Neuroanatomy Flashcards
central nervous system
brain, brain stem, spinal cord
peripheral nervous system
all other nerves and pathways
within both CNS and PNS
- somatic nervous system
- autonomic nervous system
somatic nervous system
provides communication between various parts of body with somatic effectors (skeletal muscles)
autonomic nervous system
conducts impulses to visceral effectors (smooth muscle, cardiac muscle, glandular cells)
orientation planes of the brain
horizontal, coronal, sagittal
other orientation planes
- transverse
- lateral
transverse plane
crosscut at a right angle to the longitudinal axis on a bend, because of curvature of brain stem, is diagonal to horizontal plane
lateral plane
structures away from mid or midsagittal planemedial, approaching the midsagittal plane
the cell, the neuron
- celly body and nucleus
- dendrite
- axon
cell body and nucleus
has a slightly grey color
dendrite
carries neural information towards a cell body
axon
carries neural information from the cell body to other neurons axons terminate in slight enlargements or bulges known as end feet, end plates or end terminals
afferent
lower to higher
functional division of neurons, afferent
- carry information toward a reference point in the CNS, includes fibers that innervate sensory receptors
- afferent signals travel from the peripheral nervous system to the cortex (see a picture of the dog, eyes see, and neurons send signal to the brain, touch the stove and realize it feels hot)
- found in proprioceptors, cells that transduce information regarding the movements of joints and muscles
3 primary proprioceptors
- joint proprioceptors
- golgi tendons
- muscle spindles
joint proprioceptors
allows us to determine where things are moving/where things are in space in terms of the body
golgi tendons
- deals with muscle tension/gives information on how muscle is moving
- they are distributed among the collagen fibers that form the tendons
muscle spindles
- gives information on muscle length, rate of change of muscle length (velocity of stretch)
- acts as a fine-tuning mechanism
efferent (motor) neurons
all cell bodies of both nerves are located in the motor nuclei of the CNS, cell body is either found in the spinal cord or the brain
2 types of motor neurons (both important for muscle control)
- alpha motor neuron
- gamma motor neuron
alpha motor neuron
largest, most predominant, innervates extrafusal fiber
gamma motor neuron
smaller in size and quantity
efferent neurons, motor from CNS
- all cell bodies of both nerves are located in the motor nuclei of the CNS
- both primary and secondary afferents are stimulated by the lengthening of the intrafusal fibers and by the rate of change of their length
- as muscle fibers are stretched, spindle afferents convey information to alpha motor neurons which control discharge to extrafusal fibers
- conduction is up to 120 meters/second
functional division, efferent
- nerves and tracts that course down to various muscles
- include motor neurons that innervate muscles and fibers that innervate afferent neurons (sensory)
flexion
ending movement of a limb
extension
straightening movement of a limb
abduction
move away from a central axis point
adduction
move towards a central axis point
protraction
movement that causes structure to move forward
retraction
movement that pull back the protracted structure
reflexes
are quick, involuntary, stereotyped reactions of peripheral effectors to stimulation
tracts
bundles of axons located in the brain and spinal cord, lie interior to cortex
nerves
bundles of axons, bundles of dendrites, or both , and located in PNS
ascending projection tracts
carry impulses upward toward the brain
descending projection tracts
conducts impulses downward
internal capsule
part of cortex, see both projection tracts
corticospinal fibers
- originate in sensorimotor cortex
- fan down to wedge-shaped internal capsule to form cerebral tracts
- along ventral surface of midbrain, pes pedunculi
- CS fibers recombine at medulla to form the pyramids
- contralateral
somatic nervous system: sensory pathways
consist of relays conducting impulses from any part of the body to the CNS
3 main sensory pathways in the SNS
- conduct impulses from periphery to CNS
- conduct impulses from cord or brainstem to thalamus
- impulses from thalamus to postcentral gyrus
pathway that conducts impulses from periphery to CNS
dendrites are in spinal or cranial nerve, axons terminate in gray matter of spinal cord or brainstem
motor pathways of the SNS
- anterior horn motoneuron axons are the only ones that terminate skeletal muscle cells
- any condition that makes anterior horn motoneurons unable to conduct impulses also make skeletal muscle cells supplied by these neurons unable to contract (paralyzed)
2 methods used to classify motor pathways of the SNS
- based on location of their fibers in the medulla, pyramidal/extrapyramidal tracts
- based on influence on lower motoneurons, facilitatory/inhibitory
motor control: theory 2
- cerebral motor cortex is highest command center relaying some of its orders through the basal ganglia and cerebellum
- implies cortex wills movement and the other structures refine
direct motor system
has corticobulbar and corticospinal tracts
corticobulbar pathway
- arises from motor strip premotor area and extends to the medulla
- directly affects cranial nerves that control oral mech (fibers of corticobulbar tract do not decussate)
corticospinal tracts
- arises from the sensorimotor areas of the cortex and descend directly to the spinal cord (fibers decussate)
- involved with respiration
UMNs
originate in motor region of the cortex or brainstem
direct pathway
- cerebral cortex, cranial, and spinal nerve nuclei
- carry motor information to LMNs, direct voluntary skilled movements
indirect pathway
- cerebral cortex, cranial and spinal nerve nuclei
- control posture, tone, and movements supportive of voluntary movement
upper motor neuron (UMN) lesions can occur from
stroke, MS, TBI, cerebral palsy, Freidreich’s ataxia, Wilson’s disease, ALS
UMN pathway innervates
cranial nerves, spinal nerves, and controls muscles on the opposite side of the body
UMN lesions of direct pathways
- loss of skilled movement
- hyporeflexia
- babinski sign
- decreased muscle tone
UMN lesions of indirect pathway
- spasticity
- clonus
- hyperactive stretch reflexes
- increased muscle tone
- decorticate or decerebrate posture
UMN lesion: unilateral
dysarthria due to weakness and loss of skilled movement
UMN lesion: bilateral
can have mild effects on speech to severe effects on speech
lower motor neurons (LMNs)
- involves neurons of cranial nerves and spinal nerves
- brainstem and spinal cord, muscle
- produce muscle actions reflexes and tones
- carry out UMN commands for voluntary movements and postural adjustments
what might cause lesions of LMNs
illness, accidents, TBI, ALS, surgery, Guillain Barre, MS, myasthenia gravis and other factors
