Nervous System and Special Senses Overview

The Nervous System and Special Senses

• The nervous system acts as the body's control center and communication network.
• It directs the functions of body organs and systems.
• It interprets the external environment.
• It determines the body's reaction to changes.
• Homeostasis, the balanced internal environment, is controlled by the nervous and endocrine systems.

Organization of the Nervous System

• Central Nervous System (CNS): Includes the brain and spinal cord.
• Peripheral Nervous System (PNS):
  • Afferent Peripheral System:
    • Sensory neurons
  • Efferent Peripheral System:
    • Somatic: Controls skeletal muscles
    • Autonomic: Controls involuntary functions (sympathetic and parasympathetic divisions).

Functional Organization of the PNS

• Sensory (afferent) Division:
  • Somatic Sensory:
    • General: Touch, pain, pressure, vibration, temperature, and proprioception in skin, body wall, and limbs.
    • Special: Hearing, equilibrium, vision
  • Visceral Sensory:
    • General: Stretch, pain, temperature, chemical changes, and irritation in viscera; nausea and hunger
    • Special: Taste, smell
• Motor (efferent) Division:
  • Somatic Nervous System: Motor innervation of all skeletal muscles
  • Autonomic Nervous System (ANS): Motor innervation of smooth muscle and glands (sympathetic and parasympathetic divisions)

Sympathetic and Parasympathetic Branches

• Sympathetic Division ("Fight or Flight"): Mobilizes bodily resources in response to threat.
• Parasympathetic Division ("Rest and Digest"): Replenishes bodily resources.

Neuroglial Cells

• Astrocytes: Support, connection, blood-brain barrier
• Oligodendrocytes: Support, myelin sheath formation (CNS)
• Microglial: Phagocytosis
• Ependymal: Line the ventricles of the brain
• Schwann: Myelin sheaths in the peripheral nervous system

Structure of a Neuron

• Cell body: Nucleus and metabolic center of the neuron.
• Dendrites: Receive signals.
• Axon: Extension of the cell body (conducts signals away).
• Schwann cells: Produce myelin sheaths along the axon (important for efficient signal transmission).
• Nodes of Ranvier: Gaps in the myelin sheath critical for saltatory conduction (faster signal transmission).

Classification of Neurons

• Receptors: Detect environmental stimuli (unipolar).
• Sensory Neurons: Receive impulses from receptors (unipolar).
• Interneurons: Transmit impulses for interpretation and processing (multipolar).
• Motor Neurons: React to the stimulus (multipolar).

The Reflex Arc

• The pathway resulting in a reflexive action.
• Receives a stimulus, enters the spinal cord (CNS), and produces an immediate response.
• Examples include knee-jerk reflex, maintaining homeostasis, heartbeat, breathing, digestion, coughing, sneezing, swallowing, vomiting.
• Involves sensory receptors, sensory neurons, interneurons, motor neurons, and effectors.

Grouping of Neural Tissue

• White matter: Groups of myelinated axons that form nerve tracts within the CNS.
• Gray matter: Nerve cell bodies, dendrites, and unmyelinated axon bundles.
• Cortex: Gray matter on the surface of the brain
• Nerve: A bundle of fibers outside the CNS
• Ganglia: Nerve cell bodies outside the CNS
• Tract: A bundle of fibers inside the CNS
• Nucleus: Nerve cell bodies and dendrites inside the CNS
• Horns: Areas of gray matter in the spinal cord.

The Spinal Cord

• Continuation of the medulla oblongata.
• Protected by meninges (dura mater, arachnoid, pia mater).
• 31 segments with spinal nerves.
• It transmits sensory impulses to the brain and integrates reflexes, and is crucial for reflex actions and communication between the brain and the body via the spinal nerves

The Spinal Nerves

• 31 pairs, arising from the union of dorsal and ventral roots.
• Mixed nerves, with both motor and sensory fibers.
• Exit the vertebral column between vertebrae (named based on the cord segment they arise from)

The Brain

• Divided into four main parts:
  • Brainstem: Controls breathing, heartbeat, reactions to sensory stimuli.
  • Diencephalon: Controls homeostasis.
  • Cerebrum: Processes intellect, emotions, and sensory information.
  • Cerebellum: Maintains body posture and balance.

Protection of the Brain

• Cranial bones.
• Meninges (protective membranes).
• Cerebrospinal fluid (CSF).
• Ventricles with the interventricular foramina.

The Four Major Lobes of the Brain

• Frontal lobe: Muscle movements, moods, motivation.
• Parietal lobe: Touch, pain, balance, taste, temperature.
• Temporal lobe: Hearing, smell, memory, abstract thought, judgment.
• Occipital lobe: Vision

Surface of the Cerebrum

• Motor areas: Control muscular movements.
• Sensory areas: Interpret sensory impulses.
• Association areas: Process emotions and intellect.

The Cerebellum

• Butterfly-shaped, second largest part of the brain.
• Two partially separated hemispheres, connected by vermis.
• Responsible for coordination of muscular movements, maintaining posture, and maintaining balance.

The Autonomic Nervous System

• It's a subdivision of the efferent PNS.
• It functions without conscious effort and regulates internal organ functions to maintain homeostasis
• It regulates energy and activity levels of the body, responding in times of crisis by speeding up many functions, or dealing with normal, rest and digest activities through the parasympathetic division.
• Sympathetic Division: Activates during stress or crisis. (fight or flight).
• Parasympathetic Division: Promotes relaxation and recovery. (rest and digest).

The Special Sense

• Smell: Inspired air molecules dissolved in nasal mucous trigger bipolar neurons to send impulses to the olfactory cortex in the brain.
• Taste: Taste buds on the tongue, palate, and pharynx contain taste cells, sensitive to chemicals dissolved in saliva.
• Sight: Eyes protected by eyelids and eyelashes. Tears lubricate and contain a bacteriolytic enzyme. The eyeball has various structures, including the sclera, choroid, and retina to send light signals to the brain
• Hearing and Equilibrium: The outer ear collects sound waves, traveling to the middle ear (auditory ossicles to amplify), and then the inner ear, where the cochlea contributes to hearing, and the semicircular canals contribute to equilibrium.

Explore the intricacies of the nervous system and how it interacts with special senses. This quiz covers the central and peripheral nervous systems, their functions, and the importance of homeostasis. Test your knowledge on how sensory and motor pathways contribute to body responses and environmental interpretation.