Control and Coordination in Complex Animals: Nervous & Endocrine Systems
Control and Coordination in Living Beings
The Nervous System
The response a living being makes to external stimuli is called control and coordination. The nervous system is primarily responsible for this in complex animals.
Components of the Nervous System
The nervous system comprises the brain, spinal cord, and nerves. The five sense organs (nose, eyes, ears, tongue, and skin) are also integral parts of the nervous system, playing a crucial role in its function.
Functions of the Nervous System
- Receives information from the environment through sense organs.
- Transports information to the brain via the spinal cord and nerves.
- Analyzes the information and reacts accordingly through muscles and glands.
For example, when we touch a hot object, our skin senses the heat, nerves carry the impulse to the brain through the spinal cord, and the brain sends an impulse to the muscles, causing them to contract and withdraw our hand.
Receptors
Receptors are groups of cells in sense organs sensitive to environmental changes. There are five types:
- Gustatory Receptors: Responsible for taste detection.
- Phono Receptors: Responsible for hearing.
- Olfactory Receptors: Responsible for smell detection.
- Photo Receptors: Responsible for detecting light.
- Thermo Receptors: Responsible for feeling the touch of external stimuli.
Neurons
Neurons are specialized cells that combine to form the nerves of the nervous system. They are considered the unit of the nervous system as nerves emerge from the brain and spinal cord, branching out to almost all parts of the body.
Parts of a Neuron
- Cell Body: Contains the cell’s necessary components, such as the nucleus, endoplasmic reticulum, ribosomes, and mitochondria. The neuron dies if the cell body dies.
- Axon: A long, cable-like projection of the cell that ends in hair-like structures called axon terminals or axon endings. These terminals relay nerve impulses.
- Dendrites: Small, branch-like projections that connect to other neurons and receive nerve impulses.
- Synapse: The point of contact between the axon terminals of one neuron and the dendrite of another.
Working of a Neuron
Neurons transmit messages between the brain and body parts. When receptors sense something, a chemical reaction triggers an electrical impulse in the dendrites. This impulse travels through the neuron’s body to the axon endings, where a small amount of chemical is released into the synapse. This chemical crosses the synapse, reaches the dendrite tip, and produces another electrical impulse, continuing the transmission.
Types of Neurons
- Sensory Neurons: Transmit messages from body parts to the central nervous system (brain and spinal cord).
- Motor Neurons: Transmit messages from the central nervous system to body parts.
- Relay Neurons: Relay signals within the central nervous system.
The Nervous System in Humans
The human nervous system is divided into two main parts:
- Peripheral Nervous System (PNS)
- Central Nervous System (CNS)
Peripheral Nervous System (PNS)
The PNS consists of cranial nerves, spinal nerves, and visceral nerves.
- Cranial Nerves: 12 pairs that emerge from the brain and connect to sense organs and muscles in the head region.
- Spinal Nerves: 31 pairs that emerge from the spinal cord and connect to sense organs and muscles below the head region. They carry messages to the brain through the spinal cord.
- Visceral Nerves: Emerge from the brain and spinal cord and connect to internal organs like the heart and kidneys.
Voluntary and Involuntary Actions
Voluntary actions are consciously controlled by the brain, such as writing, speaking, walking, and kicking a ball.
Involuntary actions occur without conscious control, such as heartbeat, breathing, sweating, kidney function, and digestion.
Reflex Action and Arc
Reflex action is a quick, automatic response to an environmental change (stimulus) involving only the spinal cord. These actions occur within fractions of a second.
Reflex arc is the pathway through which a reflex action occurs.
Types of Reflexes
- Cerebral Reflex: Controlled by a cranial nerve and typically occurs in the facial or head area, such as changes in pupil size in bright light.
- Spinal Reflex: Involves only the spinal nerves and spinal cord, bypassing the brain, such as withdrawing the hand from a hot object.
How Muscles (Effectors) Cause Movement
Muscles are made up of muscle cells containing special proteins that can change their arrangement upon receiving messages from the brain. This change in protein arrangement alters the muscle’s shape, allowing it to contract or expand, leading to movement.
Central Nervous System (CNS)
The CNS consists of the brain and spinal cord.
Brain
The brain controls all bodily functions and is protected by the skull (cranium) and cerebrospinal fluid. It has three parts:
- Forebrain (Cerebrum): The most complex part, responsible for thinking, memory, sensation, movement, and feelings. It controls voluntary actions.
- Midbrain: Controls cerebral reflexes like pupil size changes and blinking.
- Hindbrain: Controls involuntary actions like heartbeat, breathing, and digestion. It consists of the pons (regulates respiration), cerebellum (controls posture, balance, and motion), and medulla (controls involuntary actions like digestion, heartbeat, and blood pressure).
Spinal Cord
The spinal cord extends from the medulla (hindbrain) downward, protected by the vertebral column. It carries messages between the brain and nerves and controls spinal reflexes.
Endocrine System
The endocrine system comprises several endocrine glands.
What are Glands?
Glands are organs that secrete liquid substances containing chemicals. There are two types:
- Exocrine Glands: Have ducts that carry secretions to their target, such as sweat and salivary glands.
- Endocrine Glands: Ductless glands that secrete hormones directly into the bloodstream, which carries them to different body parts.
Hormones
Hormones are chemical substances produced by endocrine glands that control various bodily activities, such as growth.
Feedback Mechanism
The feedback mechanism ensures that glands secrete the correct amount of hormones.
Difference Between Nervous and Endocrine Systems
The nervous system uses electrical impulses for fast, short-term effects, while the endocrine system uses hormones for slower, long-term effects.
Need for the Endocrine System
The endocrine system is essential for controlling a large number of organs simultaneously and for regulating slow processes like growth, which the nervous system is less efficient at doing.