Animal Physiology - Nervous System Overview

Overview of Nervous System Functions

Command and Control Center

  • Role:

    • Controls feelings, perceptions, and movement

    • Enables learning, memory, thought, and self-awareness

    • Regulates internal body functions and behaviors

Lines of Communication

  • Components of Nervous System:

    • Three main functions:

    • Sensory Input: Sensors detect stimuli (external/internal)

    • Integration: Information processes in the CNS (brain and spinal cord)

    • Motor Output: Response initiated through motor neurons

  • Example: Doctor's knee-jerk reflex

Neuron Structure and Function

Neurons

  • Definition: Nerve cells that transfer information

  • Structure:

    • Dendrites: Branch-like extensions that receive signals

    • Axon: Long extension that transmits signals to other cells

    • Cell Body: Contains organelles

    • Glial Cells: Nourish and insulate neurons

Membrane Potential

  • Definition: Voltage difference across the plasma membrane of a cell

  • Resting Potential: The membrane potential of a neuron not sending signals

  • Ion Pumps/Channels: Maintain resting potential

Formation of Resting Potential

  • Ionic Distribution:

    • Higher concentration of K+ inside the cell and Na+ outside

    • Sodium-potassium pumps use ATP energy to maintain these gradients

  • Chemical/Electrical Potential: Changes in ion flow convert chemical potential to electrical potential

  • K+ and Na+ Currents: At resting potential, currents of K+ and Na+ are equal and opposite, keeping resting potential steady

Action Potentials

Overview

  • Phase Breakdown:

    1. Resting State: Na+ and K+ channels closed

    2. Depolarization: Na+ inflow causes internal membrane positivity

    3. Falling Phase: Inactivation of Na+ channels and K+ outflow reverts membrane negativity

    4. Undershoot: K+ channels still open before returning to resting state

Refractory Period

  • Definition: Period after action potential where a new action potential cannot be initiated

  • Importance: Ensures unidirectional impulse movement along axon

  • Mechanism: Temporary inactivation of Na+ channels and Na+/K+ pump restoration

Conduction of Action Potentials

Characteristics

  • Action potentials regenerate along the axon, preventing backward movement

  • Speed is determined by axon diameter and myelination

  • Myelin sheath created by glial cells (oligodendrocytes in CNS and Schwann cells in PNS)

Saltatory Conduction

  • Definition: Action potentials jump between nodes of Ranvier, increasing transmission speed

Synapses and Communication

Synapse Understanding

  • Definition: Junction between neurons facilitating communication

  • Types of Synapses:

    • Electrical Synapses: Direct electrical current flow

    • Chemical Synapses: Neurotransmitters carry signals across synaptic gaps

Transmission Mechanism

  • Presynaptic Neuron: Synthesizes and stores neurotransmitters in vesicles

  • Release: Action potentials cause neurotransmitter release into the synapse

  • Post-synaptic Cell: Receives neurotransmitters, opening ion channels and generating postsynaptic potential

Neurotransmitter Fate

  • Options post-release: Diffusion out, uptake by cells, or enzymatic degradation

Neural Regulation

  • Reference: Chapter 49, pg 1143, Campbell

Nervous System Types Among Animals

Variation in Nervous Systems

  • Cnidarians: Simple nerve nets with interconnected nerve cells

  • Starfish: Have nerve nets in arms connected to a central nerve ring

  • Cephalization: Cluster of sensory organs at body front in more complex species

Central Nervous System (CNS)

  • Components: Brain and spinal cord; integration of information occurs here

  • Peripheral Nervous System (PNS): Nerves and ganglia transmitting information in/out of CNS

CNS Structure

  • Gray Matter: Neuron cell bodies, dendrites, unmyelinated axons

  • White Matter: Bundles of myelinated axons

Reflexes and Response Mechanisms

Reflex Definition

  • Overview: Automatic body response to stimulus, e.g., knee-jerk reflex

  • PNS Functionality: Transmits information to/from CNS, regulates movement and internal environment

Components of PNS:

  • Efferent Neurons: Transmit information away from CNS

  • Afferent Neurons: Transmit information to CNS

Functional Components

  • Motor System: Voluntary control over skeletal muscles

  • Autonomic Nervous System: Involuntary regulation of the internal environment

    • Divisions:

    • Sympathetic

    • Parasympathetic

    • Enteric

Sympathetic vs. Parasympathetic Functions

  • Sympathetic:

    • Stimulates glucose release from liver, dilates pupils, inhibits salivary secretion, accelerates heart, relaxes bronchi, inhibits stomach, promotes ejaculation

  • Parasympathetic:

    • Stimulates salivary secretion, slows heart, stimulates stomach, promotes bowel emptying

Brain Functionality

Overview

  • Region Specificity: Different regions of the vertebrate brain serve specialized functions

Brainstem

  • Components: Midbrain, pons, medulla oblongata

  • Functions: Coordinates and conducts information between centers, regulates breathing, cardiovascular functions, and swallowing

Cerebellum

  • Role: Coordination and error-checking for motor functions and perceptual learning

Diencephalon Development

  • Regions:

    • Epithalamus: Contains pineal gland; generates cerebrospinal fluid

    • Thalamus: Input/output hub for sensory and motor information

    • Hypothalamus: Regulates homeostasis, survival behaviors (feeding, fighting, fleeing, reproduction)

Cerebrum

  • Structure: Right and left hemispheres with a cerebral cortex over white matter and basal nuclei

  • Communication: Corpus callosum connects hemispheres

Cortical Functions

  • Lobes: Four lobes in each hemisphere: frontal, temporal, occipital, parietal

  • Functions: Control of voluntary movement, integration of sensory information

Limbic System

  • Function: Involved in generating and experiencing emotions; includes amygdala and hippocampus

  • Amygdala: Emotional memory storage

Memory and Learning

Mechanisms

  • Neuronal Connections: Learning occurs through new/strengthened neuronal connections

  • Types of Memory:

    • Short-term Memory: Accessed via the hippocampus

    • Long-term Memory: Stored in the cerebral cortex

Acknowledgements

  • Source: Majority of text and PowerPoint slides from Campbell's Biology.

  • Contributor: Dr. Ramiro Crego, School of BEES