Overview
The Nervous System is one of the most important systems in the body. It consists of two parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Its organs are the brain, spinal cord, sensory organs and all of the nerves that connect them.
Functions
- Sensory: gathers info
- Integrative: information is brought together and interpreted
- Motor: respond to signals
Neurons are masses of nerve cells that transmit information.They are made up of three main important parts.
1. Cell body: contains the nucleus and two extensions
2. Dendrites: short, numerous; receive information
3. Axons: single long "fiber" which conducts impulses away from the cell body; sends information
Neurons live and function for a lifetime. They do not divide like other cells in the body and require abundant amounts of oxygen and glucose. They are also classified into four basic types.
Neurons send messages to the brain and other body parts using neurotransmitters.
Neurotransmitters
Neurotransmitters are chemicals which allow the transmission of signals from one neuron to the next across synapses (junctions between two communicating neurons). A neurotransmitter is either excitatory or inhibitory.
- Excitatory: increases membrane permeability, increases chance for threshold to be achieved
- Inhibitory: decrease membrane permeability, decrease chance for threshold to be achieved
Common Neurotransmitters
1. Acetylcholine: stimulates muscle contraction
2. Monoamines: (Norepinephrine & Dopamine) sense of feeling good, low levels = depression
3. Serotonin: sleepiness
4. Endorphins: reduces pain, inhibit receptors
The Central Nervous System
The CNS is covered in three layers of very thin membranes.
1. Dura Mater: outermost layer
2. Arachnoid Mater: no blood vessels, in between layer
3. Pia Mater: inner membrane, contains nerves and blood vessels to nourish cells
The Brain
The brain operates using impulses. An impulse is an electrical signal that travels along an axon. An impulse can be ascending or descending.
1. Ascending: travels to the brain (sensory)
2. Descending: travels to the muscles
Cerebrum
The cerebrum is the largest part of the brain. It deals with higher mental functions. The convolutions (wrinkles and grooves of the brain) are present on the cerebrum.
*Fissures: deep grooves
*Sulcus: shallow grooves
*Gyrus: bumps
There are three types of fissures.
1. Longitudinal: separates left and right sides
2. Transverse: separates cerebrum from cerebellum
3. Lateral: separates temporal lobe from the frontal and parietal lobe
As you can see from the above photo, the cerebrum is also divided into lobes. Each of these lobes has its own function.
- Frontal: reasoning, thinking, language
- Parietal: touch, pain, relation of body parts
- Temporal: hearing
- Occipital: vision
The cerebrum is further classified into specific sections of the brain that are responsible for certain actions and responses.
1. Motor Areas: control voluntary movements
2.Sensory Areas: involved in feelings and sensations
3. Association Areas: higher levels of thinking, interpreting, and analyzing info
Cerebellum
The function of the cerebellum is balance and coordination.
Brain Stem
The brain stem regulates visceral function. It consists of three parts.
1. Midbrain: controls visual reflexes, eye movements
2. Pons: relays sensory info
3. Medulla: controls heart, respiration, blood pressure
Corpus Callosum
The corpus callosum connects the two hemispheres.
Pituitary Gland
The pituitary gland is the main gland of the endocrine system. It controls hormones.
The Limbic System
The limbic system is the area of the brain that regulates emotion and memory. It directly connects the the lower and higher brain functions.
Hippocampus
The hippocampus is part of the limbic system. It is shaped like a seahorse. It is involved in memory forming, organizing, and storing. There are 4 different types of memories.
1. Episodic: personal experiences; flashbacks
2. Semantic: storage and general retrieval of general info
3. Procedural: allows us to learn activities and skills performed with little thought
4. Working: concentration and short-term retention
The Peripheral Nervous System
consists of the nerves that branch out from the CNS and connect to other body parts
The PNS is divided into two parts: the somatic nervous system and the autonomic nervous system.
Somatic: controls conscious activities
Autonomic: controls unconscious activities
Of the nerves, there are spinal and cranial. Spinal nerves come from the spine and Cranial nerves come from the brain. There are 12 Cranial nerves.
II. Optic Nerve: transmits info for the eyes
III. Occulomotor Nerves: controls most of the extrinsic muscles of the eye (move the eyelids)
IV. Trochlear Nerve: innerates an extrinsic eye muscles (move eyeballs)
V. Trigeminal Nerve: main sensory nerve of the face
VI. Abducens: controls 1 of the eye muscles (lateral rectus)
VII. Facial Nerve: innervates the muscles of facial expression
VIII. Vestibulocochlear: transmits hearing and balance (auditory nerve)
IX. Glossopharyngeal: carries info from the head and neck to the brainstem
X. Vagus Nerve: the only cranial nerve that travels into the abdomen
XI. Accessory Nerve: supplies the shoulder muscles
XII. Hypoglossal Nerve: supplies the tongue
Fun Facts
- A newborn baby's brain grows almost 3 times larger in the course of its first year.
- About 80% of brain tissue is water.
- The brain is more active at night.
- Electrical signals in the nerve fibers can travel at least 280 kilometers per hour.
- The average weight of a male's brain is heavier than the average weight of a female's brain.
- 5,000 years ago, human brains were 10% bigger than they are today.
- The average man's spinal cord is about 17.7 inches long, while the average woman's is about 16.9 inches long.
- In humans, the left side of the brain controls the right side of the body and the right side of the brain controls the left side of the body.
- Neurons are the biggest cells in the human body.
- The brain is floating in Cerebrospinal Fluid.
Recent Medical Breakthroughs
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