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Homeostasis
Homeostasis
Homeostasis is the process by which living organisms maintain a stable internal environment despite changes in the external environment. It keeps conditions inside the body within narrow, optimal ranges that are necessary for cells to function properly
How it works:
Receptors in the body detect a stimulus (increase in temp, drop in blood sugar, etc). The brain or endocrine glands process the information, and an effector responds to bring the conditions back to normal
Examples: Sweating and shivering to maintain body temperature, the use of insulin and glucagon to control blood sugar levels, and water balance in the kidneys
Positive Feedback Loop
Positive Feedback Loop
When the body goes outside the normal range, it doesn't bounce back- instead it keeps going outside the normal range
Example: Childbirth
Negative Feedback Loop
Negative Feedback Loop
When the body goes outside the normal range, it bounces back and its goal is to stay inside the normal range of the body
Example: Body temperature
Nervous System
Nervous System
Purpose: The nervous system is like the body’s communication network. Its main job is to send and receive messages between the brain, spinal cord, and the rest of the body. It helps you sense things around you (like seeing, hearing, or touching), controls your movements (like walking or writing), and keeps important body functions running (like breathing and heartbeat) without you even thinking about it. Basically, the nervous system controls everything you do, feel, and think, helping your body respond quickly to the world around you.
ORGANISATION OF THE NERVOUS SYSTEM:
The nervous system can be categorised into 9 sections:
Central Nervous system- The brain and spinal cord (thinking, movement, and feeling)
Peripheral Nervous system- Links the central nervous system to the organs
Afferent System- Input from the body to the brain
Efferent system- Signals from the brain to the receptor
Sensory nerves- Sends info to the brain from the receptors
Somatic system- Controls muscles, bones, and skin
Autonomic system- The internal organs of the body
Sympathetic system- Active stress response
Parasympathetic system- Stress recovery and calming
THE THREE MAIN NEURON TYPES: Sensory, Motor, and Interneurons
MOTOR NEURON
MOTOR NEURON
These are the action (effector) neurons
They relay signals that has been passed on by the inter-neurons to the effectors (muscles, glands, organs, etc)
The nucleus is on the top, there's lots of myelin, longer axon
SENSORY NEURON
SENSORY NEURON
These are the input neurons
They contain sensors/receptor programmed for various body conditions- they get signals through the body faster than other neurons because their nucleus is off to the side
The dendrites are very long and the nucleus is in the center but off to the side in order for signals to bypass
INTERNEURON
INTERNEURON
These are the processing neurons
They connect the sensory and the motor neurons together by receiving input from the sensory neurons and translating it to be sent to the motor neurons to take action- they decide what the output (stuff motor neuron produces) should be
Nucleus is in the middle, shorter axon, no myelin sheath
The Nerve Cell
The Nerve Cell
Dendrites- Input, receiving data
Cell body- Regular cell functions (Golgi, vacuoles, etc)
Axon- The wire that the signals travel through
Myelin sheath- Inside part of the Schwann cell that produces protein
Nodes of Ranvier- Gap between schwann cells that signals jump between
Schwann cell- Insulation for myelin sheath
Nucleus- Processor and control centre
Axon terminals- Transmit signals to other neurons
Glial Cell
Glial Cell
Glial cells provide structural support, insulation and protection, and aid with metabolism for neurons
Think of them as neurons little but mighty helpers
Neurotransmitters and Psychoactive chemicals
Neurotransmitters are chemicals that help neurons send messages across the brain and nervous system. Psychoactive chemicals, like drugs or caffeine, affect how these neurotransmitters work by changing how neurons send, receive, or process signals. Some psychoactive substances increase neurotransmitter activity by stimulating neurons to release more chemicals, while others block receptors on neurons, preventing messages from getting through. Some even mimic neurotransmitters, tricking neurons into sending fake signals. By altering how neurons communicate, psychoactive chemicals can affect mood, behavior, thinking, and how the body feels or reacts. Over time, repeated use can change the way neurons function, leading to tolerance, dependence, or addiction.
White Vs. Grey Matter
White Matter
White Matter
Myelinated axons
Connects brain regions to help with learning, attention, and motor control
Peaks at a middle age
Grey Matter
Grey Matter
Mostly neuronal cell bodies (not myelinated)
Processes and transmits information, controls movement, memory, and emotion
Fully develops in your 20's
Journey of a Signal
Stimulus
Sensory receptors in the body (eyes, ears, nose, etc) detect a stimulus (heat, texture, light, pressure, etc) and convert the stimulus into an electrical signal
Brain and Spinal Cord
The electrical signal passes through the sensory neurons. The sensory neurons transmit signals through their axons to the interneurons in the spine, and from there the signal continues on to the brain
Processing and Responding
At the brain, the signal is categorized depending on the type of signal it is (pain, light, heat, etc). The brain interprets the signal and sends out the most fitting response using motor neurons
Effector and Action
The motor neuron prompts the effector to act and perform its action (muscle contracting, release of hormones, etc)
Transmission Across a Synapse
Transmission Across a Synapse
This process involves chemical messengers called neurotransmitters that carry the signal across the synaptic gap. The signal, initially an electrical impulse (action potential), triggers the release of neurotransmitters from the presynaptic neuron. These neurotransmitters then bind to receptors on the postsynaptic neuron, potentially initiating a new electrical signal in the receiving neuron.
