When Lara is walking toward the dorm after a long day of classes she begins to feel hungry. The subcortical structure in the brain that regulates hunger is the hypothalamus. The hypothalamus is located in the prosencephalon of the brain in the sub cortex referred to as the diencephalon (Rouse, 2015). Hypothalamus’ main job is to maintain homeostasis in the body (Rouse, 2015). Hormones from the hypothalamus aides to regulate functions in the body, some including: hunger, body temperature, thirst, metabolism, mood etc. (Rouse, 2015). Hormones in the body are chemical signals which allow different cells and structures of the body to communicate.
The hormone that communicates with hypothalamus to tell the brain we are hungry is ghrelin. Once ghreline communicate with the hypothalamus, the hypothalamus releases a hormone named neuropeptide to make Lara feel hungry (Cummings, 2006; Kokot & Ficek, 1999; Mader & Windelspecht, 2012). This is the hypothalmus’ attempt to maintain homeostasis in Lara’s body. The hypothalamus also play a role in the limbic system. The limbic system includes the hippocampus, hypothalamus, cingulate cortex, thalamus and sensory cortex (Rouse, 2015).
In the limbic system the hypothalamus is responsible for physiological responses to sensory experiences. When Lara smells pizza the hypothalamus will play role in her response the sensation of smell (Rouse, 2015). Not only are subcortical structures involved in Lara’s hunger and fatigue, cranial nerves also play a role. Cranial nerve X the Vagus nerve play a role in hunger as well. It is the only nerve that connects the brain and the stomach, as well as other visceral organs. Lara smells an odor which makes her believe her friends have ordered pizza.
The odor molecule attaches to a sensory cell in the nose called exteroreceptors. Exteroreceptors are sensory receptors that receive external stimuli. The molecules activate a nerve impulse that is sent to Cranial nerve I which is the olfactory nerve, and then sent to the olfactory bulb (Rouse, 2015). The olfactory bulb is part of the CNS which lies inferior in the frontal lobes. The impulse then reaches the olfactory cortex in the temporal lobe (Rouse, 2015). The impulse is then processed and interpreted, which made her guess that her friends ordered pizza.
Lara then sees her friends gathered around a big pizza pie. In order for Lara to physically her friends the information gets is received through the eyes. The eye is made of visual receptor cells, some of these include; the iris, pupil and the retina. The iris is located in the middle layer of the eye. The pupil is located in the iris, which allows light to pass through our eyes. The inner layer of the eye is called the retia, which has three cell layers. One of the cell layers is called photoreceptors which consists of rods and cones.
Rods process information that are blue and green, and cones process red, blue and green information. The photoreceptors convert light into neural impulses. The neural impulses have two pathways to travel psylateral pathways where information does not cross over into the opposite eye, and contralateral pathways where information received in one eye is set to the opposite eye (Rouse, 2015). Information is then sent to the optic chiasm, which is located between the optic tract and optic nerve. Information travels through the optic tract to the lateral geniculate nucleus where 90% of the axons are terminated.
The remaining 10 % of the information is processed in the superior colliculus which located in the midbrain (Rouse, 2015). Information then travels to the primary visual cortex and processed. In the primary visual cortex the information is processed using two pathways, the ventral pathways processes what is happening and the dorsal pathways processes where it is happening (Rouse, 2015). This is how Lara identifies that she sees her friends surrounding a pizza pie. Alison uses the visual and auditory pathway to understand Lara’s statement about the pizza.
Alison sees Lara and cannot fully understand what she was saying because of the competing noise. Alison uses the same visual pathway that Lara did that was previously explained. However, the primary visual cortex is not the only part of the brain that processes what Alison is seeing. There are surrounding areas that also process visual information once it reaches the primary visual cortex. Areas 1&2 process orientation, spatial frequency and color. Area three integrates information that you are receiving. Area four is vital for object recognition and color perception.
Area five is important for motion perception. To hear Lara, Alison receives acoustic information traveling into her ear. The information travels past the pinna (outer ear) and into the ear canal to vibrate the tympanic membrane. When acoustic signal vibrates the tympanic membrane, the acoustic energy becomes mechanical energy. The vibration of the tympanic membrane sets the ossicles( middle ear) into vibration, which sends information to the cochlea(inner ear) via the stapes. In the cochlea there are hair cells (that sit on the basilar membrane) that receives the mechanical energy tonotopically.
