A&P 2.3 nerves Flashcards
Nerves
Definition
Bundles of axons in the PNS
All spinal nerves and many cranial nerves are mixed; they have both sensory and motor
Neuron
3 parts
Dendrite
Axon
Cell body
Mixed nerve
Sensory and motor component
Tracts
Bundles of nerves in the central nervous system
Most tracts contain fibers going in one direction
Myelin
Sheaths - multilayer wrappings around most axons of most neurons
Formed by glial cells
Each cell wraps a very small portion of the axon
Each axon is separated by unmyelionated nodes which are going to speed impulse conduction
Nodes of ranvier
Unmyelionated portion of the axion
Myelin producing cells
2
Schwann cells
Oligodengrocytes
Schwann cells
Glial cells in the PNS that form myelin sheaths
A single Schwann cell wraps around a 1mm segment of a single axon length
Oligodendrocytes
“Cells with branches”
Glial cells in the CNS that form myelin sheaths
Each oligodendrocyte extends (15-50 branches)
Multiple branches each of which creates a myelin sheath on multiple axons
White and grey matter
Located
Located in brain and spinal cord
White matter
Is regions of the CNS containing myelinated axons
ONLY IN CNS
Superhighway, has super fast speed
Grey matter
Found in the CNS
Contains little or no myelin
Comprised of mostly cell bodies, dendrites, ends of axons and unmyelionated axons
ONLY IN CNS
Where thought process happens
Multiple sclerosis
Autoimmune disease that causes progressive destruction of the myelin sheaths in the CNS
Slowing down nerve impulse conduction
Multiple regions of the nervous system
Sclerosis- plaque formation
Ventral/dorsal roots
Important. P. 431
Every spinal nerve connects to the spinal cord by two roots:
Ventral
Dorsal
Dorsal roots
Contain ONLY sensory neurons entering the cord
Ventral roots
Contain ONLY motor neurons
Reflex arc
Defined
A signal conduction route to and from the CNS
The most common form of reflex arc is the three-neuron arc
Fast and involuntary actions in response to a stimulus
**Reflex arc IS THE SIMPLEST FORM OF INTEGRATION (processing of stimulus)
Shortest pathway from a stimulus to a response
Consists of seven components
7 components of the reflex arc
Stimulus Sensory receptor Sensory neuron Integrating center Motor neuron Effector Response
Stimulus
Change in (internal/external) environment to stimulate a sensory receptor
Sensory receptor
Dendrite or specialized structure that stimulates a dendrite.
If the stimulus is strong enough it will create an impulse (action potential) to be generated in a sensory neuron
Sensory neuron
Conducts an impulse from receptors to CNS
Dorsal root if it is a SPINAL REFLEX NOT CRANIAL REFLEX
Moves to integrating center
Integrating center
Sensory neurons synapse (space between 2 neurons where communication happens) with motor neurons or with an inter neuron that synapses with motor neuron
Motor neuron
Conducts a nerve impulse from the CNS to an effector
Effector
A muscle or a gland
Response
A muscle contraction or relaxation
OR
Glandular response to secrete or inhibit secretion
Superaspinatus
A, I, O
A- abduct the shoulder; stabilize the head of the humerus in glenoid cavity
O- superaspinatus fossa of the scapula
I - greater tubercle of the humerus
Infraspinatus
A, I, O
A- laterally rotate the shoulder, adduct the shoulder, extension of the humerus
O - infraspinous fossa of the scapula
I - greater tubercle of the humerus
Rotator cuff
4 muscles
Superaspinatus
Infraspinatus
Teres minor
Subscapularis
Superaspinatus runs deep to the trapezius
S,I,T,S
