Understanding the Nervous, Endocrine, and Immune Systems
The Neuron: The Building Block of the Nervous System
A neuron is the fundamental cell of nervous tissue.
Neuron Components:
- Cell Body (Soma): Located around the nucleus, containing most of the cytoplasm. It generates nerve impulses.
- Dendrites: Short, branching extensions that receive nerve impulses from other neurons.
- Axon: A long, slender extension that transmits nerve impulses away from the cell body to other neurons or effector cells.
Types of Neurons:
- Sensory Neurons: Transmit nerve impulses from sensory organs to the spinal cord and brain.
- Motor Neurons: Transmit nerve impulses from the central nervous system (CNS) to effector organs (muscles or glands).
- Association Neurons (Interneurons): Connect sensory and motor neurons within the CNS.
Synapse: The junction between two neurons where neurotransmitters are released to transmit signals.
Central Nervous System (CNS)
The CNS consists of:
- Brain: Located within the skull, responsible for controlling various body functions.
- Cerebrum: The largest part of the brain, responsible for higher-level cognitive functions.
- Cerebellum: Controls balance and coordination.
- Brain Stem: Controls involuntary functions such as breathing and heart rate.
- Spinal Cord: Extends from the brain stem and handles simple involuntary reflexes.
Peripheral Nervous System (PNS)
The PNS consists of nerve extensions located outside the CNS.
Types of Nerves:
- Sensory Nerves: Transmit sensory information to the CNS.
- Motor Nerves: Transmit motor commands from the CNS to muscles and glands.
- Mixed Nerves: Contain both sensory and motor fibers.
Divisions Based on CNS Connection:
- Cranial Nerves: Originate from the brain.
- Spinal Nerves: Originate from the spinal cord.
Functional Divisions:
- Somatic Nervous System (SNS): Controls voluntary movements and helps the body respond to external changes.
- Autonomic Nervous System (ANS): Controls involuntary functions, maintaining internal balance (homeostasis).
Autonomic Nervous System
The autonomic nervous system operates automatically, controlling:
- Effectors: Smooth muscle, heart muscle, and glands.
- Receptors: Sensory receptors that monitor internal conditions.
The autonomic nervous system is further divided into:
- Sympathetic Nervous System: Prepares the body for stress (“fight or flight” response).
- Parasympathetic Nervous System: Returns the body to a resting state after stress and maintains normal bodily functions.
Common Nervous System Disorders
- Anxiety: A normal emotional response to perceived threats or conflicts.
- Alzheimer’s Disease: A progressive neurodegenerative disorder characterized by the loss of neurons and impaired communication between them.
Sense Organs and Sensory Receptors
Sensory receptors are specialized nerve cells that detect stimuli.
- Taste: Located in taste buds on the tongue.
- Smell: Located in the olfactory epithelium in the nasal cavity.
- Touch: Receptors in the skin detect stimuli such as cold, heat, pressure, and pain.
- Vision: Occurs in the eye. Key parts include:
Eye Parts:
- Sclera: The tough, outer layer of the eye. The cornea is part of the sclera.
- Choroid: The middle layer of the eye, containing the iris.
- Retina: Contains light-sensitive cells (photoreceptors).
- Hearing: Located in the ear. Key parts include:
Ear Parts:
- Outer Ear: Primarily protective, includes the eardrum.
- Middle Ear: Contains the ossicles (small bones):
Ossicles:
- Malleus (Hammer)
- Incus (Anvil)
- Stapes (Stirrup)
- Inner Ear: Key parts include:
Inner Ear Parts:
- Cochlea: Responsible for hearing.
- Utricle: Responsible for balance.
Endocrine System
The endocrine system consists of glands that secrete hormones directly into the bloodstream.
Endocrine Glands:
- Pituitary Gland: Secretes various hormones that regulate other endocrine glands and bodily functions.
- Thyroid Gland: Produces thyroxine, a hormone that regulates metabolism and calcium uptake by bones.
- Parathyroid Glands: Secrete parathyroid hormone, which regulates calcium levels in the blood.
- Pancreas: Secretes insulin and glucagon, hormones involved in glucose metabolism.
Insulin: Lowers blood glucose levels.
Glucagon: Increases blood glucose levels.
Immune System
The immune system defends the body against pathogens.
Components of the Immune System:
- Lymphoid Organs: Include bone marrow, thymus, spleen, lymph nodes, and lymphatic vessels.
Bone Marrow and Thymus: Produce immune cells.
Spleen and Lymph Nodes: Store and activate immune cells.
Immune Cells (Leukocytes):
Defend the body against pathogens.
Types of Immune Cells:
- T Lymphocytes: Directly attack pathogens and stimulate the formation of B lymphocytes.
- B Lymphocytes: Produce antibodies, proteins that target and neutralize pathogens.