4.6 Pathways

Question 1

What is hyporeflexia?

Answer 1

absent, decreased reflex

indicates damage to direct reflex arc

Question 2

What is hyperreflexia?

Answer 2

hyperactive or repeating (clonus) reflex

indicates damage to brainstem or cortical modulation pathways

Question 3

What is an alpha neuron?q

Answer 3

A motor neuron that starts in the ventral horn and goes to skeletal muscle

Question 4

What are upper motor neurons? What happens if damaged?

Answer 4

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

Question 5

What are lower motor neurons? What happens if damaged?

Answer 5

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

Question 6

What is the corticospinal pathway?

Answer 6

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

Question 7

What is the function of the cerebellum?

Answer 7

coordination and smooth execution of movements

Question 8

What are the sx of cerebellar damage?

Answer 8

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

Question 9

What is the function of the basal ganglia?

Answer 9

modulates movement, posture, standing, walking, writing – requires acetylcholine and dopamine neurotransmission

Question 10

What happens in Parkinsons? Sx?

Answer 10

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

Question 11

What does the ANS do? Organs involved?

Answer 11

controls smooth muscle of the organs, and cardiac muscle of the heart.
unconscious, organ-level reflexes
Hypothalamus, Brain Stem, Spinal Cord, Autonomic Ganglia

Question 12

What is the autonomic pathway for the brain stem or spinal cord? Neurotransmitters?

Answer 12

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

Question 13

What is the pathway for autonomic ganglia? Neurotransmitters?

Answer 13

cell bodies of final neurons
Diffuse varicosity-type synapses to whole organs
Acetylcholine or Norepinephrine

Question 14

What is a sympathetic varicosity?

Answer 14

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

Question 15

What is the ANS?

Answer 15

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

Question 16

How many neurons in the ANS? Where are they?

Answer 16

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)

Question 17

What are the alternate names for the SNS and PNS?

Answer 17

SNS- Thoracolumbar

PNS- Craniosacral

Question 18

Where are the nerves in the SNS? Which are short/long?

Answer 18

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

Question 19

Where are the nerves in the PNS? Which are short/long?

Answer 19

“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

Question 20

What neurotransmitters are used where in the PNS/SNS?

Answer 20

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

Question 21

Why does the ANS affect whole organs?

Answer 21

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

Question 22

What does the adrenal medulla do in the SNS?

Answer 22

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