Peripheral Nervous System and Motor Output

Exam 4

• Covers the chapter discussed today and the muscle chapter.

• Not comprehensive.

• Will be in the same room, not in the lab.

• Hardest exam of the semester; study accordingly.

Neuron Review

• Basic Neuron Structure:

  • Cell body.

  • Axon.

  • Presynaptic terminals: Release neurotransmitters onto receptors of another cell (neuron, muscle cell, etc.).

  • Synapse: The junction between neurons or between a neuron and another cell.

Nerves

• Nerve Definition:

  • A bundle of axons in the peripheral nervous system.

  • Analogy: A rope made of smaller strings (axons).

• Tract:

  • Bundle of axons in the central nervous system.

• Ganglion:

  • A group of cell bodies in the peripheral nervous system.

• Nucleus:

  • A group of cell bodies in the central nervous system.

Peripheral Nervous System Overview

• Components:

  • Receptors: Detect stimuli.

  • Nerves: Bundles of axons transmitting information.

    • Sensory nerves: Carry information to the central nervous system (brain, spinal cord).

      • Sensory Input: Information to the central nervous system.

      • Information conducts to the central nervous system via axons, through action potentials (saltatory or continuous, depending on myelination).

    • Motor nerves: Carry information away from the central nervous system to effectors.

      • Motor Output: Information from the central nervous system to effectors.

Divisions of the Peripheral Nervous System

• Somatic Nervous System.

• Autonomic Nervous System.

  • Subdivisions:

    • Sympathetic Nervous System.

    • Parasympathetic Nervous System.

    • Enteric Nervous System: Nervous system of the digestive system (to be discussed in the second semester).

Sensory Receptors

• Two types:

  • Somatic receptors: Located in the skin, muscles, joints, nose.

    • Examples:

      • Merkel's disc, Pacinian corpuscle: Detect pressure (exteroceptors).

      • Free nerve endings: Pain receptors (dendrites).

      • Olfactory receptors: Smell (exteroceptors).

    • Exteroceptors: Detect stimuli from the external environment at the body surface.

    • Proprioceptors: Muscle spindles, Golgi tendon apparatus (covered by Sievert).

  • Autonomic receptors: Located in the viscera (organs, blood vessels).

    • Receive stimuli from the internal environment.

    • Examples:

      • Baroreceptors: Detect blood pressure.

      • Mechanoreceptors: Detect stretch in organs like the stomach and bladder.

      • Chemoreceptors: Detect chemicals such as $H+$ ions (pH) and sodium bicarbonate.

      • Osmoreceptors: Detect osmolarity (concentration) of fluids.

Receptor Function

• All receptors function similarly:

  • Gather a stimulus.

  • Convert the stimulus into an electrical signal (membrane potential).

  • Translate the signal into action potential frequency.

• Action Potential Frequency:

  • Information is encoded by the frequency of action potentials.

  • Increased stimulus strength leads to increased action potential frequency.

  • Decreased stimulus strength leads to decreased action potential frequency.

Cholinergic and Adrenergic Terminology

• Cholinergic:

  • Anything associated with acetylcholine.

    • Cholinergic neuron: A neuron that releases acetylcholine.

    • Cholinergic receptor: A receptor that binds acetylcholine.

    • Types: Muscarinic and nicotinic receptors.

• Adrenergic:

  • Anything associated with epinephrine and norepinephrine (primarily norepinephrine).

    • Adrenergic neuron: A neuron that releases norepinephrine.

    • Adrenergic receptor: A receptor that binds norepinephrine.

    • Types: Alpha and beta receptors.

Somatic Motor Output

• Control of Movement:

  • Controls movement via skeletal muscles.

  • Effectors: Skeletal muscles.

  • One efferent motor neuron from the central nervous system to the effector.

  • Myelinated motor neurons for rapid conduction (saltatory conduction).

  • The motor neurons release acetylcholine (cholinergic).

  • Nicotinic receptors on skeletal muscle cells bind acetylcholine.

  • Voluntary control: Conscious control over skeletal muscles.

  • Brain stem and spinal cord send signals to skeletal muscle.

Autonomic Motor Output

• Control of Visceral Functions:

  • Controls visceral cells, smooth muscle cells, and cardiac muscle cells.

  • Effectors: Cardiac muscle, smooth muscle (around hollow organs), visceral cells (glands, fat cells, liver cells).

  • Two motor neurons between the central nervous system and effectors:

    • Preganglionic neuron: Arises from the central nervous system (brain stem, thoracic, lumbar, or sacral region); myelinated.

    • Postganglionic neuron: Synapses with the preganglionic neuron; not myelinated.

  • Ganglia: Groups of cell bodies of postganglionic neurons.

    • The cell bodies of the post ganglionic neurons make up the ganglia of the autonomic nervous system.