4.6 Pathways Flashcards
What is hyporeflexia?
absent, decreased reflex
indicates damage to direct reflex arc
What is hyperreflexia?
hyperactive or repeating (clonus) reflex
indicates damage to brainstem or cortical modulation pathways
What is an alpha neuron?q
A motor neuron that starts in the ventral horn and goes to skeletal muscle
What are upper motor neurons? What happens if damaged?
neurons that are located before alpha motor neuron
damage to descending pathways from cerebral cortex
paralysis, spasticity, positive Babinski sign (toe flaring) in adults, hyperreflexia
What are lower motor neurons? What happens if damaged?
are the final output to skeletal muscle from spinal cord (alpha motor neurons)
paralysis, loss of muscle tone, muscle atrophy, hyporeflexia
Lower motor lesion- paralysis ipsilateral, loss of tone/atrophy because electrical activity loss causes loss of growth factors for muscle
If lose alpha motor neuron, lose contractile function –> low or absent reflexes
What is the corticospinal pathway?
Primary Motor Cortex
upper motor neuron; cell body in the cerebrum, axon descends
Spinal Cord
lower motor neuron; cell body in the ventral horn, axon exits ventral root of the spinal cord
Skeletal Muscle
Neuromuscular junction
Acetylcholine release muscle contraction
What is the function of the cerebellum?
coordination and smooth execution of movements
What are the sx of cerebellar damage?
intention tremor (during movement) ataxia, loss of balance, coordination, slurred speech, difficulty swallowing childhood and adult forms, hereditary and sporadic forms, viral, alcohol induced, traumatic brain injury causes
What is the function of the basal ganglia?
modulates movement, posture, standing, walking, writing – requires acetylcholine and dopamine neurotransmission
What happens in Parkinsons? Sx?
progressive loss of dopamine producing cells in substantia nigra which supplies the striatum
bradykinesia (slow movement), resting tremor of hand, legs, head, jaw, face, muscle rigidity, abnormal spasmodic movement
also brainstem, spinal cord and autonomic pathology
disruption of sleep, gastrointestinal function, thermoregulation
What does the ANS do? Organs involved?
controls smooth muscle of the organs, and cardiac muscle of the heart.
unconscious, organ-level reflexes
Hypothalamus, Brain Stem, Spinal Cord, Autonomic Ganglia
What is the autonomic pathway for the brain stem or spinal cord? Neurotransmitters?
cell body of pre-ganglionic neurons in brain stem OR
cell body of in spinal cord, lateral gray horn
axons exit ventral root
Synapse in autonomic ganglia
Acetylcholine
What is the pathway for autonomic ganglia? Neurotransmitters?
cell bodies of final neurons
Diffuse varicosity-type synapses to whole organs
Acetylcholine or Norepinephrine
What is a sympathetic varicosity?
At level of organ control, slightly different than neuro-muscular junction
Much more diffuse– want to activate whole organ
Large varicosities- lead to a large release of neurotransmitter that regulates a whole organ
What is the ANS?
part of the efferent nervous system which controls responses of organs and glands.
Functions:
Involuntary regulation of Homeostasis
Controls responses in cardiac muscle, smooth muscle, endocrine glands, adipose tissue
How many neurons in the ANS? Where are they?
Preganglionic- last central neuron goes out lateral horn of spinal cord, generally releases Ach at autonomic ganglion
Postganglionic neuron- outside CNS, releases neurotransmitter at organ, Ach or Norepi (depending on sympathetic/parasympathetic)
What are the alternate names for the SNS and PNS?
SNS- Thoracolumbar
PNS- Craniosacral
Where are the nerves in the SNS? Which are short/long?
THORACO-LUMBAR”
pre-ganglionic neurons from lateral horn of thoracic and lumbar spinal cord
short pre-ganglionic neurons terminate near the spinal
long postganglionic neurons to effector organ
Where are the nerves in the PNS? Which are short/long?
“CRANIO-SACRAL”
long axon pre-ganglionic neurons from cranial nerves (CN III, VIII, IX, X) and sacral spinal cord
long preganglionic neurons terminate in or near the effector organ
Terminal Ganglia
short postganglionic neurons to effector organ
What neurotransmitters are used where in the PNS/SNS?
Sympathetic Nervous System (SNS)
pre-ganglionic Neurotransmitter: Acetylcholine
post-ganglionic Neurotransmitter: Norepinephrine (“Noradrenaline”)
Parasympathetic Nervous System (PSNS)
pre-ganglionic Neurotransmitter: Acetylcholine
post-ganglionic Neurotransmitter: Acetylcholine
OR- ACh everywhere but sympathetic post-ganglionic
Why does the ANS affect whole organs?
Autonomic Activity affects entire organs (vs. just a few muscle fibers in Somatic NS) due to post-ganglionic anatomy
Diffuse Synapses from Autonomic Nervous System are spread through target organs
Diffuse Release of neurotransmitter is spread across entire organ
Gap Junctions: Target organ smooth muscle and cardiac muscle connected by gap junctions
What does the adrenal medulla do in the SNS?
Enhance intensity/faster response
SNS pre-ganglionic neurons target adrenal medulla
releases Epinephrine and Norepinephrine into the bloodstream
Epi & NorEpi effects enhanced at all SNS targets
