Unit 5

 Neuroanatomy

 

 

 

TOPICS COVERED

 

Spinal pathways

Dorsal column

Anterolateral

Somatosensory cortex

Motor Cortex

Spinal Cord tracts

UNIT CONTENT

Divisions of the Nervous System:

The nervous system is comprised of central components (the brain and the spinal cord) and peripheral components (the sensory and motor nervous system). The sensory nervous systems receives information from the environment and relays it to the CNS. The motor nervous system is comprised of the somatic system and the autonomic nervous system (ANS). The somatic nervous system innervates the muscular system resulting in the contraction and relaxation of muscles. The ANS is in turn divided into the sympathetic and parasympathetic nervous systems. These two systems operate involuntarily (automatically).

Animation 1 - Animation of the parasympathetic and sympathetic nervous systems 

 

Transmission of Sensory Information within the CNS

  • Sensory impulses are transmitted via specialized pathways to the CNS: Dorsal column medial lemniscal system (DCML), Anterolateral spinothalamic tract (AST)

  • the first stage of sensory integration and perceptual awareness occurs at the level of the thalamus

m   The thalmas is capable of gating out irrelevant sensory information while directing relevant          information to the cortex

 

  • ·        sensory pathways carrying general sensory information (e.g., touch, temperature,
    proprioception) terminate in different sensory regions of the cortex

 

·       Once the information reaches the primary sensory region in the cortex we are able to recognize    both the source and intensity of the sensations

 

·   Our final perception of what is occurring in the environment or within our bodies is achieved once the sensory information has been integrated and interpreted by the associated areas of the cortex, limbic system.

The two main systems which transmit sensory signals within the CNS: 

·         The Dorsal Lemniscal System (fine precise sensations)

·         The Anterolateral Spinothalamic System (crude type sensations)

The type of sensations which are characteristically conveyed in these 2 systems are tabled below:

Dorsal Lemniscal System

Anterolateral Spinothalamic System

  • Touch sensations:
    • High degree of localization of stimulus.
    • Fine graduations in intensity of stimulus.
  • Phasic sensations (vibrations).
  • Sensations of movement against the skin.
  • Fine positional and pressure sensations.
  • Thermal sensations:
    • Cold
    • warm
  • Pain sensations
  • Crude pressure and touch sensations
  • Tickle and itch sensations
  • Sexual sensations

 

The dorsal lemniscal system begins with somatosensory axons entering the spinal cord via the dorsal root and ascending in the dorsal columns ipsilaterally. The first synapse point for this pathway is in the dorsal column nuclei located in the medulla. The axons of neurons originating in the dorsal column nuclei decussate (cross over), ascending via the medial lemniscus to the contralateral ventral posterior thalamic nucleus (VPN). Somatosensory fibers of the trigeminal nerve (CN V), carrying information from the contralateral side of the face and head, also synapse in the VPN. The majority of VPN neurons project to the primary somatosensory cortex (SI), the remaining project to the secondary somatosensory cortex (SII) of the posterior parietal lobe. The anterolateral system begins with somatosensory axons entering the spinal cord via the dorsal root and synapsing upon entry. The majority of these 2nd-order axons decussate, and ascend to the brain via the anterolateral portion of the spinal cord white matter. This ascending system is composed of three separate tracts, the spinothalamic tract, the spinoreticular tract, and the spinotectal tract. The spinothalamic tract projects to the ventral posterior nucleus of the thalamus. This tract is involved in the perception of touch, temperature, and sharp pain. The spinoreticular tract projects to the brain stem reticular formation on its way to the parafasicular nucleus and intralaminar nucleus of the thalamus. This pathway seems to be selectively involved in the perception of deep, chronic pain. The spinotectal tract projects to the tectum of midbrain. This tract is likely involved in some aspect of pain perception. The tracts of the anterolateral system project to both the primary and secondary somatosensory cortex, and to more posterior locations within the parietal lobe

 

Somatosensory pathways - required reading

 

Neuropics - Highly recommended – Awesome site for pathway and neuroanatomy images

 

Required QUIZ 1

UNIT 5

Please take in : www.uh.edu/webct

You will have 31 minutes to complete the Required Quiz - use your time wisely!

