Coordination System: The Human Nervous System

Coordination System

Sensitivity and the Human Nervous System

  • The coordination system is vital for the body's function.
  • Without a coordination system, the body would not be able to respond to stimuli or maintain internal balance.

Review of Key Concepts

  • Stimulus: A change in the environment that can be detected by the body.
  • Response: A reaction to a stimulus.
  • Receptor Organ: A structure that detects stimuli (e.g., eye, ear).
  • Effector Organ: A structure that produces a response (e.g., muscle, gland).

Components of the Human Nervous System

  • Central Nervous System (CNS):
    • Brain: Processes information.
    • Spinal Cord: Relays information between the brain and the peripheral nervous system.
  • Peripheral Nervous System (PNS):
    • Cranial Nerves
    • Spinal Nerves
    • Sensory Receptors: Detect internal and external stimuli.
  • Functional Divisions of the PNS:
    • Motor System: Controls skeletal muscles.
    • Autonomic Nervous System: Controls smooth muscles, cardiac muscles, and glands.

The Coordination Pathway

  • Stimulus: A detectable change in the environment.
  • Receptor: Structure that detects the stimulus (e.g., sensory receptors).
  • Coordination: Processing of the stimulus information in the CNS.
  • Effector: Structure that carries out the response (e.g., muscles, glands).
  • Response: The action taken as a result of the stimulus.

Receptors and Types of Energy Received

  • Eye (Retina): Light
  • Ear (Organ of Hearing): Sound
  • Ear (Organ of Balance): Mechanical (kinetic) energy
  • Tongue (Taste Buds): Chemical energy
  • Nose (Organ of Smell): Chemical energy
  • Skin (Touch/Pressure/Pain Receptors): Mechanical (kinetic) energy
  • Skin (Temperature Receptors): Heat
  • Muscle (Stretch Receptors): Mechanical (kinetic) energy

Types of Neurons

  • Sensory Neuron: Transmits impulses from receptors to the CNS.
  • Relay Neuron (Interneuron): Connects sensory and motor neurons within the CNS.
  • Motor Neuron: Transmits impulses from the CNS to effectors.

Neuron Structure

  • Cell Body: Contains the nucleus and other organelles.
  • Dendrites: Receive impulses from other neurons or receptors.
  • Axon: Transmits impulses away from the cell body.
  • Myelin Sheath: Insulating layer around the axon, increasing the speed of impulse transmission.

Sensory Neuron

  • Cell body is located off to the side of the axon.
  • Transmits impulses from sensory receptors to the CNS.

Relay Neuron (Interneuron)

  • Located within the CNS.
  • Connects sensory and motor neurons.

Motor Neuron

  • Transmits impulses from the CNS to effectors (muscles or glands).
  • Has axon terminations on muscle fibers, forming neuromuscular junctions.

Synapses

  • Gaps between two neurons where chemical neurotransmitters transmit impulses.
  • Incoming impulses cause the release of neurotransmitters into the synapse.
  • Neurotransmitters diffuse across the synapse and bind to receptors on the postsynaptic neuron.
  • This binding triggers an impulse in the postsynaptic neuron.
  • Enzymes break down the neurotransmitters to terminate the signal.

Reflex Arc

  • A neural pathway that controls a reflex action.
  • Components:
    • Sensory receptor
    • Sensory neuron
    • Relay neuron (in spinal cord)
    • Motor neuron
    • Effector (muscle)
  • The reflex arc bypasses the brain, allowing for a quick response.
  • Dorsal root ganglion contains the cell bodies of sensory neurons.
  • Synapses occur between neurons in the reflex arc.

Eye Structure

  • Cornea: The transparent outer layer that refracts light.
  • Conjunctiva: A clear membrane that covers the front of the eye and lines the inside of the eyelids.
  • Sclera: The white outer layer of the eye that provides protection.
  • Choroid: The middle layer containing blood vessels.
  • Retina: The inner layer containing photoreceptors (rods and cones).
  • Iris: Controls the amount of light entering the eye by adjusting the size of the pupil.
  • Pupil: The opening in the center of the iris.
  • Lens: Focuses light onto the retina.
  • Ciliary Muscles: Control the shape of the lens.
  • Suspensory Ligaments: Connect the ciliary muscles to the lens.
  • Aqueous Humor: Fluid in the anterior chamber of the eye.
  • Vitreous Humor: Gel-like substance that fills the space between the lens and the retina.
  • Fovea: The central focal point in the retina, where vision is sharpest.
  • Optic Nerve: Transmits visual information to the brain.
  • Blind Spot: The point where the optic nerve leaves the eye, lacking photoreceptors.

Retina

  • Photoreceptor Cells:
    • Rods: Sensitive to low light levels and responsible for black and white vision.
    • Cones: Responsible for color vision and function best in bright light.
  • Bipolar Cells: Transmit signals from photoreceptors to ganglion cells.
  • Ganglion Cells: Receive signals from bipolar cells and transmit them to the brain via the optic nerve.
  • Pigment Epithelium: Absorbs light and prevents reflection within the eye.

Functioning of the Human Eye

  • Light enters the eye through the cornea and pupil.
  • The lens focuses the light onto the retina.
  • Photoreceptors in the retina convert light into electrical signals.
  • These signals are transmitted to the brain via the optic nerve.

Reflex Actions: Controlling Light Entry

  • Bright Light:
    • Circular muscles in the iris contract.
    • Radial muscles relax.
    • Pupil constricts (becomes smaller).
  • Dim Light:
    • Circular muscles relax.
    • Radial muscles contract.
    • Pupil dilates (becomes larger).

Accommodation: Focusing on Objects at Different Distances

  • Focusing on a Distant Object:
    • Ciliary muscles relax.
    • Suspensory ligaments are pulled tight.
    • Lens becomes less convex (flatter).
  • Focusing on a Nearby Object:
    • Ciliary muscles contract.
    • Suspensory ligaments slacken.
    • Lens becomes more convex (rounded).

Brain and Spinal Cord: Gray Matter vs. White Matter

  • Gray Matter:
    • Contains neuronal cell bodies.
    • Interprets sensory information.
  • White Matter:
    • Made up of bundles of myelinated axons.
    • Connects various gray matter areas.
    • Conducts, processes, and sends information to different parts of the body.
  • Brain Development:
    • White matter develops throughout the 20s and peaks in middle age.

Stress Response

  • (a) Short-term stress response and the adrenal medulla

    • Stressful stimuli cause the hypothalamus to activate the adrenal medulla via nerve impulses.
    • The adrenal medulla secretes epinephrine and norepinephrine.
    • Effects of epinephrine and norepinephrine:
    • Glycogen broken down to glucose; increased blood glucose
    • Increased blood pressure
    • Increased breathing rate
    • Increased metabolic rate
    • Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity

  • (b) Long-term stress response and the adrenal cortex

    • Stressful stimuli cause the hypothalamus to activate the adrenal cortex via hormonal signals.
    • The adrenal cortex secretes mineralocorticoids and glucocorticoids.
    • Effects of mineralocorticoids:
    • Retention of sodium ions and water by kidneys
    • Increased blood volume and blood pressure
    • Effects of glucocorticoids:
    • Proteins and fats broken down and converted to glucose, leading to increased blood glucose
    • Partial suppression of the immune system