Spinal Cord and Reflexes Flashcards
Describe the basic anatomy of the spinal cord.
The spinal cord is located within the vertebral canal of the vertebral column, surrounded and protected by three meninges
Describe the white and gray matter of the spinal cord.
In the spinal cord white matter surrounds a centrally located H-shaped mass of gray matter.
What is the central canal?
A small space in the gray matter, extending the length of the cord and contains cerebrospinal fluid.
The spinal cord appears to be segmented because?
31 pairs of spinal nerves emerge from it a regular intervals
How are spinal nerves connected to the spinal cord?
Each connected by two bundles of axons called roots
What are the two roots called?
Posterior (dorsal) root
Anterior (ventral) root
What is the posterior (dorsal root)?
Contains only sensory axons which conduct nerve impulses from the sensory receptors in PNS into CNS. Each posterior root has a posterior root ganglion which is a bulge containing cell bodies of sensory neurons
What is the anterior (ventral) root?
Contains axons of motor neurons which conduct nerve impulses from CNS to muscles and glands.
What is a reflex?
An input that in addition to being sent to the brain can trigger an automatic response very quickly.
What are the three parts of a reflex?
Input
Relay
Output
What is a reflex input?
Event that causes reflect/ activation of sensory receptors and AP’s along sensory nerve endings
What is a reflex relay?
Connections in the CNS that are required for reflex
What is a reflex output?
Resulting muscle activity - AP’s along motor neurons resulting in muscle contraction
Describe the example of the stretch reflex.
Stretching done via small hammer, stimulates muscle fibres, sends AP’s up sensory neuron into spinal cord, SYNAPSES with motor neuron which then return to muscle, muscle contracts, stretch removed
What is the function of a reflex?
To allow body/ muscle to make automatic adjustments in length and load without waiting on brain
How does the spinal cord communicate with the brain?
Via Spinal Pathways or Tracts
What are the two divisions of Spinal Tracts?
Ascending Sensory Tracts
Descending Motor Tracts
Where are these Spinal Pathways/Tracts Located?
In the white matter of the spinal cord
What spinal pathway an AP’s taken when travelling down the spinal cord to a motor neuron depends on the…
‘type’ of muscle it is destined for (type refers to the degree of control required for the output)
For precise movement what spinal pathway is important?
The Corticospinal pathway
For control of posture/movement and whole limbs what spinal pathway is important?
The Extrapyramidal pathway
What side of brain controls what side of body?
The right cerebral hemisphere controls the left hand side of the body and the left cerebral hemisphere controls the right hands side of the body.
What is crossing over in the nervous system?
When nerve axons cross over from right hand side of body to arrive at left hand side of brain and vice versa
Where to axons cross over?
At the medulla
Name two major sensory pathways.
Dorsal Column
Spinothalamic Pathway
What sensations use the Dorsal Column route to travel to the brain?
Touch, vibration, pressure, two point discrimination, proprioception
What sensations use the Spinothalamic route to travel to the brain?
Pain and temperature (lateral pathway)
Light touch and pressure (anterior pathway)
What cells make the myelin sheaths in the PNS?
Schwann cells
What cells make myelin sheaths in the CNS?
Oligodendrocytes
Describe the segments of the spinal cord to bottom to top?
Coccyx - sacrum - lumbar - thoracic - cervical
How many spinal nerve pairs are there for each spinal segment?
1 Coccygeal, 5 sacral, 5 lumbar, 12 thoracic, 8 cervical