 

Cortex

A little history - thanks to: A Science Odyssey

  What would you do if you were a doctor and had patients who were missing pieces of their skulls? If you were Eduard Hitzig, a German doctor working at a military hospital in the 1860s, you'd conduct some experiments. Hitzig, working on patients who had pieces of their skulls blown away in battle, stimulated exposed brains with wires connected to a battery. By doing so, he discovered that weak electric shocks, when applied to areas at the back of the brain, caused the patients' eyes to move.

Later, around 1870, Hitzig teamed up with another doctor, Gustav Fritsch. Setting up a makeshift lab in Fritsch's house, the two stimulated the brains of live dogs. They found that not only could they cause crude movements of the dogs' bodies, but that specific areas of the brain controlled specific movements.

Soon after, John Hughlings Jackson, an English scientist, took the work of Fritsch and Hitzig further. Based on his observations of his wife's epilectic seizures, Jackson came up with a more-detailed theory of how the brain controls muscles. He knew that every one of her seizures followed the same pattern: It would start at one of her hands, move to her wrist, then her shoulder, then her face. It would finally affect the leg on the same side of her body, then stop.

Jackson believed that the seizures were electrical discharges within the brain. The discharges started at one point and radiated out from that point. This suggested that the brain was divided into different sections, and that each section controlled the motor function (or movement) of a different part of the body. And since the pattern never varied, the way the brain is organized must also be set.

Wilder Penfield

Photograph of exposed brain

 


 

Wilder Penfield, a pioneering brain surgeon, mapped the motor cortex using mild electric current.

Wilder Penfield took the next exploratory voyage into the brain starting in the 1940s. While operating on epileptic patients, Penfield applied electric currents to the surface of patients' brains in order to find problem areas. Since the patients were awake during the operations, they could tell Penfield what they were experiencing. Probing some areas triggered whole memory sequences. For one patient, Penfield triggered a familiar song that sounded so clear, the patient thought it was being played in the operating room.

During these operations, Penfield watched for any movement of the patients' bodies. From this information, he was able to map the motor cortex, the very part of the brain you can map in this feature's activity.

 

 

Cerebral Representation of Sensory and Motor Information (Cortex)

The cerebral surface is divided into a number of groves (a sulcus) and elevations (a gyrus). A prominent medial lateral grove is called the Central Sulcus (grove). Anterior to this grove on the precentral gyrus resides the motor cortex. Posterior to this grove, on the postcentral gyrus, resides the somatosensory cortex.

 

 

The motor cortex and somatosensory cortex have a representative mapping of regions of the body. Notice the disproportionate cortex area given to body parts used in fine movement, such at the hands and lips for both motor and somatosensory cortex.

 

Motor Cortex I - required reading

Motor Cortex II - required reading

Motor Cortex III - required reading - incredible site for entire brain - note that like the cortex, this site has multiple layers.  Quiz questions for the upcoming quiz will be focused on the cortex or spinal motor tracts.

Homunculus - let this website load and have some fun learning

Spinal motor tracts - required reading

Good supplement - your call

For those wanting to go the extra mile

Animation 2  - highly recommended – awesome site for images, MRI scans and movies - *don't spend all day in here it would be easy to.

The Brain and Neurosyllabus sites are of most relevance to this class.  Note - it takes a little bit of time for the movies to download so be patient, however, they really help you visualize your neuroanatomy.

Self Quiz - this quiz is not graded

There are two Quizzes at the bottom of this page - "Jigsaw Puzzle" and "Who Wants to be an Anatomist?"  You will need to download Java Web to complete the quizzes.

You will have 31 minutes to complete the Required Quiz - use your time wisely!