McLean Spinal Cord

how does the spinal cord terminate in humans?

below L1 as the conus medullaris

how many segments are in the dog spinal cord?

36

DRG

dorsal root ganglia

what does the DRG contain?

sensory afferents

what does the dorsal root of the spinal cord carry?

sensory (somatic and visceral afferent)

what does the ventral root of the spinal cord carry?

motor (somatic and visceral efferent)

spinal nerves

mixed with sensory and motor

what is in the gray matter?

dendrites, cell bodies and ganglia

what is in the white matter?

axons

what is located in the dorsal funiculus?

fasiculus gracilis and cuneatus

what are the divisions of the gray matter?

dorsal horn

intermediate horn

ventral horn

gray matter - dorsal horn

sensory

gray matter - intermediate

both sensory and motor inputs (some interneurons)

gray matter - ventral horn

alpha and gamma motor neurons

where are the cell bodies of preganglionic sympathetic neurons located?

lateral horn

function of preganglionic sympathetic neurons

innervate smooth muscle, cardiac muscle and glands

what neurons innervate skeletal muscle?

alpha and gamma

what is a motor unit?

one alpha motor neuron and all the muscle fibers it innervates

what is a motor neuron pool?

the collection of alpha motor neurons that innervates a single muscle

composition of the ventral root

ventral horn and intermediolateral cell column

ventral root - intermediolateral cell column

visceral efferent with preganglionic parasympathetic and sympathetic neurons

what does voluntary contraction require?

2 neurons - the upper and lower

Corticospinal tract (pyramidal tract)  - function

voluntary refined movements of distal extremities

what tract is responsible for independent finger movement in humans and non-human primates?

Corticospinal tract (pyramidal tract) 

where is the corticospinal tract (pyramidal tract) located?

lateral funinculus

descending spinal pathways

UMNs

modulate spinal reflexes and drive motor output

name the descending spinal pathways

lateral and ventromedial pathways

lateral pathways - movement

voluntary

lateral pathways - control

direct cortical control

lateral pathways -innervate

distal muscles

ventromedial pathways - function

control posture, locomotion, orienting and balance

Ventromedial pathways - control

brainstem

Ventromedial pathways - innervate

axial and proximal muscles

medial lemniscal system - function

proprioception fine touch, pressure and vibratory sense to cortex

medial lemniscal system - axon

Axon collaterals of the heavily myelinated afferents enter dorsal columns

contributing to reflex

medial lemniscal system - first neuron

Large myelinated axons of dorsal roots that carry proprioception and touch modalities into the cord.

medial lemniscal system - 2 neuron

ipsilateral medulla (crosses in the medulla)

spinothalamic tract - function

pain and temperature sensation to the cortex

spinothalamic tract - first neuron

Small diameter axons of dorsal roots that carry pain and temperature modalities into the cord.

They all synapse with sensory neurons in the dorsal horn!

spinothalamic tract - 2nd neuron

ipsilateral spinal cord

axon crosses and ascends contralaterally

summary - Conscious proprioception/touch/pain/temp

spinothalamic

medial lemniscal tract

summary - unconscious

Dorsal Spinocerebellar Tract

Cuneocerebellar Tract

somatosensory input is split into

separate submodalities

Dorsal spinocerebellar

lower limb (1) -> Clarke’s nucleus (2)

Cuneocerebellar tract

upper limb (1) -> Accessory cuneate nucleus (2)

how does the spinal cord segments differ?

configuration of gray

size and shape

amounts of gray and white

white decreases rostral to caudal

dorsal column nuclei

nuclei cuneatus and gracilis