GenEd: Lesson 12 Nervous System | Free LET Reviewer and Drill

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General Education

 Lesson 12: Nervous System

(Human Systems)  

What is the Nervous System?

The nervous system is a complex network of organs and cells that transmits signals between different parts of your body. It is the control and communication system of your body, gathering information from your environment, processing that information, and sending commands to your muscles and glands. The nervous system controls everything from voluntary movements like walking to involuntary functions like breathing and heartbeat. It also stores memories and processes emotions.

• The nervous system is your body's communication network that controls how your body works and helps you think, feel, and move.

Main Functions of the Nervous System

1. Controls sensory and motor functions
2. Processes memory and emotions
3. Maintains involuntary functions
4. Coordinates all body activities

Two Major Divisions of the Nervous System

Image from Simply Psychology

The nervous system is divided into two main parts that work together:

1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)

Division 1: Central Nervous System (CNS)

The Central Nervous System (CNS) includes the brain and spinal cord. These are the command centers of your nervous system.

The Brain - is the largest and most important organ of the nervous system. It is the control center that processes information and makes decisions. Located inside the skull, protected by bone and about 3 pounds (1.4 kilograms) in weight.

Image from Shutterstock

Main Functions:

• Processes sensory information
• Controls voluntary activities
• Stores memories
• Processes emotions
• Controls involuntary functions like breathing
• Makes decisions and controls behavior

The brain is the command center of your body that thinks, remembers, feels, and controls everything your body does.

The Spinal Cord - is a long, cylindrical bundle of neurons that connects the brain to the rest of the body. Located inside the vertebral column (backbone), running from the brain down to the lower back and about 18 inches (45 centimeters) in size.

Image from BYJU'S

Main Functions:

• Transmits signals between the brain and body
• Controls reflex actions (automatic responses)
• Carries sensory information to the brain
• Carries motor commands from the brain to muscles

Reflex Actions - a reflex action is an automatic, involuntary response to a stimulus that does not require brain involvement. For example, when you touch something hot, your hand pulls away automatically before you even feel the pain. This is a reflex action controlled by the spinal cord.

• The spinal cord is like a highway carrying messages between your brain and the rest of your body.

Image from Ask A Biologist

Brain Parts

(Structure and Function)

The brain has three main regions, each with specific functions:

1. Cerebrum - is the largest part of the brain, making up about 80% of the brain's mass. Located at the top and front of the brain

Image from visiblebody

Functions:

• Controls voluntary activities (activities you choose to do, like walking, writing, talking)
• Processes sensory information (sight, sound, touch, taste, smell)
• Controls movement
• Stores memories
• Processes emotions
• Controls thinking, learning, and judgment
• Controls speech and language
• Controls personality

Structure:

• Divided into two hemispheres (left and right)
• Each hemisphere controls the opposite side of the body

Divided into four lobes:

• Frontal lobe: Controls voluntary movement and thinking
• Parietal lobe: Processes sensory information like touch and temperature
• Temporal lobe: Processes hearing and memory
• Occipital lobe: Processes vision

The cerebrum is the thinking part of your brain. It controls your movements, thoughts, memories, and emotions.

2. Cerebellum - is the second-largest part of the brain, located at the back, below the cerebrum. Located at the back bottom of the brain, below the cerebrum. Its size much smaller than the cerebrum but very densely packed with neurons.

Image from brainfacts

Functions:

• Controls involuntary activities related to movement
• Maintains balance and coordination
• Refines and smooths movements
• Adjusts posture
• Helps with fine motor skills (like playing an instrument)
• Helps with gross motor skills (like walking and running)

The cerebellum does not initiate movement but fine-tunes it. Your cerebrum decides to kick a soccer ball, but your cerebellum makes sure your leg moves smoothly with the right force and angle.

• The cerebellum is the part of your brain that helps you maintain balance, coordination, and smooth movements.
• Example: When you ride a bicycle, the cerebrum decides to pedal forward, but the cerebellum maintains your balance so you do not fall over and coordinates your leg movements with the pedals.

