Lecture 9 - Functional Organization of Nervous Tissue

Chapter 11 - Functional Organization of Nervous Tissue

Functions of the Nervous System

  • Sensory:

    • Sense changes through sensory receptors (external/internal environment)

    • Specialized Receptors sense changes in external environment (touch, vision, hearing, pressure, temperature changes)

    • Specialized Receptors sense changes in internal environment (levels of oxygen/carbon dioxide in blood, pH changes, blood pressure changes)

  • Motor:

    • Responds to stimuli

      • Takes information from sensory receptors, decide if response is necessary → create response

    • Affects muscles in body, targets glands (secretion → signal for changes),

  • Integrative:

    • Analyze incoming sensory information, store some aspects, make decisions regarding appropriate behaviours

    • higher order processing responses

      • Mental activities, consiousness, thinking, memory, emotions

    • storing aspects of sensory information, making decisions regarding appropriate motor responses

Nervous System

  • Components:

    • Brain, spinal cord, nerves, sensory receptors

  • Subdivisions:

    • Central Nervous System (CNS): Brain + spinal cord

    • Peripheral Nervous System (PNS): sensory receptors + nerves

  • Cranial Nerves: Nerves that exit/enter into the brain

  • Spinal Nerves: Nerves that exit/enter into the spinal cord

Components of the Peripheral Nervous System

  • Sensory Receptors: Specialized endings of neurons (gathers information internally/externally) or separate, specialized cells that detect things like temperature, pain, light information from environment

  • Nerves: Bundle of axons (of many neurons going either towards/away from CNS) & sheaths that connects CNS to sensory receptors, muscles & glands

    • Cranial Nerves: Originates from the brain (12 pairs)

    • Spinal Nerves: Originates from spinal cord (31 pairs)

  • Ganglion: Collection of Neuron cell bodies outside CNS

    • Ganglion - singular

    • Ganglia - plural

      • Many cell bodies of PNS are inside CNS, just the axon leaves the spinal cord/brain

    • Sensory information that is not going to the brain - cell body outside of CNS (from spinal nerves)

      • Have neuron cell bodies in ganglion

    • Connection between one neuron and another neuron where they have the cell body

  • Plexus: Extensive network of axons, sometimes neuron cell bodies, located outside CNS

    • Nerves that join each other & exit each other, with some neurons going one way and other neurons going another way

    • Exchange neural information from one level to another

Divisions of the PNS

  • Sensory (Afferent): Transmits action potentials from receptors to CNS

  • Sensory Input → Detected by Sensory Receptors → CNS → Integrative Response → Motor Response

    • Sensory Division:

      • Sensory Receptors

  • Motor (Efferent): Transmits action potentials from CNS to effectors (muscles, glands)

    • 3 main muscle types:

      1. Skeletal Muscle - move bones & create movement

      2. Cardiac Muscle - heart

      3. Smooth Muscle - cant control consciously (autonomic)

        • Digestive system organs, stomach, pupils, etc.

    • Glands: Exocrine/Endocrine

  • Motor Division:

    • Somatic Nervous System - Effectors: Skeletal Muscle

    • Autonomic Nervous System → Sympathetic/Parasympathetic division → Effectors: Cardiac & Smooth muslce, glands


  • Sensory Inputs:

    • Light, sound, taste, smell, tough, temperature, pain, pressure

  • Motor Outputs:

    • Movement, changes in metabolism, heart rate, breathing rate, etc.

Sensory Divisions of PNS

  • Gathering information from external & internal environment

    • General Senses

      • Specialized receptors throughout the body

        • Eg. Skin

    • Special Senses

      • Very specialized receptors in very specific organs of the body

        • Eg. Vision

    • Dorsal root ganglion → Dorsal root of spinal nerve (recieves sensory input)

      • Cell body outside of spinal cord

    • Ventral carries motor information back out

Motor Divisions of PNS

Somatic Nervous System

  • Somatic Nervous System: CNS to skeletal muscles

    • Voluntary control

    • single neruon system

      • Neuron cell body located inside spinal cord, axon exits spinal cord → target tissue

    • Synapse w/ Skeletal Muscle:

      • Junction of a nerve cell w/ another cell

        • Eg. Neuromuscular junction - synapse between neuron & skeletal muscle cell

      • Synapse: Connection between one neuron & another neuron, or connection between neuron & target tissue

        • Able to make decision about if we want signal to continue or if we want to block signal

    • Once signal goes out, you cant stop it → will synapse w/ skeletal muscle & cause contraction

  • All spinal nerves in body carry both sensory & motor

Autonomic Nervous System (ANS)

  • Autonomic Nervous System (ANS): From CNS to smooth muscle, cardiac muscle, & certain glands

    • Involuntary control

    • 2 neuron system:

      1. First from CNS to ganglion

      2. From ganglion to effector

    • Autonomic Ganglion: the ganglion between the two neurons

Divisions of ANS

  • Sympathetic: Prepares body for physical activity (fight-flight)

    • Resting condition → movement

    • increases heart rate

  • Parasympathetic: Regulates resting/vegetative functions (resting & digesting)

    • Decreases heart rate

  • Sympathetic & parasympathetic are opposites

Enteric Nervous System (ENS)

  • Plexuses w/in wall of digestive tract

    • Control digestive tract independently of CNS

    • Communicate w/ CNS via ANS (parasympathetic/sympathetic neurons contribute to plexus)

  • brain does not need to know everything going on in digestive tract (involuntary)

    • Allows for processes of digestion to go on without involvment of CNS

  • Sensory: Monitor chemical environment & stretching of walls

    • Enzymes, pH change, etc.

    • Big bolus → stretches walls of digestive track → sends signal to muscle surrounding tubes → contracting → break up bolus

  • Motor: Contracts smooth muscle and control secretions of GI organs and endocrine cells

    • Eg. Stomach, intestine, etc.

Organization of Nervous System Example

  1. Sensory Input → sensory division

  2. PNS (receptors, nerves, ganglia, plexuses)

  3. CNS

  4. integrative response (Motor response)

  5. Motor division

  6. activate somatic nervous system or autonomic response (sympathetic - flight)

    • cardiac muscle, glands of body

Receptor → Sensory nervous system → CNS → motor nervous system → Effector