Question

What are the structure of nerve cell, synapse, neurotransmitter, axon, dendrite, receptor, gyri and Sulci?

Answer 1

The Nervous System Functions of the Nervous System 1. Gathers information from both inside and outside the body - Sensory Function 2. Transmits data to the processing areas of the brain and spine 3. Processes the information in the brain and spine – Integration Function 4. Sends data to the muscles, glands, and organs so they can respond appropriately – Motor Function It controls and coordinates all essential functions of the body including all other body systems allowing the body to maintain homeostasis or its delicate balance. The Nervous System is divided into Two Main Divisions: Central Nervous System (CNS) and the Peripheral Nervous System (PNS) Divisions of the Nervous System

Primary Cells of the Nervous System Neuron • Basic functional cell of nervous system • Transmits impulses (up to 250 mph) Parts of a Neuron • Dendrite – receive stimulus and carries it impulses toward the cell body • Cell Body with nucleus-nucleus & most of cytoplasm • Axon – fiber which carries impulses away from cell body • Schwann Cells- cells which produce myelin or fat layer in the Peripheral Nervous System • Myelin sheath – dense lipid layer which insulates the axon – makes the axon look gray • Node of Ranvier – gaps or nodes in the myelin sheath • Impulses travel from dendrite to cell body to axon Three types of Neurons o Sensory neurons – bring messages to CNS o Motor neurons - carry signals from CNS o Interneurons – between sensory & motor neurons in the CNS

Impulses • A stimulus is a change in the environment with sufficient strength to initiate a response. • Excitability is the ability of a neuron to respond to the stimulus and convert it into a nerve impulse • All or Nothing Rule – The incentive is either strong enough to start and impulse or nothing happens • Impulses are always the same strength along a given neuron and they are self-propagation – once it starts it continues to the end of the neuron in only one direction- from dendrite to cell body to axon • The nerve impulse causes a movement of ions across the cell membrane of the nerve cell. Synapse o Synapse - small gap or space between the axon of one neuron and the dendrite of another - the neurons do not severe at the synapse o It is junction between neurons which uses neurotransmitters to start the impulse in the second neuron or an effector (muscle or gland) o The synapse ensures one-way transmission of impulses Neurotransmitters Neurotransmitters – Chemicals in the junction which allow impulses to be started in the second neuron

Reflex Arc Components of a Reflex Arc A. Receptor - reacts to a stimulus B. Afferent pathway (sensory neuron) - conducts impulses to the CNS C. Interneuron - consists of one or more synapses in the CNS (most are in the spine) D. Efferent pathway (motor neuron) conducts impulses from CNS to the effector. E. Effector - muscle fibers (as in the Hamstring muscle) or glands respond by contracting or secreting a product. Spinal reflexes - initiated and completed at the spinal cord level. Occur without the involvement of higher brain centers.

Dendrites

The first two neuronal functions, receiving and processing incoming information, generally take place in the dendrites and cell body. Incoming signals can be either excitatory – which means they tend to make the neuron fire (generate an electrical impulse) – or inhibitory – which means that they tend to keep the neuron from firing.

Most neurons receive many input signals throughout their dendritic trees. A single neuron may have more than one set of dendrites and may receive many thousands of input signals. Whether or not a neuron is excited into firing an impulse depends on the sum of all of the excitatory and inhibitory signals it receives. If the neuron does end up firing, the nerve impulse, or action potential, is conducted down the axon.

Axons

Axons differ from dendrites in several ways.

• The dendrites tend to taper and are often covered with little bumps called spines. In contrast, the axon tends to stay the same diameter for most of its length and doesn't have needles.
• The axon arises from the cell body at a specialized area called the axon hillock.
• Finally, many axons are covered with a unique insulating substance called myelin, which helps them convey the nerve impulse rapidly. Myelin is never found on dendrites.

Towards its end, the axon splits up into many branches and develops bulbous swellings known as axon terminals (or nerve terminals). These axon terminals make connections on target cells.

Synapses

Neuron-to-neuron connections are made onto the dendrites and cell bodies of other neurons. These connections, known as synapses, are the sites at which information is carried from the first neuron, the presynaptic neuron, to the target neuron (the postsynaptic neuron). The synaptic connections between neurons and skeletal muscle cells are generally called neuromuscular junctions, and the relationships between neurons and smooth muscle cells or glands are known as neuroeffector junctions.

