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NERVOUS SYSTEM

The nervous system includes the brain, spinal cord, and a complex network of nerves. This system sends messages back and forth between the brain and the body. The brain is what controls all the body's functions. The spinal cord runs from the brain down through the back.

NERVOUS SYSTEM

• The nervous system is the major controlling, regulatory, and communicating system in the body. It is the center of all mental activity including thought, learning, and memory. Together with the endocrine system, the nervous system is responsible for regulating and maintaining homeostasis. Through its receptors, the nervous system keeps us in touch with our environment, both external and internal. Like other systems in the body, the nervous system is composed of organs, principally the brain, spinal cord, nerves, and ganglia. These, in turn, consist of various tissues, including nerve, blood, and connective tissue . Together these carry out the complex activities of the nervous system.

FACTS ABOUT THE NERVOUS SYSTEM

The nervous system derives its name from nerves, which are cylindrical bundles of fibers (the axons of neurons) that emanate from the brain and spinal cord and branch repeatedly to innervate every part of the body.

The basic unit of the nervous system is a nerve cell, or neuron. The human brain contains about 100 billion neurons. A neuron has a cell body, which includes the cell nucleus, and special extensions called axons (pronounced AK-sonz) and dendrites (pronounced DEN-drahytz). Bundles of axons, called nerves, are found throughout the body. Axons and dendrites allow neurons to communicate, even across long distances

CENTRAL NERVOUS SYSTEM

• is the body's processing centre which is made up of 2 parts or components namely the Brain and the Spinal Cord. Each part of the CNS plays an important role in how the body functions, and the two components of the CNS work together to take in information and control how the body responds.

• Brain   - controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. 

• Spinal Cord  - that lies within the spinal column is a vital aspect of the central nervous system (CNS).

​PERIPHERAL NERVOUS SYSTEM

PERIPHERAL NERVOUS SYSTEM

• is one of the two components of the nervous system of bilateral animals, the other being the central nervous system (CNS). It consists of nerves and ganglia that connect the CNS to the limbs and organs, serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the PNS is not protected by the vertebral column and skull, leaving it exposed to toxins. The peripheral nervous system is divided into the Somatic and Autonomic Nervous Systems.

SOMATIC NERVOUS SYSTEM

SOMATIC NERVOUS SYSTEM

• Is part of the peripheral nervous system associated with voluntary control of body movements via skeletal muscles. It consists of sensory nerves carrying afferent nerve fibers and motor nerves carrying afferent nerve fibers, which relay motor commands from the CNS to stimulate muscle contraction.

Multiple Choice

nerves that are used in the Somatic Nervous System

• Spinal nerve 

  A spinal nerve is a mixed nerve that carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body, there are 31 pairs of spinal nerves, grouped into eight cervical, twelve thoracic, lumbar, sacral and coccygeal regions. 

• parasympathetic Nervous System

  - The sympathetic system is activated during a "fight or flight" situation, releasing neurotransmitters such as norepinephrine and epinephrine to increase heart rate and blood flow in certain areas while decreasing activities of non-critical functions for survival.

• Parasympathetic Nervous System

  - The parasympathetic system is a mediator that allows the body to function in a "rest and digest" state. When it dominates the body, there are increases in salivation and activities in digestion, while heart rate and other sympathetic response decrease. Unlike the sympathetic system, humans have some voluntary controls, such as urination and defecation.

• NERVE CELL

Multiple Choice

nerves that are used in the Somatic Nervous System

• Cranial nerves

  Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck, including the special senses of vision, taste, smell, and hearing.

• Sympathetic Nervous System

  - The sympathetic system is activated during a "fight or flight" situation, releasing neurotransmitters such as norepinephrine and epinephrine to increase heart rate and blood flow in certain areas while decreasing activities of non-critical functions for survival. The systems are independent to each other, allowing activation of certain parts of the body while others remain rested.

