Nervous & Hormonal Coordination in Animals

Posted on Nov 7, 2024 in Physical Education

Nervous and Hormonal Coordination

Related Systems

Nervous System: Uses quick nervous impulses.

Endocrine System: Uses slow chemical messengers called hormones.

The nervous system acts first, activating the sympathetic nervous system in emergency situations. The parasympathetic system returns the body to normal.

The endocrine system secretes adrenaline (which stimulates the transfer of glycogen to glucose).

Sympathetic System

Inhibits unnecessary organs (like digestion) to allow for escape. Stimulates the heart, muscles, dilates airways, increases ventilation and glucose.

Parasympathetic System

Returns ventilation, digestion, and heart rate to normal.

Sensory Receptors

Definition: Detect changes in the internal or external environment.

Sensory receptors can be nerve endings, epithelial cells, or sensory organs.

Characteristics:

  • Specificity: Sensitive to a particular type of stimulus.
  • Adaptation: Ability to vary sensitivity to a long-term stimulus, which may even disappear even though the stimulus continues.

Types of Sensory Receptors

Chemoreceptors

Capture chemical substances in their environment.

  • Olfactory Receptors: Detect airborne substances, locate food, sexual partners, and detect dangers. Located in the antennae of many insects and in the olfactory epithelium of vertebrates.
  • Gustatory Receptors: Detect substances dissolved in water or saliva. Located in the antennae of snails, tentacles of octopus, legs and mouthparts of arthropods, and body surface of fish.
  • Taste Buds: Oval structures formed by taste receptor cells, surrounded by support cells and a pore with microvilli.
  • Pain Receptors: Nerve endings stimulated by tissue damage. Pain serves as a warning of malfunction or harmful stimuli.
Mechanoreceptors

Recognize mechanical information.

  • Tactile Receptors: Distributed across the body surface. In humans, they detect thermal sensations through dendrites covered by tissue layers, such as Pacinian and Meissner’s corpuscles.
  • Proprioceptors: Provide information on the degree of muscle contraction, tendon tension, and joint position.
  • Equilibrium Organs: Located in the inner ear with three semicircular canals that respond to movement and two static equilibrium organs (utricle and saccule).
  • Lateral Line: System for receiving vibrations, changes in hydrostatic pressure, and object movement. Located in amphibian skin and on the sides of fish.
The Ear
  • Outer Ear: Pinna and ear canal.
  • Middle Ear: Cavity limited by two membranes (eardrum and oval window) connected by ossicles (hammer, anvil, and stirrup).
  • Inner Ear: Contains the vestibule (utricle, saccule, and three semicircular canals) and the cochlea.
Thermoreceptors

Specialized dendrites of sensory neurons that detect temperature changes (e.g., Jacobson’s organ).

Photoreceptors

Cells sensitive to light.

  • Isolated Sensitive Cells and Eyespots: Groups of cells that distinguish between light and dark.
  • Compound Eyes: Formed by ommatidia.

Components of the Nervous System

Formed by two cell types: glial cells and neurons.

Neuron

The functional and atomic unit of the nervous system.

Components:

  • Soma: Integration center, processes information from dendrites and decides whether to generate a nerve impulse.
  • Dendrites: Short, branched projections of the neuronal body that receive chemical signals.
  • Axon: Long prolongation of the soma that branches at its end into synaptic boutons containing synaptic vesicles with neurotransmitters.

Other Terms:

  • Nerve: Union of many axons wrapped in connective tissue.
  • Nerve Fiber: Any neural prolongation.
  • Gray Matter: Groupings of neuronal bodies.

Types of Neurons

  • Sensory: Transmit impulses from sensory receptors to the central nervous system.
  • Association: Establish contact between neurons in the central nervous system.
  • Motor: Conduct impulses from the central nervous system to effectors (muscles and glands).
    • Somatic Motor: Responsible for reflexes and voluntary control of skeletal muscles.
    • Autonomic Motor: Innervate involuntary effectors: cardiac muscle, smooth muscle, and glands.

Nerve Impulse

An action potential that travels along the neuron membrane as an electric current.

Resting Potential: Potential difference between the inside and outside of a cell.

Synapses Between Neurons

Functional contact between two neurons or between a neuron and an effector (muscle or gland).

Types of Synapses

  • Electrical: Impulse passes directly from presynaptic to postsynaptic neuron through gap junctions.
  • Chemical: Synaptic cleft separates neurons; transmission occurs via neurotransmitters.

Neurotransmitters

Biomolecules synthesized by neurons and stored in vesicles in axon terminals.

Reflexes

Reflex Arc:

  • Receptor: Captures a stimulus and transforms it into nerve impulses.
  • Sensory Neuron: Conducts impulse from receptor to association neuron.
  • Association Neuron: Integrates information and produces a response.
  • Motor Neuron: Carries impulse from association neuron to effector.
  • Effector: Responds to the impulse (muscle or gland).

Reflex: Response to a stimulus transported by a reflex arc. Can be innate or conditioned.

Nervous System Evolution

Animals with Radial Symmetry

Cnidarians: Possess a primitive nerve plexus, a network of neurons extending throughout the body.

Animals with Bilateral Symmetry

Evolutionary Trends:

  • Increase in neurons and their concentration in ganglia.
  • Increase in axon bundles, allowing for greater complexity in reflex arcs.
  • Accumulation of neurons in central nervous system centers.
  • Hierarchy in nerve control.
  • Cephalization: Concentration of sensory organs and nerve cells in the head.

Vertebrate Nervous System

  • CNS: Brain and spinal cord, surrounded by meninges (dura mater, arachnoid mater, pia mater).
  • PNS: Sensory and motor neurons; cranial and spinal nerves.

Brain

  • White Matter: Myelinated axons.
  • Gray Matter: Neuronal bodies, dendrites, and glia.
  • Hindbrain: Myelencephalon, metencephalon, and pons.
  • Medulla Oblongata: Controls heart rate, respiratory rate, blood pressure, and swallowing.
  • Cerebellum: Integrates information from sight, hearing, muscles, joints, and brain areas.
  • Midbrain: Simple behaviors in amphibians, but controls complex behaviors in higher vertebrates.
  • Forebrain: Diencephalon (thalamus and hypothalamus), limbic system, and cerebrum.

Spinal Cord

Nerve cord extending from the medulla oblongata to the second lumbar vertebra.

Peripheral Nervous System (PNS)

Composed of the somatic and autonomic nervous systems.

Hormonal Coordination

Integrates nervous and hormonal information, responding to internal and external changes to maintain homeostasis.

Hormones

Can include proteins, amino acid derivatives, peptides, and steroids.

Endocrine Cells: Grouped in glands; products transported by blood.

Neurosecretory Cells: Specialized neurons that produce neurohormones.

Hormone Action Mechanism

Activation of membrane receptors or intracellular receptors.

Invertebrate Hormones

Regulate growth, reproduction, molting, and color change.

Pheromones

Chemical substances that influence behavior.

Glands and Hormones

Pituitary Gland

The master gland.

Thyroid Gland

  • Thyroxine: Activates metabolism.
  • Calcitonin: Lowers blood calcium.

Parathyroid Gland

Parathyroid Hormone: Increases blood calcium.

Adrenal Glands

  • Glucocorticoids: Control carbohydrate metabolism.
  • Mineralocorticoids: Control mineral salt metabolism.
  • Adrenaline and Noradrenaline: Prepare the body for stress.

Pancreas

  • Insulin: Decreases blood glucose.
  • Glucagon: Increases blood glucose.

Testes

Androgens: Determine male sexual characteristics.

Ovaries

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