidal System

• Has synapses within the brainstem
• Tracts run outside the pyramids of the medulla oblongata
• Contains various multisynaptic pathways that relay within several nuclei in the brain
• Other parts take origin from various nuclei (e.g., tectum, reticular formation) to relay to the lower motor neurons
• The cerebellum utilizes this influence to coordinate movements

CNS - Upper and Lower Motor Neurons (UMN vs LMN)

• UMNs originate in the brain or brainstem and synapse with LMNs in the spinal cord
• UMNs do not directly synapse with muscles.
• LMNs originate in the spinal cord and extend directly to peripheral muscles.

Peripheral Nervous System (PNS)

• Includes all nervous structures located outside of the brain and spinal cord
• Provides communication between receptors and the CNS (sensory), and from the CNS to effector organs (motor)
  • Peripheral nerves are myelinated fibers
  • Somatic nerves control skeletal muscles
  • Autonomic nerves control cardiac muscle, smooth muscle, and glands

Autonomic Nervous System (ANS)

• Supplies efferent information to cardiac muscle, smooth muscle and glands
• Nerve fibers are of two types: pre-ganglionic and post-ganglionic
  • Pre-ganglionic fibers originate from the CNS and synapse with post-ganglionic neurons in ganglia
  • Post-ganglionic fibers extend from the ganglia to the effector organ

Autonomic Neurotransmitters

• Acetylcholine (ACh) is a neurotransmitter produced by pre-ganglionic neurons and post-ganglionic neurons of the parasympathetic division
• Norepinephrine and epinephrine (adrenaline) are neurotransmitters produced by most postganglionic neurons of the sympathetic nervous system

Sympathetic System

• Originates in the thoracic and lumbar regions of the spinal cord, which means it connects to the spinal cord
• Ganglia are close to the spinal cord
• Postganglionic fibers are long, allowing for wide-ranging effects
• Extensive branching of the postganglionic fibers allows for multiple organs to respond simultaneously
• This leads to its importance in responding to emergency/stressful situations (fight-or-flight)

Parasympathetic System

• Originates in the brain and sacral regions of the spinal column
• Ganglia are located close to the target organ
• Postganglionic fibers are short
• Limited branching of postganglionic fibers; localized response
• Often referred to as "rest-and-digest" rather than "fight-or-flight"

Somatic Nervous System

• Allows for the processing of sensory information and controlling motor movement
• Sensory and motor neurons typically have one synapse
• Cranial and spinal nerves make up this system
• Primarily Acetylcholine (ACh) is the neurotransmitter released

This quiz covers the fundamentals of the nervous system, focusing on the central and peripheral divisions, their structures and functions. You'll explore the roles of neurons, white and gray matter, as well as ascending and descending pathways in the CNS. Test your knowledge about how these systems communicate with the external environment.