At most synapses and junctions, information is transmitted in the form of chemical messengers called neurotransmitters. When an action potential travels down an axon and reaches the axon terminal, it triggers the release of neurotransmitter from the presynaptic cell. Neurotransmitter molecules cross the synapse and bind to membrane receptors on the postsynaptic cell, conveying an excitatory or inhibitory signal.

Thus, the third essential neuronal function – communicating information to target cells – is carried out by the axon and the axon terminals. Just as a single neuron may receive inputs from many presynaptic neurons, it may also make synaptic connections on numerous postsynaptic neurons via different axon terminals.

Key Takeaways: Brain Gyri and Sulci

• Gyri and sulci are the folds and indentations in the brain that give it its wrinkled appearance.
• Gyri (singular: gyrus) are the folds or bumps in the brain, and sulci (singular: sulcus) are the indentations or grooves.
• Folding of the cerebral cortex creates gyri and sulci, which separate brain regions and increase the brain's surface area and cognitive ability.
• Gyri and sulci form boundaries within and between the lobes of the brain and divide it into two hemispheres.
• The medial longitudinal fissure is the sulcus that separates the left and right brain hemispheres. The corpus callosum is found within this fissure.
• An example of a gyrus is Broca's gyrus, an area of the brain that orchestrates speech production.

Gyri and Sulci Functions

Brain gyri and sulci serve two essential functions: They increase the surface area of the cerebral cortex and they form brain divisions. Increasing the surface area of the brain allows more neurons to be packed into the cortex so that it can process more information. Gyri and sulci form brain divisions by creating boundaries between the lobes of the brain and dividing the brain into two hemispheres.

Lobes of the Cerebral Cortex

The cerebral cortex is divided into the following four portions that each serve several essential functions.

• Frontal lobes: The frontal lobes are located in the front-most region of the cerebral cortex. They are vital for motor control, thinking, and reasoning.
• Parietal lobes: The parietal lobes are positioned above the temporal lobes near the brain's center, and they process sensory information.
• Temporal lobes: The temporal lobes are positioned behind the frontal lobes. They are essential for language and speech production, as well as memory and emotion processing.
• Occipital lobes: The occipital lobes sit at the posterior region of the cerebral cortex and are the leading centers for visual processing.

Gyri and sulci are essential features of the central nervous system. Folding of the cerebral cortex creates these ridges and grooves which serve to separate brain regions and increase cognitive ability.

Brain Sulci or Fissures

Below is a listing of several principal sulci/fissures in the brain and the divisions they create.

• Interhemispheric (Medial Longitudinal Fissure): This is a deep furrow located down the center of the brain that separates the left and right brain hemispheres. The corpus callosum, a wide ribbon of nerves, is situated in this fissure.
• Fissure of Sylvius (Lateral Sulcus): This deep grove separates the parietal and temporal lobes.
• Central Sulcus (Fissure of Rolando): This sulcus separates the parietal and frontal lobes.
• Collateral Sulcus: This furrow separates the fusiform gyrus and the hippocampal gyrus on the lower surface of the temporal lobes.
• Parieto-occipital Sulcus: This deep crevice separates the parietal and occipital lobes.
• Calcarine Sulcus: This groove is located in the occipital lobes and divides the visual cortex.

Brain Gyri

Listed below are several essential gyri of the cerebrum.

• Angular Gyrus: This fold in the parietal lobe is the area of the brain that assists in processing auditory and visual stimuli. It is also involved in language comprehension.
• Broca's Gyrus (Broca's Area): This area of the brain, located in the left frontal lobe in most individuals, controls motor functions involved with speech production.
• Cingulate Gyrus: This arch-shaped fold in the brain is located above the corpus callosum. It is a component of the limbic system that processes sensory input concerning emotions and regulates aggressive behavior.
• Fusiform Gyrus: This bulge, located in the temporal and occipital lobes, consists of lateral and medial parts. It is thought to play a role in facial and word recognition.
• Hippocampal Gyrus (Parahippocampal Gyrus): This fold on the inner surface of the temporal lobe borders the hippocampus. The hippocampal gyrus surrounds the hippocampus and plays an essential role in memory.
• Lingual Gyrus: This coil of the occipital lobe is involved in visual processing. The calcarine sulcus and collateral sulcus border the lingual gyrus. Anteriorly, the lingual gyrus is continuous with the parahippocampal gyrus and together they form the medial portion of the fusiform gyrus.