Animal Body Systems - Nervous System Quiz

Animal Body Systems - Nervous Systems

• Lecture 9 covers post-synaptic electrophysiology, the autonomic nervous system (ANS), and nervous system evolution.
• The supplementary reading material is found in textbook chapter 42, pages 1159-1164, and 1171-1175 (5th edition).

Post-Synaptic Electrophysiology

• Ions move across the post-synaptic membrane due to neurotransmitter binding to receptors.
• This creates an electrotonic potential (EP) in the postsynaptic neuron's dendrites.
• The EP flows along the membrane surface to the axon hillock.
• A postsynaptic potential (PSP) results from the EP from the dendrites.

Post Synaptic Potentials

• Postsynaptic potentials (PSPs) can depolarize or hyperpolarize the membrane.
• The type of receptor/ion channel determines whether the PSP is excitatory (EPSP) or inhibitory (IPSP).
  • Na+ channels cause depolarizing/excitatory PSPs when Na+ flows inward.
  • K+ channels cause hyperpolarizing/inhibitory PSPs when K+ flows outward.
  • Cl- channels cause hyperpolarizing/inhibitory PSPs when Cl- flows inward

PSP's are Graded Potentials

• EPSPs and IPSPs are graded potentials, not all-or-none like action potentials (APs).
• The size of the PSP at each receptor depends on the amount of neurotransmitter released.

Postsynaptic Neurons Receive Many Inputs

• A postsynaptic neuron can receive up to 1,000 inputs.

Summation of PSPs

• Summation can occur in time and space involving EPSPs and IPSPs.
• This is essential for processing inputs, learning, and memory.
• The summation of subthreshold PSPs happens at the axon hillock.

Overview of Neuronal Signaling Physiology

• This overview details the steps in neuronal signaling.

Post Synaptic Regulation

• All neurons share the same basic electrophysiology.
• Variations in postsynaptic regulation occur via differing neurotransmitters, receptors, and intracellular signaling pathways.
• This allows the nervous system to regulate virtually all cellular physiology.

Summary

• Integration is the synthesis of an output based on the sum of inputs.

Functional Divisions

• Somatic Nervous System: voluntary control.
• Autonomic Nervous System: involuntary control, encompassing:
  • Sympathetic division: "fight or flight", whole-body responses.
  • Parasympathetic division: "rest and digest", organ-specific responses.

The Autonomic Nervous System (ANS)

• Most tissues are innervated by both sympathetic and parasympathetic divisions.
• Integration also occurs in ganglia with two efferent neurons & peripheral ganglia.

The ANS Divisions

• Sympathetic Division: more widespread effects (whole body).
• Parasympathetic Division: effects are more organ-specific.

Functions of the ANS

• Sympathetic Division: Relaxes airways, increases heartbeat, inhibits digestion/stomach activity.
• Parasympathetic Division: Constricta airways, slows heartbeat, stimulates digestion/stomach activity.

Neurotransmitters & Receptors of the ANS

• Sympathetic: Preganglionic fibers release acetylcholine (ACh) and nicotinic receptors, Postganglionic fibers release norepinephrine (NE)/and renorphin/adrenoceptors.
• Parasympathetic: Preganglionic fibers release ACh/nicotinic receptors, Postganglionic fibers release ACh/muscarinic receptors.

ANS Divisions have Antagonistic (Opposing) Effects.

• Sympathetic is more active when the body's energy stores need to be used ("fight or flight".)
• Parasympathetic is more active when body energy stores are being conserved ("rest and digest").
  • Example: Sympathetic inhibits digestive tract but the parasympathetic system stimulates it.

The ANS Activity

• Both divisions (sympathetic and parasympathetic) are always active.
• The overall effect depends on which division is more active at any given moment.

ANS Summary

• A major source of integration in the body.
• Used to regulate and coordinate the majority of organ systems.
• Extensive feedback loops maintain homeostasis.

Pressures on Nervous System Development

• Nervous systems of all animals are designed for optimal functioning.
• Invertebrates and vertebrates have different nervous system organization reflecting differences in lifestyle and habitat.

Nervous System Evolution in Animals

• Sponges lack neurons but have basic cell physiology.
• Ganglia are collections of neuron cell bodies that are sites of integration.
• Cephalization is the concentration of neurons/ganglia in a head region.

Nervous System Evolution in Chordates

• Brain regions are conserved and modified in different chordate lineages.

The Mammalian Nervous System - An Example of Complexity

• Folding increases the surface area of the brain (# of neurons/synapses).

Development of the Human Brain

• Different regions of the brain develop and have specific functions.

An Example of Complexity

• The mammalian nervous system is divided into functional regions.

Functional Divisions of the Vertebrate Nervous System

• Vertebrate nervous system has a central nervous system (CNS), peripheral nervous system (PNS), afferent system, sensory receptors, somatic system, sympathetic & parasympathetic nervous system, skeletal muscles and effectors.