spinal cord (I) Flashcards
Where do primary somatic sensory afferents project to?
The spinal cord
Spinal cord dimensions
- 42-45 cm long
- ≤ 1 cm in diameter
Spinal cord segments
31 segments, each of which corresponds to the entry point of a pair of spinal nerves.
→8 cervical
→12 thoracic
→5 lumbar
→5 sacral
→1 coccygeal
Cervical and lumbar enlargements
Correspond to the segments that innervate the limbs
Lumbar cistern
The subarachnoid space in the lower lumbar spinal canal.
- no spinal cord here
- filled with CSF
- filled with nerves
(where needles are inserted to not potentially damage spinal cord higher up!)
Cauda equina
The cauda equina is the bundle of nerve roots located at the lower end of the spinal cord.
Foramen magnum
Place where the cord enters the skull to form the medulla.
Medulla
Most caudal region of the region of the brainstem.
Spinal cord composition
- Central grey matter
- Surrounding white matter
Ventral horn
-part of the grey matter
-mainly involved in movement
Dorsal horn
-part of the grey matter
-mainly involved in sensory function
Grey matter
Regions of the nervous system consisting mainly of (1) neuronal cell bodies, (2) dendrites and (3) synapses
White matter
Bundles of myelinated axons.
General cross-sectional anatomy of the spinal cord: Fill in the blanks
☆slide 37☆
Ganglion
An organized cluster of neuronal cell bodies in the peripheral nervous system.
Nucleus
An organized cluster of neuronal cell bodies in the central nervous system.
Number of spinal nerves
There are 31 pairs of spinal nerves running down the length of the spinal cord.
How do primary somatic sensory afferents enter the dorsal spinal cord?
(Draw it!)
Through the dorsal roots.
→fibers come in and branch out through the dorsal root
How do motor neurons project to skeletal muscle fibers?
(Draw it!)
Through the ventral roots.
→in the ventral horn of the spinal cord grey matter, we have the cell bodies of motor neurons that are going out to control the skeletal muscles, they then send their axons out through the ventral root
What procedure can be done in cases of SEVERE pain?
An individual may have the dorsal root cut off ONLY in the case of severe pain.
Dermatome
Each pair of spinal nerves innervates a region of the body surface called a dermatome.
(i.e. if nerve 2 is damaged, then so will sensory ability of region C2)
What does the intermediate region of the spinal cord grey matter contain?
The intermediate region contains interneurons and preganglionic autonomic neurons
Interneuron role
-connecting different neurons
-involved in integrative processes
-found in the grey matter
-allow for intrinsic circuitry
Fine touch primary afferent root in spinal cord
Primary afferents for fine touch enter the dorsal columns and ascend to the dorsal column nuclei in the brainstem.
→can go to grey matter or white matter directly
→ipsilateral
Pain & temperature primary afferent root in spinal cord
Primary pain and temperature afferents synapse in the dorsal horn of the spinal cord grey matter. The second neuron crosses over toward the anterolateral column.
→contralateral
Dorsal columns and anterolateral columns organization
They are somatotopically organized.
→fine touch: arms located laterally, legs located medially
→pain & temp.: arms located medially, legs located laterally
How far is somatotopic organization conserved?
Somatotopic organization is conserved throughout the entire sensory pathway.
Sensory-motor hierarchy
(Draw it!)
The spinal cord is part of a sensory-motor hierarchy that includes the brainstem and higher brain regions including the cerebral cortex, the cerebellum and the basal ganglia.
Sensory-motor hierarchy: Motor cortex
-complex voluntary movements
-fine motor control
Sensory-motor hierarchy: Brainstem
-automatic behaviour
-respiration
-chewing
-expressions
-stereotyped behaviour
Sensory-motor hierarchy: Spinal cord
-protective reflexes
-locomotion
Stretch reflex
-one of the simplest of sensory to motor movements
-mediated by the spinal cord
→proprioceptive neurons get activated and they send axons into the spinal cord (main branch goes up to the brainstem, so our brain has some information about what’s going on), but there’s a branch that goes into the spinal cord grey matter and directly activates motor neurons in the spinal cord, causing the muscle to contract
Withdrawal reflex
-one of the simplest of sensory to motor movements
-mediated by the spinal cord
→when you touch a hot stove, primary nociceptors are activated, which then send a signal to the spinal cord, which activates motor neurons in the spinal cord and then your hand can pull away
Central pattern generator
Formed by the intrinsic circuitry of the spinal cord responsible for rhythmic movements like walking, scratching…
→facilitated by interneurons
