BRAIN ANATOMY. The two branches of autonomic nervous system:

Transcription

1 BRAIN ANATOMY Central Nervous System (CNS) is the brain and spinal cord. The brain and spinal cord are so critical. The brain is the executive of you; and, it is as critical as the heart. It is so important to protect your brain; hence, the brain and spinal cord are protected by bone. They are encased in the skull and the vertebrate in the spine. Peripheral Nervous System (PNS)are the nerves that emanates out of the spinal cord or go into the brain or spinal cord. PNS is composed of the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS). 1. Somatic Nervous System is made up of sensory nerves and motor nerves. Sensory nerves bring in sensory information (vision, smell, touch, taste and hearing. Motor refers to movement or muscles. Motor nerves are nerves that send information to the muscles. Motor nerves make voluntary movements. 2. Autonomic Nervous System, however, is in-charge of involuntary functions such as breathing, digestion and other internal organs. Functions that happen automatically such as pupil constriction or dilation, breathing, digestion, etc. The two branches of autonomic nervous system: a. Sympathetic Nervous System (SNS) activates most of the functions mentioned above. It is activated during fight or flight situations. When one is in an emergency or stressful situation or confronted with threat, it will activate your sympathetic NS; hence, your perspiration is increased, breathing increases, blood pressure goes up, etc. SNS are functions which consumes energy to fuel your muscles so you can either fight or run from the threatening situation. It suppresses digestion, so the resources that would normally go to digestion is diverted away from digestion, and directed to other sympathetic functions instead. b.parasympathetic Nervous System (PSNS) when you re done with the fight or flight situation, PSNS helps you calm down and recover. It helps slow heart rate, drops blood pressure, constrict pupil, etc. PSNS is mostly in-charge with digestive system. It is concerned with conservation of energy which will be needed later (during the fight or flight situations). Generally PSNS and SNS work in opposition, (when one is active the other is inactive). Examples of situations of activation of SNS: stage fright or speaking in public; roller coaster ride; watching a scary movie; stressful or tension-filled situations; wherein the muscles tensed, pupil dilate, heart rate increased, blood pressure goes up. While PSNS stores calories, carbohydrates and proteins for use in times like mentioned above.

2 Nucleus (nuclei for plural) vs. Ganglion (ganglia for plural) The cluster of cells in the Central Nervous System are called Nuclei, while The cluster of cells in the Peripheral Nervous System are called Ganglia. Sulcus (sulci for plural) vs. Gyrus (gyri for plural) In the dorsal view of the cortex, gyrus, sulcus and fissure were shown. Sulci are valleys or fold, or groove in the cortex. Deep valley is called a fissure. Gyri are ridges on the cortex. The fissure that bisects the cortex is called the longitudinal fissure, that is why we have the right and left hemisphere which are lateralized. The right hemisphere controls the left side of the body while the left hemisphere controls the right side of the body. In the sagittal view of the cortex, the Central sulcus which is the major groove going down the center and another fissure called the lateral fissure were shown. Two-thirds of the cortex is contained within the sulci; hence, majority of the surface of the cortex is not visible. Tracts vs. Nerves Neuro fibers are bundles of axons. Tracts are bundles of axons in the Central Nervous System, while Nerves are bundles of axons in the Peripheral Nervous System. Gray matter vs. White matter Gray matters are densely packed of cell bodies and dendrites, while White matters are mostly of myelinated axons. Corpus Callosum connects the left and right hemispheres in very large bundles of axons. Generally we understand that it is the opposite hemisphere that controls the contralateral side of the body, so there must be some communication between the two hemispheres. It is in the corpus callosum where the crossover happens.

3 Different areas of the brain The brain stem is right after the spinal cord. It starts from the medulla all the way up to the thalamus. The structure below the cortex are the subcortical structure. The cortex is so overdeveloped in our species that it actually kind of flows over the other structures. The lower structure starts with the hindbrain. Major Division of the Brain : 1. Forebrain 2. Midbrain 3. Hindbrain HINDBRAIN has 3 major structures: 1. Medulla which is responsible for vital functions and vital reflexes including breathing, heart rate, vomiting, salivation, coughing and sneezing. Medulla is crucial to your survival. Damage to the medulla is mostly fatal and too much opiates slows down medulla activities and could lead to death. 2. Dorsal and superior to medulla are the Pons, which are involved in sleep and dreaming. This is another area like the corpus callosom where the sensory neurons and motor neurons cross over to the opposite side of the brain. Many axons from the pons cross from one side of the brain to the other. 3. Posterior to pons is the Cerebellum which is responsible for controlling movement (balance, coordination, timing and rhythm ) There is a nucleus that spans from the medulla up to the midbrain and a little bit of thalamus called the reticular formation also known as reticular activating system and is generally responsible for alertness, attention and arousal. MIDBRAIN which is superior to hindbrain has 2 major divisions: 1. Dorsal is the Tectum (latin for roof ). Tectum has 4 major bumps on it. The 2 on top are called superior colliculi, and the 2 below are called inferior colliculi. The superior colliculi receives visual information and helps you orient where things are in space. Inferior colliculi receives auditory information and helps to orient where that sound is coming from. 2. Under the tectum lies Tegmentum (latin for floor ). It has structure called substantia nigra (greek for black substance). It is important because it is a nucleus in the brain that creates dopamine and then gets projected to basal ganglia for movement pathway. There are different dopamine pathways and this is one. As in Parkinson s disease where there is difficulty initiating movement, speech impairment, and rigidity in muscles).

4 FOREBRAIN Limbic system is a collection of structures that are generally responsible for emotion, memory and smelling. 1. Amygdala the almond-shape structure involved on processing emotional information. 2. Hippocampos involved in storing and consolidating new and short term information. 3. Olfactory bulb 4. Hypothalamus Basal ganglia includes 3 major structures each linking the thalamus and all involved in movement, they are: 1. Caudate nucleus 2. Putamen 3. Globus palidus LOBES OF BRAIN 1. Occipital lobe which is located at the very back of the brain and processes visual information. 2. Frontal lobe which contains the primary motor cortex and the prefrontal cortex, extends from the central sulcus to the anterior limit of the brain. The posterior portion of the frontal lobe just anterior to the central sulcus is the precentral gyrus specialized for the control of fine movements, such as moving one finger at a time. 3. Temporal lobe is the lateral portion of each hemisphere which is responsible for auditory information and also some visual information. 4. Parietal lobe is between the occipital lobe and the central sulcus. It has very important strip of gyri, the somatosensory cortex. The parietal lobe biggest function is for somatosensory, meaning sensations from the body such as tactile, temperature, pressure, as oppose to sensation of hearing.

5 Motor cortex vs. Somatosensory cortex Motor cortex cellular representation means that the areas that have more muscles has greater representation in the motor cortex. For example, the face has more muscles, so it has greater representation in the motor cortex which make it possible to do a lot of facial expressions necessary for human interaction/relationships. Somatosensory cortex is located just posterior to central sulcus, and like the motor cortex, areas that are more sensitive has more representation in the somatosensory cortex. For example, fingertips are more sensitive as opposed to toes or back; hence, have more representation in the somatosensory cortex. Prefrontal cortex the most anterior portion of the frontal lobe, has executive functions or higher order functions: ability to plan ability to inhibit abstract thinking working memory sequencing set shifting