Control and coordination in animals
Control and Coordination
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Coordination
Definition: The effective working together of various organs in an organism to produce an appropriate reaction to a stimulus.
Mechanisms: Control and coordination in animals are facilitated by two primary systems:
The Nervous System
The Endocrine System
Important Terms
Stimulus: Any external or internal factor that causes a living organism to react.
Response: The specific reaction exhibited by a living organism in response to a stimulus.
Impulse: A self-propagated electric current that travels along the surface of nerve fibers, facilitating the passage of information.
Receptors and Effectors
Receptors: Cells, tissues, and organs capable of receiving specific stimuli and initiating impulses, which are then transmitted via sensory nerves.
Effectors: Muscles, glands, tissues, or cells that act in response to messages received from the nervous system.
Types of Receptors
Photoreceptors: Detect light and form images; located inside the eyes.
Gustatory Receptors: Detect taste; located in the taste buds.
Olfactory Receptors: Detect smell; located in nasal cavities.
Sense Organs: Structures containing receptors that gather information about both external and internal environments, such as skin, nose, eyes, tongue, and ears.
Neurons
Definition
Neuron: The structural and functional unit of the nervous system responsible for receiving, conducting, and transmitting impulses.
Structure of a Neuron
A neuron consists of three primary parts:
Cyton (Cell Body): Contains the nucleus and surrounding cytoplasm; features Nissl's granules around the nucleus. The stimulus is converted into an impulse within the cyton.
Axon: The longest part of the neuron, a single elongated fiber extending from one side of the cyton, conducting impulses away from the cell body. The axon membrane is covered by a myelin sheath, with constrictions known as the Nodes of Ranvier, and ends in branched axon terminals.
Dendrites: Short, branched cytoplasmic processes that connect to the cyton, receiving stimuli and passing them onto the cyton.
Synapse
Definition: The junction between two adjacent neurons, occurring between the axon ending of one neuron and the dendrite of another.
Nerve Impulse
Definition: Information transmitted in the form of chemical and electrical signals through neurons. Dendrites convey impulses toward the cell body (cyton).
Neuromuscular Junction: The point where a muscle fiber contacts a motor neuron carrying nerve impulses from the central nervous system, with transmission akin to that across a synapse between two neurons, facilitated by neurotransmitters.
Types of Neurons
Sensory Neurons: Carry impulses from sense organs to the brain and spinal cord; the impulses are sensory in nature.
Motor Neurons: Carry impulses from the brain and spinal cord to the effectors; the impulses are motor in nature.
Nerves
Definition: Bundles of neurons encased in a common covering called the nerve membrane, providing a unified pathway for electrochemical nerve impulses transmitted along the axons.
Types of Nerves
Sensory Nerves: Carry sensory impulses from sense organs to the brain and spinal cord.
Motor Nerves: Transmit motor impulses from the brain and spinal cord to the effectors.
Passage of Nerve Impulse
Pathway:
Stimulus → Dendrite → Cell body → Axon → Axon terminal → Neurotransmitter → Synapse → Other neurons/muscle cells/glands.
Neurotransmitter: A chemical secreted by axon terminals for the transmission of impulses to the next neuron, muscle, gland, or organ. Common examples include acetylcholine and noradrenaline.
Directionality: Impulses travel through neurons in a single direction due to neurotransmitter release at one side of the synapse.
Actions
Voluntary Actions
Definition: Actions performed under the control of will (brain).
Examples: Speaking to a friend, writing a letter, etc.
Involuntary Actions
Definition: Actions that occur without conscious control (brain) but are regulated by the spinal cord and autonomic nervous system.
Examples: Withdrawal of hand or foot from a hot surface, thorn, or needle.
Reflex Actions
Definition: Automatic, involuntary responses to a stimulus without brain consultation, controlled by the spinal cord.
Examples: Blink when an object approaches the eye, pulling away from a hot surface, sneezing, feeling hungry.
Reflex Arc
Definition: The pathway followed by an impulse during a reflex response.
Pathway: Receptors → Sensory neuron → Interneuron → Motor neuron → Effectors.
Mechanism of Reflex Action
Receptor Activation: Receptor organ (e.g., skin) perceives the stimulus and activates a sensory nerve impulse.
Message Transmission: Sensory neuron carries the impulse to the spinal cord.
Modulation: The spinal cord (relay or interneurons) transmits the impulse to the motor neuron.
Effectors Respond: Motor nerve conducts impulses to muscles, which respond by pulling away.
Examples of Reflex Actions
Withdrawal of hand from a hot surface or thorn.
Some actions can be habitually trained into reflex actions (e.g., writing, reading, walking, driving, salivating at food's sight or smell).
Differences Between Reflex Actions and Involuntary Actions
Definition: All reflex actions are involuntary by nature, but not all involuntary actions are reflexes.
Examples: Heartbeat and peristalsis are involuntary actions but not reflex actions.
Human Nervous System
Classification
The human nervous system is divided into three major systems:
The Central Nervous System (CNS)
The Peripheral Nervous System (PNS)
The Autonomic Nervous System
Central Nervous System
Components: Consists of the brain and spinal cord.
The Brain's Structure and Protection
Location: Located in the head region.
Protection:
Enclosed in a bony box called the skull (Cranium).
Encased in three membranous layers called the meninges (Dura mater, Arachnoid mater, Pia mater).
Surrounded by cerebrospinal fluid, which protects the brain from mechanical injury.
Parts of the Brain
Forebrain: Largest part including the cerebrum, thalamus, and hypothalamus (diencephalon).
Midbrain: Connects forebrain to hindbrain and controls eye and ear reflex movements.
Hindbrain: Comprises three parts - Cerebellum, Pons, and Medulla Oblongata.
Cerebrum
Hemispheres: Divided into right and left hemispheres; each has gray matter (outer) and white matter (inner).
Gyri and Sulci: The outer gray matter contains convolutions (gyri) and grooves (sulci) that increase neuronal surface area.
Functional Areas of the Cerebrum
Frontal Lobe: Associated with reasoning, planning, problem-solving, and speech control.
Parietal Lobe: Processes sensory information like taste, touch, and pain.
Occipital Lobe: Pertains to visual perception.
Temporal Lobe: Involved in auditory processing.
Lateralization of Cerebral Hemispheres
Right hemisphere controls the left side of the body; left hemisphere controls the right side.
More convolutions in the forebrain indicate higher intelligence.
Diencephalon (Forebrain)
Components: Contains thalamus and hypothalamus.
Thalamus: Major sensory and motor signaling coordination center.
Hypothalamus: Regulates hunger, thirst, fullness, body temperature, emotions, and connects the nervous system with the endocrine system.
Hindbrain Components
Cerebellum: Coordinates voluntary actions and maintains posture and balance.
Medulla Oblongata: Controls involuntary functions such as blood pressure, breathing, and salivation.
Pons: Connects different parts of the brain and regulates functions related to the body and sleeping.
Summary of Lobes and Functions
Frontal Lobe Functions: Problem-solving, reasoning, speech, voluntary motor activities.
Parietal Lobe Functions: Sensation, spatial orientation, and reading.
Temporal Lobe Functions: Language understanding, memory, and auditory processing.
Occipital Lobe Functions: Vision and color perception.
Cerebellum Functions: Balance, coordination, and fine muscle control.