Lesson 2.3 The Nervous System PDF

Lesson 2.3 THE NERVOUS SYSTEM Intended Learning Outcomes: At the end of the session, students should have: 1. differentiated the parts of the nervous system; 2. evaluated the different functions of the brain and spinal cord, an...

Lesson 2.3 THE NERVOUS SYSTEM Intended Learning Outcomes: At the end of the session, students should have: 1. differentiated the parts of the nervous system; 2. evaluated the different functions of the brain and spinal cord, and 3. illustrated the brain-behavior connection and relationship ABSTRACTION The Nervous System The nervous system is the body's primary communication and control network in the form of electrical signals, which are relayed constantly from the sense organs to and from the brain through complex networks of neurons on a timescale measured in milliseconds (Carter, Aldridge, Page & Parker, 2019). Divisions of the Nervous System. The nervous system has two primary divisions: the central nervous system and the peripheral nervous system. Central Nervous System (CNS). THe CNS comprises the brain and spinal cord. It works as the coordinating system for the body. The brain and the spinal cord together make up the CNS. These are encased and protected by the skull and vertebral column, respectively. They are the central organs of the CNS. Brain. The brain has three major divisions: hindbrain, midbrain, and forebrain. Hindbrain. It consists of the medulla, the pons, and the cerebellum. Medulla, or medulla oblongata. It controls vital functions such as the heartbeat, circulation, and respiration and acts as a relay station for afferent and efferent impulses. Its destruction results in immediate death Pons. It controls the muscles on the right side of the body, while the right hemisphere manages the left side. It acts as a relay station and is involved in reflexes controlling breathing. Damage to pons will lead to sleep disturbances, sensory problems, arousal dysfunction, and coma. Cerebellum. It is a large hindbrain structure known for controlling movement, balance and coordination, and complex information processing, such as executive functions and emotional processing. Abnormal development of the cerebellum leads to autism spectrum disorder, in which language, cognition, and social awareness are severely afflicted. Midbrain. It consists of tectum and tegmentum. Tectum. The swellings on each side of the tectum, the superior colliculus and the inferior colliculus, are essential for sensory  processing like hearing (inferior colliculus) and vision (superior colliculus). Tegmentum. The tegmentum covers the substantia nigra, a dopamine-producer that facilitates readiness for movement and is involved with reward-seeking behaviors. Degeneration of the substantia nigra occurs in Parkinson's disease, which is characterized by difficulties in initiating movement. On the other hand, the ventral tegmental area (VTA) is important in incentive motivation (i.e., motivation to an appetitive stimulus, e.g., food, sex). Forebrain. It comprises two cerebral hemispheres: the thalamus, hypothalamus, pituitary gland, limbic system, and basal ganglia. ○ Thalamus. It processes most sensory input and sends output to the cerebral cortex. Damage to the thalamus typically results in coma, and disturbances in circuits linking the thalamus and cerebral cortex are involved in some seizures. ○ Hypothalamus. It conveys messages to the pituitary gland, altering its release of hormones. The PNS directs the autonomic nervous system and controls our glands and organs. Damage to any nucleus of the hypothalamus results in disruptions to motivated behaviors, including feeding, drinking, temperature regulation, sexual behavior, fighting, or activity levels. ○ Pituitary gland. The pituitary gland is a hormone-producing gland attached to the base of the hypothalamus that produces hormones that the blood transports to organs throughout the body in response to signals from the hypothalamus. ○ Basal Ganglia. It covers the caudate nucleus, the putamen, and the globus pallidus. Damage to the basal ganglia impairs movement, such as in Parkinson's disease and Huntington's disease, which also affect learned skills and habits. ○ Limbic system. It includes the hippocampus and amygdala, which are involved in emotional and motivational processes, learning, and memory. ○ Cerebrum: The two cerebral hemispheres (also called lobes) are divided into four major divisions: (a) frontal, (b) parietal, (c) occipital, and (d) temporal. Spinal Cord. The spinal cord is a long nerve tissue cylinder extending like a tail from the medulla. It performs important functions: It is the information pathway and protects us from injury through spinal reflexes. Communicates with all the sense organs and muscles through its segmented structure. Damage to each segment: the brain loses sensation and motor control from that segment and below. It contains gray matter (shaped like an H) in the center of the cord, densely packed with cell bodies and dendrites. The white matter, which surrounds it, consists of myelinated axons that carry signals to the brain or other parts of the spinal cord. Peripheral Nervous System (PNS). It consists of peripheral nerves and ganglia (spinal, cranial, and visceral nerves), the relaying system between the brain and body. Functionally, the PNS is further subdivided into two subdivisions: Somatic Nervous System (SNS). The SNS controls voluntary movement.  It is a complex network of nerves extending across the body, extending from 12 pairs of cranial nerves originating in the brain and 31 pairs of spinal nerves that arise from the spinal cord. Autonomic Nervous System (ANS). It controls involuntary movement. The autonomic division can be split into: ▪ Sympathetic Nervous System (SANS): that controls for ‘fight or flight’ responses ▪ Parasympathetic Nervous System (PANS): that controls for ‘rest and digest’ responses. The Cerebral Cortex The cortex can be "mapped" in gross anatomy, microscopic anatomy, and neurological function. Let us look at the brain at the external level, then move down to the internal details. The cerebrum is organized into: Sulci (singular: sulcus;) They are the hill/clefts. Gyri (singular: gyrus). They are the ridges/valleys formed along the sulci Fissure. The large sulcus Cortical Layers. The outer surface of the cerebral cortex is organized into six distinct layers with distinct patterns of neuron types and shapes that communicate with other brain areas. The layers' number, organization, and size vary throughout the cortex. Layer I (molecular) consists of small neurons with no cell bodies. Instead, it comprises the nerve fibers of cells forming connections with other layers. Layers II and IV (external & internal granular) contain large numbers of small cells known as granule cells. Layers III and V (external & internal pyramidal) are characterized by large triangular-shaped pyramidal cells. Layer VI (multiform layer) has many types of neurons, merging into the white matter below the cortical layers. Cortical Lobes. The cerebral cortex is divided into four lobes, distinguished based on the structure and function of cells namely: occipital, parietal, temporal, and frontal lobes. Occipital lobe. Its main target is for visual information. Damage to any part of the primary visual cortex (posterior part) causes cortical blindness in the related part of the visual field. And a tumor in the occipital lobe ordinarily evokes only simple sensations, such as flashes of light. Parietal lobe. It tracks information about eye, head, and body positions and transmits it to brain regions responsible for movement, spatial awareness, and numerical information. The temporal lobe is the primary cortical target for auditory information. A tumor in the temporal lobe can result in complex auditory or visual hallucinations. The frontal lobe. It acts as the "control panel" for our personality and communication abilities. Functional Areas. There are different functions located in each lobe divided based on functional areas namely: sensory cortex, motor cortex, and association cortex. Sensory cortex. It is found in the occipital, temporal, and parietal lobes. It processes incoming information from the sensory systems. The occipital lobe contains the primary visual cortex. The primary auditory cortex is found within the temporal lobe. The postcentral gyrus of the parietal lobe contains the primary somatosensory cortex, which is the highest level of processing for information about touch, pain, position, and skin temperature. The precentral gyrus is the motor area of the cortex that provides the highest  level of command for voluntary movements. The primary motor cortex is located in the precentral gyrus of the frontal lobe. Association Cortex. The association cortex is primarily in the frontal, temporal, and inferior parietal lobes. Association is the area for connecting and integrating sensory and motor functions. For example, combining visual and auditory information allows us to see the world as an integrated whole rather than discrete bits.