3. Brain Stem - is the structure that connects the brain to the spinal cord. It controls all the involuntary functions needed to survive. Located at the bottom of the brain, connecting to the spinal cord

Image from MedlinePlus

Characteristics:

• Contains many vital control centers
• Controls involuntary functions
• Life-sustaining activities happen here
• Small but critically important

Main Functions:

• Controls breathing
• Controls heart rate
• Controls blood pressure
• Controls swallowing
• Controls digestion
• Controls sleep-wake cycles
• Controls reflexes like coughing and sneezing

The brain stem is the part of your brain that keeps you alive by controlling breathing, heartbeat, and other automatic functions.

Three Parts of the Brain Stem: Midbrain, Pons, and  Medulla Oblongata.

Image from Physiopedia

1. Midbrain - the upper part of the brain stem.

Functions:

• Relays information between the cerebrum and cerebellum
• Controls eye movements
• Processes auditory and visual information
• Manages reflex responses to visual and auditory stimuli

The midbrain is the relay center that passes information between different brain parts.

2. Pons - the middle part of the brain stem (pons means "bridge").

Functions:

• Acts as a bridge between the midbrain and medulla oblongata
• Relays information between cerebrum and cerebellum
• Controls facial expressions
• Controls chewing and swallowing
• Helps regulate breathing

The pons is a bridge that connects different parts of the brain and helps control chewing and swallowing.

3. Medulla Oblongata - the lowest part of the brain stem, connecting directly to the spinal cord.

Functions:

• Controls vital involuntary functions
• Controls breathing rate
• Controls heart rate
• Controls blood pressure
• Controls swallowing and vomiting reflexes
• Controls cough and gag reflexes
• Regulates body temperature

The medulla oblongata is the part of the brain that controls your heartbeat, breathing, and blood pressure to keep you alive.

Why it is important: Damage to the medulla oblongata can be fatal because it controls functions essential for survival.

The Basic Unit of the Nervous System

Neurons - are individual nerve cells that are the basic functional units of the nervous system. Neurons transmit electrical and chemical signals throughout your body. Your brain contains about 86 billion neurons, and your body has about 100 billion neurons total.

Image from Simply Psychology

Structure of a Neuron:

A typical neuron has three main parts: Cell Body, Dendrites, and Axon.

1. Cell Body (Soma) - where most of the cell's metabolic activities occur

• Contains the nucleus
• Contains the cytoplasm

2. Dendrites - increase surface area to receive many signals

• Branching structures that receive signals from other neurons
• Multiple dendrites on each neuron

3. Axon - long projection that sends signals to other neurons or muscles

• Transmits signals away from the cell body
• Can be very long (up to 3 feet in some cases)
• Ends in branches called axon terminals

Neurons are nerve cells with branches (dendrites) that receive signals and a long tail (axon) that sends signals.

How Neurons Communicate

(Synaptic Transmission)

Neurons communicate with each other through connections called synapses.

Image from Queensland Brain Institute

Synapse: The connection between two neurons or between a neuron and a muscle cell.

How synaptic transmission works:

Step 1: Signal travels down the axon - an electrical signal travels down the axon of the transmitting neuron.

Step 2: Neurotransmitters are released - when the signal reaches the axon terminal, chemical messengers called neurotransmitters are released into the synaptic cleft (the tiny gap between neurons).

Step 3: Signal crosses the synapse - neurotransmitters cross the synapse and bind to receptors on the receiving neuron.

Step 4: Signal is received - the receiving neuron generates a new electrical signal if the neurotransmitter is stimulating.

Step 5: Cycle repeats - the signal travels down the receiving neuron, and the process continues.

Neurons send signals to each other using chemical messengers called neurotransmitters that cross the tiny gap between neurons.

Types of Neurons

Neurons are classified by their function: Sensory, Motor, and  Interneurons.

Image from Earth's Lab

1. Sensory Neurons (Afferent Neurons)

• Carry signals from sensory receptors to the spinal cord and brain
• Detect stimuli like light, sound, touch, temperature, and taste
• Allow you to sense what is happening in your environment

2. Motor Neurons (Efferent Neurons)

• Carry signals from the brain and spinal cord to muscles
• Control voluntary movements
• Trigger muscle contractions

3. Interneurons

• Connect sensory and motor neurons
• Process information
• Found in the brain and spinal cord
• Allow sensory information to be processed before motor response

Sensory neurons bring information in, motor neurons send commands out, and interneurons process the information in between.

