BL1004: Animal Physiology Nervous System Quiz

Module BL1004: Animal Physiology

• Module focus is Animal Physiology
• Instructor is Professor Rob McAllen
• Email address is [email protected]
• Office hours by appointment
• Contact details: Email and office hours

Nervous System

• Topic: "Electric signals in animals"
• Source: Chapter 48, page 1125 of Campbell

Integrated Physiological Mechanisms

• Image: Barnacles on a rocky shore

Sponge Diversity

• Image: Multiple sponge varieties displayed

Sponge Film

• Mentions a video or presentation about sponges

Overview: Command and Control Center

• Controls: Feelings, perceptions, and movement
• Enables: Learning, remembering, thinking, and consciousness
• Regulates: Internal body functions and behavior

Overview: Lines of Communication

• Nervous system functions: sensory input, integration, and motor output
• Sensors detect external and internal stimuli, transmitting information
• Sensory information integrated by brain or ganglia
• CNS = Central Nervous System (brain and spinal cord)
• Motor output from brain or ganglia to motor neurons for responses
• Examples include doctor-knee-jerk responses and peripheral nervous systems.

Neurons

• Function: Transmission of signals
• Dendrites: Highly branched extensions receiving signals from other neurons
• Axon: A typically much longer extension transmitting signals from terminal branches to other cells at synapses
• Cell body: Contains most neuron organelles
• Glia: Cells nourishing and insulating neurons, crucial for structural integrity and nervous system function.

Neuron

• Every cell has membrane potential (voltage difference across plasma membrane)
• Messages transmitted via membrane potential changes
• Resting potential: Membrane potential when a neuron is not sending signals
• Ion pumps and channels maintain resting potential

Neuron - Formation of the Resting Potential

• K+ concentration is higher inside the cell, Na+ higher outside
• Sodium-potassium pumps use ATP energy to maintain K+ and Na+ gradients across the plasma membrane
• Concentration gradients represent chemical potential energy

Neuron - Formation of the Resting Potential

• Ion channel opening converts chemical into electrical potential
• K+ diffuses out of the cell, anions trapped inside contribute to neuron's negative charge

Neuron - Formation of the Resting Potential

• In a resting neuron, K+ and Na+ currents are equal and opposite, maintaining a steady resting potential across the membrane

Formation of Action Potentials

• Action potentials are formed by depolarization, creating an electrical current that depolarizes neighboring regions of the axon membrane.
• Inactivation of Na+ channels prevents backward action potential transmission; they travel only in one direction, toward synaptic terminals
• Rest and recovery phase, with inactivation of sodium channels being critical

Conduction of Action Potentials

• Speed increases with axon diameter and myelination
• Myelin sheaths made by glia (oligodendrocytes in CNS, Schwann cells in PNS)
• Saltatory conduction: Action potentials jump between nodes of Ranvier in myelinated axons.

Neurons Communicate at Synapses

• Synapse: Junction between cells controlling communication
• Electrical synapses: Electrical current flows between neurons directly across gap junction.
• Chemical synapses: neurotransmitters carry information across the gap junction, resulting mostly in chemical responses.

There Are Two Types of Synapses

• Synaptic terminals transmit information in the form of chemical messengers (neurotransmitters).
• Information transmitted from presynaptic cell (neuron) to postsynaptic cell (neuron, muscle, gland cell)

Chemical Synapses

• Presynaptic neuron synthesizes and packages neurotransmitters into synaptic vesicles in the synaptic terminal
• Action potential triggers neurotransmitter release
• Neurotransmitter diffuses across synaptic cleft, received by postsynaptic cell

Chemical Synapses

• Direct synaptic transmission: Neurotransmitters bind to ligand-gated ion channels in the postsynaptic cell inducing postsynaptic potential
• After neurotransmitter release, diffusion out of synaptic cleft and uptake by surrounding cells or degradation by enzymes

Neural Regulation in Animals

• Source: Chapter 49, page 1143 of Campbell

Plane or Axis of Symmetry

• Sponges, cnidarians, some echinoderms can have radial symmetry or no symmetry
• Some worms, mollusks, arthropods, and chordates have bilateral.

Nervous Systems Consist of Circuits of Neurons and Supporting Cells

• Simplest animals have nerve nets (interconnected nerve cells, no central pathway or organization)
• Starfish have nerve nets in each arm, connected by radial nerves to a central nerve ring.

Nervous Systems Consist of Circuits of Neurons and Supporting Cells

• Bilaterally symmetrical animals exhibit cephalization (sensory organs in anterior)
• Relatively simple cephalized animals (like flatworms) have a central nervous system (CNS) with a brain and longitudinal nerve cords

Central Nervous System

• CNS includes brain and spinal cord, where integration of information occurs
• Gray matter is composed of neuron cell bodies, dendrites, and unmyelinated axons
• White matter consists of bundles of myelinated axons

Organization of the Vertebrate Nervous System

• Reflex: Body's automatic response to a stimulus (like knee-jerk reflex)
• Sensory neurons detect stimulus, interneurons transmit the signal, and motor neurons produce the response

Peripheral Nervous System

• PNS transmits information to and from CNS and regulates movement and internal environment
• Afferent neurons transmit information to CNS; efferent neurons transmit it away
• Cranial nerves mostly connect to the head and upper body; spinal nerves connect to parts below the head

Peripheral Nervous System

• PNS components: motor system (voluntary movement) and autonomic nervous system (involuntary regulation of internal organs)
• Sympathetic/parasympathetic divisions of the ANS opposingly affect target organs.

The Brain

• Brainstem coordinates and conducts information between brain centers.
• Brainstem components: midbrain, pons, and medulla oblongata.
• Midbrain centers for sensory information, pons regulates breathing, medulla controls functions (breathing, cardiovascular activity, swallowing, vomiting, digestion)

The Brain

• Cerebellum: Coordination and error-checking during motor, perceptual, and cognitive functions. Also involved in learning and remembering motor skills (eg. hand-eye coordination).

The Brain

• Evolving diencephalon regions: epithalamus (pineal gland, cerebrospinal fluid generation), thalamus (sensory information input/motor output center), hypothalamus (homeostasis and basic survival behaviors).

The Brain

• Cerebrum has right and left hemispheres, each with cerebral cortex (gray matter) overlying white matter and basal nuclei.
• The cerebrum's largest part in humans is the cerebral cortex, highly complex in function.

The Brain

• Corpus callosum is a band of axons connecting right and left cerebral cortices, allowing intercommunication. Right hemisphere controls left body and vice-versa.

The Brain

• Each cerebral cortex side has 4 lobes (frontal, temporal, occipital, parietal).
• Each lobe has sensory areas where information is integrated and association areas

The Limbic System

• Limb system handles emotions and participates in emotional memory formation utilizing structures in the brainstem surrounding the brainstem (amygdala, hippocampus, thalamus)
• Amygdala is deeply involved in emotional experiences, and storage of emotional memories

Memory and Learning

• Learning occurs through new neuron connections or changes in existing connections
• Short-term memory facilitated by hippocampus; long-term memory stored in cerebral cortex

Acknowledgements

• Majority of content sourced from Campbell's Biology
• Specific contributor: Dr Ramiro Crego from the School of BEES.