Upper and Lower Motor Neurons

2 descending/efferent nerve cells

How many efferent neurons are required to get a signal from the brain to skeletal muscles?

1st: UMN
2nd: LMN

2 nerves cells required to get a signal from the brain to the skeletal muscle

brain/brainstem

Location of cell bodies of UMN

axons synapse with LWM in the SC

Location of axons of UMN

Influence LMN activity including reflexes by transmitting signals from the brian to the SC

Function of UMN

cell bodies in SC

Location of cell bodies in LMN

transmit signals from the SC to the motor unit (muscles)

Function of LMN

ventral horn (red)

What horn of the SC are LMN cell bodies found

1. dorsolateral motor system (blue)
2. ventromedial motor system (green)

2 regions of the SC the axons of UMNs travel down

1. conscious efferent (UMN)
2. Reflexes (interneuron)

2 stimuli of LMN

thoracic limb

UMN of the _______

pelvic limb

UMN of the __________

thoracic limb

LMN of the _________

pelvic limb

LMN of the _________

1. conscious motor function
2. muscle tone
3. reflexes
4. muscle atrophy
5. proprioception
6. sensation

Lesions to UMN and LMN cause 6 different outcome

somatotopy

UMN pathways have __________

point for point correspondence of function to location of CNS

Somatotopy

1. proximal muscles "whole limb movement"/posture and balance
2. extension

Fiber functions of the ventromedial system

1. distal muscle fine motor movement
2. flexion

Fiber functions of the dorsolateral system

decreased/absent voluntary movement of the fine motor/flexor systems caudal to the site of damage

Signs of dorsolateral motor systems

decreased/absent voluntary movement of the whole limb/extensors caudal to the site of damage

Signs of ventromedial motor systems

1. trauma
2. localized/diffuse infection
3. space-occupying lesions
4. intervertebral disk disease

4 examples of local pathology

1. muscle tone
2. muscle atrophy
3. reflexes
4. sensation

4 signs to observe when diagnosing a SC lesions

-thoracic limb deficit: UMN
-pelvic limb deficit: UMN

C1-C5 injury
-thoracic limb deficit
-pelvic limb deficit

-thoracic limb deficit: LMN
-pelvic limb deficit: UMN

C6-T2 injury
-thoracic limb deficit
-pelvic limb deficit

-thoracic limb deficit: normal
-pelvic limb deficit: UMN

T3-L3 injury
-thoracic limb deficit
-pelvic limb deficit

-thoracic limb deficit: normal
-pelvic limb deficit: LMN

L4-S2
-thoracic limb deficit
-pelvic limb deficit

1. paresis/paralysis
2. decreased to absent muscle tone
3. decreased to absent reflexes
4. rapid-onset muscle atrophy

4 LMN signs

1. paresis/paralysis
2. normal to increase muscle tone
3. normal to increased reflexes
4. slow muscle atrophy

4 UMN signs

both UMN and LMB damage

Transverse damage to the spine causes

caudal to the spinal lesion

Where will you see UMN signs

at the site of the spinal lesion

Where will you see LMN signs

pudendal n. (S1-S3)

What nerve supplies somatic innervation to the urethralis m.

efferent n. to the reflex closure of the urethral m.

What does voluntary control of the urethralis m. supply

pelvic n. (S1-S3)

Parasympathetic innervation to the urinary bladder

involuntary SM contraction of the bladder wall (detrussor m.)

Function of the pelvic n. on the urinary bladder

visceral afferent -> stretch of the bladder

Sensory afferent innervation provided by the pelvic n.

hypogastric n. (lumbar nn.)

Sympathetic innervation to the urinary bladder

inhibitory action (relaxation)

Action of the hypogastric n. on the detrussor m.

stimulatory/contraction

Action of the hypogastric n. on the SM of the neck of the bladder

pelvic n.

When the bladder fills, what n is going to send afferents to the cortex to make the animal aware of the need to urinate

stimulates somatic afferent neurons via the pudendal n -> will also inform the animal that they need to urinate

When the bladder fills a small amount of urine will enter the proximal urethra, what will this trigger

1. reflex contraction of urethralis m. via efferent pudendal n.
2. somatic voluntary control of urethralis m via efferent pudendal n.
3. sympathetic fibers via hypogastric n inhibit contraction of detrussor m.

3 things that need to happen during storage of urine in the urinary bladder

1. conscious awareness of needing to urinate via pudendal and pelvic nn.
2. conscious voluntary motor and relaxation of urethralis m via pudendal n
3. parasympathetic fibers via pelvic n. induce contraction of detrussor m.

3 things that need to happen during micturition

urinary incontinence

What can a spinal cord injury cause in terms of the urinary bladder

result from lesions cranial to sacral spinal

When would UMN lesion signs of the urinary bladder occur

result from lesions of S1-S3

When would LMN lesion signs of the urinary bladder occur

1. bladder is turgid
2. inconsistent urine leakage (incontinent)
3. resistance to manual expression

UMN lesion signs in the urinary bladder

no somatic control of the urethralis m but continual contraction from the reflex

Why is the bladder turgid and resistant to expression during an UMN lesion

continuous leakage!
-no voluntary control
-no tone
-no reflex
-minimal resistance to urine flow from bladder through urethra
-small and flaccid bladder during palpation

LMN lesion signs in the urinary bladder

lack afferent and efferent fibers for conscious control while also lacking the reflex to keep the urethralis m. contracted involuntarily

Why are we seeing continuous leakage with a LMN lesion