Introduction to the Nervous System Flashcards
The nucleus of a neuron is made up of what?
A group of CNS cell bodies (gray matter)
What is a ganglion
A group of PNS cell bodies
What are the nerve fibers of individual nerves called?
Axons
A tract is defined as what?
A group of CNS axons (White matter)
A nerve can be defined as what?
A group of PNS axons
A nerve fiber is defined as what?
A singular peripheral nerve axon
How are spinal nerves connected to the spinal cord?
By their dorsal (posterior) and ventral (anterior) roots
What does the dorsal root carry?
Sensory signals from the spinal nerves towards the spinal cord
What is the dorsal root ganglion composed of?
The cell bodies of peripheral sensory neurons
What does the ventral root carry?
Motor signals from the spinal cord towards the spinal nerve
How are spinal nerves divided (NOT “rooted”)?
Divided into dorsal and ventral rami
What is the role of the dorsal ramus?
Carry sensory and motor signals to the dorsal/posterior skin and muscle. Really only covers about 3 inches on either side of the spinal cord.
What is the role of the ventral ramus?
Carry sensory and motor signals to the ventral/anterior skin and muscle
What is a dermatome?
A strip/area of skin (derma-) that a specific spinal nerve is responsible for connecting to the rest of the nervous system
What is a myotome?
The muscle fibers (myo-) that a specific spinal nerve is responsible for connecting to the rest of the nervous system. Most muscles are divided between multiple myotomes, and each myotome includes parts of many muscles.
Each spinal nerve supplies one of each of these things
Dermatome and Myotome
What is the role of somatic sensory nerves?
Responsible for transmission of pain, temperature, touch, and proprioception of the skin and superficial structures
What is proprioception?
The sense of self-movement, force, and body position (essentially what our muscles are doing and where they are)
What is the role of somatic motor nerves?
Responsible for transmission of motor signals to skeletal muscle
What is the role of visceral sensory nerves?
Responsible for the transmission of sensations of stretch and ischemia of the internal organs (no pain, temperature, or touch)
What is the role of visceral/autonomic motor nerves?
Responsible for the transmission of motor signals to smooth muscle, cardiac muscle, and glandular tissue
What is a plexus?
A region in which peripheral nerves re-organize themselves (like a highway interchange for nerve fibers)
Describe the structure of a somatic sensory nerve and where the cell body is located
1 neuron going from the receptor to the CNS, cell body located within the dorsal root ganglion
What do visceral nerve fibers interact with?
Internal organs
Describe the structure of a somatic motor nerve pathway
Originates in the CNS > ventral root > spinal nerve > ventral/dorsal ramus > skeletal muscle (synapse occurs at target structure)
Describe the structure of a visceral sensory nerve pathway
1 neuron going from the receptor to the CNS, cell body located within the dorsal root ganglion
Describe the pathway that a motor impulse would take to get to a skeletal muscle in the body wall
There would be a cell body in the spinal cord. The axon would exit the spinal cord via the ventral root and enter the spinal nerve. The axon would continue in either the ventral or dorsal ramus and continue to its target skeletal muscle fibers. It would stimulate those cells.
What is the role of the sympathetic nervous system?
Prepares your body for rapid action (fight or flight)
What is affected by the sympathetic nervous system?
Visceral organs and body wall structures (such as sweat glands, piloerector muscles, superficial blood vessels [remember, the vessel walls consist of smooth muscle])
What is the role of the parasympathetic nervous system?
Responsible for maintaining your body’s regular maintenance activities (rest and digest)
What is affected by the parasympathetic nervous system?
Visceral organs (NOT body wall structures)
Many organs have dual innervation of the sympathetic and parasympathetic nervous system with contrasting effects. Give an example of these contrasting effects in the body.
The sympathetic nervous system increases heart rate, the parasympathetic nervous system decreases heart rate.
Describe the origin of sympathetic nerves
Preganglionic cell bodies are found in the thoracic or lumbar spinal cord, specifically from T1 to L2 (Have what is known as a thoracolumbar outflow) and exit the CNS via the lateral horn
Describe the origin of parasympathetic nerves
Preganglionic cell bodies are found in the brain or sacral spinal cord, specifically from cranial nerves 3, 7, 9, 10, S2, S3, and S4 (Have what is known as a craniosacral outflow)
Describe the pathway/anatomy of a sympathetic nerve
Short preganglionic axons, with ganglia located close to the spinal cord (2 types of ganglia: paravertebral and prevertebral) and long postganglionic axons that go to the target tissue
Describe paravertebral ganglia
One of 2 types of sympathetic ganglia, located immediately lateral to the vertebral column. These connect to form a string of ganglia known as the sympathetic trunk that runs along either side of the spinal cord
Describe prevertebral ganglia
One of 2 types of sympathetic ganglia, located anterior to the vertebral column
Describe the pathway/anatomy of a parasympathetic nerve
Long preganglionic axons that run directly to the target organ, ganglia found within the walls of the target organ, very short postganglionic axons
What is the significance of the lateral horn of the thoracolumbar spinal cord?
It is the origin of all sympathetic nerve pathways. Where preganglionic cell bodies are located
What is the role of the white ramus communicans?
It connects the ventral ramus to the sympathetic trunk (nerve goes from ventral ramus to the sympathetic trunk via the white ramus communicans)
What is the role of the gray ramus communicans?
Connects the sympathetic trunk to the ventral ramus of the spinal nerve (nerve goes from the sympathetic trunk back to the ventral ramus of the spinal nerve via the gray ramus communicans) ONLY THE BODY WALL SYMPATHETIC PATHWAY USES IT
What are cardiopulmonary splanchnic nerves?
Postganglionic, exclusively sympathetic nerves located towards the back of the body that carry signals to the heart and lungs (Relevant in the thoracic viscera sympathetic nerve pathway)
Describe thoracic, lumbar, and sacral splanchnic nerves
Preganglionic, exclusively sympathetic nerves located towards the back of the body that carry signals to the abdominal and pelvic organs (Relevant in the abdominal viscera sympathetic nerve pathway)
What type of nerve fibers would you expect to find in a nerve going to an upper limb
Somatic motor, somatic sensory, and sympathetic nerve fibers (going to sweat glands, piloerector muscles, and superficial blood vessels)
How would damage to a dorsal root differ from damage to a dorsal ramus?
Damage to a dorsal root would affect all sensory supply associated with that spinal level; damage to a dorsal ramus would affect sensory and motor supply to the portion of the back associated with that spinal level
Describe visceral sensation
Includes stretch and ischemia, not true pain. Sensations are diffuse and as a result difficult to localize (visceral=vague)
Describe somatic pain
Pain that is sharp and easy to localize (somatic=sharp)
What is referred pain?
Pain associated with internal organs that is sharp and easy to localize, however it may not localize with the affected organ (unknown for sure as to why this occurs, assumed that it is due to misinterpretation of sensory information)
