Nerve Cells or Neurons

• A nerve cell or neuron is the fundamental unit of the nervous system, responsible for transmitting electrical and chemical signals throughout the body
• Neurons are specialized to process and communicate information and play a crucial role in reflexes

Types of Neurons

• Sensory Neurons are responsible for transmitting sensory information from the body to the central nervous system (CNS), which includes the brain and spinal cord
• These neurons detect stimuli from the external environment, such as touch, temperature, sound, and internal conditions like pain
• Motor Neurons carry signals from the central nervous system (CNS) to muscles and glands, enabling movement and bodily functions
• These neurons play a crucial role in both voluntary and involuntary muscle control
• Interneurons (also known as association neurons) connect sensory and motor neurons within the central nervous system (CNS)

Structure of Sensory Neurons

• Dendrites receive sensory input from receptors
• The cell body (Soma) is located in a dorsal root ganglion near the spinal cord
• The Axon carries the signal to the CNS
• Axon terminals connect with other neurons in the spinal cord

Types of Sensory Neurons

• Mechanoreceptors detect touch, pressure, and vibration, such as in the skin
• Thermoreceptors detect temperature changes
• Nociceptors detect pain and harmful stimuli
• Photoreceptors detect light and are found in the eyes
• Chemoreceptors detect chemicals, such as taste and smell

Function of Nerve Cell/Neurons

• Neurons are specialized cells in the nervous system that transmit electrical and chemical signals throughout the body.
• Neurons send and receive electrical impulses to coordinate body functions
• Sensory neurons detect external and internal stimuli (e.g., pain, temperature, touch) and relay information to the brain
• Motor neurons carry signals from the brain and spinal cord to muscles, enabling movement
• Interneurons connect sensory and motor neurons processing
• Neurons regulate vital functions like heart rate, breathing, and digestion through autonomic signals
• Neurons in the brain form networks that store and process information, allowing for learning and recall

Types of Motor Neurons

• Upper Motor Neurons (UMNs) are located in the brain (cerebral cortex) and brainstem
• UMNs send signals down the spinal cord to lower motor neurons and are involved in voluntary movement and muscle coordination
• Damage to UMNs can cause conditions like spastic paralysis and hyperreflexia
• Lower Motor Neurons (LMNs) are located in the spinal cord and brainstem
• LMNs directly innervate muscles to cause contraction and control both voluntary and involuntary movements
• Damage to LMNs can lead to flaccid paralysis, muscle weakness, and hyporeflexia (reduced reflexes)

Structure of Motor Neurons

• Cell Body (Soma) contains the nucleus and controls cell functions
• Dendrites receive input from other neurons
• Axon is a long fiber that transmits impulses to muscles
• Myelin Sheath is a protective covering that speeds up signal transmission
• Axon Terminals release neurotransmitters (e.g., acetylcholine) to

Function of Motor Neurons

• Receive signals from the brain and spinal cord
• Transmit electrical impulses along their axons
• Release neurotransmitters at neuromuscular junctions
• Activate muscle contraction or gland secretion

Motor Neuron Diseases (MNDs)

• Amyotrophic Lateral Sclerosis (ALS) is a progressive disease that affects both upper and lower motor neurons, leading to muscle weakness and paralysis
• Spinal Muscular Atrophy (SMA) is a genetic condition that primarily affects lower motor neurons, causing muscle wasting
• Multiple Sclerosis (MS) is a condition where the immune system damages myelin, disrupting motor neuron function

Structures Of Interneurons

• Cell Body (Soma) contains the nucleus and organelles
• Dendrites receive signals from other neurons
• Axons can be short or long, depending on the function
• Axon terminals transmit signals to motor neurons or other interneurons

Types of Interneurons

• Excitatory Interneurons increase the activity of other neurons by releasing excitatory neurotransmitters (e.g., glutamate)
• Inhibitory Interneurons decrease neuronal activity by releasing inhibitory neurotransmitters (e.g., GABA, glycine)
• Relay Interneurons transmit signals over long distances within the CNS (e.g., from the spinal cord to the brain)
• Local Interneurons connect nearby neurons for rapid processing, e.g. in the brain

Functions Of Interneurons

• Interneurons process sensory input by receiving signals from sensory neurons and interpret information
• They coordinate motor output by relaying signals to motor neurons for appropriate responses
• In spinal reflexes (like the knee-jerk reflex), interneurons quickly transmit signals without involving the brain
• Higher cognitive functions involve them in complex processes like thinking

Interneurons Activity

• Reflex Arc occurs when touching something hot so sensory neurons send signals to interneurons in the spinal cord
• This allows the signal to be quickly relayed to motor neurons to pull the hand away
• Brain Function occurs as Interneurons in the cerebral cortex help process thoughts, memory, and decision-making
• Inhibitory Control involves some interneurons that suppress unwanted movements, preventing muscle spasms or tremors

Interneurons Disorders

• Dysfunction of interneurons causes various neurological disorders
• Epilepsy is due to an imbalance between excitatory and inhibitory interneurons
• Parkinson’s Disease results when a loss of certain interneurons disrupts motor control
• Schizophrenia occurs when altered interneuron function affects cognitive processing

Connective Tissue

• Connective Tissue is one of the four main types of tissue in the body; it provides support, protection, and structure

Proper Connective Tissue

• Loose Connective Tissue
• Dense Connective Tissue

Loose Connective Tissue

• Areolar Tissue supports and cushions organs, found beneath the skin
• Adipose Tissue stores fat, provides insulation, and cushions organs
• Reticular Tissue forms the framework of organs like the spleen

Dense Connective Tissue

• Dense Regular is found in tendons and ligaments; provides strong, unidirectional support
• Dense Irregular is found in dermis and joint capsules, and provides strength in multiple directions
• Elastic is found in large arteries and some ligaments; it allows stretching

Supportive Connective Tissue

• Hyaline cartilage is found in the nose, trachea, and joints, providing smooth movement
• Elastic cartilage is found in the ear and epiglottis, providing flexibility
• Fibrocartilage is found in intervertebral discs and knee

Connective Tissue

• Compact bone is dense, forming the outer layer of bones, and provides strength
• Spongy Bone is found in the inner part of bones, lightweight, and contains bone marrow

Fluid Connective Tissue

• Blood contains red blood cells, white blood cells, and platelets; transports nutrients and oxygen
• Lymph contains white blood cells and helps in immune defence and fluid balance