When information is received the basilar membrane raises which leads the hair cells to hit the tectorial membrane. The hair cells bend and calcium gates open ( mechanical energy becomes electrochemical energy). The calcium gates trigger neurotransmitters (glutamine) which synapses with the 8th nerve. Information travels to the dorsal and ventral cochlear nucleus, and then to the superior olivary complex. The superior olivary complex is where decisation( cross over) occurs and is also important for localization. The information then moves to the lateral leminiscus, followed by the inferior colliculus and then the medical geniculate body.
The information then get processes in the primary auditory cortex also known as Heschl’s Gyrus. The terms top-down and bottom-up processing are important for speech perception. Bottom up refers to receiving information in small units, and stringing the information together to understand what words or sentences you are receiving. An example of bottom up is sounding a word out. Top- down processing is looking at the big picture and using prior knowledge of language to fill in words or sound that you miss. An example of top-down is using context clues to answer a question.
Alison uses top- down process to comprehend what Lara was telling her. There was a degraded signal and competing noise, therefore Alison did not hear everything Lara was telling her, but was able to understand using top- down processing. For Lara to produce the statement “Hey, do you think I can join you guys, I am so hungry, and of course, I will pay my share” it requires her to plan on the linguistics and motor level. On the linguistic level she must conceptualize and idea and plan out what she is going to say, as well as, how she is going to say it (Rouse, 2015).
To produce the statement it requires the involvement of three different motor pathways including; the direct motor pathway, the indirect motor pathway, and the final common pathway (Rouse, 2015). The first part of the linguistic level is conceptualization. Conceptualization is a thought or idea of what you want to say. This is based on ones surroundings and thoughts (Rouse, 2015). Lara conceptualizes the idea of what she wants to say, when she sees her friends around a big pizza pie, and she is feeling hungry. The next part of the linguistic level is the planning level.
The planning level is divided into motor planning and linguistic planning. Linguistic planning is consolidating our thoughts and idea into language. This includes content, form and use and elicits activation of the hemisphere is the brain dominate for language (Rouse, 2015). This is when Lara chooses the words she wants to produce, and places them in a sentence based on semantics, phonology, syntax and pragmatics. Motor planning is the plan set in place for motor movement to be executed. This involves the coordination of speech movement and speech mechanism required to produce speech (Rouse, 2015).
This is when Lara plans out the speech movement and mechanisms to produce the statement. In order to articulate the statement, as well as making it targeted, coordinated, and balanced, this requires the involvement of three different motor pathways. The motor pathways are the direct motor pathway and the indirect motor pathway, as well as the final common pathway. The direct motor pathway is also referred to as the pyramidal system. The pyramidal tracts controls voluntary gross motor movement. The pyramidal tract is made up of two tracts, the corticospinal tract and the corticonuclear tract (Rouse, 2015).
The tracts are significant for motor movements, as well as, motor movements required for speech. The corticospinal tract originates in the cortex and travels past the pyramids located in the medulla to innervate spinal nerves through the spinal cord. The cotricospinal tract controls movement of the limbs (Rouse, 2015). The corticonuclear tract also originated in the cortex and travels past the pyramids located in the medulla to innervate the cranial nerves. The corticonuclear tract controls fine motor movements and controls the movement of the speech mechanisms.
The corticonuclear tract is the most important tract for speech and swallowing (Rouse, 2015). The indirect motor pathways are also referred to as the extrapyramidal pathways. The extrapyramidal pathways do not travel directly from the cortex to the brainstem. They loop around the pyramidal tracts and returns to the cortex to modulate and fine tune the functions of the pyramidal pathways. These tracts deliver feedback to the cortex to either increase or decrease the motor activity that has been activated by the pyramidal tracts (Rouse, 2015).
There are many tracts in the extrapyramidal system including: retoculospinal tract, vestibulospinal tract, tectospinal tract and rubrospinal tract, and basal ganglia- thamacortical tracts. The extrapyramidal tract most important for Lara to produce her statement is the corticopontine cerebellar tract. The corticopontine cerebellar tract travels from the cortex to the pons which innervates the cerebellum. This pathway is involved in motor planning, corarticulation, and coordination of motor acts together (Rouse, 2015).
The final common pathways is the last pathway involved for Lara to produce her statement. The Final common pathways innervates the cranial nerves some which are involved in speech production, phonation, and prosody. The final common pathway also innervates spinal nerves important for respiration (Rouse, 2015). The cranial nerves involved in speech include: Trigeminal nerve (V), Facial nerve(VII),Glassopharyngeal nerve (IX), Vagus nerve(X), Accessory nerve (XI) and Hypoglossal nerve (XII) (Rouse, 2015). All these nerves are involved in producing the statement that Lara shouts to Alison.