Human Nervous System Overview Quiz

Nervous System

The human body's communication and control network is known as the nervous system. It enables our bodies to respond to internal and external stimuli by transmitting information between different parts of the body. The main components of the nervous system consist of the brain, spinal cord, nerves, and ganglia. In this article, we will discuss the nervous system, its major divisions, and the types of neurons.

Central Nervous System

The central nervous system is responsible for processing sensory information from the environment and coordinating responses to maintain homeostasis. It includes the brain and the spinal cord. The brain is divided into three sections: the hindbrain, midbrain, and forebrain.

Hindbrain

The hindbrain consists of the medulla oblongata, pons, and cerebellum. The medulla oblongata controls vital functions like breathing and heart rate, while the pons is involved in various functions such as facial expressions, speech, and sleep. The cerebellum coordinates voluntary muscle movements and helps maintain posture and balance.

Midbrain

The midbrain receives sensory input from the eyes, ears, and skin, allowing us to perceive changes in light intensity, sound frequency, and temperature. It also plays a crucial role in controlling reflexes and regulating eye movement through muscles connected to the cranial nerves.

Forebrain

The forebrain is further divided into two regions: the diencephalon and telencephalon. The diencephalon contains structures like the thalamus, which processes incoming sensory information, and the hypothalamus, which regulates basic drives such as hunger, thirst, sleep, and emotional response. The telencephalon consists of the cerebrum and limbic system. The cerebrum is responsible for higher cognitive functions such as learning, memory, and reasoning, while the limbic system deals with emotions, motivation, and instinctive behavior.

Spinal Cord

The spinal cord extends from the base of the skull down to the first lumbar vertebra, acting as a key link between the brain and the rest of the nervous system. It serves several purposes including:

1. Transmitting signals between the brain and other parts of the body.
2. Controlling reflex actions without requiring conscious thought.
3. Providing a protective covering called meninges around the spinal cord.

Peripheral Nervous System

The peripheral nervous system (PNS) includes all the nerves outside the brain and spinal cord. These nerves are further classified into cranial nerves (found in the head region) and spinal nerves (located along the spine).

Cranial Nerves

There are twelve pairs of cranial nerves, each serving specific functions:

1. Olfactory nerve (olfaction - smell)
2. Optic nerve (vision)
3. Oculomotor nerve (eye movement)
4. Trochlear nerve (also for eye movement)
5. Trigeminal nerve (pain, touch, temperature sensation in face; facial muscles control)
6. Abducens nerve (eye movement)
7. Facial nerve (taste from anterior two-thirds of tongue; facial expression)
8. Vestibulocochlear nerve (balance and hearing)
9. Glossopharyngeal nerve (tasting back one-third of tongue and swallowing)
10. Vagus nerve (parasympathetic nervous system)
11. Accessory nerve (facial muscles control and neck muscles)
12. Hypoglossal nerve (tongue movement)

Spinal Nerves

Spinal nerves exit the vertebral column primarily at segmental levels along the length of the spinal cord. They can be categorized into dorsal rami (those inside vertebral columns), ventral rami (those outside vertebral columns), and mixed rami (those that have both dorsal and ventral branches). Each type has unique roles within the PNS, helping transmit messages throughout the body.

Autonomic Nervous System

The autonomic nervous system (ANS) controls involuntary physiological processes such as digestion, respiration, urination, and sexual function. It has two major components: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSN).

Sympathetic Nervous System

The SNS prepares the body for action during stressful situations, commonly referred to as "fight or flight." It does so by increasing heart rate, dilating bronchioles, constricting blood vessels, slowing down glandular activity, and releasing glucose into the bloodstream, among other effects. This occurs due to activation of the adrenergic receptors present in target tissues when SNS hormones are released.

Parasympathetic Nervous System

The PSN acts oppositely to the SNS, promoting rest and conservation of energy after a stressful event. It slows heart rate, constricts pupils, increases glandular secretions, relaxes smooth muscles, and improves intestinal motility. Like the SNS, it also involves interactions with receptor sites on target cells.

Neurons

Neurons are specialized cells that transmit electrical and chemical signals within the nervous system. Their structure comprises three main parts: cell body, axon, and dendrites.

1. Cell Body: Also known as soma, it contains genetic material and cytoplasm necessary for cell survival.
2. Axon: A single elongated projection that carries impulses away from the cell body towards other neurons or muscle cells.
3. Dendrites: Short branching extensions that receive signals from other neurons, synapses, or sensory receptors.

Neurotransmitters

Neurotransmitters are signaling molecules responsible for transmitting electrical signals across gaps called synapses between neurons. Some common neurotransmitters include dopamine, serotonin, GABA (gamma-aminobutyric acid), glutamate, acetylcholine, norepinephrine, and epinephrine.

Dopamine

Dopamine is important for reward, motivation, and motor control. Low levels have been linked with Parkinson's disease, ADHD, and depression.