Day 11 Spine Somatic NS and Reflexes

white matter

large numbers of myelinated and unmyelinated axons

white matter is organized into columns and each column contains

tracts or bundles of axons

what do white matter tracts or bundles of axons do?

they carry info to and from the brain

they carry the same type, rate, and direction of information

ascending tracts

spinal cord to brain

sensory info

descending tracts

brain to spine

motor info

gray matter

neurons, neuroglia, unmyelinated axons

horns

cell bodies of gray matter organized into functional groups called

nuclei

sensory nuclei

receives information from PNS

motor nuclei

sends motor commands to effectors

sensory nuclei are _____ from motor nuclei

separated

posterior gray horns

somatic and visceral sensory nuclei

anterior gray horns

somatic motor nuclei

lateral gray horns

only located in the thoracic and lumbar areas

visceral motor

autonomic N.S.

what is the pathway of a dorsal root (posterior)

axons + cell body of sensory neurons

unipolar neurons

what is the pathway of a ventral root

axon of motor neurons

somatic motor neurons cover

skeletal muscles

visceral motor axons cover

smooth muscles

cardiac muscles

adipose tissue glands

dermatome

a specific strip of skin that is innervated by a specific spinal nerve

Peripheral neuropathy

nerve damage that causes weakness, numbness, and pain, typically in the hands and feet

examples:

-        Trauma

-        Diabetes – peripheral axon compression

-        Sciatica

-        Shingles

-        Paraplegia

-        Quadriplegia

Paraplegia

nerve damage in the lower extremities

Quadriplegia

nerve damage in all 4 extremities

decussation

crossing over of white matter tracks in the brainstem or the spinal cord to the opposite side

-        Most motor or somatic motor does cross sides, usually around the brain stem area

somatic sensory pathway (ascending (afferent) tracts)

first-order neuron —> second-order neuron —> third-order neuron

first-order neuron

• where the cell body is in the dorsal root ganglion

• what’s detecting the stimuli

• axon travels through that posterior or dorsal root and into the posterior horn

• the body, entering the spinal cord

second-order neuron

-        Between two neurons, typically found in between the brain or the spinal cord

-        Takes the info up the spinal cord and take it to the thalamus

• spinal cord, entering the brain

third-order neuron

-        In the cell bodies in the thalamus

-        Takes the signal out of the appropriate area of cortex, goes wherever that info needs to go in the cortex to be processed

-        Shorter in length

• thalamus and sending info where it needs to be

somatic motor pathway (descending (efferent) tracts)

thalamus isn’t needed

upper motor neuron —> lower motor neuron

upper motor neuron

-        Goes from brain down to the spinal cord

-        Cell body is in the brain

lower motor neuron

axons travel out the anterior route and goes out to the effector

somatic motor

innervates skeletal muscle

types of neural pools

• diverging circuit

• converging circuit

• serial

• parallel

• reverberating circuit

diverging circuit

-        Motor neurons (upper)

-        Upper motor neurons excite lower motor neurons which excite effector cells

-        If the upper motor neuron is about to stimulate, it doesn’t mean it will give the same effect to each lower motor neuron

-        Meaning the left lower motor neuron could be excited while the right lower motor neuron is inhibited

-        Example of this is when you’re doing a bicep curl, the bicep is getting excited (used/contracted)) while the tricep is being inhibited (relaxed)

converging circuit

-        A lot of neurons going to one / receiving signals from multiple neurons (spatial summation)

-        Mostly sensory (IPSP and EPSP)

-        Sight, hearing, balance

serial circuit

-        One presynaptic neuron, one postsynaptic neuron, and maybe another neuron

-        The middle one (postsynaptic neuron) would be the interneuron

-        First order, second order, third order neurons

-        Touch and pain, sensory

parallel circuit

-        Looks like diverging

-        Signal is going down neurons at the same exact time (parallel)

-        Seen when both sides of the body want to be activated (walking, putting one foot down and raising the other)

reverberating circuit

-        Positive type feedback

-        Second neuron has a collateral that comes back to the first neuron and innervates the first neuron

-        In more detail, first neuron sends a signal down that will transmit to the second neuron. The signal gets sent down through the second neuron but then the signal gets sent back up and reactivate the first neuron

-        Seen with consciousness, keeping you awake

-        This can’t happen forever

-        Two ways to turn this off is synaptic fatigue and inhibitory stimulus

-        Synaptic fatigue: can happen in either synapse and there isn’t enough neurotransmitter anymore or can’t make anymore to where the signal can’t be sent anymore

-        Inhibitory stimulus: neuron inhibits the neuron to turn off the pathway

reflexes

rapid, automatic or involuntary responses to specific stimuli; always results in the same response

reflex arc

negative feedback loop

order:

sensory receptor —> sensory neuron —> integration center (interneurons) —> motor neuron —> effector

sensory receptor

receiving information

sensory neuron

taking information to the CNS

integration center (interneurons)

spinal cord or CNS

interneuron may or may not be present

motor neuron

carries information to the effector

effector

any muscle or gland that responds to motor neuron signals

innate reflex

born with this reflex

• feeding

• pain reflex

acquired reflex

reflexes learned throughout life

• driving

• walking

location of processing

information being processed in either the spinal cord or the brain

spinal (location of processing)

skeletal muscle

cranial (location of processing)

brain

response

somatic or visceral

somatic response

skeletal muscle

visceral response

smooth, cardiac muscle, adipose, and glands

complexity

simple or complex

simple complexity

monosynaptic

Involving only one synapse in the reflex arc

complex complexity

polysynaptic

Involving multiple synapses and neural pathways

stretch reflex - essential for posture control and coordination of movement

• Patellar reflex (knee-jerk)

• Patellar tendon is attached to the tibia and to the quad muscles

• Tendon pulls on the quadricep and stretches the muscle

• This then causes the tibia to jerk up

withdrawal reflex

-        Example: Touching something hot and removing your hand from it

-        Only affects one side of the body

-        Have info be sent down using a sensory neuron to a interneuron going down to two motor neurons

-        The first motor neuron is excited and create an EPSP, this will cause the muscle to contract

-        The second motor neuron inhibits the other side and relaxes it

why does the info get processed and sent back out to the body in the spinal cord instead of the brain?

Because it’s more quicker compared to sending the info to the brain and receiving it back

cross-extensor reflex

Example: you’re walking in the middle of the night and your right foot steps on something cold, wet, and disgusting. Your first move is to lift up your right foot but at the same time your left foot registers that it’s now standing on it’s own and has to balance the body. This happens at the same time.

-        Signals are sent to one side of the body to do one task and at the same time signals get sent to the other side of the body to perform another task

-        Right side = lifting your right foot

-        Left side = balancing your body with your left leg

lateral horn is in which sections

T1 —> L2

in the posterior horn, it goes

somatic sensory then the visceral sensory

What is the clinical importance of dermatomes?

-        To know what nerves or part of the limb or body is affected

What is a peripheral neuropathy?

-        Diabetes causes peripheral neuropathy, usually in the feet to where they can’t feel their legs or arms

-        When the limbs “fall asleep”, usually from compression

Someone with a spinal cord injury, are their spinal cord reflexes still intact?

The reflexes are still active (sensory to motor), but the brain process doesn’t exist because the signals don’t get sent to the brain