Nervous System Lecture Notes (VETM 1502)

Study Notes

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

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

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

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

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

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

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.

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

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

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

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)