Division 2: Peripheral Nervous System (PNS)

The Peripheral Nervous System (PNS) includes all nervous system structures outside the brain and spinal cord. It connects the CNS to all other parts of the body.

Two subdivisions: Somatic Nervous System and Autonomic Nervous System.

Image from Knya

1. Somatic Nervous System

• Controls voluntary movements
• Carries sensory information from skin, muscles, and joints
• Includes sensory and motor neurons

2. Autonomic Nervous System

• Controls involuntary functions
• Controls organ functions
• Works without conscious thought

Has three subdivisions:

1. Sympathetic nervous system: "Fight or flight" response
2. Parasympathetic nervous system: "Rest and digest" response
3. Enteric nervous system: Controls digestion

The PNS is like a communication network that connects your brain and spinal cord to all other parts of your body.

Neurotransmitters - are chemical messengers that carry signals between neurons.

Common neurotransmitters: Acetylcholine,  Dopamine, Serotonin, Norepinephrine, and GABA .

Image from GrepMed

1. Acetylcholine

• Controls muscle movement
• Involved in memory and learning

2. Dopamine

• Controls movement
• Affects mood and motivation
• Involved in reward and pleasure

3. Serotonin

• Regulates mood
• Affects sleep
• Controls appetite

4. Norepinephrine

• Increases attention and alertness
• Involved in the "fight or flight" response

5. GABA (Gamma-aminobutyric acid)

• Calming neurotransmitter
• Reduces nervous system activity
• Promotes relaxation

Neurotransmitters are chemical messengers that allow neurons to communicate with each other.

Memory and Learning in the Nervous System

The nervous system stores memories and learns through changes in synaptic connections.

Types of Memory: Sensory Memory, Short Term Memory, and Long Term Memory.

Image from News-Medical

1. Sensory Memory

• Very brief (less than 1 second)
• Holds sensory impressions
• Like seeing an image briefly

2. Short-Term (Working) Memory

• Lasts seconds to minutes
• Limited capacity (about 7 items)
• Used for immediate tasks

3. Long-Term Memory

• Can last for years or a lifetime
• Large capacity
• Stores knowledge and experiences

Image from Labvanced

Declarative Memory:

• Conscious memories
• Facts and events
• Can be described in words

Examples: learning a phone number, remembering your birthday

Procedural Memory:

• Unconscious memories
• Skills and habits
• Cannot easily be described in words

Examples: riding a bicycle, playing piano

Memory is how your brain stores and retrieves information. Learning happens when new synaptic connections form and memories are stored.

Emotions and the Nervous System

The nervous system processes emotions through a structure called the limbic system, which includes: Amygdala, Hippocampus, and Hypothalamus.

Image from The Reign Of The Brain

1. Amygdala

• Processes fear and other emotions
• Triggers emotional responses

2. Hippocampus

• Forms memories
• Connects emotions to memories
• Why we remember emotionally important events

3. Hypothalamus

• Connects emotions to physical responses
• Controls stress hormones
• Triggers "fight or flight" response

Emotions are processed by special brain structures that connect emotional responses to memories and physical reactions.

The Reflex Arc

(Automatic Response)

A reflex arc is the pathway of a reflex (automatic response), the simplest form of nervous system control.

Image from Microbe Notes

How a reflex arc works:

1. Stimulus occurs for instance when you touch something hot.

2. Sensory neuron detects it pain receptors send a signal through a sensory neuron to the spinal cord.

3. Synapse with motor neuron in the spinal cord, the sensory neuron directly connects with a motor neuron (or through an interneuron).

4. Motor neuron activates the motor neuron sends a signal to the muscle.

5. Muscle contracts your hand pulls away automatically.

6. Brain is notified (but too late) only after you have pulled your hand away does the brain receive the pain signal and you feel the pain.

A reflex is an automatic response that happens through the spinal cord without waiting for the brain, allowing you to react instantly to danger.

Nervous System Quiz: click here

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