Here we go! We're leaving the brain and move downward to the Spinal Cord.
Below, please find the newly revised class notes. I have also posted some preview questions to complete before class.
19.1. As we have learned, the brain is our main neural integration center, where many of the sensory pathways end, and motor ones start. The spinal cord has some rudimentary integration as we will see when we discuss reflexes, but for a large part, it carries ascending and descending nerve fibers in tracts. Those nerve fibers then travel through 31 spinal nerves to the entire body. In the cervical and lumbar region, the cord thickens. Why is that? What do we call those area?
19.2. Looking at the cord lengthwise, it starts where the medulla oblongata ends, which is around the foramen magnum. It then travels through the spinal canal all the way down to about L1 or L2, where it closes to a tip. It doesn’t go all the way to the coccyx (tailbone), because the spine grows more than the cord as we develop. What do we call the tip where the spinal cord ends? Below it, nerve roots travel freely before they exit intervertebral, or sacral foramina at the appropriate levels. What are those nerve roots collectively called?
19.3. The spinal nerves exit the spinal cord on it’s sides along the way down. The nerves then travel mostly between two adjacent vertebrae before connecting to their specific targets. We name each of them according to the vertebral level they come out of. Most of them exit below the vertebra they are named after. The exception is the cervical spine. Can you explain how we name those spinal nerves?
19.4. When we follow a spinal nerve through the intervertebral (or sacral) foramina, we find it split right after, one arm, or nerve root reaching around the cord entering in the front (anterior), and the other swelling up a little before entering into the back (posterior) side. Spinal nerves are made of both sensory and motor nerve fibers, nerve roots carry only fibers that either travel into the central nervous system, or exit it. Which of them carry sensory, and which motor fibers?
19.5. The nerve roots on the posterior, or dorsal side swell up a bit before entering the cord. Those swellings are many neural cell bodies grouped together. That way they provide protection for one another. What are those swellings called?
19.6. Looking at a cross section of the spinal cord, we find a reverse order of white and gray mater then found in the brain. In the spinal cord, the white mater, which are myelinated nerve fibers travelling up and down the cord are on the outside, where as neural cell bodies, that will provide rudimentary integration, lie centrally in the grayer looking tissue. The gray mater’s shape sort of resembles a butterfly. It has different swellings, or horns arising from the front, side, and back carrying specific types of neural cell bodies. Which type is found within each horn?
19.7. The outer layer of the spinal cord is white mater made of nerve tracts. Inside of them are nerve fibers travelling up or down the cord. Those fibers make up pathways of multiple neurons that connect the brain with their respective peripheral target or receptor. How many neurons are in a sensory pathway? How many make up a motor pathway?
19.8. The tracts in the cord are well organized and mostly named according to their origin and destination. Most of the sensory fibers carrying information destined for our consciousness make a stop in the thalamus before they reach our thought. Which tract carries pain fibers into the brain?
19.9. Many of the tracts that descend the spinal cord, the motor tracts, are connecting the primary motor cortex (in the forebrain) to skeletal muscles. The majority of them cross over from left to right or vice versa at the medulla oblongata, before continuing down the spinal cord to the level of muscle innervation, where they synapse to a second order neuron. Along the way the conscious ‘wanting’ to move a muscle is influenced by different structures. Can you name the 3 listed in the slide?
19.10. Something very cool that happens at the spinal cord level are hardwired feedback loops. This is where a receptor, such as a pain, temperature, or stretch receptor picks up a stimulus that can be reacted to the same way every time; for example, if your temperature sensor in your finger burns up, you want to pull it away from the heat source every single time. We don’t really need to think much about that, it just needs to happen. Can you explain how the patellar reflex works?
19.11. It is very important to the body, that nerve impulses to skeletal muscles, which move us around in the world, are well fed. Looking at the pathway from the brain to skeletal muscle, the nerve root is most vulnerable to damage (ex: disc herniation). Our bodies smart’s figures therefore to feed a nerve from multiple different spinal cordlevels to avoid a complete shutdown if one of them is impeded. Can you name the plexus the nerve impulses feeding the biceps brachii travel through?
19.12. The brain is enclosed by the skull, and not vertebra. Therefore, ’spinal’ nerves coming out of the brain don’t pass through an intervertebral, or sacral foramen, and are not as nicely arranged and easily identified. These cranial nerves connect the central nervous system to the head and face. They also serve the special senses. Most of them carry sensory and motor impulses, but some only deal with sensory inputs. Can you name those nerves and describe their function?
19.13. As we have already seen, much of our brain works automatically, out of our conscious control. Functions such as restricting or dilating vessels to send blood to specific body parts, regulating the rate & depth of breathing, influencing heart rate and blood pressure, enhancing or inhibiting digestion, and much more are governed by the 2 different parts of the autonomic nervous system (ANS). The sympathetic part utilizes body resources to maneuver around in the world. It is easiest understood when fully triggered as is the case in a situation we either have to ‘fight or flight’ (run away from). The parasympathetic ‘rest and digest’ part builds our resources back up. The 2 branches are physically distinct and arise from different parts of the central nervous system (cord & brain stem). Can you explain the differences?
Please send me the answers you came up with to those questions before the class meets to [email protected] Thank you.
For the Lab terms that will be on the final, please print out the test3 lab term list by going to the main 'Part 3' tab. Here is a description of the Lab terms. Please also print out the LAB Homework: Spinal Cord.
We will also do a reflex lab in class. please print out the handout for it.