Neurons and Receptors

Neurons – The Building Blocks of the Nervous System

Functions of a Neuron

1. Receive signals → Detects information from inside or outside the body

2. Integrate signals → Determines whether the information should be passed along

3. Transmit signals → Sends information to target cells (other neurons, muscles, glands)

Neuron Structure & Functions

Neuron Part Function

Dendrites Receive signals and conduct impulses toward the cell body

Cell Body (Soma) Contains the nucleus, processes incoming signals

Axon Transmits nerve impulses away from the cell body

Myelin Sheath Insulates axon, prevents electrical signal from leaking

Schwann Cells (Glial Cells) Form the myelin sheath by wrapping around the axon

Nodes of Ranvier Gaps in the myelin sheath that expose the axon, help speed up signal transmission

Axon Terminal (Synapse) End of the neuron that sends signals to other neurons or target cells

Types of Neurons

1. Sensory (Afferent) Neurons

• Carry messages from receptors (sense organs) to the CNS

• Structure: Long dendrites, short axon

2. Interneurons

• Located entirely within the CNS

• Relay messages between sensory and motor neurons

• Structure: Can have short or long dendrites/axons

3. Motor (Efferent) Neurons

• Carry messages from the CNS to muscles or glands (effectors)

• Structure: Short dendrites, long axon

Reflex Arc – Automatic Responses

• Reflexes are involuntary and automatic responses to stimuli

• Uses a simplified neural pathway that bypasses conscious brain activity

• Example: Withdrawing a hand from a hot stove

Pathway of a Reflex Arc:

1. Receptor → Detects stimulus (pain, pressure, temperature, etc.)

2. Sensory Neuron → Carries signal to CNS

3. Interneuron → Processes the signal in the spinal cord or brainstem

4. Motor Neuron → Carries response signal to muscle/gland

5. Effector → Muscle/gland carries out action (e.g., pulling hand away)

Types of Receptors – Classified by Location

Receptor Type Location Function

Exteroceptor Near the external environment (e.g., skin) Detects external stimuli (touch, temperature, pain, etc.)

Interoceptor Inside the body (organs, tissues) Detects internal changes (blood pressure, oxygen levels, etc.)

Proprioceptor Near moving parts (muscles, joints) Detects body position, movement, and coordination

Types of Receptors – How They Detect Stimuli

Receptor Type Stimulus Detected

Chemoreceptors Detect chemical stimuli (e.g., smell, taste, oxygen levels)

Osmoreceptors Detect changes in body fluid concentration

Nociceptors Detect pain (chemical & mechanical stimuli)

Mechanoreceptors Detect pressure, vibration, sound, balance

Thermoreceptors Detect temperature (heat or cold)

Types of Receptors – Stimuli & Membrane Potential Changes

1. Ions & Macromolecules

• Some receptors detect chemicals by binding to receptor proteins

• Others diffuse across the cell membrane to trigger a response

2. Physical Stimuli

• Environmental changes (e.g., pressure, vibration, stretch) affect receptor membranes

3. Electromagnetic Radiation

• Humans → Eyes detect visible light

• Other organisms:

• Snakes → Detect infrared heat

• Bees → See ultraviolet light

• Birds → Sense Earth’s magnetic field

How This Works in an AI Quizzing App

Flashcards

• “What part of the neuron transmits signals away from the cell body?” → Axon

• “What type of neuron carries signals from the CNS to muscles?” → Motor (Efferent) Neuron

• “What type of receptor detects pain?” → Nociceptor

Multiple Choice Questions

• Which part of the neuron increases the speed of signal transmission?

A) Axon

B) Dendrites

C) Myelin Sheath ✅

D) Interneuron

• Which type of receptor detects changes in body fluid concentration?

A) Chemoreceptor

B) Osmoreceptor ✅

C) Mechanoreceptor

D) Thermoreceptor

Matching Activities

• Match neuron structures to their functions

• Match receptors to what they detect

Fill in the Blanks

• “The ________ neuron sends messages from the CNS to muscles.” (Motor)

• “The ________ is the insulating layer that speeds up electrical signals.” (Myelin sheath