Peripheral + Autonomic Nervous System Flashcards
Define Peripheral Nervous System (PNS)
motor and sensory nerves extending from spinal cord
Define Autonomic Nervous System (ANS)
homeostatic coordinating system
Central and peripheral components
Spinal Cord Structure
spinal cord and roots
Total number of roots/levels? And their breakdown?
31 total
8 cervical (7 vertebrae)
12 thoracic
5 lumbar
5 sacral
1 coccygeal
How are cervical roots named?
are located above (rostral to) their respectively numbered vertebare.
C1 is above the C1 vertebra
C8 is between C7 and T1
How are the rest of the spinal cord roots named?
after C, all roots are exit below their respectively numbered vertebrae
White Matter Motor
Anterior funiculus
– Anterior corticospinal tract (90% cross)
– Reticulospinal and vestibulospinal fibers
• Lateral funiculus
– Lateral corticospinal tract (90%, cross)
– Organization: Sacral (LE, leg) Cervical (UE, arm) as you go from Lateral Medial
White matter sensory
• Posterior funiculus = “posterior (dorsal) column”
– Gracile (T7 and below) and cuneate (T6 and above) fasciculi
– Organization: Sacral Cervical as you go from Medial Lateral
• Lateral funiculus
– Anterolateral system (spinothalamic tract)
– Organization: Sacral Cervical as you go from Lateral Medial
Grey Matter
• Composed of:
– neuronal cell bodies + their dendrites
– axon terminals of synapsing fibers
– glial cells
• Rexed laminae I to IX
how is grey matter organized?
Posterior (dorsal) horn – laminae
I to VI
– Intermediate grey – lamina VII
– Anterior (ventral) horn – laminae
VIII to IX
Topographic
arrangement of
motor neurons in
the anterior horn
Where are motor efferents found?
Cell bodies =
anterior/ventral horn
(spinal gray matter)
• Innervate
– Visceral structures (smooth
muscle, cardiac muscle,
glandular) via synapse in
autonomic ganglion -
visceral motor (VM)
– Muscle - somatic motor
(SM)
Functional components of sensory/visceral tracts (afferents)
Cell bodies = posterior (dorsal)
root ganglia
• Convey sensation from:
– Body surface and
Muscle/tendon/joint - somatic
afferent (SS)
– Internal organs (smooth muscle,
cardiac muscle, glands) -
visceral afferent (VS)
spinal reflexes require what?
Reflexes require:
– Sensory (afferent) fibers
– interneurons and/or motor (efferent) neurons
– target tissue, usually skeletal muscle
• Intra-segmental – relatively simple, confined to a single cord level
• Inter-segmental – more complex, involving multiple cord segments
Muscle Stretch Reflex
Monosynaptic Reflex
– Requires 1 synapse in response to
stretch of a muscle spindle
– Elicited by tapping any large tendon
• Example: “knee jerk” or quadriceps
stretch reflex
– Afferent: muscle spindle + sensory
nerve (myelinated, group Ia fibers),
originate in the patellar tendon
– Efferent: Motor neurons
– Target : Quadriceps femoris
can also be reciprocally inhibited
reciprocal inhibition of muscle stretch reflex
Autonomic nervous sytem overview
Regulates homeostatic functions
– Involuntary, reflexive
– CNS control centers in: limbic system, hypothalamus, brainstem
– Neural control of smooth muscle, cardiac muscle, or glandular secretory cells
• regulates cardiovascular, respiratory, digestive, urinary, integumentary, and reproductive organs
•
key difference between somatic / autonomic?
The peripheral visceral motor pathway consists of 2 neurons
(rather than 1)
Sympathetic outflow
Originates from T1 through L2.
– ‘Thoracolumbar’ system
– Viscerotopic organization
activation: widespread/diffuse. fight or flight
parasympathetic outflow
Cranial nerves III, VII, IX, X and sacral rootsS2 to S4
– ‘Craniosacral’ system
1st synapse (preganglionic neuron to postganglionic neuron) is mediated by nicotinic receptors, activated by acetylcholine.
• 2nd synapse (target of postganglionic neuron) is mediated by adrenergic receptors, activated by norepinephrine or epinepherine.
• Exception: sweat glands, which receive sympathetic innervation but have muscarinic acetylcholine receptors
digestion q
Basic reflexive functions:
– Secretion, absorption, and mixing and movement of
contents
– Intrinsic rhythmic activity
(interstitial cells)
– Peristaltic reflex: sensory
neurons, motor neurons, and
several types of interneurons
– CNS influence over activities via sympathetic/para-sympathetic pathways
• Enteric neurons distributed within the myenteric and sub-mucosal plexuses
Example of an inter-segmental reflex
• Initiated by painful (nociceptive) input
– protect body part by removing it from source of injury
• Lightly myelinated/unmyelinated sensory fibers posterolateral tract (of Lissauer), ascend/descend spinal gray to excite:
– 1) ascending tract cells to higher centers (“OUCH!”)
– 2) interneurons activate flexor motor neurons
• Enhanced by:
– inhibition of ipsilateral extensors
