KIN 4571: The Spinal Cord

Gray matter is mosty?

cell bodies/dendrites

Is there more gray matter or white matter in the spinal cord?

white matter

White matter is mostly?

axons

White matter has _______ and _________ tracts

ascending and descending tracts

The spinal cord is a direct continuation of?

caudal brainstem

What is the function of the spinal cord?

conveys messages to/from higher center (cerebellum/cerebral cortex)

What are the 3 primary functions of the spinal cord?

1. sensory processing and integration

2. Motor output: contains motor neurons that innervate muscles

3. Autonomic output: contain efferents of the ANS

Upper motor neurons (UMN)

motor neurons in the cortex

Lower motor neurons (LMN)

motor neurons in the spinal cord

alpha and gamma motor neurons are considered?

lower motor neurons

3 main zones of gray matter

dorsal horn, intermediate zone, and ventral horn

Dorsal Horn (posterior horn)

mostly interneurons cell body and sensory neuron axons

Intermediate zone

mostly interneurons cell body

Ventral Horn (anterior horn)

mostly motor neurons cell body

cervical and lumbar enlargement

By testing the loss of sensory and movement, a _______ in the spinal cord can be determined

lesion

Dematone

area of skins innervated by one single spinal nerve or spinal segment

Myotome

muscles innervate by one single spinal nerve or spinal segment

Touch vibration and proprioception

stay on ipsilateral side

Pain and temperature

cross to the contralateral side

Types of motor output:

involuntary, central pattern generators, and voluntary movements

Involuntary are spinal ________

reflexes

Involuntary movements are affected by?

presynaptic inhibition and facilitation

Involuntary movements are moving in response to _________ __________

afferent stimulus

Central pattteral generators

neural circuitry that mediates rhythmic activities autonomously

Voluntary movement

choosing to move

Factors influencing muscle force

motor unit recruitment, fiber type, and rate modulation

Motor unit recruitment

# of motor units recruited

"size principle" - small first, then large

Fiver type

slow (type I) and fast (type II) twitch

Rate modulation

firing rate, # of action potentials

Autonomic Nervous Systems includes

sympathetic and parasympathetic

Sympathetitc

fight or flight

Parasympathetic

homeostasis, digestion

Central Pattern Generators (CPGs)

neural circuitry (or neuron groups) that mediate rhythmic activities autonomously

Where is the location of CPGs?

brain stem and spinal cord

What are some examples of CPGs?

respiration, mastication/chewing, scratching (only for quadrupeds), locomotion

What is an CPGs experiment that was done?

cats with spinal cords transection walk on treadmills

In animals, CPGs don't need sensory input, but are always being modified by it. Locomotion is possible without?

input from higher brain centers and sensory feedback

In animals CPGs are influenced by?

supraspinal center inputs

types and degree of afferent feedback (ex: change of speed, avoidance of obstacles)

Limb and body position

In animals, command neurons respond to these influences and initiate CPG activity. Nuerons that response to sensory descending inputs and initiates ____ ________

CPG activity

different movement and condition --> different command neurons --> activate different sequence in CPG --> different movements

Why would CPGs for humans be different?

quadruped vs. biped

evolutionary changes

research is more limited

What are findings against gait CPGs in humans?

cortical development is critical for bipedal locomotion

human descending tracts are bigger

What are findings for gait CPGs in humans?

muscle activation similar to walking has occurred in s.c. injury patients

human infants make cyclic motions

Renshaw cells (-) -- mediated recurrent inhibiton

"-" interneurons projecting to a.m.n. or Ia inhibitory i.n.

under central control, but receive input from

Convergence

several inputs from different locations sent to one neuron or location

Divergence

one neuron affects multiple targets

complete by axonal branching and the formation of multiple synapses

Lateral (surround) Inhbiiton

one neuron affects multiple targets differently

Lateral inhibition is achieved by?

inhibitory interneurons that inhibit adjacent sensory neurons

Lateral inhibition isolate _________ _________, assist in the ____________, identifying and interpreting __________ of sensory input

isolate sensory input, assist in the localization, identifying and interpreting intensity of sensory input

Parallel processing

similar information conveyed by multiple sources

Parallel processing is achieved by?

different pathways, or parallel axons within the same pathway

In parallel processing, there is an increase in the information by?

carrying abilities

In parallel processing, the redundancy is common within the?

CNS

In what situation this redundancy is useful?

injury, disease

Disinhibiton

reduces inhibition by inhibition

Propriospinal neurons

interneurons within the spinal cord

Propriospinal neurons __________ or __________ the cord to innervate with the interneurons or motor neurons up to several segments away

ascend or descend

Propriospinal interneurons never exit?

spinal cord