AUTONOMIC NERVOUS SYSTEM

• The autonomic nervous system (ANS) controls involuntary responses to regulate physiological functions. It is connected to organs that have smooth muscle, such as the heart, bladder, and other cardiac, exocrine, and endocrine related organs, by ganglionic neurons. The most notable physiological effects from autonomic activity are pupil constriction and dilation, and salivation of saliva. It is always activated, but is either in the sympathetic or parasympathetic state depending on the situation.

The following are the nerves that are used in the Autonomic Nervous System;

• Sympathetic Nervous System

- The sympathetic system is activated during a "fight or flight" situation, releasing neurotransmitters such as norepinephrine and epinephrine to increase heart rate and blood flow in certain areas while decreasing activities of non-critical functions for survival. The systems are independent to each other, allowing activation of certain parts of the body while others remain rested.

• Parasympathetic Nervous System

- The parasympathetic system is a mediator that allows the body to function in a "rest and digest" state. When it dominates the body, there are increases in salivation and activities in digestion, while heart rate and other sympathetic response decrease. Unlike the sympathetic system, humans have some voluntary controls, such as urination and defecation.

NERVE CELL

• The basic unit of the nervous system is the nerve cell. The nerve cells are called neurons. There are twelve to fourteen billions of neurons in one part of the brain alone. A neuron has a cell body containing the nucleus. Projecting out from the cell body are root-like structures. These are the dendrites and axons. Dendrites carry impulses towards the cell body.

• A cell may have as many as 200 dendrites carrying impulses toward the cell body. A single dendrite can be over one meter long. Axons pass impulses to the dendrites of other neurons or cell body of muscle cells. Axons can be grouped together into cable-like bundles called nerves.

CONTROL OF BODY PROCESSES THROUGH THE NERVOUS SYSTEM

• Neurons are cells with the special ability to carry signals or impulses. Thoughts, emotions, learning, and many body functions are carried by nerve impulses in the neurons. A nerve impulse is a combination of an electrical charge and a chemical reaction. A nerve impulse is not a flow of electricity, but an electrochemical signal moving along a neuron.

Imagine that you have a board with a row of switches. Quickly click each switch in the row on and off. This will give you an idea of how a nerve impulse travels along a neuron.

• The nervous system is assisted by five sense organs - the eyes, ears, nose, tongue, and skin. These sense organs are constantly receiving information from the environment and sending messages to the brain. These senses aid in the survival of human beings.

PARTS OF THE NERVOUS SYSTEM

• Brain & Cerebrum Location 

• - Cerebrum, large, upper part of the brain that controls activity and thoughts. Cerebellum, the part under the cerebrum that controls posture, balance and coordination. 

• Brain Stem, the part that connects the brain to the spinal cord and controls automatic functions such as breathing, digestion, heart rate and blood pressure   

• Frontal lobes are located in the front of the brain and are responsible for voluntary movement and, via their connections with other lobes, participate in the execution of sequential tasks; speech output; organizational skills; and certain aspects of behavior, mood, and memory. 

•  Parietal lobes are located behind the frontal lobes and in front of the occipital lobes. They process sensory information such as temperature, pain, taste, and touch. In addition, the processing includes information about numbers, attentiveness to the position of one's body parts, the space around one's body, and one's relationship to this space. 

• Temporal lobes are located on each side of the brain. They process memory and auditory (hearing) information and speech and language functions. occipital lobes are located at the back of the brain. They receive and process visual information.

• Central Structures of the Brain

-Thalamus integrates and relays sensory information to the cortex of the parietal, temporal, and occipital lobes. The thalamus is located in the lower central part of the brain (that is, upper part of the brainstem) and is located medially to the basal ganglia. The brain hemispheres lie on the thalamus. Other roles of the thalamus include motor and memory control. 

- Hypothalamus, located below the thalamus, regulates automatic functions such as appetite, thirst, and body temperature. It also secretes hormones that stimulate or suppress the release of hormones (for example, growth hormones) in the pituitary gland.