Functional Organization of Nervous Tissue Chapter 11

The Nervous System Components: Responsible for… Subdivisions: Brain, spinal cord, nerves, sensory receptors Responsible for… Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands Subdivisions: Central Nervous System (CNS) Peripheral Nervous System (PNS)

Central Nervous System Consists of brain and spinal cord The structural & functional center of the entire nervous system which integrates incoming pieces of information & initiates an outgoing response

Peripheral Nervous System All other nerves All pathways going toward and away from the CNS

Nervous System Organization

Concept Check What are the two divisions of the nervous system? What are their parts? CNS: Brain & Spinal Cord PNS: nerves What are the functions of the CNS? Integrates incoming information & initiates an outgoing response What is the function of the PNS? Conducts action potentials to and away from the CNS What are some functions of the Nervous system? Sensory perceptions, mental activities, stimulating muscle movement, secretions of many glands

Cells of Nervous System Neurons or nerve cells Receive stimuli and transmit action potentials Organization Cell body or soma Dendrites: input Axons: output Neuroglia cells Support and protect neurons

Types of Neurons Functional Classification Sensory or afferent: action potentials toward CNS (receives stimuli; could be a special sense organ) Motor or efferent: action potentials away from CNS (attached to a muscle or gland) Interneurons or association neurons: within CNS from one neuron to another

Myelinated and Unmyelinated Axons Myelin protects and insulates axons from one another Not continuous Nodes of Ranvier Impulse “jumps” from node to node Fast impulse Unmyelinated axons Slower impulse

Electrical Signals Cells produce electrical signals called action potentials Transfer of information from one part of body to another Electrical properties result from ionic concentration differences across plasma membrane and permeability

Nerve Impulses A wave of electrical fluctuation that travels along the plasma membrane; due to changes in chemical concentrations. Impulse +++-++++++-++++-+ ---+---+-----------+--+ ++++++-+++-++-+++++-++++++++ ----+----+--+--------+ ++++-++++++-+++++- -----+----+-------+--+-------+-------- ----+----+---+---------- ++++++++-++-++++-++ ----+-----++-----------+-----+------+--- ++++++-++-+++++++ --------+--++----------+---- +++++++-+++++++--++++++++-+++ Resting Potential “Polarized” Action Potential “Depolarized” Resting Potential “Repolarized”

Resting Membrane Potential Characteristics Number of charged molecules and ions inside and outside cell nearly equal Concentration of K+ higher inside than outside cell- negative proteins in also, Na+ higher outside than inside At equilibrium there is very little movement of K+ or other ions across plasma membrane

Action Potentials Series of permeability changes when a local potential causes depolarization of membrane Phases Depolarization More positive Repolarization More negative All-or-none principle Neuron will fire or it won’t

The Synapse Junction between two cells Electrical message transferred across the synapse by chemicals called neurotransmitters

Concept Check What are the main parts of a neuron? Axon, dendrites, myelin sheath, synapse What are the three types of neurons and what do they do? Sensory (afferent)- action potential toward CNS , Motor (efferent)- action potential away from CNS, & Interneurons- within CNS from one neuron to another How does an impulse travel along an axon? What speeds it up? Jumps from node to node; myelin How does a synapse work? Neurotransmitters transfer message across synapse

Stimulus Any change in your environment. Temp, sound, smell You may or may not respond to a specific stimulus

Reflex A predictable response to a stimulus which may or may not be conscious A reflex consists of either muscle contraction or glandular secretion Neurons involved in reflex Afferent neuron- sensory Interneuron Efferent neuron- motor

Sensory Receptors In order for a stimulus to be detected, it must be strong enough to elicit an impulse It must be at the threshold level- the minimum stimulus to start an impulse The all-or-none response means that either a neuron will fire or it won’t, there is no partial impulse Sensation- the brain’s interpretation of what the stimulus is

Characteristics of Sensations Projection- brain refers a sensation to the point of stimulation Adaptation- loss of sensation even though the stimulus is still applied Afterimage- persistence of a sensation even though the stimulus is removed Referred pain- felt in the skin near or around the organ sending the impulse Phantom pain- sensation of pain in a limb that has been amputated

Classification of Receptors Mechanoreceptors- activated by mechanical stimuli or deformation of the receptor Chemoreceptor- changing of the chemical concentrations around the body Thermoreceptors- detect hot and cold Nociceptors- any stimuli that can cause tissue damage; sensation of pain Photoreceptors- respond to light

Somatic Senses pain, temperature and touch These sensations can be felt throughout the body, yet they are distributed unevenly through the skin Exteroceptors- sense receptors located on body surfaces Proprioceptors- found in the muscles and joints Visceroceptors- found in internal organs Nociceptors- pain receptors; free nerve endings

Review Meissner’s corpuscles- touch Krause’s End Bulbs- touch Ruffini’s corpuscles- continuous touch Pacinian corpuscles- deep pressure

The Brain Parts/Functions Left vs Right Brain Activity?? Dissection notes…pre-lab??