Intro to Nervous System Flashcards
What are the 2 branches of the nervous system?
Central (Brain & Spinal cord)
Peripheral (Cranial & Spinal nerves)
What does the brain give rise to?
Cranial nerves
Describe the spinal cord
Conducts impulses to and from the brain
Divided in to segments that give rise to spinal nerves
What is the basic functional unit of the nervous system?
The neuron
Which neuron shape is responsible for most sensory neurons?
Pseudounipolar
Define nerve
A collection of cell processes and axons located in the peripheral nervous system
What are the supporting cells to a nerve?
PNS - Schwann cells
Connective tissue - Endoneurium, perineurium, epineurium
Define a tract
A collection of neuronal cell processes that travel within the central nervous system
Define a ganglion
A collection of neuron cell bodies located outside the central nervous system
Define a nucleus
A collection of neuron cell bodies located within the central nervous system
What is the alternate name for the lateral horn?
Intermediogrey column
Where are tracts located in the central nervous system?
White matter
What is the main purpose of primary afferent neurons?
Conduct sensory impulses from the peripheral to the central nervous system
What is the main function of the final efferent neurons?
Conduct motor impulses from central nervous system to effector organ
What is an alternate name for final efferent neurons?
Lower motor neurons
Why does the monosynaptic patellar reflex occur?
Hammer taps space, stretching the muscle spindle.
Primary afferent neuron sends signal to brain that the muscle spindle is stretched, brain send signal via lower motor neuron (final efferent) to contract muscle
What is an interneuron
A short neuron located between afferent and efferent neurons within the CNS
Excitatory or inhibitory
What is the main function of the interneuron?
During a reflex movement, afferent nerves will signal both excitatory and inhibitory neurons
Inhibitory neurons will send efferent signals to inhibit extensor muscle nerves and excitatory neurons will send efferent signals to activate flexor muscle nerves
What are projection neurons?
Found only in the central nervous system
Similar to interneurons with longer axons
What is an ascending tract of a projection neuron?
Cell body is in the spinal cord, and upper motor neuron projects cranially to terminate in the brain
What is a descending tract of an projection nueron?
Pathway begins in a nucleus or cortex of the brain and the axon extends to the brainstem or spinal cord terminating on a lower motor neuron (projection neuron in an upper motor neuron)
Which projection neurons are relayed first and why?
Ascending neurons send signals to the brain, descending neurons come next to send the efferent signal to the muscles
Interneurons relay the signal for the withdrawal reflex on one side of the side (activate flexors) and to the contralateral side to activate the extensors of the opposing limb
How to classify peripheral motor neurons
Afferent (towards CNS)
Efferent (Away from CNS)
Somatic (main body mass)
Visceral (organs/blood vessels)
Define General Somatic Efferent (GSE)
Multipolar neurons that supply most of the skeletal muscles
A single neuron extends from the CNS to all muscle fibers involved
Define General Visceral Efferent (GVE)
Multipolar neurons that supply smooth muscle, cardiac muscle, and glands
Form the autonomic nervous system
2-neuron chain between the central nervous system and the effector organ
Define General Visceral Afferent (GSA)
Pseudounipolar neurons that carry sensory information from the somatic body system to the CNS
Where are the cell bodies of GSA neurons located?
Sensory ganglia
Define Special somatic Afferent (SSA) and Special Visceral Afferent (SVA) neurons
SSA: bipolar neurons that carry visual and auditory information
SVA: Bipolar and pseudounipolar neurons that carry taste and smell sensations
What horn do GVE nerves originate from? GVA? GSA? GVA?
GVA and GSA originate from the dorsal horn
GVE nerves originate from the lateral horn
GSE nerves originate from the ventral horn
Describe the anatomy of a spinal nerve
Dorsal and ventral roots originate from grey matter horns and combine at the dorsal root ganglion to form the spinal nerve which then divides in to the dorsal branch, ventral branch and communicating branch
Where do spinal nerves exit the central nervous system?
Intervertebral foramen
What types of neurons are present in the dorsal root ganglion?
Sensory/afferent ganglion
Where do the dorsal branches of the spinal nerve innervate?
Epaxial muscles, dorsal 1/3 of cutaneous innervation
Where do the ventral branches of the spinal nerve innervate?
Hypaxial muscles, limbs & ventral 2/3 of cutaneous innervation
How are spinal nerves organized?
C1 comes from lateral vertebral foramen of atlas
Cervical spinal nerves come out of the IV foramina cranial to their vertebrae (Cervical 2 comes out cranial to C2)
Thoracic & lumbar spinal nerves exit the CNS caudal to their vertebrae
Sacral nerves exit pelvic and dorsal foramina
Why do thoracic and lumbar nerves exit caudal to their vertebrae?
Cervical nerve 8 exits caudal to C7 & cranial to T1