Signals in the Neuron
When resting, the neuron has an imbalance of positive and negative charges on either side of its membrane and a polarization level of -70mV. If a stimulus comes along that is higher than -55mV, the atom will meet the threshold. The threshold triggers the action potential, which means that sodium/potassium pumps will pump 3Na+ and 2K+ in, which will cause a slight positive charge outside the neuron. The sodium and potassium will diffuse across the membrane to balance the concentration. Sodium gates in the axon of the neuron will then open, and sodium will rush in, reversing the charge (depolarization). The positive sodium ions will be attracted to the negative charges in the adjacent region. This causes an electrical disturbance which will cause the sodium gates in the next region to open. As soon as the depolarized wave moves on to the next region, the sodium/potassium pump works to restore the resting potential in that area (called a wave of repolarization). After all of the excitement, the neurons won't be able to send another impulse until the membrane is polarized (called the refractory period)
All or nothing response
All or nothing response
There is a minimum amount of stimulation that is needed to trigger the threshold level. However, stimulating the nerve cells more does not increase the response. No matter how strong, the intensity and speed of the impulse will be the same, no matter what- this is what an all-or none response refers to.
Even if one neuron has a different threshold level than another, they will still have the same response
One neuron could trigger at 40°C, another at 100°C, and another at 70°C, but the signal will be the same across the board- HOT
However, neurons can still indicate the intensity of the stimulus based on the frequency (firing) of the impulse
STRESS RESPONSE AND RECOVERY
STRESS RESPONSE AND RECOVERY
The nervous system controls the stress response by using neurons to quickly send signals throughout the body. When you sense danger, sensory neurons send a message to the brain, which then signals the sympathetic nervous system to start the “fight or flight” response. This causes the adrenal glands to release adrenaline, making your heart beat faster, your breathing speed up, and your muscles prepare for action. If the stress continues, the hormone cortisol is released for extra energy. After the threat is gone, the parasympathetic nervous system uses neurons to help calm the body back to normal
Parts of the Brain:
Cerebellum: Movement and balance
Medulla oblongata: Unconscious movement- transmitting signals for autonomic activities like heartbeat and respiration
Thalamus: Relay sensory and motor signals- regulating consciousness and alertness
Hypothalamus: Homeostasis- maintaining a stable state
Corpus Callosum: Ensuring both sides of the brain can send signals to each other
Pons: Generate the rhythm of breathing
Spinal Cord: Carry nerve signals from brain to body (and vice versa), and responsible for reflexes
Cerebrum: Conscious decisions- initiate and coordinate movement and regulate temperature
Pituitary gland: Produce and release hormones to do bodily functions
The Ear
The Ear
Ear lobe: Softer, lower part of outer ear
Auditory canal: Passage that carries sound to eardrum
Eardrum: Thin membrane that vibrates with sound
Hammer, anvil, stirrup: Tiny bones that pass vibrations to inner ear
Semicircular canals: Fluid-filled loops that help with balance
Cochlea: Turns sound into nerve signals
Auditory nerve: Carries sound signals from ear to brain
Round window: Releases pressure from waves in the cochlea
Eustachian tube: Connects ear to throat and balances pressure
The Eye
The Eye
Cornea: Transparent layer that focuses light onto rear of the eye
Pupil: Focusing structure, lets light in
Lens: Focuses light onto retina
Iris: Coloured part controlling size of pupil
Retina: Back layer that detects light
Optic nerve: Carry visual signals from eye to brain
Suspensory ligament: Hold lens in place and change its shape
Aqueous humor: Clear fluid that keeps eye's shape and nourish it
Vitreous humor: Jelly like substance that keeps eye in its shape
How we have closely studied the nervous system
How we have closely studied the nervous system
MRI (Magnetic Resonance Imaging):
MRI (Magnetic Resonance Imaging):
Uses strong magnets and radio waves to create detailed pictures of the inside of your body, especially soft tissues like the brain, muscles, or organs.
The magnets line up the water molecules in your body, and the machine sends radio waves that bounce back, creating images.
Example use: Brain injuries, spinal problems, torn ligaments.
CT Scan (Computed Tomography):
CT Scan (Computed Tomography):
Uses X-rays taken from many angles around your body.
A computer puts these X-rays together to make a 3D picture of bones, organs, or blood vessels.
Good for seeing hard tissues like bones or checking for internal bleeding.
Example use: Broken bones, tumors, internal injuries.
PET Scan (Positron Emission Tomography):
PET Scan (Positron Emission Tomography):
Uses a small amount of radioactive sugar injected into your body.
Active cells (like cancer) use more sugar, and the scanner detects this activity.
Shows how tissues and organs are working, not just what they look like.
Example use: Detecting cancer, brain activity, heart problems.
NERVOUS SYSTEM OVERVIEW WEBSITE
PUBLIC SLIDESHOW
(Link below)
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