Human Body Homeostasis & Nervous System

• Homeostasis is how the body maintains a stable internal environment despite external changes.

Factors the Human Body Balances:

• Body temperature is balanced.
• Blood glucose levels are balanced.
• Water balance is maintained.
• Blood pressure is maintained.
• Blood pH is maintained.
• Salt levels are maintained.

Hypothermia & Hyperthermia:

• Hypothermia occurs when body temperature drops below the normal range, leading to slowed metabolism and organ failure.
• Hyperthermia occurs when body temperature rises above normal, causing heat exhaustion or heat stroke.

Nervous System Definition & Function:

• The nervous system is a network of nerves and cells transmitting signals between the brain, spinal cord, and body.
• Bodily functions, movement, and responses to stimuli are controlled by the nervous system.

Two Main Parts of the Nervous System:

• The central nervous system (CNS) consists of the brain and spinal cord and processes information.
• The peripheral nervous system (PNS) includes nerves outside the CNS, transmitting signals between the CNS and the body.

Somatic Nervous System (SNS):

• The SNS controls voluntary movements like walking and picking up objects.

Autonomic Nervous System (ANS):

• The ANS controls involuntary functions such as heart rate and digestion.

Sympathetic Nervous System:

• The sympathetic nervous system prepares the body for stress ("fight or flight").
• Increased heart rate, dilated pupils, and inhibited digestion are results of the sympathetic nervous system preparing the body for stress.

Parasympathetic Nervous System:

• The parasympathetic nervous system maintains rest and recovery ("rest and digest").
• Slowing heart rate and promoting digestion are results of the parasympathetic nervous system maintaining rest and recovery.

Neuron Definition:

• A neuron is a nerve cell that transmits electrical and chemical signals in the nervous system.

Main Parts of a Neuron & Their Functions:

• Dendrites receive signals from other neurons.
• The cell body (soma) contains the nucleus and processes information.
• The nucleus controls cell activities.
• The axon transmits electrical impulses away from the cell body.
• The myelin sheath insulates the axon for faster signal transmission.
• Axon terminals release neurotransmitters to communicate with other neurons.

Three Types of Neurons & Their Functions:

• Sensory neurons detect stimuli and send signals to the CNS.
• Motor neurons send signals from the CNS to muscles or glands for action.
• Interneurons connect sensory and motor neurons within the CNS.

Reflex Arc Definition & Importance:

• A reflex arc is a rapid, automatic response to a stimulus bypassing the brain for faster reaction.

Steps of a Reflex Arc:

• First there's a stimulus, such as touching something hot.
• Next there's a receptor, such as skin receptors, that detects the stimulus.
• After the stimulus is detected the sensory neuron sends a signal to the spinal cord.
• The interneuron then processes the signal in spinal cord and sends signal to the motor neuron.
• The motor neuron sends a response to arm and hand muscles.
• Response: hand moves away from stimulus

Example of a Reflex Action:

• A knee-jerk reflex is when the leg jerks involuntarily when the knee is tapped.

Role of Receptors:

• Receptors detect stimuli.
• Thermoreceptors detect temperature changes.
• Photoreceptors detect light in the eyes.
• Mechanoreceptors detect touch and pressure.

Synapse Definition & Function:

• A synapse is the gap between two neurons where neurotransmitters transmit signals.

Five Steps at a Synapse:

• An electrical impulse reaches the axon terminal.
• Neurotransmitters are released into the synaptic gap through vesicles.
• Neurotransmitters bind to receptors on the next neuron.
• A signal is transmitted to the next neuron and continues the electrical impulse.
• Excess neurotransmitters are reabsorbed or broken down.

Neurotransmitter Definition & Example:

• Neurotransmitters are chemical messengers in the nervous system.
• Adrenaline is a neurotransmitter.
• Dopamine is a neurotransmitter.
• Serotonin is a neurotransmitter.
• Acetylcholine is a neurotransmitter.

Gut-Brain Axis:

• The gut-brain axis is the communication network between the digestive system (gut) and the brain.
• It involves the nervous system, hormones, and gut microbes, allowing signals to travel in both directions.
• The Microbiome refers to the community of microorganisms (microbes) living in and on the human body, especially in the gut.
• Microbes include bacteria, viruses, fungi, and other microorganisms that can be beneficial, neutral, or harmful.

Endocrine System Definition & Role in Homeostasis:

• The endocrine system is a collection of glands that release hormones to regulate body functions.

Hormones & Their Function:

• Hormones are chemical messengers traveling in the bloodstream to regulate processes like growth, metabolism, and stress response.

Blood Glucose Regulation:

• Insulin lowers blood glucose by promoting glucose uptake into cells.
• Glucagon raises blood glucose by breaking down glycogen in the liver.

Diabetes:

• In type 1 diabetes, the body does not produce insulin.
• In type 2 diabetes, the body does not respond properly to insulin.

Comparison of Nervous & Endocrine Systems:

• The nervous system uses fast, electrical signals and has short-term effects.
• The endocrine system uses slower, chemical signals (hormones) and has longer-lasting effects.

Stimulus-Response Model Definition & Components:

• The stimulus-response model shows how the body detects and responds to changes.
• Stimulus → Receptor → Control Center → Effector → Response

Stimulus-Response Model Example:

• Stimulus: Low blood sugar due to exercise
• Receptor: Pancreas detects the change in blood sugar
• Control Center: Pancreas releases glucagon into the bloodstream
• Effector: Glucagon targets liver cells
• Response: Liver cells break down glycogen into glucose into the bloodstream
• Negative feedback: Blood sugar increases back to the normal range

Negative Feedback Definition & Example:

• Negative feedback removes or reduces the stimulus, returning conditions back to normal.
• Temperature regulation: Sweating cools the body down when overheated.
• Blood glucose control: Insulin lowers glucose when levels are high.