Neuroscience Case Study on Cns Structure Damages

Normal CNS Structure

The skull is divided into the viscerocranium which is the facial skeleton and the neurocranium which surrounds the brain and brainstem. The neurocranium is composed of 8 cranial bones; 1 ethmoid, 1 sphenoid, 1 frontal, 2 parietal, 2 temporal, 1 occipital, their role is protecting the nervous tissue of the brain underneath. All of these sections are joined together with sutures which are strong, elastic and fibrous tissues. The space between the skull and the brain is filled with the Meninges, there are three layers to this; dura mater, arachnoid and pia mater. The outer layer dura mater is dense connective tissue which lines the inside of the skull, the second layer is the arachnoid and this is quite thin and has elastic tissue and blood vessels. The inner layer is the Pia Mater which has lots of blood vessels that also follows the folds of the brain. Cerebrospinal fluid, responsible for protecting the brain and spinal cord from injury, also runs throughout the space between the arachnoid and pia mater layer. The brain itself has an outer cover called the cerebral cortex which is grey matter and surrounds the Cerebrum which is broken down into the left and right hemispheres. The left side of the brain is more to do with thinking and the right side is more visual. The sub cortex includes the basal ganglia, limbic system and diencephalon. The brain stem includes the midbrain, pons and the medulla.

There are four lobes; frontal, occipital, parietal and temporal. The frontal lobe is involved in voluntary movement and personality. Occipital is responsible for receiving and processing visual information. Parietal receives signals from all over the brain and gives meaning to it. Temporal is responsible for memory and interpreting emotions. The prefrontal cortex (PFC) is the front part of the frontal lobe and it is this sub section of the frontal lobe that is responsible for personality expression. Diving deeper into the structure of the PFC there some major subdivisions; dorsolateral PFC together with ventrolateral PFC and dorsomedial PFC are responsible for emotion regulation. Looking at the anatomy of the brain in figure 1 you can see that just next to the frontal lobe you have the motor cortex which is responsible for movement learning and execution. The right ventrolateral portion of the PFC is also thought to play a vital role in motor inhibition. The limbic system is the structure that is responsible for emotions, memory and learning, it does this by being connected to the lower and higher brain functions in order to control emotion. Grey and white matter are looped in both cerebral hemispheres and primarily links multiple structures. The processing side of the limbic system includes the prefrontal cortex, amygdala and hippocampus, the output side includes the septal nuclei and hypothalamus. The limbic lobe is located in the sub cortex and is composed of limbic gyrus and intralimbic gyrus. The hippocampus is embedded deep within the temporal lobe and is sub cortical so classed as part of the limbic lobe, it is associated with emotions including: mood, pain and memory.

In 1930 James Papez suggested that emotional response is prepared in the hippocampus and then expressed in the limbic lobe. While the hippocampus is on the posterior side of the limbic lobe the amygdala is situated near the frontal part, the amygdala is involved with emotional processing and aggression. The hypothalamus, found at the centre of the limbic system, is responsible for homeostasis and behaviour as well as having integral connections with the pituitary gland and controlling the endocrine system. Papez circuits are important pathways that are part of the limbic system and interconnects multiple components of it. The hippocampus, mamillary bodies, nucleus of the thalamus, PFC, septum, amygdala and other areas are all part of the circuit.

Damaged CNS Structure + Symptoms

As described in the case study Dr C suffered a depressed fracture of the frontal bone causing indentation damage of the frontal lobe/ PFC in the left cerebral hemisphere. The frontal bone covers and protects the frontal lobe of the brain which is responsible for lots of different cognitive processes including movement, intelligence, reasoning, behaviour, memory and personality. A depressed fracture is the indentation and breaking of the bone that pushes bone fragments below the surface of the skull which in this case was caused by the blunt force trauma of the ice axe. This means depending upon the severity of it, it can lead to damage of the brain tissue underneath.

From the MRI you can see a black spot on the frontal lobe, this is a lesion on the brain. A brain lesion is inflammation of tissue that has been damaged. It is believed that lesions in different parts of the brain may still exhibit similar symptoms due to overlap in network connectivity. Following the symptoms that are explained in the case study that Dr C suffered, the first symptom exhibited was loss of consciousness. Traumatic Brain Injury is the clinical term given to patients if they have suffered any alterations to their consciousness from injury to the brain. The traumatic injury means there is a sudden transfer of energy from an external source (e. g. blunt force trauma) to the tissue but above the amount that can be absorbed. The energy results in ruptures of vascular and cellular membranes which leads to changes in blood flow, damage to axons and release of intracellular contents. This leads to energy failure due to depletion of ATP and cell death by necrotic and apoptotic pathways. As previously explained the frontal lobe/ PFC controls functions involving emotion, problem solving, memory, language and judgement. Traumatic brain injury can cause diffuse axial injury (DAI) as a result of high energy trauma on white matter tracts. DAI results in cognitive, physical and behavioural changes and a study showed that there was a correlation between the number of lesions and the impairment of functionality. Dr C’s behavioural changes can be linked to post-concussion disorder which includes experiencing symptoms such as social inappropriateness, aggression from minor provocation and apathy. The orbitofrontal cortex has extensive connections with the limbic system via Papez circuits and can affect the amygdala. The amygdala is associated with depression, anxiety, temper/ aggression, cortisol concentration and fear conditioning.

Injury to the PFC could affect the amygdala via the orbitofrontal cortex or by local diffuse axial injury near the region depending upon the amount of force of energy from the ice axe being transferred through the brain. This would explain the side effect sudden outbursts of temper, a study done by Zheng KZ tested the abnormal hyperactivation of the limbic system and hypoactivation of the frontal cortex. The result was that damaged white matter led to dysconnectivity from the frontal cortex to the amygdala in a “top-down” pattern. The orbitofrontal cortex is a main section responsible for decision making and damage to this, even with intact cognitive abilities, would explain Dr C’s breaches of professional conduct such as urinating in a lecture. Long term disorders from traumatic brain injury can include brain atrophy, neuronal loss and axonal degeneration. Neuronal inflammation is associated with macrophage activity and the presence of microglia which can last from anywhere between months to years and is also found in patients with Alzheimer’s disease.

Case Study Comparisons

Phineas Gage a railroad foreman was involved in an accident that resulted in a 1. 1m long rod shooting through his left cheek and out of his skull causing some of his brain to be missing and severe blood loss. Despite the severity of his injuries Mr Gage remained conscious and after 5 weeks was discharged, he was blind in his left eye and had facial weakness, his left frontal cortex was damaged profusely but from a neurological standpoint there were no deficits. However, once he tried to settle back into his life it was apparent that there were some personality changes, “Fitful, irreverent, impatient and gross profanity”, the changes described in Gage resulting from damage to his frontal cortex. Several studies such as Blumer and Benson, 1975 have linked abnormal changes in behaviour to damage in the frontal or temporal lobes and their pathways to deeper regions of the brain.